Djordje Atanackovic

Distribution System State Estimation Based on Nonsynchronized Smart Meters

Distribution systems are undergoing many enhancements and developments to enable the future smart grid, and distribution system state estimation (DSSE) provides the control centers with the information necessary for several of its applications and operational functions. However, the quality of DSSE typically suffers from a lack of adequate/accurate measurements. Recently, many electric utilities have started to install fairly accurate smart meters throughout their distribution networks, which create an opportunity to achieve higher quality DSSE. However, the signals provided by smart meters are generally not synchronized and the difference between the measurement times of smart meters can be significant. Therefore, a complete snapshot of the entire distribution system may not be available. This paper proposes a method to deal with the issue of nonsynchronized measurements coming from smart meters based on the credibility of each available measurement and appropriately adjusting the variance of the measurement devices. To illustrate the effectiveness of the proposed method, two IEEE benchmark systems are used. The results show that the proposed method is robust and improves the accuracy of DSSE compared with the traditional DSSE approach.

Deployment of real-time state estimator and load flow in BC Hydro DMS - challenges and opportunities

The object of this paper is to share experiences on deployment and tuning of real-time advanced applications for distribution and distribution state estimator at BC Hydro control center. During past 4 years, BC Hydro has been engaged in the project to procure Distribution Management System (DMS) with objective to enable real-time power system monitoring and control of distribution network in an optimal manner. The emphasis was placed on advanced network applications such as Volt-Var Optimization that are expected to improve the performance and reliability of distribution network. However, a key application that provides basic inputs to advanced applications is distribution state estimator that calculates power system state of distribution network in the real-time. Deployment of state estimator is a difficult process that relies on a number of prerequisites that include, establishing of distribution network model, calibrating and mapping real-time telemetry, extensive software testing and application tuning.

Issues on security region search by online DSA

In real-time operations, online DSA applications can be used not only to perform security assessment for the current operating point but also to search boundaries of security region for operations staff to prepare for the next step generation dispatch and calculate transfer limits for market operations. This paper analyses the issues that were encountered when dealing with future re-configurations of power system resources in security region search., which include: ➢ The approach to incorporate the Remedial Action Schemes (RAS) into the security region search in case where RAS are used to enhance power system security; ➢ The types of power system resources (in particular, generation and load in various areas and regions) that should be utilized in re-configurations for security region search based on the sink-source concept; ➢ The method to determine the levels of participation of the selected resources in order to form reasonable and realistic paths from the current operating point to the potential boundary of the security region.

Implementation of OPF as a supportive system voltage control tool in real-time for British Columbia transmission network

Due to recent changes in electric power system structure and market driven operational changes electric power system operation has increased in its complexity. Engineers and Energy Management System (EMS) suppliers are driven to enhance existing tools and add new tools for control room operators for consistent and faster decisions. Among the two well recognized quality indicators of electric power system operation, viz., voltage and frequency, frequency is being maintained within a very narrow band using formal tools such as Automatic Generation Control (AGC) in North American power networks. Voltage is by and large controlled in real time by experienced dispatchers with the help of “information support” tools or informal tools. Use of formal tools such as the one based on Optimal Power Flow (OPF) technology, described in this paper, for the dispatchers to support and augment their decision making in real time for voltage control is yet to evolve in control centers. This paper describes implementation efforts and issues of one such optimization tool Voltage-Var Dispatch (VVD) to provide control recommendations in real time for system voltage control. The authors share their experiences of implementing VVD that recommends shunt reactors /capacitor, synchronous condenser, static var compensator and generating unit MVAR output controls for controlling Transmission system voltages in real time in the province of British Columbia(BC), Canada.

Voltage VAR optimization real time closed loop deployment - BC Hydro challenges and opportunities

The objective of this paper is to present and share experiences and challenges in Voltage VAR optimization (VVO) real time closed loop deployment at BC Hydro control center. VVO deployment at BC Hydro is focused to maximize energy savings and therefore the closed loop execution is required on continuous 24/7 basis. Several characteristic requirements for closed loop operation were integral for successful VVO deployment. This paper presents foundation elements for VVO closed loop real time execution and some deployment challenges from the system first year of operation.

BC Hydro approach to load modeling in state estimation

Modeling of loads in energy management system (EMS) impacts significantly the robustness and quality of state estimator solution. Loads are traditionally used as pseudo measurements to fill in for unavailable real-time analog telemetry in order to provide required observability for state estimator to solve. The quality of load model also directly impacts the quality of state estimator and power flow solution. There are several important factors to consider when modeling for real-time applications in EMS. Those include (i) the granularity of load model i.e. whether loads are lumped for the entre station bus or each individual feeder in a substation is represented as a separate load, (ii) load voltage sensitivity which describes the variations of real and reactive loads with changes of bus voltage, (iii) load frequency sensitivity which emulates impacts of frequency deviations on loads and (iv) load accuracy model that assigns accuracy class to loads to be used by state estimator. In addition, the aspects of load model such as load allocation in real-time as well as modeling of loads in the external system also need to be addressed. The objective of this paper is to discuss the load model that BC Hydro has implemented in the network model in EMS to support the state estimator and other EMS advanced applications in real-time.

BC hydro experiences with utilization of pseudo measurements in state estimation

State estimator application is the core advanced application in the Energy Management system (EMS) that provides major inputs to other network applications that are executed to determine power system security in the real-time. Those applications include transient and voltage stability analysis that are also responsible for calculation and download of the remedial action schemes arming patterns to the field in the real-time. For this reason, state estimator performance and quality of results are highly important to BC Hydro real-time operations. State estimator relies on the quality of status and analog real-time telemetry and is also strongly dependent on the availability of measurements to provide observability and redundancy. In practical world, real-time measurements are seldom available at all locations and in sufficient quantity to ensure observability of the entire transmission network. In order to overcome the lack of real-time telemetry state estimators traditionally rely on utilization of pseudo measurements to complement real-time measurement set and provide necessary observability for state estimator to solve. The objective of this paper is to discuss the approaches that BC Hydro has adopted for application of pseudo measurements as well as methods used to increase quality of pseudo telemetry.

BC Hydro approach to integration of phasor measurements in EMS state estimator

The application of synchronized phasor measurements for system monitoring and control is receiving unparalleled attention in the power industry. The availability of synchronized phasor measurements data in real-time offer unprecedented opportunities for control centre applications to expand the visibility and improve the quality of output results. In that respect, British Columbia Hydro (BC Hydro) has taken important steps to incorporate phasor measurements into key control center applications that will enable operation of a more reliable, secure and efficient power system. The focus of this paper is on recent work accomplished by BC Hydro to incorporate phasor measurements from several locations in the transmission system into a control center state estimator, the prime application for assisting the operators to understand the operating state of the power system and for making informed decisions with respect to scheduling transmission capacity and responding to contingencies.

BCTC practices in network parameter quality tracking for state estimator sustainment

State estimator application is the core advanced application in the Energy Management system (EMS) that provides major inputs to other advanced network applications that are executed to determine power system security in the real-time. Those applications include transient and voltage stability analysis that are also responsible for calculation and download of the remedial action schemes arming patterns to the field in the real-time. For this reason, state estimator performance quality is highly important to BCTC real-time operations. State estimator relies on the quality of status and analog real-time telemetry and is also strongly dependent on the quality of network model parameters such as line and transformer impedances and charging admittances. The objective of this paper is to describe the maintenance practices adopted at British Columbia Transmission Corporation to ensure high quality and robustness of EMS state estimator with an emphasis on network parameter quality tracking and improvement.

Experiences in system voltage monitoring and control in evolving power grid and application of control room tools

System voltage control has been a challenging task in the BCHydro power system due to generating resources located far from load centers. The system is supported by emergency and quasi emergency measures such as load shedding and auto-var schemes. In addition, operating orders cover extensive voltage control measures. Due to recent changes in electric power system structure and market driven operational changes electric power system operation has increased in its complexity. Historically Control Room staff have been supported by off-line tools in the past progressively increasing the use of tools in the control room. Use of emergency schemes supported by real time tools has been an approach matured over several years of use. More recent are the upgrading the stability tools with technological progress and use of formal optimization tools as well. The authors share their experiences of managing system voltages including normal and emergency measures and also procedures such as auto-var schemes, automatic under-voltage load shedding schemes supported by tools in EMS to arm the load shedding schemes, formal optimization tools, etc., with the technologies that are mature enough for use in control room.