Distribution System Training

The objective of this module is to present and discuss features of the different types of non-fault interrupting switches as installed on the distribution system. Reference is made to disconnects which have zero or minimal interrupting capacity and various types of load-break switches which are able to interrupt load current flow up to rated value, but do not have the capacity to interrupt higher level current flow produced by faults.

After completion of this module, the participant should be able to understand the following concepts and apply them in day-to-day work practice.

• The difference between fault interrupting capability and non-fault interrupting capability
• The function of disconnects (i.e. to provide isolation)
• Why disconnects are installed adjacent to circuit breakers
• Construction of disconnects (i.e. single-phase or three-phase ganged for local or remote operation)
• The importance of open disconnect switches being visible
• The operational difference between solid blade disconnects and fused disconnects
• Typical installation of disconnects on the primary distribution system
• Possible methods of reducing current flow on distribution feeders before disconnects are opened
• Provision of arcing horns and other types of auxiliary contacts on disconnects, to allow interruption of low magnitude current flow
• Application of non-load-break elbow connectors as disconnects on underground systems
• Typical arrangement of primary open loop feed, using elbow type connectors
• The function of elbow connectors with load break capability
• Other types of load break switches, including air break, SF6, vacuum, and oil for arc extinction
• Function and application of the load break tool which is fitted on the end of the linemen’s hook stick
• The use of arc chutes and auxiliary contacts on air break load interrupters
• The consequences of closing into a fault
• Features of underground load break switches
• Automatic switchover arrangements for primary feed to specific customers
• The installation of sectionalizers on the distribution system
• Features of the sectionalizer:

1. Non-fault interrupting capacity
2. Load break capacity only
3. The ability to count the number of re-closer actions upstream
4. The ability to be set to trip while recloser is open

• Operation of the sectionalizer jointly with the recloser
• Advantage of installing a sectionalizer in place of a fused disconnect on feeder branch circuits
• The significance of switching operations on safe operation of the distribution system
• Safety considerations regarding isolation of equipment and circuits for maintenance activities