I have connected 04nos. earthings to a transformer through
04nos. earthing pits seperately. 02nos. earthings are
connected to T/F body, and 02nos. earthings are connected to
T/F neutral.T/F capacity is 2000KVA, 11KV/415V. But after
completing of 02 years successful operation ,we are
facing following problems-

1. CT/PT occured blast one time
2. HT cable box occured blast two times
3. One body earthing strip and one neutral earthing strip of
transformer are overlapping at some places. Whenever these
two strips are pressed at overlapped points, they made spark.

What is the reason of spark?

Please explain the reason & rectification of above problems

Answer Posted / ullas

the answer follows.
1. ct/pt unit blast doesn't relate with the problem. it may
due to its poor quality , or some other reasons.
2. ht cable end box blast can be occured in so many ways.
may be due to rain water entered in to the end box leading
to short circuit the phases.
or due to poor quality,etc maybe the reason.
you can do one thing.
please disconnect the earthing of ht cable armour either at
transformer side or at the double pole structure.
3. this sparking indicated that your transformer neutral is
no longer maintains zero potential.
so please first measure the voltage of neutral.
this is done by inserting a spike five meters from the
transformer and take this terminal as earth terminal of
zero potential. and between this terminal and transformer
neutral measure the voltage developed.
if it is indicating a sufficient voltage, then it is true
that your neutral is shifted from its zero position.
if there is any fuse used in the neutral circuit, change
it in to a link.
check the whole circuit for any abnormal conditions.

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