While a small percentage of electricity customers are served directly from the transmission system, the vast majority of the 165 million customers in the United States are served by the distribution system. That system comprises a complex network of substations, lines, poles, metering, billing and related systems to support the retail side of electricity delivery.
A wide range of technologies are ready for adoption. Each one of them has undergone significant research and development and is available for commercial use. As with any technology, advances are continuing in most areas. The adoption of these technologies by the electric utility industry are limited, typically by the business cases — which include the costs/benefits analysis that each capital investment must undergo before implementation.
Here is a listing of some of the most promising technologies:
Expanding deployment of Distribution Automation
Distribution Automation (DA) involves the integration of Supervisory Control and Data Acquisition (SCADA) systems; advanced distribution sensors; advanced Intelligent Electronic Devices (IEDs) and advanced two-way communication systems to optimize system performance. In a dense urban network, it will also include network transformers and network protectors. SCADA systems collect and report voltage levels, current demand, Mega Volt Amp (MVA), Volt/volt ampere reactive (VAR) flow, equipment state, operational state, and event logging, among others, allowing operators to remotely control capacitor banks, breakers and voltage regulation. Substation automation, when combined with automated switches, reclosers, and capacitors, will enable full smart grid functionality.
This necessitates building intelligence into the distribution substations and into the metering infrastructure. It also must focus new solutions for the distribution feeder circuits and components that link substations with feeders and the metering infrastructure. Automating switches on the distribution system allows automatic reconfiguration. It also enables adapting protection systems to facilitate reconfiguration and integration of distributed energy resources (DERs). This makes possible integrating power-electronic based controllers and other technologies; improving reliability and system performance; optimizing system performance through voltage and VAR control to reduce losses; improving power quality and facilitating the integration of renewable resources.
Intelligent head-end feeder reclosers and relays
Replacing electromechanical protection systems with microprocessor-based, intelligent relays and reclosers are an integral part of smart grid operation. Among the advantages are: increased functionality, including both instantaneous and time-overcurrent protection; greater sensitivity; better coordination with other devices and the ability for self-diagnosis.
The use of intelligent switching and protection devices on feeders (referred to as “mid-point or tie-reclosers”) to allow isolation of segments of feeders and enhance reliability.
Remotely controlled switches: Remotely controlled switches contain distributed intelligence and use peer-to-peer communications to take actions without the need for central control intervention in order to isolate faults and restore power quickly in the event of an outage. As a result, distribution system operators will no longer be the only ones that can perform that function.
Power electronics, including distribution short circuit current limiters
Advances in power electronics allow not only greater fault protection but flexible conversion between different frequencies, phasing and voltages while still producing a proper AC voltage to the end-user.
Voltage and VAR control on feeders
Voltage/VAR controls are a basic requirement for all electric distribution feeders to maintain acceptable voltage at all points along the feeder and to maintain a high-power factor. Recent efforts by distribution utilities to improve efficiency, reduce demand and achieve better asset utilization have indicated the importance of voltage/VAR control and optimization. Utilities continue to face system losses from reactive load, such as washing machines, air conditioners and motors. By optimizing voltage/VAR control, greater efficiencies can be realized.
Accelerated Deployment of Advanced Metering Infrastructure (AMI)
AMI involves two-way communications with smart meters, customer and operational data bases and various energy management systems. AMI, along with new rate designs and intelligent energy using devices, will provide consumers with the ability to reduce electricity bills by using electricity more efficiently, to provide responsive demand and participate in demand response programs, to select service and pricing options tailored to their preferences and could help provide system operators and utilities with the ability to operate the electricity system more reliably and efficiently.
Smart meters are the main component of AMI and often have been the first technology deployed by an electric utility in a smart grid program. AMI’s three basic functions are these:
- Tools which enable both the use and control of smart meters. The more advanced version of these are capable of two-way communication with the utility, with remotely programmable firmware and, optionally, with a remotely manageable service disconnect switch. In addition to consumption measurements, smart meter functionality includes several elements: voltage measurement and alarms that can be integrated with distribution automation projects to maximize Conservation Voltage Reduction (CVR) benefits, and interval data to support dynamic pricing, responsive demand, and demand response programs.
- Communications systems which are highly-secure (encrypted), redundant and self-healing. There are related hardware and software systems which communicate between smart meters, substation and distribution automation equipment, customer energy management systems, and head-end software applications/ meter data management systems.
- Meter data management systems capable of storing and organizing data, allowing for advanced analysis and processing. These also help enable interfacing AMI head-ends with a range of other enterprise software applications.
Advanced Smart inverters
Increasing penetration of DERs, especially solar photovoltaic (PV) systems on the distribution power grid is introducing grid integration challenges for utility engineers. Over voltage, reverse power flow, excessive switching of capacitor banks and/or line tap changers — these are often experienced in circuits with higher penetration of variable generation sources. Some of these technical challenges can be resolved, or at least can be minimized, by employing the full potential of power electronics inside the inverters interfacing these sources with the electric grid. Inverters with grid supportive functionality (including reactive power support, low/high voltage ride-through, watt-frequency, watt-voltage and real power curtailment) can contribute to grid stability — and, hence, assist to increase higher rate of renewable adoption. Closely related to the inverter and control technology is the development of interconnection standards.
Technologies which Facilitate Conservation Voltage Reduction and Volt-VAR Optimization
VAR control is an operating requirement for all electrical distribution utilities. However, in preparing to serve tomorrow’s customer needs, it must now incorporate conservation voltage reduction (CVR) as utilities begin looking for ways to increase the efficiency of the power distribution system, to reduce peak demand, and to conserve energy. In tomorrow’s world, not only CVR, but Volt VAR optimization (VVO), will be needed to reduce greenhouse gas emissions, improve system losses, reduce generation requirements, and reduce critical peak impacts to the system. The advanced communications that have been developed by the industry and implemented by the utilities have changed the capabilities of the CVR and VVO systems that are available today.
To ensure the functionality required by tomorrow’s grid, the industry must move from individual voltage or VAR controllers operating independently on the feeders to systems that communicate feeder readings back to a central VVO controller. These central controllers can then calculate optimal operating set points or commands for the system equipment and send them out over the system to create the optimal scenario for CVR and/or VVO on the feeders.
Each utility needs to assess the benefits of CVR and VVO on their system using modeling tools to analyze circuits for CVR/VVO. The effects of implementing various degrees of CVR/VVO on a circuit can be evaluated by using the OpenDSS (Open Distribution System Simulator) modeling tool.