linepro pom

7/22/2019 LinePro POM

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LINE PROTECTION


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1. Distance Relay

2. Reclosing and Synchrocheck Relay

3. Breaker Failure Protection

LINE PROTECTION


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Distance Relay

- The most general relay for line protection.

- Use current and voltage from the system for operation

Z = V / I

- Fast discriminative protection

Zone1 or Aided distance scheme

- Time delayed remote back-up

Incorporated at little extra cost


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Distance Relay

- Directional

- VTs required

- Fault resistive coverage limited by load impedance

and distance protection characteristic

- Affected by power swing, Loss of VT input (fuse failure)


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Distance Relay

-Additional features can be incorporated

Directional earth fault protection

Power swing blocking

VT supply supervision

Fault locators

Event recording

Disturbance recording


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G

21

Vs

ZS ZL

ZRVR

IR

ZLOAD


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G

21

Vs

ZS ZF

ZRVR

IR

ZLOAD

ZL

FAULT



G Vs

ZS ZP

21FAULT

I1

I2

V1

V2



ZR = ZP x CT RATIO

PT RATIO



AB

C

52

DISTANCE

RELAY

Ia

Ib

IcIn

Va

Vb

Vc

FUSE

CT

VT

DISTANCE RELAY CONNECTION DIAGRAM



j X

Z

R(ohm)

tan-1 X

R

Impedance Diagram


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j X

R(ohm)

ZL = 3 + 4j = 5 53.1

4

321

2

3

1

5

53.1


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R1 + jX1 = Z1 1 R2 + jX2 = Z2 2 R3 + jX3 = Z3 3

A DB C

j X

R(ohm)

X1

X3

X2

R1 R2 R3

2

1

3

Z1

Z2

Z3

B

A

C

D


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Operated Zone

Non-Operated Zone

jX

R

IMPEDANCE RELAY

DISTANCE RELAY CHARACTERISTICS


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X

jX

R

F2

F1

21

F2F1

A

B

A BX

IMPEDANCE RELAY



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X

jX

RA

B

Directional Unit

Impedance Unit



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B

IMPEDANCE RELAY

MHO

RELAY

R

jX

A

MHO RELAY



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Zone1

RF

Zone2

Zone3

A B C D

R1 + jX1

R3 + jX3

R2 + jX2



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RF

jX

X3

X2

X1

R1 R3R2R (ohm)

B

C

D

A



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jX

R

ZONE2

ZONE1

ZONE3

OFFSET MHO



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ZONE2

ZONE1

jX

R

C

A

B

RF

REACTANCE RELAY



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B

A

C

DjX

R

ZONE1

ZONE3

ZONE2


REACTANCE RELAY


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LOAD

B

A

jX

LENS

MHO


LENTICULAR


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jX

R

LOADLOAD


BONE CHARACTERISTICS


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RF

B

jX

R

A

QUADRILATERAL



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jX

R

T4

T3

T2

T1B

T1

X+A

X3

X2

X1B

X1

R1

R1E

R1B

R2

R3 RA

X-A

7SA513 ZONE CHARACTERISTIC

Example


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Setting Distance Relay

Zone 1

80-90% of protected line

Time Delay = instantaneous


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ZONE 1can not be set to 100% of protected line

because the relay can overreach due to the following

reasons.

1. CT error

2. PT error

3. System parameter error

4. Relay error


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Zone 2

100% of protected line + 40-50% of NextShortest Line

Time delay = 0.5 sec.


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Zone 3

100% of protected line + 120% of NextLongest Line

Time delay = 1.0 sec.

Zone 3R (Offset)= 10-25% of protected line


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TELEPROTECTION


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Scheme of distance protection

1. Basic

2. Permissive Underreach Transfer Trip (PUTT)

3. Permissive Overreach Transfer Trip (POTT)


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Z3G

G

ZONE

Z2G

H

Z1H

Z2H

Z3H

A J

END

ZONEEND

Z1G

BASIC DISTANCE


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Z1

Z2

Z3

T2

T3

1 TRIP

Z1

Z2

Z3

T2

T3

1TRIP

BASIC DISTANCE


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- Zone 1 set to 80% leaves 2 end zones

- Faults in end zone results in instantaneous tripping at one end and time

delayed at the other

- Time delay may lead to system stability problems

- Longer clearance times More damage

BASIC DISTANCESCHEMEDisadvantage


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Z3G

G

Z2G

H

Z1H

Z2H

Z3H

A J

Z1G

PERMISSIVE UNDERREACH SCHEME


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Z1

Z3

T2

T3

1 TRIP

TX

RX

Z2

&

0

100

Z1

Z3

T2

T3

1TRIP

TX

RX

Z2

&

0

100

PERMISSIVE UNDERREACH SCHEME

SEND LOGIC : Z1

TRIP LOGIC : Rx + Z2


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- Only a simplex signaling channel required- Scheme is very secure as signaling channel only keyed for

internal fault (Zone 1 initiation)

PERMISSIVE UNDERREACH TRANSFER TRIP

Advantages


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Disadvantages

- If one terminal of the line is open then only Basic scheme

logic will apply

- If there is a weak infeed at one terminal then only Basic

scheme logic will apply

- If signaling channel fails then only Basic scheme logic will

apply

- Resistive coverage is governed by Zone 1 setting (may be

limited on short lines)

PERMISSIVE UNDERREACH TRANSFER TRIP


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Z3G

G

Z2G

H

Z1H

Z2H

Z3H

A J

Z1G

PERMISSIVE OVERREACH SCHEME


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TRIP

Z1

Z3

T2

T3

1

TX

RX

Z2

&

Z1

Z3

T2

T3

1

TX

RX

Z2

&

TRIP

f1

f1f2

f2

PERMISSIVE OVERREACH SCHEME

SEND LOGIC : Z2

TRIP LOGIC : Rx + Z2


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- Provides better resistive coverage, especially on short lines,

where MHO measuring elements are used

- For cases where one line terminal is open, open breaker

echo logic can be used

- For cases of weak or zero infeed at one line terminal weak

infeed logic can be used (reverse looking zone required)

PERMISSIVE OVERREACH TRANSFER TRIP

Advantages


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Disadvantages

- Duplex signaling channel required

- Scheme is theoretically less secure then PUR as signaling

channel is keyed for external faults

- If signaling channel fails then only Basic scheme logic will apply

PERMISSIVE OVERREACH TRANSFER TRIP


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- DIRECTIONAL EARTH FAULT- VOLTAGE TRANSFORMER SUPERVISION

- POWER SWING BLOCKING

OTHER DISTANCE RELAY FEATURES


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VOLTAGE TRANSFORMER SUPERVISION (VTS)

-

Distance relay may maloperate if one or more voltage inputsare removed or failure.

- The voltage transformer supervision feature is used to detect

failure of the AC voltage supply.

-After the VT fail conditions has been detected, VTS gives

alarms to operator and block the distance relay.


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A

B

C

52

DISTANCERELAY

Ia

Ib

Ic

In

Va

Vb

Vc

FUSE

VOLTAGE TRANSFORMER SUPERVISION (VTS)

VTs fuse failure


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POWER SWING BLOCKING

Power swings are variation in power flow that occur when the

internal voltages of generators at different points of the power

system slip relative to each other.

The changes in load flows that occur as a result of faults and

subsequence clearance are one cause of power swings.

G1 G2


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A power swings may cause the impedance presented to a

distance relay to move away from the normal load area and

into the relay characteristic.


jX

R

T4

T3

T2

T1B

T1

X+A

X3

X2

X1B

X1

R1

R1E

R1B

R2

R3 RA

X-A

Impedance locus of power swing


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jX

R

X+A

RA

X-A

PSW DETECTION CHARACTERISTIC

5 Ohms

5 Ohms

35 ms

APOL

PPOL

Impedance locus of power swing


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RECLOSING RELAY


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79PT LINE

PT BUS

PT LINE

PT BUS

25

79

A B

25

RECLOSING AND SYNCHROCHECK RELAY


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RECLOSING RELAY

Transmission lines are protected by line protection relays, usually

of distance type. In case of faults, the distance protection initiates the

circuit breaker tripping and the fault is cleared. The line are then brought

back into service either by manual reclosing or automatically, when auto-

reclosing relays are used


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RECLOSING RELAY

Basically 2 types of faults on power systems

1. Transient

2. Permanent


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RECLOSING RELAY

Transient faults are usually caused by lightning, and once cleared,

with the arc path de-ionized, the line can be re-energized without the fault

reoccurring.

Permanent faults can be caused by broken conductor, the

collapse of a line tower, or a tree leaning toward the line. In this case, the

line can only be energized after fault location is traced and the damage

repaired


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RECLOSING RELAY

BENEFITS

- Improve system reliability and stability

- enables the use of unmaned substation


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RECLOSING RELAY

DEAD TIME

A time between the fault clearing and the reclosing shot is

necessary to allow arc de-ionization.


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RECLOSING RELAY


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RECLOSING RELAY

t = 0

Trip CB


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RECLOSING RELAY

t = 0 t = Dead time

Close CBTrip CB


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RECLOSING RELAY

t = 0 t = Dead time t = Reclaim time

AR Blocked AR normal

Close CBTrip CB


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Setting Reclosing Relay

Dead time = 300 ms or 1000 ms

Reclaim time = 15 sec.


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SYNCHROCHECK

RELAY


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Setting Synchrocheck Relay

Undervoltage check = 30% Vn

Voltage difference = 20% Vn

Angle difference = 25 degree

Slip frequency < 200 mHz


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AUTO-RECLOSURE RELAY

1. Relay initiate

2. No blocking signal to Auto-reclosure relay

3. Signal from Synchrocheck relay

4. 79CO ON

5. CB ready

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