Energy Conservation with Voltage Reduction Fact or Fantasy (Originally Presented at the IEEE 2002 Rural Electric Power Conference)

Transcription

1 Energy Conservation with Voltage Reduction Fact or Fantasy (Originally Presented at the IEEE 2002 Rural Electric Power Conference) T.L. Wilson, Senior Member, IEEE PCS UtiliData Spokane, WA USA Abstract: Conservation Voltage Reduction (CVR) will reduce demand on an electric system. More controversial is the idea that CVR can reduce energy usage on a system. Although CVR has its proponents, it is difficult to implement over a wide area without the danger of exposing some customers to unacceptable under voltage conditions. Another issue is that CVR does not cause reduced energy usage for all loads, in fact some loads may increase energy usage when voltage is reduced. Bonneville Power Administration (BPA) has agreed to reimburse several of it s customers who are public utility districts or electric cooperatives for either the cost of installing CVR systems or the energy saved with a CVR system. This manuscript discusses systems installed by two electric utilities in the Pacific Northwest that are being used to implement CVR using new communication and control technologies to prevent under voltage conditions and assure actual reduced energy usage. Keywords: Adaptive Voltage Control, Conservation Voltage Reduction, Conservation Voltage Reduction Factor, Line Drop Compensation, Line Regulator Interface, Line Voltage Monitor, Programmable Logic Controllers, Substation Data Collector and Controller, Voltage Spread Reduction The objective of CVR is to have the customer s utilization voltage at the lowest level consistent with proper operation of equipment, within nameplate ratings of utilization equipment and within levels set by regulatory agencies and standards setting organizations. American National Standards Institute (ANSI) Standard C 84.1 sets the range for voltages at the distribution transformer secondary terminals at 120 volts +/- 5% or between 114 volts and 126 volts. Figures 1, 2 and 3 are recorded voltages at the author s home, office and at the home of one of the author s employees. Note that they are taken inside the home and office, a significant distance from the distribution transformer secondary. Neither the office nor homes are near to the serving substations. These recordings indicate there is room for implementing CVR on these two different feeders with potential for significant energy savings. Introduction Conservation Voltage Reduction or Regulation (CVR) has been identified by many utilities, organizations and individuals as a method of energy conservation. Utilities have been using, experimenting with or researching CVR for at least 25 years. Snohomish County PUD in Washington State has actively applied CVR to its system as part of its energy conservation program [2]. One study estimated that in the Pacific Northwest alone CVR could provide up to 270 average megawatts of energy savings [3]. California, in the summer of 2001, was actively pursuing widespread application of CVR to help alleviate its energy crisis. In its November 1982 newsletter, the Environmental Defense Fund published an article [1] that described CVR and the potential savings associated with it. Figure 1: Employee s Home, Avg vac, Max vac, Min vac Figure 2: Author s Home, Avg vac, Max vac, Min vac

2 Conservation Voltage Reduction Strategies Figure 3: Authors Office, Avg vac Max vac, Min vac Studies by Snohomish County PUD [2] show that the overall percent energy saved per percent voltage reduction, the CVR factor (%E/%V), varied from form.336 to depending on the customer load types. Although CVR has been shown to save energy and could provide significant energy savings if widely applied, it is little used as an active energy conservation measure by electric utilities. There are many reasons for this. Lack of engineering resources to implement CVR is a major reason. The lack of readily available financial models to analyze financial aspects of implementing CVR prevents many utilities from applying CVR. The lack of information on how effective CVR is with different types of customers is a factor that impedes implementation of CVR. There are also some people in the utility industry who hold the belief that CVR does not save energy. In recent issues of Power Engineering [4] [5] there were several very negative responses to a suggestion by one engineer who felt that CVR should be looked at in light of the current energy crisis. One critic suggested that Professional engineers should be embarrassed to propose such schemes CVR is again being recognized as a potential contributor to the overall energy conservation effort in the Pacific Northwest. The Regional Technical Forum (RTF) has recognized CVR as a valid energy conservation method. BPA has approved and is helping to fund two projects to apply automated control systems for CVR. Those two utilities are Inland Power Company, an electric cooperative located in Eastern Washington, and Clatskanie People s Utility District, a public utility in Oregon. These two utilities serve a combination of loads including suburban, small town, rural and small commercial. Historically CVR has been implemented using two different strategies according to DeSteese, Merrick and Kennedy [3]. The first method is Line Drop Compensation (LDC) and the second is Voltage Spread Reduction (VSR). In LDC a distribution feeder is modeled and the Load Tap Changer (LTC) controls or voltage regulator controls are set so that the end of line voltage remains at 114 volts while the source voltage will be adjusted as the load varies. With VSR the voltage limits are narrowed from the +/-5% range to something less, typically +/-2.5% using the regulator or LTC controls. This usually requires enhancements to the distribution lines such as load balancing, reconductoring, and addition of capacitors. Snohomish uses a combination of these two strategies. Utility engineers tend to be conservative and because of changes from light load hours (LLH) to heavy load hours (HLH), the LDC settings or voltage bandwidth settings on distribution LTCs or regulators are often made very conservatively to assure that the end of the line voltage never droops below a preset value. In addition, daily changes in temperature, day-of-the-week, etc. can lead to load changes that reduce the effectiveness of CVR settings. In fact, in many utilities the distribution LTC or regulator controls are set so that the nearest customer never has voltages above 126 volts and the end of line voltage droops and rises as loads vary. The reasons for this are many. Lack of engineering resources to perform the required studies or prepare the distribution line models design the line upgrades are often a major reason. Another is the lack of capital resources or the inability to justify the capital and expenses needed to upgrade distribution. A third strategy is to regulate the voltage at the customer s meter and the utility does not need to try to set controls for CVR. There is at least one company that is manufacturing a device that is installed at the customers meter and will regulate the voltage at the lower level within the customer s premises. A drawback to this strategy is that it depends on the customers to install equipment on their site and to pay the capital costs. Additionally, it does not have the benefit of less distribution transformer iron loss (iron loss in transformers is a function of

3 transformer voltage [6]) nor does it provide quite as much energy savings for line losses. A fourth strategy is to use an Adaptive Voltage Control (AdaptiVolt ) system to implement CVR. This strategy makes use of new automatic control and communications technologies that were unavailable at the time of earlier CVR efforts. How PCS UtiliData became involved with CVR PCS has been applying Programmable Logic Control (PLC) systems in substation automation and electric utility data acquisition and control systems for several years. With the turmoil in the industry caused by the energy crisis in California and in the Pacific Northwest, PCS began seeking ways in which to respond to electric utility needs using the PLC based technologies we were currently using. After attending regional energy conservation meetings and interviewing a retired CEO of a Pacific Northwest Investor Owned Utility (IOU), we decided to see if we could apply our current technology to help with energy conservation. Our research indicated that we could potentially expand our current product offerings to provide an automated conservation voltage reduction system. We took a multi-faceted approach to developing the system. The first was to develop the system from a technical perspective. The second was to determine what the energy savings would actually be, what utilities would be willing to do to install an automatic conservation voltage reduction system and just what the economics were. Concerns About Implementing CVR Several utilities have expressed a concern about consumer response to reduced voltage. They believe that if the customers know that the utility is manipulating the voltage, some may begin to complain, whether they are having a voltage problem or not. There is also concern about flicker becoming a problem with the voltages already being at reduced levels. There is legitimate concern about allowing the customers voltage to be too low and possibly damaging customer appliances and equipment. One of the biggest utility concerns is the fact that CVR will reduce revenue. Most utility revenue rate structures are based on delivering a certain amount of energy to customers. For most residential customers delivered energy is the only measure on which utility revenues are based. For many commercial and small to medium industrial customers delivered energy is the main measure, although time of delivery, customer power factor and peak demand may also be used to determine customer billings and utility revenue. This is a valid concern of utilities. There is a question on the justification of spending money to improve their system and reduce energy usage, on their system, at the customers point of use and on the energy suppliers system when it reduces their income and return on investment. Customer relations are extremely important to most utilities and some utilities preparing to implement CVR have expressed a desire to slowly reduce voltage to prevent a rapid drop that may irritate their customers. Example of CVR Savings Figure 4 shows the monthly energy usage and total energy used at Inland Power and Light Companies Half Moon Substation for Based on that energy use and estimated voltage reductions obtainable along with an estimated CVR factor the projected energy conservation is shown.

4 Load by month at Inland Power and Light Company - Half Moon Substation 2000 PEAK KWH KWH TOTAL MONTH KW High Load Hours Low Load Hours KWH JANUARY ,712,730 1,803,443 4, 51 6, 1 73 FEBRUARY ,332,495 1,486,781 3, 81 9, 276 MARCH ,256,457 1,041,700 3, 298, 1 57 APRIL ,159,760 1,054,324 2, 21 4, 084 MAY ,525, ,203 2, 440, 1 27 JUNE ,448, ,095 2, 297, 535 JULY ,661, ,201 2, 649, 401 AUGUST ,737, ,091 2, 667, 963 SEPTEMBER ,510, ,100 2, 408, 542 OCTOBER ,769,104 1,195,349 2, 964, 453 NOVEMBER ,640,188 1,243,740 3, 883, 928 DECEMBER ,064,776 1,970,472 5, 035, 248 Total 23,819,388 14,375,499 38,194,887 Computation of Projected Energy Conservation Volts reduced on average 5 Percentage volt reduction % CVR Factor 0. 62% %E Reduction 2. 58% Projected Annual Energy Conserved Figure 4: Inland Power, Half Moon Sub Loads, Conservation Savings and BPA Computation For utilities that are served by BPA the, the conservation value is shown and can be used to apply against the Conservation and Renawable Discount (C&RD) program if the utility has unused C&RD credit. BPA also uses these computations to determine value to the system for negotiations to determine how much it is willing to reimburse the utility installing AdaptiVolt or other CVR programs to save energy. Benefit of CVR 986,701 KWH BPA Computation for value of savings $ year economic life $0.35 $/KWH Saved $ year economic life $ year economic life Using 15 year Economic Lifie $ 345,345 = Value of 5 Volt reduction Beside the obvious advantages of energy conservation, there are other benefits of CVR and of AdaptiVolt based CVR. One advantage to utility customers is that incandescent lamps and electric hot water heater elements will have a longer life. It is not uncommon to have incandescent lamps and hot water heater elements fail well before their rated lifetime hours. (The author is personally familiar with this extremely frustrating seeming fact-oflife.) Longer lamp, element and appliance life also benefits the environment. Electrical energy is saved through reduced distribution system losses due to the lower voltage. Consumers benefit through lower energy bills, and quicker response to power outage. Inherent in an AdaptiVolt system are the communications and monitoring capabilities of a full SCADA system. Utilities benefit through lower losses, longer transformer life and increased knowledge of their system s current condition. Operating costs are reduced during outages due to a better understanding of the fault location. The information provided can form the basis of a predictive maintenance system. Utilities may control the amount of conservation and demand by quickly adjusting set points from the Master station. AdaptiVolt based CVR A simplified architecture diagram of AdaptiVolt system based automatic CVR is shown in Figure 5. The main components of the automated CVR system are the primary Substation Data Collector and Controller (SDCC), the AdaptiVolt Core (Core), the Line Voltage Monitor (LVM) and a voltage regulator. Additional components may include additional voltage regulators, Line Regulator Interface units (LRI) and additional LVMs. If data collection and monitoring is required an AdaptiVolt Master or SCADA Master may be included. The SDCC monitors the feeder kwh, kvarh, kw, kvar, current and voltage. It stores interval data for collection by a master. The master, while not strictly necessary, is used to store historical data on how the AdaptiVolt system performed and can be used to change set points and monitor system operation. The adaptive voltage control algorithms are run in the Core unit. The Core unit communicates with the LVMs and the LRIs via DNP3.0. Both the SDCC and the Core units are Programmable Logic Controller (PLC) based and they communicate with each other via a DH-485 local area network. The LVMs are in essence on-line voltmeters and are placed at the end of the line, at critical loads or at locations that the utility determines may have the lowest voltage. LRIs are an interface to voltage regulators located remotely from the substation. The interface may be either DNP 3.0 or relay isolated signals. LRIs can also be used to perform the LVM function. Basically the LVMs and LRIs are real-time input and output devices for the Core PLC.

5 Voltage at the end of the line is monitored on a continuous basis and the AdaptiVolt system controls the voltage regulator or LTC to adjust the voltage to the set point. When AdatpiVolt is applied to CVR the set point voltage is set to a low limit. (AdaptiVolt could also be set to high values to obtain the opposite effect of CVR.) The AdaptiVolt based automatic CVR sytems can be configured to meet the specific needs of the utility and the configuration of the substations and distribution feeders. For example the systems at Inland Power Company communications will occur about four times per day. At Clatskanie PUD there are three substations with six (6) feeders. Each feeder has it own bank of three (3) single phase regulators. LVMs are installed at the ends of each feeder. There are no line voltage regulators. Clatskanie PUD has a Supervisory Control and Data Acquisition (SCADA) system and existing SDCC units. Data will be archived on the existing Master. Communications with the Master from the SDCC are via dual radio links using both DF-1 and DNP3.0. Transmission 115 kv Distribution 12.5 kv Transformer 16/20/24 MVA Voltage Regulator Billing Meter LVM SDCC AVC AVC Options: To Master AVC Master: PC SCADA Master: and Clatskanie PUD are somewhat different. Figure 5: Typical AdaptiVolt Architecture Conclusion At Inland Power Company there is a single substation with four distribution feeders. All four feeders are fed from a single bank of three (3) single phase voltage regulators. Two of the feeders have banks of three (3) single phase line voltage regulators at approximately the midpoint of the feeder. LVMs are installed at the end of each feeder and LRIs are installed at each line voltage regulator. The Core unit communicates with them and controls the station voltage regulator and both line voltage regulators. Fifteen minute interval data will be archived to a separate Master via dial up line and cell phone installed in the SDCC. Archival Data collected from the Inland Power Company and the Clatskanie PUD Adaptive Voltage Control based CVR systems will be evaluated to determine the extent of energy savings. It should help other utilities to determine the efficacy and financial benefits of both AdaptiVolt based CVR and CVR in general. Operation of the AdaptiVolt based CVR should show how the strategy compares to LDC and VSR. References 1. Study Confirms Efficacy of Low Cost, Little-Used Electricity-Saving Measure, Environmental Defense Newsletter, Vol. XIII, No. 5, November 1982.

6 2. Kennedy, B. S. and Fletcher, R. H., Conservation Voltage Reduction (CVR) at Snohomish County PUD, IEEE Transactions on Power Systems, Vol. 6, No. 3, August DeSteese, J.G., Merrick, S.B and Kennedy, B. W., Estimating Methodology for a Large Regional Application of Conservation Voltage Reduction, IEEE Transactions on Power Systems, Vol. 5, No. 3 August Cut Voltage to Address Power Shortage? Power Engineering, Vol. 105, No. 6, June Line Voltage Standards, Power Engineering, Vol. 105, No. 10, Oct Smith, R. J., Circuits, Devices, and Systems A First Course In Electrical Engineering, Chapter 16, pp , Second Printing March 1967.

7 Biography Tom Wilson (M 1972, SM 1985) is a native of Spokane, Washington. After serving in the US Navy as an Electricians Mate, he earned his BSEE from Washington State University in While working as a Substation Operations Engineer at Pacific Gas and Electric Company, he attended the University of Santa Clara studying MSEE courses. In 1982 he earned his MBA from Gonzaga University. Wilson worked as an Electrical Engineer for Kaiser Aluminum and Chemical Corporation and as an Industrial Control Application Engineer for Reliance Electric. Wilson is the founder and president of PCS UtiliData, a Spokane, Washington based control system integration firm specializing in substation and utility automation solutions using PLCs. Wilson has been active in the IEEE serving with the Spokane Section in several offices including Section Chair and IAS Chair. During his tenure as IAS Chapter Chair the Spokane Chapter was awarded the Outstanding Small Joint Chapter Award by the IAS.