Shortcircuit-IEC

Short-Circuit Analysis IEC Standard

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

CORTO CIRCUITO Características principales:

 Estándar de ANSI/IEEE & IEC.  Análisis de fallas transitorias (IEC 61363).  Efecto de Arco (NFPA 70E2000)  Integrado con coordinación de dispositivos de protección.  Evaluación dispositivos.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

automática

de

Slide 2

Purpose of Short-Circuit Studies • A Short-Circuit Study can be used to determine any or all of the following: – Verify protective device close and latch capability – Verify protective device interrupting capability – Protect equipment from large mechanical forces (maximum fault kA) – I2t protection for equipment (thermal stress) – Selecting ratings or settings for relay coordination ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 3

Types of Short-Circuit Faults

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 4

Types of Short-Circuit Faults Types of SC Faults •Three-Phase Ungrounded Fault •Three-Phase Grounded Fault •Phase to Phase Ungrounded Fault •Phase to Phase Grounded Fault •Phase to Ground Fault

Fault Current •IL-G can range in utility systems from a few percent to possibly 115 % ( if Xo < X1 ) of I3-phase

(85% of all faults).

•In industrial systems the situation IL-G > I3-phase is rare. Typically IL-G ≅ .87 * I3-phase •In an industrial system, the three-phase fault condition is frequently the only one considered, since this type of fault generally results in Maximum current. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 5

Short-Circuit Phenomenon

v(t)

i(t)

v(t)= Vm∗ Sin(ω t + θ ) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 6

v(t)

i(t)

di v(t)= Ri + L = Vm× Sin( ωt + θ ) (1) dt Solving equation 1 yields the following expression - t Vm Vm i(t)= × sin( ωt + θ - φ ) + × sin( θ - φ )×e L Z Z      R

Steady State

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Transient (DCOffset)

Slide 7

AC Current (Symmetrical) with No AC Decay

DC Current

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 8

AC Fault Current Including the DC Offset (No AC Decay)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 9

Machine Reactance ( λ = L I )

AC Decay Current

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 10

Fault Current Including AC & DC Decay

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 11

IEC Short-Circuit Calculation (IEC 909) • Initial Symmetrical Short-Circuit Current (I"k) • Peak Short-Circuit Current (ip) • Symmetrical Short-Circuit Breaking Current (Ib) • Steady-State Short-Circuit Current (Ik) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 12

IEC Short-Circuit Calculation Method • Ik” = Equivalent V @ fault location divided by equivalent Z • Equivalent V is based bus nominal kV and c factor • XFMR and machine Z adjusted based on cmax, component Z & operating conditions ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 13

Transformer Z Adjustment • KT -- Network XFMR • KS,KSO – Unit XFMR for faults on system side • KT,S,KT,SO – Unit XFMR for faults in auxiliary system, not between Gen & XFMR • K=1 – Unit XFMR for faults between Gen & XFMR ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 14

Syn Machine Z Adjustment • KG – Synchronous machine w/o unit XFMR • KS,KSO – With unit XFMR for faults on system side • KG,S,KG,SO – With unit XFMR for faults in auxiliary system, including points between Gen & XFMR

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 15

Types of Short-Circuits • Near-To-Generator Short-Circuit – This is a short-circuit condition to which at least one synchronous machine contributes a prospective initial short-circuit current which is more than twice the generator’s rated current, or a short-circuit condition to which synchronous and asynchronous motors contribute more than 5% of the initial symmetrical short-circuit current ( I"k) without motors. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 16

Near-To-Generator Short-Circuit

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 17

Types of Short-Circuits • Far-From-Generator Short-Circuit – This is a short-circuit condition during which the magnitude of the symmetrical ac component of available short-circuit current remains essentially constant.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 18

Far-From-Generator Short-Circuit

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 19

Factors Used in If Calc • κ – calc ip based on Ik” • μ – calc ib for near-to-gen & not meshed network • q – calc induction machine ib for near-to-gen & not meshed network • Equation (75) of Std 60909-0, adjusting Ik for near-to-gen & meshed network • λmin & λmax – calc ik ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 20

IEC Short-Circuit Study Case

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 21

Types of Short-Circuits When these options are selected • Maximum voltage factor is used • Minimum impedance is used (all negative tolerances are applied and minimum resistance temperature is considered) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 22

Types of Short-Circuits When this option is selected • Minimum voltage factor is used • Maximum impedance is used (all positive tolerances are applied and maximum resistance temperature is considered) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 23

Voltage Factor (c) • Ratio between equivalent voltage & nominal voltage • Required to account for: • Variations due to time & place • Transformer taps • Static loads & capacitances • Generator & motor subtransient ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 24

Calculation Method

• Breaking kA is more conservative if the option No Motor Decay is selected

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 25

IEC SC 909 Calculation

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 26

Device Duty Comparison

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 27

Mesh & Non-Mesh If • ETAP automatically determines mesh & non-meshed contributions according to individual contributions • IEC Short Circuit Mesh Determination Method – 0, 1, or 2 (default)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 28

L-G Faults

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 29

L-G Faults Symmetrical Components

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 30

Sequence Networks

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 31

L-G Fault Sequence Network Connections If = 3 × Ia 0 3 × VPr efault If = Z1 + Z 2 + Z0 if Zg = 0

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 32

L-L Fault Sequence Network Connections

I a 2 = − I a1 3 × VPr efault If = Z1 + Z 2

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 33

L-L-G Fault Sequence Network Connections I a 2 + I a1 + I a 0 = 0 = I a VPr efault If =  Z0 Z 2   Z1 +   Z0 + Z2  if Zg = 0

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 34

Transformer Zero Sequence Connections

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 35

Solid Grounded Devices and L-G Faults Generally a 3 - phase fault is the most severe case. L - G faults can be greater if : Z1 = Z 2 & Z 0 < Z 1 If this conditions are true then : I f3φ < I f 1φ This may be the case if Generators or Y/∆ Connected transformer are solidly grounded.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 36

Zero Sequence Model • Branch susceptances and static loads including capacitors will be considered when this option is checked • Recommended by IEC for systems with isolated neutral, resonant earthed neutrals & earthed neutrals with earth fault factor > 1.4

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 37

Unbalanced Faults Display & Reports Complete reports that include individual branch contributions for: •L-G Faults •L-L-G Faults •L-L Faults

One-line diagram displayed results that include: •L-G/L-L-G/L-L fault current contributions •Sequence voltage and currents •Phase Voltages ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 38

Transient Fault Current Calculation (IEC 61363)

Total Fault Current Waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 39

Transient Fault Current Calculation (IEC 61363)

Percent DC Current Waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 40

Transient Fault Current Calculation (IEC 61363)

AC Component of Fault Current Waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 41

Transient Fault Current Calculation (IEC 61363)

Top Envelope of Fault Current Waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 42

Transient Fault Current Calculation (IEC 61363)

Top Envelope of Fault Current Waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 43

IEC Transient Fault Current Calculation

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 44

Unbalanced Faults Display & Reports Complete reports that include individual branch contributions for: •L-G Faults •L-L-G Faults •L-L Faults

One-line diagram displayed results that include: •L-G/L-L-G/L-L fault current contributions •Sequence voltage and currents •Phase Voltages ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 45

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 46

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 47

TEMA 2

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 48

Protective Device Coordination ETAP Star

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

ETAP START PROTECCION Y COORDINACION Características principales:  Curvas para dispositivos.

más

de

 Actualización automática Corriente de Corto Circuito.

75,000 de

 Coordinación tiempo-corriente de dispositivos.  Auto-coordinación de dispositivos.  Integrados unifilares.

a

los

diagramas

 Rastreo o cálculos en diferentes tiempos.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 50

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 51

Agenda • Concepts & Applications • Star Overview • Features & Capabilities • Protective Device Type • TCC Curves • STAR Short-circuit • PD Sequence of Operation • Normalized TCC curves • Device Libraries

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 52

Definition • Overcurrent Coordination – A systematic study of current responsive devices in an electrical power system.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 53

Objective • To determine the ratings and settings of fuses, breakers, relay, etc. • To isolate the fault or overloads.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 54

Criteria • Economics • Available Measures of Fault • Operating Practices • Previous Experience

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 55

Design • Open only PD nearest (upstream) of the fault or overload • Provide satisfactory protection for overloads • Interrupt SC as rapidly (instantaneously) as possible • Comply with all applicable standards and codes • Plot the Time Current Characteristics of different PDs ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 56

Analysis When: • New electrical systems • Plant electrical system expansion/retrofits • Coordination failure in an existing plant

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 57

Spectrum Of Currents • Load Current – Up to 100% of full-load – 115-125% (mild overload)

• Overcurrent – Abnormal loading condition (Locked-Rotor)

• Fault Current – Fault condition – Ten times the full-load current and higher ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 58

Protection • Prevent injury to personnel • Minimize damage to components – Quickly isolate the affected portion of the system – Minimize the magnitude of available short-circuit

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 59

Coordination • Limit the extent and duration of service interruption • Selective fault isolation • Provide alternate circuits

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 60

Coordination C t

D B

A A C

D

B

I ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 61

Protection vs. Coordination • Coordination is not an exact science • Compromise between protection and coordination – Reliability – Speed – Performance – Economics – Simplicity ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 62

Required Data •

One-line diagrams (Relay diagrams)

•

Power Grid Settings

•

Generator Data

•

Transformer Data – Transformer kVA, impedance, and connection Motor Data

•

Load Data

•

Fault Currents

•

Cable / Conductor Data

•

Bus / Switchgear Data

•

Instrument Transformer Data (CT, PT)

•

Protective Device (PD) Data – Manufacturer and type of protective devices (PDs) – One-line diagrams (Relay diagrams)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 63

Study Procedure • Prepare an accurate one-line diagram (relay diagrams) • Obtain the available system current spectrum (operating load, overloads, fault kA) • Determine the equipment protection guidelines • Select the appropriate devices / settings • Plot the fixed points (damage curves, …) • Obtain / plot the device characteristics curves • Analyze the results

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 64

Time Current Characteristics • TCC Curve / Plot / Graphs • 4.5 x 5-cycle log-log graph • X-axis: Current (0.5 – 10,000 amperes) • Y-axis: Time (.01 – 1000 seconds) • Current Scaling (…x1, x10, x100, x100…) • Voltage Scaling (plot kV reference) • Use ETAP Star Auto-Scale

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 65

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 66

TCC Scaling Example • Situation: – A scaling factor of 10 @ 4.16 kV is selected for TCC curve plots.

• Question – What are the scaling factors to plot the 0.48 kV and 13.8 kV TCC curves?

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 67

TCC Scaling Example • Solution

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 68

Fixed Points Points or curves which do not change regardless of protective device settings: • Cable damage curves • Cable ampacities • Transformer damage curves & inrush points • Motor starting curves • Generator damage curve / Decrement curve • SC maximum fault points ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 69

Capability / Damage Curves It 2

t

I2 t

I2 t

I 2t 2

Motor Gen

Xfmr

Cable

I

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 70

Cable Protection • Standards & References – IEEE Std 835-1994 IEEE Standard Power Cable Ampacity Tables – IEEE Std 848-1996 IEEE Standard Procedure for the Determination of the Ampacity Derating of Fire-Protected Cables – IEEE Std 738-1993 IEEE Standard for Calculating the Current- Temperature Relationship of Bare Overhead Conductors – The Okonite Company Engineering Data for Copper and Aluminum Conductor Electrical Cables, Bulletin EHB-98

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 71

Cable Protection The actual temperature rise of a cable when exposed to a short circuit current for a known time is calculated by:

Ι2 t A=  T2 + 234  0.0297log    T1 + 234 

Where: A= Conductor area in circular-mils I = Short circuit current in amps t = Time of short circuit in seconds T1= Initial operation temperature (750C) T2=Maximum short circuit temperature (1500C)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 72

Cable Short-Circuit Heating Limits Recommended temperature rise: B) CU 75-200C

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 73

Shielded Cable The normal tape width is 1½ inches

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 74

NEC Section 110‑14 C •

(c) Temperature limitations. The temperature rating associated with the ampacity of a conductor shall be so selected and coordinated as to not exceed the lowest temperature rating of any connected termination, termination conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

•

(1) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for Nos. 14 through 1 conductors, shall be used only for conductors rated 600C (1400F).

•

Exception No. 1: Conductors with higher temperature ratings shall be permitted to be used, provided the ampacity of such conductors is determined based on the 6O0C (1400F) ampacity of the conductor size used.

•

Exception No. 2: Equipment termination provisions shall be permitted to be used with higher rated conductors at the ampacity of the higher rated conductors, provided the equipment is listed and identified for use with the higher rated conductors.

•

(2) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than No. 1, shall be used only with conductors rated 750C (1670F).

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 75

Transformer Protection Standards & References

• –

National Electric Code 2002 Edition

–

C37.91-2000; IEEE Guide for Protective Relay Applications to Power Transformers

–

C57.12.59; IEEE Guide for Dry-Type Transformer Through-Fault Current Duration.

–

C57.109-1985; IEEE Guide for Liquid-Immersed Transformer ThroughFault-Current Duration

–

APPLIED PROCTIVE RELAYING; J.L. Blackburn; Westinghouse Electric Corp; 1976

–

PROTECTIVE RELAYING, PRINCIPLES AND APPLICATIONS; J.L. Blackburn; Marcel Dekker, Inc; 1987

–

IEEE Std 242-1986; IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems

–

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 76

Transformer Category ANSI/IEEE C-57.109

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 77

Transformer Categories I, II

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 78

Transformer Categories III

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 79

Transformer FLA

200

t (sec)

Thermal I2t = 1250

(D-D LL) 0.87

Infrequent Fault (D-R LG) 0.58

2

Frequent Fault

Mechanical K=(1/Z)2t Inrush

2.5

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Isc

25

I (pu)

Slide 80

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 81

Transformer Protection

M Any Location – Non-Supervised

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 82

Transformer Protection •

Turn on or inrush current

•

Oil Level

•

Internal transformer faults

•

Fans

•

External or through faults of major magnitude

•

Oil Pumps

•

Pilot wire – Device 85

•

Repeated large motor starts on the transformer. The motor represents a major portion or the transformers KVA rating.

•

Fault withstand

•

Thermal protection – hot spot, top of oil temperature, winding temperature

•

Devices 26 & 49

•

Harmonics

•

Reverse over current – Device 67

•

Over current protection – Device 50/51

•

Gas accumulation – Buckholz relay

•

Ground current protection – Device 50/51G

•

Over voltage –Device 59

•

Voltage or current balance – Device 60

•

Differential – Device 87

•

Tertiary Winding Protection if supplied

•

Over or under excitation – volts/ Hz – Device 24

•

Relay Failure Scheme

•

Breaker Failure Scheme

•

Sudden tank pressure – Device 63

•

Dissolved gas detection

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 83

Recommended Minimum Transformer Protection Protective system

Winding and/or power system grounded neutral grounded Up to 10 MVA

Winding and/or power system neutral ungrounded Up to 10 MVA

Above 10 MVA

Above 10 MVA -

√

-

√

Time over current

√

√

√

√

Instantaneous restricted ground fault

√

√

-

-

Time delayed ground fault

√

√

-

-

√

-

√

√ √

√

√ √

Differential

Gas detection Over excitation Overheating ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

-

-

Slide 84

Question What is ANSI Shift Curve?

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 85

Answer • For delta-delta connected transformers, with line-to-line faults on the secondary side, the curve must be reduced to 87% (shift to the left by a factor of 0.87) • For delta-wye connection, with single line-toground faults on the secondary side, the curve values must be reduced to 58% (shift to the left by a factor of 0.58) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 86

Question What is meant by Frequent and Infrequent for transformers?

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 87

Infrequent Fault Incidence Zones for Category II & III Transformers Source Transformer primary -side protective device (fuses, relayed circuit breakers, etc.) may be selected by reference to the infrequent -fault incidence protection curve Infrequent -Fault Incidence Zone*

Category II or III Transformer Fault will be cleared by transformer primary -side protective device Optional main secondary –side protective device. May be selected by reference to the infrequent -faultincidence protection curve Fault will be cleared by transformer primary -side protective device or by optional main secondary side protection device Feeder protective device

Frequent -Fault Inciden ce Zone*

Fault will be cleared by feeder protective device Feeders

* Should be selected by reference to the frequent -fault -incidence protection curve or for transformers serving industrial, commercial and institutional power systems with secondary -side conductors enclosed in conduit, bus duct, etc., the feeder protective device may be selected by reference to the infrequent -fault -incidence protection curve. Source: IEEE C57 ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 88

Motor Protection •

Standards & References –

IEEE Std 620-1996 IEEE Guide for the Presentation of Thermal Limit Curves for Squirrel Cage Induction Machines.

–

IEEE Std 1255-2000 IEEE Guide for Evaluation of Torque Pulsations During Starting of Synchronous Motors

–

ANSI/ IEEE C37.96-2000 Guide for AC Motor Protection

–

The Art of Protective Relaying – General Electric

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 89

Motor Protection • Motor Starting Curve • Thermal Protection • Locked Rotor Protection • Fault Protection

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 90

Motor Overload Protection (NEC Art 430-32 – Continuous-Duty Motors)

• Thermal O/L (Device 49) • Motors with SF not less than 1.15 – 125% of FLA

• Motors with temp. rise not over 40°C – 125% of FLA

• All other motors – 115% of FLA ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 91

Motor Protection – Inst. Pickup I

1 = XS + X d "

LOCKED ROTOR

Recommended Instantaneous Setting:

I

RELAY PICK UP =

I

PICK UP

∗ 1.6 TO 2

LOCKED ROTOR

If the recommended setting criteria cannot be met, or where more sensitive protection is desired, the in-stantaneous relay (or a second relay) can be set more sensitively if delayed by a timer. This permits the asymmetrical starting component to decay out. A typical setting for this is:

RELAY PICK UP =

I I

PICK UP

∗ 1.2 TO 1.2

LOCKED ROTOR

with a time delay of 0.10 s (six cycles at 60 Hz) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 92

Locked Rotor Protection • Thermal Locked Rotor (Device 51) • Starting Time (TS < TLR) • LRA – LRA sym – LRA asym (1.5-1.6 x LRA sym) + 10% margin

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 93

Fault Protection (NEC Art / Table 430-52) • Non-Time Delay Fuses – 300% of FLA

• Dual Element (Time-Delay Fuses) – 175% of FLA

• Instantaneous Trip Breaker – 800% - 1300% of FLA*

• Inverse Time Breakers – 250% of FLA

*can be set up to 1700% for Design B (energy efficient) Motor ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 94

Low Voltage Motor Protection • Usually pre-engineered (selected from Catalogs) • Typically, motors larger than 2 Hp are protected by combination starters • Overload / Short-circuit protection

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 95

Low-voltage Motor Ratings Continuous amperes

Range of ratings 9-250 —

Nominal voltage (V)

240-600

—

Horsepower

1.5-1000

—

—

00-9

Quantity

NEMA designation

Overload: overload relay elements

3

OL

Short circuit: circuit breaker current trip elements

3

CB

Fuses

3

FU

Undervoltage: inherent with integral control supply and three-wire control circuit

—

—

Ground fault (when speci-fied): ground relay with toroidal CT

—

Starter size (NEMA)

Types of protection

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

—

Slide 96

Minimum Required Sizes of a NEMA

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

UM

TER E

C FLC

R HP

Combination Motor Starter System

Slide 97

Required Data - Protection of a Medium Voltage Motor •

Rated full load current

•

Service factor

•

Locked rotor current

•

Maximum locked rotor time (thermal limit curve) with the motor at ambient and/or operating temperature

•

Minimum no load current

•

Starting power factor

•

Running power factor

•

Motor and connected load accelerating time

•

System phase rotation and nominal frequency

•

Type and location of resistance temperature devices (RTDs), if used

•

Expected fault current magnitudes

•

First ½ cycle current

•

Maximum motor starts per hour

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 98

Medium-Voltage Class E Motor Controller Ratings

Nominal system voltage Horsepower Symmetrical MVA interrupting capacity at nominal system voltage Types of Protective Devices

Class El (without fuses)

Class E2 (with fuses)

2300-6900 0-8000 25-75

2300-6900 0-8000 160-570

Quantity

NEMA Designation Phase Balance

Overload, or locked Rotor, or both: Thermal overload relay TOC relay IOC relay plus time delay

3 3 3

OL OC TR/O

Thermal overload relay

3

OL

TOC relay

3

OC

IOC relay plus time delay

3

TR/OC

3

FU

3

OC

1 1

GP GP

Short Circuit: Fuses, Class E2 IOC relay, Class E1 Ground Fault TOC residual relay Overcurrent relay with toroidal CT

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Current balance relay

1

BC

Negative-sequence voltage 1 relay (per bus), or both

—

Undervoltage: — Inherent with integral control supply and threewire control circuit, when voltage falls suffi-ciently to permit the contractor to open and break the seal-in circuit

UV

Temperature: — Temperature relay, operating from resistance sensor or ther-mocouple in stator winding

OL

NEMA Class E1 medium voltage starter

NEMA Class E2 medium voltage starter

Slide 99

Starting Current of a 4000Hp, 12 kV, 1800 rpm Motor First half cycle current showing current offset.

Beginning of run up current showing load torque pulsations.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 100

Starting Current of a 4000Hp, 12 kV, 1800 rpm Motor - Oscillographs

Motor pull in current showing motor reaching synchronous speed

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 101

Thermal Limit Curve

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 102

Thermal Limit Curve Typical Curve

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 103

(49) I2 T

O/L

tLR

MCP

(51)

ts

200 HP

Starting Curve

MCP (50)

LRAs

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

LRAasym

Slide 104

Protective Devices • Fuse • Overload Heater • Thermal Magnetic • Low Voltage Solid State Trip • Electro-Mechanical • Motor Circuit Protector (MCP) • Relay (50/51 P, N, G, SG, 51V, 67, 49, 46, 79, 21, …) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 105

Fuse (Power Fuse) • Non Adjustable Device (unless electronic) • Continuous and Interrupting Rating • Voltage Levels (Max kV) • Interrupting Rating (sym, asym) • Characteristic Curves – Min. Melting – Total Clearing

• Application (rating type: R, E, X, …) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 106

Fuse Types • Expulsion Fuse (Non-CLF) • Current Limiting Fuse (CLF) • Electronic Fuse (S&C Fault Fiter)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 107

Total Clearing Time Curve

Minimum Melting Time Curve

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 108

Current Limiting Fuse (CLF) • Limits the peak current of short-circuit • Reduces magnetic stresses (mechanical damage) • Reduces thermal energy

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 109

Current (peak amps)

Current Limiting Action Ip

t a = tc – t m

Ip’

ta = Arcing Time tm = Melting Time ta

tm

Time (cycles)

tc ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

tc = Clearing Time Ip = Peak Current Ip’ = Peak Let-thru Current

Slide 110

© 1996-2009 OperationInc. Technology, Inc. Notes: – Workshop Notes: Protective Device Coordination ©1996-2009 Operation Technology, – Workshop Short-Circuit IEC

Slide 111

Let-Through Chart Peak Let-Through Amperes

7% PF (X/R = 14.3) 230,000

300 A 100 A

12,500

60 A

5,200

100,000

Symmetrical RMS Amperes ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 112

Fuse Generally: • CLF is a better short-circuit protection • Non-CLF (expulsion fuse) is a better Overload protection • Electronic fuses are typically easier to coordinate due to the electronic control adjustments

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 113

Selectivity Criteria Typically: • Non-CLF:

140% of full load

• CLF:

150% of full load

• Safety Margin: 10% applied to Min Melting (consult the fuse manufacturer)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 114

Molded Case CB • Thermal-Magnetic • Magnetic Only

Types

• Motor Circuit Protector (MCP) • Integrally Fused (Limiters)

• Poles

• Current Limiting • High Interrupting Capacity

• Interrupting Capability

• Frame Size • Trip Rating • Voltage

• Non-Interchangeable Parts • Insulated Case (Interchange Parts)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 115

MCCB

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 116

MCCB with SST Device

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 117

Thermal Maximum

Thermal Minimum

Magnetic (instantaneous)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 118

LVPCB • Voltage and Frequency Ratings • Continuous Current / Frame Size / Sensor • Interrupting Rating • Short-Time Rating (30 cycle) • Fairly Simple to Coordinate • Phase / Ground Settings • Inst. Override ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 119

LT PU

CB 2

CB 1 LT Band

CB 2

ST PU

480

kV

CB 1

IT

ST Band If =30 kA

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 120

Inst. Override

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 121

Overload Relay / Heater • Motor overload protection is provided by a device that models the temperature rise of the winding • When the temperature rise reaches a point that will damage the motor, the motor is deenergized • Overload relays are either bimetallic, melting alloy or electronic

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 122

Overload Heater (Mfr. Data)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 123

Question What is Class 10 and Class 20 Thermal OLR curves?

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 124

Answer • At 600% Current Rating: – Class 10 for fast trip, 10 seconds or less – Class 20 for, 20 seconds or less (commonly used)

20

– There is also Class 15, 30 for long trip time (typically provided with electronic overload relays) 6

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 125

Answer

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 126

Overload Relay / Heater • When the temperature at the combination motor starter is more than ±10 °C (±18 °F) different than the temperature at the motor, ambient temperature correction of the motor current is required. • An adjustment is required because the output that a motor can safely deliver varies with temperature. • The motor can deliver its full rated horsepower at an ambient temperature specified by the motor manufacturers, normally + 40 °C. At high temperatures (higher than + 40 °C) less than 100% of the normal rated current can be drawn from the motor without shortening the insulation life. • At lower temperatures (less than + 40 °C) more than 100% of the normal rated current could be drawn from the motor without shortening the insulation life.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 127

Overcurrent Relay • Time-Delay (51 – I>) • Short-Time Instantaneous ( I>>) • Instantaneous (50 – I>>>) • Electromagnetic (induction Disc) • Solid State (Multi Function / Multi Level) • Application

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 128

© 1996-2009 OperationInc. Technology, Inc. Notes: – Workshop Notes: Protective Device Coordination ©1996-2009 Operation Technology, – Workshop Short-Circuit IEC

Slide 129

Time-Overcurrent Unit • Ampere Tap Calculation – Ampere Pickup (P.U.) = CT Ratio x A.T. Setting – Relay Current (IR) = Actual Line Current (IL) / CT Ratio – Multiples of A.T. IL

CT

= IR/A.T. Setting

= IL/(CT Ratio x A.T.

I Setting) R

51

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 130

Instantaneous Unit • Instantaneous Calculation – Ampere Pickup (P.U.) = CT Ratio x IT Setting – Relay Current (IR) = Actual Line Current (IL) / CT Ratio – Multiples of IT CT

IL

= IR/IT Setting

= IL/(CT Ratio x IT Setting)

IR 50

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 131

Relay Coordination • Time margins should be maintained between T/C curves • Adjustment should be made for CB opening time • Shorter time intervals may be used for solid state relays • Upstream relay should have the same inverse T/C characteristic as the downstream relay (CO-8 to CO-8) or be less inverse (CO-8 upstream to CO-6 downstream) • Extremely inverse relays coordinates very well with CLFs ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 132

Situation 4.16 kV CT 800:5

50/51

Relay: IFC 53

CB

Cable CU - EPR

1-3/C 500 kcmil

Isc = 30,000 A DS

5 MVA 6%

Calculate Relay Setting (Tap, Inst. Tap & Time Dial) For This System

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 133

Solution Transformer:

5,000kVA = 694 A 3 × 4.16kV 5 IR = IL × = 4.338 A 800

IL =

I Inrsuh = 12 × 694 = 8,328 A Set Relay:

IL IR R

CT

125% × 4.338 = 5.4 A TAP = 6.0 A TD = 1

(6/4.338 = 1.38)

Inst (50) = 8,328 ×

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

5 = 52.1A = >55 A 800

Slide 134

Question What T/C Coordination interval should be maintained between relays?

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 135

Answer B t

A

CB Opening Time + Induction Disc Overtravel (0.1 sec) + Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.)

I ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 136

Recloser • Recloser protects electrical transmission systems from temporary voltage surges and other unfavorable conditions. • Reclosers can automatically "reclose" the circuit and restore normal power transmission once the problem is cleared. • Reclosers are usually designed with failsafe mechanisms that prevent them from reclosing if the same fault occurs several times in succession over a short period. This insures that repetitive line faults don't cause power to switch on and off repeatedly, since this could cause damage or accelerated wear to electrical equipment. • It also insures that temporary faults such as lightning strikes or transmission switching don't cause lengthy interruptions in service.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 137

Recloser Types • Hydraulic • Electronic – Static Controller – Microprocessor Controller

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 138

Recloser Curves

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 139

TEMA 3

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 140

Transient Stability

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Topics • What is Transient Stability (TS) • What Causes System Unstable • Effects When System Is Instable • Transient Stability Definition • Modeling and Data Preparation • ETAP TS Study Outputs • Power System TS Studies • Solutions to Stability Problems ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 142

What is Transient Stability • TS is also called Rotor Angle Stability Something between mechanical system and electrical system – energy conversion

• It is a Electromechanical Phenomenon Time frame in milliseconds

• All Synchronous Machines Must Remain in Synchronism with One Another Synchronous generators and motors This is what system stable or unstable means ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 143

What is Transient Stability • Torque Equation (generator case)

T = mechanical torque P = number of poles

φ

air

= air-gap flux

Fr = rotor field MMF

δ = rotor angle

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 144

What is Transient Stability • Swing Equation

M

= inertia constant

D

= damping constant

Pmech

= input mechanical power

Pelec

= output electrical power

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 145

What Causes System Unstable • From Torque Equation T (prime mover) Rotor MMF (field winding) Air-Gap Flux (electrical system)

• From Swing Equation Pmech Pelec Different time constants in mechanical and electrical systems ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 146

What Causes System Unstable • In real operation Short-circuit Loss of excitation Prime mover failure Loss of utility connections Loss of a portion of in-plant generation Starting of a large motor Switching operations Impact loading on motors Sudden large change in load and generation ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 147

Effects When System Is Instable • Swing in Rotor Angle (as well as in V, I, P, Q and f)

Case 1: Steady-state stable Case 2: Transient stable Case 3: Small-signal unstable Case 4: First swing unstable ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 148

Effects When System Is Instable • A 2-Machine Example

• At δ = -180º (Out-of-Step, Slip the Pole)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 149

Effects When System Is Instable • Synchronous machine slip poles – generator tripping • Power swing • Misoperation of protective devices • Interruption of critical loads • Low-voltage conditions – motor drop-offs • Damage to equipment • Area wide blackout • … ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 150

Transient Stability Definition • Examine One Generator

• Power Output Capability Curve

∀ δ is limited to 180º ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 151

Transient Stability Definition • Transient and Dynamic Stability Limit  After a severe disturbance, the synchronous generator reaches a steady-state operating condition without a prolonged loss of synchronism  Limit: δ < 180° during swing

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 152

Modeling and Data Preparation • Synchronous Machine

 Machine  Exciter and AVR  Prime Mover and Governor / Load Torque  Power System Stabilizer (PSS) (Generator) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 153

Modeling and Data Preparation

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 154

Modeling and Data Preparation • Typical synchronous machine data

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 155

Modeling and Data Preparation • Induction Machine  Machine  Load Torque

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 156

Modeling and Data Preparation • Power Grid  Short-Circuit Capability  Fixed internal voltage and infinite inertia

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 157

Modeling and Data Preparation • Load  Voltage dependency  Frequency dependency

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 158

Modeling and Data Preparation • Load

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 159

Modeling and Data Preparation • Events and Actions

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 160

Modeling and Data Preparation Device Type

Action

Bus

3-P Fault

L-G Fault

Clear Fault

Branch

Fraction Fault Clear Fault

PD

Trip

Generator

Droop / Isoch Start

Loss Exc.

Grid

P Change

V Change

Delete

Motor

Accelerate

Load Change

Delete

Lumped Load

Load Change Delete

MOV

Start

Wind Turbine

Disturbance

Gust

MG Set

Emergency

Main

Close

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

P Change

V Change

Delete

Ramp

Slide 161

Power System TS Studies • Fault  3-phase and single phase fault  Clear fault  Critical Fault Clearing Time (CFCT)  Critical System Separation Time (CSST)

• Bus Transfer  Fast load transferring

• Load Shedding  Under-frequency  Under-voltage

• Motor Dynamic Acceleration  Induction motor  Synchronous motor ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 162

Power System TS Studies • Critical Fault Clearing Time (CFCT) Fault

Clear fault Clear fault

1 cycle

1 cycle unstable

unstable

unstable

stable

CFCT

Clear fault Clear fault

Cycle

• Critical Separation Time (CSST) Fault

Separation Separation

1 cycle

1 cycle unstable

unstable

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

unstable

stable

CSST

Separation Separation

Cycle

Slide 163

Power System TS Studies • Fast Bus Transfer Motor residual voltage 1 0.8 Vmotor 0.6 0.4 0.2 0 -1

-0.8

-0.6

-0.4

-0.2

0

s

0.2

0.4

0.6

0.8

1

-0.2 -0.4 -0.6 -0.8 -1

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 164

Power System TS Studies • Fast Bus Transfer δ

Ttransfer

ES = System equivalent per unit volts per hertz EM = Motor residual per unit per hertz ER = Resultant vectorial voltage in per unit volts per hertz

≤ 10 cycles

δ ≤ 90 degrees ER ≤ 1.33 per unit (133%) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 165

Power System TS Studies • Load Shedding

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 166

Power System TS Studies • Motor Dynamic Acceleration Important for islanded system operation Motor starting impact Generator AVR action Reacceleration

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 167

Solution to Stability Problems • Improve System Design  Increase synchronizing power

• Design and Selection of Rotating Equipment  Use of induction machines  Increase moment of inertia  Reduce transient reactance  Improve voltage regulator and exciter characteristics ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 168

Solution to Stability Problems • Application of Power System Stabilizer (PSS) • Add System Protections  Fast fault clearance  Load shedding  System separation Out-Of-Step relay …

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 169

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

TEMA 4

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 171

Harmonic Analysis

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

ARMONICAS Características principales:

 Exploración de frecuencia.  Flujo Armónico de Carga.  Dimensionamiento y Diseño de Filtros.  Evaluación Automática del límite de distorsión.  Factores de la influencia teléfono (TIF & I*T)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

del

Slide 173

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 174

Types of Power Quality Problems

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 175

Waveform Distortion • Primary Types of Waveform Distortion – DC Offset – Harmonics – Interharmonics – Notching – Noise

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 176

Harmonics • One special category of power quality problems • “Harmonics are voltages and/or currents present in an electrical system at some multiple of the fundamental frequency.” (IEEE Std 399, Brown Book)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 177

Nonlinear Loads • Sinusoidal voltage applied to a simple nonlinear resistor • Increasing the voltage by a few percent may cause current to double

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 178

Fourier Representation • Any periodic waveform can be expressed as a sum of sinusoids • The sum of the sinusoids is referred to as Fourier Series (6-pulse)

I ac =

2 3 1 1 1 1 I d (cosωt − cos 3ωt + cos 7ωt − cos11ωt + cos13ωt π 5 7 11 13

∞

⇒ ∑ I h cos(hωt + Φ h ) h =1

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 179

Harmonic Sources • Utilities (Power Grid) – Known as “Background Harmonic” – Pollution from other irresponsible customers – SVC, HVDC, FACTS, … – Usually a voltage source

• Synchronous Generators – Due to Pitch (can be eliminated by fractionalpitch winding) and Saturation – Usually a voltage source ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 180

Harmonic Sources (cont’d) • Transformers – Due to magnetizing branch saturation – Only at lightly loaded condition – Usually a current source

• Power Electronic Devices – Charger, Converter, Inverter, UPS, VFD, SVC, HVDC, FACTS (Flexible alternating current transmission systems) … – Due to switching actions – Either a voltage source or a current source

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 181

Harmonic Sources (cont’d) • Other Non-Linear Loads – Arc furnaces, discharge lighting, … – Due to unstable and non-linear process – Either a voltage source or a current source

• In general, any load that is applied to a power system that requires other than a sinusoidal current

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 182

Harmonic I and V

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 183

Classification of Harmonics • Harmonics may be classified as: – Characteristic Harmonics  Generally produced by power converters

– Non-Characteristic Harmonics  Typically produced by arc furnaces and discharge lighting (from non-periodical waveforms)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 184

Phase Angle Relationship • Fundamental Frequency

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 185

Phase Angle Relationship • Third Order

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 186

Phase Angle Relationship • Fifth Order

• Seventh Order

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 187

Order vs. Sequence

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 188

Characteristic Harmonics

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 189

Characteristic Harmonics (cont’d)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 190

Harmonic Spectrum %

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 191

Harmonic-Related Problems • Motors and Generators – Increased heating due to iron and copper losses – Reduced efficiency and torque – Higher audible noise – Cogging or crawling – Mechanical oscillations

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 192

Harmonic-Related Problems (cont’d) • Transformers – Parasitic heating – Increased copper, stray flux and iron losses

• Capacitors (var compensators) – Possibility of system resonance – Increased heating and voltage stress – Shortened capacitor life ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 193

Harmonic-Related Problems (cont’d) • Power Cables – Involved in system resonance – Voltage stress and corona leading to dielectric failure – Heating and derating

• Neutrals of four-wire systems (480/277V; 120/208V) – Overheating

• Fuses – Blowing ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 194

Harmonic-Related Problems (cont’d) • Switchgears – Increased heating and losses – Reduced steady-state current carrying capability – Shortened insulation components life • Relays – Possibility of misoperation • Metering – Affected readings ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 195

Harmonic-Related Problems (cont’d) • Communication Systems – Interference by higher frequency electromagnetic field

• Electronic Equipment (computers, PLC) – Misoperation

• System – Resonance (serial and parallel) – Poor power factor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 196

Parallel Resonance • Total impedance at resonance frequency increases • High circulating current will flow in the capacitance-inductance loop

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 197

Parallel Resonance

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 198

Capacitor Banks

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 199

Capacitor Banks

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 200

Capacitor Banks

Say, Seventh Harmonic Current = 5% of 1100A = 55 A

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 201

Capacitor Banks

Resistance = 1% including cable and transformer CAF = X/R = 7*0.0069/0.0012 =40.25 Resonant Current = 55*40.25 = 2214 A ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 202

Parallel Resonance (cont’d) Cause:

Source inductance resonates with capacitor bank at a frequency excited by the facilities harmonic sources

Impacts: 1. Excessive capacitor fuse operation 2. Capacitor failures 3. Incorrect relay tripping 4. Telephone interference 5. Overheating of equipment ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 203

Harmonic Distortion Measurements • Total Harmonic Distortion (THD) – Also known as Harmonic Distortion Factor (HDF), is the most popular index to measure the level of harmonic distortion to voltage and current – Ratio of the RMS of all harmonics to the fundamental component – For an ideal system THD = 0% – Potential heating value of the harmonics relative to the fundamental

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 204

Harmonic Distortion Measurements (cont’d) – Good indicator of additional losses due to current flowing through a conductor – Not a good indicator of voltage stress in a capacitor (related to peak value of voltage waveform, not its heating value) ∞

THD =

2 F ∑ i 2

F1

Where Fi is the amplitude of the ith harmonic, and F1 is that for the fundamental component. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 205

Harmonic Distortion Example Find THD for this waveform

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 206

Harmonic Example • Find THD for this Harmonic Spectrum

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 207

Adjustable Speed Drive – Current Distortion

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 208

Adjustable Speed Drive – Voltage Distortion

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 209

Harmonic Distortion Measurements (cont’d) • Individual Harmonic Distortion (IHD) - Ratio of a given harmonic to fundamental - To track magnitude of individual harmonic Fi IHD = F1

• Root Mean Square (RMS) - Total - Root Mean Square of fundamental plus all harmonics - Equal to fundamental RMS if Harmonics are zero ∞ 2 RMS =

∑F

i

1

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 210

Harmonic Distortion Measurements (cont’d) • Arithmetic Summation (ASUM) – Arithmetic summation of magnitudes of all components (fundamental and all harmonics) – Directly adds magnitudes of all components to estimate crest value of voltage and current – Evaluation of the maximum withstanding ratings of a device ∞

ASUM = ∑ Fi 1

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 211

Harmonic Distortion Measurements (cont’d) • Telephone Influence Factor (TIF) – Weighted THD – Weights based on interference to an audio signal in the same frequency range – Current TIF shows impact on adjacent communication systems ∞

∑ (W F ) i

TIF =

2

i

1

∞

∑F

2

i

1

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 212

Harmonic Distortion Measurements (cont’d) • I*T Product (I*T) – A product current components (fundamental

and harmonics) and weighting factors I •T =

H

2 ( I ⋅ T ) ∑ h h h =1

where Ih = current component Th= weighting factor h = harmonic order (h=1 for fundamental) H = maximum harmonic order to account ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 213

Triplen Harmonics • Odd multiples of the third harmonic (h = 3, 9, 15, 21, …) • Important issue for grounded-wye systems with neutral current • Overloading and TIF problems • Misoperation of devices due to presence of harmonics on the neutral

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 214

Triplen Harmonics

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 215

Winding Connections

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

•

Delta winding provides ampere turn balance

•

Triplen Harmonics cannot flow

•

When currents are balanced Triplens behave as Zero Sequence currents

•

Used in Utility Distribution Substations

•

Delta winding connected to Transmission

•

Balanced Triplens can flow

•

Present in equal proportions on both sides

•

Many loads are served in this fashion

Slide 216

Implications • Neutral connections are susceptible to overheating when serving single-phase loads on the Y side that have high 3rd Harmonic • Measuring current on delta side will not show the triplens and therefore do not give a true idea of the heating the transformer is subjected to • The flow of triplens can be interrupted by appropriate isolation transformer connection • Removing the neutral connection in one or both Y windings blocks the flow of Triplen harmonic current • Three legged core transformers behave as if they have a “phantom” delta tertiary winding ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 217

Modeling in Harmonic Analysis • Motors and Machines – Represented by their equivalent negative sequence reactance

• Lines and Cables – Series impedance for low frequencies – Long line correction including transposition and distributed capacitance

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 218

Modeling in Harmonic Analysis (cont’d) • Transformers – Leakage impedance – Magnetizing impedance

• Loads – Static loads reduce peak resonant impedance – Motor loads shift resonant frequency due to motor inductance ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 219

Reducing System Harmonics • Add Passive Filters – Shunt or Single Tuned Filters – Broadband Filters or Band Pass Filters – Provide low impedance path for harmonic current – Least expensive

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 220

Reducing System Harmonics (cont’d) • Increase Pulse Numbers – Increasing pulse number of convert circuits – Limited by practical control problems

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 221

Reducing System Harmonics (cont’d) • Apply Transformer Phase Shifting – Using Phase Shifting Transformers – Achieve higher pulse operation of the total converter installation

• In ETAP – Phase shift is specified in the tab page of the transformer editor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 222

Reducing System Harmonics (cont’d) • Either standard phase shift or special phase shift can be used

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 223

Reducing System Harmonics (cont’d) • Add Active Filters – Instantly adapts to changing source and load conditions – Costly – MVA Limitation

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 224

Voltage Distortion Limits Recommended Practices for Utilities (IEEE Bus Voltage Individual Total Voltage 519): Distortion Distortion At

(%)

THD (%)

69 kV and below

3.0

5.0

69.001 kV through 161kV

1.5

2.5

161.001 and above

1.0

1.5

PCC

In ETAP: Specify Harmonic Distortion Limits in Harmonic Page of Bus Editor:

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 225

Current Distortion Limits Recommended Practices for General Distribution Systems (IEEE 519):

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 226

TEMA 5

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 227

Motor Starting Dynamic Acceleration

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

ARRANQUE DE MOTORES Características principales:

 Aceleración motores.

dinámica

de

 Parpadeo (Flicker) de tensión.  Modelos dinámicos de motores.  Arranque estático de motores.  Varios dispositivos de arranque.  Transición de carga.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 229

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 230

Why to Do MS Studies? • Ensure that motor will start with voltage drop • If Tst 80% • Generation bus voltage > 93%

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 231

Why to Do MS Studies? • Ensure motor feeders sized adequately (Assuming 100% voltage at Switchboard or MCC) • LV cable voltage drop at starting < 20% •

LV cable voltage drop when running at full-load < 5%

•

HV cable voltage drop at starting < 15%

•

HV cable voltage drop when running at full-load < 3%

• Maximum motor size that can be started across the line •

Motor kW < 1/6 kW rating of generator (islanded)

•

For 6 MW of islanded generation, largest motor size < 1 MW

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 232

Motor Sizing • Positive Displacement Pumps / Rotary Pumps

•

p = Pressure in psi

•

Q = fluid flow in gpm

•

n = efficiency

• Centrifugal Pumps

•

H = fluid head in feet

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 233

Motor Types • Synchronous • Salient Pole • Round Rotor

• Induction • Wound Rotor (slip-ring) • Single Cage CKT Model

• Squirrel Cage (brushless) • Double Cage CKT Model

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 234

Induction Motor Advantages • Squirrel Cage • Slightly higher efficiency and power factor • Explosive proof

• Wound Rotor • Higher starting torque • Lower starting current • Speed varied by using external resistances

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 235

Typical Rotor Construction

• Rotor slots are not parallel to the shaft but skewed

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 236

Wound Rotor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 237

Operation of Induction Motor • AC applied to stator winding • Creates a rotating stator magnetic field in air gap • Field induces currents (voltages) in rotor • Rotor currents create rotor magnetic field in air gap • Torque is produced by interaction of air gap fields

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 238

Slip Frequency • Slip represents the inability of the rotor to keep up with the stator magnetic field • Slip frequency S = (ωs-ωn)/ωs where ωs = 120f/P ωn = mech speed

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 239

Static Start - Example

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 240

Static Start - Example

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 241

Service Factor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 242

Inrush Current

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 243

Resistance / Reactance • Torque Slip Curve is changed by altering resistance / reactance of rotor bars. • Resistance ↑ by ↓cross sectional area or using higher resistivity material like brass. • Reactance ↑ by placing conductor deeper in the rotor cylinder or by closing the slot at the air gap.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 244

Rotor Bar Resistance ↑ • Increase Starting Torque • Lower Starting Current • Lower Full Load Speed • Lower Efficiency • No Effect on Breakdown Torque

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 245

Rotor Bar Reactance ↑ • Lower Starting Torque • Lower Starting Current • Lower Breakdown Torque • No effect on Full Load Conditions

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 246

Motor Torque Curves

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 247

Rotor Bar Design • Cross section Large (low resistance) and positioned deep in the rotor (high reactance). (Starting Torque is normal and starting current is low). • Double Deck with small conductor of high resistance. During starting, most current flows through the upper deck due to high reactance of lower deck. (Starting Torque is high and starting current is low). ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 248

Rotor Bar Design • Bars are made of Brass or similar high resistance material. Bars are close to surface to reduce leakage reactance. (Starting torque is high and starting current is low).

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 249

Load Torque – ID Fan

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 250

Load Torque – FD Fan

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 251

Load Torque – C. Pump

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 252

Motor Torque – Speed Curve

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 253

Double Cage Motor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 254

Motor Full Load Torque • For example, 30 HP 1765 RPM Motor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 255

Motor Efficiency • kW Saved = HP * 0.746 (1/Old – 1/New) • $ Savings = kW Saved * Hrs /Year * $/kWh

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 256

Acceleration Torque • Greater Acceleration Torque means higher inertia that can be handled by the motor without approaching thermal limits

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 257

Acceleration Torque

P

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 258

Operating Range • Motor, Generator, or Brake

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 259

Rated Conditions

Terminal Current

Load(kva)

• Constant Power

kvar

0.8

Terminal Voltage

1.0

L1

Ir

0.8 Terminal Voltage

1.0

P = Tm Wm , As Vt ( terminal voltage ) changes from 0.8 to 1.1 pu, Wm changes by a very small amount. There fore, P is approx constant since Tm (α w²m) is approx. constant

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 260

Starting Conditions • Constant Impedance Starting Conditions

Constant Impedance

P

It

Kva LR

I LR

.8 kva

.9 I LR

LR

0.9

Terminal Voltage

1.0

Vt

(pu)

0.9 Terminal Voltage

1.0

Vt

(pu)

KVA LR = Loched - rotor KVA at rated voltage = 2HP 2 ≡ Code letter factor ≡ Locked – rotor KVA ∕ HP Z st =

______ KVA B KVA LR

KVR = rated voltage

____ KVR ² KVB

Pu, Rst = Zst cos θ st , Xst= Zst sin θ st

KVB = Base voltage KVAB = Base power

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 261

Voltage Variation • Torque is proportional to V^2 • Current is proportional to V I 100% voltage

v1

80% voltage p R

ws

0 I

wm

0

ws

wm

Load 100% V

Tst α ( operating voltage) ² _____________ Rated voltage

80% V

Ist α ( _____________ operating voltage) Rated voltage T st

T’ st

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

T

Slide 262

Frequency Variation • As frequency decreases, peak torque shifts toward lower speed as synchronous speed decreases. • As frequency decrease, current increases due reduced impedance. I

T em

F1

F1

F2 › F1

F 2 › F1

0

W3 = 120 ___f RPM P

0 WS1

WS2

Wm

WS1

WS2

Wm

Adjustable speed drive : Typical speed range for variable torque loads such as pumps and fans is 3/1,maximun is 8/1 ( 1.5 to 60 Hz)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 263

Number of Poles Variation •

As Pole number increases, peak torque shifts toward lower speed as synchronous speed decreases. Nro. of poles variation

T em

2 P - poles

W′S =

P - poles

WS ___ 2

P

Load

0

R

W′S

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

WS

Wm

Slide 264

Rotor Z Variation • Increasing rotor Z will shift peak torque towards lower speed. Rotor – Resistance Variation

r2

r3

r4

r1 P R

Q

S

r1 › r2 › r3 › r4

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 265

Modeling of Elements • Switching motors – Zlr, circuit model, or characteristic model • Synch generator - constant voltage behind X’d • Utility - constant voltage behind X”d • Branches – Same as in Load Flow • Non-switching Load – Same as Load flow • All elements must be initially energized, including motors to start ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 266

Motor Modeling 1. Operating Motor – Constant KVA Load

1. Starting Motor – During Acceleration – Constant Impedance – Locked-Rotor Impedance – Circuit Models

Characteristic Curves After Acceleration – Constant KVA Load ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 267

Locked-Rotor Impedance • ZLR = RLR +j XLR

(10 – 25 %)

POWER FACTOR

• PFLR is much lower than operating PD. Approximate starting PF of typical squirrel cage induction motor:

HORSE POWER RATING ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 268

Circuit Model I • Single Cage Rotor – “Single1” – constant rotor resistance and reactance

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 269

Circuit Model II • Single Cage Rotor – “Single2” - deep bar effect, rotor resistance and reactance vary with speed [Xm is removed]

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 270

Circuit Model III • Double Cage Rotor – “DB1” – integrated rotor cages

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 271

Circuit Model IV • Double Cage Rotor – “DB2” – independent rotor cages

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 272

Characteristic Model • Motor Torque, I, and PF as function of Slip – Static Model

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 273

Calculation Methods I • Static Motor Starting – Time domain using static model – Switching motors modeled as Zlr during starting and constant kVA load after starting – Run load flow when any change in system

• Dynamic Motor Starting – Time domain using dynamic model and inertia model – Dynamic model used for the entire simulation – Requires motor and load dynamic (characteristic) model ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 274

Calculation Methods II

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 275

Static versus Dynamic • Use Static Model When – Concerned with effect of motor starting on other loads – Missing dynamic motor information

• Use Dynamic Model When – Concerned with actual acceleration time – Concerned if motor will actually start

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 276

MS Simulation Features • Start/Stop induction/synchronous motors • Switching on/off static load at specified loading category • Simulate MOV opening/closing operations • Change grid or generator operating category • Simulate transformer LTC operation • Simulate global load transition • Simulate various types of starting devices • Simulate load ramping after motor acceleration

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 277

Automatic Alert • • • • •

Starting motor terminal V Motor acceleration failure Motor thermal damage Generator rating Generator engine continuous & peak rating • Generator exciter peak rating • Bus voltage • Starting motor bus • Grid/generator bus • HV, MV, and LV bus • User definable minimum time span ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 278

Starting Devices Types • Auto-Transformer

• Y/D Winding

• Stator Resistor

• Partial Wing

• Stator Reactor

• Soft Starter

• Capacitor at Bus

• Stator Current Limit

• Capacitor at Motor Terminal

– Stator Current Control

• Rotor External Resistor

– Torque Control

– Voltage Control

• Rotor External Reactor ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 279

Starting Device • Comparison of starting conditions

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 280

Starting Device – AutoXFMR

• C4 and C3 closed initially • C4 opened, C2 is closed with C3 still closed. Finally C3 is open ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 281

Starting Device – AutoXFMR • Autotransformer starting EX. 50% Tap Vmcc 3IST MCC

line

M

VMCC

50% tap

5VMCC

IST

VM

Autotransformer starter

PFST ( with autotransformer) = PFST ( without autotransformer)

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 282

Starting Device – YD Start

• During Y connection Vs = VL / √3 • Phase current Iy = Id / √3 and 3 to 1 reduction in torque ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 283

Starting Device – Rotor R

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 284

Starting Device – Stator R

• Resistor

RL

5VMCC

VMCC

PFST ( with resistor) =

50% tap

VM

RLR XLR

1-[pu tap setting ]² * [ 1- (PFST

=

XL

without resistor)²]

1- (0.5)² * [1-(PFST)²]

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 285

Starting Device Stator X • Reactor RL

5VMCC

VMCC 50% tap

PFST ( with reactor) = [pu tap setting ] * PFST

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

XL

VM

RLR XLR

(without reactor)

Slide 286

Transformer LTC Modeling • LTC operations can be simulated in motor starting studies • Use global or individual Tit and Tot

V limit

Tit

Tot T

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 287

MOV Modeling I • Represented as an impedance load during operation – Each stage has own impedance based on I, pf, Vr – User specifies duration and load current for each stage

• Operation type depends on MOV status – Open statusclosing operation – Close statusopening operation

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 288

MOV Modeling II • Five stages of operation Opening

Closing

Acceleration

Acceleration

No load

No load

Unseating

Travel

Travel

Seating

Stall

Stall

• Without hammer blow  Skip “No Load” period • With a micro switch  Skip “Stall” period • Operating stage time extended if Vmtr < Vlimit

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 289

MOV Closing • With Hammer Blow- MOV Closing

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 290

MOV Opening • With Hammer Blow- MOV Opening

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 291

MOV Voltage Limit • Effect of Voltage Limit Violation I

ACCL

STALL

VMTR < V LIMIT

UNSETTING

TRAVEL

Tacc

Tpos

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Travel

Tstl

Slide 292

TEMA 6 ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 293

Short-Circuit ANSI Standard

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

CORTO CIRCUITO Características principales:

 Estándar de ANSI/IEEE & IEC.  Análisis de fallas transitorias (IEC 61363).  Efecto de Arco (NFPA 70E2000)  Integrado con coordinación de dispositivos de protección.  Evaluación dispositivos.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

automática

de

Slide 295

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 296

Short-Circuit Analysis Types of SC Faults •Three-Phase Ungrounded Fault •Three-Phase Grounded Fault •Phase to Phase Ungrounded Fault •Phase to Phase Grounded Fault •Phase to Ground Fault

Fault Current •IL-G can range in utility systems from a few percent to possibly 115 % ( if Xo < X1 ) of I3-phase

(85% of all faults).

•In industrial systems the situation IL-G > I3-phase is rare. Typically IL-G ≅ .87 * I3-phase •In an industrial system, the three-phase fault condition is frequently the only one considered, since this type of fault generally results in Maximum current. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 297

Purpose of Short-Circuit Studies • A Short-Circuit Study can be used to determine any or all of the following: – Verify protective device close and latch capability – Verify protective device Interrupting capability – Protect equipment from large mechanical forces (maximum fault kA) – I2t protection for equipment (thermal stress) – Selecting ratings or settings for relay coordination ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 298

System Components Involved in SC Calculations • Power Company Supply • In-Plant Generators • Transformers (using negative tolerance) • Reactors (using negative tolerance) • Feeder Cables and Bus Duct Systems (at lower temperature limits) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 299

System Components Involved in SC Calculations • Overhead Lines (at lower temperature limit) • Synchronous Motors • Induction Motors • Protective Devices • Y0 from Static Load and Line Cable ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 300

Elements That Contribute Current to a Short-Circuit • Generator • Power Grid • Synchronous Motors • Induction Machines • Lumped Loads (with some % motor load) • Inverters • I0 from Yg-Delta Connected Transformer ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 301

Elements Do Not Contribute Current in PowerStation • Static Loads • Motor Operated Valves • All Shunt Y Connected Branches

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 302

Short-Circuit Phenomenon

v(t)

i(t)

v(t)= Vm∗ Sin(ω t + θ )

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 303

v(t)

i(t)

di v(t)= Ri + L = Vm× Sin( ωt + θ ) (1) dt Solving equation 1 yields the following expression - t Vm Vm i(t)= × sin( ωt + θ - φ ) + × sin( θ - φ )×e L Z Z      R

Steady State

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Transient (DCOffset)

Slide 304

AC Current (Symmetrical) with No AC Decay

DC Current

© 1996-2009Operation OperationTechnology, Technology,Inc. Inc.––Workshop WorkshopNotes: Notes:Short-Circuit Short-CircuitIEC ANSI ©1996-2009

Slide 305

AC Fault Current Including the DC Offset (No AC Decay)

©1996-2009 © 1996-2009Operation OperationTechnology, Technology,Inc. Inc.––Workshop WorkshopNotes: Notes:Short-Circuit Short-CircuitIEC ANSI

Slide 306

Machine Reactance ( λ = L I )

AC Decay Current

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 307

Fault Current Including AC & DC Decay

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 308

ANSI Calculation Methods 1) The ANSI standards handle the AC Decay by varying machine impedance during a fault.

ANSI

2) The ANSI standards handle the the dc offset by applying multiplying factors. The ANSI Terms for this current are: •Momentary Current •Close and Latch Current •First Cycle Asymmetrical Current ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 309

Sources and Models of Fault Currents in ANSI Standards Sources •Synchronous Generators •Synchronous Motors & Condensers •Induction Machines •Electric Utility Systems (Power Grids)

Models All sources are modeled by an internal voltage behind its impedance. E = Prefault Voltage R = Machine Armature Resistance X = Machine Reactance (X”d, X’d, Xd) ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 310

Synchronous Generators Synchronous Generators are modeled in three stages.

Synchronous Motors & Condensers Act as a generator to supply fault current. This current diminishes as the magnetic field in the machine decays.

Induction Machines Transient Reactance

Treated the same as synchronous motors except they do not contribute to the fault after 2 sec.

Subtransient Reactance

Electric Utility Systems

Synchronous Reactance

The fault current contribution tends to remain constant. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 311

½

Cycle Network

This is the network used to calculate momentary short-circuit current and protective device duties at the ½ cycle after the fault.

1 ½ to 4 Cycle Network This network is used to calculate the interrupting short-circuit current and protective device duties 1.5-4 cycles after the fault.

30-Cycle Network This is the network used to calculate the steady-state short-circuit current and settings for over current relays after 30 cycles.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 312

Reactance Representation for Utility and Synchronous Machine ½ Cycle

1 ½ to 4 Cycle

30 Cycle

X”d

X”d

X”d

X”d

X”d

X’d

Hydro-Gen with Amortisseur winding

X”d

X”d

X’d

Hydro-Gen without Amortisseur winding

0.75*X”d

0.75*X”d

X’d

X”d

X”d

X”d

1.5*X”d

Utility

Turbo Generator

Condenser

Synchronous Motor

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

α

α

Slide 313

Reactance Representation for Induction Machine ½ Cycle

1 ½ to 4 Cycle

>1000 hp , 250, at 3600 rpm

X”d

1.5*X”d

All others, >= 50 hp

1.2*X”d

3.0*X”d

< 50 hp

1.67*X”d

α

Note: X”d = 1 / LRCpu

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 314

Device Duty and Usage of Fault Currents from Different Networks ½ Cycle Currents (Subtransient Network)

1 ½ to 4 Cycle Currents (Transient Network)

HV Circuit Breaker

Closing and Latching Capability

Interrupting Capability

LV Circuit Breaker

Interrupting Capability

-----

Fuse

Interrupting Capability

SWGR / MCC

Bus Bracing

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Relay

Instantaneous Settings

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30 Cycle currents are used for determining overcurrent settings.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 315

Momentary Multiplying Factor

MFm is calculated based on: • Fault X/R (Separate R & X Networks) • Location of fault (Remote / Local generation) Comparisons of Momentary capability (1/2 Cycle) SC Current Duty

Device Rating

HV CB

Asymmetrical RMS Crest

C&L RMS C&L RMS

HV Bus

Asymmetrical RMS Crest

Asymmetrical RMS

Symmetrical RMS Asymmetrical RMS

Symmetrical RMS Asymmetrical RMS

LV Bus

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Crest

Slide 316

Interrupting Multiplying Factor MFi is calculated based on: • Fault X/R (Separate R & X Networks) • Location of Fault (Remote / Local generation) • Type and Rating of CB

Comparisons of Interrupting Capability (1 ½ to 4 Cycle)

HV CB LV CB & Fuse

SC Current Duty

Device Rating

Adj. Symmetrical RMS*

Adj. Symmetrical RMS*

Adj. Symmetrical RMS***

Symmetrical RMS

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 317

HV CB Closing and Latching Duty Calculate ½ Cycle Current (Imom,rms,sym

) using ½ Cycle Network.

• Calculate X/R ratio and Multiplying factor MFm

• Imom,rms,Asym=

MFm * Imom,rms,sym

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 318

HV CB Interrupting Duty Calculate 1½ to 4 Cycle Current (Imom,rms,sym

) using ½ Cycle Network.

• Determine Local and Remote contributions (A “local” contribution is fed predominantly from generators through no more than one transformation or with external reactances in series that is less than 1.5 times generator subtransient reactance. Otherwise the contribution is defined as “remote”). • Calculate no AC Decay ratio (NACD) and multiplying factor MFi NACD = IRemote / ITotal ITotal = ILocal + IRemote (NACD = 0 if all local & NACD = 1 if all remote) • Calculate Iint,rms,adj

= MFi * Iint,rms,Symm

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 319

HV CB Interrupting Capability • CB Interrupting kA varies between Max kA and Rated kA as applied kV changes – MVAsc capability. • ETAP’s comparison between CB Duty of Adj. Symmetrical kA and CB capability of Adjusted Int. kA verifies both symmetrical and asymmetrical rating. • The Option of C37.010-1999 standard allows user to specify CPT. • Generator CB has higher DC rating and is always compared against maximum through SC kA. ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 320

LV CB Interrupting Duty •

LV CB take instantaneous action.

•

Calculate ½ Cycle current Irms, Symm (I’f) from the ½ cycle network.

•

Calculate X/R ratio and MFi (based on CB type).

•

Calculate adjusted interrupting current Iadj, rms, symm = MFi * Irms, Symm

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 321

Fuse Interrupting Duty Calculate ½ Cycle current Iint,rms,symm

from ½ Cycle Network.

• Same procedure to calculate Iint,rms,asymm

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

as for CB.

Slide 322

L-G Faults

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 323

L-G Faults Symmetrical Components

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 324

Sequence Networks

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 325

L-G Fault Sequence Network Connections If = 3 × Ia 0 3 × VPr efault If = Z1 + Z 2 + Z0 if Zg = 0

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 326

L-L Fault Sequence Network Connections

I a 2 = − I a1 3 × VPr efault If = Z1 + Z 2

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 327

L-L-G Fault Sequence Network Connections I a 2 + I a1 + I a 0 = 0 = I a VPr efault If =  Z0 Z 2   Z1 +   Z0 + Z2  if Zg = 0

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 328

Transformer Zero Sequence Connections

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 329

Solid Grounded Devices and L-G Faults Generally a 3 - phase fault is the most severe case. L - G faults can be greater if : Z1 = Z 2 & Z 0 < Z 1 If this conditions are true then : I f3φ < I f 1φ This may be the case if Generators or Y/∆ Connected transformer are solidly grounded.

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 330

Unbalanced Faults Display & Reports Complete reports that include individual branch contributions for: •L-G Faults •L-L-G Faults •L-L Faults

One-line diagram displayed results that include: •L-G/L-L-G/L-L fault current contributions •Sequence voltage and currents •Phase Voltages ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 331

©1996-2009 © 1996-2009Operation OperationTechnology, Technology,Inc. Inc.––Workshop WorkshopNotes: Notes:Short-Circuit Short-CircuitIEC ANSI

Slide 332

©1996-2009 © 1996-2009Operation OperationTechnology, Technology,Inc. Inc.––Workshop WorkshopNotes: Notes:Short-Circuit Short-CircuitIEC ANSI

Slide 333

SC Study Case Info Page

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 334

SC Study Case Standard Page

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 335

SC Study Case Adjustments Page

Tolerance Adjustments

•Transformer Impedance •Reactor Resistance •Overload Heater Resistance

Length Adjustments •Cable Length •Transmission Line Length

Temperature Corrections

Adjust Fault Impedance

•Transmission Line Resistance

•L-G fault Impedance

•Cable Resistance

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 336

Tolerance Adjustments Z 'Transforme r = Z Transforme r * (1 ± Tolerance ) Length 'Cable = LengthCable * (1 ± Tolerance ) Length 'Transmissi onLine = LengthTransmissi onLine * (1 ± Tolerance ) Positive tolerance value is used for IEC Minimum If calculation. Negative tolerance value is used for all other calculations.

Adjustments can be applied Individually or Globally

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 337

Temperature Correction (234.5 + Tc ) R'Copper ' = RBASE * (234.5 + Tb ) ( 228.1 + Tc ) R' Alumi = RBASE * ( 228.1 + Tb ) RBASE = Resistance at base tempereatu re R' = Resistance at operating temperatur e Tb = Conductor base temperatur e in C Tc = Conductor temperatur e limit in C

Temperature Correction can be applied Individually or Globally ©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 338

System for SC Study Power Grid U1 X/R = 55

Transformers T1 X/R PS =12 PT =12 ST =12 T2 X/R = 12

Gen1 Voltage Control Design Setting: %Pf = 85 MW = 4 Max Q = 9 Min Q = -3

Lump1 Y open grounded

©1996-2009 © 1996-2009Operation OperationTechnology, Technology,Inc. Inc.––Workshop WorkshopNotes: Notes:Short-Circuit Short-CircuitIEC ANSI

Slide 339

System for SC Study

Tmin = 40, Tmax = 90

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 340

System for SC Study

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 341

Short-Circuit Alerts • Bus Alert • Protective Device Alert • Marginal Device Limit

©1996-2009 Operation Technology, Inc. – Workshop Notes: Short-Circuit IEC

Slide 342

Bus SC Rating Type of Device MV Bus (> 1000 Volts)

LV Bus (