Safe handling of direct current in the (ev) high voltage range – especially with the high voltage battery
DC networks are gaining in importance and establishing themselves as a future-proof electrical infrastructure, and this is also true of any (ev) high voltage battery. This also increases the number of environments in which direct current with high operating voltage is used. Therefore, user protection is also an important issue for DC applications in electromobility and photovoltaics. The operating voltage in the high-voltage networks of electric vehicles is up to 1500 V DC. All persons who come into contact with high-voltage networks must be aware of the hazards posed by DC networks. Repairs and maintenance therefore require an electrical specialist who has a high-voltage qualification based on high-voltage training and is familiar with the special hazards of (ev) high voltage and thus also of direct current.
Effects of direct current on humans
In (ev) high voltage DC systems, such as a high voltage battery, the danger is not only from electric shocks due to contact but also from electric arcs. The perception threshold for the human body starts at currents above 2 mA. The tingling sensation changes to a stinging sensation as the current strength increases. In the double-digit range – between 10 mA and 20 mA – a feeling of pressure is added. The flow through here is already perceived as unpleasant and painful. Dangerous are currents above 20 mA. If more than 40 mA is used, effects on the heart are to be expected. Symptoms manifest as irregular contractions and arrhythmia. Above 130 mA, ventricular fibrillation can occur with fatal consequences. Although these values are significantly higher than those of alternating current, the direct current hazard should not be underestimated, especially by specialists for high-voltage systems and electrical specialists.
Important factor: the duration of exposure
In practice, direct current accidents do not cause the kind of cramping of the limbs known from alternating current accidents, which makes it difficult for the person affected to detach from live contacts. As a result, the exposure time is often shorter in the event of electrocution under direct current. However, if the flow is prolonged, damage to the blood cells, ventricular fibrillation and chemical burns are often the consequences.
Do not underestimate the dangers of direct current
Just because the permissible contact voltages are always higher with direct current than with alternating current due to the effects on the heart and circulation does not mean that direct current is fundamentally more harmless than alternating current. In contrast to alternating current, the strongest stimuli in electric shocks under direct current occur with the beginning and end of the flow. At high voltages and currents, the uncontrolled muscle contractions associated with leakage from the circuit precipitate violently and can throw the affected person off. It is not uncommon for serious indirect injuries to occur that are first caused by impact and fall. These include skull injuries, fractures, and internal injuries. In addition, DC arcs are more stable. Direct current in the (ev) high voltage range is therefore to be considered as dangerous as alternating current, even if the effects and physiological effects differ in some areas. In any case, this is also a topic of the (ev) high voltage battery training.
PS: Our recommendation here: There are also courses offered by various providers, such as the aforementioned course “Specialist high voltage (ev)” or also the small course for the specialist instructed person for high voltage. More information about this can be found on our homepage
We offer various open seminars as well as customer-specific in-house seminars.
Our free(REALLY free, even WITHOUT having to provide an email address!) paper “6 Things You Need to Know About High-Voltage Qualification of Your Employees in Advance” can be accessed here (click) .
If you want to know more about the different roles, especially those of the responsibilities and especially those of the CRES and their interaction, I recommend our publications, for example the audio book “The chief responsible electrical specialist: CRES structure and operational electrical safety for entrepreneurs, specialists and managers”. Information and sources of supply can be found on the usual audio book portals as well as on the homepage tcs-engineering.de