1. CIRCUIT BREAKER www.engineersportal.in

2. Definition  Device designed to open the circuit automatically under abnormal conditions without damage to itself when properly applied within its rating. www.engineersportal.in

3.  Circuit breakers are categorized by the method employed to interrupt the circuit current (extinguishing the arc) when the current contacts open. www.engineersportal.in

4. Four major types  Air  Oil  Vacuum  Gas (SF6 or SF6/CF4) www.engineersportal.in

5. Two methods circuit breakers sense circuit current  Thermal  Magnetic www.engineersportal.in

6. Thermal circuit breaker  Sense circuit current through the production of heat  Generally uses some type of heating element in series with the load  The heater is located close to a bimetallic strip  The bimetallic strip is mechanically connected to the moveable contacts www.engineersportal.in

7. Thermal circuit breaker  There is a time delay before the circuit opens  The time delay depends on the amount of overcurrent www.engineersportal.in

8. Thermal Circuit Breaker  Schematic symbol  Schematic www.engineersportal.in

9. Magnetic circuit breaker  Also known as Instantaneous trip circuit breaker  Senses circuit current by connecting a coil in series with the load  When current flows thought the circuit, a magnetic field is established around the coil  The magnetic field attracts the metal arm of a solenoid www.engineersportal.in

10. Magnetic circuit breaker  When the magnetic field becomes intense enough the metal arm mechanically opens the contacts  There is very little time delay in opening the contacts when an abnormal condition occurs www.engineersportal.in

11. Magnetic Circuit Breaker  Schematic symbol  Schematic www.engineersportal.in

12. Thermomagnetic circuit breaker  Most common type  Schematic symbol  Employs both thermal and magnetic current sensors www.engineersportal.in

13. Four Major Types  Air  Oil  Vacuum  Gas (SF6 or SF6/CF4) www.engineersportal.in

14. Air circuit breaker  Divided into four basic types  1 Moulded Case CB (120V – 750V)  2 Low-Voltage Power CB (120V – 750V)  3 Medium-Voltage CB (1.5kV – 69kV)  4 High-Voltage CB (115kV – 230kV) www.engineersportal.in