DC Ground Fault

Re-check the system with DC ground fault detector to track the location of the fault.

http://www.freepatentsonline.com/4929901.pdf

http://samcoeng.com/manuel.html

Above are attached two links explaining apparatus for DC ground fault detection. May, it will help you.

Vinu_Answers Sure_answers

1. Do you have earth fault detection EF on system?
2. EF usually works with two resistors, one from + to earth and one from - to earth, equal by design - maybe not anymore? One system I know has 50 kohm resistors.
3. If you do not have EF detection, insulation resistance [high!] to earth is unlikely to be equal and if you are using a digital voltmeter its resistance is likely 1 or 10 megohm. So your resistance to earth is about 0.25 or 2.5 megohm from each pole - why worry!
4. Somewhere in your control load, you have a device with low insulation resistance to earth? Have you tried disconnecting the load totally and then by fuse & link section? Does it make any difference to voltage to earth?
5. You probably have plenty of AC powered kit with relays connected to DC bus, whose insulation has a capacitance to AC power and will feed in a trace of AC.
6. Have you tried connecting a small resistor - say 10000 ohm 3 watt to earth from each pole? Until you do that, you have no idea of the actual resistance to earth and if it is low enough to be a nuisance.
7. When I had this problem, isolating the battery from everything left volts to earth of battery much the same and the 10k did not make much difference. So it was the battery
8. The battery is full of conducting fluid, some escapes as vapour. When did you last wash the cells exterior, especially the tops near the terminals? Is there a leak (check cell fluid level)? Count down the cells in proportion to voltage to earth, or use voltmeter to earth on banks and cells until you find nearest to earth (0V). Maybe it is just that cell or those near it. But it may be a summation of the differing insulation of all the cells. Any contamination around battery cable glands?
9. Pushing plastic floor tiles under suspect cells or crates might prove a point!
   

It is generally seen that, for battery charging system, input supply of the battery charger is A.C. suply, after rectification and filteration, the D.C. voltage is used for battery charging, for malfunctioning of filter networks, various levels of harmonics are generated, specially tripplen harmoincs, which are flowing to ground, completing the circuit through voltmeter since neutral of the incoming A.C. supply is also grounded. This may generate A.C. voltages between positive bus to ground and negative bus to ground. The quantum of this voltage is depending on the zero sequence impedance of the circuit.

When the A.C. supply is disconnected, and found voltages between positive bus to ground and negative bus to ground, it is obviously due leakage in the system( D.C. part) may be surface leakages from batteries specially, the top part of the batteries may be contaminated with elctrolytes, leakage may also occurs at the wire terminations, connector blocks, even insulation failure or mechanical injury of wiring networks. So to detect this type of failures thorough inspection is required.

It is very possible that there is a connection between an AC line and the Negative side of the DC distribution system, sometime the connection is the result of miss-wiring. First you has to find the DC ground fault to see if that is the problem