With growing dependency on electricity for almost everything in our daily lives, the necessity to have 24x7 electricity is a basic need rather than luxury. Impact on economy and disruption in public life goes much beyond the economics related to building transmission infrastructure to withstand multiple contingencies.
November 03, 2020. By News Bureau
With growing dependency on electricity for almost everything in our daily lives, the necessity to have 24x7 electricity is a basic need rather than luxury. Impact on economy and disruption in public life goes much beyond the economics related to building transmission infrastructure to withstand multiple contingencies. The societal cost of energy not served could be huge and the cost-benefit of same can far outweigh the cost-benefit of a transmission project from only utility’s perspective. Governments and regulators need to consider this aspect as well, to support investment in such cases.
The power failure event of 12 th Oct’20 in Mumbai once again reminds us that the Grid can never be taken for granted. Plans must be in place to survive multiple contingencies which may occur simultaneously. These can be in form of network suitable to withstand these contingencies on a sustained basis or at least to allow sufficient time for operators to take preventive actions, while such situation is developing.
The two 400 kV substations of Kalwa & Kharghar, are the main source for power infeed for Mumbai, and both of them suffered outage of elements during the unfortunate sequence of events of 12 th Oct’20, as per the POSOCO report on the event. The power to these substations is fed from Padghe and Pune substations, among others. While the system may be designed for n-1 contingency, more than one events which happened on that day can occur again as well. Moreover, due to the need to keep the system ready to meet such eventualities, the shutdown windows available for carrying out maintenance or repair of the assets, also get limited. This further adds to the problem as the risk of breakdown increases. Hence, it is very important to plan for multiple contingencies and have system built accordingly.
Having said that, it is also true that it has always been a challenge to build new lines and substations in & around Mumbai, given Mumbai’s severe ROW limitations. Thus solutions, which can enhance capacities of existing corridors and transmission lines can be of great advantage here. Some of these solutions could be as follows:
a) Reconductoring of existing transmission lines from existing ACSR conductors to HTLS (high temperature low sag) conductors, on the same towers, can help to double the power carrying capacity of the existing lines. Such reconductoring and capacity enhancement can be executed in much shorter time as compared to building a new line. With the use of HTLS (high temperature low sag) conductors, even the ground clearances of these transmission lines can also be improved, which can bring collateral benefits to other stakeholders along the transmission line route.
b) It may be worthwhile to explore if any of the existing single circuit transmission line(s) can be converted into double circuit lines within the same corridor, by use of space saving tower designs such as monopoles or narrow base towers, minimizing the need of new ROW (right of way).
c) Going a step further, an existing 220 kV line corridor can be utilized to build a 400 & 220 kV multi circuit multi voltage corridor, where, by suitable tower design, additional ROW can be minimized. This would in turn help to ensure that projects get commissioned as per plan, as risk of work stoppages due to ROW issues get minimized.
d) In addition to above, Battery energy storage systems (BESS), placed at appropriate locations in the grid can bring in additional degree of security. They can come in automatically to the rescue of the Grid and sustain the load for pre-planned durations, thereby allowing breathing time to grid operators to review the situation and take appropriate preventive actions. Mumbai transmission system is already having some islanding schemes. Benefit of BESS solutions in each of these islands can be evaluated.
All the above solutions can be first validated by conducting a power system study for Mumbai and for that matter any other network. The study can be undertaken to simulate varied operating scenarios including multiple contingencies, to decide the strengthening required to ride through them. Field survey of the existing lines and corridors can be quickly carried out to check the feasibility of above solutions.
From the perspective of time, space & capital, these solutions score over the option of building new lines, while they also help to minimize the impact on environment, as existing ROW is used instead of new ones.
Hence, while construction of new lines and new substations to feed power to Mumbai (and other such critical areas) can continue to be studied, above options can also be looked into by system planners and utilities. Such solutions can go a long way to achieve the desired capacity increase / improving resiliency of the grid, and avoid such events in future.
(Opinions expressed by the author are personal)
- Amitabh Singhal, Head Technology and Power Systems, Solutions Business, Sterlite Power
