Synchrophasor

A phasor measurement unit (PMU) is a device which measures the electrical waves on an electricity grid using a common time source for synchronization. Time synchronization allows synchronized real-time measurements of multiple remote measurement points on the grid. The resulting measurement is known as a synchrophasor. PMUs are considered to be one of the most important measuring devices in the future of power systems. A PMU can be a dedicated device, or the PMU function can be incorporated into a protective relay or other device.

In 1893, Charles Proteus Steinmetz presented a paper on simplified mathematical description of the waveforms of alternating current electricity. Steinmetz called his representation a phasor. With the invention of phasor measurement units (PMU) in 1988 by Dr. Arun G. Phadke and Dr. James S. Thorp at Virginia Tech, Steinmetz’s technique of phasor calculation evolved into the calculation of real time phasor measurements that are synchronized to an absolute time reference provided by the Global Positioning System. We therefore refer to synchronized phasor measurements as synchrophasors. Early prototypes of the PMU were built at Virginia Tech, and Macrodyne built the first PMU (model 1690) in 1992. With the growth of increasingly more distributed energy resources on the power grid, more observability and controls systems will be needed to monitor power flow. Historically, power has been delivered in a uni-directional fashion through passive components to customers. With an increasingly more complex network of generation and loads, it is imperative that the electrical conditions of transmission and distribution networks are continuously being observed through advanced sensor technology––PMUs and uPMUs.

In simple terms, the public electrical grid that a power company operates was originally designed to take power from a single source: the operating company's generators and power plants, and feed it into the grid, where the customers consume the power. Now, some customers are operating power generating devices (solar panels, windmills, etc.) and to save costs (or to generate income) are also feeding power back into the grid. As the electric utility is required by law to buy power produced by customers, the utility wants to make sure this does not damage the grid. The grid must now be measured and controlled in order to ensure the power going into the grid from other sources is of the same quality and standards that customer equipment has been expecting from it, or, if this is not done, as Rob Landley put it, "people's light bulbs start exploding." This measurement function is what these devices do.

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