Generator Protections

4

SINGLE LINE DIAGRAM OF 32MW GENERATOR FEEDER - I

FEEDER - II

G.T. BREAKER

GENERATOR TRANSFORMER 40MVA

11 KV / 138KV

UNIT AUXILIARY TRANSFORMER 11KV/6.9 KV 4MVA

GENERATOR 32 MW

NGT 11KV/240V

Figure 2.1: Single line diagram.

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GENERATOR SPECIFICATIONS Make : T.D.P.S [ Toyo Denki Power Systems] MVA : 40 MW : 32 Stator voltage : 11kV Stator current : 2099A Rotor voltage : 358V Rotor current : 552A Frequency : 50 Hz No. of Poles : 4 Power factor : 0.8 lag No. of Phases : 3 Insulation class : ‘F’ (155°c) Excitation system : Brush less Enclosure : Ip 54 Speed : 1500 r.p.m Type of cooling : Air

6

GENERATOR PROTECTIONS

1. Generator differential protection 2. Under or over frequency 3. Non – directional over current 4. Negative phase sequence 5. Over voltage 6. Fuse Fail 7. Loss of excitation 8. Back up Impedance 9. Low forward power (or) Reverse active power 10. Under voltage 11. Voltage restraint over current 12. Rotor, Earth fault relay 13. IDMT Back up Earth Fault 14. 100% stator Earth Fault relay

1 - 11 protections are covered in REM 543 relay 12,13 and 14 are covered in ABB relay

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ABOUT REM 543 NUMERICAL RELAY

5.1. INTRODUCTION: 5.1.1. General: REM 543 rotating machine terminal is a part of the ABB Substation Automation System and extends the Functionality and flexibility of the concept further increased performance is achieved by utilizing the multi processor architecture, Digital Signal Processing Combined with a Powerful CPU and distributed I/O handling facilitates parallel and improves response times and accuracy. The HMI including an LCD display with different views makes the local use of the REM 543 rotating machine terminal safe and easy. The HMI instruct the user how to proceed.

5.1.2. Hardware Versions: The REM 543 rotating machine terminal contains several hardware versions, depending on the number of I/O’s available, the product is called REM 543.

5.2. APPLICATION: The REM 543 rotating machine terminals are designed to be used as the main protection system of generator and generator – transformer units in small and medium – power diesel, hydro electric and steam power plants etc. the protection of large and/or important MV synchronous and asynchronous motors used. e.g in pumps, mills and crushes. During startup and normal run forms another application area.

8

By means of graphic HMI display, the control functions in the machine terminal indicate the status of disconnectors or circuit breakers locally. Further the machine terminal allows status information from the circuit breaker and the disconnectors to be transmitted to the remote control system. Controllable objects. Such as CBS, can be opened and closed over the remote control system. Local control is also possible via the push buttons on the front panel of the machine terminal.

The protection functions of the REM 543 are designed for selective short – circuit and earth fault protection of rotating machines, rotating machines also need protection against abnormal operating conditions such as over current unbalanced load, over temperature, over and under voltage over and under excitation, over and under frequency, generator motoring and under impedance function is provided for line backup.

REM 543 terminal measures phase currents, phase to phase or phase to earth voltages, neutral current, residual voltage, frequency and power factors, active and reactive power is calculated from measured currents and voltages, energy can be calculated on the basis of the measured power, measured values can be indicated locally and remotely as scaled primary values.

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5.3.1 Functions of the Machine Terminal: i)

Protection functions

ii)

Measurement functions

iii)

Control functions

iv)

Condition monitoring functions

v)

Communication functions

vi)

Standard functions

5.3.1.1) Protection Functions: Protection is one of the most important functions of the REM 543 machine terminal. The protection function blocks are independent of each other and have their own setting groups, data recording etc. The non – directional over current protection, for example includes the three stages NOC3 LOW, NOC3 High and NOC3 Inst, each with independent protection functions.

5.3.1.2) Measurement Functions: These functions includes measurement of i)

Neutral current measurement

ii)

Three – phase current measurement

iii)

Three phase power and energy measurement

iv)

Residual voltage measurement

v)

Three phase voltage measurement

vi)

System frequency measurement

vii)

Transient disturbance recorder

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5.3.1.3) Control Functions: The control functions are used to indicate the status of switching devices i.e. circuit breakers and disconnectors and to execute open and close commands for controllable switching devices of the switchgear. Further more, there are supplementary functions for control logic purposes e.g. on/off switches MIMIC alarm LED control, numerical data for MIMIC and logic controlled control position selector.

5.3.1.4) Condition Monitoring Functions: These functions includes monitoring of the i)

Spring charging control

ii)

Trip circuit supervision

iii)

Breaker travel time

iv)

Supervision function of the energizing voltage input circuit

v)

Supervision function of the energizing current input circuit.

5.3.1.5) Communication Functions: The machine terminal has three serial communication ports, one on the front panel and two on the rear panel.

5.3.1.6) Standard Functions: Standard functions are used for logics such as interlocking alarming and control sequencing.

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BRIEF DESCRIPTION OF PROTECTIONS

6.1. PROTECTIONS COVERED IN REM 543: 6.1.1) GENERATOR DIFFERENTIAL PROTECTION: 6.1.1.1. Introduction:  Three phase current differential protection with stabilized and instantaneous stages providing winding short-circuited protection for generators.  The stabilized stage is provided with saturation detection that blocks the stage internally in case of current transformer saturation at external faults.  The differential and stabilizing currents are calculated for every phase on the basis of the fundamental frequency components of currents  A separately adjustable instantaneous differential current stage for severe internal faults. Instantaneous stage is not affected by saturation detection.  Delayed trip output for the circuit – breaker failure protection (CBFP) function  High stability at external faults, also with partially saturated current transformers.

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6.1.1.2. Description of operation: 6.1.1.2.1. Operation Criteria: The differential protection function block includes two stages for generator differential protection.

6.1.1.2.2. Stabilized Stage: The operating characteristics of the stabilized stage 3 ∆I> is determined by the parameters ‘Basic setting’ and ‘starting ratio’ as well as by the parameters “Turn point 1” and “Turn Point 2” for the turning points of characteristics. The settings are the same for each phase. When the differential current exceed the operating characteristics, the function block trips unless it internally blocks the trip function ‘or’ is blocked by the external blocking signal. The phasons Ī1 and Ī2 denote the fundamental frequencies components of the CT Secondary Currents on the input side and output side of the protected object. The amplitude of the differential current Id is obtained as follows Id = (Ī1 – Ī2). In a normal situation there is no fault in the area protected by the function block. Then the currents Ī1 and Ī2 are equal and differential current I d = 0. In practice however the differential current slightly deviates from zero in normal situations. In generator protection the deviation is caused by CT inaccuracies. In a stabilized differential relay the differential current required for tripping is the higher the higher the load current is the stabilizing current I b of the relay is obtained as follows

Ī1 + Ī 2 Ib = 2

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The operation of the relay is affected by stabilization as shown by the operating characteristics illustrated in figure below Id In

Default settings Maximum settings

3

OPERATION Ib2

Ib2

2 Minimum settings

1

NO OPERATION Id1 In

Turn- Point 1

Turn- Point 2

Id3

Id2

1

2

3

4

5

Ib In

Figure 6.1: Operating characteristic for the stabilized stage of the generator differential protection function block Diff6G

The basic setting for the stabilized stage of the function block is determined according to the above figure: Id1 Basic setting = In The starting ratio is determined correspondingly: Id2

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Starting ratio = Ib2 The first turning point “Turn Point 1” can be set at a desired point with in the range 0.0 – 1.0 accordingly the second turning point “Turn Point 2” can be set within the range 1.0 – 3.0

The slope of the operating characteristics for the function block varies in different parts of the range. In part 1 (0.0≤ Ib/In < Turn Point 1), The differential current required for tripping is constant. The value of the differential current is the same as the basic setting selected for small inaccuracies of current transformers but it can also be used to influence the overall level of the operating characteristics.

When turn-point 1 ≤ Ib/In < turn point 2, is called influence area of the setting, “starting ratio” In this part variations in the starting ratio affect the slope of the characteristics i.e how big the change in the differential current required for hipping is in comparison with the change in load current. The starting ratio allows for C.T errors.

At high stabilizing currents i.e when Ib/In ≥ turn point 2 the slope of the characteristics is constant. The slope is 100%, which means that the increase in the differential current is equal to the corresponding increase in the stabilizing current.

15

The required differential current for tripping at a certain stabilizing current level can be calculated using the formulas.

If stabilizing current is lower than turn point 1 Id, operate = Basic setting If stabilizing current is greater than turn point 1 But lower than turn point 2 Id, operate = Basic setting + (Ib – turn point 1) × starting ratio For greater stabilizing current values, that is beyond turn point 2, Id, operate = Basic setting + (Turn Point 2 – Turn Point 1) × starting ratio + (I b – turn point 2)

6.1.1.2.3. Instantaneous stage: In addition to the stabilized stage the differential function block includes an instantaneous stage, which does not allow for stabilization. This stage trips when the amplitude of the fundamental frequency component of the differential current exceeds the set operate value “Inst. Setting” (or) when the Instantaneous value of the differential current exceeds 2.5 × Inst Setting.

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6.1.1.3. SET VALUES: CT ratio – 2500/1A

Parameter Basic setting Starting ratio Turn point 1 Turn point 2 Inst. Setting

Code

Values

Units

S1

5 – 50

%

S2

10 – 50

%

S3

S4

S5

0.0 – 1.0 1.0 – 3.0 5 – 30

×In

Explanation The lowest ratio of differential and nominal current to cause trip Slope of the second line of the operating characteristics Turn point between the first and second line of operating

Actual settings 5% 10% 0.5

characteristics Turn point between second and ×In

third line of operating characteristics

×In

Trip value of Instantaneous stage

TABLE 6.1.1.1

6.1.2. UNDER OR OVER FREQUENCY PROTECTION:

1.5 5

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6.1.2.1. Introduction:  Selectable under frequency or over frequency protection.  Selectable frequency rate of change function.  Start and trip indication in terms of output signals.  Definite time operation.

6.1.2.2. Application: The frequency function blocks are specially designed for applications such as generator protection,. load shedding, load restoration and disconnection for island operation.

6.1.2.3. Operation criteria: The function block freq1St_ can be used for under frequency (f) protection. The function block operates as either underfrequency or over frequency relays depending on whether the set operate value is above or below the rated frequency of the relay or feeder terminal.

The function block also includes a starting element that measures the rate of change of the power system frequency; so that the need for protection can be anticipated even before a major frequency change occurs. The parameter “Operation mode” is used for setting the operation direction of the df/dt function. When the set value is indicated as “df/dt”, the positive rate of change of frequency is measured (the function block operates as a positive derivative function). The frequency rate of change function can also be set out of use.

The output START1 is activated when the f function starts. Correspondingly, START2 is activated when the f or df/dt function starts, depending on the operation mode used. The trip signals of both the f function and the df/dt function (TRIP1 and TRIP2) can be used for load shedding. The operate time of the f function can be set via the parameter “Operation time 1” and the operate time of both the f function and the df/dt function via the parameter “Operation time 2”. Active START1 and START2 signals are both indicated by steady start LEDs (yellow) and active TRIP1 and TRIP2 signals by steady trip LEDs (red) on the MMI.

The blocking signal BS1 can be used for blocking the operation of the under frequency and over frequency function f. When the blocking signal BS1 is active, the DT timer 1 is frozen. In the same way, the blocking signal BS2 can be used for blocking the operation of the df/dt or f function.

In an under voltage situation the function block is internally blocked. The under voltage limit value is set according to the application.

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6.1.2.4. SETVALUES: PT ratio : 11000/110 V Parameter

Code

Operation mode Voltage limit Start frequency Operate time

S1

0…6

-

1

Data direction R

S2

0.30…0.90

× Un

0.30

R

S3

25.00… 75.00 0.10… 120.00

Hz

48.70

R

S

20.00

R

S4

Values

Unit

Default

Explanation Operation mode for frequency protection Under voltage limit for blocking Start value for U/O frequency protection Operate time for U/O frequency protection

TABLE 6.1.2.1 Set values for 32MW Generator: Under frequency Operating mode Voltage limit Start frequency Operating time

1 f< 0.3 × Un (3.3 KV) 47.5Hz 3 sec TABLE 6.1.2.2

Over Frequency 1 f> 0.3 × Un (3.3KV) 52.5Hz 3 sec

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6.1.3. NON-DIRECTIONAL OVER CURRENT PROTECTION:

6.1.3.1. Introduction:  Non directional over current protection  Definite-time (DT) operation  NOC3 Low: fourteen inverse-time (IDMT) characteristics 6.1.3.2. Application: The three phase non-directional over current function blocks are designed for non-directional two-phase and three-phase over current and short-circuit protection whenever the DT characteristics or, as concerns NOC3 Low, the IDMT (Inverse Definite Minimum Time) characteristics is appropriate. Suppression of harmonics is possible. 6.1.3.3. Operation Criteria: When the function block starts, the START signal is set to TRUE. Should the over current situation exceed the set definite operate time or, at the inverse-time operation, the time determined by the level of the measured current, the function block operates. The internal delay of the heavy-duty output relay is included in the total operate time. When the function block operates, the TRIP signal is set to TRUE. Operation mode instantaneous is selectable in the function blocks NOC3 high and NOC3Inst. in instantaneous mode the TRIP signal is set active immediately. Additionally, the function blocks NOC3High and NOC3Inst have a fast blocking output to be used in interlocking-based busbar protection. Once a phase current exceeds the set start current.

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6.1.3.4. SET VALUES:

Parameter Code

Values

Operation mode

S1

0…15

Start current Time multiplier

S2

0.10… 5.00 0.05… 1.00

S4

NOC3Low Defaul Unit t 1

× In

0.10

Data Actual Explanation direction setting R Selection of Normal operation Inverse mode and inverse-time characteristics R Start current 1 ×In

-

0.05

R

Time multiplier ‘k’ in IDMT mode

0.05

TABLE 6.1.3.1 NOC3Inst Parameter

Code

Operation mode

S1

Start current Operate time

S2 S3

Unit

Default

0…2

-

1

Data direction R

0.10… 40.00 0.05… 300.00

×In

0.10

R

Start current

3×In

S

0.05

R

Operate time in DT mode

0.1

Values

Explanation Selection of operation mode

Actual setting DT

TABLE 6.1.3.2 NOC3 High Unit

Default

0…21)

-

1

Data direction R

S2

0.10…40.00

×In

0.10

R

S3

0.05… 300.00

S

0.05

R

Parameter

Code

Operation mode

S1

Start current Operate time

Values

TABLE 6.1.3.3

Explanation Selection of operation mode Start current

Actual setting DT 1.5×In

Operate time 0.05 in DT mode sec

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6.1.4. NEGATIVE PHASE SEQUENCE PROTECTION: 6.1.4.1. INTRODUCTION:  Negative-phase sequence protection  Definite-time (DT) or inverse-time (IDMT) operation  Definite minimum time for high-level negative-sequence currents in inversetime operation.  Limited maximum operate time for long-time low-level negative-sequence currents in inverse-time operation.  Adjustable start delay in inverse-time operation.  Input signal for selecting the direction of rotation  Output for blocking the reconnection of an overheated machine.

6.1.4.2. Application: The function blocks NPS3 Low and NPS3 High are designed for negativephase-sequence protection whenever the operating characteristic is appropriate. They are applied for the protection of power generators or synchronous motors against thermal stress and damage.

6.1.4.3. Operation criteria: The function block has the two operation modes “Definite time” and Inverse time”. The type of operation is selected via the setting parameter “Operation Mode”.

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In both operation modes the function block starts if the calculated negative phase-sequence exceeds the set start current, which is set via the “Start Value” parameter. The parameter is common to the two operations modes. The default value of the “Start value” parameter is 20% of nominal, which is usual for motor protection. Generators are more sensitive to current unbalance and the negative sequence current value that a generator can stand continuously is usually between 5% and 10%. Therefore in case of generator protection a safer value for the “Start value” parameter is 5%.

Inverse-Time Operation: The operate time of the function block in the inverse-time mode is expressed mathematically as follows: K t= I2

2

- Start Value2 IN Where, t = relay operate time in seconds I2 = negative-sequence current IN = rated current of the machine Start value = Setting parameter that corresponds to the continuous negative-sequence current withstand of the machine, the I2 current expressed in xIN (rated current of the machine).

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K = Setting parameter that corresponds to the machine constant, equal to the I 22t constant of the machine, as stated by the machine manufacturer

Figure 6.1.4.1: The time/negative sequence current characteristics of NPS3Low and NPS3High When the measured negative-sequence current exceeds the set start current I 2, the function block starts accumulating a sum, the accumulate rate being proportional to the subtraction of the squared value of the actual negative-sequence current and the squared value of the "Start value" parameter. When the sum exceeds the level corresponding to the setting parameter K, the function block operates. The higher the degree of current unbalance, the faster the sum increases, and as the operate level of the sum is defined only by the constant K, the negative-sequence relay will have an inverse-time operating characteristic which conforms to the thermal load characteristic of a rotating machine. When the overload disappears, the subtraction (12" - Start Value2) becomes negative and the sum decreases. Thus, decrease of the

25

sum indicates cooling of the machine, and the cooling speed depends on the value of the I2 current. When the sum reaches 0, the accumulation is stopped. In inverse-time operation, the delay of the START output can be set via the parameter “Start delay". The start delay can be used for definite-time alarming when the START output is used as an alarm output. The set start delay does not affect the operate time of the function block. The maximum operate time is limited for long-time low-level negativesequence currents. The maximum operate time can be set via the “Maximum time” parameter and the minimum operate time via the "Minimum time" parameter. The meaning of the minimum and maximum time settings is illustrated in the figure below. I2/IN

Operating curve K t= (I2/IN)2 – Start Value2

Start value Minimum time

Minimum time

Figure 6.1.4.2: Operating characteristic

t

26

The setting parameters “K”, Start delay”, “Minimum time” and “Maximum time” do not affect the definite-time mode.

6.1.4.4. SET

Paramete r Operation mode

VALUES:

S1

0…2

-

Defaul t 1

Start value

S2

0.01… 0.50

×In

0.20

K

S4

5.0… 100.0

-

5.0

Start delay

S5

0.1…60.0

S

1.0

Maximum time

S7

500…. 10000

S

1000

Cooling time

S8

5… 10000

S

50

Code

Values

Unit

Data Explanation direction R Selection of operation mode (definite-or inverse-time mode) R Start value of negativesequence current I2 R Operating characteristic constant R Definite start time in inversetime mode R Maximum operate time regardless of the inverse characteristics R Time required to cool the machine

TABLE 6.1.4.1

Actual settings Inverse time

0.15×In

K= 14.11 2 sec 500sec

60 sec

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6.1.5. OVER VOLTAGE PROTECTION: 6.1.5.1. Introduction:  Single-phase, two-phase and three-phase over voltage protection.  Definite-time (DT) operation.  OV3Low: two inverse-time (IDMT) characteristics.  Voltage measurement with conventional voltage transformers or voltage dividers.  Two alternative measuring principles: the average value of consecutive instantaneous peak-to-peak values of voltages or the numerically calculated fundamental frequency voltages. 6.1.5.2. Application: Faults in the network or a faulty tap changer or voltage regulator of a power transformer may cause abnormal busbar voltages. The function blocks OV3Low and OV3High are designed for the single-phase, two-phase and three-phase over voltage protection whenever the DT characteristics or, as concerns the low-set stage, the IDMT (Inverse Definite Minimum Time) characteristic is appropriate. Suppression of harmonics is possible. 6.1.5.3. Measuring mode: When phase-to-phase voltages are measured, the function block operates on two alternative measuring principles: the average value of consecutive instantaneous peak-to-peak values of voltages or the numerically calculated fundamental frequency voltage. The measuring mode is selected with either an MMI parameter.

28

6.1.5.4. Operation criteria: If at least one phase-to-phase voltage measured by the function block exceeds the set start voltage, the module delivers the START signal. When the function block starts, the START signal and the STATUS_ output signal of the specific phase-toearth or phase-to-phase voltage are set to TRUE. Should the over voltage situation exceed the "preset definite operate time or, at the inverse-time operation of OV3Low, the time determined by the level of the measured voltage, the junction block operates. At the, inverse-time operation, two different sets of voltage/time curves, A and B, are available. The delay of the heavy-duty output relay is included in the total operate time. 'n operation, the TRIP signal is set to TRUE. The DT or IDMT timer, is allowed to run only if the blocking signal BS1 is inactive, i.e. its value is FALSE. When the signal becomes active, i.e. its value turns to TRUE; the timer will be stopped (frozen). When the blocking signal BS2 is active, the TRIP signal cannot be activated. The TRIP signal can be blocked by activating the BS2 signal until the function block drops off. 6.1.5.5.

SET VALUES:

PT ratio: 11000/110V Parameter Code Values

Unit Default

Operation mode

S1

0…3

-

1

Start voltage Operate time Time multiplier

S2

0.10 … 1.60

×Un

1.10

Data Explanation direction R Selection of operation mode and Inverse-time characteristic R Start voltage

S3

0.05 … 1.00

S

0.05

R

Operate time in DT mode

S4

0.05 … 1.00

-

0.05

R

Time multiplier in IDMT mode

TABLE 6.1.5.1

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6.1.6. FUSE FAIL PROTECTION: 6.1.6.1. Introduction: 

Detection of failures in a voltage measurement circuitry



A failure is detected in a voltage measurement circuitry when the negativesequence voltage rises to a significant level while the negative-sequence current does not rise correspondingly.



If only one phase-to-phase voltage is measured, detection is based on the amplitude of the measured voltage and the absence of high negative-sequence current



If all the measured voltages are lost while the currents remain at a normal level, a failure is recognized in the voltage measurement circuit.

6.1.6.2. Application: Some voltage based protection function may maloperation if a voltage measurement circuitry is damaged or if the miniature circuit breaker (MCB) of the measurement circuitry has opened for example due to an operation of the short circuit protection. Such protection functions, e.g. U16Low, are therefore blocked by Fuse Fail to avoid a wrong operation of the protection during the absence of the correct voltage measurement.

30

6.1.6.3. SET VALUES:

Parameter Code Values

Ratio U2/U1>

Ratio 12/11<

Unit

Defaul t

Data Direction

S41

10…50

%

25

R/W

S42

10…50

%

20

R/W

TABLE 6.1.6.1

Explanation Minimum ratio of negativesequence voltage to positivesequence voltage to allow blocking Maximum ratio of negativesequence current to positivesequence current to allow blocking

Actual setting

25%

20%

31

6.1.7. LOSS OF EXCITATION PROTECTION: 6.1.7.1. INTRODUCTION:



Single-phase or three-phase protection against under excitation/loss of excitation for motors and generators.



Definite-time (DT) operation.



Under excitation protection based on the offset-mho characteristic.



Internal under voltage blocking (

KI >

Voltage limit

Voltage level

Figure 6.1.11.1: Functionality of VOC6Low and VOC6High in the control mode “Voltage step” The following equations determine how the start current is influenced by the voltage in “Voltage step” mode: When U < “Voltage limit”: IStart (U) = KISetting When U ≥ “Voltage limit”: IStart (U) = Isetting Voltage slope: If the measured voltage is below the value “ Voltage Limit 2”, the start current is dropped by multiplying it by the current multiplier (K). If the voltage is above the

46

value “Voltage Limit 2” but below the value “Voltage limit 1”, the start current is calculated from the slope from point (Voltage limit 2, KI) to point (Voltage limit 1, I>). If the measured voltage rises above the value “Voltage limit 1”, the set start current value is valid. The procedure is shown in figure. Current level

I>

KI >

Voltage limit 2

Voltage limit 1

Voltage level

Figure 6.1.11.2: Functionality of VOC6Low and VOC6High in the control mode “Voltage slope” 6.1.11.4.

SET VALUES:

47

TABLE 6.1.11.1 6.2. PROTECTIONS COVERED IN ABB RELAY:

6.2.1. ROTOR, EARTH FAULT: 6.2.1.1. INTRODUCTION: 

Single-stage relay, constructed as a plug-in sub-assembly



Adjustable pick-up value in ohms (fault resistance)



Adjustable trip delay



Simple testing facility

Parameter

Code

Values

Unit Defaul t 1

Data direction R

Operation mode

S1

0 …7

Start current

S2

Operate time

S3

Time multipli er Control mode

S4

Explanation

0.10 … 5.00 0.05 … 300.0 0 0.05 … 1.00

×In

0.10

R

S

0.05

R

Operate time in DT mode

-

0.05

R

Time multiplier in IDMT mode

0.1

S5

0…2

-

0

R

Voltage slope

Voltage limit 1

S7

0.60 … 1.00

×Un

0.60

R

Voltage limit 2

S8

0.10 … 0.59

×Un

0.10

R

Selection of mode for voltage control Upper voltage setting value for voltage slope mode Lower voltage setting value for voltage slope mode

Selection of operation mode and inversetime characteristic Start current

Actual settings Normal inverse

1×In

0.6×Un

0.1×Un

48

6.2.1.2. Application: The electronic relay type IWX161a-1 in combination with an ancillary relay either type YWX111-11 is designed for the detection of earth faults on the rotor windings of turbo-alternators or synchronous motors. The protection scheme is connected to the positive and negative poles of the excitation supply and to the earth of the rotor shaft via condensers, which provides D.C. isolation. In normal operation the ancillary relay YWX111-11, the coupling condensers and the normal capacitance of the rotor to ground (shaft) form a balanced bridge. The leakage resistance of an earth fault on the rotor winding shunts its ground capacitance and disturbs the balance of the bridge. The resulting differential voltage is detected by the IWX161a-1, causing it to trip.

6.2.1.3. Operation criteria: The winding capacitance CR of the machine, coupling capacitance CK, the calibration capacitance CX and two high-value resistors R7 and R8 form and RC bridge, which is balanced provided the insulating properties of the machine are correct. The bridge is fed from voltage transformer of the generator via terminals 4 and 5. When a fault occurs, balance of the bridge is disturbed in that branch CR is shunted with the insulation fault resistance.

6.2.1.4. SET VALUES:

Description

Setting range

Actual setting

49

Fault resistance setting

0 … 5000 ohms.

5KΩ 1st stage Alarm

Time delay setting

0.5 …. 5s ± 5%

3 sec

Fault resistance setting

0 … 5000 ohms.

2KΩ 2nd stage Trip

Time delay setting

0.5 …. 5s ± 5%

3 sec

TABLE 6.2.1.1

6.2.2. IDMT BACKUP EARTH FAULT:

6.2.2.1. INTRODUCTION:

 Range of time setting 10 – 100%  Range of current setting 1:4, adjustable in 7 steps by means of noninterrupting setting switch  High resetting current, at least 90% of relay setting

50

 Max. overrun time of 0.5  Temperature – compensated measuring system  Instantaneous maximum-current trip with own contact and own visual signal  Instantaneous trip is continuously adjustable in either I × 2.5 – 10 or I × 4-20 range and to infinity.  Plug-in active part, the C.T. connections being automatically short-circuited when the relay is withdrawn.  Tropical zed design.

6.2.2.2. Application:

The relay type ICM is an over current relay with an inverse-time characteristic. That means to say, its tripping time is shorter, the greater the fault current. As secondary relay parts it is fed by current transformers. It is used to protect parts of electrical installations and simple line systems against over current, earth fault and short circuits. For the protection of solidly earthed systems against earth faults, relays are available with current setting up to 0.1 A. The relays are manufactured with two-current/time characteristic for 50Hz (Fig. 6.7). The characteristic determines the type designation of the particular relay.

It is possible to incorporate two separate indicating contactors, one for the inverse-time tripping, and the other for the instantaneous maximum-current tripping.

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The active part of the relay is plugged into the dust-tight casing. The locking arm, normally vertical, can then be pulled down, in which position the active part of the relay is already disconnected from the leads and the C.T. connections automatically short-circuited. The relay can now be entirely withdrawn from its casing, for instance for testing or repair.

6.2.2.3. SET VALUES: CT ratio: 2500/1A Description

Setting range

Actual settings

Setting range

0.1A – 0.8A

0.1A

Operating time at twice set current or over

0.5s. Max

0.1

TABLE 6.2.2.1

6.2.3. 100% STATOR EARTH FAULT: 6.2.3.1. Application: The RAGEK provides 100% stator ground-fault protection for most generators and large transformer-connected motors, which have a neutral connection available and are not solidly grounded. The RAGEK can also be used for generators with unearthed neutral.

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The relay is applied to provide the conventional ground-fault protection for 90-95% of the stator winding by monitoring the fundamental frequency component of the neutral voltage. In addition, it is used to detect ground faults on the remaining parts of the winding and the entire neutral system by monitoring the third harmonic components in the neutral voltage. To avoid a continuous alarm when the machine is out of service and during running up/down, a supervisory relay is generally used.  The 100% protection overlaps the 95% protection of the stator winding and, in addition, monitors the integrity of the entire neutral system for both short circuits and open circuits. Faults in this area, while not critical by themselves, can result in a devastating machine fail are should a second ground-fault occur.  When more than the minimum 1% third-harmonic voltage exists, the operating zone of the 100% protection can be further extended and the operating value of the 95% protection can be increased. A reduction in the operating time for the 95% protection is then feasible without any loss in security. 6.2.3.2. Operation Criteria: If a fundamental voltage arises in the neutral point, the over voltage relay will operate and give a start indication and after set delay it energies the signal relay RXSF, which initiates tripping and alarm for earth fault 0 – 95%. When the generator voltage has sufficient third harmonic, the under voltage relay resets. After operation of the supervision relay, the undervoltage voltage relay operates after set time when

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an earth fault occurs close to or at the neutral point. Then the signal relay RXSF initiates tripping and alarm for earth fault 95-100%.

6.2.3.3.

SET VALUES:

Description Fundamental RXEDK 2H 3rd harmonic RXEDK 2H Voltage supervision RXEDK 2H

Setting Range U1 = 5 – 80 V U2 = 0.1 – 16V U1 = 20 – 320V Table 6.2.3.1

Actual setting 40V 5V 230V