Northwest Lineman College
SUBSTATION TECHNICIAN CERTIFICATION PROGRAM
CURRICULUM SAMPLE EXCERPTS
CIRCUIT BREAKERS
1.1 INTRODUCTION Circuit breakers control the flow of power on the system by energizing and de-energizing lines and equipment. They are a critical piece of equipment in the substation. When needed, circuit breakers interrupt fault current flow and isolate faulted sections of the system. They must be capable of closing into a fault. Circuit breakers must be properly designed, properly maintained and tested, and very reliable. Circuit breakers work in conjunction with relays. Settings can be coordinated with other devices to meet system conditions. Circuit breakers can be operated manually at the breaker, remotely in the control building or at the operations center. There are three key specifications for selecting circuit breakers for installation: 1. The continuous load current that the breaker must carry under normal and emergency conditions. 2. The level of fault current that the breaker must be capable of interrupting. 3. The speed of the fault current interruption. The system must have circuit breakers able to interrupt faults as rapidly as possible. The rapid clearing of faults reduces the chances of extensive damage or fire.
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Substation breakers trip all three phases during operations, though some transmission systems will install single pole tripping on breakers so that power can still be delivered on the other two phases when a phase to ground fault is experienced. Single pole tripping can improve the stability of the transmission system. Circuit breakers are also selected based on economics, and the type of breakers available for the voltage level being considered. The advantages and disadvantages of the interruption methods (such as oil or vacuum) are also thoroughly evaluated.
1. 2. 3. 4.
OCB – Oil Circuit Breaker PCP – Power Circuit Breaker Circuit Switcher Transrupter
CHAPTER ONE | INTRODUCTION TO CIRCUIT BREAKERS
The following is a list of common names for devices that perform the basic function of a circuit breaker:
Bushing
Tank Dome
Crank Box Capacitance Tap Oil Gauge Current Transformer
Tank Upper Static Shield
Lift Rod Guide Guide Block
Lift Rod Interrupter
Contact Button
Lower Static Shield
Cross Arm Drain Valve
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Manhole
Oil circuit breaker.
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© 2016 Northwest Lineman College Published February 2016