power transformer 132kv/11kv huge humming sound problem 2

[Anand Gupta]

One of our Power Transformer 132kv/11kv generating humming sound and also had vibration, transformer body and nearby steel structure are vibrating too much.
1. its WTI and OTI temp increasing 2 degree/Hrs without load, we isolated the T/R power after 60' temp.

this prob occurred after short circuit the outgoing Bus one ph. with "RAT" inside the VCB breaker.

T/R HV (STAR connection) Resistance is 1.155 ohm to 0.859 ohm between different taps
T/R LV (Delts connection) Resistance is 17.28, 19.48, 17.5 of R-Y, Y-B, B-R ph in mili Ohms

Voltage and Current are balance in Secondary winding.

TR megger are ok,

please help what to do

 

[itsmoked]

The first thing you can do is move your question to the correct forum:
forum238

Copy and paste it over to that forum.
Then come back here to this forum and DELETE this one and all the (phoolish answers you might get in this one) as cross posting is not allowed.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[thermionic1]

You were wise to take transformer offline. You may have saved yourself a transformer. I would recommend contacting a power transformer diagnostic expert (or manufacturer). They will likely request a dissolved gas analysis. The fault caused by the rodent may have caused shifting inside the transformer, leading to a poor connection, some kind of winding distortion, maybe something in the core if the sound is unusual. A Frequency Response Analysis test may provide more information as well as an internal inspection, which will require draining the oil and processing of the oil on the way back in. You may get lucky with "just" a loose connection, or it may be more severe. It would be impossible to determine with the limited amount of information provided.

Some years ago, I was at a new generating station after a fault. The GSU was first energized and sat for 24 hours. The new plant staff monitored the OTI/WTI every hour and duly noted the increasing temperature, but did not take off line. When the transformer finally faulted, it was discovered that whomever did the "commissioning" forgot to un short the CT's feeding the transformer protection. The 345kV/13.8kV 300MVA unit fault was finally cleared by upstream overcurrent protection after 30 cycles.

 

[Palletjack]

Doble testing and SFRA been done ever on this unit?
May be time to do another and compare results.
It could be the fault changed the geometry of the transformer.

 

[prc]

It looks like overvoltage or under-frequency is coming on the transformer causing saturation of the core. This increases core losses and noise. It may be from the continuous arcing somewhere. Replace faulty VCB with a new one and check that line for any defect anywhere.
SFRA test may not be useful. Go for an oil DGA test.
Why B phase R is more? Some loose contact somewhere. Based on the DGA result, partially drain the oil and look for loose contacts or joints in the B phase. Did the fault in VCB occur in the B phase?