protective relaying

1. 1
P R O T E C T I V E R E L AY I N G
 Vital Part of Electric Power system
 Quite unnecessary during normal
operation.
 Very important during abnormal System
condition.

2. 2
P R O T E C T I V E R E L AY I N G
Faults in a Power system
 Over head line 30-40%
 (Lightning ,storm etc.)
 Underground cables 8-10 %
– (Joint failures.)
 CT/PT 15-20 %
 Transformer 10-12 %
 Circuit Breaker 10-12 %
 Generator 6-8 %

3. 3
P R O T E C T I V E R E L AY I N G
R E L A Y
An electric device that is designed to
interpret input conditions in a
prescribed manner and after specified
conditions are met respond to cause
contact operation or similar abrupt
change in associated electric control
circuits

4. 4
P R O T E C T I V E R E L AY I N G
Functions
 1. Closes TRIP circuit (Trips the Circuit Breaker )
 2. Sounds Alarm
 3. Disconnects faulty sections
 4. Prevents subsequent Failure
 5. Causes least disturbance
 6. Improves system stability

5. 5
P R O T E C T I V E R E L A Y S
TYPES
1.Electromechanical
(Movable)
E/M attracted type
Induction type
2.Thermal
3. Static
4.Programmable

6. 6
Elements of a Protective
system
EQPT / FEEDER
BREAKER
RELAY
BATTERY
INSTRUMENT
TRANSFORMERS

7. 7
PROTECTIVE RELAYS
 RELIABLE Certainty / Assurance
SELECTIVE
SENSITIVE
SPEEDY
STABLE

8. 8
P R O T E C T I V E R E L A Y S
RELIABILITY FACTORS
 The protection scheme
 Measuring principle
 Quality of relays
 General working condition of relays
 setting of relays
 Maintenance of relays
 Maintaining adequate setting/general working
conditions due to system configuration change.

9. 9
P R O T E C T I V E R E L A Y S
DESIGN OBJECTIVES
1. Removes the Faulted Section
Prevents or minimize the effect of disturbance
on the healthy sections
2. Prevent Or Minimize Damage To Equipment
3.Ensures That No Single Contingency Will Totally
Disable the Protection on Any System.
4. Means to Return the Service of Affected
Equipment /Feeder

10. 10
P R O T E C T I V E R E L A Y I N G
Scheme Selection
( i ) System configuration
Type of equipment/feeder.
( ii ) Stability consideration.
effect of service continuity ,
speed/time for clearing fault.
(iii) Co-ordination and matching requirements.
( iv) Economic considerations.