Distribution System Training

The objective of this module is to present the major features of switching devices which have the capability of interrupting high magnitude fault currents, including circuit breakers, reclosers, circuit switchers, and fused disconnects. The need for coordination between the different protective devices is also discussed.

On completion of this module, and associated workbook, the participant should be able to understand the following concepts, and employ them in day-to-day work practice.

• The mechanism of interrupting current flow
• The means of extinguishing the arc
• Extinguishing mediums, i.e. oil, vacuum, SF6, air
• Types of contacts used in circuit breakers
• Circuit breaker actuating mechanism
• Tripping control circuits
• Circuit breaker ratings
• The circuit breaker as a protection device
• The function of the recloser
• Interrupting capacity of reclosers in comparison with circuit breakers
• Typical locations of reclosers on the distribution system
• The advantages of installing reclosers on the distribution system
• Recloser construction and types of extinguishing medium
• Function and operation of the hydraulic actuator
• Function and operation of the electronic actuator
• The reason for slow and fast trip and recloser settings
• The inverse time characteristics for tripping a recloser
• The application of circuit switchers
• The application of fused disconnects on the distribution system
• Construction of different types of expulsion fuses
• The inverse time current characteristics of fuse operation
• Maximum interrupting capability of fuses
• The function and operation of current limiting fuses
• Application of current limiting fuses as back up to expulsion type fuses
• Basic coordination of fuses
• The application of “cable limiters” to underground cable networks