Phase Comparison

Phase Comparison protection

Sankara Subramanian

GRID

History of Phase comparison .…..

Principle of Phase Comparison Normal Load Conditions End Y

End X I Y(+)

Mark

-

Space

Terminal currents

Modulated signals

-

+

Space

+

I X (+)

Mark

Mark Mark Composite - (usually no PLC signal transmission for load) ON-OFF channel

Principle of Phase Comparison External Fault End Y

End X I Y(+)

I X (+)

-

+

Mark Space

Terminal currents

Modulated signals Mark Mark Composite modulated signal

ON-OFF channel

+

Mark

-

Space

Principle of Phase Comparison Internal Fault End X

I Y(+)

I X (+) IF

+

-

Mark Space

Terminal currents

Modulated signals

+

Mark

End Y

-

Space

Mark Space Composite modulated signal ON-OFF channel

180°

180°

GAP = TRIP

Channel Equipment Phase-segregated channel Phase ‘A’

Phase ‘B’

Phase ‘C’

IA

IB

IC

Channel Equipment Single-phase channel

Phase ‘B’ – typically

I A , I B , I C ???

Line Faults – Current sequences Fault Load

3-Ph

Ph-Ph

PhGround

Ph-PhGround

Positive (1)

+

+

+

+

+

Negative (2)

-

-

+

+

+

Zero (0)

-

-

-

+

+

Sequence

Modulating quantity HISTORY

I1 k I 0

H.W. Lensner, Westinghouse (1946), A.P. Pleshko, Russia (1941)

I2

I1 (for 3-Ph fault)

k I0

Phase-segregated (3 channels)

A.J. McConnel, General Electric (1947)

France

MODERN APPROACH Russian manufacturers Alstom

General Electric

Line Faults – Modulating quantity Fault Load

3-Ph

Ph-Ph

PhGround

Ph-PhGround

Positive (1)

+

+

+

+

+

Negative (2)

-

-

+

+

+

Zero (0)

-

-

-

+

+

Sequence

Current angle errors • Sources angle difference • Signal propagation delay

• Measurement errors • Charging currents

Stability angle (1)

Load and external faults

Internal faults

x - y =180° BLOCK

s

x - y = 0°

s

SYSTEM STABILITY ANGLE - s.

TRIP

Stability angle (2) •

s is the system stability angle, recommended setting for short lines is 30o.

•

s compensates for general tolerances in PLC, relay, CT nonlinearity and changes in atmospheric conditions since the last propagation delay measurement.

• A 30o setting (-30o to +30o) means that a carrier ‚gap‛/space of longer than s /360, is needed to trip.

Long lines – charging current End X

UX

End Y

IX

Y 2

IX, cap.

IY, cap.

IY I Y, cap. U

IY

Id Θ

I’ Y

Y 2

180°

IX I’X

I X, cap.

HV lines with LENGTH > 150km require charging current compensation

UY

Starters • PLC cannot be activated permanently

• LOW STARTERS – initiate RF communication through channel (start PLC) • Some gap could appear in RF signal under normal condition • HIGH STARTERS – activate phase comparison element and allow trip to be issued. • IMPORTANT: − If any HIGH starter operated at one line terminal, some LOW starter MUST be active at all other terminals (all PLCs should be active)

!!!ONE-SIDED START OF PHASE COMPARISON = FALSE TRIP!!!

Phase Comparison classification

Phase Comparison protection Voltage-independent (purely current) - current starters - current modulation Voltage-independent Phase Comparison should be used whenever possible, as it’s much more reliable (immune to VT failure). Unfortunately, it’s not suitable for long HV lines.

Voltage-dependent Starters: - current - voltage - distance - complex modulation Voltage-dependent Phase Comparison is universal, but prone to VT failure.

Phase Comparison – Typical functional diagram Sequencer

Ia

Charging current Compensation Yc setting

Ib Ic

I

I2

I1

Phase comparison

High set Starter

Gap Detectio n

Sequencer

I2

RX Mixer

V

Angle shift

Trip Decision Trip / Block

Low set Starter

TX Mark / Space

Va Vb Vc

Voltage Input

Sequencer

Compensating V2 Zneg

Distance Starter Input

V2_comp

Working Starters & Modulator • Phase comparison protection utilizes sequence components based starters for sensitivity. • Current Modulator to do the mixing of the positive sequence and negative sequence currents to enable the phase angle detection. • The calculated modulated current positive half cycle is communicated to the remote end and is compared with the received remote Modulated current to do the phase angle measurement. • Phase angle Gap measurement starts only when the High set starter pick up.

Starters Application -Setting Tips(1) • As continuous transmission is not permitted Starter units are provided (sensitive-to provide high speed operation) such that Low set initiates transmission of carrier signal while high set initiates Gap measurements & trip in phase comparison protection. • Positive(I1) and negative sequence (I2)starters are provided to cover for balanced and unbalanced fault conditions. • Low set and high set starters are provided – to cater for the differences in the magnitude between the currents at 2 ends and also to account for the magnitude errors in the CT, hence 2 levels are required. • Impulse (Delta ) starters and Non-Impulse (threshold) starters are provided. • While generally, Impulse starters finds its application for most system fault conditions, Non- impulse starters can be set for system conditions like evolving fault scenarios from external to internal with out much rise in the fault currents.

Starters Application -Setting Tips(2) Impulse Positive sequence starters (I1): •

High set Impulse must be set above total line charging current (2 x Ich) to avoid tripping for closing CB.

•

High set should be set < 3 phase fault level, typically 50% of If min 3 .

•

In order to make protection stable during through fault conditions, ensure the difference between the minimum effective high set setting and maximum effective low set setting is > than the Positive sequence capacitive current. To meet this requirement set the ratio of HSS / LSS to a factor of 2.

Non-Impulse Positive sequence starters (I1): •

I1 low set must be set above the maximum load current

•

I1 low set must be set above peak power swing current, to prevent ‚continuous transmission‛ Alarm being raised for slow swings .Typical swing = 2 In ; set to 2.5 or 3 In

•

I1 high set needs to be 125% to 200% of I1 low set to give adequate margin

Starters Application -Setting Tips(3) Impulse Negative sequence starters (I2): • Impulse negative starters should be set to provide sensitivity for high resistance faults less than 10% of the rated current. • (3 x Impulse I2 High Set) = Effective earth fault sensitivity of the scheme. • Ensure the following for long transmission line. (same can be adopted for medium lines):

• Impulse I2 High set is NOT < IS * ((1/SIN) ( s - - )) Where IS –is sending end current (only line charging current is present under no load condition, when the local breaker is closed); s – is stability angle setting; - is typically taken as 15 deg (set to cover phase angle errors introduced by CT); - is typically taken as 10 deg ( set to cover the phase angle difference between compared line terminal currents due to signal propagation time and may be taken as 0.1 deg per mile). • Ensure HSS to LSS ratio is not less than 1.5 (alternatively, set Low set to 66% of High set setting).

Starters Application -Setting Tips(4) Non-Impulse (Threshold) Negative sequence starters (I2): • Non impulse I2 starters are set less sensitive than the impulse I2 starters. • Non-Impulse starters are set above the standing I2 in the system. • Example: Transmission system feeding 1-phase traction feeders.

• Non-impulse I2 ensures, operation for certain faults-like slow developing faults / evolving external to internal faults with no increase in I2 current magnitude. • Non-impulse also provided with Low set and High set starters. • Set Non-Impulse I2 to typically between 1.5 and 5 times the Impulse I2 starters.

1-ph AR (single pole autoreclose) • Phase comparison is exceptionally good in case of 1-ph AR • Evolving faults are cleared during 1-ph AR dead time

• Typically LOW and HIGH starters are active at both line ends as line mode is non-symmetrical (though that depends on load current and usage of voltage starters). Phase Comparison protection awaits only for GAPs.

IMPORTANT: −PLC transmission should be active at both line ends during 1-ph AR dead time !!!ONE-SIDED PLC TRANSMISSION = FALSE TRIP!!!

Teed-off transformers Phase comparison can be applied to teed-off transformer application

Internal Fault

IF R

R

IL

LOAD

IF DIRECTION

LOAD

IL DIRECTION,DEPENDING ON THE STRENGTH OF SOURCES & CONNECTED LOAD

- In many applications, there can be a step-down transformer teed-off the protected line. This transformer is not part of the protected unit, but is teed-off to out feed local load. The difficulty is this tee-line is NOT treated as the third-end of the phase comparison protection. - Hence the 2 end Phase comparison protection must function correctly for such scenario. The protection must refrain for internal load and also operate for internal fault scenarios.

Teed-off transformers – Distance permissive External Fault – beyond the transformer Z2

Z2 DISTANCE permission

R

R LOAD

IF DIRECTION

LOAD

IF

Permissive Scheme

• If teed-off transformer is extremely weak, it could be possible to select High Starters higher then external fault currents (still sensitive for internal faults) • Otherwise we must use Distance permissive scheme. This scheme doesn’t require any additional equipment

Teed-off transformers – with blocking kit External Fault – beyond transformer

PC

Block

Block

PLC

Injects continuous carrier

Phase Comparison

Power Direction PLC

Transfo prot.

Blocking Kit

Direction

PC

LOAD

PLC

Distance

IF DIRECTION

PC

LOAD

IF

Sometimes Distance permissive scheme can’t be used because of settings issue Blocking-scheme works for most of teed-off cases, but requires additional PLC and, sometimes, relays

3-ended Lines Phase comparison can be applied to 3-ended lines I1

I2

PC

PC

IF DIRECTION

PC

LOAD

I3

IF

LOAD



For any through-fault one current is in opposite phase to others.

I1 I2 I3 SUM NO GAPS = BLOCK

Weak Infeed

Phase comparison should be considered with great care in case of weak infeed. Weak Source

IF

Strong Source

PC

PC LOAD

IF DIRECTION

LOAD DIRECTION

If fault current is comparable with load current, this could lead to protection inaction (the angle of modulating quantity [–I1+K*I2] is hard to predict)

General advantages of Phase Comparison •Absolute selectivity •Reliable channel (power line itself) •Immune to Power Swings •Immune to VT failure (in ‘voltage-independent’ version) •Channel is under the utility’s control, unlike third party telecommunications

Coupling Scheme Behind

Front To remote

Line Trap

substation Coupling Capacitor

Line Matching Unit

•Transformer(s) •BusBar

Coaxial

Local substation PLC terminal

The PLC signal is routed to HV Line The PLC signal is not absorbed by the substation

Line Trap function = PLC signal Blocking HV Line Power energy (50/60 Hz)

PLC Signal (High Freq)

Substation

Line Trap = High Impedance for PLC signal (High Freq) Low Impedance for Power energy (50/60 Hz)

Two types of modulation

Signal

AM

FM

Effect of bad weather on PLC communication

Losses increase for all inclement weather conditions

n

The worst offender is when heavy frost is formed on the line n

n

Because of the skin effect, the carrier signal tries to propagate on the ice instead of the conductor. The attenuation can change as much as 4:1 depending on the frequency.

The contaminants (on the insulators) have a larger effect when it is raining than when the line is dry. n

The worst condition is a light rain with the presence of contaminants on the insulators n

33

Dedicated PLC for Phase Comparison • Requirements: − SPEED (Fast pick-up, fast drop-off) − REPEATABILITY (STABILITY) − SYMMETRICAL • Communication PLCs: − Encoding – Audio Frequency (AF) – Radio Frequency (RF) – Channel – Radio Frequency (RF) – Audio Frequency (AF) – Decoding − Guard Frequency: at first a receiver must detect guard freq. drop, then appearance of signal frequency − Command length: 5-10 ms for detection − Several commands and other data transmission with different priorities • Communication PLCs don’t provide desired speed and stability • Specific PLC for phase comparison − Fast keying – Radio Frequency (RF) – Channel – Radio Frequency (RF) - Output to relay Translation : User audio signal (AF) into radio Spectrum (RF) Amplification : To compensate the line attenuation

RF Noise RF noise in HV line  two mains effects • Impulsive Noise = Caused by atmospheric discharges, breakers and isolator close/open operation

• Corona effect = Due to sequences of pulse streams caused by arcs over conductors. It appears during positive-going half-cycle of the Line voltage (occurrance frequency for a 50Hz 3-phase system is 150 Hz)

• The corona noise could be subject to considerable variations due to differences in the design parameters of the overhead line.

• Other variations are possible due to the construction, altitude and age of the line

• Weather effect can also be significant

35

ON-OFF and FSK channels ON-OFF channel ON

Hi_F

180° OFF

Lo_F

ON

Hi_F

FSK channel

180° OFF

Lo_F

ON

Hi_F

P547 80TE Protection Functions Distance protection

Phase Comparison

DEF protection Negative Sequence Protection

Charging Current Compensation

Broken Conductor Detection

Single End Tripping

Unstabilising Facility

1 &3 Pole Tripping Breaker Failure

Overcurrent & SEF Thermal Protection

MiCOM P547 80TE The MiCOM P547 provides: High-speed phase comparison protection using proven phase comparison technique.

Phase Selection is based on proven techniques. 1 & 3 pole tripping High performance sub cycle distance protection:

 Universal mho characteristics  Quadrilateral characteristics for short lines/cables, and where boosting of resistive fault coverage is required

Phase segregated aided directional earth fault DEF to provide high resistance ground fault detection MiCOM P54x - 1-Jul-13 - P 38

MiCOM P547 80TE • Phase Comparison and Distance protection can work independently, as a main 1 or main 2 protection. • Alternatively, each zone can be set independently to work in case of communication failure. • Distance elements may run in parallel with the Phase Comparison protection, offering dual main protection. • A phase segregated aided directional earth fault DEF can also be configured as a main 1 or main 2 or backup protection to provide high resistance ground fault detection

PLC - Ensuring PLC Repeatability, Compatibility & Suitability End X

End Y

Line Trap

Third Party PLC, Coupling Equipment

Line Trap

Coupling

Coupling

PLC

PLC

PLC Interface

MiCOM P547 80TE

PLC Interface

Pulsar PLC, from the USA or PZSU which is widely used in the Russian network.

Third Party PLC, Coupling Equipment

Connections Relay - PLC - Relay: Two Copper Wire Pairs (4 Leads)

• P547 and PLC ‚contacts‛ are static outputs for fast switching

PLC

+

• Not a comms. protocol, simply Cu leads Opto

Out +

• P547 dedicated fast scan I/O is additional to standard I/O

Opto Out

P547

Modulating Quantity • Unbalanced faults will have negative sequence component

• The positive sequence component is used to counter the effects of the negative sequence component due to unbalanced charging current in the case of three phase faults. • The modulating quantity is − where 3K20

-I1 + KI2

Adaptive K - ‚Intelligent‛ Mode Setting 35 For heavy prefault load, or power swings, need to boost I2 effect to keep earth fault sensitivity

30 25 K

20

15 10 5 0

0

2

4

6

8

Pre Fault Load /Earth Fault Setting

10

Earth Fault Sensitivity if Set to ‚User‛ Mode Local End Current Contribution, IF

K > 3*IFLC /IF + 1

Load, IFLC

LOAD

Remote end AN fault

Starters - to Detect the Fault and Control Carrier Send & Tripping Starters − Delta/Impulse negative sequence • (0.05- 0.6 In)

Fault

Prefault

Current :-

− Delta/Impulse positive sequence • (0.05-0.6 In)

i rly

− Threshold negative sequence (I2) • (0.05 -5.0 In)

=

− Threshold positive sequence (I1) • (0.05 - 5.0 In)

i mem

− Threshold negative voltage (V2) • (0.001 - 1 Un)

+

− Distance (chosen Zone) − Delta could be set more sensitive = Superimposed

ir

Propagation Delay Where is the Propagation delay introduced? − Delay in supplying i/p pulse to PLC equipment, PLC equipment processing time (rising edge and lag at switch off burst on falling edge). − Delay at receiving end - PLC processing time and delay by the relay in measuring the time period of the input pulse. − Propagation delay of the HF carrier along the power line (negligible = 3 s per km).

Propagation Delay • Why does the propagation delay need to be considered ? − If it is not considered the effective stability angle s has to be set much higher − This would limit the maximum line length

− Propagation delay test is automatically instigated at user set time intervals

MiCOM P547 Channel Auto Test • Channel autotest − Relays must be configured as one MASTER and one or two SLAVEs − ‚Chan Test‛ should be enabled at least for MASTER − Channel Fail ALARM: • MASTER: no reply (5 ms pulse) from SLAVE after request during Test Time • SLAVE: no request (pulse 15 ms) from MASTER during Test Time • If channel failed, Phase Comparison isn’t disabled, channel propagation time is kept from previous test • If SLAVE has ‚Chan Test‛ disabled, autotest works Ok. Channel Failure ALARM isn’t raised in SLAVE relay

Recommended Stability Angle Setting Variation with km Length (km) Length (miles) s

150 km

200 km

250 km

300 km

350 km

400 km

90 mi

125 mi

155 mi

185 mi

215 mi

250 mi

30

35

40

45

50

55

• For lines longer than 150 km, a 5 degree increase in s is recommended for each additional 50 km. • Capacitive charging current constraints limit phase comparison application to a practical maximum of 400 km line length (250 miles).

MiCOM P547 Charging current compensation, Mode 1 Mode 1

End X

UX

IX

Y 2

IX, cap.

IY, cap.

IY I Y, cap. U

Y 2

IY

Id Θ

I’ Y

End Y

180°

IX I’X

I X, cap.

I comp (A,B,C) = I meas (A,B,C) – I cap (A,B,C) I comp (A,B,C) = I meas (A,B,C) – j*U (A,B,C) * Y/2 * f/fnom compensated

measured

UY

Stability angle – Mode 1

Icap 1

x - y =180° BLOCK

s

x - y = 0°

s

SYSTEM STABILITY ANGLE - s.

TRIP

MiCOM P547 Charging current compensation, Mode 2 Mode 2

End X

UX

IX

Y 2

IX, cap.

End Y

IY, cap.

Y 2

IY

UY

In Mode 2 the relay doesn’t measure real voltage

с

Icap = Unom. ph*Y/2

s

Mode 2 increases stability angle by Θс

s

Θс = 2*arcsin(Iемк./Iмod)

с

Iмod = - I1 + K*I2

Stability angle – Mode 2

Icap Mode-2

c

x - y =180° BLOCK

x - y = 0°

s

TRIP

s

c

SYSTEM STABILITY ANGLE - s. Charging Current Compensation - C.

MiCOM Phase Comparison Advantages • Mode of protection where PLC exists. • Provides unit protection without fibre optic connection.

• Communication medium is as reliable as the Power Line itself • No additional Phase selection relay required along with phase comparison relay.

• No seperate charging current compensation setting needed. • Charging current compensation works all time. • Applicable to all lines, long or short, strong and weak infeeds • Applicable to teed-off transformer and 3-line terminal application.

GRID