Induction motor test rig 1

[ccdubs]

If I use an induction motor with a variable frequency drive as the prime mover for a synchronous generator. Can I use the VFD as a way of regulating the power generated?

I.e., can I increase speed to reduce the power generated.

This is for an electric test rig.

 

[electricpete]

Real power output of a a generator is dependent upon the load and how it responds to the frequency and voltage supplied by the generator.

Let's say your loads are pumps and fan motors. Those will respond to increasing frequency (due to increasing prime mover speed) by drawing increased load.

I'm not sure if I understand what you're tring to accomplish.

 

[electricuwe]

Do you want to test the induction motor or the synchronous generator ?

 

[ccdubs]

Sorry for the lack of info.

We are wanting to test a gearbox under load. Under normal operating conditions this gearbox (step up) will drive a mains connected synch generator (one referred to above). To test the gearbox we intend to drive it with an induction motor and variable speed drive with the generator connected to the grid. We will want to test the gearbox at different loads, so what I was considering was to use a VFD as the load control.

I thought that if the genny is synched to the grid and we try to drive the motor above synch speed, we load the gearbox. I imagine that the changes can be quite sensitive judging by the torque speed curve of an induction motor. Does the torque speed curve still apply with a VFD or do you need a seperate t/s curve for each frequency? So I guess the question is, how do I set the load on the generator and hence gearbox?

The above is only one option. We are also considering using a diesel engine (throttle control) and a load bank or grid connection for power dump. Or an induction motor drive and a load bank.

Personally I am in favour of the engine and load bank as we are talking 500kW and if we can avoid dealings with power co's even better.

 

[electricpete]

Your thinking about the control of loading makes sense. Shaft speed will be controlled constant by the grid since generator is always in sync with grid. By varying the frequency supplied to the motor with asd you will be adjusting it's slip (varying stator frequency, constant rotor speed). Torque will be in accordance with torque speed curve for small positive or negative slips.

Connecting your generator to the grid will of course require utility approval, with appropriate relaying, controls etc.