With one of the most highly available systems and lowest transmission losses, Delhi Transco Limited (DTL) is amongst the few best-run state transmission utilities in the country. DTL, incorporated in 2002 after the unbundling of the erstwhile Delhi Vidyut Board, has been continuously taking initiatives and reducing its transmission losses to keep pace with the manifold challenges in the power sector through the deployment of advanced technology. The transco has been an early adopter of gas-insulated switchgear (GIS) substations, underground cables, substation automation and other technologies. It has implemented the islanding scheme for Delhi that isolates the state grid from the central grid in case of exigencies to ensure uninterrupted power supply to critical segments. In the coming years, the transco plans to focus on installing high temperature low sag (HTLS) conductors, monopole and multicircuit towers, as well as implement voltage source convertor (VSC) transmission technology to further enhance its operational performance and improve power quality.
DTL’s transmission network consists of a 400 kV ring around the periphery of Delhi that is interlinked with the 220 kV network spread across the city. The transco has 43 substations, of which, 39 are at the 220 kV level and the remaining four are at the 400 kV level. The utility’s transformer capacity at the 400 kV and 220 kV levels stood at 5,095 MVA and 12,820 MVA respectively. The total transmission line length was 1,075.03 ckt. km. Of this, around 249.19 ckt. km is at the 400 kV level and 825.81 ckt. km is at the 220 kV level. The 220 kV transmission lines include 622.37 ckt. km of overhead lines and 203.43 ckt. km of underground lines.
DTL’s transmission system availability stood at 99.11 per cent during 2018-19, just a notch lower than the 99.35 per cent in the previous year. The utility’s transmission losses have remained below 1 per cent in the past three years and stood at 0.92 per cent during 2018-19.
The transco has successfully handled the growing peak demand in Delhi on a year-on-year basis. The peak demand met has increased from 6,261 MW during 2016-17 to 7,016 MW during 2018-19, recording an increase of 12.05 per cent. Further, the energy supplied went up by 5.1 per cent from 30,787 MUs during 2016-17 to 32,360 MUs during 2018-19. Meanwhile, load shedding declined from 31.5 MUs to 17.8 MUs in the same period. On July 2, 2019, DTL met the highest ever peak demand of 7,409 MW.
In order to enhance its efficiency and productivity, DTL is using state-of-the-art technologies in its operations. Owing to land acquisition issues and in order to minimise its associated impact on the environment, DTL is focusing on setting up space-saving GIS substations in place of air-insulated switchgear (AIS) substations. DTL has 15 GIS substations at present – 14 at the 220 kV level and one at the 400 kV level. Also, due to non-availability of right of way (RoW) for the erection of overhead transmission lines, DTL has laid nearly 200 ckt. km of underground cables at the 220 kV level. Further, the company has been installing substation automation systems (SASs) for the past 10 years. Currently, 14 of its substations have SASs with remote operation capability.
In addition, the company has implemented SCADA systems for accessing real-time data of the entire network. It is one of the first utilities in India to operationalise SCADA, as early as in 2002. The company was the first state transmission utility in India to operationalise intra-state availability-based tariff metering, on April 1, 2007.
DTL has also implemented the enterprise resource planning (ERP) software, which offers integrated management applications for the main business operations of an organisation.
DTL has earmarked a capital expenditure of Rs 40 billion by 2022-23. The majority of this (60 per cent) is planned for the construction of transmission infrastructure. About 10 per cent will be utilised for creating a fully automated power transmission grid network in Delhi.
By 2022-23, the utility plans to add transformation capacities of 6,500 MVA at the 220 kV level and 6,000 MVA at the 400 kV level. The associated transmission corridors are planned for upgradation with high ampacity corridors through the utilisation of HTLS conductors, and monopole and multicircuit towers. At present, about 114.82 ckt. km of 220 kV transmission lines have been upgraded with HTLS conductors and another 280 ckt. km of transmission lines are planned for conversion to high capacity transmission corridors.
DTL also plans to set up digital substations in its network. To this end, the process for setting up a centralised control centre in a phased manner is in progress.
Although the transco has its own centralised testing lab (CTL) with capbilities for conducting specialised tests such as BDV, DGA, Tan delta and SFRA on power transformers, it is now planning to secure NABL accreditation. In addition, the concept of smart grid is being implemented in a phased manner, and most of the control and protection transducers have been replaced with intelligent electronic devices. Further, a roadmap has been prepared by the utility to expand the smart grid concept in the coming years.
Issues and the way forward
Some of the key challenges being faced by DTL are lack of RoW permission for the construction of transmission lines and issues in reactive power management during off-peak periods, that is, in winter nights. It must be noted that the load pattern of Delhi is quite dynamic with 7,500 MW in peak periods and 1,500 MW in off-peak periods; this affects power quality supply. In order to overcome this issue, DTL plans to install reactors. It is in discussion with the Central Electricity Authority/Northern Regional Power Committee for the installation of static synchronous compensator/ static VAR compensator so that reactive power management can be carried out in real time.
DTL plans to install VSCs and other devices to utilise minimum RoW for optimal power transfer as underground cables have limitations in comparison to overhead transmission lines. While the installation of GIS substations has to some extent solved the problem of availability of space, the company is in the process of establishing substations on a floor basis. Also, DTL has taken up the matter of land acquisition and RoW permissions with land-owning agencies and is seeking their help to provide a single-window system.
Despite challenges, DTL is well positioned to meet the anticipated power demand growth in the state. Further, its continued focus on deployment of advanced technology will ensure that it remains among the leading state transmission utilities in the country.