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1. Protection of transmission line and feeder
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2. Need of transmission line
protection
 Many types of costly and important equipment like
generator, switch gear, CT, PT, overhead transmission
line, underground cable, control equipment are used
in power system
 In this possibility of occurrence of fault in any
equipment of any time and they may get damaged and
system can interrupted hence it is necessary to provide
protection for the system

3. Different types of transmission line
protection
 Different methods of protection are used for
protection of transmission lines. There are two types
of protection:
1) Non unit type:
 Non directional time graded over current protection
 Non directional current graded over current
protection
 Directional time graded protection
 Distance protection

4. Conti…
2) Unit type:
Circulating current system
Voltage balanced system
Transley relay system

5. Non directional time graded
protection system

6. Conti…
 No directional relay means the relay will operate when
the power flow in either direction
 This type of protection is useful for the protection of
radial feeders in which the direction of power flow is
the same
 In this time grading of different over current relay kept
at different locations is done
 This means the operating time of the relay decreases
as the distance from the power station increases

7. Non directional current graded
protection system

8. Conti…
 Current grading system of protection can be employed
when impedance of the feeder between the two
substation is sufficient
 For this high speed, high set over current relays are
employed which operate instantaneously at preset
current setting

9. Directional time graded protection
for parallel feeders

10. Conti…
 Many a times use of parallel feeders is made to
increase the reliability of power system
 Non directional over current relay can not be used as
discrimination is not obtained
 To overcome this difficulty Non directional type relay
with inverse time characteristic are provided on the
feeder on the generator side and directional relay with
instantaneous time characteristic are provided on the
feeder on the load side

11. Protection of ring mains

12. Conti…
 Ring mains system is used in power supply system to
increase the reliability that the power can be fed via
other routes when a fault is developed at one place
 In ring mains also directional and non directional
relays are used effectively so that the faulty section is
isolated and healthy sections remains in the circuit

13. Thank you