Mine and quarry electrical installation design expectations
Electricity is a potential hazard found in all areas of mining operations, from extraction and processing to accommodation, storage and administration facilities, and it can range from a few volts up to 220 kV.
Electric shocks as low as 50 V AC may cause serious ill effects. More significant electrical faults may cause arc flashes, cubicle explosions and fires, and depending on where this occurs, have potentially catastrophic implications.
So it is important the design, construction, commissioning, operation and decommissioning of electrical equipment and installations is carried out to relevant legislation, standards, codes and good engineering practice. A maintenance strategy, including consideration of failure modes of protection equipment and the use of back up protection should be developed before completion and implemented immediately after the equipment is commissioned.
Queensland mining safety and health legislation requires electrical installations on mine sites to be designed, constructed, tested and maintained so that risks are at acceptable levels. On non-coal mines and quarries, the Mining and Quarrying Safety and Health Regulation 2001, (the Regulation) applies. In the Regulation:
- Section 22 General requires that the operator or site senior executive must ensure switchgear at a mine reliably interrupts circuits, under fault conditions, throughout the mine’s electrical distribution system; and that each electrical circuit at the mine is protected against overload, short circuit and earth fault under all operating conditions
- Section 30 Prospective touch voltage relates to ensuring prospective touch voltage at the mine is limited to a level necessary to achieve an acceptable level of risk
- Section 100 Selection and design requires that the plant must be fit for its intended use, used in its intended work environment, does not fail catastrophically or by common mode or cascade failure; and incorporates appropriate engineering controls to protect the plant operator and other persons, and
- Section 112 Specifications instructions and other information about plant, requires that specifications and operating instructions are available to and readily accessible by any worker required to use the plant or undertake activities related to the instructions at the mine.
For coal mines, the Coal Mining Safety and Health Regulation 2001 has mostly similar provisions.Reported high potential accidents and incidents also reflect the importance of these requirements, and safety alerts and bulletins published as a result of incidents include:
- Safety alert 75 Recent 1000 Volt circuit breaker failures http://mines.industry.qld.gov.au/assets/inspectorate/safety_alert075.pdf
- Safety alert 109 Transformer primary protection fails to isolate fault http://mines.industry.qld.gov.au/assets/inspectorate/safety_alert109.pdf
- Safety alert 220 Arcing fault causes flash burns and equipment damage (see photo) http://mines.industry.qld.gov.au/assets/mines-safety-health/safety_alert220.pdf
- Safety alert 231 Arc flash injuries received from 22 kV ring main unit http://mines.industry.qld.gov.au/assets/mines-safety-health/safety_alert231.pdf
- Safety bulletin 26 Switchboards—exposed live parts http://mines.industry.qld.gov.au/assets/inspectorate/safety_bulletin026.pdf
- Safety bulletin 73 Switchboard incoming supply hazards http://mines.industry.qld.gov.au/assets/mines-safety-health/safety_bulletin73.pdf
- Significant incident report 68 Severe burns received from 11 kV arc flash explosion http://mines.industry.qld.gov.au/assets/inspectorate/incident_report068.pdf
Certain electrical design and testing data are required to determine that the electrical installations and equipment will be safe for use, fit for purpose and to determine that risks are at acceptable levels throughout the life cycle of the mine. Taking into account that this varies somewhat with the size and complexity of the mining operation and plant, it is recommended that any new or significantly upgraded electrical installation, or installation that carries in excess of 800 Amps, has:
- fault level and load flow calculations
- protection / coordination calculations
- step and touch potential calculations
- arc flash assessments
included among the data used to determine that risks are at acceptable levels.
As well as the types of installation mentioned above, mining safety and health regulators can require any other site, appearing to have an unacceptable level of risk in any of these areas, to show how these risks have been addressed.