Running battery faults to ground

Andy Sagl - Product manager

Ground faults in ungrounded battery systems, often caused by electrolyte leakage and other forms of contamination, are by no means unusual. However, especially in large battery installations, faults of this type can be difficult to locate, especially when the battery cannot easily be taken out of service. Then conventional sectionalisation of the battery string, to find the short can take a great deal of time and be quite labour intensive.

There is now however, an efficient and cost effective solution to this problem. This is based on injecting a low-frequency signal of around 20 Hz into the battery system, and testing the feeder cables for signal amplitude, which is inversely proportional to the fault impedance. With this technique, faults up to 100 kO are easily traced and isolated by clamping a direction-sensitive probe on the feeder cable and monitoring the signal strength.

This method, which is adopted in Megger’s BGFT battery ground fault tester, works reliably even in the presence of ripple and electrical noise, and it can be used without taking the batteries out of service. The built in resistance and capacitance bridge in the Megger instruments will find the pure resistive value of the short and in addition it will find capacitive phantom shorts allowing the operator to locate the true short quickly and easily.

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