CONVERSION OF LOAD LOSSES AND NO LOAD LOSSES BETWEEN SINGLE PHASE AND THREE PHASE TRANSFORMERS

[subash148]

I have a GSU transformer with the following rating and would like to know if I am given a single phase no load and load losses or three phase no load and load losses, how to convert these losses between single phase and three phase GSU transformer and vice versa. I am in the process of selecting a vendor for a GSU transformer bid.

Here is the rating of GSU transformer:

MVA Rating: 54/72/90 MVA
Class Type: ONAN/ONAF/OFAF
Primary Voltage Rating: 13.8 kV
Secondary Voltage Rating: 242 kV
The transformer is single phase with Delta-Primary and Wye-grounded-secondary. These three single phase transformers will be connected in parallel to make a three phase step up transformers.

Here is a two different values with the load losses and no load losses given by two different bidders(vendor) for single phase and three phase GSU transformer respectively:

Bidder-A:90 MVA- Single Phase Unit
No Load Losses= 41.5 kW
Load Losses= 187 kW

Bidder-B:270 MVA- Three Phase Unit
No Load Losses= 84 kW
Load Losses= 889.5 kW

Based on the above scenario, please let me know how to convert single phase losses to three phase losses and three phase losses to single phase losses?

Thank you for your help in advance.

SG

 

[davidbeach]

Multiply or divide by 3.

 

[prc]

First of all you cannot compare the losses of one vendor with another as they will be quoting on different designs.
Even with one vendor, you cannot compare losses of single phase with three phase as design parameters can be different.
If your question is - if single phase transformer bank is formed with same windings as of a three phase unit, then the load losses of the bank will be same as three phase unit,but no-load losses of the bank compared to three phase will be 125 %.

 

[subash148]

PRC,
Thanks for the answer. My situation is exactly as you mentioned above. Single phase transformer bank is formed with same windings as of a three phase unit. The reality is that some vendors have given load losses and no load losses for a single phase unit and some have given for a three phase unit. If I understand correctly, if losses have been given for a single phase; to convert to three phase losses I can multiply the single phase losses by 3.

IS it a similar calculation for no load losses as well? If a single phase no load losses is given, is it correct to multiply by 3 to get three phase no load losses?

Can you please also elaborate more on " no-load losses of the bank compared to three phase will be 125%.

SG

 

[davidbeach]

I guess I'm not sure what you're trying to achieve. If you have a single three-phase transformer you have one load and one non-load loss value to deal with and it should be the actual values that would be measured. If you have three single-phase transformers each will have its own losses and these have to be summed (one unit multiplied by 3) to get the total losses. To compare options using both types of installations you need to look at everything on a three-phase basis.

 

[subash148]

Davidbeach,

Thanks for your reply. I was just trying to confirm, how to calculate 3 phase losses of Power Transformer when single phase losses are given. Three single phase GSU transformers are connected for a three phase application.

SG

 

[prc]

When single phase units work as a bank, total losses will be 3times the losses of a single phase unit. But if you compare the bank loss with losses of a 3 phase unit, load losses will be same,but no-load losses of bank will be 1.25 times the loss in 3 phase unit. This is because the core weight will be more in the bank.In 3 phase units there will be only 3 nos limbs while bank will have 3 nos 100 % area limbs and 6 nos 50 % area limbs.

 

[stevenal]

OP has the manufacturer guaranteed values, which should have included any effect core weight has on the losses. No adjustment other than the factor of three should be needed.