Safety of electric vehicles

by | Apr 28, 2017 | Electrical Safety

Electric cars represent a new technology  introducing electrical components on board the vehicle;  the various risks associated must be rigorously identified.

When dealing with safety related to electric cars, several aspects need to be taken into consideration:

  • Safety of the electrical system
  • Safety of the operational part
  • Safety of battery charging operations
  • Maintenance, operation and level of training

Most of the standards dealing with the safety of electric cars are in the development phase. Examples include:

  • IEC TC 69
  • CENELEC TC 69X
  • ISO TC22 / SC21
  • CEN TC 301

The regulatory framework is also lagging behind the technological evolution of electric cars.

In this article, only electrical, chemical and explosion hazards will be addressed.

  1. Safety of the vehicle’s electrical system:  protection against electric shock
    • Protection against direct contact:
      Protection of people against direct contact with the active electrical parts of the traction system must be ensured by adequate insulation and by an inaccessible positioning of said parts.
    • Protection against indirect contact
      The issue of indirect contact is often related to structural problems. Contact between the traction circuit and the structure can lead to dangerous situations such as:

      • Short circuits
      • Electrocution
      • Unplanned and / or uncontrolled vehicle behavior
  1. Battery safety
    For an electric car, the battery is the most important component. It is the origin of several dangerous phenomena such as electrical, mechanical and chemical hazards, not to mention the risk of explosion.
  1. Electrical hazard:
    • Protection against electric shock:
      The battery cases must be reinforced as needed
    • Short-circuit protection:
      Traction batteries have considerably high short-circuit currents, and safety devices such as fuses must be installed, in particular at the electrical center of the battery. The arrangement of the battery must be designed to avoid any risk of unmanageable contact or short-circuit. To minimize leakage currents, especially in ventilated batteries, a creepage calculation is required.
  1. Chemical hazard
    • Lead batteries
      For this type of battery, the main hazard originates from the electrolyte (sulfuric acid), and additional precautions must be taken during maintenance. In the event of an accident, care must be taken to ensure that the electrolyte is not spilled on passengers or anyone else nearby.
    • Nickel-Cadmium batteries
      For this type of battery, the electrolyte is a solution of potassium hydroxide. The same precautions need to be taken during maintenance as with lead batteries. Handling and maintenance operations for this type of batteries must absolutely be separated.
    • Sodium-Sulfur batteries
      This type of battery is fully sealed, a thermal safety container contains the reagents (sodium and sulfur). This battery usually contains several smaller cells which limits the amount of hazardous material released in case of an accident.
    • Sodium-Nickel Chloride Batteries
      These types of batteries are similar to those of sodium-sulfur, except that nickel chloride is a salt, and is therefore less reactive than sulfur.
    • Zinc-Bromine batteries
      This type of batteries’ intrinsic safety is generally high. The bromine solution is highly toxic, but is characterized by a low degree of reactivity. The major danger associated with this type of battery is the release of bromine or brominated substances in case of fire.
  1. Explosion hazard:
    Batteries having an aqueous electrolyte emit hydrogen as a result of electrolysis of the electrolyte, especially during the end of charging. Special precautions must therefore be taken:

    • Hydrogen concentration must not exceed 0.8% during normal operation and 3.5% anywhere in the vehicle in the event of failure.
    • Devices capable of generating heat or sparks must not be placed in places where a possible air/gas mixture could occur.
    • The smoke from the batteries must be ventilated, and never reach the inside of the vehicle.
      When using recombinant gas lead batteries (VRLA), the release of hydrogen in the case of  overload  should be taken into consideration.
  1. Safety of battery charging operations
    During the charging of the battery, the car is connected to the main power grid, preventive measures must thus be taken in order to avoid the risk of electric shock. These preventive measures depend mainly on the type of charger:

    • External charger
    • On-board charger
  1. Maintenance
    For electric cars, there are three maintenance levels to consider:

    • First level maintenance: by the user
      Examples:  vehicle cleaning
    • Second level maintenance: in a workshop, by qualified people
      Examples: routine mechanical maintenance, replacement of controllers
    • Third level maintenance: in the manufacturer’s workshop
      Examples: major electrical repairs, to be performed by qualified persons only

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Intervention Prévention Inc.

Intervention Prévention concentrates its operations in the field of work safety, offering specialized services following Standards CSA Z462 – Workplace Electrical Safety, CSA Z460 – Control of Hazardous Energy: Lock-out and Other Methods, and CSA Z432 – Safeguarding of Machinery.

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