Overcurrent protection has different types based on characteristics. Generally it is used to protect the different electrical component.

1. A presentation on
Prepared by,
Mr. Chetan D. Patil
Assistant Professor
Department of Electrical Engineering
Overcurrent Protection
Sharad Institute of Technology,
College of Engineering,
Yadrav (Ichalkaranji)

2. Contents:
• Over Current Protection For Radial System
Time Graded System
Current Graded System
• Over Current Protection For Ring Main System
• Directional Overcurrent Relay
• Microprocessor Based Relay
• Earth Fault And Phase Fault Protection

3. Types Of Overcurrent Relay :
• Definite time overcurrent relay
• Instantaneous overcurrent relay
• Inverse time overcurrent relay
• IDMT relay
• Very inverse time overcurrent relay
• Extremely inverse time overcurrent relay

4. Over Current Protection For
Radial System :
1.Time Graded System
2.Current Graded System

5.  1) Time Graded System:
• In this scheme the definite time overcurrent relay is used
• In definite time relay the operating time for the relay is fixed and it
is independent of magnitude of fault current
• The difference in time setting of each relay is 0.5 sec
• This method is used for the system where the distance between
substation is very low

6.  2) Current Graded System:
• In this system the relay have high pick up value of current towards
the source. The relay used for this method is high speed
instantaneous overcurrent relay
• The operating time for each relay is constant
• Such system can’t protect the entire feeder. For obtaining the proper
discrimination the relay are set to protect only 80% part of the
feeder

7. Over Current Protection For Ring
Main System:
• The relay should have proper time setting forming a closed
loop i.e. G-S1-S2-S3-S4-G the relay are set with decreasing
time i.e. A=2.5sec, C=2sec, E=1.5sec, G=1sec, I=0.5sec
• Similarly the another loop J=2.5sec, H=2sec, F=1.5sec,
D=1sec, B=0.5sec
• Suppose the fault occurs at E and F should operate sections
then the relay E & F should operate at the 1.5sec, after
occurrence of fault

8. Directional Overcurrent Relay:
• The directional relay is energized by two ways,
 Voltage
 Current
• The fluxes Φ1 and Φ2 are produced by the voltage and
current respectively
• The eddy current induces on the disc due to fluxes and torque
is exerted on the disc
• Basically this type of relays are used for protection against
motoring action

9. Microprocessor based Relay:
• This type of protection scheme is more accurate, compact,
reliable and fast
• The microprocessor compares the digital output of A/D
converter with a fixed reference value and send signal for
tripping

10. Earth Fault And Phase Fault
Protection:
• The plug setting for each earth fault relay varies from 20% to
80% of C.T. secondary rating
• And plug setting for the phase fault relay varies from 50% to
200% 0f C.T. secondary rating
• The sensitivity of earth fault relay is higher than phase fault
relay

11. Conclusion:
The overcurrent relay has many types such as definite time, inverse time, IDMT,
microprocessor based etc. these gives protection to the ring main and radial system.
Microprocessor based overcurrent relay is more accurate, compact, reliable and fast
than other and provide protection from earth fault and phase fault.

12. Thank you ….