High voltage – Basic information
What is high voltage in a vehicle ?
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High-voltage systems in electric mobility require special safety measures and a high-level qualification in handling high-voltage components. To avoid danger posed by the high voltage, safe isolation from the supply voltage must always be ensured. Strict safety rules must be followed when working on high-voltage vehicles, especially when handling cables and high-voltage batteries.
The requirements for skilled workers trained in high-voltage technology are high, as they need to understand the complex systems and energy-storage systems. Low-voltage systems differ significantly from high-voltage systems, so a sound knowledge of the different voltage ranges is essential.
Continuous development in electric mobility also demands continuous training to ensure that all protective measures are implemented effectively. This is the only way to ensure the safety of everyone involved.
What is high voltage in a vehicle?
In general vehicle technology, voltage ranges are specified in “volt”.
Voltages
Battery-electric vehicles (BEV), hybrid vehicles and vehicles with fuel cells operate with DC voltages of up to 800 volts and current strengths of up to 125 amperes, depending on the manufacturer.
Voltages
- greater than 30 volts alternating current (AC) or
- greater than 60 volts direct current (DC) are considered “high voltage” in vehicles.
Battery-electric vehicles (BEV), hybrid vehicles and vehicles with fuel cells operate with DC voltages of up to 800 volts and current strengths of up to 125 amperes, depending on the manufacturer.
Why high voltage?
A high level of electric power is required to power a vehicle electrically.
Advantages of higher electric voltage:
Advantages of higher electric voltage:
- A lower current strength is required for the same level of electric power. Example: if the voltage is doubled, half the current is sufficient.
- With higher voltages, it is easier to realise driving and charging performance than with high currents.
- Cables with a lower cross-sectional area can be used in the vehicle, which helps to save on material, weight, cooling and costs.
- Loss of power is reduced.
High-voltage components
The drive system of a hybrid or electric vehicle generally has the following HV components:
01 HV air-conditioning compressor
02 PTC auxiliary heater (cabin heating)
03 HV wiring harness
04 Electric motor/drive motor
05 Inverter (DC-AC converter, converts the direct current of the HV battery into 3-phase alternating current for the motor)
06 HV battery (accumulator)
07 DC-DC converter (HV -> 12 V)
08 Battery charger (on-board charger, OBC, AC-DC converter)
09 Charging socket
01 HV air-conditioning compressor
02 PTC auxiliary heater (cabin heating)
03 HV wiring harness
04 Electric motor/drive motor
05 Inverter (DC-AC converter, converts the direct current of the HV battery into 3-phase alternating current for the motor)
06 HV battery (accumulator)
07 DC-DC converter (HV -> 12 V)
08 Battery charger (on-board charger, OBC, AC-DC converter)
09 Charging socket
Safety measures
Organisational /personnel
- Only persons with one of the required qualifications (levels 1S, 2S, 3S) are permitted to work on vehicles with high-voltage systems and their components.
- Wearing personal protective equipment (PPE) according to DIN EN 60903 is compulsory, depending on the work step.
- Familiarisation among all repair shop personnel is essential.
- Vehicle-specific work information must be available (manufacturer documentation, rescue cards).
Technical
- All high-voltage components are indicated by orange cables and warning signs.
- In the event of thermal overload, disconnection of the pilot line or a short circuit, the HV network is disconnected from the battery through contactors.
- An IT system (“isolé terre”) is used in HV vehicles. The IT system is galvanically isolated from the vehicle earth and not earthed via the body.
- All live parts have covers to protect them against direct contact. These covers can only be removed with tools or by being destroyed.
- The HV system can be deactivated by means of an isolating facility (maintenance plug, service disconnect, emergency stop).
- Plug contacts are used to connect all HV components to a safety loop (pilot line, interlock) electrically in series in the 12V on-board power supply system. If the pilot line is interrupted in one place, the HV contactors open, the HV battery disconnects from the HV network and the capacitors are deliberately discharged.
- The isolation monitoring ensures that there is sufficient isolation (galvanic separation) between the body and the HV components.
- All HV components are connected to one another and to the vehicle body through “potential equalisation”. This compensates for differences in potential.
ATTENTION: Observe the vehicle manufacturer’s documentation!
Commonly used abbreviations
| BEV | Battery electric vehicle |
| BMS | Battery management system |
| DGUV | German Social Accident Insurance (see DGUV 209-093) |
| EuP | Elektrotechnisch unterwiesene Person (electrically instructed person) |
| EV | Electric vehicle |
| FHV | Fachkundige Person Hochvolt (a person who possesses the expertise and specialist knowledge to perform a special task on high-voltage systems), Qualification Level 2S |
| FuP | Fachkundig unterwiesene Person (a person who has received instructions by an FHV), Qualification Level 1S |
| HV | High voltage |
| IT | “Isolé terre” (French) = isolated earth (the IT network is a non-earthed electrical supply) |
| PHEV | Plug-in-hybrid electric vehicle (vehicle with a combustion engine and an electric drive) |
| S to 3S | Qualification and training levels for series production vehicles |
| SoC | State of charge |
| SoF | State of function (describes the performance of the battery) |
| SoH | State of health (describes the age condition of the battery) |
| ZEV | Zero emission vehicle |
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