Medium voltage soft starters

[thewarb]

Is it possible to use say a 15Kv rated soft starter on other voltages ie. 6.6Kv, 3.3kv and 4160v. Can the protection be adjusted to suit the relevent voltage.

Also would there be any adverse effects using temp. diesel generators and transformers to feed the starter?

 

Any info//weblinks etc would be much appreciated.

[marke]

Hello thewarb

 

That is entirely dependent on the design of the soft starter, however a 15KV soft starter would be very expensive, much more expensive than the appropriately rated starter.

The starter would need to be rated for Amps rather than KW. i.e. a 3000KW soft starter rated at 15KV would be good for about 1000KW at 5KV.

Perhaps jraef can shed more light on this one?

 

Best regards,

[thewarb]

thanks for the reply the reason i ask about it being able to do multi voltages is because i work for a hire company and you will appreciate that buying one soft starter for each voltage would be expensive. We are still looking at the best way to do motor starts. They are only temp. jobs and mainly for testing the motors, another method suggested was to use a cpacitor bank to assist with a DOL start, not sure bout this. Thanks for your help.

[marke]

Hello thewarb

 

OK, that make sense. I would suggest that you talk to the manufacturers and see what they say. It is possible that they could modify a unit to do what you want.

The capacitors to reduce the reactive current is OK provided that you are on a very strong bus. If you have an inductive supply, you can get major resonance problems and severe voltage surges and transients.

 

Good luck,

[jraef]

It is possible to make a 15kV starter that could be used on lower voltages, the power section would be unaffected. However it would mean having either a custom PT with taps for sensing multiple primary voltages, or several different sets of PTs and a switch system to select. What range of power do you test?

 

As Marke mentioned, the 15kV Class is going to be the most expensive because not only do you need more SCRs in series to handle the voltage, all of the switchgear involved goes up 1 class and so is more expensive as well. That said, we have made just such a unit for a pump manufacturer for testing 3300, 4160 , 6600, 11k and 13.8k systems. We used separate PTs for each voltage, and they took liberties with fusing (another problem) since it was only for functional testing.

[thewarb]

jraef,

The voltages you mentioned would be the most common we use, thanks for your advice. I will mention it at our next company meeting

[jraef]

One more suggestion.

Depending on the power rating you need, you might find it slightly less expensive to have a low voltage soft starter and step-up transformers on the output to get to your motor terminal voltage. Obviously that would be impractical if your motor is 2000HP because the low voltage current would be impossible to attain, but if it is 500HP that may be the best way to go.