Source: CNB Daily( View article )
The dire need for a solution to the new energies power grid connection problem behind the Feb.24 Jiuquan wind farm accident
China’s State Electricity Regulatory Commission(SERC) reported yesterday on the Feb.24 Gansu Jiuquan wind farm massive grid disconnection accident, they called it China’s largest and most severely affecting the power grid wind power accident in the last few years. CNB Daily learned during their research that the accident was caused by “low voltage ride through capability” failure and power grid development falling behind new energies development. This accident exposed the reality of new energy grid connection difficulties: projects pushing forward on a stagnant power grid.
Projects pushing forward
Experts point out that the Jiuquan wind farm accident is an important warning: Ignoring technology standards and lack of coordination between relevant parties will become a great problem for new energy power grid connection.
China State Grid Energy Research Institute Deputy Chief Economist Bai Jianhua told CNB Daily that the main reason for the accident was that although the Jiuquan wind farm had very detailed specifications in their product purchase contract, most of the wind power units did not have low voltage ride through capability.
Low voltage ride through capability allows the power grid time to self adjust during temporary faults by maintaining uninterrupted grid connection, thus increasing power grid stability.
The Regulations for Wind Farm Connection to Power Grid Technology put forward by the State Grid in 2009 require that the wind turbine units in wind farms have low voltage ride through capability that maintains grid connection for 0.625 seconds when there is a power grid fault.
According to understanding, equipment tenders for the Jiuquan wind farm were complete in 2008, at that time China had not yet set clear requirements for low voltage ride through, in the end the relevant requirements were set by an additional technical agreement. Currently nearly all manufactured wind turbine products don’t have low voltage ride through capability. Since October 2010, when the Jiuquan wind farm checked and accepted the products, there have already been many wind turbine grid disconnection accidents due to lack of low voltage ride through capability.
Bai Jianhua also believes a lack of coordination in review and approval between the regional governments and the National Energy Administration and State Grid was also a leading cause in these accidents. He says the Government requires the State Grid to guarantee full purchase of wind power, and the State Grid does not have enough control.
Stagnant power grid development
An executive for Guodian China Longyuan Power Group Co., Ltd told newspapers that low voltage ride through technology is not complicated, calling it a “trifling matter”.
According to understanding, some of the equipment that had low voltage ride through capability was activated during this accident, the main cause of the accident was safety and reliability management shortcomings in the power grid, grid faults are much too frequent. “Regardless of whether a wind farm has tens or hundreds of wind turbines, not having low voltage ride through capability is not a major problem, but as soon as there are power grid problems there is nothing that can be done on the wind turbine side.”
He says wind turbines normally operate within parameters, spinning at about 20 revolutions per second, but spin speed can immediately get out of control and reach 30-40 revolutions per second if it is disconnected from the grid. This uncontrollable spin rate can lead to what the Chinese industry calls a “flying car accident”, these are extremely dangerous accidents that can lead to wind tower collapse, turbine destruction and can even cause fatalities.
For these reasons, even the earlier wind turbine designs included safety features, if power grid faults cause voltage to rise or drop, it will first of all disconnect from the grid automatically, and then halt turbine spinning automatically. The reason there was no damage from this most recent accident is because when the grid fault occurred the turbines disconnected from the grid.