Answer / mushtaq ahmed

Dear Sir, The OLTC of Generator Transformer should not be operated when Generator is in parallel with Grid. OLTC step change introduces a step voltage difference, which results in very high circulating currents. Generator AVR takes some time to adjust to this new voltage. But by that time, a very high current has flown thru the circuit. OLTCs are not rated for this, especially during changeover.

Answer / k.prakashchandra

Generator voltage is decided by excitation and not by OLTC which is provided on HV side . If the voltage on Generator side ( LV ) is reduced with OLTC ,then the voltage difference will be more resulting in more current due to poor lagging pf . AVR maintains the set voltage if apfc mode is not selected . This happened due to wrong operation of OLTC and loose contacts in OLTC . You could have equalized the voltage operating AVR voltage control .

Answer / jayesh n patel

failure is happend after tap operation , chances of contact stucking in between positions and full load current passes more time through transition resistance( as per design current passes for 60 to 90 mili seconds only, while snape action)and it got burnt ,and voltage has cut with big spark, sudden pressure has develop in side the tank and oil has got expand which result in bulging of top cover and oil spread,(mechanical failure result in electrical failure).

Answer / sakono

May be explode from
1. During moving the OLTC contact, some part was lossen and
OPEN circuit occure.
2. Some material of OLTC was fail and loosen. then the OPEN
circuit was occure in OLTC.
3. Contaminate inside OLTC chamber
4. Oil was contaminated
5. TAP Position of OLTC was not in step.

Answer / jayesh n

 while contact changing if it stuck in between position and if full load current is pass more time from transition resistance than resistance got break and heavy spark has occure, due to which sudden  pressure develope in side the oltc tank and top cover got bulged and oil spread out side the tank (transition resistance is carrying current for short time only that is  60 to 90 miliseconds only, while contact snapping action).

Answer / j.kesavan

oltc always problem,why its opration is motorised in auto
cotrol ,thats why disc breake every time

Answer / sudheer

please check the OLTC inside
connections ,carefully .because some times the connector
plate rollers not touch properly. so the winding temp.
increases continuously and oil will over-heated.

Answer / j.ikesavan

my friend please check your inter lock system how to
working motor on load tap changer your winding failure its
going up and down voltage thats why this disc is breake.

Answer / brad stroh

where did this happen at? what is your location? we
specialize in failure analysis.

Brad Stroh

alineeds.com

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