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Reactive Current for the Middle Kingdom
PCS Green Line 1000 Proves Itself in China’s Largest Trial Wind Park
On the Chinese market, which has experienced brisk growth for several years now, an intense effort is underway to develop feed-in directives for wind turbines and their feasibility in the field. In sync with the steady increase in renewable energy production, the technological requirements in regenerative energy are mounting. For renewable energy sources need to face up to the same challenges as classic power plant units: need-based energy generation, security of supply, and system support. It should be added in this context that the Chinese authorities are known to have taken wind parks off-line if they failed to meet their standards. PCS reactive power converters offer an affordable, easy-to-integrate retrofit solution even for this market.
After decades of a coal-dominated power generation in China, the Chinese government is now focusing increasingly on wind energy as a clean and economic alternative. 2010 was the first year in which China became the country with the highest installation rate for new wind turbines - with a total of over 14,000 MW installed. This brings the installed wind power up to more than 40,000 MW, making China the world leader as it is.
Test Centre in Zhangbei
One answer to the current challenges in the Chinese wind power industry is the wind turbine test centre opened in January 2010. The National Wind Power Integration Research and Test Center (NWIC) in Zhangbei, Hebei Province, offers a specialised environment for research and development, testing cycles, training classes and professional development. This, the country largest test park, is organised and controlled by the China Electric Power Research Institute (CEPRI), a subsidiary of the State Grid Corporation of China (SGCC). Set up in 1951, the institute is seated in the north of Beijing. Its main task consists of R&D activities on anything having to do with China's energy supply.
The test park in Zhangbei is laid out for extensive prototype testing of wind turbines as well as for the typical tests for compliance with the grid fault tolerance standards (grid codes). All the necessary requirements are set up at the grid connection point. The set-up includes a system for producing voltage dips (low voltage ride through, LVRT), grid simulators with a capacity of 6 MW, and an energy storage system with an output of 2.5 MW.
Researching the Grid Compatibility
Together with one of the top ten wind turbine manufacturers, the extensive tests now underway at the Zhangbei test park are intended to clarify whether the systems are capable of feeding reactive current into the grid in compliance with the grid codes. Also tested are the frequency control requirements for supporting the grid stability and the grid-stabilising properties of the wind turbines in the context of certain power supply issues.
As a supplier and technology partner of many years, PCS is contributing its Green Line 1000 reactive power converter, which satisfies the grid operators' requirement to provide a reactive current during temporary voltage dips involving a wind turbine. More than 130 MW worth of wind power capacity has already been fitted with the Green Line 1000 reactive power converter.
LVRT Requirements Fully Satisfied
PCS Green Line 1000 is installed on the 690 V side parallel to the wind generator of the respective wind turbine. It consists of a pulsed IGBT power converter with voltage link. As long as line-side reference conditions are met, the converter operates in the stand-by mode. In the event of a line-side voltage drop, it switches into the active mode and supplies an adjustable reactive current of up to 2500 A for a maximum period of six seconds.
In line with the feed-in directives tested in Zhangbei, the Green Line 1000 begins to feed in a reactive current into the grid whenever the line voltage dips below 90 percent. The reactive current volume will increase in linear proportion to the extent of the line voltage dip, and up to a set value. All standard LVRT requirements are fully met by the device: Balanced grid faults are mastered up to 15 percent of the line voltage, and unbalanced grid faults actually up to 0 percent of the line voltage. The device is also able to ride through several consecutive line voltage dips. The DCU control unit developed by PCS will autonomously and intelligently detect and handle such incidents.
Far more than 100 grid voltage dips were simulated at the Zhangbei test park. Green Line 1000 units performed flawlessly during all of these. It was especially good to see that the harsh climatic conditions in Zhangbei occasioned neither thermal nor electrical problems - a major success for PCS, and proof for the wind turbine manufacturer that their own units demonstrably feature the defined grid quality along the lines of international feed-in directives even today.
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