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(C) Pilot Relaying Schemes: Communication Medium May Be Pilot Wire (Metallic Wires), Power-Line

This document describes permissive overreaching relay schemes. Each terminal of a transmission line has underreaching and overreaching distance relays. The overreaching relays send permissive signals to the other terminal, and will trip local breakers if a permissive signal is received. This allows faults to be cleared quickly by tripping breakers at both terminals for internal faults. Backup protection is also provided in case a breaker fails to operate. Typical fault clearing times are in the range of 64-180 milliseconds depending on the location and type of fault.

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131 views6 pages

(C) Pilot Relaying Schemes: Communication Medium May Be Pilot Wire (Metallic Wires), Power-Line

This document describes permissive overreaching relay schemes. Each terminal of a transmission line has underreaching and overreaching distance relays. The overreaching relays send permissive signals to the other terminal, and will trip local breakers if a permissive signal is received. This allows faults to be cleared quickly by tripping breakers at both terminals for internal faults. Backup protection is also provided in case a breaker fails to operate. Typical fault clearing times are in the range of 64-180 milliseconds depending on the location and type of fault.

Uploaded by

adau
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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(c) Pilot Relaying Schemes

Use communication channels (pilots) between the terminals of the line that they protect Determine whether the fault is internal or external to the protected line, and this information is transmitted For an internal fault, circuit breakers at all terminals of the protected line are tripped; for an external fault the tripping is blocked Communication medium may be pilot wire (metallic wires), power-line carrier, microwave, or fibre optic

Permissive Overreaching Scheme:

Fig. 13.30 Permissive overreaching relay


Each terminal station of the line has: Underreaching zone 1 phase and ground directional distance relays covering about 75-80% of the line

trip local breakers instantaneously


Overreaching zone 2 phase and ground directional distance relays covering about 120% of the impedance of the protected line.

send permissive signal to remote end trip local breakers if permissive signal received from remote end if apparent Z remains inside relay characteristic for fixed time (typically 0.4

Fig. 13.31 Relay characteristic at station A

Fig. 13.31 Fault locations F1, F2 and F3

Fault Clearing Times


Composed of relay time and breaker operating time
EHV relays: 1-2 cycles Circuit breakers: 2-4 cycles

Breaker failure backup protection provided for each breaker on all critical circuits
if a breaker fails to operate at a local

Local (Bus A) breakers 1 and 2

Remote (Bus B) breakers 3 and 4

Primary relay time (Fault detection) Auxiliary relay(s) time Communication time Breaker trip module Breaker clearing time Total Time

25 ms 3 ms 3 ms 33 ms (2 cycles) 64 ms

25 ms 9 ms 17 ms (microwave) 3 ms 50 ms (3 cycles) 104 ms

Fault cleared from bus A in 64 milliseconds Fault cleared from bus B in 104 milliseconds

Notes: (i) For purposes of illustration, 2 cycle breakers have been assumed at A and 3 cycle breakers at B (ii) Communication time depends on channel medium used. With power line carrier, the time may be longer

Fig. 13.34 Typical fault clearing times for a normally cleared fault

Breaker 4 assumed to be stuck Breakers 1, 2, 3, 4, and 5 assumed to be 2 cycle air-blast breakers (33 ms) Breakers 6 and 7 assumed to be 3 cycle oil breakers (50 ms)
Local Breaker 5 Primary relay time (at bus B) Auxiliary relay(s) time Communication channel time Breaker failure timer setting Breaker tripping module time Breaker time 25 ms 3 ms 3 ms 33 ms Remote breakers 6 and 7 25 ms 9 ms 17 ms 3 ms 50 ms Local backup breaker 3 25 ms 6 ms 90 ms 3 ms 33 ms Remote backup breakers 1 and 2 25 ms 12 ms 17 ms 90 ms 3 ms 33 ms

Total time Fault cleared from bus C in 104 milliseconds Fault cleared from bus B in 157 milliseconds Fault cleared from bus A in 180 milliseconds

64 ms

104 ms

157 ms

180 ms

Notes: Breaker failure timer setting has been assumed to be 90 ms for the 2 cycle breaker 4. This could vary from one application to another. For a 3 cycle oil breaker a typical value is 150 ms

Fig. 13.34 Typical fault clearing times for a stuck breaker fault

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