O.H.L protection

[electric]

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main protection


distance relay

Backup protection

EF, DEF,DOC,O.C,O.L
[line]

***DISTANCE RELAY

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THIS RELAY READS VOLTAGE FROM VT & CURRENT FORM CT

IN ORDER TO CALCULTAE THE IMPEDANCE OF THE LINE (Z)

Z= V/ I

ZONE 1 = 80 - 90% FROM THE PROTECTED LINE

WITH ZERO DELAY TIME.
[line]

THE REASON OF MAKING ZONE1 COVERY 90% OF THE PROTECTED LINE IS THAT THE RELAY MUST HAVE PERCENTAGE OF ERROR AND MIGHT TRIP ON A FAULT THAT TAKES PLACE IN THE BUS BAR AREA OR OTHER ZONE.



ZONE2= 120-150% FROM THE PROTECTED LINE

= 100% FROM FROM PROTECTED LINE + 50% FROM NEXT LINE WITH DELAY TIME 400 msec

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next is communication scheems >>to arrange and to manage the zones.

[electric]

COMMUNICATION SCHEMES IN DISTANCE PROTECTION:


PERMISSIVE UNDER REACH TRANFER TRIP ( PUTT)

If Z2 + Carrier recieve = aided trip (comm trip)

in case if the relay saw a fualt in Z2 and it recieves a signal from the other side it will trip at Z1 time.
[line]

PERMISSIVE OVER REACH TRANSFER TRIP(POTT)

Z2 + CR = COMM TRIP CR: CARRIER RECIEVE

Z2+WITHOUT CR = Z2 TIME

In this scheeme the relay that sences the fault as Zone1 sends an immedite signal CS to the relay in the other side that sences the fault as Z2.

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[line]

BLOCKING SCHEEM:

THE MAIN PRINCILPE OF THIS SCHEEM OS TO ACT IN THE FOLLOING WAY:

Z2 + WITHOUT CR = AIDED TRIP COMM
Z2+CR = Z2 TIME DELAY TRIP

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The simplest definition for this scheem is that the logic says to the relay:

if you see z2 then make a trip in z1 time unless you recieve a signal from the relay in the other side