- Dr Michael McDonagh
In this Blog, Dr Mike examines the requirements for the very difficult underground duty of mining locomotive batteries. Whilst the safety requirements are understandably the main focus for mining locomotive battery designs and materials, we must not forget the importance of performance and the practical difficulties of maintenance and charging mining locomotive batteries in this environment. The challenges posed by this application are many and the consequences of getting even a small part of the design or manufacture wrong can lead to disastrous consequences.
Requirements for mining locomotive batteries
There are several important features for underground mining locomotive batteries which are dictated by the working environment. The problem areas for the mining locomotive batteries and the solutions offered by Microtex in the mining locomotive battery range are listed below:
1. Reliability – there must be an absolute guarantee that the battery provides the rated performance from day one of installation. Mining companies cannot afford a single incident of not meeting a working days production or take a chance with any aspect of safety. For this, quality control at each stage of mining locomotive battery manufacture and final safety checks are essential. Microtex take this responsibility very seriously and under their ISO 9000 accreditation, have ensured that every manufacturing stage and every component is checked for electrical, chemical and physical properties. The final product mining locomotive battery is 100% tested for both performance and safety.
2. Ease of installation – when fitting a traction battery underground, often with limited space, there should be minimal skill and effort required. For this reason, Microtex supply the traction battery pre-assembled with charging plugs, fully tested and at top of charge ready to make a complete operational shift. The lifting eyes of the container are positioned to provide maximum stability when hoisted into and out of the loco battery compartment.
3. Operation – the mining locomotive batteries should have enough capacity over their lifetime to deal with the operational requirements and maintenance should be minimal. In addition, the traction batteries must not overheat. Overheating leads to greater water loss, shorter working life from grid corrosion and greater gas evolution on charge. To ensure good operational characteristics, Microtex use traction batteries whose plates have a tubular construction. This is an important design principle as amongst other advantages, it provides the highest energy density of all lead acid battery constructions.
This tubular traction battery range from Microtex has some unique design features which enables these batteries to meet or exceed the performance requirements. The starting point is the active material in the plates which provides the traction battery with its capacity and ability to achieve its duty and provide a high cycle life. The active material balance in the Microtex cells was designed in collaboration with Dr. Rusch an eminent battery scientist from Germany. The processes to achieve this were devised in collaboration with myself. The problem of overheating is minimised by use of bolted connectors with guaranteed connection area and solid brass and copper components.
Another unique design feature of our mining locomotive battery is the lead alloy used in the manufacture of the tubular positive grid or spine. This has a very low concentration of antimony which reduces the evolution of hydrogen and oxygen on the plates (gassing) created from the breakdown of water in the electrolyte when charging the mining locomotive battery. Maintenance is also made easier by use of an electrolyte level indicator which shows without intrusive measures when the cells need topping up.
Additions of tin, arsenic and selenium to the alloy provide corrosion resistance and creep strength. This alloy combination has the benefits of not only practically removing the explosion risk due to hydrogen evolution and reducing the number of times the mining locomotive battery needs to be topped up, but it also helps to prevent positive plate growth thereby extending battery life.
4. Safety – fire and explosions are the two main worries attached to underground electrical equipment. Regarding explosions the most common cause attributable to batteries is that of internal arcing when the mining locomotive battery has completed or is near the end of its charging cycle. Arcing can occur inside a mining locomotive battery if there are weak or inadequate joints between lead alloy components, often between the internal bus bar and the plates. A spark generated here due to switching current on or off, or even a jolting movement of the loco, in association with a high hydrogen concentration from charging, will result in an explosion. This is why the welding processes in the Microtex mining locomotive battery assembly procedures are monitored and the bus bar and plate weld for every cell is inspected before passing to the next stage. There is also a random destructive test carried out each shift to test the integrity of these critical welds
Apart from explosions, fire is possibly the greatest threat that can be posed by an underground electrical device including a mining locomotive battery. And there are many ways that a mining locomotive battery may catch fire. From experience in UK coal mines I am aware that the most common causes of mining mining locomotive battery fires are due to incidents involving external components. Almost all of these are due to electrical tracking or arcing between exposed metal parts on the mining mining locomotive battery or the container. The conductor for tracking can be surface acid or even conducting dust or mineral deposits from the mining activity. High current loads, poorly insulated cell terminals and exposed steel on a container, will, under large current loads will lead to tracking across a cell lid contaminated with acid or conducting mineral dust. Because the conducting media has a high resistance it creates heat which can cause smouldering and charring of the cell lids or even fires in extreme cases.
The Microtex mining locomotive battery design eliminates these threats with specific design features: the use of flame-retardant (FR) materials for the cell lids, insulated bolted connectors with no exposed metal and a special polyester coating for the steel container which is both insulating and flexible enough to avoid damage which would expose bare metal (Fig.1). The container is particularly important due to the risk of earth leakage if metal is exposed and a conducting path from the terminals to the container is created. This not only poses a fire risk it also reduces the operating voltage of the mining locomotive battery, essentially giving a lower energy output and therefore a reduction in the mining locomotive battery capacity and service life.
Fig 1 Mining Locomotive Battery
A risk of fire also exists from the ignition of flammable gases released during charging. This threat can be minimised by having properly vented areas designated for charging. Microtex can both design and advise the customer on its proper operation, if required, free of charge. In addition, the production of gas during charging is minimised by use of a dedicated charger developed by Microtex over decades experience in this application. When this is combined with the high strength low gassing lead alloys used in the battery plates, it provides the safest system available with flooded lead acid technology.
5. Battery sizing options – another key aspect of ensuring a long and trouble-free service life is to install a correctly sized mining locomotive battery. Matching the capacity to the operating cycle is key in obtaining the best value for money and lowest TCO. The standard mining locomotive battery sizes offered by Microtex (Table 1) are comprehensive. There is also flexibility for capacity and cost options within the standard batteries due to the variety of sizes within the tubular traction 2v battery range. The 2v cells are offered in DIN and BS dimensions with a high capacity rating.
I hope that this blog has covered the more important aspects of battery requirements for mining locomotives. The problems which can be caused by having an incorrectly designed and/or specified battery can literally be devastating. This is why it is important to have a trusted supplier with the experience, knowledge and resources available to help with your choice and in-service requirements of your mining locomotive battery. The Microtex team has over 15 years of supplying mining locomotive batteries and have never stopped building on that knowledge. Do not take chances with safety or reliability, for your next mining locomotive battery, get in touch with the Microtex team to ensure you have best possible product and the highest degree of professional battery service available in the industry.