Guest Article by Vince Martinelli
The reliable operation of the North American power grid is testament to the quality of design, planning and execution over multiple generations of utility engineers. As part of this progression, previous grid modernization efforts added high-performance sensing and communications technologies, first to generation and transmission, and eventually to the distribution system. These technologies helped utilities squeeze more capacity and resiliency out of existing assets cost-effectively, reacting to changes driven by load growth and diversification, as well as industry restructuring.
These trends led to broadly deployed “automation” in the medium-voltage (MV) portion of the distribution system. Medium-voltage substations, where high-voltage power is stepped down to MV on its path toward end customers, have seen the greatest degree of automation. Combined with automation at some of the MV devices downstream from the substation, such as reclosers, capacitor banks and line regulators, this provides the ability to measure and control the system with higher fidelity as compared to managing from the transmission layer. Utilities have evaluated technologies, tested specific solutions in trials, validated use cases and financial models, and made prudent investment choices in rolling out MV automation.
History Repeating Itself
A similar “automation” transition is now happening at the low-voltage (LV) level. Driven by higher reliability expectations, growth of rooftop solar PV generation, energy efficiency programs, the emergence of electric vehicles in the transportation mix, and the promise of battery storage for a range of grid-connected applications, new pressure is being placed towards the edge of the grid. It is more acute in some service areas than others, and can be clustered within one utility’s territory – or even within specific feeder circuits. Driven by these trends, the next frontier in grid modernization is at the interface between the MV distribution layer and the LV distribution layer, centered on the humble distribution transformer, as represented in Figure 1.
Figure 1. LV Substations provide critical new capabilities for grid modernization.
Similar to the MV automation rollout, LV substation modernization will happen first at acute “pain points,” becoming more widespread as the technology matures and the detailed use cases are developed.
Active LV Substations Solve Multiple Problems
Among the variety of potential applications, local voltage regulation is a clear “pain point” that cannot be addressed at the MV layer alone. Whether for increasing PV hosting capacity at the neighborhood level by countering voltage rise during reverse power flow, or for supporting energy efficiency programs where the goal is to deliver voltage to customers at the lower end of the acceptable ANSI A range, the benefits of adding automation to the distribution transformer – what we refer to as an LV substation – are becoming clear.
Figure 2 shows two examples of LV Substations deployed by U.S. electric utilities. In each case, a standard distribution transformer is paired with a grid automation device providing control with power electronics-based multi-function regulating capabilities, visibility with onboard current and voltage sensors, and automation with processing and memory components and communications capabilities. These regulating functions include voltage regulation in forward and reverse power flow, power factor correction, and harmonics mitigation. The system also reduces voltage sags, swells, and flicker for the customer connected downstream.
These compact, maintenance-free systems take advantage of existing “real estate” on poles and pads, simplifying the easement process and providing an alternative to costly upgrades on the MV system. The flexible communications platform can integrate with SCADA on the MV system and interact with downstream LV devices, such as AMI (“smart meters”) or behind-the-meter resources, such as next-generation smart inverters, EV chargers or energy storage resources.
Figure 2. LV Substation implementations for (a) an overhead system and (b) underground plant, featuring coupled integration with a distribution transformer for siting on a standard pad in a residential area. Adding a power electronics-based regulator with integrated sensing, computing, communications and control software brings grid modernization to legacy distribution transformers.
Figure 3 shows voltage data at a particular customer meter over several months without grid automation; then with the voltage regulation from the LV Substation in place. Voltage variability before upgrading the system reflects MV voltage variations, with dips well below ANSI limits, as delivered to the distribution transformer. When the power electronics regulator is activated with an initial setpoint at 240 V, the only variability at the customer is the load-dependent voltage drop on the LV line itself. This particular customer, and neighboring customers behind this LV substation, now receive compliant voltage and superior power quality, independent of the bulk MV system.
Figure 3. Customer voltage delivery improvement measured by utility AMI voltage data showing the control provided by power electronics voltage regulation after introducing the automated LV Substation.
Looking Toward the Near Future
The daily news cycle reminds us that the forces putting pressure on the distribution grid are accelerating, driven largely by changes in how customers choose to participate in their energy future. Whether it’s Hawaii mandating a 100% renewables goal; solar power’s levelized cost of energy continuing to plummet; New York’s REV plan; the ongoing retirement of coal-fired power plants; or nationwide deployment of EV charging stations, the trends are clear.
Fortunately, the concept of automated LV Substations – elevating the status of the long-serving distribution transformer – provides a capital-efficient blueprint for a path forward, modeled after the successful rollout of automation in the MV distribution layer. The difference today is that localized pressure points call for localized solutions appropriate for the demands of the LV layer. The evolution of power electronics-based system designs has resulted in compact, reliable and cost-effective options to consider.
Vince Martinelli is responsible for managing the company’s product roadmap and articulating the business case for agile grid infrastructure. Vince brings over 25 years of product experience and an in-depth understanding of how to effectively drive new technology into legacy systems, transforming them in the process. He joined Gridco Systems in 2013 from Amazon Robotics (formerly Kiva Systems), where he led a team responsible for the integration of Kiva’s robotic order fulfillment system into Amazon’s global network. Prior to Amazon, Martinelli led the North American arm of Professional Services at Sycamore Networks. He has also held senior management positions at Corning Inc., including product management roles in the Optical Fiber business. Vince earned both the SB and SM degrees in Materials Science & Engineering, with a concentration in Economics, from MIT, where he was a Tau Beta Pi Fellow and an Academic All-American athlete.
For further information on multi-function power electronics-based regulation systems that turn distribution transformers into automated LV Substations, please visit www.gridcosystems.com