Introduction to the Structure of Electric Power System Automation

Electric power system automation is the development direction that our electric power system has been striving for. It includes: automation of power generation control (AGC has been realized, but needs to be developed), automation of power dispatching (comprehensive program with online power flow monitoring, fault simulation and SCADA system implementation In order to realize the automation of the distribution network, the most popular comprehensive automation of substations today is to build comprehensive self-stations to achieve better unattended. DTS (dispatcher training simulation system provides convenience for dispatchers to learn), distribution automation (DAS has been realized, yet to be developed).

1. Structure of electric power system automation

Electric power system automation realizes automatic control, automatic scheduling and automatic management of electric energy production, transmission and management. The electric power system is a complex large-scale system with unified scheduling and operation composed of power plants, substations, transmission and distribution networks and users with a vast geographical distribution.

The field of electric power system automation includes automatic detection, adjustment and control of the production process, automatic security protection of systems and components, automatic transmission of network information, automatic scheduling of system production, and automated economic management of enterprises. The main goal of electric power system automation is to ensure the power quality (frequency and voltage) of power supply, ensure the safe and reliable operation of the system, and improve economic benefits and management efficiency.

1.1 Transmission system

Electric power system information automatic transmission system referred to as telecontrol system. Its function is to realize the real-time information transmission between the dispatching center and the substation of the power plant. The automatic transmission system consists of a telecontrol device and a telecontrol channel. There are various forms of telecontrol channels such as microwave, carrier, high frequency, audio frequency and optical communication. Telecontrol devices are divided into three categories according to their functions: telemetry, remote signaling, and remote control. The process of transferring the analog quantity of the factory station to the receiving end located in the dispatch center through conversion and displaying it is called telemetry. The process of transmitting the switching value of the factory station to the receiving end and displaying it is called remote signaling. The process of transmitting the control and adjustment signals from the dispatching end to the receiving end located in the plant station to realize the control of the adjustment object is called remote control or remote adjustment. Telecontrol devices can be divided into wired logic telecontrol devices and stored program logic devices according to their composition. The former realizes its function by the hardware logic circuit in the way of fixed wiring, and the latter is a kind of computerized telecontrol device.

1.2 Accident device

The function of the anti-accident automatic device is to prevent accidents in the electric power system from endangering the operation of the system and electrical equipment. There are two basic types of anti-accident automatic devices installed in electric power systems.

Relay protection device: Its function is to prevent damage to electrical equipment due to system failures, and is often used to protect electrical equipment such as lines, busbars, generators, transformers, and motors. According to the principle of protection, relay protection devices are divided into overcurrent protection, directional protection, differential protection, distance protection and high frequency protection.

System safety protection device: It is used to ensure the safe operation of the electric power system and prevent catastrophic accidents such as system oscillation, out-of-step decoupling, network-wide frequency collapse and voltage collapse. The system safety protection device is divided into 4 forms according to the function:

1.2.1 It belongs to the automatic input of backup equipment, such as automatic input of backup power supply, automatic reclosing of transmission lines, etc.;

1.2.2 It belongs to the control of power shortage at the receiving end, such as low-frequency automatic load shedding device, low-voltage automatic load-shedding device, low-frequency self-starting device of the unit, etc.;

1.2.3 It belongs to the control of excess power at the transmission end, such as fast automatic machine cut-off device, fast closing valve device, electric brake device, etc.;

1.2.4 belongs to the out-of-synchronization of control system oscillation, such as system oscillation automatic decoupling device, automatic parallel device, etc.

2. Contents of electric power system automation

Electric power system automation mainly includes three aspects: regional dispatch real-time monitoring, substation automation and load control.

Real-time monitoring system for regional dispatch: usually composed of small or microcomputers, its function is similar to that of central dispatching monitoring system, but simpler.

Substation automation: the development direction is unattended, and its telecontrol device adopts a microcomputer programmable method.

Load control: Power frequency or audio frequency control is often used. Automation is not only about hardware, but also all-round support for software systems, such as production management and auxiliary decision-making systems, power plant operation inspection barcode systems, power plant electronic operation log systems, power Enterprise office automation management (OA) system, etc., can realize comprehensive automation.

The automation of the management system is realized by computer. The main projects include power industry planning management, financial management, production management, personnel and labor management, data retrieval, design and construction, etc.

3. Automation classification of electric power system automation

According to the production and distribution process of electric energy, including power grid dispatching automation, thermal power plant automation, hydropower station comprehensive automation, electric power system information automatic transmission system, electric power system anti-accident automatic device, power supply system automation, power industry management system automation, etc. 7 Aspects, and form a hierarchical automation system. The lowest level consists of regional dispatch centers, regional substations and regional power plants; the middle level consists of provincial (municipal) dispatch centers, hub substations and directly affiliated power plants, and the highest level consists of the general dispatch center. In each level, power plants, substations, distribution networks, etc. constitute multi-level control.

3.1 Power grid dispatching

Modern power grid automation dispatching system is a computer-based control system, including real-time information collection and display systems, and software systems for real-time calculation, analysis, and control. The information collection and display system has the functions of data collection, screen display, safety detection, calculation and analysis of operating conditions and real-time control. The part that collects information in power plants and substations is called the remote end, and the part located in the dispatch center is called the dispatch end. The software system consists of programs such as static state estimation, automatic power generation control, optimal power flow, automatic voltage and reactive power control, load forecasting, optimal unit start-up and stop planning, safety monitoring and safety analysis, emergency control and circuit restoration.

3.2 Thermal power generation

Automation projects for thermal power plants include:

3.2.1 Safety inspection of machines, furnaces, and electrical operating equipment in the factory, including data collection, status monitoring, screen display, over-limit alarm, fault detection, etc.

3.2.2 Real-time computer control to realize the entire automatic starting process from ignition to grid connection.

3.2.3 Economic distribution and automatic increase and decrease of active load.

3.2.4 Bus voltage control and automatic increase or decrease of reactive power.

3.2.5 Stability monitoring and control. There are two types of control methods: one is that computer output is used to adjust the set value of conventional analog regulators through peripheral equipment to achieve supervisory control; the other is to use computer output peripheral equipment to directly control the production process to achieve direct digital control. control.

3.3 Hydropower

The projects that need to implement automation include three aspects: dam monitoring, reservoir dispatching and power station operation.

3.3.1 Dam computer automatic monitoring system: including data collection, calculation and analysis, over-limit alarm and provision of maintenance programs, etc.

3.3.2 The automatic monitoring system of reservoir hydrological information: including the automatic collection of rainfall and hydrological information, the formulation of reservoir dispatching plan, and the selection of flood control and storage schemes, etc.

3.3.3 Computer automatic monitoring system in the factory: including safety monitoring of the electromechanical operating equipment of the whole plant, automatic control of generator sets, optimized operation and economic load distribution, stable monitoring and control, etc.

4. The development process of electric power system automation

Before the 1950s, the electric power system capacity was around several million kilowatts, and the capacity of a single unit did not exceed 100,000 kilowatts. The automation of electric power systems was mostly limited to single automatic devices, and focused on safety protection and process automatic adjustment. For example, various relay protections for power grids and generators, emergency safety devices for steam turbines, safety valves for boilers, automatic adjustment of steam turbine speed and generator voltage, automatic synchronization devices for grid connection, etc.

From the 1950s to the 1960s, the scale of the electric power system developed to tens of millions of kilowatts, and the capacity of a single unit exceeded 200,000 kilowatts. Regional networking was formed, and new requirements were put forward in terms of system stability, economic dispatch and comprehensive automation. In terms of factory automation, centralized control of machines, furnaces and electric units has begun to be adopted. The system began to install analog frequency modulation devices and economic power distribution devices based on off-line calculations, and widely used telecontrol communication technology. Various new automatic devices such as transistor protection devices, thyristor excitation regulators, electro-hydraulic speed regulators, etc. have been popularized and used.

In the 1970s and 1980s, the computer-based real-time monitoring system (SCADA) with a complete set of software and hardware began to appear. Large-scale thermal power generating units above 200,000 kilowatts began to adopt real-time safety monitoring and closed-loop automatic start-stop whole-process control. Computer monitoring of reservoir dispatching, dam monitoring and power plant comprehensive automation of hydroelectric power stations has begun to be promoted. Microcomputers are widely used in various automatic adjustment devices and relay protection devices.