What Are Over And Under Current Relays

Overcurrent and undercurrent relays are protective devices used in electrical systems to detect abnormal current conditions and initiate appropriate actions to prevent damage to equipment and ensure system stability. Here's an overview of each type of relay:

1. Overcurrent Relay:

   • An overcurrent relay operates when the current flowing through a circuit exceeds a predetermined threshold.
   • It is designed to detect overloads, short circuits, and other abnormal current conditions that could lead to equipment damage or system instability.
   • Overcurrent relays are typically used to protect distribution feeders, transformers, motors, and other electrical equipment from excessive current flow.
   • When the current exceeds the set threshold, the relay triggers a trip signal to disconnect the circuit or initiate other protective actions, such as opening circuit breakers or activating alarms.

2. Undercurrent Relay:

   • An undercurrent relay operates when the current flowing through a circuit falls below a predetermined threshold.
   • It is primarily used to detect abnormal conditions such as load loss, fault clearing, or system malfunctions that result in reduced current flow.
   • Undercurrent relays are commonly used in applications where a minimum current level is required for proper equipment operation or system stability.
   • When the current falls below the set threshold, the relay triggers a trip signal to disconnect the circuit or initiate corrective actions, such as activating backup power sources or alarms.

Both overcurrent and undercurrent relays play crucial roles in power system protection by detecting abnormal current conditions and initiating appropriate responses to prevent equipment damage, minimize downtime, and ensure the reliable operation of electrical systems. These relays are often used in combination with other protective devices, such as differential relays, voltage relays, and frequency relays, to provide comprehensive protection against various types of faults and disturbances in electrical networks.