Frequent energization of a Dry Type Power Transformer?

[majesus]

We have a 4160/600V 1.5MVA/2MVA (ANN, AFN) dry type transformer that is used to run load banks for testing the upstream 4kV gensets. Curious to know how frequent (per hour) can this transformer be cycled (re-energized)?

Energisation of any transformer will produce a magnetic phenomena called magnetising inrush current. These transient currents will be of considerable amplitude and will produce electro-dynamic stresses within the winding. Transformer are designed to withstand such stresses however it is understood that repeated operation should be kept to a minimum. Would there be any thermal consideration that should be also accounted for?

 

[waross]

I don't know the answer to your question but if this is a concern there are some techniques to reduce the inrush current.
There has been discussion of a circuit that aids in reducing the residual magnetism to avoid worst case inrush currents.
There is also a technique of energizing at a lower voltage and then shunting out the series impedance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

I am not aware of any thermal limitations - the inrush current dies down very rapidly. I would be more concerned with the mechanical stresses on the windings.

If you are energizing the transformer from a generator, you can ramp up the voltage to the transformer gradually.