Scheduling automation is the use of computer-based control systems and telecontrol technology to realize the scheduling automation of power system scheduling, which includes safety monitoring, safety analysis, state estimation, online load forecasting, automatic power generation control, automatic economic scheduling and other items. Scheduling automation is an important part of the comprehensive automation of the power system. It can help dispatchers on duty to improve their operation and management level, keep the power system in a safe and economical operating state at any time, and ensure the supply of high-quality electric energy to users.
1. Overview of the development of scheduling automation
Early power system scheduling was directed by dispatchers by telephone. Due to the limitations of communication equipment, they can only grasp limited information reflecting the status of the system through the phone, and make judgments based on this information and personal operating experience to complete the dispatching of the power system. At this stage, a large part of the monitoring and control functions of the power system are directly completed by the operators of the power plants and substations to which the system belongs. Therefore, the speed and correctness of power system monitoring and control are greatly limited. The development of power system makes the structure and operation mode of the system more and more complex and changeable, and the society's requirements for power quality and the safety and economy of power system operation are also increasing. For such a large-scale system with strict operating constraints and randomness in load changes and accidents, it is difficult to perform dispatching management by dispatchers alone in traditional dispatching stations. Taking a power system with a capacity of 3 million kilowatts as an example, the amount of necessary information that needs to be collected at the same time amounts to 2954 (including 864 remote measurements, 1863 remote signaling data, 32 pulse accumulations, 130 remote control data, and 65 remote control data. indivual). Obviously, it is unimaginable to rely solely on dispatchers to monitor a system with such a large amount of information, but also to conduct comprehensive analysis and make correct judgments. In the event of an accident, emergency measures must be taken decisively. At this time, it is even more difficult to rely on the dispatcher alone to deal with it.
In the late 1960s, there were many large-scale power outages in the world. Among them, the power outage in eight states in the eastern United States and Canada was the largest at 17:16 on November 9, 1965, covering an area of about 200,000 square kilometers. The power outage lasted 13 hours and 32 minutes, and the power outage load reached 25 million kilowatts. The safe operation of the power system has increasingly become a prominent issue and has attracted the attention of the whole society. To solve the safety problem of the power system, in addition to considering the rationality of the power system structure, the reliability of the equipment, various relay protections and the perfection of automatic devices, it is more important to strengthen the safety of the power system during operation. monitor. After any local failure occurs, it can be quickly dealt with to restore normal operation, avoiding the expansion of the accident or even the system crash. Because of this characteristic of the power system, it has played a major role in promoting the invention of electronic computers, the formation of cybernetics, and the emergence of system engineering; moreover, as soon as these new inventions come out and new disciplines are formed, they immediately spread in the power industry. The system has been applied to realize the scheduling automation of the power system.
2. Development stage of scheduling automation
According to the different stages of the development of the power system operation technology level, the power system scheduling automation can be divided into four stages.
2.1 Data collection and monitoring (SCADA): The main task at this stage is to monitor and display the frequency of the power system, the voltage of the pivot point, the output of the power plant, the flow of the branch, the load of the substation, and the status of the circuit breaker and the isolating switch . Operators monitor the operation of the entire system according to the displayed results, and make corresponding adjustments and operations.
2.2 Status evaluation: In addition to completing the above monitoring functions, analyze and display the expected accidents, and the countermeasures are decided by the dispatcher.
2.3 Display of countermeasures: The computer system determines and displays the countermeasures for dealing with accidents, and then issues control commands through the final judgment of the dispatcher.
2.4 Automatic control: The control computer system analyzes the state of the power system, proposes decisions, sends out control information, and realizes closed-loop control.
The application of digital technology and computer Since the 1960s, digital technology has replaced traditional analog telecontrol communication technology, which has greatly improved the accuracy, speed and reliability of information collection and transmission. The application of digital information transmission device enables the dispatching center to obtain the real-time parameters of power system operation correctly, quickly and economically, and provides convenience for the connection of information and computer. The digital computer configured in the dispatch center is further divided into an online dispatch control computer and a management computer in terms of function. The way of man-machine dialogue has also developed from recording instruments, typewriters, indicator lights, signal alarms and console buttons to black and white display or color screen display (CRT). This update and change is not only reflected in the change of dispatch management equipment, but also from the limited concept of single control of dispatch (such as automatic frequency regulation, economic load distribution, automatic voltage regulation, etc.) to a more comprehensive comprehensive monitoring of power A modern automatic scheduling control system for safe and economical system operation. The more extensive concept of safety and economic comprehensive monitoring promotes the rapid and gradual improvement and development of computer hardware and software functions for power system scheduling.
3. Scheduling automated system functions
Power system scheduling automation is a complex system engineering, which includes data collection, communication, man-machine dialogue, main computer and advanced application software. The various parts are closely integrated and restrict each other. In this system, the scheduling of operators becomes an integral part of the scheduling automation of the entire system. This automatic control system can not only fully grasp the situation of the whole system, but also make timely and correct control decisions in the case of normal operation and accidents.
Scheduling automation functions General power system scheduling automation functions include:
3.1 Security monitoring;
3.2 Automatic power generation control;
3.3 Economic dispatch control;
3.4 Circuit breaker monitoring;
3.5 State estimation;
3.6 Accident prediction evaluation;
3.7 Online power flow monitoring;
3.8 Voltage monitoring;
3.9 Optimize the flow;
3.10 Automatic voltage and reactive power control.
In some systems, it also has the following new functions: emergency control; automatic restoration of wiring; automatic analysis of system faults; complete analysis of steady state; emergency constraint scheduling; online short circuit calculation; power distribution fault analysis.
It is the control of the normal state that has the main influence in power system scheduling. It is the level of research and realization of normal state control that represents the technical level of power system scheduling automation. As for emergency control and recovery control, the scope and technical level of their implementation are still extremely limited so far. The effectiveness of security controls depends primarily on the control of normal conditions. If a power system can be controlled to be normal 100% of the time, then all load constraints can be met without any problems, and the possibility of gaining the full economic benefit from good operation is greatest. Therefore, the goal of safety control is to keep the power system in normal operation, to prevent the power system from deviating from the normal state and becoming an emergency or recovery state, or to limit the deviation to the minimum. In scheduling automation, online load forecasting has an important impact. It means that scheduling and control centers at all levels use real-time data to update the forecast samples online and correct the forecast results in time when performing load forecasting. Online load forecasting generally refers to daily load curve forecasting. It is also possible to carry out ultra-short-time (5-15 minutes) load forecasting. Online load forecasting plays a guiding role in power scheduling.
4. Reliability level of scheduling automation
Measures to improve the reliability of control equipment The consequences of accidents in the power system are very serious, especially large-scale power outages will cause great losses to the national economy. Therefore, the computer system, which is the core of the entire power grid scheduling automation control system, must be very reliable. A computer system is composed of a computer and its related interfaces and peripheral devices. As long as one link fails, the entire system will not work. So the reliability of the whole system is always lower than that of a single device. The reliability of equipment is generally expressed by the mean time between failures (MTBF), which is the average time between two accidental failures. The reliability of computer systems is usually expressed by availability.
The outage time in the above formula includes failure and maintenance time. The important factors affecting the availability rate are: the quality of equipment, the level of maintenance and repair, environmental conditions, power supply and reserve level, etc. Due to the continuous improvement of the technical level and maintenance and operation level, the availability rate of the dual-machine system has reached more than 99.9%.
In order to improve the reliability of operation, an important measure is to adopt a multiple system (redundant system), that is, to set up several identical (or mutually standby) computers and corresponding peripheral equipment. Generally, a dual system is used, that is, two identical computers are used, and they have their own central processing unit (CPU), internal memory, external memory, and input/output devices. For the division of labor between two computers, the main computer and the standby computer are generally used. The main machine undertakes the real-time monitoring function, and when the main machine fails, the standby machine is put into operation immediately and becomes the main machine. The standby machine, also known as the auxiliary machine, undertakes unimportant real-time functions and offline computing functions. During the standby period, the auxiliary machine can also carry out debugging procedures, extended function tests, training operators and simulating various accidents.
In order to speed up the response time of the host and reduce the burden on the host, a front-end processor can also be added to complete data collection and some simple man-machine contact functions.