Introduction to Detection of Power Equipment Condition Monitoring

The purpose of equipment condition monitoring is to use effective detection methods and analysis and diagnosis techniques to timely and accurately grasp the equipment operation status and ensure the safe, reliable and economical operation of the equipment.

1. Introduction to the terms of equipment condition monitoring

In order to ensure the safe operation of the power system, the monitoring and detection of the operating status of the important equipment of the system is carried out. The purpose of monitoring is to discover the development of various deterioration processes of equipment in time, so as to repair and replace them in time before possible failures or performance degradation affect normal work, and avoid accidents that endanger safety.

Power equipment is subjected to electrical, thermal, and mechanical loads during operation, as well as the influence of the natural environment (air temperature, air pressure, humidity, and pollution, etc.). Long-term work will cause aging, fatigue, and wear, resulting in gradual decline in performance and reliability. Gradually decreases. Under the long-term action of high voltage and high temperature, the composition and structure of the insulating material of the equipment will change, the dielectric loss will increase, and the insulation performance will decrease, which will eventually lead to the destruction of the insulation performance; insulators working in the atmosphere are also affected by environmental pollution. The surface insulation performance is reduced, which causes surface discharge faults. The conductive material of the equipment will be oxidized and corroded under long-term heat load, which will increase the resistance and contact resistance, or reduce the mechanical strength, and gradually lose the original working performance. The mechanical structural parts of the equipment are subjected to long-term load or operation, causing corrosion and wear, resulting in action failure, air leakage, liquid leakage, or other structural damage. The process of these changes (called degradation) is generally a slow gradual process. As the operating period of the equipment increases, the performance and reliability gradually decrease, and the failure rate of the equipment gradually increases, which may endanger the safe operation of the system. It is necessary to monitor the operating status of these equipment.

2. Brief introduction to the development of equipment condition monitoring

The traditional methods of power equipment condition monitoring are frequent manual inspections and regular preventive maintenance and testing. During the operation of the equipment, the personnel on duty often inspect it, and make judgments based on the appearance, indicating instruments, etc., to find possible abnormalities and avoid accidents; in addition, the routine inspection of the equipment to stop running is carried out regularly, and preventive insulation tests and mechanical actions are performed. Tests, timely treatment of structural defects, etc. This system of frequent inspections and regular maintenance plays an important role in ensuring the safe operation of electrical equipment.

With the development of sensing technology and computer technology, the state monitoring method of electric power equipment is developing towards automation and intelligence, and the regular maintenance system of equipment is developing towards the early warning maintenance system. The monitoring of the status of power equipment involves a wide range of fields. A large number of non-electrical parameters (thermal, mechanical, chemical parameters, etc.) require various corresponding sensors. The development of sensor technology provides the possibility for this. With the emergence of practical sensing elements, new power equipment with state monitoring functions equipped with various sensors is the basis of an automated power system. The development of microelectronics technology and computer technology provides powerful tools for the recording, processing and judgment of sensor signals. In addition, it can also perform necessary control operations, which provides the possibility for intelligent control of power systems.

3. Online detection of equipment condition monitoring

Direct detection of electrical equipment in operating state. The detection does not affect the normal operation of the system, and can directly reflect the status of the equipment in operation, which is more effective, timely and reliable than the offline detection when the operation is stopped.

The main difficulty of online detection is that it cannot affect the running state of the equipment. Power equipment operates in the power system and usually works at rated voltage. The detection system must be reliably isolated from high-voltage working parts. Power equipment is generally a closed structure, such as transformers and switches, which are filled with oil or other insulating media inside. The internal state detection should have corresponding internal sensors, or judge through external state detection.

Applicable sensing method or judging method is the guarantee to realize online detection. The state of the device can be detected by applying various electric and non-electrical sensing methods. For example, radiation sensing is used to detect the heating and discharge (luminescence) of equipment, and overheating and partial discharge phenomena can be judged; sound and vibration sensing can be used to detect faults in the mechanical structure system of equipment and gap discharge; surface potential changes or induced currents can be used The detection can judge the integrity of the internal insulation and so on.

Since the operating equipment is generally in an industrial environment, various interferences are inevitable, and the sensing signal is often mixed with interference signals. Therefore, the processing and judgment of the measurement signal are very important, and the judgment of the equipment status often requires the synthesis of various signals. judge. For various devices, specific processing and judgment procedures are required, which are completed by a computer system, usually an expert system.

4. Photoelectric detection for equipment condition monitoring

The measurement of various electrical and non-electrical quantities is realized by using the conversion of optical/electrical and electrical/optical signals. With the development of optoelectronic devices and optical fibers, various optical fiber sensing methods are widely used in industrial fields.

Photoelectric detection usually converts the measured signal into an optical carrier signal by the sensing part (that is, the measured signal determined by the intensity of light or the phase and frequency of the light wave), and transmits it to the receiving side through the optical fiber, and then converts the light to the receiving side through the optical/electrical conversion. The carrier signal is demodulated to get the signal under test. Many optical physical effects have been used for modulation detection, such as the photoelastic effect for the measurement of pressure and deformation; the electro-optic effect for the measurement of electric field and voltage; the magneto-optic effect (Faraday effect) for the measurement of magnetic field and current; the fluorescence effect For temperature measurement, etc. The use of optical fibers provides a powerful tool for these detection methods.

The advantage of photoelectric detection is that it has good insulation performance, overcomes the difficulty of high voltage insulation, and makes many physical measurements at high potential positions possible; optical signals are transmitted through optical fibers and are not interfered by external electromagnetic fields, especially suitable for severe electromagnetic interference. Power system use; In addition, the frequency response of photoelectric detection is high. Optical fibers are also commonly used in computer data transmission to form a photoelectric communication network.