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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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Which of the following is non unit type of protection in feeder?
Balanced voltage system
Circulating current system
Translay relay system
Distance protection
Distance protection
Quick Summary: Distance protection is a non-unit type of protection because it does not cover a specific 'zone' defined by the physical boundaries of the equipment (like unit schemes). It operates based on the impedance measured at the relay location, which is proportional to the distance of the fault from the relay.
Distance protection is a non-unit type of protection because it does not cover a specific 'zone' defined by the physical boundaries of the equipment (like unit schemes). It operates based on the impedance measured at the relay location, which is proportional to the distance of the fault from the relay.
Z=IV — Basic impedance measurement principle
Zset=k×Zline — Setting the relay reach
The relay measures the ratio of voltage to current (Z=IV). When a fault occurs, the line impedance drops below a pre-set reach value. Since it measures impedance and not just current magnitude or phase comparison of terminals, it does not require a communication link between the ends of the feeder to define the protected zone.
Unit protection covers a specific piece of equipment (e.g., busbar, transformer).
Non-unit protection (like Distance or Overcurrent) provides backup protection for adjacent sections.
Distance protection is primarily used for long transmission lines.
It is independent of communication channels between feeder ends.
Provides inherent backup protection for adjacent lines.
Does not require pilot wires or communication channels for operation.
Affected by fault arc resistance.
Can be influenced by power swings or heavy load conditions.
Less selective than unit protection schemes.
High voltage and extra-high voltage transmission line protection.
Primary protection for long feeders.
| Feature | Unit Protection | Non-Unit Protection |
|---|---|---|
Dependency | Communication link required | Self-contained impedance measurement |
Unit protection systems (Balanced voltage, Circulating current, Translay) compare conditions at the ends of the protected zone and trip only if a difference is detected within that zone.
Distance relays are classified as non-unit because their 'reach' is not strictly confined to the feeder length and can extend into neighboring line sections.
D is correct — Distance protection is a non-unit scheme as it relies on local measurements of impedance rather than comparing currents at both ends of the feeder.
Always remember: if a protection scheme requires a pilot wire or fiber-optic communication to compare currents (like Differential Protection), it is a Unit System. If it makes a decision based only on local V and I, it is a Non-Unit System.