EARTH FAULT RELAY OPERATION FOR JUMPER OPENING 2

[appunni]

Sir,
We have one substation where 66KV is stepped down to 11KV through two 4 MVA, 66/11KV Ynyn transformers, which are connected in parallel. From 11KV side there are 6 outgoing feeders. In these 11KV feeders there are some 11/0.44KV Dyn transformers for power distribution. The 66KV supply was from another substation through a 66KV line.
Some days ago, the substation was charged and loaded after a maintenance work in the substation yard. The earth fault relay on the 66 KV side of the transformer was acted. After a thorough verification the transformer was charged. While the 11 KV feeders were loading the earth fault relay in 66KV side of the transformer acted again.
Later it was found that one phase of the 66 KV supply line from the remote substation was open due jumper breaking.
How the earthfault relay will act which is connected in the residual circuit of the 66KV side phase CTs for a jumper opening in 66KV line? Is there any possibility or any other reasons? Please note that there is only one circuit breaker and one set (3No.s) of phase CTs in 66 KV side common to both transformers.
I request for your valuable comments.
With regards,
appunni

 

[hsj]

The earth fault relay could operate:
a) due to in rush current as a result of transformer energisation.
b)if the transformers are loaded then unbalanced load currents due to one phase open
c)harmonics. relays are supposed to be immune to harmonics but that is not always the case

 

[jghrist]

If all loads are connected ø-ø, then opening one phase will not produce zero-sequence currents, even with an intervening grd wye-grd wye transformer.