Inducing unwanted voltages onto control wiring when a DC rectifier ramps up to steady state.

[bdn2004]

We are installing a large rectifier that converts AC power to 735VDC and 30,000A.
I'm looking at the how the control wires are shown coming into this rectifier. They are in very close proximity to this open DC bus, like within inches. The control wires are run from separate 120VAC and 24 VDC sources.

My question is when the rectifier is off and then re-started, the voltage obviously ramps up to it's DC voltage. With this many Amps, wouldn't there be a concern about inducing voltage onto the control wiring and perhaps giving false signals? The vendor doesn't state to use any special kinds of wires or any minimum distance requirements that I can find. Is this something to worry about?

 

[rasevskii]

Obviously the control wiring should be moved as far as reasonably possible from the DC bus at this level of current. There will be some induction from the harmonic content of the DC output into the control wiring. At the very least this wiring should be in metal conduit (non-magnetic material) as far as possible away. Also at his voltage level of over 700V there has to be a safe separation.
Has this OEM done such equipment before without problems with the same design?

rasevskii

 

[PHovnanian]

The coupling between the DC bus and control wiring depends on a few factors. If the bus carries clean, ripple free DC, then the coupling will only occur once, on energizing the DC. If the DC bus has a high ripple content due to the rectifier/filter topology, this could be a continuous problem.

Aside from separating the control wiring from the DC bus as far as possible, you can twist the control circuit wiring where it travels near the high current bus. Also, the type of control circuit (high vs low impedance, balanced vs unbalanced, etc.) will affect the circuit's susceptibility to interference. A low impedance, balanced circuit with high CMRR (common mode rejection ratio) will help. Pay close attention to grounding between the two ends of each control circuit. You don't want to create any large area loops that will inductively couple noise from the high current bus.