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800kw, 415volt Motor Through Vfd


Pragathees...

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This topic has already been discussed that starting a 800KW, 415V motor in DG power.

The DG set has to be well designed on higer side to handle the starting current of the motor taking the losses in consideration..

 

Instead of having higher size DG Sets exclusively to handle the starting current of this motor, why don't I can have a Variable frequency Drive for this application?? I hope my problem is only starting the 800KW motor..on DG power..

 

Whether 800KW, 415V motor (Water pump application) can be smoothly started and operated using Variable frequency drive ? What will be the starting current ?? In this case, it is no need to have a higher capacity DG sets and I can go with normal rating suitabel for handling the running load only.. Is it correct??

 

For example, my running load is say 1100 KW including the 800KW motor load, I can select the DG set capacity of approx. 1500KVA ?? Is it ok ??

 

Will be any problem on the performance of LV VFDs(415V) for 800KW capacity since higher rating ??

 

Please suggest..

 

Pragathees...

 

 

 

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Hello Pragathees...

 

Yes, you can use a VFD to limit the starting current on the DG set.

You need to allow an overhead on the DG rating to cope with the harmonic currents on the input to the VFD.

I always recommend that you oversize all supply components (including the DG) by about 35%. i.e. assume that the VFD has a load requirement of 800 x 1.35 KVA and you should be right.

 

Best regards,

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Thanks Mr Marke for your immediate response & solutions to all my technical queries..

 

Pragathees...

 

Hello Pragathees...

 

Yes, you can use a VFD to limit the starting current on the DG set.

You need to allow an overhead on the DG rating to cope with the harmonic currents on the input to the VFD.

I always recommend that you oversize all supply components (including the DG) by about 35%. i.e. assume that the VFD has a load requirement of 800 x 1.35 KVA and you should be right.

 

Best regards,

 

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Hello Pragathees...

 

Yes, you can use a VFD to limit the starting current on the DG set.

You need to allow an overhead on the DG rating to cope with the harmonic currents on the input to the VFD.

I always recommend that you oversize all supply components (including the DG) by about 35%. i.e. assume that the VFD has a load requirement of 800 x 1.35 KVA and you should be right.

 

Best regards,

 

Marke

Can we use soft starters in This case for limit starting current on DG ,

Please suggest

Regards

Subhash.

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Hello subhash

 

Yes, you certainly can use soft starters to limit the start current. We do this all the time.

The reduced start current allows you to reduce the DG size, but the minimum start current is a function of the driven load curves and the motor curves.

 

Once you have determined the minimum start current, you can size the DG set.

Note:

There are a number of factors involved in determining the DG set sizing. By using three phase averaging AVRs and Permanent magnet excitation, you can achieve much higher overload capacities than when self excitation and single phase AVRs are used. The design of the DG set is very important if you want to have a good overload capacity. See http://www.lmphotonics.com/genset.htm

 

 

Best regards,

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Soft starters are used to limit the starting load on DGs all the time, in fact that is one of the chief benefits.

 

By comparison though, a soft starter ill always need more starting power than a VFD, but always less than DOL.

 

 

"He's not dead, he's just pinin' for the fjords!"
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