Wind Power Quality Test for Comparison of Power Quality Standards

Power quality testing is important to wind power applications for several reasons. The nature of wind turbine generation is different from conventional power plants. Although windfarms are growing in capacity and diversifying in nature in the U.S. and throughout the globe, there is no standard that addresses the power quality of wind turbines or wind farms. The International Electrotechnical Committee (IEC) has convened Working Group 10 (WG10) to address testing and assessment of power quality characteristics of wind turbines. A IEEE task force has been appointed to reconsider flicker measurement procedures in the U.S. Lastly, power quality tests are now required as part of the certification process for wind turbines. NREL began this work both in response to industry request and in support of the IEC working group. (Mr. Gregory is a member of the IEC working group) This paper presents the NREL Certification Testing Team's effort in developing procedures and equipment for power quality testing for wind turbine certification. Summaries of several power quality standards that are applicable to this process are also presented in this paper. Introduction Power quality testing measures the impact of a device’s electrical loading on the voltage at the point of utility connection. The importance of such testing is increasing as more wind turbines are being placed into service and diversify in technology, operational strategy and size. The formation of a new international standard on wind turbine power quality further indicates the importance of proper assessment of the impact of the wind turbine generation on the utility. This new standard (IEC CD), which when completed will be designated IEC Standard 61400-21, is at the committee draft stage. Currently, only general information on this standard is available to the public. The IEC CD could potentially become an international standard for power quality measurement of wind turbines by the end of 1999. Presently, there is no single recommended practice or standard governing testing for wind turbine power quality. Current U.S. practices require adherence to IEEE-519, published by the Institute of Electrical and Electronics Engineers (IEEE) which is a current ANSI standard oriented towards steady electrical system loads. A study commissioned by the International Energy Agency (IEA) providing procedures specific to wind turbines is referenced to lend additional background to this work. Also referenced is the IEC CD so NREL could establish a report format to satisfy the requirements of this document, should it become a standard. This paper discusses four characteristics concerning the quality of power from wind turbines: • Rated power • Reactive power requirements • Voltage variations, or Flicker • Harmonic emissions Test Description Tests were conducted at a windfarm with minimal disturbance to normal operations. The tests were conducted at the request of the turbine manufacturer so the results have been normalized to protect the confidentiality of this agreement with NREL. The configuration of the test instruments is specified in Figure 1. Data sets were examined by an NREL engineer when collected for quality assurance purposes, then