Batteries are utilised in conjunction with the inverter/charger to provide a reliable Uninterruptable Power Supply (UPS) to power the refuge chamber’s life support systems (including scrubbing units, air conditioning and lighting), in the event of a loss of mains power.
Western Australia's Mine Safety Guidelines
The 2017 Government of Western Australia’s Department of Mines, Industry Regulations and Safety guidelines, 'Refuge Chambers in Underground Mines' stipulates that should power provided from the mine’s electrical system fail, a backup supply (e.g. batteries permanently on charge, rotated through service) should be provided and maintained, and a refuge chamber should be capable of 36 hours of self-sustained operation to allow sufficient time for a rescue to be completed. Batteries should also be externally located to minimise the potential for explosions, fires or exposure to fumes.
Valve Regulated Lead Acid Absorbent Glass Mat Batteries
A Valve Regulated Lead Acid (VRLA) battery utilises a one-way pressure-relief valve system where the oxygen normally produced on the positive plate is absorbed by the negative plate, suppressing the production of hydrogen at the negative plate and producing water instead which retains the moisture within the battery.
Absorbent Glass Mat (AGM) is a class of lead-acid deep cycle battery in which a sponge-like material suspends loose electrolytes within highly porous glass fibre mat separators, eliminating the hazards associated with acid spills and leaks. AGM batteries are robust, completely sealed and are easy and safe to transport. The sealed design avoids the need for regular topping-up of electrolytes. AGM batteries work in high ambient temperatures and have low internal resistance and low self-discharge rates, enabling faster recharge and longer shelf life.
MineARC Refuge Chamber Batteries
MineARC refuge chambers have been extensively tested with MineARC branded AGM batteries. The charging and controller systems have been calibrated for this specific battery type. This UPS system is designed to ensure that the refuge chamber’s standalone duration will meet required Government specifications.
MineARC batteries have a robust casing for added protection in harsh industrial environments and are stored in a secure steel cabinet at the rear of portable refuge chambers and outside the main chamber for permanent refuge shelters. The battery monitoring sensors are linked to the refuge chambers digital control system and will automatically alert occupants to any anomalies.
The batteries themselves are maintenance free, however, regular testing and inspection are required to ensure refuge chambers are able to operate for the full safe-refuge entrapment time relevant to the chamber. The safe-refuge duration is the time that critical life support systems will continue to operate after the mine compressed air or mains power supply fails; a minimum of 36 hours.
MineARC performs and recommends testing batteries as part of a comprehensive refuge chamber service every four months to ensure a refuge chamber and their interdependent technologies and components function optimally in standby mode and during an emergency; the battery bank and individual batteries, as well as each battery string, should be tested.
Battery Bank Configuration
The battery bank configuration of MineARC refuge chambers varies between each control system Series and customer specifications. Generally, this is a 48-volt system comprising of at least three strings of four batteries in series. Compact Designs have a standby bank and an emergency bank of batteries, generally with a total of 8 batteries (2-Standby, 6-Emergency).
Power Inverter/ Charger
A power inverter is an electronic device or circuitry that changes direct current (DC) to alternating current (AC).
When mains power becomes unavailable, UPS uses batteries and an inverter to supply AC power to the refuge chamber’s life support systems such as the scrubbing unit and air conditioning, to ensure a safe, breathable atmosphere within an occupied refuge chamber is maintained. When mains power is restored, a rectifier supplies DC power to recharge the batteries.