HIGH PROFILE
The redundant configuration of the battery pack contactors allows the circuit to be broken in the case of over / under voltage , isolation fault , over temperature or overcurrent , the company says . This may also be triggered by a high-voltage interlock loop ( HVIL ) system . Lastly , the inclusion of 600 A fuses provides protection against overcurrent and damage from external shorts .
Finally , this battery pack is enclosed in a cage that offers , Sandvik says , robust mechanical protection , mobility and swapability , plus quick access to the pack modules without cage disassembly .
Beyond design controls
“ We start with the assumption that , however good , design controls should never be believed to be 100 % effective ,” Huff said . “ You cannot just approach the issue by never considering the likelihood of thermal runaway , for instance . It is unrealistic , especially in a mining environment where accidents happen , damage occurs and mistakes in servicing can arise .”
This leads the company on to the active controls it includes in its battery systems .
“ All this starts with monitoring ,” Huff said . “ It could be looking at temperatures – the case temperature , terminal temperature , as well as the temperature of the conductors – and voltage .”
The Battery System Controller ( BSC ) is responsible for protecting the battery – calculating the limits and thresholds , monitoring the HVIL , isolation , temperature and currents and connecting the battery and communicating the status – but it is not the system that implements the controls and limitations .
“ The battery system controller communicates what the limits are – only 400 A in discharge due to heat , for example – but the master controller unit ( MCU ) is the one responsible for accomplishing those limits ,” Huff explained . “ If the MCU fails to do that – drawing too much current , for instance – then the battery system controller opens its connectors and disconnects power as a last resort .”
The battery monitoring system ( BMS ) monitors the cell voltage and temperature ( case temperature , terminal temperature and conductor temperature , for instance ), manages the cell balancing and communicates data to the BSC .
This monitoring will be further enhanced with the incorporation of Akkurate ( a battery analytics company acquired by Sandvik earlier in the year ) and its remote battery diagnostic and prognostic platforms into the BHEV business unit , with Rutqvist saying that “ embedded ” monitoring software on the battery and “ remote health monitoring ” applications are the first development priorities , post-integration .
Such monitoring can go a long way in ensuring
The Artisan battery system architecture has been designed to move with both mining market demands and battery technology
safety from within the system , but you cannot always limit external threats , Huff said .
“ In terms of electrical failure modes , you can prevent overcharging and over-discharging through monitoring-based functions , but you can ’ t prevent deformation , mechanical damage or penetration from foreign objects ,” he said .
This is where the ‘ suppression ’ element comes into play .
Sandvik uses a potassium-based , electrically non-conductive chemical emulsion for its fire suppression system . It acts by filling the battery pack interior with an aerosol agent that chemically interrupts combustion and stops a potential fire in its tracks .
“ We ’ ve had a couple of incidents in the past , which were minor , and these suppression systems came in and did the job we prescribed for them ,” Huff said . “ They are not designed to put out a widespread battery fire , where , instead , the chemistry selection and the other passive controls we have designed in are the safety barriers .”
No expense spared
This three-step safety approach is indicative of the company ’ s focus on risk reduction for its customers , with Huff saying the company often looks beyond industry standards and regulations when designing features in .
“ The volume and value proposition of our products change the battery system design requirements ,” he said . “ We ’ re not trying to save a dollar here by reducing the thickness of , say , the enclosure , or amending some design feature for cost effectiveness .
“ Safety and reliability are way more important than the cost of manufacturing the system .”
There are plenty of examples of this safetydesign-over-cost philosophy on board its battery systems .
For instance , the company has minimised the
use of cables , designing as much as possible with busbars to avoid potential electrical shorting . All these busbars are powder coated and protected from an electrical perspective , meaning any “ casual ” contact from operators or service technicians will not result in the live conductors being engaged .
When it comes to isolation monitoring , the company has also designed in safety precautions .
“ Isolation monitoring was originally mandated for battery systems to notify technicians about the potential for an electrical shock if there was an isolation fault ,” Huff said . “ Beyond that , it can be used as an early warning for a higher current short circuit where an isolation fault occurs that is lower than a certain resistance .” Huff and his team have carried out some research and chosen 5,000 ohms as the relevant threshold for this particular risk .
“ If you have a 5,000-ohm isolation fault in a location and have a direct connection from another point to the chassis , you can create a short circuit with enough power to melt some of the protective materials in the battery system and potentially accelerate this to a much higher current short circuit ,” he said .
This second isolation monitoring consideration requires a differentiated response .
“ Shock hazards are a warning situation – you need to notify people there is a hazard and behave differently ,” he said .
“ You need to handle a short circuit risk – a low impedance isolation fault – differently . For us , it means shutting the machine down and isolating the fault through removing the modules or locating the fault and transferring the modules .”
With Artisan ’ s battery systems designed to be broken down into individual batteries and transported individually as needed , the company can do exactly this .
“ There have been a few battery fires reported in mines over the last five or so years , involving different types of equipment ,” Huff said . “ The two I know about had nothing to do with a BMS response and everything to do with isolation faults . How you handle a battery with this issue is , therefore , a key consideration .”
Having solved the obvious teething problems that came with introducing BEVs at underground mines over the last decade-or-so , Sandvik is moving into a consolidation phase where refinements to its system design will take place as opposed to major overhauls .
At a time when mining companies require improved performance and uptime from these machines to achieve their own electrification and productivity goals , the company ’ s mining-focused , safety-conscious battery system design philosophy continues to set it apart . IM
OCTOBER 2022 | International Mining 33