Design of Temperature Monitoring System for High Voltage Switchgear Based on Fluorescent Optical Fiber Sensor
In the development process of my country's power system, the problem of electricity safety has become increasingly prominent. Accidents occur frequently, mostly because the current passes through certain parts, causing local overheating, and the cause is not discovered in time. Based on this, temperature monitoring, display, and alarm for certain key parts, and timely treatment measures if accidents occur, are the key to avoiding safety accidents.
Temperature measurement methods in traditional power systems mainly include contact and non-contact measurement. Thermal resistance temperature measurement, thermocouple temperature measurement and infrared temperature measurement are common temperature measurement methods in practical applications. Traditional methods are susceptible to environmental temperature and electromagnetic interference due to device measurement limitations, and cannot be accurately measured. At the same time, traditional sensors also bring some problems to the insulation protection of the power system, so the insulation protection level of the power system is reduced. In order to make up for the limitations of traditional methods, optical fiber temperature measurement technology came into being. The new sensor with optical fiber as the medium overcomes the electromagnetic interference in the power system environment, and due to the excellent physical, chemical, mechanical properties and transmission performance of the optical fiber, the optical fiber sensor has the incomparable advantages of the traditional sensor.
1 Current status of online temperature monitoring of high-voltage switchgear
The commonly used temperature measurement methods at home and abroad mainly include two types, contact and non-contact measurement. These two methods have extensive research and application in the field of temperature monitoring. This article focuses on the infrared temperature measurement and wireless measurement in non-contact measurement methods. Temperature measurement, optical fiber temperature measurement method.
1.1 Infrared temperature measurement method
The principle of infrared temperature measurement is Stefan-Boltzmann and Planck's black radiation theory. As we all know, a black body is an ideal radiator, which can emit the same electromagnetic waves at the same temperature, and has nothing to do with its specific composition and shape. Within a certain range, there is a functional correspondence between the surface temperature of an object and the magnitude and wavelength of the infrared radiation energy. Therefore, the surface temperature of the object can be calculated by measuring the infrared energy radiated by the object and the functional mapping relationship between the two.
The basic composition of the infrared thermometer includes four parts: optical system, infrared detector, signal amplifier, signal processing and display output. In these parts, the infrared detector is the measurement component of the system and the core part of the system. It converts the incident infrared radiation into an electrical signal that can be measured, and the electrical signal acts as a carrier for the temperature of the object in the subsequent processing. , Through the amplifier and signal processor circuit, and according to the internal algorithm of the instrument, after calculation and correction, it can be converted into the measured target temperature value.
1.2 Wireless temperature measurement method
The wireless temperature measurement system consists of a distributed temperature measurement point, a data receiver, and a background processing system. This method is an improvement of the contact temperature method and is a new type of temperature measurement method, which can isolate the high and low voltage between the temperature measurement equipment and the power system. Install distributed temperature measurement points directly where temperature measurement is required, and place the data receiver at a certain distance from the switch cabinet. The data transmission between the temperature measurement point and the receiver is realized by wireless communication, thereby realizing high-voltage isolation and temperature data collection.
Although the wireless temperature measurement method solves the safety problem of the temperature measurement device, it also causes many other problems. The most important thing is the stability of the temperature measurement device at the position of the switch contact. In practical applications, the module power supply is an inductive power supply, which obtains energy from the power line. The amount of energy obtained is determined by the size of the power line load. Due to the large randomness of the power line load, the module often has insufficient power supply. Based on this, the industry has also adopted methods such as using batteries and reducing the power consumption of temperature measuring devices. The battery has a limited storage capacity, so it needs to be replaced regularly. At the same time, electromagnetic interference will occur due to too small wireless power, which will cause data transmission. Caused certain harm and caused errors in temperature data transmission. If the battery of the device is replaced, the high-voltage switchgear needs to stop the power supply, thus failing to meet the working requirements of the continuous operation of the high-voltage switchgear. These limitations severely restrict the application of wireless temperature measurement methods. .
1.3 Optical fiber temperature measurement method
In recent years, with the development of optical fiber communication and integrated optical technology, optical fiber sensing technology is in the ascendant in the sensor field. Compared with the traditional, the advantages of optical fiber sensors are not functional characteristics, but derived from their own physical characteristics. The optical fiber sensor has the characteristics of light weight, small diameter, small signal attenuation, strong corrosion resistance, anti-electromagnetic interference, high temperature resistance, and has the advantages of integrating information sensing and transmission and integration, which can solve measurement problems that cannot be solved by conventional detection technology . First of all, the optical fiber itself has good insulation performance, which can isolate the high voltage between the power system and the measuring equipment, avoiding equipment safety accidents caused by the temperature measuring device, and greatly improving the safety. Using optical fiber as the carrier of transmission and sensing signals can overcome the problem of strong electromagnetic interference in data transmission in the power system environment, so more accurate measurement results can be obtained. Secondly, due to the good flexibility of the optical fiber, it can detect parts that cannot be reached by conventional sensors. These advantages make the optical fiber sensor show itself in power system temperature measurement, gradually replacing other sensor measurement methods, and more suitable as the main means of high-voltage switchgear temperature measurement.
2 Working principle of fiber grating temperature sensing
The temperature demodulation system drives the LED to send out a light pulse. The light pulse reaches the probe coated with rare-earth materials through the optical fiber to excite fluorescence. The fluorescence is transmitted through the optical fiber to the temperature demodulation system for photoelectric conversion to obtain the corresponding temperature data and display on the corresponding panel. , And transmit and display the temperature through the demodulator.
3 Composition of optical fiber temperature measurement system
Fluorescence optical fiber temperature measuring device mainly includes optical fiber temperature demodulator, display instrument, fluorescent optical fiber sensing probe, monitoring host and human-computer interaction interface, etc.;
(1) The optical fiber temperature demodulator emits light pulses in real time and receives the optical signal carrying temperature information transmitted by the fluorescent optical fiber sensing probe, and demodulates it into a temperature value, and transmits the temperature value to the display instrument. The instrument gives corresponding warnings and other prompts according to the temperature situation. When the actual measured value is greater than the alarm set value, an alarm signal is issued. It can work independently on a single machine or in a network of multiple units, and is suitable for application requirements of various scales. Corresponding display module can also be selected for local display, and the display instrument is installed on the door panel and other places by embedded installation.
(2) The display instrument has the functions of real-time temperature display, alarm setting, sound and light alarm and fault diagnosis. It is generally installed in a convenient place for observation, such as a cabinet door. It accepts the temperature information from the optical fiber temperature demodulator, and judges and alarms according to the preset threshold value. It also has a system self-check function, which can diagnose and display its own state. Information such as alarm threshold and alarm mode can be set through the menu on the surface of the instrument, as shown in Figure 4.
(3) Fluorescent optical fiber sensing probe (temperature-measuring fluorescent optical fiber fire detector) The probe is extremely small in size and can be directly installed on the measured point, with accurate temperature measurement and rapid response; its pigtail is made of special optical fiber, which has transmission The advantages of large bandwidth, stable signal, anti-electromagnetic interference, anti-deflection, high impact resistance and fast connection; the pigtail jacket has the characteristics of high temperature resistance, aging resistance, corrosion resistance, high insulation, non-adhesion, etc., which can adapt to high pressure , High temperature, strong electromagnetic and other harsh environment.
(4) The monitoring host can receive and process normal information, fault information, and disaster information from multiple optical fiber temperature demodulators in real time, and quickly process and manage them. The monitoring host has fault monitoring, display, alarm, and information. Switching and other functions, while remote monitoring can be achieved through the network.
(5) The main functions of the human-machine interface software system include real-time temperature local monitoring, real-time data remote monitoring, high/low temperature alarm, high/low temperature warning, historical data playback, curve before and after alarm, temperature export to Excel and other functions.
4 summary
Aiming at the problem of real-time monitoring of high-voltage switchgear temperature, the current common monitoring methods and their advantages and disadvantages are briefly described, and the application of optical fibers in the field of temperature control of power systems is emphasized. Fluorescent optical fibers, as a novel sensing detection technology, have emerged since then Since then, it has received widespread attention. Based on the full study of optical fiber temperature measurement, this article understands the optical fiber-based sensor temperature measurement system, and introduces the functional structure of each logic module in detail, which has certain guiding significance for the solution of similar problems in the power system.