Study of voltage harmonic contamination in the(MV) cables with metallic screen of multipoint earthand sheath voltage limiter in the micro gridnetworks

In recent years, with the growth of usingrenewable energy sources and their connection to the network,some unexpected problems in electrical equipment areobserved. By integrating renewable energy sources with theability to produce megawatts and two-way electrizing thecables, we observe the complexity of utilization issues, damageand cable failure arising from harmonic contamination.Renewable energy sources, due to the use of power electronicsequipment’s and static converters with high switchingfrequency in their manufacturing technology, are a potentialsource of voltage and current harmonic contamination.Generally, in the medium voltage cables to reduce and removeelectric field, the metallic screen method with single-point,double-point, multipoint earth with the sheath voltage limiteror cross bonding is used. However, use of multipoint methodearth method with sheath voltage limiter is more efficient thanthe other methods and reduces the rate of losses in the metallicscreen and the number of eddy current loops in the metallicscreen circuit, but this method results in increase of harmonicemission in the main conductor voltage of cable. By integratingrenewable sources of energy and changing the operatingconditions, especially the two-way electrizing of equipment’sand increase of the harmonious contamination arising fromconnection of such resources in micro grids, it is necessary toevaluate the effects of such resources on the performance ofsensitive network equipment’s such as cables and shields. Inthis article it has been attempted, first, the matrix parametersof RLC of three-phase cable (monopole) are calculatedaccording the conduction and insulation features. Then therate of increase of voltage harmonic contamination in the mainconductor of cable is examined by multipoint earthing methodand sheath voltage limiter with presence of renewable sourcesof energy. Also the rate of annual energy losses in the metallicscreen is calculated by the two techniques of multipointearthing equipped to sheath voltage limiter and cross bondingis calculated and compared. Results show that in themultipoint method with sheath voltage limiter the rate ofvoltage harmonic contamination has increased ۵۵%in the cablemain conductor. While, the rate of losses energy in the metallic screen has reduced ۷۱% compared to the cross bondingmethod. It is necessary to mention that in both methods theamount of the induced voltage in the metallic screen of cable iswithin the range determined by provisions of ۵۲۳-۰۵-۰۱.Simulation for this study has been performed in theMatlab/Simulink setting and in a real time form.

Keywords:

Harmonic contamination , Metallic screen , Eddycurrent , harmonic emission , renewable sources of energy