Power Transformer Rating

[CuriousElectron]

Greetings,
What determines whether we go with single forced cooled rating, or natural cooling/first stage cooling/second stage cooling for oil filled, power transformers above 100MVA rating?
Is this evaluation based on engineering judgement/industry best practices, or?
Thanks,
EE

 

[waross]

Designed for anticipated load growth.
Actual rating depends on installed equipment.
Selection of operating cooling mode by thermostat(s).

 

[CuriousElectron]

What if this is a GSU transformer sizing exercise for a big generator? Would you match the GSU rating to Generator rating but provide a bit more MVA capacity on the GSU to account for any future unit uprate as a result of a unit rewind and to compensate for higher-than-average summer temperatures?
Thanks,
EE

 

[System Protection]

What if this is a GSU transformer sizing exercise for a big generator? Would you match the GSU rating to Generator rating but provide a bit more MVA capacity on the GSU to account for any future unit uprate as a result of a unit rewind and to compensate for higher-than-average summer temperatures?
Thanks,
EE

Yes, but I would also look into transformer operating temperature vs longevity.

Could be more economical to run a larger transformer at less than max capacity vs a running a smaller one at 100% rating.

There are papers on sizing transformers (economically). Not sure if there is one specific to GSUs.

 

[bacon4life]

A transformer running at rated temperatures for their entire life may have a lifespan of only 10 years. Sizing slightly larger can dramatically increase lifespan.

One consideration is the lifetime cost of losses based on the anticipate generation profile. The ideal design for a generator that runs 24x365, will have far fewer losses than the transformer for a peaker plant that only operates 50 hours per year.

Fans use energy to run and require maintenance, so it can be desirable to size the transformer to run the fans less than half the days.

Using pumps allows the transformer to be physically much smaller, or to have the radiators mounted remotely from the transformer. However, pumps introduce additional failure points.

For an owner with many transformers, there is also a benefit to standardization. Nearly all the transformers on my system have two stages, so the putting in transformers with just a single stage require some changes to the SCADA implementation.