1 Types of Relay Protection Accidents
1.1 Setting Value Issues ① Errors in setting calculation ② Human setting errors ③ Drift of device setting values a. Aging and damage of components b. Influence of temperature and humidity c. Setting drift issues
1.2 Power Supply Issues ① Inverter stabilized power supply problems a. Excessive ripple coefficient b. Insufficient output power or poor stability ② Configuration issues of DC fuses ③ Operating plug-ins with DC power supply
1.3 TA Saturation Issues As a relay protection measurement TA plays a key role in the operation of the secondary system. With the sharp increase of system short-circuit current, the saturation problem of current transformers in medium and low voltage systems has become increasingly prominent, affecting the correctness of relay protection device actions. On-site accidents have occurred where feeder protection fails to operate due to current transformer saturation, and main transformer backup protection trips all three-side switches of the main transformer. Since digital relays use microcomputers, their main working power supply is only about 5V, and the effective level range of the data acquisition part is only about 10V, so the signal range that can be effectively processed is smaller, and the saturation of current transformers has a greater impact on digital relays. ① Influence on auxiliary criteria ② Influence on algorithms based on power frequency components ③ Influence on different data acquisition methods ④ Methods and countermeasures to prevent TA saturation.
1.4 Anti-interference Issues Operating experience shows that microcomputer protection has poor anti-interference performance. The use of walkie-talkies and other wireless communication devices near the protection panel can cause misoperation of some logic components. On-site accidents have occurred where an electric welding machine, during argon arc welding, induced high-frequency signals onto the protection cable, causing microcomputer protection to trip incorrectly. New installations, capital construction, and technical renovations must strictly implement relevant anti-accident technical measures. Try to avoid problems such as operational interference, impact load interference, and DC circuit grounding interference.
1.5 Protection Performance Issues Protection performance issues mainly include two aspects: device function and characteristic defects. Somerelay protection devices may misoperate when DC power is applied; high-frequency blocking protection may misoperate when there is a frequency-beat phenomenon; some microcomputer protections have dynamic characteristics that deviate far from static characteristics, leading to incorrect action results. In accident analysis, the deviation between the above two performances should be fully considered.
1.6 Plug-in Insulation Issues Microcomputer protection devices have high integration density and tight wiring. After long-term operation, due to electrostatic effects, a large amount of electrostatic dust accumulates around the solder joints of plug-in wiring. When external conditions permit, a conductive channel forms between two solder joints, causing device faults or accidents.
1.7 Software Version Issues Problems due to the device's own quality or program loopholes can only be discovered after a considerable period of on-site operation. Therefore, relay protection personnel should promptly report any abnormal or unreliable phenomena found during protection debugging, inspection, and fault analysis to superiors or manufacturers.
1.8 High-Frequency Transceiver Issues In the operation of 220kV line protection, transceiver problems are still the main factor causing incorrect actions of longitudinal protection. The main problems are component damage, poor anti-interference performance, etc. The problematic transceivers basically include those produced by various manufacturers. Therefore, the production quality of transceivers must be emphasized. Attention should be paid to checking the reliability and redundancy of signal transmission of relay protection communication equipment (optical fiber, microwave, carrier), to prevent incorrect protection actions due to communication equipment problems. In addition, abnormal operation of high-frequency protection transceivers is also one of the reasons for incorrect actions of high-frequency protection. For example: damage to transceiver components, gaps in the starting signal of the transceiver, strong interference causing false transmission in the high-frequency channel, transceiver faults, internal wiring errors in the transceiver, forgetting to power on the transceiver, the transceiver failing to perform its blocking function, and misoperation during external faults, etc.
