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By Don Parker, Alabama Power Company and
Jared Green, Electric Power Research Institute
Optimization of the electric distribution system has received an enormous amount of interest over the past few years with smart grid initiatives. By controlling the voltage and VAR levels of the system, many utilities are creating programs to optimize the power flow from the distribution substation to the customer meter and even beyond the meter.
Historically, utilities have controlled the voltage level at the point of regulation, either at the load-tap changing transformer (LTC) or line regulator, so that the voltage at all points along the feeder is maintained within established standards such as ANSI Standard C84.1-1995 or CAN3-C235-83 (R2000). Capacitor banks are then added along the distribution line to maintain the power factor as high as possible for reduced losses and additional voltage support. Typically, the controllers for these devices operate the system based on a standard set of parameters and the local conditions at the device.
With the proliferation of communication capability into every area of the electrical system over the last decade, utilities now utilize the data from communicating devices to aid in improving the power flow across the electrical system. In the future, utilities will be able to use sensors along the line, including AMI meters, as communication nodes to relay information back to the regulation devices and capacitor banks. This remote feedback will allow utilities to fine tune the system for its most efficient operation for any given time of the day or year.
Currently, the two primary modes of Volt-VAR optimization (VVO) under consideration are energy efficiency (EE) and demand response (DR). The energy efficiency mode would call for the system to be operated year-round at a near-unity power factor with the voltage as near as possible to the lowest ANSI allowable voltage. As determined in the Electric Power Research Instituteâ€™s Green Circuits project and other documented research, end-use equipment typically operates most efficiently at the lower end of the usual operating voltage band. Operation of the distribution system at the lowest ANSI voltage would increase the risk of power quality and reliability issues for customers, such as voltage sags and more sustained outages. Based on findings by Alabama Power in the Green Circuits project, system line and transformer losses only accounted for a percentage, typically less than 5 percent, of the overall energy reduction when VVO was implemented.
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