The GEC Alsthom TMRA 20940475 is a specialized protection-grade timing relay designed for high-reliability delay functions within industrial power systems, substation control logic, and protection schemes.
Product Parameters (Datasheet)
- Model Number: TMRA
- Part Number: 20940475
- Relay Type: Time Delay Auxiliary Relay
- Rated Voltage: Typically 110V/125V DC (standard for utility control)
- Timing Range: Adjustable range (typically 0.1s to 10s or 1s to 100s depending on internal setting)
- Contact Configuration: Multi-contact arrangement (e.g., 2 N/O and 2 N/C or 4 C/O)
- Reset Type: Self-resetting upon removal of input voltage
- Enclosure: Size 2 or 1/2N modular draw-out case
- Accuracy: High-precision repetitive timing within ±5%
- Compliance: IEC 60255 series for electrical protection relays
Country of Origin
This protection component was engineered and manufactured by GEC Alsthom (now part of GE Grid Solutions) in France or the United Kingdom.
Application Fields
The TMRA 20940475 is utilized in critical timing sequences, including:
- Substation Automation: Coordinating the delay between “Trip” signals and “Close” commands in auto-reclosure schemes.
- Motor Protection: Managing the delay for under-voltage or over-current startup bypass.
- Power Generation: Timing logic for turbine auxiliary systems and cooling pump sequences.
- Industrial Plants: Providing precise time-delayed interlocks in complex manufacturing processes.
Product Usage Instructions
- Mounting: Insert the TMRA module into its compatible terminal base or rack. Ensure the locking tabs engage to maintain electrical continuity.
- Wiring: Connect the control supply to the coil terminals. Ensure the DC polarity matches the diagram on the relay case to avoid damaging the internal timing circuit.
- Setting: Adjust the front-facing potentiometer or DIP switches to the desired time delay. It is recommended to verify the timing with a stopwatch or secondary injection set.
- Operation: When the input voltage is applied, the timing circuit initiates. After the set delay, the output contacts will change state.
- Maintenance: Periodically check the mechanical flag (if equipped) for proper operation and ensure the case is free from dust or corrosive buildup.
Product Technical Description
The GEC Alsthom TMRA is an electronic-timer auxiliary relay. Technically, it uses a stable internal RC (Resistor-Capacitor) circuit or a digital oscillator to provide precise “Pick-up” or “Drop-out” delays. Unlike standard industrial timers, the TMRA is built to protection-grade standards, meaning it features high surge immunity and can operate reliably in environments with significant electromagnetic interference (EMI). The 20940475 model is specifically tuned for the 110V DC bus common in power utility grids, ensuring the timing does not drift despite slight fluctuations in the battery system voltage.
Q&A (Common Questions)
Q: Can this relay be used for an “Off-Delay” function? A: Most TMRA models are “On-Delay” (Pick-up delay), but specific wiring or sub-models may support “Off-Delay.” Check the logic diagram on your specific 20940475 unit.
Q: Is it safe to swap this relay while the system is live? A: While the draw-out case is designed for easy removal, always ensure the “Trip” or “Control” circuit is bypassed or disabled to prevent accidental equipment operation during the swap.
Q: Why is the relay clicking but the timing is inconsistent? A: This may indicate that the input DC voltage is dipping below the operating threshold or that the internal timing capacitor has aged beyond its service life.
Q: What is the benefit of the modular case? A: It allows for rapid replacement without disturbing the rear-panel wiring, which is critical for reducing downtime in power system maintenance.
Similar Model Recommendations
- GEC Alsthom TMRA 20940470 (Alternative Voltage variant)
- GEC Alsthom TDB (Time Delay Board/Relay)
- Alstom MVAA (Instantaneous Auxiliary Relay)
- GEC Alsthom GTT (Multi-range Timer Relay)
- GE/Alstom MiCOM P12x (Modern Digital Alternative)
For technical specifications or to purchase the GEC Alsthom TMRA 20940475, please contact our protection relay specialists.
