Line Reactors in Series/Parallel - Simple? Crazy?

[DrDrreeeaaa]

Hi All,

I need to source a 600A 5% line reactor for notching and harmonic mitigation of a 400V 550A three phase AC controller.

I am in Australia, and availability of such things is very difficult. 5% line reactors are not stocked at all, and 3% reactors are stocked but only in sizes below, say, 400V 300A. Anything else we generally ship them from the US at a 12 week lead time which our project can't tolerate.

Smaller reactors are available here in Australia and I was thinking maybe it's practicable to combine several smaller reactors to satisfy our requirements

We would need 4-off total reactors, 2 in series, and then each group of 2 in parallel. Each reactor would be 320A 3% (0.075mH approx).

Is this totally crazy? Or is it simple, bread and butter? Obviously it seems simple when you do a calculation of parallel and series inductances, but I have never seen such a thing done practically.

Or are there even advantages to such an arrangement?

Or does anyone have an MTE RL-50013 lying around that I can buy off them!

Appreciate anyone's thoughts.

 

[iop95]

In series to increase inductance.
And in parallel to split current... but, will be hard to get same (close) currents.
At such current values, resistance of reactors/cable/connections need to be below 1mOhm for each branch to limit power losses/heating.

 

[DrDrreeeaaa]

Thanks mate

Yeah I think we could do that. We’d use 240mm2 cable lugged in parallel… for all intents it could be close to identical. Ie the cable arrangement - see the attached sketch (excuse the dodge detail, did it on my phone). 

 

[bacon4life]

iop95- Why does it need such good matching of conductor impedance? This is a somewhat different case that ensuring sort runs of parallel cables having nearly identical impedances.

Typically sibling transformers placed in parallel can have a difference of impedances of up to 7.5%. I assume the mismatch in inductor impedance would dominate over differences in cable impedance. The inductor amp ratings should be sized based on the largest allowed impedance variation per the IEEE/IEC specs for inductors. If the allowed tolerance for inductors is the same as for transformers, that would mean two 320A inductors in parallel are not quite enough for a total of 600 A capacity. Relying on as-tested impedance values would leave a trap for future replacement.

 

[iop95]

bacon4life

Need good matching of resistance cable/connections to keep a good current sharing (presume all 4 inductors are pretty identical,with close enough impedance variations with temperature/current).
Even if the sharing of the currents will not be quite equal, it can still be a temporary solution, especially if the VFD will not work at maximum load.