Total Line-Side harmonic current of multiple VSDs

[EddyWirbelstrom]

A 2.5MVA, 11/0.433kV transformer supplies multiple 6 pulse VSDs ABB type ACS800-01. ( single quadrant, non-controlled rectifier ).

I used "ABB DriveSize" program to calculate the magnitude of the individual harmonic current orders on :-
a) The line-side of each individual VSD.
b) The transformer secondary (supplying all VSDs ).

I used the harmonic currents of the individual VSDs to build 'harmonic source generators' with the SKM-PTW HIWAVE software.

The transformer secondary harmonic currents calculated by "ABB DriveSize" and SKM-PTW HIWAVE are the same when only one VSD is supplied by the transformer, however for multiple VSDs the harmonic currents calculated by "ABB DriveSize" are significantly less than those calculated by SKM-PTW HIWAVE.

When the VSD drives and loads are identical, the SKM-PTW HIWAVE calculated harmonic currents of the transformer secondary are equal to the harmonic currents for one VSD multiplied by the number of VSDs, however the harmonic currents calculated by "ABB DriveSize" are significantly less.

Assuming identical VSDs and loads; are the harmonic currents on the transformer secondary the arithmetic sum of the individual VSDs as indicated by SKM-PTW HIWAVE ?

 

[ScottyUK]

You can't apply arithmetic sum here. You must use vector summation methods because the relative phase of the harmonics referred to a common datum will shift with load. Thus at some loads harmonics may add, and at other loads they may cancel.


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I don't suffer from insanity. I enjoy it...

 

[ozmosis]

It would appear that the ABB Drivesize is using vector summation method(using the relative coincidence factors) and therefore the THID is lower than the possible 'worst case' scenario of arithmetic summation? I think the recommendations from G5/4 in the UK advise you to use the arithmetic sum method to calculate the harmonic distortion of multiple drives and then you know the worst case scenario at your PCC (point of common coupling)