Transmission grid extension for Lake Turkana Wind Farm Wessel Bakker Business Line Director ETD BMEA DNV KEMA The Netherlands wessel.bakker@dnvkema.com
Contents Drivers for grid expansion Suswa and Loyangalani substations Transmission line Suswa-Loyangalani Design aspects and features of the transmission line Project status
Transmission grid Kenya Grid is being rapidly and significantly expanded 3
Drivers for 220/400 kv grid extension West of Nairobi Expected high demand growth in Kenya Planned extension of geothermal generation at Olkaria and other sites Planned Lake Turkana Wind farm Connection point for Ethiopian HVDC interconnector KPLC/KETRACO planned for a new 400/220kV substation near Mount Suswa, also as part of the Nairobi Ring project
Suswa substation 1,5 breaker design 1 reactor bay 2 capacitor bank bays 14 line bays Central control building Focus on high reliability Space for extension (HVDC)
Lake Turkana Wind Farm Laisamis District (Marsabit) 300 MW wind farm 365 Vestas V52 WTG Connects to new KETRACO Loyangalani 220(400) kv substation
Grid connection of LTWP/Rift Valley: Loyangalani-Suswa transmission line KPLC/KETRACO planned for a transmission line from the new Suswa substation to Loyangalani: Connection of Lake Turkana Wind Farm Connection of geothermal power plants in the Rift Valley Strengthening the distribution grid and rural electrification of the Rift Valley along the route Ethiopia HVDC to terminate at Suswa
Development of the transmission line and substations As the first party to be connected to the line, LTWP, together with KPLC, KETRACO and the Ministry of Energy, have started to develop the Loyangalani and Suswa substations and the transmission line up to tender evaluation KETRACO have taken over the lead and contracted the substations and the transmission line DNV KEMA supported as owners engineer
Design considerations for transmission line and substations The Kenya grid may not survive 300 MW trip on an outage Hence, the substations are fully redundant with 1½ breaker systems Also, the transmission line was designed as a double-circuit line with proper mechanical safety factors and good lightning performance Specific attention to loss optimization Specific attention to lightning performance
Transmission line: features 428 km length double-circuit transmission line for full redundancy with steel lattice towers, composite insulators and ACSR conductors Design rating 400 kv, initial operation at 220 kv proposed (same was applied to Mombasa line) Double OPGW for maximum communication redundancy
Loss optimization study Ohmic losses Corona losses Conductor configurations: 3 x 315 mm 2 4 x 315 mm 2 3 x 400 mm 2 4 x 400 mm 2 2 x 560 mm 2 3 x 500 mm 2 4 x 500 mm 2 2 x 710 mm 2
Corona losses are significant Average altitude about 1750m Corona losses considerable Bundle conductors attractive
Economic analysis Cost model for transmission line to account for differences in conductor, insulator, tower and foundation costs between the conductor configurations Sensitivity analysis for moment to switch to 400 kv operation after 3, 7 and 25 years Capitalized cost of losses at 8%/a interest rate Time period 25 years
400 kv operation after 7 years 250 200 USD 150 100 50 Initial investment Capitalized losses 0 2 x 560 2 x 710 3 x 315 3 x 400 3 x 500 4 x 315 4 x 400 4 x 500
400 kv operation after 25 years, i.e. operation at 220 kv 250 200 USD 150 100 50 Initial investment Capitalized losses 0 2 x 560 2 x 710 3 x 315 3 x 400 3 x 500 4 x 315 4 x 400 4 x 500
400 kv operation after 3 years 250 200 USD 150 100 50 Initial investment Capitalized losses 0 2 x 560 2 x 710 3 x 315 3 x 400 3 x 500 4 x 315 4 x 400 4 x 500
Observations If the transmission line remains operated at 220 kv, the 2-bundle conductors lead to lowest evaluated costs; however, a conversion to 400 kv would be prohibitively expensive due to excessive corona losses In the other cases, the 3x400 mm 2 configuration is most economic As 400 kv conversion is assumed to take place in foreseeable future, 3x400 mm 2 was chosen
Lightning performance Double-circuit outages due to back flashover are to be avoided Soil resistivity and tower footing resistance expected to be high at some places Lightning performance specified in EPC contract Still, a detailed ATP simulation study was carried out on a preliminary tower design in order to determine up-front the feasibility of the functional requirements
Lightning performance (2) Asymmetric insulation in order to have one strong circuit rarely experiencing back flashovers Shielding failures are negligible Switching transients acceptable The back flashover performance was shown to be OK provided the tower footing resistance is low enough
Status Contracts for the substations have been closed Suswa 220 kv substation under construction, completion expected in May 2014 Loyangalani 220(400) kv substation contracted, Notice to Proceed expected Fall 2013 (at Financial Close of LTWP), completion expected Summer 2015 400 kv Transmission line contracted, Notice to Proceed expected Spring 2013, completion expected Spring 2015 20
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