How to improve relay protection

1 Types of possible accidents

       1.1 Setting value issues ①Errors in setting calculation ②Human setting errors ③Drift of device setting values aAging and damage of components bEffects of temperature and humidity cSetting drift issues

       1.2 Power supply issues ①Inverter stabilized power supply issues aExcessive ripple coefficient bInsufficient output power or poor stability ②Configuration issues of DC fuses ③Operating plug-ins with DC power supply

       1.3 TA saturation issues As the measurement TA for relay protection 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 operations. On-site accidents have occurred where feeder protection failed to operate due to current transformer saturation, and main transformer backup protection tripped all three sides 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 will have a greater impact on digital relays. ①Impact on auxiliary criteria ②Impact on algorithms based on power frequency components ③Impact on different data acquisition methods ④Methods and countermeasures to prevent TA saturation.

       1.4 Anti-interference issues Operating experience shows that the anti-interference performance of microcomputer protection is poor. The use of walkie-talkies and other wireless communication devices near the protection panel can cause some logic components to malfunction. On-site accidents have occurred where during argon arc welding by an electric welding machine, high-frequency signals were induced onto the protection cable, causing the microcomputer protection to trip incorrectly. New installations, capital construction, and technical renovations must strictly implement relevant anti-accident technical measures. Try to avoid operational interference, impact load interference, DC circuit grounding interference, and other problems.

       1.5 Protection performance issues Protection performance issues mainly include two aspects, namely device functions and characteristic defects. Some protection devices may malfunction when DC power is applied; high-frequency blocking protection may malfunction when there is a frequency beat phenomenon; some microcomputer protection dynamic characteristics deviate far from static characteristics, which can also lead to incorrect operation 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 static electricity, a large amount of electrostatic dust accumulates around the solder joints of the plug-in wiring. When external conditions permit, a conductive path 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 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 220 kV line protection, transceiver problems are still the main factor causing incorrect operation of longitudinal protection. The main problems are component damage, poor anti-interference performance, etc. The transceivers with problems 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 (fiber optic, microwave, carrier), to prevent incorrect protection operations due to communication equipment problems. In addition, abnormal operation of high-frequency protection transceivers is also one of the reasons for incorrect operation of high-frequency protection. For example: damage to transceiver components, gaps in the transmitted signal when the transceiver starts, strong interference causing false signal transmission on 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.

2 Ideas for handling relay protection accidents

       2.1 Correctly and fully utilize fault information provided by the microcomputer Simple accidents that occur frequently are easy to eliminate, but for a few faults, relying solely on experience is difficult to solve. Correct methods and steps should be adopted.

       2.1.1 Correctly handle human-caused accidents After some relay protection accidents, the cause cannot be found according to on-site signal indications, or there is no signal indication after the circuit breaker trips, making it impossible to determine whether it is a human-caused accident or equipment accident. This situation often occurs due to insufficient attention from staff, ineffective measures, and other reasons. Human-caused accidents must be truthfully reported for analysis and to avoid wasting time.

       2.1.2 Fully utilize fault recording and time records Microcomputer event records, fault recording waveforms, and device light display signals are important bases for accident handling. Making correct judgments based on useful information is the key to solving problems. If a comprehensive inspection of the primary and secondary systems reveals that the primary system fault caused the relay protection to operate correctly, then there is no relay protection accident handling problem; if it is determined that the fault lies in the relay protection, try to maintain the original state, make records, and develop a fault handling plan before starting work, to avoid unnecessary trouble caused by destroying the original state.

       2.2 Use correct inspection methods

       2.2.1 Reverse order inspection method If the root cause of an accident cannot be found in a short time using microcomputer event records and fault recording, attention should be paid to starting from the result of the accident and checking level by level backwards until the root cause is found. This method is often used when protection misoperates.

       2.2.2 Sequential inspection method This method uses inspection and debugging techniques to find the root cause of the fault. It proceeds in the order of external inspection, insulation testing, setting value inspection, power supply performance testing, protection performance inspection, etc. This method is mainly applied in accident handling where microcomputer protection fails to operate or logic problems occur.

       2.2.3 Use the whole group test method The main purpose of this method is to check whether the protection device's action logic and action time are normal. It can often reproduce the fault in a very short time and determine the root cause of the problem. If abnormalities occur, combine with other methods for inspection.

2.3 Precautions for accident handling

       2.3.1 Requirements for test power supply When conducting microcomputer protection tests, a separate power supply is required, and it should be verified whether the test power supply meets the requirements of three-phase positive sequence and symmetrical voltage, and check whether the sine wave and neutral line are good, and whether the power capacity is sufficient.

       2.3.2 Requirements for instruments and meters Multimeters, voltmeters, oscilloscopes and other instruments that take voltage signals must use those with high input impedance. Relay protection testers, phase shifters, and three-phase voltage regulators should pay attention to their performance stability.

3 How to improve relay protection technology

       Mastering and understanding the basic types and ideas of relay protection fault and accident handling is an important condition for improving the level of relay protection fault and accident handling. At the same time, the following issues should be strengthened.

       3.1 Master sufficient necessary theoretical knowledge