How to Improve Relay Protection

1 Types of Possible Accidents

       1.1 Setting Value Issues ①Errors in setting calculation②Human setting errors③Drift of device settings a.Aging and damage of components b.Effects of temperature and humidity c.Setting drift issues

       1.2 Power Supply Issues ①Inverter regulated power supply problems a.Excessive ripple coefficient b.Insufficient output power or poor stability②Configuration issues of DC fuses③Operating 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 rapid 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, feeder protection has failed to operate due to current transformer saturation, and accidents where the main transformer backup protection trips all three sides of the main transformer have occurred from time to time. Since digital relays are implemented using microcomputers, their main working power supply is only about 5V, and the effective level range of the data acquisition part is also only about 10V, so the signal range that can be effectively processed is smaller, and the impact of current transformer saturation on digital relays will be greater. ①Impact on auxiliary criteria②Impact on algorithms based on power frequency components③Impact on different data acquisition methods④Methods 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 some logic components to malfunction. On-site, there have been accidents where an argon arc welding machine caused high-frequency signals to be induced onto the protection cable, leading to false tripping of the microcomputer protection. 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 grounding interference.

       1.5 Protection Performance Issues Protection performance issues mainly include two aspects: device functionality and characteristic defects. Some protection devices may malfunction when DC power is applied; high-frequency blocking protection may malfunction when there is a frequency beating phenomenon; some microcomputer protection dynamic characteristics deviate far from static characteristics, which can also lead 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 the 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 with the device's own quality or program loopholes can only be discovered after a considerable period of field 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 220 kV 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 current manufacturers. Therefore, the production quality of transceivers must be taken seriously. 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 actions caused by 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, incorrect internal wiring of the transceiver, forgetting to power on the transceiver, the transceiver failing to provide blocking function, and false actions 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 frequently occur 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 and ineffective measures by the staff. 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 a primary system fault caused the relay protection to act 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 tracing back level by level until the root cause is found. This method is often used when protection malfunctions.

       2.2.2 Sequential inspection method This method uses inspection and debugging techniques to find the root cause of faults. It is carried out in the order of external inspection, insulation testing, setting value inspection, power supply performance testing, and protection performance inspection. 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 action logic and action time of the protection device 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, it is required to use a separate power supply, and verify whether the test power supply is 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.