Earth’s changing climate necessitates that fossil fuel based power production facilities be phased out in favor of renewable energy sources. As rooftop solar panels, small solar energy production facilities, and other distributed energy resources (DERs) expand, electric utilities need to consider maintaining voltage within the range of ±1% of nominal at all locations along every distribution line. This will be challenging because electric utilities have more than 100 years of experience designing and building distribution lines that maintain voltage within the range of ±5%.
Electric utilities must install new devices to regulate voltage as DERs expand. Current devices, such as voltage regulators, shunt capacitors, and tapped transformers, only enable energy to flow in a single direction – from substations along distribution lines to consumers. DERs demand that energy flow in multiple directions, as energy can be produced throughout the grid. Electric utilities’ history of distributing energy in only one direction makes implementing multi-directional devices a challenge.
However, the challenges of providing reliable power in an age of DERs must be met so that consumers continue to get the reliable energy they expect. Electric utilities should update their distribution lines to next generation electric serviceways, which use innovative voltage compensators to allow energy to flow in multiple directions.
Electric serviceways are vital if DERs are to successfully integrate into the grid. Read on to learn more.
Distributed Energy Resources: Solar Panels
During sunny, spring days, numerous distributed rooftop solar panels provide 4 KW to 10 KW of energy to the power grid. This is because they are producing surplus energy during a time of relatively low demand. During night and evening hours, distributed rooftop solar panels stop producing energy. At this time, power flows revert to their traditional mode of operation, from substations across distribution lines to consumers.
Similarly, small solar farms provide energy to the power grid whenever the sun is shining, usually between 1000 KW to 5000 KW. During night and evening hours, when solar panels stop producing energy, power flows from substations across distribution lines.
Voltage Variations and Customer Expectations
Customers expect electricity to always be available via outlets throughout their homes and businesses. Though they may not know it, customers expect that electricity be within a standard range of no less than 114 Volts, Alternating Current (VAC) and no more than 126 VAC, and ideally 120 VAC, at customer meter bases.
When voltage is too low, motors overheat, incandescent lights dim, and toasters take longer to toast bread. When voltage is too high, motors overheat, incandescent lights lose hours of service life, and transformer noise becomes noticeable.
Traditionally, to raise voltage to a consistent value within the ±5% range, some electric utilities install voltage regulators. Other electric utilities install shunt capacitors to provide consistent system voltage levels. Still other electric utilities install customer service transformers with taps that can be set to optimize customer voltage.
Controlling Distribution Line Voltage
Because of the small range of acceptable voltage, electric utilities need to control distribution line voltage so that the voltage at customer outlets is not too low during peak load conditions, nor too high during light load conditions.
For the twelve mile, three phase, 12.47 KV distribution line illustrated in Figure 1, electric utilities decided where and what type of distribution system voltage controlling devices to install before DERs were installed. This is the case for most distribution systems in service today. Note, Figure 1 does not show voltage regulators, shunt capacitors, or tapped transformers.
Figure 1 shows a twelve mile, three phase, 12.47 KV distribution line designed before DERs were installed on the grid.
The system in Figure 1 is not designed to support the additional, distributed energy that DERs add to the grid. This makes it challenging for electric utilities to consistently provide voltage within the required range.
Standard Voltage Regulator Operation
12.47 KV voltage regulators can increase voltage 10% or decrease voltage 10% in 1% steps. When the controller is set to maintain 12,470 volts on the secondary, and secondary voltage is above 12,470 volts, the controller moves the tap to a position that lowers the voltage to 12,470 volts.
When the secondary voltage is below 12,470 volts, the controller moves the tap to a position that increases the voltage to 12,470 volts.
DERs Harm Voltage Regulator Operation
When power flow has been reversed through the voltage regulator, such as when energy flows from distributed rooftop solar panels into the grid, voltage sensors change voltage regulator taps to control voltage. When voltage regulators experience this change frequently, as occurs on days with moving clouds, their service life is reduced.
Electric Serviceways Utilize Voltage Compensators
To alleviate this problem, voltage regulators should be replaced with voltage compensators, that enable multi-directional power flow. Voltage compensators are a key component of next generation distribution lines, also known as electric serviceways.
Voltage compensators are fast acting, skid mounted, totally enclosed, small, static voltage compensation devices, rated from 600 KVA through 2400 KVA. They will enable distribution lines to be loaded to their maximum current rating with and without DERs, and will support rapid electric vehicle (EV) charging, as well as EV charging in neighborhoods with high densities of EVs. These innovative devices, shown in Figure 2, should replace voltage regulators and capacitors, and eliminate the need for tapped transformers.
Figure 2 shows an electric serviceway with voltage compensators located at regular intervals.
Voltage compensators consists of a self-protected transformer, capacitors, inductors, a controller, and SCR switching devices that are mounted in a skid type enclosure. Voltage compensators are standalone components that require no ancillary connections.
The Challenge of Implementing Change
Because the electric utility industry has provided reliable, economical electric energy to consumers for more than 100 years, there is little incentive to innovate. But the challenge of operating distribution systems with distributed energy resources is only just beginning. Innovative solutions must be implemented so that the grid is prepared to support expanded DERs in the next decade.