The GEC Alsthom MBCH13D1AB0752B is a high-speed, biased differential protection relay belonging to the renowned MBCH series. Developed by GEC Alsthom (now Alstom/AREVA), this relay is a global standard for the protection of two-winding power transformers, generators, and large motors. It is designed to detect internal faults with extreme speed while remaining stable during external “through-faults” or heavy load swings. The MBCH series is celebrated for its dual-slope biased characteristic, which provides optimum sensitivity for low-level internal faults while preventing nuisance tripping.

 

Technical Description & Parameters

The MBCH13D1AB0752B utilizes a sophisticated harmonic restraint circuit to distinguish between actual fault currents and the high inrush currents typical during transformer energization.

• Model Number: MBCH13D1AB0752B
• Relay Type: Three-Phase Biased Differential Protection (Two-Winding).
• Bias Characteristic: Dual-slope (provides stability against CT saturation and tap-changer errors).
• Harmonic Restraint: 2nd harmonic (for inrush) and 5th harmonic (for over-excitation).
• Current Rating: Dual-rated for 1A or 5A secondary CT inputs.
• Auxiliary Power (AB Code): 24-125V DC (Wide-range universal DC supply).
• Operating Time: Typically <30ms at 3x setting current.
• Mounting: Standard horizontal draw-out case (Size 4 or 6 depending on I/O).

 

Product Technical Description

The MBCH13D1AB0752B is a “unit protection” device, meaning it only monitors the zone between the sets of CTs. It calculates the vector difference between the current entering and leaving the transformer. Under normal conditions, this difference is nearly zero. If an internal fault occurs, the balance is disrupted, and the relay trips the associated circuit breakers. The “13” designation indicates a three-phase unit, while the “D” suffix signifies the standard modular draw-out case which allows for safe testing without disconnecting primary wiring.

 

Product Datasheet Essentials

The MBCH series features high-speed “instantaneous” high-set elements for severe internal faults, bypassing the biased logic for maximum equipment protection. The “752B” revision includes improved filtering to handle modern high-efficiency transformer inrush profiles. It is equipped with mechanical flags for local trip indication and multiple sets of silver-alloy output contacts for tripping, interlocking, and SCADA signaling. The relay is fully tropicalized and designed to meet IEC 60255 standards for vibration, shock, and seismic resistance.

 

Country of Origin

United Kingdom / France (GEC Alsthom Protection & Control)

 

Application Fields

The MBCH series is a critical protection element in:

• Utility Substations: Primary protection for main power transformers.
• Power Plants: Protecting generator-transformer units (GSU).
• Heavy Industry: Safeguarding large industrial transformers in steel mills and paper plants.
• Renewable Energy: Differential protection for collector-step-up transformers in wind farms.

Product Usage Instructions

1. Installation: Slide the relay into its housing. Ensure the “Running” and “Incoming” CT circuits are correctly phased according to the transformer vector group (e.g., Dyn11).
2. Matching: Use the internal matching taps (if equipped) or interposing CTs to compensate for the difference in CT ratios on the primary and secondary sides of the transformer.
3. Bias Setting: Set the initial slope (e.g., 20%) to account for transformer tap-changer variations and CT inaccuracies.
4. Testing: Perform a “Stability Test” by injecting current to simulate an external fault; the relay should remain stable. Then perform an “Operating Test” by simulating an internal fault to verify trip timing.
5. Commissioning: Check the 2nd harmonic restraint by observing the relay’s behavior during actual transformer energization.

 

Common Questions & Answers (Q&A)

Q: Why does the MBCH relay use “Harmonic Restraint”? A: When a transformer is first turned on, it draws a massive “inrush” current that looks like a fault to a simple differential relay. This inrush is rich in 2nd harmonics. The MBCH detects this and “restrains” the trip, preventing a false operation.

Q: Can this relay be used for a 3-winding transformer? A: No, the MBCH13 is designed for 2-winding protection. For 3-winding transformers, the MBCH16 or similar three-input models are required.

Q: What is the benefit of the “Draw-out” case? A: It allows for the relay to be removed for testing or replacement while the transformer remains energized. The case automatically short-circuits the CT secondary leads to prevent dangerous high-voltage arcing.

 

Explore More Protection & Control Parts

For expert support and to source the MBCH13D1AB0752B along with other legacy GEC Alsthom and Alstom components, visit our online technical catalog.

 

Recommended Similar Models

1. MBCH12 – A single-phase version for specialized protection schemes.
2. MiCOM P63x – The modern numerical successor to the MBCH series.
3. MFAC – A high-impedance differential relay often used for busbar protection.
4. KBCH – An Alstom numerical transformer differential relay with advanced logic.
5. DTP – A legacy Westinghouse/ABB differential relay found in similar vintage plants.