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Transmission Line & Feeder Protection

This document discusses protection methods for transmission line feeders. It notes that feeders need protection from faults like overloading, over voltage, under frequency, and short circuits. Protective relays are used to detect faults and isolate defective elements. Methods of feeder protection include time-graded overcurrent protection, current-graded overcurrent protection, distance protection, differential protection, and carrier-current protection. The document also discusses protection schemes for parallel feeders and ring main feeders.

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Ravindra Vankina
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231 views13 pages

Transmission Line & Feeder Protection

This document discusses protection methods for transmission line feeders. It notes that feeders need protection from faults like overloading, over voltage, under frequency, and short circuits. Protective relays are used to detect faults and isolate defective elements. Methods of feeder protection include time-graded overcurrent protection, current-graded overcurrent protection, distance protection, differential protection, and carrier-current protection. The document also discusses protection schemes for parallel feeders and ring main feeders.

Uploaded by

Ravindra Vankina
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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transmission line & feeder protection

Objective
Introduction
Need for protection
Protective relay
Methods of protection of feeder
Protection of parallel feeder
Objective
Feeder is the line that transfers the power
from source end to the distribution end.
To have a uninterrupted power supply for
consumers, feeders need to be protected
from various faults using different schemes.
Introduction
The word FEEDER may be referred as the connecting link
between the two circuits. The feeder could be in the form
of transmission line that is short, medium, or long or this
could be a distribution circuit.
Feeders form the integral part of power system, as power
is transferred through feeders from source to load.
Hence it is important to protect feeders from faults for
continuous supply of power to consumers.
Need for protection
Following conditions lead to various faults:
Over loading
Over voltage
Under Frequency
Power Swings
Transient Faults
Permanent Faults
Atmospheric Conditions(Temperature, Lightening)
Short circuit Faults
Protective relay
It is a device that detects the fault and initiates the
operation of the circuit breaker to isolate the defective
element from rest of the system.

Fig: basic relay operation


Methods of protection of
feeder
Non Unit Type Protection:
1. Time-graded over-current protection
2. Current-graded over current protection
3. Distance protection

Unit Type Protection:


1. Differential protection
2. Carrier-current protection
Non unit type protection
Time
Time--graded protection

Drawbacks:
Drawbacks:
Time lag is provided which is not desirable on short circuits.
Suitable for radial feeders with supply at one end only
Difficult to coordinate and requires changes with addition of load.
Current graded protection

As time graded system provides delay which is not required at


high faulty currents, we use current graded system.
It cannot differentiate the zone in which fault occurred due to
low difference in their magnitudes.
So time graded IDMT relays are used along with current grading
scheme to overcome the limitations.
Protection of parallel feeder:

Fig: parallel feeder protection

Due to the limit of loading of a single line, parallel feeders


are used to meet the increased demand .
As the power may flow in opposite direction at faults ,
directional relays are also used to provide protection.
Protection of ring main feeder

Fig: ring main feeder protection

For reliability of power supply to all consumers even during


faults in one path ring main feeder is used .
In this feeder an alternative path is established to load end and
power is supplied without any interruption .

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