Electromagnetic interference and the effect of low-voltage protective measures at electric vehicle charging stations

Abstract

The nominal power of electric vehicle charging stations or charging parks is constantly increasing. Most of the users are ordinary persons and handle such equipment with a rated power of several 100 kW. Until now, equipment with such power ratings was only common in electrical operating facilities such as industrial plants where the users are at least instructed and protective measures are specified. If ordinary persons handle equipment with such power ratings in the field, the question arises as to whether the conventional safety goals are met in the event of an electrical fault. The consideration is: If the power increases so much, it can be assumed that the short-circuit power and thus the fault current increase and so does the risk of a dangerous electric shock. In this contribution, calculations of line-to-earth short-circuits on the low-voltage AC side of the three-phase system and their effects in typical configurations of charging stations are carried out. Considering the electromagnetic interference, the calculations provide the fault current and its distribution to determine the electrical potentials during the fault. From this, the (partial) fault voltages and active fault voltages are calculated. Based on the active fault voltage, the expected body impedance and consequently, the body current can be determined. With the body current and the break time of the protection device the risk of electric shock using international standards as guidelines is evaluated. As a result, recommendations for the planning, installation and safe operation of charging stations are given. It turns out that considering certain aspects like the conductor cross-sections or the electromagnetic interference, the risk of electric shock can be reduced to a conventional level. Periodic testing of the electrical system is necessary for safe and reliable operation. For example, follow-on faults due to unintended, improper use by ordinary persons can be prevented. Also, regular inspection of the electrical system is necessary for safe and reliable operation to prevent hazards due to aging or wear. However, it seems challenging to define an installation guideline that applies to all configurations as the boundary conditions vary depending on the type of system, installations in the area of interference and environmental influences.