Testing substation circuit breakers safely

Damon Mount, UK and Southern Africa sales manager at Megger, discusses safety and accuracy when testing circuit breakers.

Testing substation circuit breakers safely

When a circuit breaker requires maintenance it needs to be isolated and grounded on both sides for safety. This can distort the test readings but removing the ground creates a safety hazard. Test instruments with DualGround capability make fast and accurate circuit breaker testing possible with both sides of the circuit breaker grounded.

With DualGround measurements, engineers and technicians are protected against receiving dangerous shocks from voltages induced in the breaker, by current flow in nearby live conductors. This is critically important in the substation environment.

It has been possible to measure timing with both sides of the circuit breaker grounded with dynamic resistance measurement (DRM) techniques, but the results are not always consistent and reliable. Dynamic capacitance measurement (DCM) technology is able to produce dependable timing results safely on all types of circuit breaker including GIS.

Engineers and technicians are protected against receiving dangerous shocks from voltages induced in the breaker

The test configuration for DCM testing is identical with that used for DRM measurements but, instead of looking at resistance changes in the main contact circuit during the operation of the breaker, DCM treats the contact assembly as a variable capacitor. As the breaker operates, the distance between the fixed and moving contacts changes, which means that the capacitance between them also changes. DCM evaluates these capacitance changes and uses them to provide accurate and repeatable timing measurements.

This method significantly increases safety and accuracy and reduces testing time, since it is no longer necessary to remove one of the ground leads before making a measurement and reattaching it afterwards.

For further information email: info@megger.com


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