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Vfd Testing Load


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#1 invertek.hans

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Posted 07 November 2007 - 03:05 AM

Hi
Gentlemans!
Every repaired drive need test before devilery to customer. I test repaired by checking the PWM wave and listening the sound of driving samll motor. But I found this way is not good enough for large drive.
Itwas said that the reactor (choke) could be used as a load for test VSD output. If possible,I hope make a reactor could test the VSD for 400v, 50Hz~60Hz, load current up to 50Amps.
Please give me more detail information about how to caculate the involved parameter.
Any others way could meet above demand of testing?

Best regards!

Hans



#2 invertek.hans

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Posted 07 November 2007 - 07:29 AM

further expaination of above queation:
I mean that I want use a three phase reactor,It would be modified suit for the load test. connect the winding of the reactor as Y type. then connect the 3 lead to VSD's output terminal.

#3 marke

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Posted 07 November 2007 - 07:02 PM

Hello Hans

I see no problem with using a three phase reactor for testing drives provided that the drives are running in open loop V/Hz mode. If the drives are operating in any form of vector control algorithm, even if it appears to be in V/Hz mode, I expect that it will get totally confused and cause problems.
If the drive as an ID run function or similar at power up or the beginning of a run, where it measures the motor parameters, then it needs to be a motor with parameters within an acceptable limit for that size of drive. - good for older drives, but probably limited for more modern drives.

I would suggest that you select the reactance such that the current flow is in the order of one third of the rating of the drive. This will then look like the magnetising current of the motor. You could have the reactor would for a number of different reactances and have different windings or tappings to give the reactances, but if you did this, you would need to have very high insulation rating on the reactor as when you tapped well down in reactance, the total winding would act like an auto transformer and develop very high voltages. An alternative way, is to use a variable air gap to alter the inductance. This technique was used extensively as a means of controlling the current on arc welders. Perhaps you can use the control reactor from the input of an arc welder to do what you want?

Best regards,

#4 invertek.hans

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Posted 08 November 2007 - 02:12 AM

Hello Marke
Thanks!
First,I undersdand that this way is limited to test modern vector control drives even the drive work at V/F mode.
Second, I should adjust reactance to meet the demand of one third drive rating current flow principle. Variable air gap control is the best solution.

one more question:
Would you like tell me why one third rating of the drive current flow in reactor, it will look like the magnetising current of the motor.

Best regards!
Hans

#5 marke

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Posted 08 November 2007 - 02:25 AM

Hello Hans

QUOTE
Would you like tell me why one third rating of the drive current flow in reactor
The magnetising current in motors is typically in the order of 20% to 40% of the current rating of the motor.
Smaller motors have a higher magnetizing current, as do submersible pump motors, but generally the current is around 30% +/-
If you have too much inductive current with some inverters, it can cause a problem.

Best regards,




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