Posted to News on 9th Dec 2006, 12:25
QFE soft starters used in wind turbines
Fairford is demonstrating the ongoing relevance of well-established soft starter technology to a newer and greener form of energy generation: the company is supplying its QFE range of soft starters for use in wind turbines, providing the means to synchronise operation of the turbines to distribution networks and obviating the problems of direct-on-line starting.
QFE soft starters from Fariford Electronics are a cost-effective and highly reliable way to bring wind turbine generators on-line smoothly. They provide the means to synchronise the output of the turbine generator to power networks without massive inrush currents on the supply, and without the harsh shocks that can damage and break mechanical equipment such as bearings, couplings and gears.
The QFE soft starter comes into operation when the wind generator, under the action of its aerodynamic rotor, reaches a point just below synchronous speed (approximately 93 per cent). Working in reverse mode, the QFE unit is used to put the generator on-line. It ramps the generator voltage up to the system voltage and, as the generator accelerates further to synchronous speed, a by-pass contactor is closed by the wind turbine controller (WTC), once it has received a 'top of ramp' signal from the soft starter unit.
When the by-pass contactor is closed, the wind turbine's power factor capacitors are connected and the turbine rotor then accelerates the generator up to a greater-than-synchronous speed, allowing generation to begin.
Reduced magnetic inrush currents
The QFE soft starter units that perform this operation are Fairford Electronics standard 690V range. They are designed to reduce the magnetic inrush currents that are an order of ten times rated line current when starting the generator direct–on-line, to about one times rated line current.
This current is held as an acceleration current during progression from 93 per cent to full synchronous speed and, finally, freewheeling current. This is load current not drawn by the generator while it is at synchronous speed; it is handled by the QFE controller until the by-pass contactor is switched in.
"Having led the development of the soft starter since the late seventies, it is appropriate that Fairford is taking the technology to new and developing industry sectors," says Nigel Follett, Fairford's Sales and Marketing Manager. "With our involvement in wind energy systems, we are demonstrating the relevance of our soft starters to a still evolving method of power generation, proving that existing technology can still provide answers even in today's fast-developing markets."
