Power transmission & distribution (T&D) lines are used to carry electrical energy from one substation to another before it reaches a consumer from generation units. Power network can be broadly classified in to low(<1000V), medium (Upto35kV) and high voltage(>35kV) lines. Low voltage distribution lines are used for last mile connections. Recently, we read about damaged power network in West Bengal, Orissa due to cyclone Amphan which affected lakhs of consumers. Whenever, power network gets damaged in storm or any other natural calamity, we often wonder about alternate solutions such as underground cables which prima facie looks like a safer option than overhead lines and less prone to external damages. Underground network is not only safer than overhead network but also increases the aesthetic value. However, share of underground cables in transmission & distribution is low in India, for e.g. MSEDCL has ❤% underground T&D network. It is slightly better in urban areas for e.g. ~12% for Tata power in Mumbai. It seems very strange that for a seemingly useful solution, the uptake is astoundingly low not just in India but also in developed nations.
Before, we jump into the comparisons, if one is interested in details of overhead or underground network, can read here.
Under-grounding as a concept is not new, has been in discussions for quite some time. In fact, govt. has earmarked large sum of money under IPDS scheme mentioned here. Few DISCOMS such as BESCOM have a 3-year plan to lay underground cables.
“The scheme has earmarked Rs 20 billion for executing these projects. It envisages the implementation of underground cables aggregating 18,008 km across various states. Maharashtra has the highest target with 5,762 km, followed by Uttar Pradesh with 2,864 km and Rajasthan with 2,179 km. Underground cabling projects have also been proposed under the Smart Cities Mission to ensure reliable power supply and enhance aesthetics”
But there are certain operational, economic etc. challenges with the underground network which needs to be addressed. Before getting into potential solutions, let us take a quick look at the comparison of underground and overhead network.
Most prohibiting factor for an underground network is the economics. As can be seen below, it costs 3–4 times higher than overhead network for a 11kV voltage line. It is costly primarily due to insulation requirements in cables. Insulation is cheaper for overhead network since air, which is free of cost, insulates the lines. Also, road restoration costs get added up to the per km estimates for an underground network.
Also, in case any fault occurs, the outage time increases for a cable as mentioned here. Hence, under-grounding makes sense if fault occurrence in cable is 25+ times lower than fault occurrence in cables.
“If a fault occurs on a 400kV underground cable, it is on average out of service for a period 25 times longer than 400kV overhead lines. This is due principally to the long time taken to locate, excavate and undertake technically involved repairs. These maintenance and repairs also cost significantly more.”
Additionally, any mending work for underground network requires a lot of co-ordination with civic bodies. There might be challenges with co-ordination leading to damage to lines as seen here.
“450 underground cables laid by the power supplier have been “destroyed” during works undertaken by the Pune municipal corporation (PMC) and Maharashtra Natural Gas Limited (MNGL)”
In addition to challenges such as economics, fault location under-grounding suffers from operation challenges as well. As captured here, one of the challenges is that underground system cannot be operated above 66kv due to insulation difficulties whereas overhead lines can manage up to ~400KV. This prohibits underground network being used for transmission network since transmission occurs at high voltage levels.
Does this mean that under-grounding cannot be a solution going forward? Under-grounding is a necessity in certain highly populated areas and cost dynamics get better in certain cases depending on the terrain as captured here.
“…As a sub-transmission and distribution line cover the landscape and population structure within the city/town/village throughout its length, the choice between OH and U/G cabling system has be taken based on safety, esthetic look, clearance available, rules and regulations in force and other factors . The sub transmission and distribution lines may also be a mix of both as per actual site conditions. Underground power distribution system is an expensive choice but is mandatory to supply electricity in highly populated areas”
European nations are ahead in adoption of underground network technology. Finland has an adoption rate of ~40% for low voltage network and ~20% for medium voltage as captured here. Moreover, lot of advancements are occurring in this space to address the current challenges. For e.g. advancements are taking place to address the voltage levels underground network can manage.
“Concurrently, the operating voltage levels have also increased significantly in the range of 220 kV to 400 kV. These developments can definitely take the cable technology to the new technical dimension and make them more deployed in the transmission and distribution networks.”
DISCOM in India made advancements to address fault detection and resolution challenges as mentioned here.
“Tata Power Delhi Distribution (Tata Power-DDL) has implemented GPS mapping technology to map its underground cables along with RFID (Radio-frequency Identification Detector) marker installation on cable splices for speedier fault location and resolution”
Moreover, the overall cost of laying the underground network can be shared with other players such as communication players, as planned by BESCOM (Karnataka DISCOM). BESCOM is planning to lay optical fiber alongside power distribution network. Such arrangement may lead to cost sharing for ground digging and restoration work.
However, advancements are not only taking place in the underground technology, overhead network is making advancements to address its challenges primarily to address service response and outages due to storm, as captured here.
“Many utility companies also deploy drones in unique ways. Commercial drones like those from Yuneec can reduce the response time for customer calls. In some utility districts, data from drones is used to share the latest information with technicians and customers on everything from the height of utility lines to the functionality of neighborhood storm drains. And in a pinch, drones can aid in aerial reconnaissance at sites that have been rendered otherwise inaccessible by storms.”
To summarize, whether underground network in India will catch up or not boils down to economics, terrain requirements and government support. However, comparative economics should include economics of the solutions that can be deployed to address the current challenges in underground as well as overhead network. Another important question that remains is that who pays for this — government, TRANSCO (Transmission companies) & DISCOMS (Distribution companies) or consumers?