Transmission & Distribution Channels

Category Archives: Breakers & Relays

Breakers & Relays

Protective Relay Frustrations

Solving misoperation with line parameter measurements


Between 80 to 90 percent of all power system faults involve ground. Many protective relaying schemes depend on ground distance protection to accurately sense and locate ground faults on multi-terminal sub-transmission and transmission lines. In addition to the need of dependable ground fault detection, protective relay devices must provide adequate selectivity to avoid overtripping for faults outside of its zone of protection and other undesired consequences, such as undertripping or unintended automatic reclosing initiation. Read more


Breakers & Relays

Partial Discharge & Circuit Breaker Asset Management

Detecting and avoiding preventable failures

BY JAY GARNETT, Doble Engineering Company

While metal clad switchgear can be very reliable, sometimes operating for over 50 years, throughout the aging process, this group of electrical disconnect switches, fuses and circuit breakers can experience issues such as moisture ingress, animal intrusion, enclosure rusting, and insulation deterioration. One efficient approach to detect incipient failures is partial discharge (PD), a leading indicator of various failure modes. Using both acoustic and electrical partial discharge techniques, sources of partial discharge can be detected and pinpointed to a source, such as a particular metal clad compartment.

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Breakers & Relays

Circuit Breaker Time and Motion Testing

Determining mechanical condition of high-voltage circuit breakers

BY JOZEF LEVI, Doble Engineering Company

Life expectancy of a newly installed high-voltage circuit breaker is approximately 40 years. Throughout its life, under normal circuit conditions, the circuit breaker will operate less than ten minutes. During abnormal circuit conditions, the breaker will operate less than one minute in its lifetime.

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Breakers & Relays

Circuit Breaker Lubrication

Developing circuit breaker lubrication procedures

BY RICK YOUNGBLOOD, Doble Engineering Company

Circuit breaker analyzers are used to determine operating speeds and velocity. This information enables the tester to determine if a breaker is safe to place back into service. The data recorded by a test set allows technicians to measure the time it takes from the moment the trip or close button is activated until the breaker closes or opens fully. This is an electrical testing method to determine the mechanical health of the operating mechanism used to open and close the current carrying contacts. Subsequently, the results can be compared to the manufacturer’s design specifications.

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