On-line monitoring and analysis of the dielectric loss in cross-bonded HV cable system

Abstract

Dielectric loss has long been recognized as one of the most important indicators of cable insulation health. Although huge efforts have been made in the past to measure the dielectric loss of cable circuits, there has been no report of any successful on-line techniques for the purpose. This paper proposes a new on-line insulation dielectric loss monitoring method, based on separation of currents collected from the co-axial cables connecting the cable sheathes and the cable link boxes. The principle and theoretical foundation of the method are demonstrated. MATLAB simulations, based on the real cable parameters in a 110 kV cable tunnel in China, indicate the error of the proposed method is less than 1×10 -3 %. The criteria for determining the relative dielectric loss in cable segments, based on the leakage current separation results, are demonstrated at the end. Initial results and analysis of implementation of the proposed method in the real world 110 kV cable tunnel are presented.

Monitoring of MV Cable Screens, Cable Joints and Earthing Systems Using Cable Screen Current Measurements

“…Unfortunately, it is possible that some earthing systems which have not been tested are damaged. It is worth underlining that DSOs have problems with thieves, who steal copper elements of earthing systems, or unreliable contractors, who use iron rods instead of copper or a combination of both-copper rods close to the surface and iron rods underground in order to pass visual inspection and get the work approval [77]. It is noted that monitoring of cable segments may be improved if the return factor (RF 110/15 ), which occurs under phase to earth fault conditions, is analyzed.…”

Feasibility Study on Online Diagnosis of Aging and Deterioration of Medium Voltage (MV) Three-Core Cable Based on Impedance Spectroscopy

“…Then the impedance spectroscopy of the single-phase cable with local deterioration can be calculated segment by segment. Firstly, the impedance Zb at position x = lb can be directly calculated by (13). Secondly, the impedance Za at position x = la can be calculated by taking Zb as the load.…”

“…Currently, the value of tan δ can be obtained either through offline testing or online monitoring [12]. The method of online monitoring is realized by calculating the phase difference of the monitoring values of voltage and current at both ends of the cable [13]. However, it is difficult to obtain the voltage signals from the cable joint without affecting normal operation.…”

Simulation of sheath voltage, losses and loss factor of high voltage underground cable using MATLAB/Simulink

“…Sheath losses are current-dependent and can be divided into two categories according to the type of bonding [4], [24], [25]. Sheath circulating losses appear due to the sheath bonding from both ends as a result of passing a current between the sheath and the ground.…”

“…It was connecting the second cable's sheath end-point with the third cable's beginning sheath point in the last section to make the directional summation of induced voltages in all parts equal to zero without flowing any circulating current except the eddy currents. This method is most likely to be employed in very high voltage cables because its expansiveness [4], [23]− [25].…”