--- title: "New EHV trends and adoption in Nepal" subject: "High Voltage Engineering" chapter: 1 key: "semester_8/high_voltage_engineering:ehv-trends-nepal" source: https://www.bctengineer.com/q/semester_8/high_voltage_engineering/ehv-trends-nepal site: BCT Engineering --- # New EHV trends and adoption in Nepal High Voltage Engineering · Chapter 1: Evolution of Power System - Asked in: 2080 Chaitra, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/high_voltage_engineering/ehv-trends-nepal - Whole chapter: https://www.bctengineer.com/md/semester_8/high_voltage_engineering/chapter-1 ## Question Discuss the different new trends emerging in EHV systems worldwide and how Nepal can adopt those trends to modernize and upgrade its power sector. ## Short answer Global EHV trends include UHV AC/DC, VSC-HVDC, FACTS, GIS, smart grids and cross-border interconnections. Nepal should complete a 400 kV backbone, add HVDC for bulk export and asynchronous links, deploy STATCOM for voltage support, adopt GIS in narrow valleys, and expand SCADA and PMU-based wide-area monitoring. ## Answer EHV (Extra High Voltage) systems work at about 300–765 kV AC, and UHV above that. Worldwide, power systems are changing because of the need to carry large amounts of renewable power over long distances, to control power flow, and to make the grid smart and reliable. #### New trends in EHV systems worldwide 1. **Higher voltages (UHV AC and DC):** China uses 1000 kV AC and ±800 to ±1100 kV DC lines carrying 8–12 GW over 2000–3000 km. India has 765 kV AC and ±800 kV DC. 2. **HVDC and VSC-HVDC:** voltage-source converters (MMC) allow multi-terminal DC grids, offshore wind connection and black-start ability. 3. **FACTS devices:** SVC, STATCOM, TCSC, UPFC increase line loading, control voltage and damp oscillations. 4. **Compact and high-capacity lines:** bundled conductors, compact towers, HTLS (high temperature low sag) conductors for re-conductoring, and multi-circuit towers to save right-of-way. 5. **Gas-insulated substations (GIS) and GIL:** SF6 or SF6-free (clean-air, g³) insulation in small space; very useful in hilly or urban areas. 6. **Underground and submarine XLPE cables** at 400–525 kV. 7. **Smart grid and digital substations:** IEC 61850, PMU-based wide-area monitoring (WAMS), SCADA/EMS, dynamic line rating, digital protection. 8. **Renewable integration and storage:** large solar/wind parks, pumped storage and battery storage connected through EHV networks. 9. **Regional interconnections and power trading:** cross-border grids (e.g. Europe, SAARC/BBIN) and electricity markets. #### How Nepal can adopt them - **400 kV backbone:** complete the east–west 400 kV corridor (Inaruwa–Dhalkebar–Hetauda–Butwal and beyond) and north–south 400 kV corridors from hydropower areas (Koshi, Kaligandaki, Karnali) to load centres and border points. - **Cross-border links:** strengthen 400 kV links with India (Dhalkebar–Muzaffarpur, New Butwal–Gorakhpur) and plan links with China and Bangladesh to export surplus wet-season hydropower. - **HVDC for export:** for large storage and export projects in the far west or east (several GW over long distance to Indian load centres), an HVDC or HVDC back-to-back link will allow controlled trading and asynchronous operation. - **FACTS:** STATCOM/SVC at weak substations to hold voltage on long radial lines and lightly loaded 220/400 kV lines in the dry season. - **GIS substations** in narrow valleys and Kathmandu, where land is scarce. - **HTLS re-conductoring** of old 132 kV lines to raise capacity without new right-of-way. - **Smart grid:** expand SCADA/load dispatch, PMUs, smart meters and automation in NEA's network to cut losses and outages. - **Storage and solar:** pumped-storage and reservoir projects plus solar to balance the run-of-river surplus/deficit. - **Capacity building:** training of engineers, national grid code, and private/foreign investment through clear policy. By adopting these trends, Nepal can evacuate its hydropower reliably, reduce spill in the wet season and earn from regional power trade. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is an example of the UHV trend worldwide? A. All countries have limited lines to 132 kV B. India has only 33 kV lines C. UHV is used only for submarine cables D. China uses 1000 kV AC and +/-800 to +/-1100 kV DC lines carrying 8-12 GW over 2000-3000 km Answer: D. UHV lines carry bulk power over very long distances. (Key point: UHV trend) 2. What does MMC-based VSC-HVDC allow? A. Multi-terminal DC grids, offshore wind connection and black-start ability B. Only a single point-to-point line C. Operation without any converter D. Use only at 11 kV Answer: A. Voltage-source converters add flexibility over line-commutated converters. (Key point: VSC-HVDC) 3. Why is GIS recommended for Nepal? A. It has no insulation requirement B. It needs little space, useful in narrow valleys and Kathmandu where land is scarce C. It is cheaper than air-insulated in all cases D. It increases line length Answer: B. Gas insulation makes compact substations. (Key point: GIS for Nepal) 4. What is the use of HTLS re-conductoring in Nepal? A. Reducing frequency of old lines B. Replacing transformers with converters C. Raising capacity of old 132 kV lines without new right-of-way D. Lowering voltage to 33 kV Answer: C. HTLS conductors carry more current with low sag on existing towers. 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