I. Analysis of traditional temperature measurement methods for high voltage switchgear
At present, the methods for measuring the temperature of the high-voltage switchgear mainly include the wax sheet temperature measurement method and the thermal infrared temperature measurement method.
1. Wax sheet temperature measurement method
The color of the paraffin wax varies with temperature, so a paraffin sheet can be used to measure the temperature of the high voltage switchgear. The specific method is that the paraffin wax sheet is attached to the connection portion of the device , and the measured temperature is judged according to the color thereof. This method is widely used because of its simple principle and low cost. However, it is necessary to judge the temperature based on personal experience, so the accuracy and reliability are relatively low, and quantitative measurement and real-time online monitoring cannot be performed. Moreover, it is impossible to measure a heat-prone portion such as a high-voltage switch contact or a cable joint because it is hardly visible during operation.
2. Thermal infrared temperature measurement technology
The high-temperature switchgear based on thermal infrared is measured by non-contact temperature measurement using thermal sensors such as infrared temperature detectors, infrared imagers and ultraviolet imagers. The advantages are that the measuring range is large, the accuracy is high, and the reliability is good, but the equipment and instruments are expensive, and a large amount of manpower is required for regular patrol testing, and real-time online monitoring of temperature cannot be realized. In addition, because the internal components of the high-voltage switchgear are in high voltage, strong magnetic field and closed operating environment, the conventional temperature measurement methods such as temperature measurement paraffin film and thermal infrared temperature measurement cannot achieve the temperature measurement of the components inside the cabinet. At present, real-time monitoring of high-voltage power supply equipment based on wireless temperature sensing technology is an ideal solution to overcome the above problems.
Second, the working principle of the wireless temperature measurement system of the high voltage switchgear
The high-temperature switchgear temperature monitoring system based on wireless temperature measurement technology first senses the surface temperature of the device through a wireless temperature sensor, then transmits the temperature signal to the wireless temperature monitor through electromagnetic waves, and then connects the wireless temperature monitor to the central monitoring computer through the network. Realize wireless temperature measurement. The high-voltage switchgear wireless temperature measurement system is mainly composed of a field measurement unit (wireless temperature sensor), a field monitoring unit (wireless temperature monitor) and a remote system monitoring terminal.
Field measurement unit
The field measurement unit is mainly composed of a wireless temperature sensor, a measurement circuit, a logic control circuit, a wireless transceiver circuit, and a power supply circuit. The wireless temperature sensor is used to measure the temperature of the surface of a charged object, such as the operating temperature of the exposed contacts and busbar connections in the high voltage switchgear. The field measurement unit sends the temperature signal to the wireless temperature monitoring via a 2.4G wireless network.
2. On-site monitoring unit
The on-site monitoring unit is mainly implemented by a wireless temperature monitor. Each wireless temperature monitor is equivalent to a wireless access point and can simultaneously access 6 wireless temperature sensors. The wireless temperature monitor is generally installed outside the high-voltage switch cabinet, and has functions such as on-site inquiry, parameter setting and alarm. The wireless temperature monitor uses an LCD display to display the on-site monitoring temperature and connects to the remote monitoring system via an isolated RS-485 industrial bus interface to upload temperature data to the remote monitoring terminal.
3. Remote system monitoring terminal
The remote monitoring terminal is installed in the substation control room, receives the data uploaded by the on-site monitoring unit, and transmits the data to the substation integrated automation system according to the power system communication standard protocol (such as the power system 101 protocol). When the system is not connected to the network, the measuring unit and the on-site monitoring unit can be operated away from the remote control terminal to form an independent temperature measuring device, and the temperature of the contact of the high-voltage switch cabinet is monitored on site; when the network is connected, the high-voltage switchgear can be realized. Temperature on-site and remote two-level monitoring.
Real-time online monitoring and management analysis software for high-voltage equipment installed on the monitoring system computer can realize functions such as real-time temperature display, historical data recording and comparison analysis, early warning and alarm, full running status record and report printing. It can effectively help the operator to monitor and analyze the temperature change of the monitoring point of the high-voltage equipment, and predict the location of the fault in time to ensure the safe operation of the high-voltage equipment.
Third, the field application design example
Here, the high-voltage switchgear monitoring of a 110kV substation 10kV power distribution room is taken as an example to illustrate the application of wireless temperature measurement technology in high-voltage equipment monitoring. As shown in Figure 3, the wireless temperature sensor is installed in the part connected to the equipment in the high-voltage switchgear (easy to heat, such as the outlet spacing and busbar connection, cable head connection, etc.). The temperature detector is installed outside the cabinet. Each of the six temperature sensors shares a temperature monitor to form a simple on-site wireless temperature measurement network. The RS-485 industrial bus interface is connected to the remote monitoring system to form a high-voltage device. The wireless temperature monitoring system realizes on-line monitoring of the temperature of the switchgear equipment of the substation.
Fourth, the advantages of wireless temperature measurement system
Compared with traditional high-voltage equipment temperature measurement technology, wireless temperature measurement system has the following advantages:
(1) High security: It avoids the interference of the electric field and magnetic field by the transmission of the analog signal output from the sensor by adopting the advanced digital temperature sensor.
(2) High reliability: By adopting advanced spread spectrum communication, data error correction and adaptive frequency modulation technology, the reliability of data wireless transmission is effectively guaranteed; in addition, wireless RF sensing technology is not affected by vibration and external dust. The temperature measurement accuracy is high.
(3) High level of intelligence: In the normal mode, the temperature value is collected at minute intervals and transmitted to the monitoring center. When an unexpected event causes the temperature to rise to the alarm threshold or the temperature rises faster, the temperature measurement node will Enter the rapid response state, continue to collect temperature intensively at intervals of seconds and transmit alarms to avoid missing any possible temperature rise accidents.
(4) Convenient installation: The wireless temperature sensor is small in size and has no wiring. It can be easily installed on the measured points with small installation space such as switch contacts and cable joints.
(5) Free debugging: It can be used when power is on, no need to debug, especially suitable for retrofitting projects with short power outage time and tight installation schedule.
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