Electrical Safety – Use of reclosers on mine sites

Electrical inspectors of mines are still asked if reclosers may be used to control and protect high voltage (HV) electrical equipment and HV overhead distribution powerlines located on mine sites.

Reclosers are self-contained HV switching devices programmed with the logic to trip the line when over-currents and fault currents are detected, and to re-energize the line by reclosing automatically. If a fault is permanent, the recloser locks open after a preset number of operations (usually between one and four), isolating the faulted section from the healthy part of the system. A short duration fault, such as a bird strike, will usually be cleared after the first trip, allowing the recloser to reclose and restore supply automatically.

The prohibition on the use of reclosers on mine sites was included in the old SECWA Electrical Requirements, Part 14 – Mining Installations. It was included to limit the consequences of mobile machinery contact with overhead power lines. This document has been through several revisions to become the Western Australian Electrical Requirements (WAER), which does not contain a section dealing with mining electrical installations. The prohibition on the use of reclosers on overhead powerlines located on mine sites has not been continued in any other Western Australian legislation or Australian Standards.

Reclosers are now commonly used to control and protect overhead powerlines on mine sites. In many cases, reclosers are cheaper and more readily available than air break switches or expulsion dropout fuse assemblies. The benefits and advantages of using reclosers, including protection coordination and metering functions, must now be considered when deciding equipment specifications. Reclosers can be particularly useful with overhead powerlines to borefields or other remotely located loads.

Many sites disable the reclose function and select one shot and lockout, effectively using the recloser as a circuit breaker. This is advisable where there is the potential for mobile machinery contact and should be considered in the risk management process.

Also complete a careful and thorough risk evaluation before specifying the use of a recloser to control and protect overhead distribution powerlines in towns or accommodation villages, where a motor vehicle accident could damage power distribution assets.