Voltage Levels

[joan271273]

We have a project were the engineer has requested to modify our 21kV transformer taps in order to achieve a secondary voltage level of 510V. I know motors have rating of +/-10% so it should be Ok. However I would like to understand other impacts

 

[dpc]

That's pretty high for a 480 V nominal system. Remember the plus 10% for a NEMA motor starts at 460, not 480. So you'd be at +9% at the bus (voltage the motor will be lower, of course). Probably still OK, but what if the primary voltage goes up a percent or two?

Basically, everything will be seeing a high voltage, including all of the 120 V, 208 V, and 277 V loads, unless the taps of all of these transformers are adjusted.

Motors and transformers are probably the main concern, since they operated pretty close to magnetic saturation due to economics.

Motor operating parameters such as efficiency and power factor are based at operating at nominal voltage, so these will definitely change if you operate them at +9%.

 

[joan271273]

Tnkas DPC, when you state 9% at the bus? What do you mean. Is it a deviation at the output of the transformer of 9% and then 1% voltage drop at the motor feeder?

 

[dpc]

Oops - calculator operator error. 510 V would be 111% of 460 V. Sorry about that. The voltage at the motor will be lower, but that would be too high a bus voltage for me.

 

[itsmoked]

Any lighting cost may go up too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[burnt2x]

How about equipment smoking hot? Is this a new installation project or really a modification?
Transformer get hot when operated at higher than rated voltages. I can still remember the smell of frying winding insulation in that case.