Emergency protection for wind turbines guaranteed by PSE battery packs

In a country such as China where economic growth is unprecedented, the demand for energy increases daily. It will continue to increase in the coming years; coal-fired power stations do not offer a future-proof solution for this demand. For this reason, China is investing in wind energy on a large scale. Unitron in Zeeland, the Netherlands, supplies all of the control equipment for the innovative direct-drive wind turbines made by Hunan Hara XEMC Windpower. This equipment guarantees not only constant 'power' and reliable supply to the grid, but also protects the turbines with various emergency circuits. In the event of a power failure, the emergency functions are powered by pbq battery packs made by PSE.

Unitron: total solutions

Unitron develops and produces high-quality electronic products for the medical and industrial sectors. The company's ISO 9001:2000 and ISO 13485:2003 certifications guarantee the continual quality of its products. And where necessary, Unitron also has its products certified. One of the markets the company serves is the wind turbine market. For instance, the company has been supplying the control equipment for the wind turbines that are marketed by the Chinese company Hunan Hara XEMC Windpower (XEMC) for years. The wind turbines are characterised by their innovative direct-drive turbine. This originally Dutch technology is fully accepted in China, due to its high efficiency and reliability. Direct-drive wind turbines are distinguished by the direct transmission of power from the blades into a specially designed permanent-magnet generator. This makes vulnerable parts, including gears between the rotor and generator - and the associated maintenance - a thing of the past.

Three controllers

The blades of the XEMC wind turbines rotate at a variable speed depending on the wind conditions. To be able to deliver constant power in spite of the varying wind conditions and speeds, specially developed Unitron control equipment is used. Thanks to the unique combination of intelligence and electronics, it is still possible to generate electricity even when the wind speed is low. The result is greater efficiency.

The control equipment consists of three parts. One part is centrally located in the rotor. The electronics in it controls among other things the position of the blades while various emergency circuits protect the turbine. A control cabinet is located in the top part of the wind turbine, also called the nacelle, that controls its orientation depending on the wind direction. A third control system is located in the bottom of the wind turbine. This controls among other things communication with the back-to-back converter that feeds power into the grid and provides the communication with the manager of the wind park.

Reliable emergency provision

What is striking is that the wind turbines do not have a brake. To be able to stop the turbine even in strong winds, the blades are turned perpendicular to the wind direction. Mains electricity is used to achieve this. However, the reliability of mains power in China is not the same as in the West. An emergency power supply is therefore required. This emergency supply is provided by the VRLA (Valve Regulated Lead Acid) battery packs made by PSE. These batteries combine a compact design with a long life. Moreover, their almost fully sealed construction prevents them needing to be topped up regularly. The battery's name is taken from the valves that are located below the cover. They are designed to safely vent any over pressure that arises in the battery when it is charged too quickly or when it is overloaded. Everything is contained in a reinforced plastic housing that is sealed to prevent electrolyte leaks.

VRLA battery packs

The battery packs are assembled from low-maintenance VLRA-batteries that are constructed from positive lead plates and negative lead oxide plates with a grid made of a lead calcium alloy. The plates are separated by a non-woven fibreglass mat that offers not only excellent oxidation resistance, but also excellent heat resistance. The fibreglass mat is used for the optimum absorption of the electrolyte and the improved conductivity of ions. The batteries contain several lead and lead oxide plates in parallel to allow the greatest possible capacity to be obtained from the smallest possible area. By alternating the positive and negative plates, both sides of the plates are used, which also raises the capacity.

Unitron has developed its own battery pack management system to manage the batteries and that forms part of the total control system. This management system ensures that the separate batteries are continually monitored, and remotely tracked via Unitron's control system. The battery pack management system is combined with a preventive exchange programme, which ensures that all of the batteries are replaced once every two years.