Transformer Differential Protection
Transformer Differential Protection
(OP)
I have a query on Transformer differential protection. How is the harmonic restraining feature is set in the relay? I thought the relay should sleep( block operation) only when there is second harmonics in all three phases. But Iam told cross blocking is used nowadays so that relay will operate only when there is no second harmonics in all three phases. Is this not a dangerous situation? In case there is an internal winding failure in one phase and if the unit is energised then the relay will not operate as the healthy phases will draw current with second harmonics and relay will sleep. The transformer will be isolated by relays such as gas operated relay only after much time delay. What is the practice followed in various parts of the world for large power transformers?






RE: Transformer Differential Protection
Harmonic blocking - set a threshold to block the 87 element
To detect internal turn-to-turn fault, may try negative sequence differnetial
RE: Transformer Differential Protection
RE: Transformer Differential Protection
RE: Transformer Differential Protection
RE: Transformer Differential Protection
I think you'll find that tripping on inrush into an un-faulted transformer is a bit more common than failure to trip on a faulted one.
RE: Transformer Differential Protection
its depend of protective terminal type.
Cross blocking is very important function, especially in case of one phase autorecloseres in the grid.
You can use additional functionality in few newer protective terminals: waveform blocking.
RE: Transformer Differential Protection
RE: Transformer Differential Protection
Link
RE: Transformer Differential Protection
RE: Transformer Differential Protection
RE: Transformer Differential Protection
I guess the Link button on the forum has some issues...
RE: Transformer Differential Protection
RE: Transformer Differential Protection
The general settings I have come across is 15% for second harmonics(I2/I1 - I2 is second harmonic current and I1 is the fundamental)and 25% for 5th harmonics.
During a turn to turn fault,since the rise in the magnitude of fundamental is high than the second harmonics, the possibility of harmonic blocking getting activated is remote.
However, in the unlikely event of such a case where the ratio has been exceeded, schemes mentioned by davidbeach will ensure the operation of differential protection.