What exactly does high voltage mean?

Electrified vehicles are increasingly entering the market, be it due to stricter emission regulations, improved efficiency and controllability or a new green awareness among buyers. This also brings up questions such as “What exactly is high voltage?” In STW’s Electrical Systems series, it sheds a light on the subject and explains the new terminology.

With 35 years of experience in the digitalisation, automation and electrification of mobile machines, Sensor-Technik Wiedemann GmbH (STW) supports its customers with customised workshops, the right concepts and suitable system architectures. But what exactly is this electrification? And how can you integrate it into your business model?

In the automotive sector, generally only low voltages in the on-board power supply are known for vehicles with combustion engine. 12 V DC (Direct Current = DC voltage) in cars, 24 V DC for commercial vehicles and, in mild hybrid vehicles, 48 V DC as an additional, second voltage level. This means that the voltages remain below the touch protection limit of 60 V DC, up to which there is no risk of dangerous electric shocks. However, in an electrified drive line, higher powers – from 50 kW upwards – are necessary. For voltages below the touch protection limit, currents of more than 800 A are required. However, high currents mean very high costs and increased weight due to thicker cables and also high power losses. For this reason, the driving power in electrified vehicles is provided with higher voltages.

Four hundred V systems are used in the automotive sector and 800 V systems for buses, trucks and larger machines.

In order to make a lay person aware of the increased risk potential, the terms ‘high voltage’ (HV) for voltages of 60 – 1500 V DC and “low voltage” (LV) for voltages less than 60 V DC were introduced in automotive engineering. These terms are used differently in the area of electrical power engineering, which describes the range of 0 to 1,500 V DC as ‘low voltage’. This means that the automotive engineering term high voltage should not be confused with the power engineering term high voltage, which refers to voltages greater than 1,500 V DC.

The increased risk potential is not only illustrated through the terminology, but also through the label on the HV system. HV components must feature the warning sign ‘Danger: high voltage’ and HV cables must be colour-coded orange (according to ISO 6469-3 and ECE-R 100).

Series vehicles with HV systems must be designed to be intrinsically HV-safe, i.e. technical measures on the vehicle ensure complete protection against contact and electric arcs with respect to the high-voltage system. As the owner of an Audi e-tron, no additional training is therefore required to operate the vehicle.

However, anyone who designs such vehicles as prototypes before SOP (Research & Development) or who maintains, repairs, rebuilds or retrofits series vehicles (service workshops), cannot guarantee HV intrinsic safety for these vehicles. In this case, the employer is obligated to train their employees so that they are able to assess work on the HV vehicle, recognise hazards and take the necessary protective measures.