Protective relays are used to protect electrical power distribution systems from faults. They do this by monitoring the system for conditions that could lead to a fault, such as overcurrent, overvoltage, and Undervoltage. When a fault is detected, the relay will open the circuit breaker, which will isolate the faulted section of the system and prevent damage to the equipment.
There are many different types of protective relays, each of which is designed to protect against a specific type of fault. Some of the most common types of protective relays include:
1. Overcurrent relays: These relays are designed to protect against excessive current flow. They typically work by measuring the current flowing in a circuit and opening the circuit breaker if the current exceeds a preset value.
2. Overvoltage relays: These relays are designed to protect against excessive voltage. They typically work by measuring the voltage across a circuit and opening the circuit breaker if the voltage exceeds a preset value.
3. Undervoltage relays: These relays are designed to protect against excessive voltage. They typically work by measuring the voltage across a circuit and opening the circuit breaker if the voltage falls below a preset value.
4. Directional relays: These relays are designed to protect against reverse power flow. They typically work by measuring the direction of power flow in a circuit and opening the circuit breaker if the power flow is in the wrong direction.
5. Differential relays: These relays are designed to protect against internal faults. They typically work by measuring the current flowing in each leg of a circuit and opening the circuit breaker if the current flowing in one leg is significantly different from the current flowing in the other leg.
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