Max. Motor starting capability of DG set

Thanks MS for your reply

You had several responses that are correct.

Simply: The remaining available power divided by 6 will be adequate most of the time.

Don't forget that a DG rating should include a surge capacity for several seconds and an overload capacity for an hour. these will help take care for the very short time demand of more than 6 times the normal nominal current of the motor (~ 10 times for DOL).

Thanks.

It depends upon the amount of energy held in the weight of all the rotating mass (Flywheel etc) as to how big an overload can be supplied for a second or two.....

But I used to work with 6:1 as a rule of thumb. This would allow a motor to start without stalling or noticeably slowing the prime mover.....

That is I needed the motor not to exceed about 1/6 of the generator max load.....

Motor and starter design play a significant role and should not be forgotten, as the right combination will/may allow a slightly larger motor to be safely started.

It is as good as impossible to use the fully Alternator output with motors, the generator will always be "lightly" loaded, except at big motor start time.....that you have to accept.

A 1000 KVA DGset is already supplying a load of 300 KVA. It means the genset capacity available for motor startup is 700 KVA. A squirrel cage motor draws about 6to 8 times of its rated current at start up depending upon the starting load conditions. Hence, approx 1/8th of the balance capacity i.e. approx 90KVA OR 90 HP motor can be DOL started. But again the number of starts you can have in a given time will also be limited and the genset supplier is the best advisor. The max capacity of the DOL started motor will also depend upon the engine and the governor characteristics and here again the engine manufacturer needs to be consulted. The inertia of the load coupled to the motor will also play an important role in making this decision.

PRIYADARSHAN

Isn't that what I said in my post? Mine is simply written and uses less words.....

Dear P,

I disagree with your explaination to question. Pl refer more appropriate reply of msamad.

check your mail box and revert back i can send you the application and installation of DG sets

murali

One thing is the ability of the generator to recover during motor starting.This depends upon the AVR.Most motors in India are designed to accelerate at 80% Voltage.So a drop below this can stall the motor.You can calculate the voltage and a rule of thumb is tolimitit to 20%.So sizing has to be done accordingly.This holds good for low inertia applications like pumps etc.But if a high inertia is involved then one has to do detailed calculations including the acceleartion time, The drop , recovery time of AVR all have to be seen.