Relay protection is the most important secondary system of the power system. It plays an extremely important role in the safe and stable operation of the power system. With the continuous investment of microcomputer relay protection in recent years, the previous inspection standards have gradually adapted to the development of the system. We need to find a more complete inspection method, only the system, comprehensive and accurate relay protection test. To ensure the safety of the entire power system. Based on years of work experience, the author summarizes the role of relay protection in electricity. The reasons for interference with the internal and external influences, and how to strengthen the protection measures.

1 Power system relay protection and requirements

1.1 The role and composition of relay protection

When the protected component of the power system fails, the relay protection device shall automatically, quickly and selectively remove the faulty component from the power system to ensure that the fault-free part quickly resumes normal operation and the faulty component is exempt from continuing. Suffer damage. Reduce the scope of power outages; by the early 1990s, the development, production, and application of integrated circuits and large-scale integrated circuit protection were in a dominant position, and the era of computer relay protection for intelligent information processing is currently being studied.

1.2 Basic requirements for relay protection

Relay protection should meet the requirements of reliability, selectivity, sensitivity and fastness. Reliability means that the relay protection device should operate reliably during the action within the protection range. In the normal operation state, it should be reliable when not operating. Quick action means that the protection device should cut off the short circuit fault as soon as possible to reduce the damage degree. The protection device should remove the short circuit fault as soon as possible. The purpose is to improve the stability of the system, reduce the damage degree of the faulty equipment and the line, and narrow the fault coverage. Improve the automatic input of automatic reclosing and standby equipment.

2 Interference factors of relay protection

2.1 lightning strike

When the grounding component or lightning arrester of the substation is struck by lightning, because the grounding of the substation is high impedance or the grounding wire from the equipment to the grounding network is high impedance, the high frequency current generated by the lightning strike will be temporarily caused in the grounding system of the substation. An increase in the potential can cause the relay protection device to malfunction or damage sensitive equipment and control loops.

2.2 high frequency interference

If the operation speed of the power system in the isolating switch is slow, the arc contact will be generated at the two contacts of the isolating switch during operation, resulting in an operating overvoltage, high frequency current, and high frequency current will be in the busbar when passing through the busbar. Strong electric and magnetic fields are generated around, which cause interference to the relevant secondary circuit and secondary equipment. When the interference level exceeds the interference level allowed by the logic components of the device, it will cause abnormal operation of the relay protection device, thereby making the entire device The work logic or the exit logic is abnormal, which causes great damage to the stability of the system. The high-frequency current flows through the grounded capacitor device and will cause the ground potential to rise.

2.3 Radiation interference

In the new era, tools such as walkie-talkies and mobile communications are often used around the power system, and a strong radiated electric field and corresponding magnetic field are generated around it. The varying magnetic field is coupled into the loop of a nearby weak electronic device. The loop will induce a high frequency voltage to form a false signal source, causing the relay protection device to operate incorrectly.

2.4 Electrostatic discharge interference

In a dry environment, workers may have high voltages on their clothes. In the case of insulated boots, they can carry the charge far away, so when the worker touches the electronic device, it will discharge. The degree of discharge depends on the grounding condition of the equipment and the environment is different. In severe cases, the electronic components are burned and the relay protection system is destroyed.

2.5 DC power supply interference

When a ground fault occurs in the substation, the ground fault current flows through the ground in the substation and in the earth, and the grounding potential of the substation is higher than the ground potential after the ground fault, and the amplitude of the potential is determined by Grounding grid grounding resistance and the magnitude of ground current, according to the relevant regulations of China, its maximum value can reach 10V per thousand amps of fault. For short-term power interruptions on DC circuits or other causes, the main interference is DC and recovery. Because of the anti-interference capacitance and distributed capacitance, DC recovery may be extremely short or long. During the recovery process. The logic loop inside the electronic device is distorted, causing a transient potential difference of the relay, thereby affecting the entire protection system.

3 Methods and measures to strengthen relay protection of power systems

3.1 Coordinated configuration protection personnel

In relay protection, dispatch, relay, and operation personnel will participate in it. The three parties must be proud of the same pace and unified thinking. Let the cooperation awareness of the three parties keep up with the new protection. Set your position. It is necessary to clarify that the relay personnel are the same as the grid dispatching and grassroots operators. It is the first line of personnel in the production of power grids. It works the same and has the same goal.

3.2 Improve the rules and regulations

According to the characteristics of relay protection, it is necessary to improve and perfect the rules and regulations of the operation and management of protection devices. The files of relay protection equipment, operation and maintenance, accident analysis, periodic verification, defect processing, etc. should be gradually followed by computer management tracking, strict assessment, and implementation of rewards and punishments. Effectively promote the development of relay protection work. At the same time, the power system should strengthen the reward and punishment of relay protection work in the management, suggest the establishment of the annual relay protection professional labor competition awards and other awards, and develop incentives to reward, thus enhancing the sense of honor and responsibility of relay protection personnel.

3.3 State monitoring method for secondary equipment

With the development of microcomputer protection and self-diagnosis technology of microcomputer automatic device, the improvement of substation relay protection fault diagnosis system lays a technical foundation for the state monitoring of electrical secondary equipment. The protection device can automatically test each device and component by loading an online monitoring program. On the one hand, it should be from the equipment management link, such as equipment acceptance management, offline maintenance data management, combined with online monitoring to diagnose its status. On the other hand, existing measurement methods should be fully utilized without adding new inputs.

3.4 Focus on low voltage distribution line protection

In China, whether it is the distribution network in the city or the rural distribution network, the voltage level is generally 10kV, but the structural characteristics of the 10kV distribution line are poor. At the same time, according to the general grid protection configuration and operation experience, the standard protection calculation method can be used, and various conditions can be calculated, which can generally meet the requirements.

3.5 Implementation of relay protection intelligence and network -

In recent years, artificial intelligence technologies such as neural networks, genetic algorithms, evolutionary programming, and fuzzy logic have been applied in various fields of power systems, and applications in the field of relay protection have gradually begun. In the new era, computer networks, as information and data communication tools, have become the technical pillars of the information age. They have profoundly affected various industrial fields and provided powerful communication means for various industrial fields.

So far, except for differential protection, all relay protection devices can only respond to the amount of electrical protection at the installation. The role of relay protection is also limited to the removal of faulty components. Reduce the scope of the accident. This is mainly due to the lack of strong means of data communication. Obviously, the basic condition for realizing such system protection is to connect the protection devices of the main equipments of the whole system with computer networks, and even if the network protection of the microcomputers is now, this is completely possible under the current technical conditions.

4 Conclusion

In summary, when carrying out relay protection, it is necessary to fully consider various factors according to the principle to ensure that the relay protection action does not mismatch or not. After a problem occurs during the operation, the system should be thoroughly and carefully analyzed.