T&D World Magazine

S&C Provides VAR Compensation for a Large Wind Farm

To connect a wind farm to the power grid, it must meet certain interconnection requirements, which vary from state to state. In most cases, there are three criteria:

  • It must meet specified power factor or dynamic VAR requirements.
  • It must be able to ride through faults and contingencies on the grid.
  • It must communicate its status to the local transmission operator via a SCADA system.

In 2004, a wind farm developer contracted with a nationally based engineering firm to prepare a feasibility study for a 200-MW wind farm in New Mexico, to be connected to the 345-kV transmission system of the local utility. The engineering firm subsequently worked with S&C to determine the requirements for a substation-based S&C DSTATCOM Distributed Static Compensator. A PureWave DSTATCOM can provide the overall compensation necessary to meet the interconnection requirements with respect to power factor or dynamic VARs, and allow the wind farm to ride through faults and contingencies on the grid.

In a typical wind farm application, the PureWave DSTATCOM consists of a dynamic VAR system that provides 10 to 25% of the total VAR requirement. A series of switched capacitor (or reactor) banks meet the overall interconnection requirement for power factor. If necessary, additional VARs can be provided to assist the wind turbine generators meet low-voltage or zero-voltage ride-through requirements.

For this particular application, two ±12 MVAR PureWave DSTATCOMs were specified to minimize reactive power interchange with the 345-kV utility system. The PureWave DSTATCOMs can also control voltage, allowing the wind farm to ride through a transmission event, and continue to deliver power until the contingency has cleared. The PureWave DSTATCOMs control two 26-MVAR switched capacitor banks to maintain the 34.5-kV collector bus voltage at acceptable levels. The collector bus is connected to the transmission system through a 34.5-kV/345-kV step-up transformer.

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