The Impact of Dispersed Generation Upon the Quality of Electric Power: The CSW Wind Farm

BALDA, JUAN CARLOS; OLIVA, ALEJANDRO RAUL

1994-09-01/1996-06-01

1-51

Electrónica

Energia-Eolica

The Impact of Dispersed Generation Upon the Quality of Electric Power: The CSW Wind FarmEPRI Report AbstractEconomic and environmental concerns have propelled the utility industry toward renewable and clean energy sources as alternatives to coal- and gas-fired power stations. This report presents the results of an evaluation to determine the power quality characteristics of a wind turbine generator at an Oklahoma wind farm which is connected to a 69-kV subtransmission system.BackgroundLocated near the town of Ft. Davis, Texas,in an area that offers a good combination of both solar and wind resources, the wind farm connects to a 69-kV subtransmission system near the town of Valentine, Texas, through a dedicated, 17-mile, 25-kV three-phase distribution line. The twelve 500-kW wind turbine generators are connected in parallel, constituting a windmill array generating at 480 V. Each induction generator has two three-phase wye-connected stator windings and two 480-V, 50-kVAr capacitor banks. Finally, each wind turbine generator is interfaced tothe 25-kV distribution line through a main switch and a 480- to 25,000-V, three-phase step-up transformer. EPRI and Central and South West Services (CSW) cosponsored this project via tailored collaboration to evaluate the impact that wind-based generating systems installed in the Ft. Davis area would have on the quality ofelectric power. It was felt that the results of this evaluation would be valuable when these renewable energy sources become sufficiently cost-effective to warrant their applications throughout the CSW system. ObjectiveTo establish the power quality characteristics of the CSW Wind Farm. ApproachThe project team selected asone monitoring site the Valentine tap at the Valentine substation (the connecting point between the 25-kV distribution line from the wind farmsystem and the 69-kVsubtransmission system). The other monitoring point was the windfarm itself. They placed EPRI´s PQNode power disturbance monitor and acquisition system to monitor the current and voltage waveforms at the Valentine tap and characterize the harmonic injection at the wind farm. Finally, they analyzed the recorded current and voltage data for compliance with the IEEE 519-1992 limits. ResultsMonitoring the Valentine tap and the wind farm during different one-week periods produced the following results: o The voltage regulation was acceptable at both sites. o The maximum apparent power generated by the wind farmwas 3730 kVA, a value recordedat the Valentine tap. o The wind farm, when generating, operated at a power factor of approximately 0.9 leading. o The 5% IEEE 519 voltage total harmonic distortion (THD) limit was exceeded by less thana quarter of 1% at the wind farm for only a short period of time. o The 3% IEEE 519 individual voltage harmonic distortion limit was exceeded for the seventh harmonic component at the wind farm by approximately 1% during only a short period of time.o The fifth harmonic voltage component at the wind farm showed a large value;hence, there is a possibility that this component could also exceed the 3% IEEE 519 individual voltage harmonic distortion limit. o The current THDs at the windfarm were smaller than 5%. EPRI PerspectiveBased on an analysis of all measured results, wind farms should not pose a problem to the quality of electric power in utility distribution systems in general and the Valentine distribution system in particular.