Motor Solo Run Test on Diesel GenSet

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Dear Lyn,

I checked the links provided by you and understand that it provides the DEG rating required when 3 Phase motor has to be started DOL on genset.

However, my real worry is that we want to use the DEG for no load run for 4 hours continuously. During this period, power factor of motor will be very poor like 0.2 to 0.3.

Hence, even after large motor starting, Generator will still have low power factor load i.e. high reactive power requirement.

Now, if we select Generator with small rating and PF=0.8, it may not be able to satisfy VAR requirement. Then, I understand that either we have to select small generator with wide power factor range or large generator with 0.8 power factor. Then, I may be required to check the relay settings so that it will not trip in low PF region.

Please confirm my understanding is correct or not.

The starting current for a motor is the same irrespective as to whether or not it is connected to a load.

The load determines how fast the motor accelerates up to full speed.

The requirement needs to be discussed with <...DEG...> suppliers and rental agencies. After all, these people are in a position to provide commercial warranty that the selected equipment is suitable for the requirement at the point of purchase order placement, which is something that this forum cannot do.

How will you be starting the motors? One at a time? Step starting will reduce the starting current significantly such that with no load on motors, the load can be sized at total RLA+ starting current for largest motor...I don't know why you would want to start all the motors at once...How are the motors started?

No load trial run of the motors on DG set means the DG will be working at low load <30% for extended periods (>4hrs in your case). This can cause exceesive carbonisation in the engine cylinders and troubles associated with it.

It could be helpful if you could find a low kW rated DG set but generator rated at low power factor so that large VARs and low kW requirements can be met without sacrificing the engine health.

But, it could be a challenge to get such a DG set readily in the market.

You should talk to the genset people.

You could always put a resistive load on the gensets to keep them running in the proper range.

I would have to agree the proper way to test these is with a load bank...

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