ABB ACS1000 common mode choke

[hhhansen]

Hi all of you
I ABB design manual for ACS1000 12-pulse medium frequency drive a maximum cable length of 30 m is allowed between converter transformer and converter. Above 30 m a DC common mode choke shall be installed to minimize voltage overshoots.

My question is what are limitation for cables length if there are parallel cables between transformer and converter. Is the distance then to be divided by the number of cables ?

Does anyone have experience within this field ?

B.R. Hans-Henrik Hansen

 

[Electic]

I 'believe' the length is independent of paralleling but this should be verified with the VFD manufacturer. The reason I say this is because it seems some allowance is made for various conductor sizes yet the length requirment is fixed, perhaps some function of reflected waves and the speed of electricity?

 

[ozmosis]

Firstly, on your post you mention DC common mode choke.
Between the converter transformer and the two rectifiers, this will still be AC, and so AC line reactor is necessary. Between the rectifiers and inverters, a setup we would call an inter-bridge DC choke arrangement is generally necessary.
Your comment about the cable length between transformer and rectifier is important as it is critical the best load equalisation is obtained. The longer the distance between the TRX and the rectifiers, the greater the risk of imbalance and therefore the risk of secondary transformers being imbalanced is increased. Any imbalance in the secondary windings will result in a lack of harmonic cancellation and potential overheating of the trx's. This is very important in a no-load situation. The figure we use within Siemens is the no-load voltages of the two secondary windings should not differ by more than 0.5%. This is therefore enhanced by the addition of the AC line reactors (usually around 2% Uk). I'm guessing the advise from ABB will be similar to Siemens.

 

[hhhansen]

I am aware about the problems with trx load sharing if cable lenght are not equal. However my question has not been answered:
Does parallel cables influence the allowable length of cables between trx and rectifier as regards to common mode current peaks ?