It appears you are referring to the **PK-R series**, which is commonly associated with **Phase Failure or Phase Monitoring Relays** (often manufactured by companies like PK, Entes, or similar industrial automation brands). These components are critical for protecting three-phase electric motors. --- ## 1. Primary Function The PK-R phase protection relay monitors the voltage of a three-phase system to protect motors from common electrical faults that could lead to overheating or winding failure. ### Key Monitoring Features: | Feature | Description | | :--- | :--- | | **Phase Loss** | Detects if one of the three phases is disconnected. | | **Phase Sequence** | Ensures the phases are in the correct order (L1, L2, L3) to prevent reverse motor rotation. | | **Voltage Asymmetry** | Detects imbalances between phases (e.g., if one phase drops below a certain % of the others). | | **PTC Protection** | (In specific models) Monitors motor temperature via a thermistor. | --- ## 2. Internal Electronic Components The PK-R is an "Electronic Relay," meaning it uses solid-state circuitry rather than purely mechanical movements to sense faults. ### Core Components: 1. **Comparator/Microcontroller:** The "brain" that compares incoming phase voltages against a fixed or adjustable reference point. 2. **Electromagnetic Relay:** An internal switch (usually 1 CO - Changeover) that opens or closes the control circuit. 3. **Capacitive Dropper / Power Supply:** Converts high-voltage AC input into low-voltage DC to power the internal logic. 4. **Potentiometers:** Small dials on the faceplate used to set the **Asymmetry %** or **Delay Time**. 5. **LED Indicators:** * **Power/Normal:** System is healthy. * **Fault:** Indicates a phase failure or sequence error. --- ## 3. Technical Specifications Typical specs for a PK-R series relay include: | Parameter | Typical Value | | :--- | :--- | | **Nominal Voltage** | 380V - 400V AC (3-Phase) | | **Operating Range** | (0.8 - 1.2) x Un | | **Output Contact** | 5A / 250V AC (Resistive) | | **Mounting** | DIN Rail (35mm) | | **Asymmetry Adjustment** | Fixed (e.g., 40%) or Adjustable (5% - 15%) | --- ## 4. Connection Diagram Example The wiring logic for a standard PK-R relay usually follows this structure: ```text L1, L2, L3 --> Input Phases (Monitoring) 1 (Common) --> Connected to Control Voltage 2 (NC) --> Fault Signal/Alarm 3 (NO) --> Connected to Contactor Coil (K1) ``` ---