"Accurate Electro-magnetic Transient Modelling of Arbitrarily Shaped Cables"
Anuradha Kariyawasam (Ph.D. student)
Supervisor: Dr. Aniruddha Gole
Aim of Project
In present power systems, underground cables are increasingly being preferred to overhead transmission lines. Underground power cables are available in many different varieties such as coaxial, sector-shaped, pipe type, etc. When it comes to electro-magnetic transient (EMT) modelling, frequency dependant parameters of these cables (which also depend on the cable cross-section) should be calculated throughout a large frequency range. However, some of these cable shapes are unconventional and there are no analytical formulae available to do the parameter calculations. Purpose of this research is to successfully create models for such cable shapes.
Description of Project
Frequency dependant resistances and inductances of arbitrary-shaped cables can be calculated using the conductor subdivision method, in which each conductor of the cable is partitioned into a number of small sub-conductors. The shape of the sub-conductor can be circular, square or elemental. However circular and square sub-conductors require a large number of subdivisions to get accurate results, thus requiring significant computational effort and memory. The elemental sub-conductor technique which is directly applicable for cables with circular and coaxial cross-sections requires a smaller number of subdivisions to reach accurate results.
This research initially investigated applying the elemental sub-conductor technique to sector-shaped cables. Impedance of the ground return path is calculated by subdividing ground into rectangular sub-conductors, size of which change with the frequency. Impedances calculated using this method are compared with those obtained by closed form approximate formulae. Already-developed simplified equations are used to calculate capacitances of sector-shaped cables approximately. This method is refined to include the effect of ground and the approach is validated using a finite element analysis. For a sector-shaped cable example, the frequency domain characteristics are discussed in detail. Different propagation modes are analyzed by plotting velocities, attenuation of the modes (e.g. ground mode) as a function of frequency. The parameters obtained are then used to perform time-domain electromagnetic transient simulations of the sector shaped cable system. The EMT-simulation results are verified by simulating a case with linear terminating impedances and comparing the time-domain results with those obtained using a numerical inverse Laplace transform approach.
As a complete time domain model is developed for sector-shaped cables using the proposed method, it is identified as a potential method to be used for other cables shapes. Next, this research will focus on building models for other arbitrarily shaped-cables using the proposed method along with other new approaches.
Accepted/Published Papers
K.K.M.A. Kariyawasam, A. M. Gole, B. Kordi, H.M.J.S.P. De Silva, "Accurate Electromagnetic Transient Modelling of Sector-Shaped Cables", International Conference on Power Systems Transients, Delft, Netherlands June 2011 FULL TEXT