The question of Infeed : Zonal Protection
The question of Infeed : Zonal Protection
(OP)
The book (Horrowitz) says even if an infeed exists, we can ignore it for the purpose of Setting Zone one, but must consider it for Zone 2 & 3. Why? Whats the latest trend?






RE: The question of Infeed : Zonal Protection
RE: The question of Infeed : Zonal Protection
RE: The question of Infeed : Zonal Protection
RE: The question of Infeed : Zonal Protection
Yes a generator that turns it into a 3 terminal line. Go on.
mutimuti
RE: The question of Infeed : Zonal Protection
RE: The question of Infeed : Zonal Protection
Are you refering to the book Power System Relaying by Horowitz and Phadke?
http://i16.tinypic.com/2hyfozc.jpg
Consider the relay to be located at Bus 1
When the tap current is an infeed (also contributing to the fault) the apparent impedance is greater than the correct value, due to the fact that both lines will contribute to the fault.
E1 = Z1.I1 + Zf.(I1 + I2)
E1 = Voltage at bus 1
Z apparent = E1 / I1 = Z1 + Zf.(1 + I2/I1)
If we set zone 1 setting to be 85% of line length 1 - 2, many faults inside the zone of protection will appear to be outside the zone, and the relay will not operate. This condition must be accepted, since when the tap is out of service, the correct performance of the relay is restored.
Hope it helps
Regards
Ralph
Above is taken from the book "Power System Relaying", with a few changes been made. It seems for me to be almost self-explaining.
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