Needle-Nozzle Assembly Replacement at Puwakhola Hydropower Station

Overview

The project was executed for the Nepal Electricity Authority (NEA) under Contract No. NEA-IHPS-2079/080-ST-EM-01, awarded through national competitive bidding, and covered the design, supply, delivery, installation, testing and commissioning of replacement needle-nozzle assemblies and associated works for the Pelton turbines of Puwakhola Hydropower Station at Golakharka, Ilam-09. Puwakhola is a run-of-river station whose horizontal double-jet Pelton units operate under a head of 304 m. The existing needle-nozzle assemblies and associated governing components had operational limitations and were replaced under this contract. Manufacture was preceded by reverse engineering: the installed equipment was assessed and 3D scanned on site, and dimensions, materials, mechanical strength, hydraulic compatibility and compatibility with the existing governing system were verified before design and final drawing submission. The work covered both units — four needle-nozzle assembly sets in total — together with new deflector servomotors, brake jet valves, cooling water valves, interfacing with the existing oil pressure and governing systems, and reprogramming of the station's ABB Symphony Plus SCADA. Nepal Electricity Authority took over the assemblies and associated systems with effect from 11 June 2026.

Scope & Deliverables

• Site assessment, reverse engineering, 3D scanning, design and calculation, design submission and final drawing submission for the replacement assemblies
• Four hydraulically operated needle-nozzle assembly sets, two per unit, complete with needle position feedback systems, deflectors, deflector operation mechanisms and associated equipment, manufactured, workshop assembled and workshop tested
• Two hydraulic servomotors for the deflectors, with spring return mechanism and inbuilt LVDT for faster deflector closure on normal and emergency shutdown, with seamless pipe, flexible pipe, fittings and valves
• Two hydraulically operated brake jet valves for 2 inch pipe
• Two electrically operated 4 inch valves for the cooling water system
• Interfacing with the existing oil pressure unit and governing system, including supply, modification and installation of hydraulic control valves and associated equipment for the new control mechanism, and oil piping and fittings between the servomotors and the governor oil system
• Dismantling of the existing needle-nozzle assemblies, deflectors, deflector servomotors and oil pressure unit components on both units, isolation of the hydraulic systems, removal of associated piping, cleaning of mounting surfaces, and handover of the dismantled components to the store designated by Puwakhola Hydropower Station
• Installation, testing and commissioning of the needle-nozzle assemblies, deflector servomotors, brake jet valves and cooling valves with their hydraulic and electrical control systems on both units, including alignment verification, torque verification, mechanical movement inspection and leakage inspection
• Integration, reprogramming and final tuning of the ABB Symphony Plus SCADA system for the new needle-nozzle, deflector, brake and cooling system operation mechanisms, with signal wiring verification, feedback signal calibration, local and remote operation testing, SCADA signal verification, alarm and indication testing, interlock verification and control response tuning
• Priming and finish coating of equipment requiring paint, corrosion protection after installation and testing, seaworthy packing with protective varnishing or greasing of surfaces left unpainted in service, and sea and land transport, insurance, unloading, storage and erection at the powerhouse site
• Mandatory spare parts: needles with tips, seat and nozzle rings with seat ring covers, servomotor LVDTs, deflector tips and plates, bearings and bushings for the operating mechanism, rings, liners, gaskets and sealing material for each servomotor, servomotor spring sets, hydraulic control valves and fittings, instruments and indicators, bolts, screws, nuts and washers, and braking needle valves with packing and sealing sets
• Special tools and devices for assembly and maintenance, maintenance devices and equipment, and submission of documents
• After-commissioning service for one year, comprising a site visit of at least five days following issue of the plant completion certificate

Outcome

The replacement assemblies were installed on both units and tested with calibrated instruments in the presence of the Employer's representatives, with Nepal Electricity Authority station staff participating. Mechanical testing covered alignment, needle movement, deflector operation and fastener tightening; hydraulic testing covered leakage, pressure stability and valve operation; electrical and control testing covered continuity, feedback signal verification, SCADA integration, and alarm and interlock function. Trial operation under normal operating conditions recorded smooth needle movement, stable governing response, stable hydraulic pressure, no abnormal vibration, noise or oil leakage, and correct operation of the SCADA monitoring, control, protection and alarm signals. Operator training on the reprogrammed SCADA was carried out in the station control room, where needle position, deflector position, hydraulic oil pressure, brake jet status and cooling system status are now monitored. Nepal Electricity Authority took over the needle-nozzle assemblies and associated systems with effect from 11 June 2026; the commissioned system was handed over to the project office for commercial operation and the spares were stored at the station store room.