3. Voltage Reduction Experience and Potential
The Governor's request for us to consider reducing distribution system voltage is best understood in the context of past voltage reduction experience, and present potential.
The Commission developed a conservation voltage reduction program in 1976. The objective was to conserve energy by reducing voltage, with as many residential and commercial customers as possible served within the lower half of the allowable band of 114 to 126 volts at the customer meter (for normal 120-volt service). That is, as much service as feasible was provided between 114 and 120 volts at the meter. It is estimated that more than one billion kilowatt-hours were conserved through the end of 1978 on PG&E's system by this program, with additional savings on other utility systems. (D.91107, 2 CPUC2d 596, 718; also see D.89315, 84 CPUC 221; D.89711, 84 CPUC 733.)
Additional voltage reduction potential may exist. Summarized briefly, PG&E states that it operates its distribution circuits at the lowest peak load voltage level consistent with PG&E Electric Tariff Rule 2 (Rule 2). As a result, service voltage is typically between 114 and 120 volts for normal 120-volt service, with some service voltage as high as 126 volts.3 In response to the Governor's voltage reduction initiative, PG&E implemented a plan in July 2001 to review and, as necessary, modify over 2,000 voltage regulating devices to ensure that these devices maintain voltage within Rule 2 limits. The modifications required manual adjustments to voltage regulators at substation banks and feeders. PG&E completed this effort in October 2001. PG&E estimates that this project will reduce system peak demand up to, but no more than, 50 megawatts (MW), with some benefits also occurring during mid-peak and off-peak periods. PG&E states that it will continue to pursue opportunities to reduce demand during both peak and non-peak times as it undertakes normal substation related work. While some potential may exist for additional capacity savings during periods of minimum load, PG&E estimates no more than an additional 15 MW on a system wide basis. PG&E does not have automatic or remote capability to quickly implement voltage reduction only during system emergencies.
SCE states that it operates its system within SCE Rule 2 limits, or between 114 and 120 volts at the customer meter for typical 120-volt service. Some voltage may routinely be up to 126 volts.4 SCE reports that it can further reduce voltage on most of its distribution system. If ordered by the Commission, SCE recommends a reduction of 2.5%, limited to no less than 117 volts at distribution substations. SCE says that it can implement this voltage reduction on very short notice, such as at the beginning of a Stage 3 emergency, by remotely changing tap settings on transformer banks. 5 Given 117 volts at the substation, SCE says most customers should experience service voltage at the meter of not less than 110 volts.
SCE estimates that its proposal may reduce peak demand by up to, but no more than, 160 MW. This plan is effective, however, only during high load periods, such as summer on-peak. This occurs because voltage control devices (e.g., capacitors, boosters, regulators) are not remotely controlled, and will automatically respond, as designed, to offset voltage reduction at times other than high load periods. In contrast, the majority of, if not all, voltage control devices are already operating during high load periods, and a change in tap settings will produce a change in voltage. If the Commission orders emergency voltage reduction, SCE states that utilities must be exempt from liability for damages that might occur from voltage reductions below the Rule 2 specification (i.e., below 114 volts at the customer meter).
SDG&E, like PG&E and SCE, reports that it has implemented a voltage reduction program for many years, with almost 75% of its distribution circuits operating between 114 and 120 volts at the customer meter, as specified in SDG&E Rule 2.6 According to SDG&E, the remaining 25% of circuits may be outside this range due to the type of customer load served, circuit loading, or circuit configuration constraints.7 SDG&E, like PG&E, does not have automatic or remote capability to implement voltage reduction. The reduction in demand on SDG&E's system from additional voltage reduction efforts would be very limited.8
3 PG&E Rule 2 allows a minimum of 114 volts, and a maximum of 120 volts, at the customer meter on most residential and commercial distribution circuits (normal two wire, 120 volt service), and up to 126 volts for some residential and commercial service. Voltage may also be as high as 126 volts at the customer meter on agricultural and industrial distribution circuits. Voltage may be outside specified limits during several conditions (i.e., temporary action of the elements, momentary fluctuations, service interruptions, temporary separation of system parts from the main system, causes beyond PG&E's control). (Rule 2, Section C.) Rule 2 is consistent with national guidelines designed to promote standardization, and provide the basis for safe and reliable service. 4 SCE Rule 2 is similar to PG&E's Rule 2. One difference is that all residential and commercial distribution circuits are limited to a maximum of 120 volts at the customer meter. Similar to PG&E's Rule 2, voltage may be routinely as high as 126 volts for agricultural and industrial distribution circuits, and voltage may be outside specified limits during the same conditions as stated in PG&E's Rule 2. 5 The California Independent System Operator (ISO) declares a Stage 1 emergency when forecast or actual operating reserves are less than 7% of available capacity. A Stage 2 emergency is declared when forecast or actual operating reserves fall below 5% of available capacity. A Stage 3 emergency is declared when forecast or actual operating reserves fall below 1.5% of available capacity. The California ISO may call for rotating outages during Stage 3 emergencies. 6 SDG&E's Rule 2 is similar to SCE's Rule 2. 7 For example, voltage may be up to 126 volts on agricultural and industrial distribution circuits for SDG&E, just as it may be for PG&E and SCE. 8 SDG&E does not present a specific estimate of capacity savings. SDG&E estimates, however, that under the most optimistic projections, the maximum reduction in demand would be approximately 225 MW statewide. (Opening Brief, page 2.) This would be 15 MW for SDG&E, based on subtracting 160 MW for SCE, and 50 MW for PG&E.
