The testing practices advocated in the mining industry are equally applicable to industry in general. Because of the inherent dangers and rigorous working demands, the mining industry, rather than being an isolated example, can serve as a maintenance 'bellwether' for less mandated industries.
An article in the June/July 1998 edition of Miners News discusses the recommendations for testing and maintenance of trailing cables. By 'trailing cable' it is meant one that trails behind equipment. In mining, because of the constant expansion, redirection and relocation of the operation, such cables are particularly stressed, both physically and electrically.
The mining industry appreciates the concept of preventive maintenance for cable weaknesses to be recognised early and serviced conveniently. Timely action prevents unexpected downtime, which can be ruinous in the intensive atmosphere of mine production. Maintenance testing also supports the critical function of safety. The dangers of electric shock, arcing in an explosive atmosphere or the initiation of fires are of greater concern in, but hardly peculiar to, the mining industry. The example set by the mining industry has wide applicability.
Moving a damaged or incorrectly wired or terminated cable during rewiring or reconnection can result in unexpected downtime, shock, combustion or explosion. Accordingly, it is recommended that cables are given an acceptance test when new, a proof test when placed back into service or when relocated and periodic maintenance tests in-situ. This practice will reveal damage in transit, faulty splices and termination, poor repairs and installation as well as 'normal' deterioration.
Various applications and situations call for a variety of test instruments, with the Megger Insulation Tester providing a simple, fast, convenient and comparatively inexpensive first line of defence. For mining cable, high voltages are generally mandated, so that at least a 5 kV model would be required. Remember that DC testers are lighter, more portable, easier to operate, and less expensive than their AC counterparts. The extra safety features will be especially appreciated by the mining industry. In particular, mining applications need the safe discharge of tested cables, and the monitored discharge circuit of Megger Insulation Testers will be invaluable.
The Model BM21 offers 25 V test increments that will enable the precise voltage setting, based on cable condition and reference tables, advocated by the mining industry. The ability to switch measurement between resistance and leakage current enables the operator to conveniently employ either of these commonly used parameters for evaluation, and refer to either type of table, while eliminating the tedious mathematical conversion from one to the other. The 'burn' mode helps pinpoint where localised damage actually occurs, so that repair can be facilitated.
The Model BM25 adds two more features attractive to the mining industry: step voltage testing, and RS232 port. The former is preferred in the mining industry for cable evaluation while the BM25 eliminates the need to perform the test manually. Just select, press, and walk away; the tester does the rest! Test data can also be downloaded into a report for separate evaluation by anyone involved in making critical determinations about cable maintenance.
The conclusion of the Miners News article is good advice for any industry: "The greater degree of safety afforded mining personnel and the reduction of downtime and the accompanying increase in productivity far outweigh the equipment and man-hour costs of a well designed acceptance-maintenance test program."
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