So I get called to confirm if changing from DOL to a softstarter will get a motor started with limited generator power.
Is it unfair to respond and say I don’t know – It all depends on the dynamics of the load and the machine design and finally the generator load graph.
The caller gets furious – how can I not know!
First problem is: This is a DOL – What if the motor is just sized for the load such as it will not start if any sizable torque was dropped.
Second problem is- Is this low enough for the generator to start – I don’t know!
The only response I could give him was: Without having fancy measuring equipment – If you listen to the existing start of the motor under worse load conditions and you can ascertain it starts without ANY strain we can assume its got some “spare torque”
Also, with all the different motor starting technologies the softstarter is the most flexible solution to ensure one can start the motor with the minimum amount of starting current since one can control the exact amount of energy required for the motor to start and speed up.
There is also the star/delta starter solution – It will pull 40% less current but also loose a third of the toque at startup.
He cooled down a bit by then – I say: There is a load curve one can get for the alternator(generator) – it will give you a good idea how far the motor starting current crosses into this graph.
I also reminded him to not forget the motor starting current is a function of the motor load – have they even tried starting with minimum motor load on the machines part. That will cost nothing!
Softstarter panel design if you decide to go this way.
But here is a much cheaper trick to solve this problem.
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[wpedon id=2236]
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