Portable earthing equipment-an advanced maintenance technique for 400 kV double circuit transmission line under induced voltage condition

There has been tremendous growth in the power industry in India during the last five decades. Presently, more than 35000 circuit kilometers of 400 kV and above transmission lines are transmitting bulk power within the regional grids and also from one regional grid to another regional grid. As India is a vast country with area about 3 million sq.kms, the 400 kV transmission lines are quite long of the order of 250 to 350 kms. Most of the transmission lines are on double circuit towers. For maintenance of transmission lines, shut down of both the circuits is not normally available. Maintenance of these double circuit lines with one circuit live has to be done under induced voltage conditions. However, very high level of induced voltage of the order of 23-82 kV under various operating conditions persist for a 300-350 kms. Long 400 kV double circuit line connected with 63 MVAr shunt reactors at both ends. This paper describes how we have been able to control the induced voltage to a very low level of 8-10 kV. Further, design of portable earthing equipment and earthing schemes suitable for such maintenance work under these conditions with utmost safety are also described in the paper.