Transient analysis of mechanically switched capacitors with and without damping network connected to A.C grid

Abstract

Mechanically switched capacitors (MSC) are very well known reactive power compensation devices which are extensively in use in power transmission systems. However, during switching of MSC in a high voltage grid, significant transients are found to appear across the capacitor bank bus as well as different elements of MSC which may lead to insulation degradation affecting the long term performance of the capacitor banks. An improved version of the MSC is MSCDN where a damping network is employed with the capacitor banks to damp out the transient oscillations. However, during switching of a MSCDN plant significant transients are observed across its different elements. Considering the afore-said fact, in this contribution, a comparative study of transient behavior of mechanically switched capacitors with and without damping network is presented during switching in a 400 kV A.C grid. Transient simulations are performed on an exemplary MSC and MSCDN model using PSCAD/EMTDC software. It has been observed that there is a significant reduction in transient overvoltage and inrush current in switching a MSCDN plant when compared to a mere MSC switching. Moreover, the percentage reduction in transient overvoltage and inrush current during switching a MSCDN plant is found to depend on the design of damping network which may be important to analyze the transient behavior during switching in a high voltage A.C grid.