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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Merz prize protection system works on principle of
Current balance
Voltage balance
Power balance
None of above
Current balance
Quick Summary: The Merz-Price protection system, also known as Differential Protection, operates on the principle of circulating current or current balance. It compares the current entering and leaving the protected zone (such as a generator or transformer); under normal conditions, the currents are equal, resulting in zero net current in the relay coil.
The Merz-Price protection system, also known as Differential Protection, operates on the principle of circulating current or current balance. It compares the current entering and leaving the protected zone (such as a generator or transformer); under normal conditions, the currents are equal, resulting in zero net current in the relay coil.
Idiff=∣I1−I2∣ — differential current representing the relay operating condition
I1=I2 — normal operating condition (no fault)
In this scheme, current transformers (CTs) are placed at both ends of the protected equipment. If a fault occurs, the currents at the two ends become unequal, causing a differential current to flow through the relay, which triggers the circuit breaker. This system is inherently fast and selective because it only reacts to faults within the protected zone.
It is primarily used for the protection of generators and large transformers.
It is a unit protection system, meaning it only protects the specific equipment between the CTs.
The pilot wires connect the secondary windings of CTs at both ends in a circulating current arrangement.
High speed of operation.
Excellent discrimination between internal and external faults.
Requirement of pilot wires between the ends of the equipment.
Sensitivity to CT saturation errors under heavy external faults.
Generator winding protection
Power transformer winding protection
Busbar protection
Option B (Voltage balance) is the principle behind the Translay system, not Merz-Price.
The term 'current balance' refers to the comparison of magnitudes and phase angles of currents entering and leaving the protected zone.
A is correct — Merz-Price protection works on the principle of circulating current or current balance, where the difference between input and output currents triggers the relay.
Always remember that Merz-Price uses a circulating current arrangement, while the Translay system utilizes an opposing voltage arrangement.