Lone Crapshooter

I have a 480 ungrounded system with split delta ground detection. The primaries are connected to the 480 bus in a grounded wye. The secondaries are connected in a delta with a 64 (ground detection relay ) and a dampening resistor between the 2 phases that form the apex of the delta. It looks to have 2 high resistance grounds on 2 phases and the 3rd phase is ungrounded. We connect the thumper and there is no current flow during the pulses. The 64 relay does not pick up there is anout .2 amps of current through the resistor. No breakers have triped and the line to line voltage is 480. The line to ground voltages are like 150 220 and 390 from memory .
Any ideas ?

THANKS

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Electrician licensing without continuing education is just another form of TAXATION

Big John

Are your voltages normally pretty constant? I wouldn't expect voltages on faulted phases to be that high.

Depending on how well sized the resistor is on your broken delta, you can have a good bit of circulating current flowing through it, and this will change if system capacitance changes. Do you know for sure that's a new problem?

-John

Lone Crapshooter

We have faught this problem off and on for more than a year. I know that the transformers have been replaced twice . What determines the setting of the resistor. I believe that we had 3 volts and .2 amps today. I will get the correct figures tomarow.
LC

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Electrician licensing without continuing education is just another form of TAXATION

Lone Crapshooter

The voltage readings are as follows
A-B 484
B-C 489
C-A 482

Ground Detection Fuses Out
A-G 159
B-G 336
C-G 372

Ground Detection Fuses In
A-G 260
B-G 253
C-G 333

The line to line voltages are the same with the ground detection fuses in or out.

There are 120 volt indicator lamps across the secondary of each of the transformers and their voltages are as follows
A- 32
B- 88
C- 102

That is all I can tell you

__________________
Electrician licensing without continuing education is just another form of TAXATION

Big John

Can you guys put a monitor on this to see how it changes with load? I think you have a single soft ground on A and the rest of the voltages are just floating to follow it.

How big is this system, what kind of loads are on it?

-John

Lone Crapshooter

Feeder to a building probably 500' long to a MCC then HVAC motors and duct heaters

__________________
Electrician licensing without continuing education is just another form of TAXATION

Big John

Is it impossible to isolate downstream loads by opening breakers and seeing if the voltage stabilizes? It's really strange that you're getting no current flow at all with your thumper.... Any change in phase voltage when it's connected?

Also: Why have you had to replace the transformer twice?

-John