High-Altitude Cascade Hydropower Plant in Tajikistan

A high-altitude cascade hydropower plant project in Tajikistan, featuring advanced step-up systems and seismic-resistant design for sustainable energy.

Project Scope and Supply Range

For the two 22.2 MW hydro-generator units, we designed a classic “one-generator-one-transformer, high-voltage bus” main connection scheme:

A. Core Step-Up System

• Equipment: Two 25 MVA 110 kV/10.5 kV three-phase oil-immersed dual-winding on-load tap-changing power transformers.

• Quantity Logic:

  • Capacity matching: The generator power is 22.2 MW with a power factor of 0.9, making the apparent power approximately 24.6 MVA. We selected 25 MVA standard transformers, achieving 100% matching without waste.

  • Unit connection: We connect each generator directly to one main transformer, stepping up 10.5 kV generator voltage to 110 kV transmission voltage.

  • On-load tap changer: Considering the large power fluctuations between dry and wet seasons, we configured a ±8×1.25% OLTC to stabilize output voltage.

B. Station Service and Auxiliary System

• Equipment: Two 630 kVA 10.5 kV/0.4 kV epoxy resin cast dry-type transformers.

• Quantity Logic:

  • Mutual backup: One transformer powers the station gate oil pumps, lighting, and excitation systems, while the other remains on standby. If the main supply fails, the backup transformer automatically switches in to prevent a total station blackout and runaway accidents.

C. High- and Low-Voltage Switchgear

• Generator outlet side: 16 sets of KYN28-12 (10 kV) metal-clad withdrawable switchgear (including generator outlet breakers, PT cabinets, and excitation transformer cabinets).

• 110 kV high-voltage side: One set of 110 kV GIS interface cabinet.

  • Logic: Due to the limited flat land in the high-altitude canyon area, we recommended using a compact GIS solution instead of building a large outdoor switchyard. Our equipment perfectly matches the GIS interfaces.

“Split Transport + Slim Design” Logic

• Pain point: Sections of the Pamir highway leading to the site are narrow and must pass through the Anzob Tunnel, limiting cargo height and width.

• Solution: We designed the 25 MVA main transformer with a “slim design.” Radiators and oil tanks are detachable and packed separately for transport. We designed the transformer body in a long, narrow shape to ensure it can pass through tunnels and culverts.

“9-Intensity Seismic” Design Principle

• Pain point: Tajikistan lies on the Eurasian seismic belt, requiring equipment to withstand intensity 9 (0.5g acceleration).

• Solution: We used a mechanical interlock structure for the transformer body instead of relying solely on friction. Reinforced seismic angle steel is welded to the oil tank bottom, and we used flexible composite silicone rubber for all high-voltage bushings to prevent brittle fracture during earthquakes.

“High-Altitude External Insulation” Logic

• Pain point: At 2,400 meters, air is thin and corona discharge easily occurs.

• Solution: We corrected the creepage distance for 110 kV bushings according to 3,000 meters altitude and extended it by 20% to eliminate insulation breakdown in the high-altitude environment.

Market Research and Technical Insights for Tajikistan

• Understanding “Barki Tojik” Company:

  • Research: The national power company places great importance on equipment durability due to limited maintenance funding and technical resources.

  • KeRun Response: We adopted fully sealed corrugated oil tanks, promising 10 years of maintenance-free operation without oil leakage or silicone replacement, fitting the local “install and forget” maintenance style.

• Continuation of GOST Standards:

  • Research: Despite years of independence, the power system still follows Soviet GOST standards.

  • KeRun Response: While the core equipment complies with IEC standards, we retained Russian-style layouts for secondary wiring terminals, CT/PT polarity marks, and nameplate parameters, making local engineers feel familiar.

• Winter Cold Start:

  • Research: The Pamir Plateau can reach -30°C in winter.

  • KeRun Response: We selected -45°C grade low-temperature transformer oil and added high-power heating and dehumidification units to switchgear cabinets to prevent condensation freezing and short circuits.