Keeping Guard on Power Quality for Better Quality of Service
- Written by Richard Walsh
With much more comprehensive data and faster, denser communications, it is possible now to keep a much closer watch on volts and Vars (Volt-amperes reactive). The implications for grid stability and quality of service are more far-reaching than you might suppose.
Technology innovation and new market advancements to support real-time voltage and reactive power management have come a long way in the past ten years. These advancements have heralded newer generations of automation control software, greater choices in data transmission and storage, more robust functionality in two-way controllers, and a new range of powerline sensing systems to enable centralized and decentralized control schemes on a round-the-clock basis.
As utilities examine the potential benefits of various investments required to engineer a 21st century smart grid, real time voltage and Var monitoring is quickly emerging as a multi-purpose vehicle that can not only improve efficiency in power delivery but also help manage power quality excursions at the edge of the grid—instabilities that accompany renewable generation sources and loads.
Real-time voltage and Var control schemes deliver more than efficiency improvements in the form of reduced line losses, peak demand savings and sustained energy reductions. Collection and analysis of real time voltage and Var data along the entire span of the distribution grid will also enable control room operators to monitor the reliability of the system as load profile shifts occur in real time and traditional power flow models become invalid.
An effective closed-loop control scheme, based on real-time data collection, will dynamically manage power quality and prevent harmful voltage excursions that can affect quality of service, cause damage to equipment, reduce its useful life or— in the worst case scenario—lead to catastrophic failure. Looking ahead to nip such problems in the bud, utilities may even consider sending performance signals in advance of a significant load control event to make appropriate adjustments and avoid an instance that might otherwise cause grid instability.
Voltage and Var management programs that rely on the use of real time data have field design and operating requirements that must be met to optimize performance. That task includes the proper placement of field regulation devices with two-way intelligence, adequate deployment of sensing hardware with sufficient accuracy, powerful software and analytics to handle data sampling at real time intervals, properly designed communications networks with prioritization of data, and adequate storage capacity and security for the collected data. More specifically, the criteria for a successful voltage and Var management scheme include the following:
- Quality of Geographic Information System data—need to verify that grid topology records are accurate and complete. This can be the most time consuming portion of the project but it is a prerequisite to any successful deployment.
- Adequately engineered voltage regulation with two-way controls—need to flatten voltage profiles on the entire feeder system and ability to adjust voltages up and down.
- Proper quantity, sizing, placement of capacitor banks with two-way controls—need to flatten voltage profiles on the entire feeder system and regulate power factor near unity on all feeders based on real-time load conditions. This will require engineering analysis to determine fixed load requirements for auto Var compensation and the proper mix of controllable banks to address various load profiles.
- Proper system construction to minimize line losses—need to the flatten voltage profiles with proper conductor sizing, acceptable splice point conditions, and proper transformer sizing.
- Proper quantity, placement and accuracy of line sensing hardware with two-way controls—accuracy becomes more important as voltage is managed within tighter norms, both within and outside the substation.
- Adequately engineered communications infrastructure—frequency and latency requirements for real time data collection must be met. Converged networking requirements with other solutions must also be considered and prioritized accordingly. Avoid the need to design and build the communications network twice.
- Automation software to collect and store real time data and ability to adapt to dynamic changes in feeder state at the substation level—the state of the grid will change so the control schemes and modeling will change on the feeder system with load profile shifts, DA switching events, and new bidirectional powers loads and sources.
- Installing operational procedures to respond to uncorrectable events when individual performance requirements cannot be met without sacrificing others (high/low voltage conflicts, for example). Design inadequacies in the system must be addressed in real time.
Real time voltage and Var monitoring programs should be designed and deployed in advance of high penetration of renewables on the system. It is a custodial step that will provide a view into events that can otherwise impact quality of service.