| Power cable plays a key part in the transmission of electric energy in modern industry.On-line inspection of cable insulation status is an key link to ensure the secure-safe,dependable and jarless running of cables.The commonly used cable insulation detection methods are mostly carried out under the operating voltage,but it is necessary to withdraw the power cable from the line operation for off-line detection.Moreover,repeated tests may cause damage to the cable insulation,thus expediting the aging of insulation.To figure out these conundrums,according to the transmission peculiarities of electromagnetic transient signal in the cable,this paper presents a cable insulation detection method on the basis of the transmission peculiarities of transient voltage in the cable.The dominating part of this article are as shown below:(1)Based on the distribution parameter models of uniphase and triphase cables,the numeration methods of cable distribution arguments,characteristic impedance and propagation coefficient are presented.According to the aging model of cable insulation,the aging model of insulation layer is given,and the numeration formula and measurement method of insulation resistance and capacitance are given to evaluate the insulation condition of cable.The expression of the voltage transfer function in frequency domain is derived from the distributed parameter model of the aging insulation cable and the centralized parameter model of the insulated fault cable of the intermediate joint.Furthermore,the conformance of the frequency domain voltage transfer function under the standard lightning impulse voltage and the oscillating impulse voltage is verified by simulation,and then the transient voltage transfer characteristics in the cable are analyzed in theory.(2)A method of cable insulation state monitoring based on transient voltage transfer characteristics is proposed,and the realization way of the detection method is given.Based on the PSCAD simulation terrace,uniphase and triphase cables models under standard lightning shock voltage are built.Two kinds of means are proposed to simulate the aging of cable insulation.One is to simulate the aging of cable insulation by changing the ply and relative permittivity of cable insulation lagging.The insulation fault of intermediate joint is simulated by changing the insulation resistance of intermediate joint in parallel.Finally has carried on the standard lightning impulse voltage cable insulation condition detection of the simulation calculation,get the good cable insulation and insulation degradation cable voltage under the frequency domain transfer function,and put forward by solving Pearson correlation coefficient of P and remaining amount D to the aging of the insulation cable voltage under the frequency domain transfer function has carried on the quantitative analysis,the simulation results verify the feasibility of the theoretical analysis.(3)The laboratory test platform for testing the cable integral insulation state was built,and the accelerated thermal aging and accelerated electrical aging test schemes were proposed to simulate the cable integral insulation aging,and then the field test platform for the insulation fault detection of the cable intermediate joint was built.By injecting standard lightning impulse voltage into uniphase and triphase cables,the simulation results are verified by measuring the insulation resistance of the cable insulation and quantitative analysis of the voltage transfer function in the frequency domain.The results indicate that the suggested means is accurate and effective. |
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