Electrical safety in opencast mining

The big excavators used for open-cast mining have lots of different drives. They use both medium voltage engines and low voltage drives. The large drives, in particular, are normally supplied by unearthed systems. These are monitored by an ISOMETER® with a coupling device. For smaller drives, we recommend monitoring with RCMS residual current monitoring systems or ISOMETER® insulation monitoring with EDS, as in both cases the faults occurring are immediately detected and reported to significantly improve availability.

Electric motors are generally employed for conveyor belts used in mining, which are driven by soft starters or frequency converters. However, these generate critical harmonic vibrations and DC currents which would normally not be present in the feeding AC system. With regular RCD or simple insulation monitors (e.g. 3 lamp method or 2 voltmeter process), this cannot be monitored with the requisite precision. There is a need for modern monitoring equipment which can recognise and report these problems quickly. Some standards even require a quick shutdown, which can be achieved via insulation monitoring devices.

Heavy lorries are increasingly being powered by electric drives. Bender insulation monitoring devices monitor the complete electrical drive system for utility vehicles, irrespective of whether they have electric or hybrid drives (often single-wheel drive). This means they provide effective protection against electric shocks and minimise the fire risk.

Primary crushers and crushers are needed in mining to break down the stone extracted from the ground. These use very large, powerful motors which are powered by soft starters or frequency converter due to their size. The resulting harmonic vibrations and DC currents are not recognised by normal RCDs. The use of a freely adjustable RCMA residual current monitoring system is therefore advisable. It guarantees fault detection. 

The power supply is decisively important when it comes to operating mines. The medium voltage fed in is transformed down to 400 V in the transformer stations and fed to the mine via cable bars or busbars and the low-voltage distribution boards and sub-distribution boards. Bender ISOMETER®s or RCMS residual current monitoring systems monitor this and ensure continuous operation. Power quality is the perfect solution for monitoring the main and the sub-distribution boards.