Study On Temperature Field And Ampacity Of Multi-circuit Cable Lines Considering Its Current Distribution And Circulating Current In Sheaths

Because of the complex urban terrain and limited underground space, more andmore multi-circuit power cable lines with muli-cable parellel per phase have been usedin order to meet the power supply in big cities. While the exiting design criterions arenot applicable for calculating the parameter of multi-circuit power cable lines withmuli-cable parellel per phase. The past researches often focus on the circulating currentin sheaths, uneven current distribution and temperature field ampacity independently.Most literatures only involved one of these research areas, instead of forming them intoa system. Furthermore they often adopted recommended values in IEC-60287standardas parameters in researches, which are quite different from the actual operation of cabledata, leading to distinct deviations between theoretical numeral value and practicalresult of Ampacity.In this paper, other than traditional research, a fine modle is built to calculate thetemperature field and ampacity of multi-circuit cable lines considering its currentdistribution and circulating current in cheaths. And then take220kV Pingjiang and otherfive cable lines as examples to make deep research. The main achievements are asfollows:①Classify the power cables by insulating material, voltage class, structural featureand installation conditions etc. Take YJLW02-127/220kV twisted polyethylene cablewith2000mm2Cross-sectional area as an example to introduce its basic structure. Thencontrastive analysis on characters and applied scopes of four kinds of typical cable linesinstallations, including direct burying, installation in pines, cable trench laying andtunneling method installation. Based on the existing lituratures, build the optimalselection evaluation index system of installation ways taking the reliability, economy,detectability and ampacity into consideration.②Build the equivalent calculation model of circulating current in cheaths inmulti-circuit power cable lines. Deduce the method computing the circulating current insheaths and current distribution of multi-circuit power cable lines with muli-cableparellel per phase, solving by programming. Take220kV Pingjiang and other five cablelines as an example to test circulating current in sheaths of No.1-24cables according to4current-loading phase sequence arranges under2different arrangements, and also testcurrent distributions of power cable lines with muli-cable parellel per phase. All of the above is the foundation of setting up the modle to calculate the temperature field andampacity of220kV Pingjiang and other five cable lines considering its currentdistribution and circulating current in sheaths.③According to the detail parameters and installations methods of220kV Pingjiangand other five cable lines, build the physical model computing the cable lines’temperature field. Based on the principle of heat transfer, heat conduction differentialequations of cables and surrounding installation areas are established. Then select andcalculate initial condition, Internal heat loss and thermodynamic parameters separately,with which the mathematical model can be built of calculating the temperature field andampacity of220kV Pingjiang and other five cable lines considering its currentdistribution and circulating current in sheaths. Divide the computational domain withtriangle mesh automatically and solve the heat conduction differential equations to getthe temperature distributions of cables and surrounding installation areas under100%rated current and120%rated current. Finally, subtense truncation is used to analyze thecables’ ampacity under different installation ways.④For the increasing complexity of underground cable lines’ installation conditonsand external environment, this paper takes220kV PingJiang1stLine and2ndlines undercable trench laying method as an example. Analyze the influence on ampacity of220kVPingJiang1stLine and2ndLine from the changes of installation conditions, such ascable trench depth and cable layer spacing etc, and external environment factors, suchas air temperature and Soil thermal resistance coefficient etc. Finally conclude theregularities.