Fault Current limiter using Series reactors in indian Power System

The Indian Transmission Grid is divided into five regions viz. Eastern Region (ER), North-eastern Region (NER), Northern Region (NR), Western Region (WR) and Southern Region (SR) with each region comprising of several states. All the above five regions are presently synchronised to form a single pan India Power Grid resulting in increased stiffness of the Indian Grid and improved system reliability. Further, the Indian Grid is interconnected with the neighbouring countries viz. Bangladesh, Nepal, Bhutan with plan for further interconnection with Sri Lanka. Further, each region has utilities, which are responsible for Generation, Transmission and Distribution of power in the state. To meet the growing power demand, particularly in Northern region and Western region, generation capacity addition associated with commensurate expansion and strengthening of the transmission and distribution network are being carried out due to which the short circuit (fault) levels at a number of stations are approaching or exceeding the designed equipment ratings. This may cause severe mechanical & thermal stresses on the equipments leading to insulation problems, equipment failure/damage and unwanted operation of the associated protection systems. One way to restrict fault levels within the design limits would be to upgrade the substation by replacement of switchgear, earth mat and other associated material/equipments. However, the option is costly and may not be feasible as it involves long periods of continuous shutdown. This paper explains the planning process and the studies carried out to limit fault current through implementation of the series reactor in context of the Indian national grid. Various aspects like economic benefits of the series reactor compared to up gradation of the switchyard equipments corresponding to higher Short Circuit levels, selection of reactor ratings and its placement in substation, performance of series reactor under steady state and under transient conditions have also been discussed. Mitigation measures adopted to control the Transient recovery voltage (TRV) associated with switching of dry type air core reactors have also been mentioned. The paper also describes the field experience gained during installation & commissioning of these Series reactors in 400kV Bus and on 400kV Lines in 400kV Ballabhgarh and Mandola existing substations in NCR area.