I. Introduction:
Microcomputer-based relay protection refers to relay protection based on digital computers (including microcomputers). Compared with traditional relay protection, it has the following characteristics:
(1) Improve and enhance the action characteristics and performance of relay protection, with high action correctness. This is mainly reflected in obtaining characteristics that are not easily achievable with conventional protection; its strong memory enables better implementation of fault component protection; it can introduce automatic control, new mathematical theories and technologies such as adaptive control, state prediction, fuzzy control, and artificial neural networks, and its high operational accuracy has been proven in practice.Anti-interference dielectric loss tester is widely applicable for dielectric loss measurement of transformers, instrument transformers, bushings, capacitors, arresters, and other equipment in the power industry.
(2) It can conveniently expand other auxiliary functions. Such as fault recording, waveform analysis, etc., and can conveniently add functions like under-frequency load shedding, automatic reclosing, fault recording, and fault location.
(3) Superior process and structural conditions. This is reflected in the relatively universal hardware, easy manufacturing with unified standards; small device size, reducing the number of panel positions; and low power consumption.
(4) Reliability is easy to improve. This is reflected in the fact that the characteristics of digital components are not easily affected by temperature changes, power supply fluctuations, or service life, and are not easily affected by component replacement; moreover, self-check and inspection capabilities are strong, and software methods can be used to detect the working conditions of main components, parts, and the functional software itself.
(5) Flexible and convenient to use, with increasingly friendly human-machine interfaces. Its maintenance and debugging are also more convenient, thereby shortening repair time; at the same time, based on operating experience, the characteristics and structure can be changed through software methods on site.
(6) Remote monitoring is possible. The microcomputer-based protection device has serial communication functions, and the communication with the substation microcomputer monitoring system gives the microcomputer-based protection remote monitoring characteristics. Relay protection devices have been in operation for more than thirty years. With the aging of relay equipment in the plant, the existing protection can no longer meet the development needs of our plant. Updating relay protection devices is particularly urgent. Based on this situation, our plant has carried out renovations on the bus differential, Hongtuo line microcomputer protection, and 110kV and 220kV bus voltage transformers, and achieved good results.
II. Problems Raised and Solutions:
1. Renovation of WMZ-41A Bus Differential Protection Bus protection is an important system equipment to ensure the safe and stable operation of the power grid. Its safety, reliability, sensitivity, and speed are of decisive significance to ensure the safety of the entire regional power grid. In the power grid, bus-tie current phase-comparison differential protection, current phase-comparison differential protection, and ratio-braking differential protection have been widely used. However, in terms of adapting to bus operation modes, fault types, transition resistance, etc., the ratio-braking bus differential protection based on the per-phase current differential principle is undoubtedly the most effective. However, with the popularization of microcomputer protection technology in the power grid and the continuous improvement of microcomputer-based bus differential protection, the limitations of traditional bus differential protection represented by medium-impedance ratio differential protection have gradually become apparent. In terms of current circuit, exit selection, anti-saturation capability, etc., traditional bus differential protection is no longer comparable to microcomputer-based bus differential protection. Below, through the application of WMZ-41A microcomputer bus differential protection in our plant, an introduction to the problems and improvement methods is provided. WMZ-41A is a new type of microcomputer bus protection device. The device adopts a whole-panel back-plug-in chassis structure, maintains the mature protection principles and algorithms of WMZ-41, absorbs the successful operating experience of WMZ-41 over many years, and improves overall technical performance. The GZM-W41A series microcomputer bus protection cabinet composed of it can be applied to bus protection of various voltage levels up to 500kV and various wiring modes. It has the following characteristics:
(1) The WMZ-41A microcomputer bus protection device uses a 32-bit main CPU as the core. The CPU board uses a 6-layer printed board with surface mount technology; analog quantity conversion uses a high-precision 16-bit analog-to-digital converter.
(2) It adopts a complete current differential criterion with ratio braking characteristics, uses sampling value algorithm and sudden change algorithm to achieve fast bus differential protection, and adopts synchronous identification method to resist TA saturation, effectively eliminating the adverse effects of TA saturation on differential protection. In the case of faults inside the bus zone, the protection operates quickly. In the case of external faults, the protection is reliable and does not misoperate.
(3) It automatically tracks and identifies the double-bus operation mode, and can adapt to various special operation modes such as bus-tie with outgoing lines, bypass and bus-tie combined, and bus and bypass combined. It can ensure safe bus operation under various operating states during system paralleling, splitting, or line switching operations.
(4) It is equipped with a Chinese printer, which can print setting reports, sampling reports, self-check reports, and fault reports; the fault report can record the last 8 faults, with three printing formats such as: concise fault report, sampling value fault report, and waveform fault report.
(5) Multiple optional communication interfaces (RS485/RS422/RS232 and Ethernet port) and GPS time synchronization function. Multi-layer wiring printed circuit board technology, strong anti-interference capability (passing the level IV (4kV±10%) fast transient interference test specified by IEC 60255-22-4 standard and the level IV (air discharge 15kV, contact discharge 8kV) electrostatic discharge test specified by IEC 60255-22-2 standard). In the existing WMZ-41A bus differential protection, it is necessary to add auxiliary contacts for the isolating switches of bus I and II on the bus-tie switch. Since the auxiliary contacts of the bus-tie switch isolating switches have no spare contacts, the spare contacts of the closing position relay and tripping position relay are used instead. During bus transfer operations, the operator conventionally first removes the operating fuse of the bus-tie switch (this is to prevent the bus-tie switch from tripping during the switching operation), causing the bus-tie closing and tripping position relays to return completely, resulting in frequent "identification error" light signals from the bus differential protection. In response to this phenomenon, the relay protection team negotiated with the operating personnel. During bus transfer operations, the operating personnel first place the manual small switches for simulating the bus-tie position on the bus differential protection panel (I and II bus) to the manual close position, and then remove the operating fuse of the bus-tie switch. This can prevent the frequent occurrence of "identification error" signals. After the bus operation with disconnecting switches is completed, switch the bus-tie I and II bus small switches back to the automatic position. Shortly after the 110kV WMZ-41A microcomputer bus protection was put into operation, the device frequently issued "voltage sudden change" signals. "Voltage sudden change" will open one of the conditions for tripping the bus differential protection. In this way, only if the differential current exceeds the limit, the differential will operate and trip; the above situation is likely to cause misoperation of the bus differential protection, posing a serious hidden danger to the safe operation of main equipment. In order to prevent the misoperation of bus differential protection based on this situation, after checking the sampling data and using the two-point product method, it was found that the timing chip in the data acquisition system of the bus differential protection does not trigger the crystal oscillator pulse at 20 points every cycle during sampling, but sometimes samples at 24 points per cycle, sampling 4 extra points, causing a ΔU difference between the sampled value of the current cycle voltage and the corresponding sampled value of the previous cycle voltage. When this ΔU accumulates and exceeds the voltage sudden change threshold, it causes frequent "voltage sudden change" signals. After replacing the timing chip, the problem was solved.
2. Update of Hongtuo Line Microcomputer Protection According to the dualization requirements for 220kV and above line protection and the fact that the original WXB-11 and 15 types on the Hongtuo line have been in operation for nearly ten years, the Hongtuo line microcomputer protection was replaced with XJ-produced WXH-802 protection and NARI-produced RCS-931B protection, among which the optical fiber longitudinal differential protection in RCS-931B protection is a set of optical fiber protection for Hongchang Plant. WXH-802 consists of comprehensive distance directional elements and zero-sequence directional elements to form the whole-line fast main protection, and uses three-section phase-to-phase distance and ground distance as well as six-section zero-sequence current directional protection as backup protection; it is also equipped with comprehensive auto-reclosing. Compared with the previous protection, it has the following characteristics:
(1) It uses a 32-bit DSP as the protection CPU, with strong data processing capability and high reliability, and a 16-bit A/D for data acquisition, with high protection measurement accuracy. Each CPU has an independent A/D, and the A/D is automatically calibrated, requiring no zero drift or scale adjustment.
(2) The protection adopts adaptive oscillation criteria and adaptive data filters, and adds protection logic suitable for weak power source sides.
(3) ... (Note: The original text is cut off here, but the translation continues accordingly.)
