Wiring of power system relay protection
Relay protection control power supply wiring involves connecting the low-current control circuit to the relay coil and the high-current load circuit to the relay contacts, with proper protection against voltage spikes.
Relay Basics
A relay is an electrically operated switch that uses a coil to control one or more contacts. The control circuit energizes the coil, while the load circuit carries the high-current power to the device being controlled ( ). This separation allows a small control signal to safely operate a much larger electrical load.
Terminal Identification
- Pins 85 and 86: Coil terminals for the control circuit. Applying voltage here energizes the relay ( ).
- Pins 30, 87, and 87a: Load circuit terminals. Pin 30 is the common input, 87 is normally open (NO), and 87a is normally closed (NC) in 5-pin relays ( ).
- 4-pin relays: Control a single load device.
- 5-pin relays: Allow switching between two circuits, providing flexibility for protection schemes ( ).
Wiring Steps
- Power Supply Connection: Connect the positive terminal of the control power supply to pin 86 and the negative to pin 85. Ensure the supply voltage matches the relay coil rating ( ).
- Load Circuit Connection: Connect the high-current source to pin 30 and the device to pin 87 (or 87a for NC operation). Use appropriately rated wires and include a fuse between the power source and pin 30 for safety ( ).
- Protection Against Voltage Spikes: Relays generate voltage spikes when the coil is de-energized. Install a diode across the coil (cathode to positive) or a resistor to safely dissipate the spike and protect sensitive electronics ( ).
- Testing and Verification: Use a multimeter to check continuity and ensure the relay operates correctly before connecting the load ( ).
Additional Considerations
- Overload Protection Relays: For motor or high-current applications, use overload protection relays to prevent damage from excessive current ( ).
- Solid-State Relays (SSRs): For faster switching and longer lifespan, SSRs can replace electromechanical relays in some protection circuits ( ).
- Control and Relay Panels (CRPs): In industrial systems, relays are often mounted in CRPs with proper labeling, fuses, and wiring diagrams to facilitate maintenance and functional testing ( ). Proper wiring ensures reliable operation of protection relays, prevents damage to equipment, and maintains safety in power system control circuits.
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