phase comparison

8/10/2019 Phase Comparison

1/55

GRID

Sankara Subramanian

Phase Comparison protection


2/55

History of Phase comparison ...


3/55

Principle of Phase Comparison -Normal Load Conditions

ON-OFF

channel

End X End Y

X (+)I Y(+)I

Mark Mark

Composite - (usually no PLC signal transmission for load)

MarkSpace

Modulated signals MarkSpace

-+

Terminal currents

+

-


4/55

Principle of Phase Comparison -External Fault

Composite modulated signal

End X End Y

X (+)I Y(+)I

-+

Terminal currents -+

Modulated signals MarkSpace

MarkSpace

Mark Mark

ON-OFF

channel


5/55

Principle of Phase Comparison -Internal Fault

Composite modulated signal

End X End Y

X (+)I Y(+)I

FI

-+

Terminal currents -+

Mark

SpaceModulated signals Mark

Space

Mark Space

ON-OFF

channel

180 180

GAP = TRIP


6/55

Channel EquipmentPhase-segregated channel

Phase A

Phase B

Phase C

AI

BI

CI


7/55

Channel EquipmentSingle-phase channel

Phase B typically

???,, CBA III


8/55

Line Faults Current sequences

Fault

SequenceLoad 3-Ph Ph-Ph

Ph-Ground

Ph-Ph-Ground

Positive (1) + + + + +

Negative (2) - - + + +

Zero (0) - - - + +


9/55

Modulating quantity

HISTORY

MODERN APPROACH

A.J. McConnel,

General Electric (1947)

H.W. Lensner, Westinghouse (1946),

A.P. Pleshko, Russia (1941)1 0I k I

2 0 1 (for 3-Ph fault)I k I I

Russian manufacturers

Alstom

General Electric

Phase-segregated (3 channels) France


10/55

Line Faults Modulating quantity

Fault

Sequence

Load 3-Ph Ph-PhPh-

GroundPh-Ph-Ground

Positive (1) + + + + +

Negative (2) - - + + +

Zero (0) - - - + +


11/55

Current angle errors

Sources angle difference

Signal propagation delay

Measurement errors

Charging currents


12/55

Stability angle (1)

x - y =180

x - y = 0

BLOCK TRIP

s

s

SYSTEM STABILITY ANGLE- s.

Load and external faultsInternal faults


13/55

Stability angle (2)

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

s compensates for general tolerances in PLC, relay, CT non-linearity and changes in atmospheric conditions since the last

propagation delay measurement. A 30osetting (-30o to +30o) means that a carrier gap/space

of longer than s /360, is needed to trip.


14/55

Long lines charging current

End X

End Y

Y

2

Y

2I

XIYUX UY

IY, cap.X, cap.

U

IY

IX

I X, cap.

IY, cap.

IYIX

Id

180

HV lines with LENGTH > 150km require charging current compensation


15/55

Starters

PLC cannot be activated permanently

LOW STARTERSinitiate RF communication through channel(start PLC)

Some gap could appear in RF signal under normal condition

HIGH STARTERSactivate phase comparison element andallow trip to be issued.

IMPORTANT:

If any HIGH starter operated at one line terminal, some LOWstarter MUST be active at all other terminals (all PLCs should

be active)

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


16/55

Phase Comparison classification

Phase Comparison protection

Voltage-independent

(purely current)

Voltage-dependent

Starters:

- current

- voltage

- distance

- current starters

Voltage-independent Phase Comparison

should be used whenever possible, as itsmuch more reliable (immune to VTfailure). Unfortunately, its not suitable forlong HV lines.

- current modulation

- complex

modulation

Voltage-dependent PhaseComparison is universal, butprone to VT failure.


17/55

Phase Comparison Typicalfunctional diagram

Sequencer

Ia

Ib

Ic I2

Charging

current

Compensation Yc

setting

Sequencer

I1High set

Starter

Mixer

RX

Angle

shift

Voltage

Input

Va

Vb

Vc

Sequencer

Compen-

sating

Zneg

Distance

Starter

Input

Low set

Starter

TX

Trip

Decision

Gap

Detectio

n

Phasecomparison

Mark / Space

Trip /

Block

V2 V2_comp

I I2

V


18/55

Phase comparison protection utilizes sequence components based startersfor sensitivity.

Current Modulator to do the mixing of the positive sequence and negativesequence 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 Modulatedcurrent to do the phase angle measurement.

Phase angle Gap measurement starts only when the High set starter pickup.

WorkingStarters & Modulator


19/55

As continuous transmission is not permitted Starter units are provided

(sensitive-to provide high speed operation) such that Low set initiatestransmission 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 forbalanced and unbalanced fault conditions.

Low set and high set starters are provided to cater for the differences inthe magnitude between the currents at 2 ends and also to account for themagnitude errors in the CT, hence 2 levels are required.

Impulse (Delta ) starters and Non-Impulse (threshold) starters areprovided.

While generally, Impulse starters finds its application for most systemfault conditions, Non- impulse starters can be set for system conditionslike evolving fault scenarios from external to internal with out much rise inthe fault currents.

StartersApplication -Setting Tips(1)


20/55

Impulse Positive sequence starters (I1):

High set Impulse must be set above total line charging current (2 x Ich) to avoidtripping 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 effectivelow set setting is > than the Positive sequence capacitive current. To meet thisrequirement 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 continuoustransmission Alarm being raised for slow swings .Typical swing = 2 In ; set to 2.5or 3 In

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



21/55

Impulse Negative sequence starters (I2):

Impulse negative starters should be set to provide sensitivity for high resistance faults lessthan 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 takenas 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).



22/55

Non-Impulse (Threshold) Negative sequence starters (I2):

Non impulse I2 starters are set less sensitive than the impulse I2starters.

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 slowdeveloping faults / evolving external to internal faults with noincrease 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 theImpulse I2 starters.



23/55

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 linemode is non-symmetrical (though that depends on load current andusage of voltage starters). Phase Comparison protection awaits only forGAPs.

IMPORTANT:

PLC transmission should be active at both line endsduring 1-ph AR dead time

!!!ONE-SIDED PLC TRANSMISSION = FALSE TRIP!!!


24/55

Teed-off transformers

Phase comparison can be applied to teed-off transformer application

Internal Fault

- In many applications, there can be a step-down transformer teed-off the protected line. Thistransformer is not part of the protected unit, but is teed-off to out feed local load. The difficulty isthis 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. Theprotection must refrain for internal load and also operate for internal fault scenarios.

RLOAD

R

IF

IL

IF DIRECTION

IL DIRECTION,DEPENDINGONTHESTRENGTH

OFSOURCES& CONNECTEDLOAD

LOAD


25/55

Teed-off transformers Distance permissive

External Fault beyond the transformer

If teed-off transformer is extremely weak, it could be possible to select High Starters higherthen external fault currents (still sensitive for internal faults)

Otherwise we must use Distance permissive scheme. This scheme doesnt require anyadditional equipment

Permissive Scheme

R

LOAD

R

IFIF DIRECTION

LOAD

DISTANCE permission

Z2 Z2


26/55

Teed-off transformers with blocking kit

External Fault beyond transformer

Sometimes Distance permissive scheme cant be used because of settings issue

Blocking-scheme works for most of teed-off cases, but requires additional PLC and, sometimes,

relays

PCLOAD

PC

IF

IF DIRECTION

LOAD

PLC PLC

Distance

Power

Direction

Transfo

prot.

PLC

Direction

PC Phase

Comparison

Blocking Kit

Injects continuous carrier

Block Block

3 ended Lines


27/55

3-ended Lines

Phase comparison can be applied to 3-ended lines

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

I1

PCLOAD

PC

LOAD

PC

IF

IF DIRECTION

I1 I2

I3

I2

I3

SUM

NO GAPS = BLOCK

Weak Infeed


28/55

Weak Infeed

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

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)

PC

LOAD

PC

IF

IF DIRECTION

LOAD DIRECTION

Strong Source

Weak Source


29/55

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 utilitys control, unlike third partytelecommunications


30/55

FrontBehind

Local substation

To remote

substation

Coupling

Capacitor

Line

Matching

Unit

PLC terminal

Coaxial

Transformer s)

BusBar

Line Trap

The PLCsignal isrouted to HVLine

The PLC

signal is notabsorbed bythe substation

Coupling Scheme

Line Trap function


31/55

= PLC signal Blocking

HV Line

Substation

Line Trap = High Impedance for PLC signal (High Freq)

Low Impedance for Power energy (50/60 Hz)

Power energy 50/60 Hz)

PLC Signal High Freq)

Line Trap function


32/55

Two types of modulation

Signal

AM

FM

Effect of bad weather on PLC communication


33/55

33

Losses increase for all inclement weather conditions

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

n Because of the skin effect, the carrier signal tries to propagate on

the ice instead of the conductor.n The attenuation can change as much as 4:1 depending on the

frequency.

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

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

Effect of bad weather on PLC communication

Dedicated PLC for Phase Comparison


34/55

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 appearanceof signal frequency

Command length: 5-10 ms for detection Several commands and other data transmission with different priorities

Communication PLCs dont provide desired speed and stability

Specific PLC for phase comparison

Fast keying Radio Frequency (RF) Channel Radio Frequency (RF) - Outputto relay

Translation : User audio signal (AF) into radio Spectrum (RF)

Amplification : To compensate the line attenuation

RF Noise


35/55

35

RF noise in HV linetwo mains effects

Impulsive Noise = Caused by atmospheric discharges, breakers andisolator close/open operation

Corona effect = Due to sequences of pulse streams caused by arcs overconductors. 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 todifferences in the design parameters of the overhead line.

Other variations are possible due to the construction, altitude andage of the line

Weather effect can also be significant

RF Noise


36/55

ON-OFF and FSK channels

180 180ON ON ON

OFF OFF

Hi_F Hi_F Hi_FLo_F Lo_F

ON-OFF channel

FSK channel


37/55

Breaker

Failure

Single End

Tripping

Thermal

Protection

Negative Sequence

Protection

BrokenConductor

Detection

1 &3 PoleTripping

Phase

Comparison

Overcurrent

& SEF

Unstabilising

Facility

Charging Current

Compensation

P547 80TE Protection Functions

Distance

protectionDEF

protection


38/55

MiCOM P54x - 1-Jul-13 - P 38

MiCOM P547 80TE

The MiCOM P547 provides:

High-speed phase comparisonprotection 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 shortlines/cables, and where boosting of

resistive fault coverage is required

Phase segregated aided directional

earth fault DEF to provide high

resistance ground fault detection


39/55

MiCOM P547 80TE

Phase Comparison and Distance protection can workindependently, as a main 1 or main 2 protection.

Alternatively, each zone can be set independently to work incase of communication failure.

Distance elements may run in parallel with the PhaseComparison protection, offering dual main protection.

A phase segregated aided directional earth fault DEF can alsobe configured as a main 1 or main 2 or backup protection toprovide high resistance ground fault detection

PLC E i PLC R t bilit


40/55

PLC - Ensuring PLC Repeatability,Compatibility & Suitability

MiCOM

P547 80TE

End X End Y

PLC

Interface

PLC

CouplingThird Party

PLC,

Coupling

Equipment

Third Party

PLC,

Coupling

Equipment

Line Trap Line Trap

PLC

Interface

PLC

Coupling

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

Connections Relay PLC Relay:


41/55

Not a comms. protocol,simply Cu leads

P547 and PLCcontacts are staticoutputs for fast

switching

P547 dedicated fast scanI/O is additional tostandard I/O

PLC

P547

Out

Opto

OptoOut

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


42/55

Unbalanced faults will have negative sequence component The positive sequence component is used to counter the

effects of the negative sequence component due tounbalanced charging current in the case of three phasefaults.

The modulating quantity is

where 3K20

-I1+ KI2

Modulating Quantity


43/55

Adaptive K - Intelligent Mode Setting

0

5

10

15

20

25

30

35

0 2 4 6 8 10

Pre Fault Load /Earth Fault Setting

K

For heavy prefault load, or power

swings, need to boost I2 effect to keep

earth fault sensitivity

Earth Fault Sensitivity if


44/55

Remote end AN fault

Load, IFLC

Local End Current

Contribution, IF

LOAD

K > 3*IFLC/IF + 1

Earth Fault Sensitivity ifSet to User Mode

Starters - to Detect the Fault and


45/55

Control Carrier Send & Tripping

Starters

Delta/Impulse negative sequence (0.05- 0.6 In)

Delta/Impulse positive sequence

(0.05-0.6 In) Threshold negative sequence (I2)

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

(0.05 - 5.0 In) Threshold negative voltage (V2)

(0.001 - 1 Un)

Distance (chosen Zone) Delta could be set more sensitive

irly

=

imem

+

ir

Current :-

Prefault Fault

= Superimposed


46/55

Propagation Delay

Where is the Propagation delay introduced?

Delay in supplying i/p pulse to PLC equipment, PLCequipment processing time (rising edge and lag at switchoff burst on falling edge).

Delay at receiving end - PLC processing time and delay bythe 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).


47/55

Why does the propagation delay need to be considered ? If it is not considered the effective stabilityangle s has to be set much higher

This would limit the maximum line length

Propagation delay test is automatically instigated at user settime intervals

Propagation Delay

MiCOM P547 Channel Auto Test


48/55

Channel autotest

Chan Test should be enabled at least for MASTER

Relays must be configured as one MASTER and one or twoSLAVEs

Channel Fail ALARM:

MASTER: no reply (5 ms pulse) from SLAVE after request duringTest Time

SLAVE: no request (pulse 15 ms) from MASTER during Test Time

If channel failed, Phase Comparison isnt disabled, channel

propagation time is kept from previous test

If SLAVE has Chan Test disabled, autotest works Ok. Channel

Failure ALARM isnt raised in SLAVE relay

MiCOM P547 Channel Auto Test

Recommended Stability Angle Setting -


49/55

For lines longer than 150 km, a 5 degree increase in s is recommended foreach additional 50 km.

Capacitive charging current constraints limit phase comparison application toa practical maximum of 400 km line length (250 miles).

Recommended Stability Angle Setting -Variation with km

Length(km)

150 km 200 km 250 km 300 km 350 km 400 km

Length(miles)

90 mi 125 mi 155 mi 185 mi 215 mi 250 mi

30 35 40 45 50 55

MiCOM P547 Charging current compensation


50/55

MiCOM P547 Charging current compensation,Mode 1

End X

End Y

Y

2

Y

2

Mode 1

IX

IYUX UY

I

Y, cap.X, cap.

U

IY

IX

I X, cap.

IY, cap.

IY

IX

Id

180

Icomp (A,B,C) = Imeas (A,B,C)Icap (A,B,C)

Icomp (A,B,C)= Imeas (A,B,C)j*U(A,B,C) * Y/2 * f/fnom

compensated measured


51/55

Stability angle Mode 1

x - y =180

x - y = 0

BLOCK TRIP

s

s

SYSTEM STABILITY ANGLE- s.

Icap 1

MiCOM P547 Charging current compensation,


52/55

Icap =

Unom. ph*Y/2

= 2*arcsin(I./Iod)

In Mode 2 the relay doesnt measure real voltage

Mode 2 increases stability

angle by s

s

Iod= - I1 + K*I2

End X

End Y

Y

2Y

2

Mode 2

IXI

YUX UYIY, cap.X, cap.

MiCOM P547 Charging current compensation,Mode 2

bili l d


53/55

c

c

Stability angle Mode 2

x - y =180 x - y = 0

BLOCK TRIP

s

s

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

IcapMode-2

MiCOM Phase Comparison


54/55

MiCOM Phase ComparisonAdvantages

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 phasecomparison 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.


55/55

GRID

phase comparison

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