The status of a relay protection device is divided into

Relay protection devices are classified by operational status into main, auxiliary, and signal relays, and by functional condition into calibration and functional test statuses.

Classification by Function

1. Main Relays: These are the primary protective elements that respond directly to changes in actuating quantities such as current, voltage, or power. They detect abnormal conditions and initiate tripping of circuit breakers to isolate faults .
2. Auxiliary Relays: Controlled by main relays, auxiliary relays perform supporting functions such as introducing time delays, increasing contact capacity, passing signals between relays, or energizing alarms .
3. Signal Relays: These relays indicate the operation of other relays through visual flags or audible alarms, helping operators monitor the system status .

Classification by Actuating Quantity

• Over Relays: Operate when the measured quantity exceeds a preset value (e.g., overcurrent relays).
• Under Relays: Operate when the measured quantity falls below a preset value (e.g., undervoltage relays), .

Classification by Connection

• Primary Relays: Sensing elements are directly connected to the circuit or equipment being protected.
• Secondary Relays: Sensing elements receive signals through current or voltage transformers, allowing safer monitoring of high-voltage or high-current circuits .

Status by Testing and Operational Condition

Relay protection devices, especially modern microprocessor-based relays (MPD), are also classified by their operational and testing status :

1. Calibration Tests: Verify relay settings and configurations, ensuring the relay operates according to design parameters. Typically required for electromechanical relays at periodic intervals.
2. Functional Tests: Check the relay's ability to operate correctly under simulated fault conditions, including dynamic and combined operation modes. Functional tests are performed during type testing, commissioning, and routine inspections. Routine tests focus on serviceability rather than recalibration for MPDs .
3. Type Tests: Assess basic characteristics and functional performance of the relay.
4. Commissioning Tests: Include calibration and verification of internal logic for specific applications.
5. Routine (Periodic) Tests: Ensure the relay remains operational and can respond to faults, without necessarily testing internal settings for MPDs .

Summary

The status of relay protection devices can be understood in two complementary ways: by their functional role in the protection scheme (main, auxiliary, signal) and by their operational condition or testing status (calibration, functional, type, commissioning, routine). This classification ensures that relays are correctly monitored, maintained, and capable of protecting power system equipment effectively .