What is secondary equipment?

The so-called secondary equipment is the equipment that controls, measures, monitors, protects and adjusts the primary equipment, including control and signal instruments, measuring instruments, relay protection devices, automatic devices, remote control devices, operating power supplies and secondary cables.

The drawings of the secondary part of the reaction include the principle and wiring diagram: the principle diagram mainly reflects the working principle of the secondary device (usually using the expansion diagram); The wiring diagram is mainly used for installation and maintenance.

Control circuit: a circuit that turns on and off the circuit breaker and monitors the position and state of the circuit breaker. According to the way of monitoring loop integrity, it can be divided into two types: optical monitoring and acoustic monitoring.

Central signal: It consists of accident signal and early warning signal, which mainly reflects the faults and anomalies of power system through tripping and signaling, and consists of two parts: light and sound.

Measurement and monitoring system: It is mainly composed of current and voltage conversion devices and various measuring instruments. Its main function is to monitor the operation of primary equipment through the measurement of operation parameters, so that operators can adjust and control the operation state, and analyze and deal with problems in operation.

Synchronous circuit: the conditional voltage amplitude of parallel operation of generators in power system is equal; Same frequency; The phase difference is zero, so there are synchronous devices running in parallel in the power plant and substation of the power system.

Operating power supply: the power supply that provides working power for secondary equipment in power plants and substations. Now commonly used are:

(1) battery DC system: it has high reliability, large capacity and stable voltage, and is widely used in the system, but there are many ancillary equipment and heavy maintenance workload.

(2) Rectifier DC system: the secondary part converts alternating current into DC through a converter. According to the working principle, it can be divided into capacitor energy storage rectifier system and composite DC system. Because of its poor reliability, it is only suitable for small and medium-sized substations.

Function of relay protection

The primary task of relay protection is to reflect the fault of power system, automatically, reliably, quickly and selectively remove the faulty components from the system through circuit breakers, and ensure that the fault-free parts continue to operate.

Reflecting the abnormal working state of power system is another task of relay protection, which generally acts on signals and sometimes trips, but there is a certain delay.

Basic composition of relay protection

Measurement: reflect the change of operating parameters of protected components and compare it with the set value of protection. If it reaches the set value, it will send a signal to the logic part;

Logic part: comprehensively judge the signals transmitted by the measuring part and decide whether the protection device acts.

Executive part: according to the nature and function of the protection device, send a trip pulse or signal to the circuit breaker.

Analysis of common protection in power system;

Over-current protection: protection realized by using the phenomenon of current increase during short circuit. In order to ensure selectivity and rapidity, it is usually set to three sections. The first section is quick break, which only protects a part of the lines. Section ⅱ protects the whole length of the line, but it needs to increase the delay; Section ⅲ is used as backup protection. The direction of power supply is usually added to the lines with power supply on both sides to ensure the reliability of the action. Its disadvantage is that it is greatly influenced by system operation mode and short circuit type, and it is generally applied to lines below 1 100 kV.

Undervoltage protection: When the power system is short-circuited, another phenomenon is voltage drop, and the resulting relay protection is called undervoltage protection. Because the voltage signal is usually taken from the bus, undervoltage protection is usually used together with other protections, such as overcurrent protection for low voltage lockout.

Distance protection: When the line runs normally, the ratio of voltage to current (impedance) is large, but when the system is short-circuited, this ratio will decrease. Protection that works by reducing the ratio of voltage to current is called distance protection (or impedance protection). The advantage of this protection is that it is less affected by the system operation mode, but the disadvantage is that it can not run quickly in the whole plant, and it is usually set to three sections. It is generally used as the main protection of 1 10KV line and the backup protection of 220KV line.

Differential protection: When the line runs normally, the current flowing through both ends of the line is in opposite directions, while when the line is short-circuited, the current direction is the same. The protection formed by this principle is called differential protection. Its advantage is that it is not affected by the system operation mode and short circuit type, and it is mainly used for the protection of main equipment and important lines, which can be divided into longitudinal difference and transverse difference.

High-frequency protection: The differential protection that uses high-frequency signals to compare the electrical quantities at both ends of the line is called high-frequency protection, which is divided into directional high-frequency protection (power direction) and phase difference high-frequency protection (current phase) according to the compared signals. As the main protection of 220KV line and the backup protection of 500KV line.

Optical fiber differential: the cost is high, and it is generally used as the main protection of 500KV lines.

In order to avoid the influence of protection failure, the components of general power system have multiple protections, which are divided into:

Main protection: it can cut off the short circuit fault in the protected line (or component) at the required speed.

Auxiliary protection: generally used to make up for some performance deficiencies of the main protection.

Back-up protection: the relay protection that works when the main protection or circuit breaker refuses to operate can be divided into near back-up and far back-up.

The development history of relay protection technology has experienced four periods: (1) electromagnetic type, (2) transistor type, (3) integrated circuit type, (4) microcomputer type;

Characteristics of microcomputer protection device:

Convenient maintenance and debugging

high reliability

The action accuracy is high

It is easy to obtain various additional functions.

The protection performance is easy to improve.

Convenient and flexible to use

With remote monitoring characteristics.

Development of Microcomputer Protection in China

-1978 ~1980 The world's first prototype of microcomputer protection PRODAR-70 was put into trial operation, and some universities (North China Electric Power University, Huazhong University of Science and Technology, etc.) carried out research on microcomputer protection. ), the first domestic microcomputer protection prototype MDP- 1 (distance protection) was put into operation. The second generation "1 1" microcomputer protection device was put into trial operation in 1990. The representative products are WXH- 1 1 and WXB- 1 1. The third generation products are CS series, such as CSL-65438. The LFP-900 series of Automation Research Institute of State Power Company has broken through the current situation of rapid protection in China.

Hardware structure of microcomputer protection device

Signal input circuit: processing switches and analog signals.

Microcomputer system: A control system consisting of a single microcomputer and an expansion chip, which can complete intelligent tasks such as numerical measurement, calculation, logical operation, control and recording. In addition, microcomputer protection also has remote function.

Man-machine interface: such as keyboard, monitor, printer, etc. , to complete the input of setting value, the change of working mode, the check of system status, etc.

Output channel: realize the control operation of the controlled object.

Power?Supply?

In order to improve the reliability of power supply, ensure power quality, improve the economy of power production and distribution, and reduce the labor intensity of operators, automation devices are widely installed in power systems.

Power system automation generally has two aspects:

(1) Conventional automatic devices: reclosing device, standby power automatic input device, generator automatic excitation adjustment device, frequency automatic load shedding device and automatic quasi-synchronous device;

(2) Power system dispatching automation: that is, real-time dispatching, real-time monitoring and control of the operation state of the power system, so as to improve the safe and economic operation level of the system and improve the power quality. Mainly through the remote control device, using four remote (telemetry, remote control, remote communication, remote adjustment) technology.

Problems existing in traditional substations: safety and reliability can not meet the requirements of high reliability of modern power systems; The quality of power supply lacks scientific guarantee; Covers a large area; Does not meet the requirements of fast calculation and real-time control of power system; Heavy maintenance workload

Substation integrated automation is to combine and optimize the functions of secondary equipment (including measurement, signal, relay protection, automatic device, telecontrol device, etc.) in substation. ), and the advanced computer technology, modern electronic technology, communication technology and signal processing technology are used to realize the automatic monitoring, measurement, automatic control and microcomputer protection of the main equipment and transmission and distribution lines in the whole station, as well as the comprehensive automation function of dispatching communication. It is a comprehensive application of automation technology, computer technology and communication technology in the field of substation. Therefore, the substation integrated automation system has the characteristics of comprehensive functions, microcomputer structure, screen operation monitoring and functional operation management.