Transformer Secondary Faults

hi,

equivalant fault is reflected on the primary side also. As energy out put = energy input.

relays co ordination decides which relay shall operate. Normally,faults within the transformers & up to the bus link connecting the breaker on transformer out put - secondary or primary, ht relay on primary side shall isolate the transformer. But if earth faults occoured out side the transformer i.e. after breaker on secondary side, it is set such that secondary side breaker should operate by its relay.

A fault on the secondary side should be cleared by the protection elements on the secondary side, not the primary side, leaving the primary side unaffected. The whole point of secondary side protection is to sectionalise the fault to minimise the effected area. This is a basic fundamental point of electrical discrimination protection.

Is this a homework question?

Thats correct for external fault, But I think primary can not be isolated from fault if fault is with in secondary of transformer. for example turn to turn short in secondary.

Regards.

Correct, secondary side protection will not protect the transformer from an internal fault because the fault is before the secondary protection elements. In a case such as a transformer failure the primary side transformer protection provides the transformer protection.

Hi all

=----OO----= wht it is on the one line diagram ..

lets take an example for this . 1000KVA D/Y 13800/480 5.75% --- normal current

is 41.83 A / 1202 A .

max current may be 20KA on secondary side ....

1- 3 phase fault at secondary side then primary current will be 419 A which is sufficient to operate the HRC fuse on secondary side as 63---100 A can be used .

my question is

what will be the condition on single phase to ground and phase to phase fault on secondary side .. take 20kA as fault current on any phase ....

please correct if i am wrong ..