The GEC Alsthom MCAG34F1BD0002B is a high-stability circulating current relay from the legendary MCAG family. Designed for high-speed differential protection, this relay is a critical component in safeguarding electrical power systems. It is primarily used for the protection of AC generators, motors, reactors, and busbars against internal faults. The MCAG series is known for its “unit protection” capability, meaning it remains completely stable during heavy through-faults while providing instantaneous tripping for faults within the protected zone.

 

Product Datasheet & Technical Specifications

The MCAG34F1BD0002B is engineered for precision and reliability in high-fault environments:

• Model Type: MCAG34 (Three-pole high-stability relay)
• Configuration Code: F1BD0002B
• Operating Principle: High-impedance differential protection
• Current Rating: Typically 1A or 5A secondary rating (standard for CT interfaces)
• Trip Settings: Adjustable via internal calibrated potentiometers or plug-setting bridges
• Burden: Very low burden on the current transformers to prevent CT saturation
• Contacts: Heavy-duty, high-speed trip contacts designed for direct circuit breaker interface
• Reset: Hand-reset mechanical flag for clear fault indication

 

Country of Origin

This protection relay was manufactured in the United Kingdom (UK) at the Stafford production facility, a site famous for the development of GEC, Alsthom, and eventually AREVA protection technologies.

 

Application Fields

The MCAG series is a staple in high-voltage infrastructure protection:

• Busbar Protection: Utilizing high-impedance principles to protect substation busbars.
• Generator & Motor Protection: Detecting internal phase-to-phase and phase-to-earth faults.
• Transformer Differential Protection: Protecting the windings of large power transformers.
• Reactor Protection: Safeguarding shunt and series reactors in transmission grids.
• Industrial Power Distribution: Ensuring stability in large-scale manufacturing electrical plants.

Product Instructions & Technical Notes

When commissioning the GEC Alsthom MCAG34F1BD0002B, it is essential to calculate and install the correct value of the external stabilizing resistor (Rstab​). This resistor ensures that the relay remains stable during external faults when one of the current transformers might saturate. Ensure that all CTs in the differential circuit have the same ratio and similar knee-point voltages. During installation, the mechanical flag must be checked for free movement, and the relay should be mounted in a vibration-free environment to prevent nuisance tripping.

 

Q&A – Frequently Asked Questions

Q1: What is the primary advantage of the MCAG high-impedance relay? A: Its primary advantage is “stability.” It can distinguish between a massive fault occurring outside its zone and a small fault occurring inside its zone, preventing unnecessary power outages.

Q2: Does this relay require an external Metrosil? A: Yes, in high-impedance applications, a Metrosil (non-linear resistor) is often required to limit the peak voltage across the relay and CT secondary wiring during internal fault conditions.

Q3: Is the MCAG34 a three-phase or single-phase unit? A: The MCAG34 is a three-pole unit, meaning it contains three separate relay elements within a single case, providing protection for all three phases.

Q4: Can this relay be used for restricted earth fault (REF) protection? A: Absolutely. The MCAG series is one of the most common relays used for REF protection in transformers and generators.

 

Similar Model Recommendations

1. GEC Alsthom MCAG14 (Single-pole version)
2. GEC Alsthom METI series (Earth fault protection)
3. Alstom MiCOM P12x (Modern digital overcurrent equivalent)
4. AREVA/Schneider MFAC (High-stability circulating current relay variant)
5. GEC Alsthom MCGG (Standard overcurrent and earth fault series)