1 In industrial enterprises, with the development of large-scale equipment and modernization, the transmission line voltage level is also getting higher and higher, 110kV, 35kV, 10kV has become the factory power supply voltage level, the current factory high voltage equipment rated voltage rating For 10kV, the power supply and distribution station and the voltage level of the transformer are also 10kV. Most of the laying and laying methods of the plant power distribution system are cable bridges, cable tunnels, and cable trenches, all of which are hidden projects.
In terms of safety requirements for electrical design, safety distances and shielded isolation devices are very strict: High-voltage switchgears are often equipped with "5-proof" neutral cabinets, and the high-voltage circuit breakers' static and dynamic contacts are completely isolated. Low-voltage switchgear inside the knife switch, circuit breaker insulation protection is strict, busbars, contacts, heads are sealed by the insulating shell, conductive parts can not be checked through the appearance; to ensure that personnel safety and environmental beauty and integrated wiring requirements and other design aspects Line laying is basically a hidden project. Therefore, due to the high voltage level, the safety distance and insulation requirements are high, and some low-voltage switches, circuit breaker contacts, tool heads, and concealed wires and cables are difficult to check in the daily check of the equipment. These devices are in operation. Changes in temperature are not easily detected in time, and internal defects in electrical equipment are masked. If the electrical equipment is running for a long time without being processed in a timely manner, it will cause the equipment to burn out excessively and the circuit will be short-circuited and burned. At the same time, the temperature of the contacts of the switch and the circuit breaker will increase, the contact resistance will increase, the degree of heating will intensify, and the final contact will be burned. Insulation damage, single-phase grounding, phase-to-phase, three-phase short circuit. Once a failure occurs, it directly affects production and safety. Therefore, the author analyzes the situation of temperature rise of electrical equipment in the production site, and adopts preventive measures to prevent problems and provide protection for forward production.
2 Analysis of Temperature Rise of Electrical Equipment 2.1 Judgment of Internal Thermal Defects of Electrical Equipment The internal thermal defects of electrical equipment mainly refer to the thermal defects caused by solid electrical insulation, oil insulation, and internal electrical circuit faults and insulation degradation. Because such defects occur in the interior of electrical equipment, such as high-voltage switches or transformer outlet bushings, enclosed knife switches, circuit breakers, enclosed busbars, etc., they cannot be detected as intuitively as external thermal defects. However, according to the internal structure of the equipment, operating conditions, the formation of heat transfer at the fault point, combined with the operating conditions of the equipment, and based on the infrared radiation location presented by the faulty equipment, the temperature sensor is used to detect and analyze the possible internal thermal defects.
According to common internal thermal defects of electrical equipment, it can be divided into the following types: (1) poor connection of internal conductive parts or excessive contact contact resistance; (2) internal moisture, increased dielectric loss; (3) aging of insulation materials, Cracking and detachment; (4) Uneven voltage distribution and excessive leakage current; (5) Oil loss inside the casing; (6) Internal resistance of different metal materials is likely to cause contact resistance; (7) Defects in the manufacturing process of cable ends and intermediate heads; 8) Core eddy currents produce temperature rise.
The characteristics of the internal thermal defects: the fault point is sealed on the metal conductor wound by the insulating material, and the infrared penetrating ability of the temperature measuring gun is relatively weak. Therefore, the actual temperature rise of the fault point cannot be accurately determined by the infrared temperature measuring gun. However, the heat can be transmitted to the exterior of the equipment. Due to the complexity of the internal structure of the respective equipment, the measured temperature rise is also very different and it is impossible to accurately judge the internal thermal defects of the electrical equipment. Therefore, different parts of different equipment can be classified according to their heat. Defect level, classification processing.
2.2 Judgment of External Thermal Defects of Electrical Equipment The external thermal defect of electrical equipment is the intuition of the surface of the equipment. The fundamental problem of the external thermal defect of the conductor is mainly the poor connection defect. Because it is exposed in the air, it is easier to diagnose and its failure. The main causes are as follows: (1) poor connection of switches, busbars, and cable connectors; bolts are not compressed; (2) electrochemical oxidation of conductors and contacts over a long period of time; (3) harmful gases and dust in the atmosphere Corrosion caused; (4) Poor equipment material quality, poor processing and installation process resulting in conductor damage; (5) Mechanical conductor vibration and other reasons caused by the reduction of the actual cross-section of the conductor 6) load current instability or excessive; (7) iron Core oversaturated operation; (8) contact with the air to form an oxidation resistor to generate temperature rise.
The characteristics of external thermal defects: the point of exposure is exposed to the air, the temperature gun can directly detect the surface temperature of the electrical equipment, and can reflect the actual temperature rise of the fault point.
2.3 Installation and use of electricity caused by improper operation Temperature rise due to external factors caused by thermal defects of electrical equipment, mainly equipment installation, use, operation caused by electrical heating thermal defects. The main causes of failure are the following: (1) The installation of electrical equipment is not in place, the metal contact surface is not even, and the contact pressure is not enough; (2) The temperature rise caused by the short circuit, the insulation of the equipment is damaged, and the aging is not enough, the insulation strength is not enough, and the insulation is damaged by external forces. . Humans or animals mistakenly enter the live interval, and birds and short-circuits lead across bare conductors; (3) arc short-circuit heating due to load pull; (4) unreasonable conductor cross section, unreasonable equipment selection, and overloaded operation of electrical equipment; (5) non- Thermal overload caused by high-order harmonics caused by linear load; (6) Bad heat dissipation, damaged ventilation equipment, heat generated by operating equipment cannot effectively dissipate heat, causing temperature rise of equipment; (7) Improper installation and use of electric heating equipment Causes fever.
3 Measures for real-time monitoring of temperature rise of electrical equipment Because of the plant's power supply and distribution systems, high and low voltage switchgear, and power transmission lines, and other important equipment are in long-term operation, cable ducts, cable ducts, cable heads, intermediate heads concealedly laid, Enclosed busbars, wall bushings, switch contacts, and busbar connections are subject to heat generation due to oxidation or contact resistance that is too large, and the heating part cannot be detected. Once the equipment fails, the power of the equipment will be reduced, and even a short circuit will be jumped out, resulting in an electrical accident. .
Therefore, on-line monitoring of the temperature rise of these important parts of the electrical equipment is performed, the operating status of the electrical equipment is known at any time, and the focus of the electrical equipment inspection is shifted to preventive maintenance.
For power supply and distribution equipment, transmission and distribution lines, electrical loads, and types of primary and secondary loads, the key parts of electrical equipment are selected, and temperature collectors cannot be installed at locations where manual inspection of temperature is not possible. Pay attention to the following points regarding the type and location of the installation: (1) Mount the wireless temperature collectors on the contacts, cable joints, outlet busbars, disconnectors, and wall bushings of the high-voltage switchgear; (2) Cable trays, cable tunnels Cable glands shall be installed on power cables, cable ends and cable joints to install wireless temperature collectors; (3) Transformer enclosed bus bars, first and second casings, and a wireless temperature collector shall be installed at the wall casing.
Because the wireless temperature collectors are relatively narrow and concealed in installation and installation, and these electrical equipments are in a live state for a long time, they are not suitable for power outage and replacement. Furthermore, the insulation requirements of these installation locations are high, and monitoring data is not easily transmitted through cables. This requires that the power supply of the temperature collector has a long life (the battery life should not be less than 5 years). The power consumption of the temperature collector is low to prolong the service life of the battery; the monitoring data communication method should adopt the wireless transmission method.
Temperature monitoring capacity selection: due to the large number of factory equipment, the system is huge, the distribution of the number of detection points needs to be scattered, and the distance is long. This requires the capacity of the temperature monitoring system to be large enough, and it can be managed uniformly and monitored in real time.
In order to meet the equipment management requirements, the temperature monitoring of electrical equipment achieves the purpose of real-time monitoring. The monitoring system shall have the following functions: display the temperature value, temperature rise value and monitoring position of each monitored point in the upper computer screen of the central control room; automatically generate real-time Temperature histogram, change curve, history curve, online alarm, alarm query, monthly report, annual report, support for Internet remote query. The real-time temperature monitoring network system of electrical equipment is shown.
General Receiver Receiver Receiver/Continuity Receiver Siemens Acquisition Convergence M-Retrace Acquisition Real-Time Temperature Monitoring Network System Monitoring Electrical Equipment Temperature Rising Processing Requirements For the real-time detected electrical equipment temperature profile, run against the equipment Working conditions, according to GB73-90 specified electrical equipment temperature classification analysis, thermal defects according to the level of temperature rise and the degree of damage to the equipment can be divided into general thermal defects, serious thermal defects and dangerous thermal defects three.
General thermal defect: The temperature rise range is 1020C. Compared with the equipment under the same operating conditions, this cable or connector has a certain temperature rise. The infrared imager measures only the slight thermal image characteristics. Attention is drawn to check whether the load current exceeds the standard and to strengthen the tracking to prevent the deepening of the defect level.
Severe thermal defect: The temperature rise range of the hot spot is 20 40C, or the actual temperature is 6080C, or the temperature difference between the devices is in the range of 1.52.0. The thermal image feature is obvious. The defect has caused serious thermal damage and poses a serious threat to the equipment operation. This kind of defect must be strictly monitored and the conditions permit the blackout.
Hazardous thermal defects: The temperature rise of the hot spot exceeds 40C, or the maximum temperature has exceeded the maximum allowable value of the material specified in International GB 763-90. The thermal image is very clear and visual inspection can see severe burn marks. This kind of defect may cause sudden power failure or short circuit explosion at any time. It should immediately exit the operation and conduct a thorough overhaul.
The division of the standard is only a basic principle. During application, attention should be paid to the actual operation of the equipment. Different types of thermal defects should be distinguished, and the causes of heat generation should be identified in order to obtain accurate fault criteria and provide basis for maintenance.
5 Concluding remarks The reliable control of the temperature of electrical equipment is an important guarantee for the safe operation of the company's production. It fully grasps its operating conditions, real-time monitoring of the temperature value, temperature rise value and monitoring position of the monitoring points of the electrical equipment, through the change of the temperature history curve, timely and accurately. Judgment, timely treatment of equipment defects and hidden dangers to avoid the occurrence of equipment accidents, strengthen preventive management of equipment, and improve the reliability of the entire system safe operation. Utilize computer network management technology to improve online monitoring, hierarchical management, and integrated control functions.
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