Technical library
The Megger technical library provides access to a range of additional content and resources such as technical guides, application notes and more. Use the filters to browse specific content (e.g. application notes) or refine your search to a particular electrical application area.
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Ground fault tracing: stray capacitance
Tracing a ground fault on an isolated DC system can be simple or quite difficult depending on the nature of the fault and the characteristics of the DC system. This application note explores why a DC system’s characteristics may impede efforts to locate a ground fault and offers a simple solution.
Published: 9 March 2023
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Ground fault tracing: CT magnetization
When tracing ground faults on ungrounded DC systems, one should not assume that there will be no DC current flowing through the circuit. If a current clamp (CT) is placed on a line with DC current, the DC current will cause the CT, namely its iron core, to magnetize. The higher the DC current, the stronger the magnetization will be. This can make removing the CT quite difficult. The CT can be damaged in the process of removal. In some cases, the CT cannot be removed from the line.
Published: 9 March 2023
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Ground fault tracing: AC tracing vs pulse tracing
When searching for ground faults, a transmitter injects a current through the fault (fault current) and a receiver is then used to trace the path of the fault current. The injected current can be either an AC signal or it can be a pulsed DC output. A pulsed output often needs to be synchronised with the receiver. This way the receiver knows when to look for the pulse. This is required due to potential noise on the system. Random noise can look like a pulse. However, on very noisy systems this can still be problematic. In addition, if the sync is lost, then the receiver needs to be reconnected to the transmitter in order to acquire the synchronisation again. Capacitance can also be a large problem for pulsed outputs. There will always be some amount of capacitance on a DC system. Shielded cables have a capacitive property. They consist of 2 conductors separated by an insulator. This is, in essence, a capacitor.
Published: 9 March 2023
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