Transformer fault because of full load energize

[iphapppi]

Hi.
Is there any paper or study describe relationship between operation mode and failure rate of a power transformer. example if the transformer often energize on load (load side CB close) it will raise the probability of transformer fault due to higher inrush current if compare to energizing transformer off load ( load side CB open)
thank you for the answer

 

[hooverdale]

Hello iphappi,

What types of loads are connected to the transformer? Size of transformer? Transformer protection used?
Why do you energize the transformer directly without disconnecting the load first?

The transformer itself exhibits inrush current during initial energizing which is full of harmonics plus the inrush current drawn by the connected load specially if you have electric motors.

if the transformer IS energize on load (load side CB close)

Yes the probability of failure will be higher.

 

[Skogsgurra]

Not so sure. If secondary is loaded, the voltage drop will increases so that available volt-seconds are reduced and hence saturation less likely. It is only when connected loads draw more current than idling inrush that it may be a disadvantage.
My take is that you get more inrush when secondary is not connected.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[stevenal]

Why not disconnect load first? Consider a transmission level outage. Prior to re-energizing the line you must disconnect all substation transformers on the circuit. Then prior to reconnecting each substation transformer you must open each distribution feeder. Now prior to re-energizing the feeder, disconnect each distribution transformer on the circuit. Prior to re-energizing each distribution transformer contact each customer in case they wish to disconnect their devices that might have transformers within. Or you can close the switch to keep the outage as short as possible.

 

[oldfieldguy]

Considering that I know of several captive transformers where the secondary is directly connected to the windings of substantially sized motors in the range of several thousand kW, I do not see this as a problem with properly sized transformers.

"Cold load pickup" is often a problem in distribution applications but it is handled by specific application of protective relays.

old field guy