When we change the tap position of 10MVA transformer it suddenly tripped with O

When we change the tap position of 10MVA transformer it
suddenly tripped with Out of step indication and also with
Static differential relay indication, Transformer Bucholz
relay indn and Low oil level indication. Before 1 week the
same problem occured by changing the tap position. but at
that time only oltc bucholz relay activated. After testing
the TxR Relay team & PET team cant find any solid reason.
The values are ok also. So plz answer wat's the reason for
this incident? anybody plz help.

Question Posted / jiru2009

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When we change the tap position of 10MVA transformer it suddenly tripped with Out of step indicatio..

Answer / k.prakashchandra

OLTC has contact switches on rotating spindle and diverter
switch. Bucholtz relay acts as the oil is burnt in the
chamber due to arcing caused by loose contact .The spring
tension of the switches are to be checked for correct
tightness.If the contact is not correct ,the differential
relay may also act due to imbalance of currents.Do not
operate OLTC till the fault is set right.And the oil may
have to reconditioned.

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When we change the tap position of 10MVA transformer it suddenly tripped with Out of step indicatio..

Answer / k.prakashchandra

There is a loose connection in one of the phases of OLTC
contacts.

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When we change the tap position of 10MVA transformer it suddenly tripped with Out of step indicatio..

Answer / priyanka

Problem seems to be around the OLTC. More than 70% of
problems in transformer are due to OLTC.
Get your OLTC motor checked,surely you can find the
tripping reason there. Now about the tripping indications
following is the possibility-
Out of step - OLTC is a kind of stepper motor, when you
change the tap position the motor moves at a particular
step angle. In case your motor is faulty, it will move out
of step leading to frequent sparking across contacts
(Buccholz indication) and current imbalance due to improper
step angle (static differential).
Low oil level indication has no link with this, it simply
shows that conservator level is down.

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