Question
Download Solution PDF______ distance relays are used for protection of phase fault in medium transmission lines.
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
Impedance relay
\(K_1I^2-K_2V^2\)
- The capacity for both arc resistance and power swing is medium on this relay, so it is used in medium transmission lines.
- It is voltage-restrained over the current relay.
- It is a circle in the R-X plane.
Reactance relay
\(K_1I^2-K_3VIcos(\theta-\tau)\)
- The capacity for arc resistance is high and power swing low, so it is used in short transmission lines.
- It is directionally restrained over the current relay.
- It is a straight line in the R-X plane.
Mho relay
\(K_3VIcos(\theta-\tau)-K_2V^2\)
- The capacity for arc resistance is low and power swing is high, so it is used for long transmission lines.
- It is voltage-restrained over the current relay, with the directional relay as an actuating quantity.
- It is a circle that passes through the origin, in the R-X plane.
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