Single Line Diagram of 400/220/66/11 KV Interconnecting Substation, Malbase, Pasakha, TOMS P/Ling
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General
The Malbase Substation is the primary 400/220 kV interconnecting station and the first 400 kV class substation in Bhutan. It was designed and engineered as part of the Tala Hydroelectric Project (THEP), with consultancy by WAPCOS in association with the Central Electricity Authority (CEA), Ministry of Power, Government of India. THEP has an installed capacity of 1,020 MW, consisting of 6 units of 170 MW each. Power is evacuated to the Eastern Grid of India at Siliguri through four 400 kV circuits. One of the 400 kV circuits is looped-in and looped-out (LILO) at Malbase (Pasakha) near Phuentsholing. The 336 MW Chhukha Hydro Power Corporation (CHPC) is also connected to the Malbase system at 220 kV. Together, THEP and CHPC are interconnected through 400/220/33 kV single-phase interconnecting transformers.
Operation & Maintenance
The 400/220 kV Malbase Substation was commissioned by THPA and is currently in operation. Proper operation and maintenance of the equipment are critical to ensure safety, reliability, and long service life. Any incorrect operation may lead to severe equipment damage and prolonged outages. All personnel must be properly trained, qualified, experienced, and fully familiar with the substation equipment. Unauthorized personnel are strictly prohibited from operating any equipment within the substation.
Layout
The substation covers an area of 377 meters in length and 263 meters in width, constructed on two elevation levels: EL. 408 m and EL. 400 m. The switchyard is divided across the two levels based on voltage class. The 400 kV section and a portion of the 220 kV switchyard are located on the upper level (EL. 408 m). The remaining part of the 220 kV, along with the 66 kV and 11 kV switchyards, are positioned on the lower level (EL. 400 m). This lower level also accommodates the control room building, fire-fighting pump house, and DG set building. The control room building is a three-storied structure, with the top floor aligned with the 400 kV switchyard elevation. The first floor functions as a cable vault hall, while the ground floor houses the AC/DC system, office spaces, and the air-conditioning plant. All control and relay panels for the 400 kV and 220 kV protection systems, including PLCC panels and RTCC panels for transformers, are installed on the top floor. This floor also includes sufficient space for future expansion of protection and control systems.
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