Sacramento Municipal Utility District Tackles Distributed Generation Challenges

In-Line Power Regulators enable utilities to deliver a more reliable voltage.
Published: Thu 17 Sep 2015

With an increased interest in distribution-connected renewable generation and distribution system efficiency, utilities find themselves having to adapt to the changing energy landscape. New technology and techniques have to be considered to help distribution engineers plan and operate their (more complex) grid. Smart investments to help modernise the grid are essential if distribution utilities are to maintain the safety, reliability and affordability that customers expect.

A good example of this is community-owned electric utility, Sacramento Municipal Utility District (SMUD).  Over the past few years, SMUD has successfully deployed new technologies and implemented programmes that have streamlined metering operations, increased situational awareness across the grid, reduced outages and outage response times, and optimized grid operations. All of this has been done with the aim of keeping tariffs down, whilst also ensuring a high quality service for many years to come.

Sacramento’s (and the surrounding area) energy landscape has certainly been evolving. Due largely to the growth in rooftop PV generation, the area has become one of the cleanest energy states in the US. And, this trend towards the customer becoming an energy producer is growing fast. According to a 2014 SEIA (Solar Energy Industry Association) US Solar Market Insight report, in the US alone, solar PV has grown 15 times over in the last five years, with California leading the nation.

Challenges of distributed generation

SMUD has been working hard towards creating a more efficient energy distribution and usage so that the state can achieve its ambitious clean energy objectives which are aimed at supporting a cleaner and more sustainable energy future.  

SMUD is augmenting customer-oriented energy efficiency programmes by testing utility-side energy efficiency measures such as conservation voltage reduction (CVR), which can reduce customer energy consumption by lowering voltage across distribution circuits.

Although the increase in customer adoption of distributed generation and improvements in energy efficiency from systemic voltage reduction will result in economic savings for the utility and its customers, these developments add pressure to the local distribution system. The grid was never designed to cope with reverse power flows from residential PV (and other forms of distributed generation) and this is causing a rise in voltage levels 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 (set American limits), preventing a system wide rollout 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.

Overcoming distribution challenges

SMUD's distribution engineers knew they needed a new approach for planning and operating their distribution system. They knew they needed a more decentralized and dynamic solution to manage voltage, explains Jim Parks, programme manager of the energy research and development department at SMUD.

SMUD chose the Gridco Systems emPower Solution™ and tested several In-Line Power Regulators™ (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.

According to Jeff Lo, vice president of business development at Gridco Systems, the Gridco IPRs are multi-function hardware systems designed to dynamically regulate voltage, providing buck or boost of +/-10%, 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 a more reliable voltage delivery within specific levels to increase PV hosting capacity and ensure that CVR energy savings targets are met.

The utility chose Gridco Systems' IPRs 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. Gridco then applied specialized power system modelling 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.

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  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.