SCR Heater Controller - Grounds or Leakage Current Issues

[rodroche]

Can anyone help me with the following? I have several SCR controlled heaters on a three phase, 3 wire 480VAC system, ungrounded. They are on a casino vessel. Under generator power we keep getting ground fault indication, via the three light indicator system. When we switch to shore power, which is a solidly ground system at the transformer neutral all the fault indications clear up. I am thinking there could be a leakage current occuring in the SCR based controller that the ungrounded system configuration picks up, but the shore power system justs sees as a very low ground fault, and does not trip out. The SCR controllers only control A and C phase, with B phase constantly energized right up to the heater elements. Any ideas?

 

[Jraef]

There are several ways of configuring a "3 light system" based on what you have and how you want it to indicate. You didn't really provide enough detail to work with here.

How does your 3 light system function, dim all the time but brighter if a GF exists or bright all the time and no lamp if a GF exists, or no light from any of them UNLESS a GF exists?
.
So that shore power system is 4 wire? If so, is it using an NGR?

What's the GF detection system for the shore power?

Do you isolate the generator system completely when connected to shore power?

SCRs do have "leakage current" but it is leakage ACROSS the SCR, not to ground. If however someone configured your heater elements in a Y and then grounded the Neutral on it, that would be incorrect and you WOULD have leakage to "ground" and since your ship generator system was 3W, that might explain it.

Need more information.