Wind power in the United States is a rapidly growing industry. In fact, the Department of Energy states that wind power could generate 20% of US electricity by 2030. Wind power plants, once in a state of infancy, are now growing up to be “adults”. They are now required to be good neighbors to the transmission power grid. Power quality issues which may have been overlooked when the industry was smaller must now be dealt with proactively.
The interconnection agreements between the wind power plants and the utility grids reflect this greater maturity of the industry. Wind power plants are now required to provide a fair share of reactive power. However, they must provide low voltage ride through while not creating disturbances on the power grid.
Wind Power: A New Challenge
New wind power plants are being designed to meet these new requirements, while also providing for improved operation and efficiency at lower wind speeds; however, changing technology can usually be counted on to bring new challenges. Capacitor banks, now being regularly installed in wind power plants to provide reactive power, carry the unwanted difficulties of potential inconsistency in harmonic resonance. At one site that was investigated, the capacitor banks failed noticeably due to harmonic resonance. Plant collector systems can now comprise over 250,000 feet of underground cable, and these systems are susceptible to switching transients and harmonics resonances. Power system grounding also has to be carefully designed to avoid over voltages due to self-excitation phenomena that can occur when the plant becomes isolated from the power grid.
The above noted challenges are not confined to the wind power plant. Transmission grid operators must deal with power flow, stability, relaying, and power quality concerns. It can be extremely frustrating when an investment in excess of $100 million is stymied by the inability of the power grid to connect the facility. In one case in Europe, the utility consultant had to evaluate the effects of the new underground transmission feed and make certain that harmonic resonance on the transmission system would not cause objectionable harmonic voltage distortion before the facility could be connected. (1)
The Right Test Equipment for a Brighter Future
Power quality monitoring and other test equipment provides a possible solution to successfully meeting the above noted challenges. Often, the monitors utilize remote communications (done by a telephone line, the internet, or even satellite communications) to provide longer term trend data during various wind conditions and weather seasons. Handheld test equipment, with advanced capabilities to capture micro-second transient conditions, are important tools used for commissioning and testing. Web based monitoring, where the data is automatically downloaded and available for display over the internet, is also an important tool to help coordinate the knowledge and efforts of the power quality control teams at various locations.
New wind plant technology is introducing new electrical power quality issues that can challenge even the most experienced engineering groups. In analyzing these new issues, it is necessary to have the most advanced monitoring and testing equipment. Site measurement and testing provides the needed insight for wind plant developers and owners to understand these new concerns. Field information is required to correct analytical models and studies, so that the lessons learned today will be used for future wind power plant designs. These efforts will help create a bright future for the wind power industry so that it can be counted on to provide clean, reliable power.
(1) Electrotek Concepts provided consulting and information for this article. Dranetz-BMI has provided the analyzers and test equipment used on many wind farm investigations and studies.