2. ISTANCE RELAYS
PERATION-depend on the
agnitude of the current or
ltage of the circuit .
tio of the voltage and
rrent (expressed in terms of
impedance)
lled ratio or impedance relay
5. MPEDANCE RELAY
lements in relay-
1.torque proportional to current-operating torque+
2. torque proportional to voltage-restraining torque
rrent element is energized by CT
ltage element is energized by PT
ring fault – voltage drop while current increases . Ratio V/I –I increases impedance- reduces(ZL).
pedance reduce then its predetermined value ,it trip and makes the circuit breaker open.
6. 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
7. SE OF IMPEDANCE RELAY FOR
RANSMISSION LINE PROTECTION
Voltage coil of the
elay is fed from
T while its
urrent coil is fed
rom CT.
Non directional
AC
10. 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.
13. 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 .
14. ngle can be adjusted
450 is used for high
ltage(33 to 11 kv)
600 is used for 66 to 132kv
750 is used for 275 to
0kv
