Harmonic Block

Hello byj,

Perhaps you have gotten started in the wrong direction. The second harmonic should not be a consideration unless you lost a phase and your instrumentation has misinterpreted the event.

Make sure you are connected as directed by the manual.

Your explanation of the situation you are in - is totally inadequate.

Was this a "through-fault" ? Or did the transformer fail ??

The harmonic content of faults varies far and wide . . . NO it is NOT 45%.

Second harmonic is caused only by a saturating transformer, typically present when a transformer is energized. The presence of second harmonic is always restraining the tripping.

Fault is at OLTC

OLTC damaged

The waveform shows 2nd harmonic content above 49%

how it happened ???

how it happened ???

you asking about the damage or the harmonic?

2nd harmonic block is a standard feature of all transformer differential relays and is intended to give stability to the protection during energisation.

The transformer inrush current is rich in 2nd harmonics and that is the reason the 2nd harmonic threshold is used to differentiate inrush from faults.

It is true that this may prevent protection operation when transformer fault were to coincide with the energisation.

But, will the 2nd harmonics be dominant if the fault were to be in the transformer!! I am not sure. It will help if you can detail the problem a little more.

200 MVA , 220KV/110KV Transformer - independent units

Y-phase OLTC failed

Bucholz, PRV acted.

But differential trip blocked by harmonic

We analysed the waveform and observed that 2nd harmonic contect exceeded above 45%.

It appears the failure occur at the time of energisation. Is that true, byjuram!!