Written by Ian Richardson, National Sales Development - Surge and Lightning Protection

According to the Australian Bureau of Meteorology, there are as many as 8 million lightning strikes per day worldwide, and around 44 strikes per second are recorded at any one time.

The electrical infrastructure of the EV charging network is highly vulnerable to direct and indirect lightning, as well as the impact of switching overvoltages. This vulnerability arises from the exposure of typical installations and the sensitivity of the equipment, highlighting the critical importance of surge and lightning protection for EV networks.

If a lightning strike occurs, buildings and other infrastructure can often suffer damage, even if the strike is many kilometres away. The effects of a lightning strike can include fires and/or surge damage to electrical devices and systems. In addition, switching electrical power through so-called grid switching and local load switching can generate switching overvoltages which can also have adverse effects. These switching operation transients may only be a small amount of energy however they can cause significant damage over time. Repeated low-level transients can degrade the insulation of semiconductors and microprocessors, leading to premature failure. 

Across Australia, the threat of lightning can vary from low to high risk. The Bureau of Meteorology and the Australian Lightning Protection Standard AS 1768 provide excellent information to allow assessment of the risk associated with lightning strikes and transients.

Damage caused during electric vehicle charging

The need for constant availability of electrical power is a decisive factor in the charging process. Electric vehicle charging stations are primarily outside, which means that they are especially susceptible to the effects of direct and indirect lightning discharges and the resulting surges that may exceed the dielectric strength of the electrical components within the charging post. The voltage peaks in the power grid from switching operations, earth faults and short-circuits should also be regarded as a possible threat. The consequences of these occurrences include defective electronic components and a charging post that is out of order. Should the surge occur during the charging process, it can even damage the vehicle-based equipment, such as the onboard charge controller or battery, and compromise operator safety.

It is advisable to consider a reliable lightning and surge protection solution for any charging infrastructure to avoid the inconvenience of the loss of charging capability and the financial burden of repairs and maintenance.

What happens if lightning strikes when charging?

A partial lightning current can flow to the charging post in a direct lightning strike on a street lighting pole. This can be conducted directly into the vehicle via the attached charging cable, which may destroy the charging electronics or battery. 

Suppose a surge protection device has been installed. In that case, the lightning current and the overvoltage are discharged directly via the surge protective device and the charging equipment, and the vehicle remains protected (Figure 1). 

What do regulatory standards have to say?

Surge protection is compulsory in some countries where infrastructure and safety threats have been recognised for many years. In Australia, lightning and surge protection is not mandated in the legislated Electrical Safety Acts in each state and territory jurisdiction. However, the risk assessment recommendations in the Australian Lightning Protection Standard AS 1768 will often indicate the need for protection measures to be taken.

All electrical equipment installed in Australia must be rated for an appropriate overvoltage category. The Wiring Rules AS/NZS 3000 refers to Annex G of the switchboard standard AS/NZS 61439.1 for the categories related to various supply systems. In brief, the rated impulse withstand voltage at various parts of a 230/400 V AC installation are:

Surges and transients generated from lightning or grid/load switching operations can often have a peak value greater than the overvoltage category of the installed equipment. The damage may be immediate or could contribute to degradation over time. The result will likely be equipment failure and the EV charging asset out of service.

To avoid the possibility of damage to chargers and the vehicle onboard equipment, it is crucial to ensure the overvoltage categories of the charger and vehicle manufacturer are not exceeded.

Some EV charger manufacturers may include basic surge protection in their standard design. Depending upon the site's risk assessment, this level of protection may not be suitable to provide adequate protection. In many installations, additional protection should be applied to the supply of the charging infrastructure in the form of Type 1, Type 1+2 or Type 1+2+3 surge protection devices.

A Lightning Protection System (LPS) should also be considered in high-exposure, high-risk sites. Installing an LPS does not negate the need for surge protection; AS 1768 Lightning Protection Standards states that surge protection shall be installed where an LPS is used to protect from direct lightning strikes.

Causes of transient overvoltage

A direct strike to the charging post or the supply line produces a lightning current which is simulated under test conditions with the impulse shape 10/350 µs. A distant or indirect lightning strike leads to conducted partial lightning currents with an impulse shape 10/350 µs in the supply lines or to inductive/capacitive coupling with an impulse shape 8/20 µs in the charging stations themselves. In addition, overvoltage can be caused by switching operations, earth faults and short circuits or when fuses and circuit breakers trip (SEMP - switching electromagnetic pulse) (Figures 2 and 3).

Surge protection should be selected according to AS 1768, depending on the location of the charging post or wall box (Figure 4). If the charging post or its wiring is in zone LPZ 0A, galvanic coupling of partial lightning currents and inductive and capacitive coupling would be expected in the case of a nearby or distant lightning strike. Type 1+2 combined arresters should be installed in the charging posts to control these interference impulses. If the charging posts or wall boxes and their wiring are in zone LPZ 0B, the area protected against direct strikes, the solution is to protect inductive and capacitive coupling from the lightning discharge. In this case, Type 2 surge arresters should be installed:

If it is impossible to reliably assess the potential threat, installing a compact and space-saving type 1+2 combined arrester is the best option. These devices ensure very low residual energy throughput, protecting even the most sensitive electronic equipment.

Many medium to large EV installations have communications such as Ethernet and building automation to allow load management and reporting. These communication lines are also exposed to lightning and surge interference and can be a source of input for the transient energy to enter the EV charging equipment and cause catastrophic damage. For this reason, all copper data interfaces should also be protected.

This is the only way to ensure reliable protection and thus achieve the desired protection goal.

Earthing & equipotential bonding

Where Type 1 lightning current arresters or Type 1+2 combined lightning current and surge arresters are installed in the charging posts, care must be taken to ensure the local earthing provides equipotential bonding in accordance with AS/NZS 3000 and AS 1768. 

IPD has a range of lightning arrestor and surge protection solutions from class-leading suppliers, Dehn and Novaris. We also offer local expertise and application support for these solutions. Contact an IPD representative today at 1300 556 601 or discover more here.