SCR Heating Control

[nhcf]

What would be the potential negative impact of imbalanced load on a 3 ph. 480 VAC SCR heating controller.

Heating load consists of multiple elements connected as 3 wire, wye connected - there is no neutral conductor run to the load so that the 'wye' point at the load end is floating.

Assuming the phase currents are not balanced due to design and/or heater element failure - are there any negative consequences to the SCR controller, assuming phase currents are maintained within the overall current rating? Is there a imbalance threshold where the SCR controller would malfunction and/or be damaged? (an open circuit on one phase?)

 

[sibeen]

I doubt there will be any problems with the heating controller under this scenario, but there certainly may be an issue with the load elements. Under the unbalanced load condition, and a floating wye point, the voltages across each leg of the load will be at different potentials as the wye point has been shifted. The leg with the least amount of load (lowest current) will have a proportionally higher voltage across it compared to the other legs.

 

[ScottyUK]

The heating element won't care as long as it is rated for the full voltage at zero delay angle.

 

[Skogsgurra]

Agree fully with what has been said.But there may be a problem, I had that with a primitive UAL SCR unit, if the gating is incomplete.

The one that gave me problems did not have any "slave" gating pulses to keep the return path open and could not work with wye connected loads without Neutral connected to star point.

But if the unit says that it can work with floating wye - no probs.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[nhcf]

Thanks for the replies - I am not concerned with the imbalanced voltage impact on the load.

Was not sure if there was a potential negative impact on the SCR. The SCR has been working with the floating wye configuration for many many years. Issues on the load side are now causing the unbalanced load, and there were questions related to any potential for SCR damage. The responses so far are consistent with what I was thinking.