Regen VFD as a load bank for testing
Regen VFD as a load bank for testing
(OP)
I am consulting for a new start-up company who makes a small alternative energy generation system (hey, aren't we all?) that uses a 25kW SCIM as the generator. For acceptance testing, they have been using a set of halogen lamps to load up the generator, staging them on and off by wattage as they put the system through its paces. The test is actually of the regulation system that is controlling the prime mover, so they want to be able to fully load the generator and shed load very quickly to determine the step change response capability.
I proposed they consider using a Regen VFD on the 25kW motor instead, with a plan to convert the "load" command to a "brake" command via a PID loop. For example they tell the PLC to "Load to 50%", which has the PLC send a commanded speed signal to the VFD that scales lower and lower until the regen output is 12.5kW, then holds there.
Anyone done something like this before? Anything I'm missing here? It just seems too simplistic!
I proposed they consider using a Regen VFD on the 25kW motor instead, with a plan to convert the "load" command to a "brake" command via a PID loop. For example they tell the PLC to "Load to 50%", which has the PLC send a commanded speed signal to the VFD that scales lower and lower until the regen output is 12.5kW, then holds there.
Anyone done something like this before? Anything I'm missing here? It just seems too simplistic!
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RE: Regen VFD as a load bank for testing
This sounds like an interesting challenge. I hope that you are able to keep us posted on the progress.
Bill
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"Why not the best?"
Jimmy Carter
RE: Regen VFD as a load bank for testing
RE: Regen VFD as a load bank for testing
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Regen VFD as a load bank for testing
Keith Cress
kcress - http://www.flaminsystems.com
RE: Regen VFD as a load bank for testing
Some of these actuators were running 12-14000rpm, too.
RE: Regen VFD as a load bank for testing
RE: Regen VFD as a load bank for testing
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RE: Regen VFD as a load bank for testing
RE: Regen VFD as a load bank for testing
However this is a special case.
As I understand it, the transient response of the control gear of the prime mover is being tested. In such case the transient response of the VFD becomes part of the equation. The transient response of the VFD may interact with the control scheme under test in an unknown and non linear manner. This may render the test result meaningless. Much expense for nothing, and for transient testing very little returned energy. By all means use the regenerative drive for most of the testing, but go with a load bank to test the transient response of the prime mover control scheme.
Bill
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"Why not the best?"
Jimmy Carter
RE: Regen VFD as a load bank for testing
Compared to that, the AVR or speed controller or just about anything that needs to be tested is slow. So, I wouldn't hesitate at all. VFDs are good for all torque, load, speed testing that I have seen.
There is one case where water brakes or lamp banks are needed and that is when your grid isn't strong enough to 'swallow' the power your prime mover delivers. But, at 25 kW, that is probably not a problem.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Regen VFD as a load bank for testing
When I mentioned the possibility of using a regen VFD it piqued their interest and although I have done this for motor test stands, I was not 100% sure on the issue of doing it for an induction generator. I know it's not much of a difference really, it's just my being overly cautious with something new. You have reinforced my confidence that the differences and limitations are no more than I thought they might be.
Bill, although I'm not comfortable revealing the exact nature of the system (my customer may be reading this), there is an inherent lag in the step change capability anyway.
May the power of the Forum be with you all!
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