Design Of On-line Temperature Monitoring And Forecasting System For Switch Cabinet

As an important electrical control and protection equipment in the power system,the switch cabinet has the double functions of switching and protecting the system.Switch cabinet usually adopts closed structure and works in the environment of high current,strong magnetic field and high voltage.Due to manufacturing process,fault,human,environmental and other factors,the contact of the circuit breaker or busbarconnection in the switch cabinet are prone to overheating,resulting in contact resistanceincreasing,mechanical strengthreducing,insulation material aging and other issues.The phenomenon will affect normal power supply,even cause accidents such as casualties and economic losses.Therefore,asystem of wireless temperature monitoring,early warning and forecasting for the switch cabinetisdesignedin this paper,then real-time temperature monitoring on hot spots and temperature warningand prediction isachieved.The research of this paper is of great significance to the reliable and stableoperation ofswitch cabinet.Firstly,the commonly used methods of temperature measurement in the switch cabinetare introducedin this paper,thentheir advantages and disadvantagesare compared.In view of the advantages of wireless temperature measurement in high voltage isolation and signal transmission,a wireless temperature measurement system is designedbased on ZigBee communication.The system consists of wireless temperature measurement module,coordinator and host computer.The temperature measurement module is composed of a DS18B20 temperature sensor and a CC2530 main control unit,which is responsible for collecting and transmitting temperature data in the switch cabinet.The coordinator is composed of the main control unit and peripheral circuits,which is responsible for creating a network,receivingthe data fromthe temperature measurement module and communicating withthe host computer through the serial communication.Through the hardware and software design of the temperature measurement system and the host computer program written in Lab VIEW software,the on-line temperature measurement and the real-time displayis realized.Secondly,aiming at the problem of the safety and the need of replacement of battery,or the existence of dead zone in the current transformer,the power supply mode which takes the energy from the electric field is adopted in this paper.The potential difference generated by the coupling capacitance between the busbar and copper sheet can supply power for temperature measurement module.The distribution of electrostatic field around high voltage conductor is simulated by Ansoft software.The parameters of parallel plate capacitor and the influence of load impedance on the output voltage are experimentally studied.Considering the load circuit easily affects the output voltage,a synchronous charge extraction circuit controlled by PIC16LF1824 is designed and tested.The results show that the energy harvesting circuit basically realizes the self-sufficiency of temperature measurement module.Thirdly,a temperature warning and forecasting systemis designedinthis paper.Through the calculation of four kinds of early-warning values,such as temperature rising rate,similar temperature difference,relative temperature difference and temperature threshold in the hostcomputer,the comprehensive analysis and judgment are carried out,the early warningof the temperature fault is realized and the sensitivity of the temperature early warning is improved.On the basis of relevant operation data such as working current,contact temperature and room temperature,the support vector machine algorithm is appliedto establish the regression prediction model of contact temperature,and the prediction of the changetrend of contact temperature is realized.Through the temperature rise test of switch cabinet,the validity ofthe wireless temperature measurement and pre-warning system is verified.The collected data are processed and analyzed through the established regression prediction model,the prediction of the contact temperature is achieved.The results show that the system can achieve the on-line monitoring,early warning and prediction of temperature in cabinet.