2 dir. oc + ef protn_apps_areva_pn

8/22/2019 2 Dir. Oc + Ef Protn_apps_areva_pn

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This document is the exclusive property of Alstom Grid and shall not betransmitted by any means, copied, reproduced or modified without the prior

written consent of Alstom Grid Technical Institute. All rights reserved.

GRID

Technical Institute

Appl icat ion of Direct ional

Overcurrent

and Earthfaul t Protect ion


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> Directional Overcurrent and Earthfault Protection2 2

Direct ional Protect ion


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Need for Direct ion al Con trol

Generally required if current can flow in both directions

through a relay location

e.g. Parallel feeder circuits

Ring Main Circuits

2.1 0.50.9 0.11.31.7


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Ring Main Circuits

Grading has now been lost !

2.1 0.50.9 0.11.31.7


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Ring Main Circuits

Relays operate for current flow in direction indicated

(Typical operating times shown)

0.9 0.10.5 0.90.50.1


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Ring Main Circui t

With ring closed :

Both load and fault current may flow in eitherdirection along feeder circuits

Thus, directional relays are required

Note: Directional relays look into the feeder

Need to establish setting philosophy

51 67

51

Load

67 67

Load

6767 67

Load


7/56> Directional Overcurrent and Earthfault Protection7 7

Ring Main Circui t

Procedure :

1. Open ring at A

Grade : A'

- E'

- D'

- C'

- B'

2. Open ring at A'

Grade : A - B - C - D - E

Typical operating times shown.

Note : Relays B, C, D, E may be non-directional.

1.30.1

0.1 0.90.5

0.9

0.5

B'

A'

B

E E'

A

1.7

D'

D

1.7

1.3

C' C



Ring Sys tem w ith Two Sources

Discrimination between all relays is not possible due to differentrequirements under different ring operating conditions.

For F1 :- B must operate before A

For F2 :- B must operate after A

Not

Compatible

B' B C' C

D D'

F1

B

F2

A

A'



Ring Sys tem w ith Two Sources

Option 1

Trip least important source instantaneously then treat as normal ringmain.

Option 2

Fit pilot wire protection to circuit A - B and consider as common sourcebusbar.

A

B

Option 1Option 1Option 1

Option 2 Option 2

50

PW PW



Parallel Feeders

Non-Directional Relays :-

Conventional Grading :-

Grade A with C

and Grade B with D

Relays A and B have

the same setting.

51

51

A

D

Load

51 B

51 C

A & B

C & D

Fault level

at F

Operat

ingTime



Parallel Feeders

Consider fault on one feeder :-

Relays C and D see the same fault current (I2). As C and

D have similar settings both feeders will be tripped.

51 A 51C

51 B 51D

LOAD

I1 + I2

I1

I2



Parallel Feeders

Solution:- Directional Control at C and D

Relay D does not operate due to current flow in the reverse

direction.

51 A 67C

51 B 67D

LOAD

I1 + I2

I1

I2



Parallel Feeders

Setting philosophy for directional relays

Load current always flows in non-operate direction.

Any current flow in operate direction is indicative of a fault

condition.

51 A 67

E

51 B 67

C

D

Load

51



Parallel Feeders

Usually, relays are set :-

- 50% of full load current (note thermal rating)

- IDMT rather than DT

- Minimum T.M.S. (0.1)



Paral lel Feeders - Applicat ion No te

P

B

B

D

D

Load

Load

If3

A C

If1If2/2 If2

BC

D

Ifmax

A

Grade A with B with C at If1

(single feeder in service)

GradeBwithDatIf3=If1

(upper feeder open at P)

Grade A with B at If2

(both feeders in service)

- check that sufficient margin existsfor bus fault at Q when relay A seestotal fault current If2, but relay Bsees only If2/2.

If1

If2

M

M = MarginM

M

Q



Establ ish ing Direct ion



Establ ishing Direct ion :- Polar ising Quant i ty

The DIRECTION of Alternating Current may only bedetermined with respect to a COMMONREFERENCE.

In relaying terms, the REFERENCE is called the POLARISING

QUANTITY.

The most convenient reference quantity is POLARISINGVOLTAGE taken from the Power System Voltages.



Direct ional Decision by Phase Comparison (1)

S1 = Reference Direction = Polarising Signal = VPOL

S2 = Current Signal = I

OPERATION when S2 is within 90 of S1 :-

S 1

S 2

S 2

S 2S 2

S 2

S 2

S 2



Direct ional Decision by Phase Comparison (2)

RESTRAINT when S2 lags S1 by between 90 and 270 :-

S2

S1

S2

S2

S2

S2S2

S2



Polarising Voltage for A Phase Overcurrent Relay

OPERATE SIGNAL = IA

POLARISING SIGNAL :- Which voltage to use ?

Selectable from

VA

VB

VC

VA-B

VB-C

VC-A



Directional Relay

Applied Voltage : VA

Applied Current : IA

Question :

- is this connection suitable for a typical power system ?

IA

VA

Operate

Restrain

VAF

IAF



Polar ising Voltage

Applied Voltage : VBC

Applied Current : IA

Polarising voltage remainshealthy

Fault current is near centreof characteristic

IA

VBC

ZERO SENSITIVITY

LINE

VA

IAF

IVBC

VBC

MAXIMUM SENSITIVITY LINE


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Relay Connect ion Angle

The angle between the current applied to the relay and thevoltage applied to the relay at system unity power factor

e.g. 90 (Quadrature) Connection : IA and VBC

The 90 connection is now used for all overcurrent relays.30 and 60 connections were also used in the past, but nolonger, as the 90 connection gives better performance.

IA

VA

90

VBC

VC VB

Relay Characteris tic Ang le (R C A )


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Relay Characteris tic Ang le (R.C.A .)

for Electronic Relays

The angle by which the current applied to the relay must be

displaced from the voltage applied to the relay to produce maximumoperational sensitivity

e.g. 45

OPERATE

IA FOR MAXIMUM OPERATE

SENSITIVITYRESTRAIN

45

VA

RCA

VBC

90 C ti 45 R C A


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90Connec tion - 45R.C.A .

RELAY CURRENT VOLTAGEA IA VBC

B IB VCA

C IC

VAB

IA

VA

90

VBVC

MAX SENSITIVITY

LINEOPERATE

IA FOR MAX

SENSITIVITYRESTRAIN 45

45

135

VA

VBC VBC

90 C ti 30 R C A


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90Connec tion - 30R.C.A .

RELAY CURRENT VOLTAGEA IA VBC

B IB VCA

C IC

VAB

IA

VA

90

VBVC

VBC30

30

OPERATE

MAXSENSITIVITY

LINERESTRAIN

IA FOR MAX

SENSITIVITY

150

VA

VBC

S l ti f R C A (1)


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Selec tion o f R.C.A . (1)

90 connection 30 RCA (lead)

Plain feeder, zero sequence source behind relay

Overcurrent Relays

S l ti f R C A (2)


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Selec tion o f R.C.A . (2)

90 connection 45 RCA (lead)

Plain or Transformer Feeder :- Only Zero Sequence Source is inFront of Relay

Transformer Feeder :- Delta/Star Transformer in Front of Relay


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Direct ional Earth faul t Protect ion

Di t i l E th F lt


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Directional Earth Fault

Requirements are similar to directional overcurrent

i.e. need operating signaland polarising signal

Operating Signal

obtained from residual connection of line CT's

i.e. Iop = 3Io

Polarising Signal

The use of either phase-neutral or phase-phase voltage as

the reference becomes inappropriate for the comparison withresidual current.

Most appropriate polarising signal is the residual voltage.

Residual Voltage (1)


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May be obtained from broken delta V.T. secondary.

Notes :

1. VT primary must be earthed.

2. VT must be of the '5 limb' construction (or 3 x single phase units)

VRES = VA-G + VB-G + VC-G = 3V0

A

BC

VRES

VC-GVB-GVA-G



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Solidly Earthed System

Residual Voltage at R (relaying point) is dependant upon ZS / ZL ratio.

3ExZ2ZZ2Z

ZV

L0L1S0S1

S0

RES

E S R FZLZS

A-G

VCVC VC

VB VBVB

VRESVA

VA VRES

VBVCVCVC VBVB

VAVA



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Resistance Earthed System

3Ex3ZZ2ZZ2Z

3ZZV

EL0L1S0S1

ES0

RES

VA-G

VA-GVA-G

VA-G

VB-GVC-G

G.FG.F

VB-G

VRES VRESVRES

VC-GVC-GVC-G

VC-G VB-GVC-G

VB-G VB-G VB-G

E

N

G

S R FZLZ

S

ZE A-G

G.F

Relay Characteris tic Ang le (R C A )


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Relay Characteris tic Ang le (R.C.A .)

Voltage Polarising Signal

Rotate VRES by 180O

to obtain voltage polarisation signal0O, -45O or -60O R.C.A. applied for maximum sensitivity

e.g. -45VA

VC VB

VF

VRES

Rotate VRES by 180

MAX SENSITIVITY

LINE

IRES FOR MAX

SENSITIVITY-45

OPERATE

RESTRAIN

Residual Voltage Polarisat ion


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Residual Voltage Polarisat ion

Relay Characteristic Angle

0 - Resistance/Petersen Coil earthed systems

-45 (I lags V) - Distribution systems (solidly earthed)

-60 (I lags V) - Transmission systems (solidly earthed)

+90 (I leads V) - Insulated systems

Zero Sequence Network :-

V0 = 0 - I0 (ZS0 + 3R)

(Relay Point)

ZL0ZS0 I0

V03R

Insulated Systems (1)


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a b c

Source

Icb

Ica

Ic

IcbIca

Ic

I

cb

Ica

2Ic3Ic

Location CT's



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Faulty Feeder

VRES

a b

cIca

IcbIc -3

Ic

Healthy Feeders

VRES

Ic = Ica + IcbRCA

OperateRestrain

VPOL

-2IcRCA

OperateRestrain

VRES

VPOL

Peterson Coil Earthed Systems (1)


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IL


a b c

Source

IcbIca

Ic

IcbIca

Ic

IcbIca

2Ic

Location of CT's

3Ic

Ic

IL

IL



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Negative Phase Sequence Voltage Polarisat ion


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Negative Phase Sequence Voltage Polarisat ion

Transmission Systems

Directional earth fault used as back-up protection

Can form part of a directional scheme

VRES might be unreliable due to mutual coupling

Unsuitable VT for VRES measurement (i.e. open delta, 3-limb)

Negative Sequence Network :-

V2 = 0I2 (ZS2)

ZL2ZS2 I2

V2

(Relay Point)

ZS1=ZS2

ZL1=ZL2

Current Polar ising


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Current Polar ising

A solidly earthed, high fault level (low source impedance)system may result in a small value of residual voltage at the

relaying point. If residual voltage is too low to provide a reliablepolarising signal then a current polarising signal may be usedas an alternative.

The current polarising signal may be derived from a CT locatedin a suitable system neutral to earth connection.

e.g.

POL

OP

DEF Relay

Current Polarising (1)


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POL

DEF RELAY

INCORRECTOP

Direction of current depends on faultposition



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POLDEF RELAY

CORRECT

OP



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POL

DEF RELAY

CORRECT IF

ZLO + ZSO IS

POSITIVE

S

OP



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POL DEF RELAY

OP

CORRECT

Au to Trans formers (1)


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ZT

ZLZHSOURCE

ZS SOURCE

DEF

RELAY

Neutral connection is suitable for currentpolarising if earthfault current flows up the

neutral for faults on H.V. & L.V. sides.



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Check :

For correct application

(Note : there is also a possibility that neutral current may be zero.

Alternative : Use C.T. in one leg of winding)

1V

Vx

ZZZ

Z

L

H

T0L0S0

T0

Unloaded

Delta

Loaded

Delta

For LV Faults


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o au s

T

H L

IN= 3 (ILO - IHO)

IH

IL

For HV Faults


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T

H L

IN = 3 (IHO - ILO)

IH IL

Au to-Transfo rmer Example


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p

T

H L

IN = 3 (IHO - ILO)

ZS

ZS0ZL0ZH0IH0 IL0

I0

ZT0



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p

kAinkVx3

MVAx

p.u.in

H

base0

0H0

kAinkVx3

MVAx.

ZZZ

Z

p.u.in.ZZZ

Z

L

base0

L0S0T0

T0

0L0S0T0

T0L0



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p

1ZZZ

Z

kV

kVor

ZZZ

Z

kV

1

kV

1ifveis

ZZZ

Z

kV

1-

kV

1

3

.MVA3

L0S0T0

T0

L

H

L0S0T0

T0

LHN

L0S0T0

T0

LH

base0N



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p

T

H L

I

N= 3 (I

LO

- IHO

)

ZS

ZS0ZL0ZH0IH0 IL0

I0

ZT0

IH0 = 0

IN = 3IL0 which is +ve.

Direct ional Contro l


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Static Relay (MCGG + METI)

Characteristic Selectable

51 I

Overcurrent Unit

(Static)

67

V

I

M.T.A. Selectable

Directional Unit

(Static)

Numerical Relay Direct io nal Characteris t ic


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y

Characteristic angle cc = -95 0 95

in 1 steps

Polarising thresholdsVp 2V to 320V

in 2V steps

VT supervisionselectively block operation

Zone offorward start

forward operation

Reverse start

(c - 90) (c + 90)c

+Is

-Is

2 dir. oc + ef protn_apps_areva_pn

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