356 / 2019-03-08 14:41:17

The Suitability Analyses of Sheath Voltage Limiters for HV Power Cable Transmission Lines

power cable,sheath voltage limiter,suitability,lightning current,short-circuit current

With the rapid development of urban power system, the proportion of high voltage (HV) power cable transmission lines used in urban power grid was increasing. Under the lightning striking, switching or fault conditions, a high induced voltage could generate between the metal sheath of cable and grounding, which could cause great harm to the insulated sheath of cable, so it was necessary to protect and limit the sheath induced voltage of HV cable. The sheath voltage limiter (SVL, or sheath protectors or surge arresters) could be installed on the metal shields at the cross-bonding joints in cross-bonding grounding cable lines or insulated joints (or ends) with one single-point grounding cable lines. In the case of high short-circuit current, the excessive power frequency (or temporary) overvoltage on the insulated sheath of cable may exceed the voltage withstand ability of the SVL. Due to the long duration of power frequency overvoltage, it may cause the SVL to explode due to the overheating. Therefore, it was important to choose the SVL parameters to be suitable for the energy and current rating of SVL. In order to clarify the temporary and transient characteristics of sheath induced voltage and its influences with the SVL, the models of simulating calculations were established based on a typical 220kV cable transmission line and with the PSCAD/EMTDC software in this paper. The modeling processes for the power cables and SVL were also presented. The transient characteristic of sheath induced voltage and its influence with the SVL were calculated under the conditions of different short-circuit currents and lightning strike currents, respectively, through the cable core. Two kinds of sheath SVLs with two grounding manners, i.e. cross-bonding grounding and single-point grounding, were investigated. According to the energy absorption capacity of each SVL, the suitability curves of SVL for different cable lengths and short-circuit currents were obtained, which provided the basis and the improvement approaches for the engineering design of cable grounding. Furthermore, based on the different suitability curves of SVLs, the design principles and typical parameters of the improved SVLs were presented. The improvement effect of a newly improved SVL was analyzed also. The methods used in this research could also be extended to other voltage class cable transmission lines and/or other laying methods. The studied results would provide a certain reference for the system design and safe operation of HV cable engineering, which should have a very important significance in practice.