DC earth fault locator –Working Principle

DC earth fault locator is an instrument that is used to detect earth fault in a live DC system. DC system is used for the running of protection systems in substations, generating stations, communication & networking equipment, and other electronic devices.

Due to cable insulation failure or wrong wire connection, the DC terminal can be grounded. When one of the DC terminals is grounded, generally it may not create any issue to the system. When both the DC terminals are connected, it will create a short circuit and the connected DC breaker got tripped. It is commonly observed outage of the system due to earth fault in the DC system.

Why does DC earth fault locator use in the DC system

The frequent shutdown of the DC system may not be possible due to system constraints and stability issues. So, it is always preferred to detect and isolate the DC earth fault in the live system without taking any shutdown of the DC system.

When any of the DC terminals is grounded, it can detect by using the DC earth fault locator in the live DC system. By using the DC fault locator, DC short circuits can be avoided due to earth fault and system stability can improve.

Working Principle

There are many types of DC earth fault locators available. A portable DC earth fault locator is commonly used to detect the fault. As shown in the drawing, the following 02 components are available.

  • Pulse Generator
  • Pulse Receiver
DC earth fault locator
  • Pulse Generator

As the earth fault needs to detect in the live system, external DC voltage or current cannot apply to the system to avoid the malfunction due to mixing with the external source. The external pulse generator is used to apply the pulse of around 2 kHz to 10 kHz to the DC system.

  • Pulse Receiver

A pulse receiver is used to detect the pulse at the individual feeders or terminal point. The pulse receiver has two components, the CT unit which is used to detect the pulse, and the processing unit which is used for filtering and analyzing the pulse.

For detection of the fault, at first, the pulse generator is connected to the DC system at the source point. The pulse generator is extended the signal with respect to the ground to the whole DC system. After that, by using the receiver unit, the pulse needs to check in every individual feeder and terminal point.

As shown in the diagram, if there is no DC earth fault in the system, it will not create any close loop and the pulse will not detect by the receiver unit.

In another case, if any earth fault is available in the system, it will create a close loop through the earth and the receiver unit will detect the pulse and it indicates the DC earth fault in the system.

DC earth fault locator can also detect DC source mixing in the dual source DC system. For identification of DC source mixing, one terminal of the pulse generator is connected to one DC source and another terminal is connected to the other DC source. Pulse will apply across both the DC source. If there is any source mixing present, the same will be reflected by the receiver unit during the checking of the pulse at the individual feeders.

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