Electro-Mechanical Works and 33 kV Switchyard at Maya Khola Hydropower Project

Overview

The project was executed for Maya Khola Hydropower Company Limited under turnkey contract MKHP-EM, signed on 29 March 2018, and covered the design, manufacture, supply, erection, testing and commissioning of the electro-mechanical works, sub-station switchyard and interconnection facilities of the 14.9 MW Maya Khola Hydropower Project at Dharmadevi Municipality-4, Sankhuwasabha. The plant comprises two horizontal two-nozzle Pelton units running at 600 rpm, each with the runner mounted directly on the extended generator shaft, driving a three-phase 8,920 kVA, 6.6 kV generator. Generation is stepped up to the station's 33 kV system, which feeds the switchyard and the interconnection to the grid. The turbines, governing equipment, unit and common control systems and plant SCADA were supplied through WWS Wasserkraft GmbH & Co KG, Austria. Maya Khola Hydropower Company Limited issued the certificate of completion on 2 July 2023.

Scope & Deliverables

• Two horizontal Pelton turbines with two nozzles per unit, the runner mounted directly on the extended generator shaft; welded turbine housings in S355J2+N steel to DIN EN 10025-2, hot-dip galvanised and coated, pressure tested to 1.5 times working pressure, with condensation drainage, pressure measurement points and vent and drain ball valves
• Pelton runners machined from forged chrome-nickel steel (X5CrNi13.4) monoblocks on a 5-axis CNC mill and dynamically balanced to ISO 1940-G2.5
• Nozzle assemblies with hardened stainless steel mouthpieces (1.2316) and replaceable wear rings, needles (1.4021) and needle bars (1.4305), one hydraulic actuation system per nozzle with electrical position feedback and mechanical position indication, and jet deflectors (1.2313) with counterweight-actuated fail-safe closing and end-position limit switches
• Hot-dip galvanised DN50 bypass lines with manual ball valve, DC motor-driven valve and pressure gauges, and labyrinth shaft sealing with Robalon S splash protection rings
• Two three-phase brushless synchronous generators rated 8,920 kVA at 6,600 V, 600 rpm, 50 Hz and 0.85 power factor, star connected, class F insulation with class B temperature rise, IP 23 enclosure, IC 01 cooling, sleeve bearings, dual PT100 sensors per phase in the stator winding and per bearing, three vibration sensors, anti-condensation heaters and a forward-acting brake system operating at 10 per cent of nominal speed
• Digital excitation and voltage regulation using Basler DECS-250 excitation control systems, with generator voltage and current transformers for protection and measurement
• Generator neutral cubicles with neutral grounding resistors rated 364 ohm at 20 degrees C, 10 A maximum fault current for 5 s, 3,640 V across the resistor and 7.2/20/60 kV insulation level
• Closed-circuit lubrication and oil-water cooling units per unit, with oil reservoir and water compensation reservoir, AC and DC gear pumps, shaft-driven pump at the non-drive end, oil/water heat exchanger and stainless steel water/water heat exchanger in the tailrace, filters, check valves, and flow, level, pressure and temperature monitoring
• Two DN800 PN63 inlet ball valves with counterweight and single-acting hydraulic servo actuation, position sensors and adjustable closing time, and DN800 PN63 dismantling joints to EN 1092-2 with plus or minus 25 mm axial movement
• Hydraulic power units with pressure accumulator, safety pressure switch, dual 400 V three-phase pump units, manual pump for powerless operation, Parker proportional valves for the servo motor and a Parker 3/2 pilot valve for the generator brake, including first oil filling and all pressure piping to the nozzles, jet deflectors and main inlet valves
• Unit control and protection panels, one per unit, 1200 x 2000 x 600 mm and IP 44, each with a Siemens ET200SP PLC configured for 80 digital inputs, 48 digital outputs, 20 analogue inputs 4-20 mA, 16 PT100 inputs, 8 analogue outputs and a counter module over Ethernet, a 7-inch operator panel and a multimeter, providing turbine governing, opening, speed and head pond level control, island and parallel grid operation, start/stop and emergency shutdown, and manual, sequence and full automatic modes
• Common control panel, 1200 x 2000 x 600 mm and IP 44, with a Siemens ET200SP PLC configured for 64 digital inputs, 32 digital outputs and 4 analogue inputs, and a 7-inch touch operator panel, for station auxiliary and DC supply, MV switchgear and group control of the units
• Electrical protection by a Woodward easYgen protection device with additional numerical relays, covering ANSI 46, 27, 59, 81, 78 ROCOF, 32R, 50/51/67, 51V, 49, 40, 32F, 24 and 59N functions, and MV line feeder protection covering ANSI 50/50N/51/51N, 67/67N/67Ns, 49, 27/59, 46 and 81
• Automatic synchronising by Woodward SPM-D, with manual synchroniser, double voltmeter, double frequency meter and LED phase display
• SCADA workstation with 22-inch monitor on a UPS supply, Ethernet TCP/IP plant bus linking all subsystems, process and supervision screen pictures, alarm, event and measurement logging, trend displays and remote access over an industrial VPN router
• Instrumentation and power cabling with NYY 0.6/1 kV LV copper power cables to DIN VDE 0276 part 603 and IEC 60502-1, LiYCY instrumentation cable to VDE 0812 and YSLY control cable to VDE 0245, with POLT and Raychem terminations
• Sub-station switchyard and interconnection facilities at 33 kV, including equipment support and take-off structures and their foundations
• Erection, testing and commissioning on site by mechanical and electrical engineers, operator training during erection and commissioning, and commissioning spares for the turbine and main valve, governor and hydraulic power unit, generators and electrical equipment
• Two series of technical documentation in English, comprising operating and maintenance manuals, installation and assembly drawings, single-pole schematics, switchboard, circuit and wiring diagrams, release diagrams, equipment and cable lists, clamp plans, PLC program documentation, hydraulic schemes, testing protocols and spare parts lists

Outcome

Both generating units were erected, tested and commissioned on site, together with the unit and common control panels, the excitation, protection and synchronising equipment, the 33 kV switchyard and the interconnection facilities. Pre-commissioning and commissioning tests covered generator no-load and short-circuit characteristics, insulation and high-voltage tests, protection relay functions, excitation and voltage regulator adjustment and synchronising, and the SCADA workstation was configured for supervision of both turbines, the 33 kV system and the station auxiliaries. Operator training was delivered during erection and commissioning. Maya Khola Hydropower Company Limited certified the contract works as complete on 2 July 2023, and the station operates two Pelton units feeding the 33 kV interconnection.