A new standard for lightning protection of wind turbines

The IEC has launched a new standard (IEC 61400-24) for the protection of wind turbines against lightning, which demands documentable reliability for new wind turbine designs. What impact will this have on companies in the wind power sector?

The sector has strived to design reliable wind turbines during the last few years, but without specific requirements for what was really necessary. Finally, the industry has a standard that sets specific demands - and the industry should start preparing itself to meet these requirements.

The new standard mandates the electromagnetic environment to be taken into consideration when designing complete wind turbine systems, blades or control systems. How will this affect wind turbine design?

Designers will realise that the electromagnetic environment in a turbine exposed to lightning is very harsh during the event. The standard will help the designer to understand the necessity of doing everything related to EMI-protection in a stronger way. The industry has been used to use 'normal industrial standard' or using earlier designs as reference for the new up-scaled design. From our experience, this is not an acceptable approach. With the new standard as a reference this is finally described and it will be easier to work with for everybody in the technology chain.

When having a standard, all suppliers and their sub-suppliers have a common reference point for starting requiring that all components can withstand the environmental conditions - or at least can be installed in a way that secures reliable operation.

It is also important to realise that not only large damages should be addressed as lightning damages. Also smaller lightning strikes - which are more frequent - can start the wearing of insulation components and the accumulated or delayed effect will, at a later stage, result in damages that cannot directly be related to a specific lightning event.

As an example, the generator windings could be exposed to higher voltages than usually tolerated - even with low level lightning - and this can start partial discharge, which later may result in damaged insulation demanding replacement of the generator. Other systems such as control systems, sensors or even mechanical bearings are installed very exposed to indirect effect from lightning and the individual components must be protected against wearing or immediately damage.

As wind turbines continue to grow in size, they are more exposed to blade-triggered lightning than ever. Does it require special technologies to protect these wind turbines?

As wind turbines grow in size they tend to be more exposed to lightning strikes - and the lightning strikes can attach in different location than what is normally experienced on smaller turbines. Only by performing laboratory testing with artificial lightning or simulations these new designs can be verified. The new IEC standard is demanding new designs to be documented either by testing, simulation or comparison with similar designs. When using new materials as i.e. carbon fibre, tests can be necessary.

Are there products available to help protecting already installed wind turbines?

It is a good business case to upgrade the protection of already installed wind turbines. To protect the most sensitive and expensive main components, such as the generator or converter, can be done relatively simple. In general, the protection makes sure that the electric voltages are not exceeding the tolerable level and this should be done by shielding or voltage suppression tailored the specific case. We have several good solutions for doing this taking into consideration cost effectiveness and easy to install methods. Also blade protection solutions can and often have to be upgraded.

New offshore projects and remote locations are complicating access to the wind turbines. What can companies do to make their turbines as efficient as possible?

Even though wind turbines are complex machines, they are expected to run without onsite supervision and accessibility are often complicated by bad weather conditions. This demands that the turbine can be continuously running without even minor disturbances.

Biography

Kim Bertelsen, owner of Electricon, has worked with lightning protection and system reliability for more than 15 years, the last 10 years in the wind turbine industry. Bertelsen is participating in the Danish national IEC committee and has a seat in the international IEC PT 24 group, responsible for wind turbine lightning protection.