1. Substation Equipment's
Switchgear Protection and Power Systems
By Sunil S. Rao

2. Substation Equipment's
Circuit Breaker
Isolator
Earthing switch
Surge Arrester
Current transformer
Potential transformer
Relay

3. Circuit Breaker
A Circuit breaker is a switching and current interrupting device in a switchgear
Function of CB
Switching during normal operating conditions for the purpose of operation and maintenance.
Switching during abnormal (Faulty condition) to interrupt the fault current

4. Requirements of Circuit Breaker
The normal operating current and short circuit current must be safely interrupted by the circuit breaker.
The faulty system must be isolated by CB as quickly as possible keeping minimum delay.
It should not operate with the flow of over current during healthy condition
The faulty circuit must be isolated without affecting the healthy one

5. Types of Circuit Breaker (on the basis of arc extinction medium
Air break circuit breaker
Up to 0.415kV application
Current 100 to 4000 A
Breaking capacity 80KVA
Oil CB
Oil is used as arc extinction medium
Breaking capacity 500MVA
Air blast CB(ABCB)
Used force air mechanism
breaking capacity 3500 MVA
current carrying capacity ( )KV.

6. Types of Circuit Breaker (on the basis of arc extinction medium
SF6 circuit breaker
Mostly used CB
High rate of recovery of dielectric strength
Breaking capacity to MVA
Vacuum CB
Most modern and recent technology
Voltage rating up to 33 KV
Breaking capacity 500 MVA

7. Isolator, Earthing switch & Surge arrester
Function of Isolator
Disconnect a part of the system from the live parts under no load condition.
Function of Earthing switch
Discharge the voltage on the lines to earth after disconnecting them
Function of surge arrester
Diverting the high voltage surges to earth and maintaining continuity during normal voltage

8. Opening and Closing sequence of CB, isolator and Earthing switch
While opening,
CB open------ Isolator Open----- Earthing switch close
While closing,
Earthing switch open---Isolator close----CB close

9. Instrument transformer (Current transformer and potential transformer)
Function of current transformer
Stepping down the current for measurement, protection and control
Function of Potential transformer
Stepping down the voltage for measurement, protection and control

10. Relay
An automatic device which closes its contacts when the actuating quantity reach a certain predetermined magnitude. Relay senses the fault and circuit breaker clears the fault

11. Classification of ac faults
Unsymmetrical faults
Single line to ground fault (Most common)
Double line to ground fault
Line to line fault
Symmetrical fault
Three phase fault (most severe but often occurs)

12. Classification of ac faults
The other abnormal conditions in ac system
Voltage and current unbalance
Under frequency and over frequency
Temperature rise
Over voltage and under voltage
Instability---- Reverse power flow

13. Classification of ac faults
The other abnormal conditions in ac system
Voltage and current unbalance
Under frequency and over frequency
Temperature rise
Over voltage and under voltage
Instability---- Reverse power flow

14. Operation of trip circuit

15. Bus bar Conductor to which a number of circuits are connected
Types of Bus bar
Open bus bar
Enclose bus bar
Outdoor bus bar
Indoor bus bar
Compound immersed bus bar
Oil immersed bus bar
Compressed gas insulated bus bar and solid-insulated bus bar