Jianzhong Tong

Development and applications of system-wide automatic voltage control system in China

Traditionally voltage control is done in a decentralized way at the power plant or substation level in China. Such a traditional mode, lacking of automatic coordination in a system level, is no longer fit for the higher requirements of security and economy of modern large power system operation. In recent years, development and field site applications of close-looped system-wide automatic voltage control (AVC) technique were actively done in China. In the paper, a novel control architecture based on online adaptive network zone division is proposed. Logically such a system is in a three level hierarchical structure, however, both secondary voltage control and tertiary voltage control here are implemented with software in a control center, and the control zones are no longer fixed according to variation in power systems, which is more suitable for the fast developing Chinese power grids. Some key techniques implemented in the AVC system are introduced, such as adaptive zone division, strategies of Tertiary Voltage Control (TVC), strategies of secondary voltage control (SVC), etc. Finally some field experiences, especially some results not from simulation tool but from field site applications, are reported. The excellent performance of the AVC system and significant improvements on power system security and economy are validated. The developed AVC system has been applied to more than a dozen control centers in China, such as the North China Power Grid with generating capacity of 119GW. Evaluation of the potential profits of the proposed AVC system on PJM system in USA is ongoing.

Optimal Voltage Control of PJM Smart Transmission Grid: Study, Implementation, and Evaluation

PJM Interconnection operates the largest synchronized transmission system in North America, where one of the great challenges is being able to meet the system-wide voltage control performance requirements both pre- and post-contingency. Based on a characteristic analysis of the contingencies distribution, a practical method using an iteration scheme between the optimal power flow (OPF) and a contingency assessment (CA) is proposed to develop a control strategy, so that the calculated optimal voltage schedule solutions are better not only for pre-contingency system conditions, also for the post-contingency (N-1) system conditions. At step T, a CA considering all contingencies is carried out and those that may lead to the maximized voltage violations are saved as active contingencies for step T+1. At the same time, another CA, considering only the current active contingencies, is computed in parallel using a trial OPF result as input. According to the post-contingency indices, the new voltage constraints will be compressed and the final OPF is called again to calculate the optimal strategies. The detailed architecture of the PJM optimal voltage control (OVC) system is presented in this paper. The system has completed four-months of online operation, and the results have been evaluated using third-party software. It has been proven that the OVC system presented here will greatly improve both the pre- and post-contingency performance. The PJM OVC is a typical application of a smart transmission grid. Phase III of this study is currently under way.

Study of system-wide Automatic Voltage Control on PJM system

The feasibility and potential benefits of the system-wide Automatic Voltage Control (AVC) in PJM system are studied in this paper. A test AVC system with a hierarchical structure is adopted for simulation study, which is based on eight typical real-time snapshots from the solutions of state estimator in the PJMs Energy Management System (EMS). For each snapshot, the control action simulation is executed in a recursive way by power flow (PF) calculation until the result is no longer changed. Simulation results on adaptive zone division, tertiary voltage control and secondary voltage control are presented here, and comparison of transmission losses and reactive power reserve for all the eight cases before and after AVC are carried out. About 1% reduction of transmission system loss, which means saving energy more than 100 million kWh/year and saving money more than

On-Line Transient Stability Screening of a Practical 14,500-Bus Power System: Methodology and Evaluations

10 million/year, and about 1% increase of system MVAR reserve can be achieved in PJM system thanks to AVC. The research results are evaluated by existing CA (Contingency Assessment) tool with 4745 contingencies, which prove that the performance indices in security after AVC is improved significantly than that before AVC. The Phase II of PJMs AVC project, online implementation of AVC at PJM control center, is ongoing now.

On-line transient stability screening of 14,000-bus models using TEPCO-BCU: Evaluations and methods

This paper describes an effective methodology for on-line screening and ranking of a large set of contingencies. An evaluation study of the on-line methodology in a real-time environment as a transient stability analysis (TSA) screening tool is presented. Requirements for an on-line screening and ranking tools are presented. The methodology of BCU classifiers implemented in the TEPCO-BCU package was evaluated on the PJM system as a fast screening tool to improve on-line performance of the PJM TSA system. This evaluation study is the largest in terms of system size, 14,500-bus, 3000 generators, for a practical application of direct methods for on-line TSA. The total number of contingencies involved in this evaluation is about 5.3 million. The evaluation results were very promising and confirm the practicality of the methodology based on direct methods, in particular the BCU method for on-line TSA of large-scale systems with a large set of contingencies.

Voltage control practices and tools used for system voltage control of PJM

PJM Interconnection has successfully designed and implemented a Transient Stability Analysis & Control (TSA&C) system. This is the first on-line transient stability analysis ever performed in the control center of a large power network. TEPCO-BCU was selected as a leading fast screening tool to improve the performance of PJMs TSA system. This paper will present an evaluation of TEPCO-BCU in a real time environment as a transient stability analysis screening tool. This evaluation represents the largest practical application of the theory of a stability region in terms of the system size (14,000-bus), the number of contingencies (a total of 5,293,691 contingencies), and over a wide range of operating conditions. This extensive numerical study reveals that TEPCO-BCU is an effective tool for performing on-line dynamic contingency screening of large-scale power systems‥

On-line voltage stability monitoring of large power systems

PJM has developed a pilot program of on-line (real time) voltage control in which a system wide Optimal Voltage Control (OVC) demonstration system has been implemented and run on-line parallel with PJM existing system at PJM control center since Jan. 2010. The pilot program was for nine months. The OVC system consists of Data I/O Management, Control Strategy Calculation, Operation Log Management and Control Process Dispatch. It is interfaced with PJM EMS system, automatically receives real-time snapshot from PJM EMS periodically, and calculates optimal voltage schedules for each generator, LTC and switchable shunt in the PJM system. The practices, experiences and results of the pilot program are presented in this panel paper. Significant potential benefits can be achieved with OVC techniques in both aspects of security and economy: (1) average reduction of transmission system loss is about 1.19%, which means energy savings of more than 220 million kWh/year and monetary savings of more than

Look-ahead multi-time frame generator control and dispatch method in PJM real time operations

17 million/year; (2) Average increase of system VAR reserve is about 1.08%; (3) Improvement on system security for pre-contingency and post-contingency is significant, including improvement on these security indices in voltage limits violations, and voltage stability limits violations.

Net interchange schedule forecasting of electric power exchange for RTO/ISOs

An on-line tool developed for voltage stability analysis and enhancement (VSA&E) of large-scale power systems is presented in this paper. The tool has several major functions related to voltage security assessment, load margin calculations, contingency analysis, fast identification of insecure contingencies and critical contingencies, development of preventive control against insecure contingencies and development of enhancement control for increasing load margins for critical contingencies. The parallel version of this tool currently handles on-line models of 20–000 buses with the contingency list in the order of thousand. Some analytical results behind this tool are described.

A stepwise regression method for forecasting net interchange schedule

Summary PJM operates the transmission system with the generation capacity of 164, 000 MW, and the peak load of 145, 000 MW as part of the East Interconnection of US. With the great increase of renewable resources, such as Wind, Solar, Battery, PHV, etc. in the PJM power grid, the conventional generator control and dispatch approach became more and more difficult because of the issues and challenges of uncertainties and new modeling. Facing the issues and challenges, a new look-ahead multi-time frame generator control and dispatch (GCA) method was developed and the GCA software system was installed in the PJM real time system to determine the optimal dispatch solutions for each generator. Every five minutes, PJM GCA system provides dispatch solutions for 20 minutes, one hour, two hours and four hours time ahead. The analysis of dispatch solutions and impact of PJM energy markets will be presented in details. The further development of the GCA will be discussed in the presentation, such as the different optimization of technologies being used in the different time frame to handle the uncertainties and stochastic behaviors of renewable generations.