600HP on 600V
600HP on 600V
(OP)
Hi everyone like me
I'd have a 600HP motor to connect on a 600V plant network.
It seems to me a too powerful motor to be connected to such a low voltage. I have thought about a VFD or a soft-start to start that motor.
The available power of the plant is enough for that motor in steady state mode.
Is someone here have encountered such a case? I figure that the starting is the big issue here but is there something else that I really should take care about? Could an autotransformer be adequate?
Thank you
I'd have a 600HP motor to connect on a 600V plant network.
It seems to me a too powerful motor to be connected to such a low voltage. I have thought about a VFD or a soft-start to start that motor.
The available power of the plant is enough for that motor in steady state mode.
Is someone here have encountered such a case? I figure that the starting is the big issue here but is there something else that I really should take care about? Could an autotransformer be adequate?
Thank you






RE: 600HP on 600V
If your system is relatively weak (regardless of voltage), reduced voltage staring (autotransformer) or VFD as you mention may be helpful to minimize voltage dip when starting. You should perform a motor starting analysis if there is any question.
RE: 600HP on 600V
You can determine the starting impact with more details on the motor and load and power system.
RE: 600HP on 600V
I'll chime in strongly on the suggestion of doing a motor starting analysis on anything 500HP and up. Nasty surprises can be very expensive in that realm. If you don't have some system analysis software such as SKM or ETAP, contract with a PE who does even if it is just for that job. Think of it as a form of insurance.
RE: 600HP on 600V
I've actually had the opposite experience pricing motors in the 1000 hp range. 480V came in somewhat less than 4160V. I suppose it depends on the mfg. The cost difference could be small in comparison to the feeder.
RE: 600HP on 600V
One thing to consider with a VFD. It will start the motor without putting undo stress on the network but the installation will likely be around 96% efficient. So, if you just use the VFD to accelerate the motor to full speed then the VFD losses will be like adding a 18kW heater to the plant system. Running on 8 hour shifts that would be around 1000kWh a week or 50000kWh a year. No small amount of hydro - likely $7.5k to $10k of hydro depending on you rates.
The 2000hp motor was on a ship - bow thruster.
RE: 600HP on 600V
RE: 600HP on 600V
Interesting comment about VFD losses. I am working on 600 V, 250 HP Fan application but I never heard about losses being significant like you explained. Could you kindly elaborate why there are losses in a VFD case and not in a typical soft starter or DOL application.
Thanks
Sorry for interjecting in your question Eclair.
RE: 600HP on 600V
RE: 600HP on 600V
A soft starter will have losses too. But because they are switching much differently the losses are far less. Often SS losses are completely stopped by having the system transition to a bypass contactor. So any switching is avoided.
ykee is correct in that there are rectification losses into a VFD and there are switching losses out of the VFD too. Hence the greatest loss of eff.
But as mentioned you could also bypass a VFD to avoid all these losses. You will need a VFD that can 'catch' a load if you want the load controlled on the way down too.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 600HP on 600V
A soft-starter will have losses too. The SCR's have about a 1V drop across them so with 600A the losses are 3 phases x 600A x 1V = 1800W. However, most good soft-starters these days have a built-in bypass which lowers the voltage drop to <200mV.
A typical ATL will have a small voltage drop too, usually <200mV, meaning it will have 300W to 400W of losses.