Diesel Generator Capacity for 75 kW Motor

Use a Variable Frequency Drive to soft start the pump motor. Maximum load should be around 55KW (your value) regardless of power source.

Asitha,

ACE Boeringa has a good point to provide a soft start.

You bring out the use of a transformer in your description of the Diesel Generator setup and the motor configuration. Can you explain in more detail what the voltage rating is of the motor. Is it a single or three phase, and what is the lock rotor amps on the name plate.

You mentioned that the operating power consumption is going to be about 55kW which is at the high end of the continuous operation range rating for some 75kW generators, and could shortent the life expectancy of the generator.

What is the duty cycle of the operational period for the generator, or how long is the generator going to be running on a normal bases. how many expected hours a year will the generator be running? number of start stop cycles? etc.

Improving the efficiency of the system will help reduce the stress on all of the equipment, so a better understanding of the requirements will help in the design point of the 75kW generator working capacity.

This does not give you a direct answer but it will help in the design of your system that will be most reliable and efficient for your application.

Thanks for the opportunity to respond.

If you wanted to just run the pump then best thing would have been to buy diesel engine directly connected to the pump. You could have saved cost of the electric motor and energy loss.

If you are not going to run the pump at variable speed, an AC drive is an overkill. Use a thyristor soft start or a transformer starter. You will save $. If the pump is centrifugal OR positive displacement will have an effect on the inrush current. Do you start against the full pressure head or does the pressure build up progressively? With this information, the application eng. of the equipment supplier will be able to size it properly. Use their expertise don't just guess and buy.

Yes, I would agree with this. I work for a company who makes soft starters which are typically used in pumping applications. They can be programmed to limit the inrush current to whatever the application requires and also can allow for a soft stop funtionality which prevents water hammer. See www.aucom.com for more details.

I will like to reply you one by one.

A) The starting methods may be the followings:

1)Frequency inverter

2) Soft Starter

3) Inductor method

The best one is frequency inverter but it is costly. Soft starter can solve your purpose in economical way.

B) When you will use one of the method then the starting load and torque will not effect your generator required capacity. As your maximum load is 55 KW. Keeping this in mind, Generator should be always of greater capacity. Normally it is best to select the diesel generator rating 10%-20% higher than the required, In other words, Select a generator of capacity approximately 70 KW to run this on prime load.

C)I think motor, you are using of higher voltage motor. Due to this you have to use transformer to transform the voltage as per requirement. As in case of starting methods mentioned in (A), starting current problem will not any issue because you can programme the start (acceleration) as per requirement.

STAHIR

Asitha,

The most important piece of advice here is to talk to the generator manufacturer before selecting any different methods of starting the pump. Tell him/her what you have and ask them to select a generator to suit the needs of your system and then ask them to comment on the options of different starting methods.

There is no reason why you should not go to several manufacturers with the same information and get them to offer their best solution.

The generator selection is not simply a case of matching the maximum load to a generator load. Everything will hinge on the performance of the generator so it is important to get it right.

Good luck, Mike

Asitha,

As noted before Kodiak Energy Systems is hear to help you with gathering that which you seek. Give us a call markr@kodiak-energy-systems.com. I have access to nes and used models of generators and equipment top help with your needs.

Mark Reid

i agree what MIKE says below....

Mike is right

The most important piece of advice here is to talk to the generator manufacturer before selecting any different methods of starting the pump. Tell him/her what you have and ask them to select a generator to suit the needs of your system and then ask them to comment on the options of different starting methods.

There is no reason why you should not go to several manufacturers with the same information and get them to offer their best solution.

The generator selection is not simply a case of matching the maximum load to a generator load. Everything will hinge on the performance of the generator so it is important to get it right.

Good luck, Mike"

In generator rating selection. please keep in mind that operational duration. The duration will guide you generator ratings keeping all the already discussed factors.

STANDBY- Output available without varying load for the duration of the interruption of the normal source power. Standby power in accordance with ISO8528. , ISO3046

PRIME- Output available with varying load for an unlimited time. Prime power in accordance with ISO8528. 10% overload power in accordance with ISO3046/1, AS2789, DIN6271, and BS5514.

My suggestion would be a 225 kva gen-set with a soft-start or a 150 kva gen-set with a VFD.

Cheers,