DISTANCE RELAY

DISTANCE RELAYS

OPERATION-depend on the

magnitude of the current or

voltage of the circuit .

Ratio of the voltage and

current (expressed in terms of

an impedance)

Called ratio or impedance relay

TYPES OF DISTANCE RELAYS

• IMPEDANCE RELAY

• REACTANCE RELAY

• ADMITTANCE RELAY

1. IMPEDANCE RELAY(BASIC

OPERATION)

IMPEDANCE RELAY

2 elements in relay-

1.torque proportional to current-operating torque+

2. torque proportional to voltage-restraining torque

Current element is energized by CT

Voltage element is energized by PT

During fault – voltage drop while current increases . Ratio V/I –I increases impedance- reduces(ZL).

Impedance reduce then its predetermined value ,it trip and makes the circuit breaker open.

OPERATING CHARACTERISTICS

• Fault is nearer to relay , this ratio will be low and as fault position moves away from the relay the ratio

becomes higher and higher

• Effect of spring, non directional ,arc resistance of line fault affect the performance of relay

USE OF IMPEDANCE RELAY FOR

TRANSMISSION LINE PROTECTION

Voltage coil of the

relay is fed from

PT while its

current coil is fed

from CT.

Non directional

AC

USE OF IMPEDANCE RELAY FOR

TRANSMISSION LINE PROTECTION

2. REACTANCE RELAY

REACTANCE RELAY

Operating torque is obtain by current and restraining torque due to a current-

voltage directional relay

Structure-induction cup type

Operating torque -interaction of fluxes produced by 1,2 and 3- proportional to

square of the current.

restraining torque -interaction of fluxes produced by 1,3 and 4-proportional to

product of v and I.

Desired maximum torque angle is obtain with the help of RC circuit.

OPERATING CHARACTERISTICS

3. ADMITTANCE RELAY

ADMITTANCE RELAY

Induction cup type structure

Operating torque -1,2 and 3-proportional to product of voltage and

current

Restraining torque -1,3 and 4-proportional to square of the voltage

Torque angle is adjusted using series tuning circuit .

Angle � can be adjusted

1.450 is used for high

voltage(33 to 11 kv)

2.600 is used for 66 to 132kv

3.750 is used for 275 to

400kv