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In an ever-growing world of sustainable environmental vehicle solutions, Principal Electrical Consultant Paul Hopton discusses the risk of Arc Flash when working with batteries installed in Electric Vehicles. Concerns of Competency for mechanics required to work on these systems, the types of activities that could cause an electrical incident, and what can be done to mitigate risk.
Introduction
I read a very interesting article that was shared by a colleague on LinkedIn about “What are the fire risks of electric vehicles?”
However, it struck me that the article had not explored the arc flash hazard associated with electric vehicles and their batteries.
My first introduction to this topic came through some work we did for Honda Racing in 2019. They had some concerns about the arc flash hazard associated with lithium-ion batteries that were used in Formula 1 and Formula e.
We have since gone on to design an Electric Vehicle Arc Flash Hazard training course in response to this arising concern. This course looks at the Arc Flash hazard whilst maintaining and repairing vehicle battery systems or whilst working alongside them. Work can include testing and fault finding as well as repairs and replacements; whilst not teaching people how to perform these tasks, delegates will have an understanding of the risks posed to them and how best to control them.
Arc Flash Hazard & Electric Vehicles
Arc Flash
What is arc flash? Electrical arcing (sometimes called a ‘flashover’ or ‘arc flash’) produces heat leading to burn injuries that can be life changing or fatal. Often those working with or near electricity do not appreciate the risk of serious injury and consequential damage to equipment that can arise from arcing.
A typical electric vehicle battery
Lithium-ion batteries are made up of a number of individual cells. Each cell has a voltage that can vary but typically when fully charged will be about 4.2Vdc, even with a low value of charge the cell can have a voltage of 3Vdc. The lithium-ion batteries in electric vehicles have a number of these lithium-ion cells connected together. These batteries can produce voltages approaching 1000Vdc and can produce arc flash currents of 1000s of Amps.
Danger
The following diagram show the hazards that you can be exposed to when an arc flash event occurs:
The potential level of hazard that you could be exposed to, can be calculated, and is called “Incident Energy”. The higher the Incident Energy, the higher the hazard. Incident Energy is normally quoted in Cal/cm2 or J/cm2 and unsurprisingly the arc flash personal protective equipment that you can wear is also rated in Cal/cm2 or J/cm2. Provided that the PPE has a higher rating than the Incident Energy level, you are protected against the worst effects of an arc flash, should one occur.
If we take a risk-based approach to the control measures that might be appropriate, let’s consider:
Incident Energy >8 Cal/cm²
We recommend risk reduction measures are considered to reduce incident energy and/or working practices are developed to eliminate energised electrical work. Where a PPE system has been put in place to mitigate the risk of injury, the PPE system shall be tested and certified to exceed incident energy values calculated for the electrical equipment to be worked on.
Incident Energy 1.2 – 8 Cal/cm²
Since it is unlikely that incident energy levels can reasonably be reduced, we recommend appropriate risk control measures (typically arc flash PPE) and safe electrical work practices are implemented.
Incident Energy < 1.2 Cal/cm²
At levels of incident energy below 1.2 Cal/cm² it is unlikely that second degree burns will be inflicted in the event of an arcing incident and therefore arc rated PPE is not required. However, it may be appropriate to wear additional protection for parts of the body such as the hands when carrying out activities such as diagnostic testing.
Electrical Incidents
Ok, so we have this thing called arc flash and the level of hazard is given by the incident energy we could be exposed to. How can we be exposed to arc flash? Here are some examples of some of the activities that could initiate an arc flash:
- Connecting cables into battery fed systems
- Changing components
- Handling and moving batteries
- Repairing batteries
- Working on associated battery systems
- Taking measurements
- Testing and fault-finding
- Replacing electric motors
- Working with batteries post-accident
- Using hand tools and power tools
- Insulation defects
- Incorrect operation/personnel not competent
- Atmospheric Conditions
It is important to point out that these activities can be carried out safely but human error or equipment failure could result in an arc flash event.
Protective Measures
Normally when working with electrical equipment our first line of defence is to isolate the equipment from all sources of supply, secure and label those isolation points and then finally test for dead before we touch conductive parts.
With battery systems this first line of defence may not be available to us as a battery is a source of supply. Working on or near a battery therefore means effectively we are working live. So what control measures do we have available to us to control the hazard?
- Reduce the batteries state of charge to a minimum. There may still be enough energy in the battery to produce an arc but you will have substantially reduced the potential Incident Energy that you could be exposed to, should one occur.
- For batteries that are connected in series by connecting or fused links, removal of the links will reduce the battery voltage by effectively splitting a larger battery into a series of smaller batteries. This will again substantially reduce the potential Incident Energy that you could be exposed to, should an arc flash occur.
- By using insulated tools manufactured to an appropriate BS EN IEC Standard.
- By using temporary insulating shrouding. Insulated shrouding can be purchased to place over live conductive parts to prevent accidental contact with tools, test equipment or material.
- By using test equipment and test leads rated and manufactured to appropriate BS EN IEC Standards and guidance.
- Wearing appropriately rated arc flash personal protective equipment.
Further Guidance
Want more information?
If you’d like more information about risk of Arc Flash with Battery systems, working on Electrical Vehicle Batteries and electrical safe systems of work & competency why not drop one of our ELectrical Engineers a message below, who would be happy to discuss your requirements further. Or take a look at our Automotive Battery Arc Flash Awareness Course for more detail.
