Big motor starting
Big motor starting
(OP)
I want to start a 5000HP motor andthe system is too weak. I thinking of using Auto-tranformer and softstarting methods to start it. But whenever I tried it by ETAP, it always caused the bus Voltage drop to exceed the requirements. Does anybody here have better solution for this system?






RE: Big motor starting
Gunnar Englund
www.gke.org
RE: Big motor starting
yours
RE: Big motor starting
A Pony motor is using a smaller motor to spin the big motor so it's moving when the starter is activated.
Lots of factors determine wheater it will work for you. What are the details on the motor, the load?
RE: Big motor starting
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RE: Big motor starting
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Big motor starting
RE: Big motor starting
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RE: Big motor starting
victa 1288 hasn't said what his application is but his options may be moving the plant or doing nothing.
RE: Big motor starting
RE: Big motor starting
Detailed utility information; voltage, transformer(s), fault MVA, etc.
Load information; inertia, torque/speed, etc.
Motor voltage and your main distribution voltage
If you need to start a load, you could use a combination of pony motor and fluid clutch - start with pony motor and clutch disengaged, once main drive is up to speed, slowly engage the clutch to turn the load.
Note that at this power range, there are no cheap options to make this work. You need to provide much more information before the members here can give you the most feasible and reliable starting method for this machine.
RE: Big motor starting
RE: Big motor starting
As you guys have said, VFD could be an option.
In ETAP, I used Aoto transformer, the combination of fixed tap and LTC, I started the motor without causing unacceptable voltage drop on the buses (20%, which is still too low.
RE: Big motor starting
You can pick 'Current Limit' to model a basic softstart, and start by limiting it to the running current. Then adjust up from there to get the voltage drop below 10%, which is typical for acceptable limits. (If you still have an unacceptable voltage drop at running current, then you can't even run the motor in your system, never mind start it.)
If you model the motor and load correctly, and use the Dynamic Start module, you can see if and how long it will take to come up to speed at the starting settings you have set.
You can also model a VFD or a ramp softstart by using a Current, Voltage, or Torque Control model. ETAP alows you to practically draw the start curve from there.
RE: Big motor starting
A magnetic or hydraulic clutch may also work if you can start the motor unloaded. Try running your ETAP with no load on the motor first before investing time on a mechanical solution. Remember for any mechanical solution you need to start the motor first!
If you were close with the Autotransformer you might want to consider changing motors. I had several projects in that size arena where motor performance made a big difference. I use SKM instead of ETAP but I suspect they are similar. The software takes the motor and load inertia data, motor performance data such as the torque-speed, power factor and current curves, then plots that against the load torque-speed requirement curve to determine the interaction of all of those elements. I found that since motors in that size range are all engineered differently they tend to have very different curves and sometimes you can find one that gives you what you need for that particular load profile.
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RE: Big motor starting
RE: Big motor starting
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RE: Big motor starting
RE: Big motor starting
Another would be to make sure you are specifying the smallest starting current (highest code letter) compatible with your application.
If you can unload the motor for starting you don't need a 5000HP drive, you can spin it up with a smaller VFD and then bypass the drive before loading the motor.
Easier with a synchronous motor, you can do it with a low-voltage drive if you are very very careful.
Yet another option: add stiffness locally with another motor (or generator) with a large inertial load.
I've seen remote pumping stations that start their emergency generators during plant startup to add stiffness.
RE: Big motor starting
Trust the above is helpful.
RE: Big motor starting
Are the transformer and motor new equipment? ie can you change the parameters? Where are your voltage drop limits?
The A/T can be tapped down to as low as 50%, however the torque will drop as the square of the voltage so the load torque needs to be low. What is the driven load and can it be started unloaded? The lower you can get the load torque during starting, the lower the voltage dip will be. Obviously a clutch or fluid coupling would be the best option but they present operational difficulties (maintenance, efficiency).
A VFD will get your motor away no matter what the load is - but again, the lower the starting torque the smaller and cheaper the VFD. You might 'only' need a 1500kW drive.
apowerengr's suggestion of a wound rotor is a good one and the resistance can be varied to get the inrush down to an acceptable level. Modern designs (eg WEG) have an elegant rotor shorting and brush lifting arrangement which means brush wear is very low.
Other alternatives that we have been involved with that might be worth a try: capacitors, capacitors and A/T together.
RE: Big motor starting
RE: Big motor starting
Any and all of the suggestions given here can be modeled in ETAP, which I suggest you try before you actually spend money on equipment changes. Good luck.
RE: Big motor starting
Regards
RE: Big motor starting