The term **AD-R** most commonly refers to the **AD-R series of Electronic Overload Relays** (often manufactured by companies like Schneider Electric, ABB, or specialized industrial automation brands). These components are critical for protecting electric motors from damage due to overheating or phase failures. --- ## 1. Primary Components of an AD-R Relay An electronic overload relay like the AD-R consists of several internal electronic and mechanical parts that work together to monitor current flow. | Part Name | Function | | :--- | :--- | | **Current Transformers (CTs)** | Internal sensors that step down high motor currents to measurable levels for the electronic circuit. | | **Microprocessor/MCU** | The "brain" that calculates the $I^2t$ (thermal memory) to determine when the motor is overheating. | | **Potentiometer** | Adjustable dials on the front face used to set the Full Load Amps (FLA) and trip class. | | **Auxiliary Contacts** | Small switches (usually 1 NO + 1 NC) used to signal a PLC or disconnect the contactor coil. | | **Test/Reset Button** | Mechanical interface to manually trip the circuit for testing or clear a fault after cooling. | --- ## 2. Technical Features and Operation Unlike traditional thermal relays that use bimetallic strips, the AD-R uses **electronic sensing**. This provides higher accuracy and a wider adjustment range. ### Key Working Principles: 1. **Current Monitoring:** The internal CTs monitor the current in all three phases. 2. **Phase Loss Protection:** If the relay detects a significant imbalance or loss of one phase, the electronic circuit triggers a trip much faster than a thermal relay would. 3. **Selectable Trip Classes:** Most AD-R models allow you to select Trip Class 10, 20, or 30 (representing the seconds it takes to trip at 600% of the set current). --- ## 3. Terminal Mapping The wiring terminals on an AD-R relay follow international standards for industrial control: ```markdown Main Power Terminals: - L1, L2, L3: Input from the Contactor - T1, T2, T3: Output to the Motor Control Terminals: - 95 & 96: Normally Closed (NC) - Breaks the circuit on fault. - 97 & 98: Normally Open (NO) - Closes to trigger an alarm/light on fault. ``` --- ## 4. Comparison: Electronic (AD-R) vs. Thermal Relays | Feature | Electronic (AD-R) | Thermal (Bimetallic) | | :--- | :--- | :--- | | **Accuracy** | High (±2-5%) | Moderate (±10-20%) | | **Power Consumption** | Very Low | Higher (due to heat generation) | | **Setting Range** | Wide (e.g., 1:5 ratio) | Narrow (e.g., 1:1.5 ratio) | | **Ambient Temperature** | Compensated electronically | Affected by external heat | ---