Circulating MVAR control in Rajasthan (India) transmission system

Large number of substations have been upgraded to higher voltage level by loop in loop out of existing transmission lines to meet the increasing load demand. Therefore; large number of loops of different voltage levels has been created between substations. Transformers of different MVA ratings; percentage impedance and tap ratios have been installed at the substations. Presently there is no coordination between adjoining substation operators for tap setting of transformers. Therefore; due to mismatch of transformers tap ratio and percentage impedance; circulating MVARs are flowing on transmission lines resulting in higher transmission losses; increase loading of transformers & lines and poor voltage profile. In this paper impact of circulating MVAR flow and its control through coordinated tap setting of transformers has been studied. Rajasthan power system has been considered to carry out the studies and has been modeled in Mi-Power software. Rajasthan Power System have total 750 buses comprising 2 nos. 765 KV; 35 nos. 400 KV; 147 nos. 220 KV; 504 nos. 132 KV and 62 nos. generator buses with load of 10000 MW. Effect of coordinated Tap setting of transformers on circulating MVAR flow; transmission losses; network voltage profile and lines & transformers loading have been analyzed. Proposed methodology has been successfully tested on Rajasthan power system to remove the circulating MVAR flows on 220 kV and 132 kV network.