Calculation of resistors for premagnetizing a transformer

[Marcopolo]

Existing situation: 3150kVA transformer, 11kV/450V no load losses 6300W.
Existing premagnetizing resistors with power losses 322kW for 5s.
Due to increase in power demand, a new transformer has to be installed: 11kV/470V no load losses 8500W.
Would the above mentioned resistors be enough?
And what is the best way to calculate these resistors?

 

[marconi]

PRE INSERTION RESISTORS - Cressall - https://www.cressall.com/products/pre-insertion-resistors/

Your question is best answered by asking a specialist company like Cressall. You will need to give them the specification for the new transformer . They can then advise what premagnetisation/preinsertion resistors are required for the new transformer and whether the current ones will be suitable. If not suitable they can guide you on the purchase of the correct new resistors. (If I was replacing such a large kVA transformer I would buy and install new resistors even if the old ones were suitable). Do you know the impedance of the supply to which the primary is to be connected? The supply impedance contributes as well the resistors some damping down of the magnitude of the initial magnetisation surge current.