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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which is type of balanced relay?
Current relay
Voltage relay
Impedance relay
All of above
All of above
Quick Summary: Balanced relays, often called differential or comparison relays, operate on the principle of comparing two or more electrical quantities. Since current, voltage, and impedance relays can all be configured in differential or balanced bridge circuits to detect faults, they are all classified under this category depending on the protection scheme.
Balanced relays, often called differential or comparison relays, operate on the principle of comparing two or more electrical quantities. Since current, voltage, and impedance relays can all be configured in differential or balanced bridge circuits to detect faults, they are all classified under this category depending on the protection scheme.
Idiff=∣Iˉ1−Iˉ2∣ — Differential current magnitude
Zrelay=IV — Impedance relay measurement
The fundamental mechanism of a balanced relay is the comparison of currents or voltages entering and leaving a protected zone. In a perfectly balanced condition (no fault), the net output of the measuring element is zero. When a fault occurs, the balance is disturbed, creating a differential quantity (Idiff=I1−I2) that energizes the relay to initiate a trip signal.
Balanced protection works on the principle of Kirchhoff's Current Law (KCL).
Under normal operating conditions, the sum of currents entering and leaving the zone is zero.
Differential relays are highly sensitive and provide high-speed protection.
They are primarily used for transformer, generator, and bus-bar protection.
High sensitivity to internal faults.
Fast operating time due to instantaneous tripping.
Ability to discriminate between internal and external faults.
Requires pilot wires or communication channels for long-distance zones.
Sensitive to current transformer (CT) saturation errors.
More complex and expensive than non-directional overcurrent relays.
Generator differential protection (Merz-Price scheme).
Transformer protection against internal winding faults.
Bus-bar protection schemes.
The 'balanced' designation refers to the circuit configuration where two identical electrical inputs are compared.
Impedance relays utilize a balanced bridge circuit to measure the ratio of voltage to current.
D is correct — All listed relay types (current, voltage, and impedance) can be designed to function as balanced relays depending on the comparison circuitry employed.
Always remember that 'Balanced' refers to the circuit topology (like a Wheatstone bridge or differential CT arrangement) rather than the relay's sensing mechanism.