Circuit breakers in substations serving as a source to distribution circuits are actuated by protective relays that recognize which on a circuit?

• A. damaged poles
• B. defective hardware
• C. short circuits and grounds
• D. broken strands

Answer: (C)

Protective relays are designed to detect abnormal electrical conditions that indicate a fault on the line. When a fault occurs, such as a short circuit or a ground fault, the current and/or voltage pattern changes in a distinctive way. Short circuits create a very high current quickly, while ground faults introduce current returning through an unintended path to ground. Relays monitor current (via current transformers) and voltage (via potential transformers) and trip the circuit breaker to interrupt the fault and protect equipment, personnel, and the network. Mechanical issues like damaged poles, defective hardware, or broken strands don’t produce the specific electrical fault signals that relays are designed to identify, so they aren’t the conditions that trigger a trip.