Voltage / VAR Monitoring & Control - Low hanging fruit for the Smart Grid
Electric distribution cooperatives have long used real time voltage / VAR monitoring and control for:
1. Traditionally, to maintain voltage within reasonable limits for consumers,
2. To improve power factor / reduce losses, and
3. To reduce wholesale purchased power demand.
This has been accomplished through automatic voltage regulators and tap changing transformers as well as through automatically or manually switched shunt capacitors. The level of control that has been possible has been limited because of: (1) limited voltage monitoring and control, usually only at the point of voltage regulation or shunt capacitance, (2) relatively loose control systems and coarse control increments for the regulators and capacitors and (3) conservative upper and lower limits on the amount of voltage control attempted to prevent unacceptable voltage excursions elsewhere on the distribution system.
With the advent of the Smart Grid, electric utilities are contemplating better monitoring and control capabilities throughout the electric distribution system. This will facilitate more aggressive and effective use of voltage / VAR control, not only for the purposes outlined above, but also:
4. To reduced power demand by consumers and
5. To reduce total energy supplied to consumers (sometimes known as conservation voltage control).
In fact, many Smart Grid experts and vendors consider demand reduction and conservation through voltage / VAR control to be one of the most immediate and significant benefits of Smart Grid technologies.
Utilities will be able to do this because of (1) improved voltage monitoring capabilities through SCADA, distribution automation and Smart Meters (i.e., those Smart Meters that are capable of monitoring and reporting voltage), (2) improved system monitoring, analysis and control software, and (3) refined control capabilities for voltage regulators, capacitors and consumer energy management systems.
There are a number of requirements for better voltage / VAR control. They include:
1. Voltage / VAR control can only be optimized with fast, two-way digital telecommunications between and among SCADA, distribution automation and Smart Meters along with the IT platforms and software being used by utilities for system montoring, analysis and control.
2. Smart Meters will be helpful but only if they have the capability to monitor and report voltage.
3. Wider deployment of distribution SCADA and other distribution automation technologies will facilitate increased capability for voltage / VAR control.
4. A detailed distribution grid circuit model along with the best electric distribution analysis software, eventually including real-time distribution analysis or state estimation, will enable more effective voltage / VAR control.
5. Deployment of more and better voltage regulators / tap changing transformers, shunt capacitors, customer EMS systems and the associated monitoring and control systems.
I am not aware of any electric utilities that are fully engaged in daily, seasonal or year around conservation voltage / VAR control. This represents a huge cultural shift in a business that has from its inception considered growth in energy sales to be essential. There are some vendors that sell devices to retail consumers to enable them to reduce their energy consumption through voltage control. These range from simple resistive buttons that go in the base of incandescent light fixtures to sophisticated energy management systems.
The traditional benefit of voltage / VAR control has been the ability to maintain adequate voltage for consumers during peak periods. The newer applications of voltage / VAR control have several potential benefits:
1. Reduced wholesale purchased power demand charges (or, for vertically integrated utilities, deferred generation capacity additions),
2. Reduced capacity and energy losses,
3. Reduced need to upgrade or add distribution system capacity,
4. Improved customer service through better voltage control,
5. Enabling residential consumers to reduce their power bill by consuming less energy,
6. Enabling C&I consumers to reduce their power bill by reducing their power demand and energy consumption, and
7. One more degree of freedom in active grid management to accommodate distributed, stochastic generation and storage (e.g., wind, solar, PHEVs).
There are several challenges for voltage / VAR control:
1. Voltage / VAR control works best with resistive loads.
2. Non-resistive loads (e.g., induction motors, electronics) many not demonstrate reduced power demand and energy consumption when voltage is reduced or power factor is improved. However, so long as the controlled voltage and power factor is maintained within industry standard limits, the implementation of voltage / VAR control should not have any adverse effects on non-resistive loads.
3. When shunt capacitance is used to improve power factor (to reduce losses) it increases voltage and can actually increase demand and energy consumption.
4. If voltage is not monitored carefully at the endpoints farthest from the voltage regulation devices, it is possible for consumers to experience unacceptably high or low voltages.
5. If the voltage monitoring and control systems are not adequately pervasive and sophisticated, the desired voltage / VAR benefits may not be possible.
6. The speed and bandwidth of the underlying telecommunications system must be sufficient. Few if any of the conventional AMR/AMI systems being deployed today have sufficient speed and bandwidth to optimize voltage / VAR control.
7. Maximizing the extent of voltage / VAR control may require changes in how the electric distribution system is designed and deployed. The traditional approach has emphasized maintaining adequate voltage at the far extremes of the system during peak load periods. The new objectives may require a new way of thinking about distribution system analysis, planning and operations.
For the layman, voltage / VAR control is similar to the pressure reducers that are used to reduce the amount of water use for showers. It is also similar to driving a vehicle at a lower speed or more gradually accelerating and decelerating to improve gas mileage.
Unexpected benefits include better monitoring and control of the electric distribution system, better customer service, better modeling and analysis of the electric distribution grid for planning and operations, and expertise and experience for the evaluation and deployment of other technologies and applications for monitoring and controlling the electric distribution system (e.g., distributed generation, consumer EMS, PHEVs).
Voltage / VAR control is an option that electric distribution cooperatives should be analyzing and planning for now. It is one of the first and foundational milestones on the way to a smarter grid.
Written by Steve Collier | Jan 25, 2011