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The advantages and disadvantages of using infrared temperature measurement and wireless temperature measurement in switchgear

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Why does the power system need temperature measurement

The primary electrical equipment in the power system generally consists of circuit breakers, transformers, cables, busbars, switchgear and other electrical equipment; They are connected to each other by busbars, leads, cables, etc. Due to the current flowing through the connection point, heat is inevitably generated, and almost all electrical faults will cause changes in the temperature of the fault point; Therefore, temperature monitoring of equipment in power systems such as switchgear is a common practice for timely detection of faults. For many years, due to technological limitations, the safe operation level of the power system has been restricted to a certain extent. Although infrared thermometers, infrared imaging devices, temperature sensing cables, and traditional point temperature measurement systems have been used to solve the above problems, real-time monitoring cannot be achieved, and only periodic inspections can be carried out, resulting in safety hazards of missed detection and reporting. For switchgear, in order to improve its operating condition and protect personnel safety, conventional switchgear is now all metal sealed structure. Traditional temperature measurement methods for switchgear are no longer applicable to new switchgear, especially for central movable switchgear. The conductive parts are all covered by insulation materials during operation, and conventional infrared temperature measurement methods cannot measure the internal equipment. Therefore, it is necessary to use internal measurement methods in the switchgear to monitor the operation of internal components in high current switchgear in real time, detect the source of faults early, and prevent accidents from occurring.

Contact temperature measurement and non-contact temperature measurement

For switchgear, there are two commonly used temperature measurement methods at home and abroad: contact temperature measurement and non-contact temperature measurement:

The principle of contact temperature measurement: The contact temperature measurement method is to directly contact the sensor with the object being measured, so that the sensor and the object being measured maintain the same temperature;

The principle of non-contact temperature measurement: The sensor does not directly contact the measured object, but measures the temperature of the measured equipment through the principle of thermal radiation, which is a non-contact measurement method.

Infrared temperature measurement:

Infrared temperature measurement method is a typical non direct contact measurement method. The basic basis of infrared thermometry is the blackbody radiation law of Stefan Boltzmann, Planck, and others. Blackbodies are ideal objects that emit the same electromagnetic spectrum at the same temperature, regardless of the specific composition and shape of the blackbody. The size and wavelength distribution of the object’s own infrared radiation energy are closely related to its surface temperature. By measuring the object’s own infrared radiation energy, its surface temperature is determined, which is the basic principle on which infrared radiation thermometry is based. Nowadays, infrared thermometers are generally composed of optical systems, infrared detectors, signal amplifiers, signal processing, display outputs, and other parts. The core is the infrared detector, which converts the incident infrared radiation energy into other measurable forms of electrical signals. The signal is calculated and corrected by the amplifier and signal processing circuit according to the internal algorithm of the instrument, and then converted into the temperature value of the measured object, which is displayed on the optical system.

The infrared temperature measurement method began around World War II, and the infrared temperature measurement technology was first applied in the military field. The first generation of infrared imaging devices used in the military field was developed and developed by Texas Land Instruments in the United States, known as the Infrared Sight Finding System (FLIR). In the mid-1960s, the Swedish company AGA developed the first industrial real-time imaging system (THV), but it had the characteristics of high cost, large volume, heavy weight, and inconvenient portability. After several generations of improvements to the instrument, a fully functional thermal imager was launched in 1988, which integrated temperature measurement, modification, analysis, image acquisition, and storage. The instrument’s functionality, accuracy, and operability were significantly improved. In the mid-1990s, FSI Corporation in the United States was the first to successfully develop and commercialize an infrared thermal imager (CCD), which was transformed from military technology (FPA) to civilian use. The technical functions were more advanced, and on-site temperature measurement only needed to aim at the target to capture images, and store the above information on the PC card inside the machine to complete all operations. The setting of various parameters can be returned to indoor software for modification and analysis of data, and finally, the detection report can be directly obtained. Due to technological improvements and structural changes, complex mechanical scanning has been replaced, and the instrument weighs less than two kilograms. It is used like a handheld camera, and can be easily operated with one hand. Subsequently, infrared temperature measurement technology was widely applied in the power industry, and various infrared temperature sensors were successfully developed and put into the market in large quantities.

Advantages of infrared temperature measurement: easy to operate and compact in size. Currently, infrared thermometers only need to set parameters and align with the measured object to immediately measure the surface temperature of the object. They also have the function of taking photos and automatically finding the highest temperature measurement point. They are very convenient for on-site use and have been widely used, becoming the main technical means for temperature measurement in many power industry equipment.

Disadvantages of infrared temperature measurement: It can only measure equipment exposed to air. Although some universities have also developed infrared temperature measurement systems for high-voltage switchgear, the infrared probe temperature measurement method for high-voltage switchgear is easily affected by the obstruction of the infrared radiation path by internal components of the switchgear, and cannot accurately measure the contact temperature. Although certain corrections can be taken, there are many factors that affect infrared radiation and they are time-varying, making it difficult to calibrate them one by one. Therefore, this method has poor universality and cannot be promoted for use. This method is only applicable to early switchgear structures and cannot be used for measuring high-voltage switchgear with insulation wrapping.

The working principle of wireless temperature measurement

Wireless temperature measurement method is an improvement on contact temperature measurement method, mainly aimed at solving the problem of high and low voltage isolation between temperature measurement equipment and power system. Generally, wireless temperature measurement system is composed of three parts: distributed temperature measurement node, data receiver, and backend data processing system. Distributed temperature measurement nodes are directly installed in the parts that need to be measured, which belongs to the contact temperature measurement method. The data receiver is placed at a certain distance from the switchgear body. Wireless communication is used between the distributed temperature measurement nodes and the data receiver for data transmission, thereby achieving high-voltage isolation and temperature measurement data collection, solving the problem of the operating temperature of the contacts inside the high-voltage switchgear not being easily monitored by infrared temperature measurement.

Disadvantages of wireless temperature measurement
Although wireless temperature measurement effectively solves the safety issues of temperature measurement devices, there are also some problems in practical applications. Among them, the stability of the temperature measurement device placed at the switch contact position is the most core problem. In practical applications, the power supply of this module is often a current induction power supply that obtains energy from the power line (if battery power is used, not only does it need to be replaced regularly, but the battery is also prone to false alarms in high temperature environments and battery feeding states, greatly affecting monitoring accuracy). The magnitude of the energy obtained by this power supply varies greatly with the load of the power line, so the module often experiences insufficient power supply. In response to this problem, some have proposed using batteries, reducing the power consumption of temperature measurement devices, etc. Method, This method has problems such as the need to regularly replace the battery after it has been consumed, and it can also result in low wireless transmission power and electromagnetic interference from the surrounding environment, leading to errors in temperature measurement data transmission. The battery replacement device requires the high-voltage switchgear to stop power supply, which cannot meet the continuous operation requirements of the high-voltage switchgear.

Passive wireless temperature measurement

Some companies use surface acoustic wave devices to make temperature sensors, which provide feedback on temperature changes through antennas. There is no need to power the sensor components to solve the related problems caused by active wireless temperature measurement batteries. However, this type of device is immature, uses crystal materials with poor thermal stability, is expensive, and does not improve the signal quality of wireless transmission methods.

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