Research And Experimental Verification Of The Influence Of Harmonics On Cable And Its Joint Based On FEM Coupling Model

Compared with the traditional overhead line,power cables can meet the complex application environment,achieve a further transmission distance,and greatly saving urban land resources,so it’s widely used in modern power grid..Most of the existing researches on cable and its joint temperature are based on the fundamental wave,the influence of harmonics on their temperature was not quantitatively analyzed.With the large number of distributed energy and nonlinear load connected to the power grid,the harmonic problem in cable is becoming increasingly serious.Harmonic will cause additional loss of cable and joint,and then lead to temperature rise,accelerated aging and even burnout fault,which means the influence of harmonics on cable and its joint cannot be ignored.Therefore,study the influence of harmonic problem on power cable and its joint,and determine the temperature field distribution,are of practical significance to evaluate the current-carrying capacity of cables under harmonic environment,optimize cable operation in time and improve the safety and stability operation level of power system.In order to deeply study the influence of harmonics on cables and their joints,the following researches are carried out in this paper:1.The harmonic impedance model of cable is established,and the resonance phenomenon caused by cable is analyzed based on the harmonic impedance model.2.In order to solve the problem that the one-dimensional equivalent thermal circuit model of IEC-60287 standard can’t calculate the temperature of cables and their joints under harmonic environment accurately,an iterative formula considering temperature characteristics of materials based on electromagnetic-thermal coupling method is proposed,which provides a theoretical basis for quantitative analysis of the influence of harmonics on the loss and temperature of cables and their joints.3.In order to quantitatively analyze the influence of harmonics on the cable body,the2 D electromagnetic-thermal coupling model of 10 kV three-core cable and 110 kV single-core cable under harimonic environment are established.On the basis of the numerical simulation calculation models,the relationship between the temperature of cable and core current carrying is proposed.The influence law of harmonic on cable is discussed,and the relationship between AC resistance,loss and temperature of cable and harmonic degree and harmonic content are obtained.4.Compared with the cable body,the structure of cable joint is more complex,which is the weakest link of the line.In order to quantitatively analyze the influence of harmonics on cable joints,the 3D electromagnetic-thermal coupling model of 110 kV cable joint under harimonic environment is established.The influence of contact resistance on joint temperature is analyzed.The temperature distribution of the cable and its joint under the fundamental and harmonic environment are compared and analyzed,which provides a theoretical basis for determining the current carrying capacity of the whole line.5.In order to verify the validity of the electromagnetic-thermal coupling method for calculating cable temperature under harmonic environment,an experimental system of cable temperature rise under harmonic environment is built.Taking the low-voltage cable as the research object,the cable temperature rise test under harmonic environment is carried out,and the results are compared with the numerical simulation results,which proves the effectiveness of the electromagnetic-thermal coupling method.The research results of this paper can provide reference for power dispatching and operation and maintenance departments to evaluate the operation of cables under harmonic environment.