MEP-005A Motor Starting

[Krc002]

Hey Guys,

Quick question regarding the 005a motor starting capabilites. im interested in knowing if these sets are capable of starting a 20hp 3 phase motor and if there are any documents floating around pertaining to using the mep sets for motor starting. i have one for some of the older onan sets, but feel comfortable only speculating from them. any help is appreciated.

KRC002

 

[strycnine]

This may help you.

SIZING A GENERATOR FOR ELECTRIC MOTOR LOADS

 

[Ken_86gt]

Starting motors can take anywhere from 2 to 10 times the FLA (full load amps). There really isn't anyway for me to tell you what your motor is going to be. I can tell you that if you use a soft-start or VFD you have a much better chance for success. If you currently have this motor connected to a utility you could measure the inrush current to make a more educated guess. Do you know the LRA for this motor? (Also the voltage)

Sizing a generator for a single large motor is very difficult since you end up getting a generator that may only have 15% load once the motor is running- this is bad for generators.

 

[Krc002]

Yeah, thats more or less the problem i have been having with them. ill probably end up getting a VFD when im ready. it was a 20hp running on 208v. but i have back burner-ed that idea for the time being due to the starting requirements.

 

[ETN550]

I have been in this situation with a homeade rotary phase converter. Here are some other ideas. It can help a lot if the motor is unloaded. It helps if the temperature of the motor and driven equipment is above 60 degrees. It greatly helps if you have other smaller, but still significant motors running at speed but no load when you start the big one. If you have access to some smaller motors such as half the hp of the big one and can get them started and running idle then start the big one and once up to speed turn off the small ones. Three phase motors all tied on the same line work together on the line. I once started a 30 hp motor with a 5 hp homemade phase converter but had a 10 hp and a 15 hp motor running first. The 5 hp converter would not start the 30 without the 10 and 15 already running on it.

Take the voltage to the high side of spec and max out the Hz on the gen (65)and have the gen fully warmed up from another load, then, after a brief cooling at no load apply the motor start load.

Parallel a smaller gen to it, make the start then switch off the big gen. Most gens can be paralled even if not set up that way, for a short time. The big start load will force both generators into a loaded condition dropping below their setpoints so there will be no compatability issues while loaded.

VFD is a great idea and the cleanest approach.

 

[Ken_86gt]

Some good ideas about using smaller motors - but please don't try to parallel generators that are not set up to do this and an education on how to do this manually. I can see many issues with this approach.

 

[Krc002]

Thanks for all the replies, i greatly appreciate it, i had considered using some smaller motors to bump over the big one. most of this was for filling the need for a loadbank for a college project i am doing. it is incredibly inefficent to use just inductive loads and so i changed my mind and designed and built a 30kw or so water cooled loadbank for the purpose of loading the generator. its pretty neat i think, waiting on some more parts but drew a solid 65 amps today and that running at 2/3rds capacity. its a sweet deal really