Votlage Regulator Sizing

[rasprice]

I am a recent college graduate and was at a job site yesterday. Project involves automating voltage regulators at a small distribution substation. Per the namesplates, I copied down the following information:

Substation transformer bank is comprised of 3 single-phase transformers rated at 500 kVA each, 2400 V secondary. Secondary winding configuration is Wye solidly grounded with 4160 V line-to-line.

Substation regulators are comprised of 3 single-phase regulators rated at 125 kVA each, 2400 V.

If the entire feeder load is connected to the voltage regulators, why are they sized so much smaller than the substation transformers?

 

[davidbeach]

The regulators are auto-transformers while the power transformers are two winding transformers. The ratings of auto-transformers are much lower than two winding transformers for the same current capacity.

 

[magoo2]

I like to think of it as regulating a percentage of the full voltage, like 10%. With the rated load current from the substation bank and the % voltage, you only need a set of 50 kVA regulators as a minimum size (i.e., 10% of 500). The 125 kVA is likely the minimum regulator rating, so you should be fine.

 

[dpc]

This is always a source of confusion. Use the regulator ampere rating as a sanity check.

Regulator technical data generally has a listing of standard ratings at each voltage level with both current and kVA ratings.



David Castor

http://www.cvoes.com

 

[tinfoil]

To restate:

kVA rating on a voltage regulator is NOT the throughput.
It is the amount of energy being TRANSFORMED.

So a 125kVA regulator could handle 125/500 = 25% voltage adjustment (up and down) on the full load your 500kVA power xmfrs.

It is likely that the voltage regulating range they actually cover (you didn't say) is less than that.