The General Electric 12CEH51A4A is a specialized Type CEH protective relay designed to detect a loss of excitation in synchronous generators, ensuring the machine is disconnected before damage occurs from overheating or system instability.
Product Parameters (Datasheet)
- Model Number: 12CEH51A4A
- Relay Type: CEH (Loss-of-Excitation)
- Application: Synchronous Generator Protection
- Voltage Rating: 120V AC (Nominal)
- Current Rating: 5A (Secondary)
- Operating Frequency: 50/60 Hz
- Contact Arrangement: Multi-contact configuration for tripping and alarming
- Measurement Principle: Offset Mho characteristic (Impedance-based)
- Adjustment Range: Selectable reach and offset settings for various machine sizes
- Enclosure: Standard GE vertical drawout case for easy maintenance
Country of Origin
This precision protective device is manufactured by General Electric (GE) in the United States, part of their legacy of grid-scale power management and protection hardware.
Application Fields
The 12CEH51A4A relay is primarily utilized in large-scale power generation environments:
- Thermal Power Plants: Protecting steam turbine generators from field failure.
- Hydroelectric Dams: Monitoring synchronous motors and generators in remote sites.
- Industrial Cogeneration: Ensuring local power plants do not destabilize the internal factory grid.
- Gas Turbine Stations: Rapidly detecting excitation loss during peak load operations.
Product Usage Instructions
- Mounting: Install the relay in a standard vertical switchgear panel. The drawout design allows for testing without disturbing the rear terminal wiring.
- Wiring: Connect Potential Transformers (PTs) and Current Transformers (CTs) to the relay terminals following the specific GE wiring diagram for Type CEH units.
- Setting: Calculate the required Mho characteristic settings based on the generator’s capability curve and impedance parameters.
- Testing: Utilize a secondary injection test set to verify the relay’s trip points and timing characteristics before commissioning.
- Maintenance: Periodically inspect contacts for oxidation and verify the mechanical alignment of the induction unit.
Product Technical Description
The GE Type CEH relay functions as a single-phase distance relay with an offset mho characteristic. When a synchronous generator loses its field excitation, the machine begins to operate as an induction generator, drawing reactive power from the system. This causes the impedance measured at the generator terminals to move into the “trip zone” of the relay. The 12CEH51A4A is engineered to distinguish between transient swings and actual field loss, providing high-speed protection to prevent rotor overheating and system-wide voltage collapse.
Q&A (Common Questions)
Q: What is the main cause of “Loss of Excitation” in a generator? A: Common causes include accidental tripping of the field breaker, short circuits in the field windings, or failure of the exciter system itself.
Q: Why is an impedance relay used instead of just monitoring field current? A: Impedance monitoring is more reliable because it looks at the machine’s impact on the grid, providing a definitive indication of whether the generator has become an inductive load.
Q: Can this relay be tested while the generator is running? A: Due to the drawout case, the relay can be removed for testing; however, external protection logic must be in place to ensure the generator remains protected during the swap.
Q: Is the 12CEH51A4A suitable for small brushless exciters? A: Yes, it can be applied to any synchronous machine regardless of the excitation method, as it monitors the stator terminals.
Similar Model Recommendations
- General Electric 12CEH51A1A (Standard basic version)
- General Electric 12CEH51A2A (Different contact configuration)
- General Electric 12CEH51A11A (Enhanced sensitivity model)
- General Electric 12GGP11C1A (Complementary generator protection relay)
- General Electric 12CFD11A1A (Differential protection variant)
For technical support or procurement of the General Electric 12CEH51A4A and other GE protection systems, please visit our professional catalog.
