by Jim Parks, Sacramento Municipal Utility District, and Jeff Lo, Gridco Systems
As a community-owned electric utility, the Sacramento Municipal Utility District (SMUD) is focused on making smart investments in its distribution system to ensure safe, reliable and affordable electricity for its customers. Over the past few years, SMUD has successfully deployed new technologies and implemented programs that have streamlined metering operations, increased situational awareness across the grid, reduced outages and outage response times, and optimized grid operations, all with an eye towards keeping rates low while ensuring high service availability for years to come.
The energy landscape continues to evolve in and around Sacramento, however. As the capital of one of the cleanest energy states in the U.S., it is not surprising that more and more customers are taking advantage of rooftop solar photovoltaic (PV) generation, becoming producers, not just consumers, of power. According to a 2014 GTM Research/SEIA (Solar Energy Industry Association) U.S. Solar Market Insight report, in the U.S. alone, solar PV has grown 15 times over in the last five years, with California leading the nation.
In addition, both SMUD and its customers understand the need to be more efficient with energy distribution and usage in order to help the state achieve objectives supporting a cleaner and more sustainable energy future. SMUD is augmenting customer-oriented energy efficiency programs by testing utility-side energy efficiency measures such as conservation voltage reduction, (CVR), which can systematically reduce customer energy consumption by lowering voltage across distribution circuits.
Although the increase in customer adoption of distributed generation (DG) and improvements in energy efficiency from systemic voltage reduction will result in economic savings for both SMUD and its customers, these developments are putting new pressure on the local distribution system in ways that existing grid equipment was not designed to handle. Specifically, reverse power flow from residential PV (and other forms of DG) is causing voltage rise and dynamic voltage fluctuations on distribution circuits. Voltages on these circuits are not typically monitored by the utility today. CVR should be curtailed if the voltage at distant customer locations on certain feeders falls below ANSI limits, preventing a system wide roll-out of CVR and limiting the benefits of the initiative. Other utilities that have tried CVR have found it challenging to generate significant cost savings. This is especially true when relying solely on medium voltage equipment that doesn’t monitor or compensate for excessive secondary voltage fluctuations and drops, which are often scattered throughout the distribution feeder network.
SMUD’s distribution engineers recognized these challenges, and proactively sought out new approaches for planning and operating their distribution system. Knowing that they needed a more de-centralized and dynamic solution to manage voltage, SMUD chose the Gridco Systems emPower Solutionà¢â€ž- and tested several In-Line Power Regulatorsà¢â€ž- (IPRs). IPRs are power electronics devices that are deployed on the low voltage customer side of the distribution transformer at the “edge” of the grid. The Gridco IPRs are multi-function hardware systems designed to dynamically regulate voltage, providing buck or boost of +/-10 percent, reactive power support, power factor correction, and active harmonic cancellation, all under both forward and reverse (when customers are exporting power back onto the grid) power flow. The IPRs enabled SMUD to more reliably deliver voltage within specific levels to simultaneously increase PV hosting capacity and ensure that CVR energy savings targets are consistently met.
Gridco Systems’ IPRs were selected based on their ability to cost-effectively and continuously regulate voltage where SMUD needed it the most. IPRs are built using power electronics, providing continuous voltage regulation with a maintenance free, 25-year life. The IPRs are more cost-effective than reconductoring primary or secondary distribution circuits, when evaluated using industry-standard value frameworks and the total resource cost test.
For the joint project, the team identified candidate locations by analyzing data from SMUD’s AMI voltage data warehouse. SMUD extracted one year of voltage data from more than 100 distribution circuits, anonymized it to protect customer privacy, and turned it over to Gridco. Girdco then then applied specialized power system modeling and AMI data manipulation techniques to produce recommendations for IPR locations. The data set included voltage readings from meters associated with thousands of distribution transformers. While most of the meters recorded voltages within the acceptable range most or all of the time (based on California’s Rule 2 voltage standard, similar to ANSI C84.1), a relatively small population of distribution transformers delivered out-of-range voltages to customers for multiple readings over the course of the year (Figure 1).
As part of its power system modeling and AMI data analysis techniques, Gridco also investigated the daily and seasonal patterns present in the data. This was done in part to help determine whether the observed voltage violations were likely to be the result of reverse power flow due to PV, as SMUD had anticipated, or related to more conventional loading patterns associated with peak loading due to air conditioning, for example. Results of the study were used to make recommendations for mitigating voltages. Analysis of the AMI voltage data in the context of circuit models and operational data (Figure 2) was leveraged to develop a new understanding of how best to evolve the distribution system. This evolution is planned using existing assets and practices, while introducing new voltage management strategies and systems where they are most effective to deliver customer voltage within the acceptable range.
In a changing energy landscape that is seeing growing amounts of distribution-connected renewable generation and increasing emphasis on distribution system efficiency, new tools and techniques now exist to help distribution engineers plan and operate their grid. By making smart investments that help modernize the grid, distribution utilities can continue to maintain the safety, reliability and affordability which customers expect.
Jim Parks is program manager of the energy research and development department at Sacramento Municipal Utility District, and Jeff Lo is vice president of business development at Gridco Systems.