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Now Is the Time to Develop Industry Standard Load Models for Voltage Optimization By Guest Editorial May 4, 2010 - 9:37:55 AM
By Mark McGranaghan
Voltage optimization is becoming an integral part of the distribution control strategy in the Smart Grid. Adjustment of feeder voltage at the substation and along the distribution feeder has long been used to maintain service voltage within the limits set forth in industry standards, such as ANSI C84.1 in North America (see Figure 1). Similar standards exist in Europe (EN 50160) and elsewhere that define the range of voltages that need to be maintained at the customer interface.
Figure 1
The term “voltage optimization” has been adopted to describe control of the distribution voltage to achieve improved efficiency both on the distribution system itself but, more importantly, within customer facilities. This control objective has also been referred to as Conservation Voltage Reduction (CVR) when it is applied specifically for the purpose of reducing energy consumption. For many years utilities have used voltage reduction to reduce demand during periods of peak consumption. The practice of voltage regulation is now seeing renewed interest from utilities as both a demand management function and even for total energy use reduction.
EPRI created a Green Circuits project that has expanded on initial work performed by the Northwest Energy Efficiency Alliance’s (NEEA) Distribution Efficiency Initiative (DEI) to evaluate the potential benefits of voltage optimization for a large cross-section of distribution systems across North America and Europe. The results are clearly showing that voltage optimization for energy savings can be one of the most attractive energy conservation investments in terms of investment per kilowatt-hour saved.
Currently, the analyses of potential benefits of voltage optimization are based on estimating a Conservation Voltage Reduction factor, or CVRf. CVRf is the percent change in load consumption resulting from a one percent reduction in voltage. A positive CVR factor indicates that a reduction in applied voltage resulted in a reduction in load consumption. CVR factors were estimated based on the NEEA DEI project and have been further refined based on initial testing in the Green Circuits project. CVR factors in the range of 0.7 have been found to be typical (that means that there is 0.7% total energy savings for each 1% drop in voltage).
In order to evaluate investment alternatives for energy savings or demand reduction, tools are needed to accurately predict the energy savings and/or demand reduction that will be associated with the investment. The Green Circuits project has demonstrated that the modeling tools are available to evaluate the performance of the distribution system operation with different strategies for controlling the voltage. The unknown for evaluating the impact of voltage optimization is the response of different types of loads to the voltage reduction. This requires a new industry-wide initiative that addresses the modeling need from two different approaches:
This understanding can form the basis of “industry standard load models” that can be used to determine the potential benefits of voltage optimization for specific circuits and specific conditions. Standard methods of performing these assessments will allow utilities to characterize the expected benefits from a distribution investment so that the investment decision can be justified with regulators and customers.
EPRI is organizing a Load Modeling Initiative that can provide the technical basis for these industry standard load models and the application guide for applying them. This work will be coordinated with a new Volt/Var Task Force under the IEEE Smart Distribution Working Group so that the results can be incorporated into an IEEE Application Guide for assessing the benefits of voltage optimization. Background information for the Guide will be developed at an upcoming workshop where utilities will describe existing voltage optimization implementations and the load modeling requirements will be discussed.
Flow diagram for project to develop industry standard load models for voltage optimization assessments.
Mark McGranaghan is Research Director at the Electric Power Research Institute (EPRI).
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