AC / DC Earth
Leakage Unit

Residual current detection

Residual current detection

An AC / DC earth leakage unit detects current imbalance in trainborne and wayside cabling.

Early detection of cable degradation can prevent further cable damage. Moreover, it can stop potential hazards we associate with this type of fault.

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What do AC / DC earth leakage units do?

The AC / DC Earth Leakage Unit is a residual current detection unit which is powered from the vehicle’s battery or AC supply and measures the sum of the current in the primary ‘supply and return’ conductors passing through its aperture.

During normal operation when there is no earth fault present in the system, the current in the “positive” and “negative” conductors cancel each other out so no fault is triggered.

The measured residual current signal is filtered and rectified before it is fed into a comparator. If the current is greater than a set detection level, then a fault is signalled via relay contacts. The fault output may reset after a delay if residual current falls below detection level or remain latched in the fault state until the unit is powered off and on again. Rowe Hankins’s has developed a new dual trip AC Earth Leakage Unit that is digitally programmed and is the next evolution for current imbalance detection applications.