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Join Date: Sep 2010
Location: Saudi Arabia
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Post Fault Pre Fault

10/17/2010 3:25 PM

can any one please explain the terms prefault Time , post fault Time and max fault Time in distance relay testing ? also pre post fault voltages..

regards

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#1

Re: post fault pre fault

10/17/2010 6:31 PM

If t0 = arbritrary starting time, t1 = initiation of fault, t2 = clearing of fault, and tn = now; then maybe:

t1 = prefault time, (tn - t2) = postfault time, and (t3 - t2) = max fault time?

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#2

Re: Post Fault Pre Fault

10/19/2010 8:18 AM

In relay testing, pre-fault is the length of time you program your test set to output normal ("pre-fault") conditions of voltage & current. Pre-fault voltage would usually be nominal voltage conditions for that state. Most relays need to sense nominal system conditions for some pre-set time to know the system is stable before you can apply fault conditions and expect it to act properly on them.

Max fault time is the length of time the simulated fault conditions are applied to the relay under test by the test set. It would be a set of voltage and current values at appropriate phase angles that represent a phase-ground or phase-phase fault at some specific distance from the terminal, for which you have calculated expected values, and the relay is expected to pick up and trip in a predetermined time.

Post-fault time the length of time you program the test set to give expected post-fault conditions of voltage & current tothe relay, i.e., what it is expecting to sense once it has tripped the circuit breaker or whatever the action it is supposed to initiate.

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#3
In reply to #2

Re: Post Fault Pre Fault

10/20/2010 6:54 AM

let

pre-fault time =1.5sec

Max-fault time = 3.0sec

post-faulttime = 2.0sec

is this means the test set will output nominal relay volts and amperes for 1.5sec then fault volts and amperes for 3.0 sec ? i realy dont get the idea of post fault voltage and current.

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#4
In reply to #3

Re: Post Fault Pre Fault

10/20/2010 9:35 AM

It could be used for example in reclosing schemes, where the measured quantities return to some nominal value after tripping a circuit breaker, and then apply the fault again when the breaker is reclosed. It could also be used for breaker failure schemes where a pole (or multiple poles) of a breaker doesn't trip and you want to simulate what conditions are so that backup relays will function. Anything where you need to apply different conditions after the trip signal is given by the relay.

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#5
In reply to #4

Re: Post Fault Pre Fault

10/21/2010 6:58 AM

thank you dear, i get the point cleared ..

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