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Genesis Energy supplies 19 percent of New Zealand's electricity from thermal and renewable power stations, with hydropower as a key component. Their Tuai and Kaitawa hydro-generating stations have five Francis turbines in total with a combined capacity of 100 megawatts. When the Woodward 505H Hydro-governors and mechanical controls on the turbines were approaching 20 years of service, the company saw an opportunity to increase operating efficiency and grid reliability by modernizing these systems.
GE had demonstrated expertise in hydro-turbine applications by successfully executing similar projects for Genesis Energy, and was the natural choice for this critical project. Obsolete components were replaced while retaining much of the original hardware, substantially saving on material and labor costs. The new digital-based 505H system supports remote monitoring and control, a key objective for the upgrade. Also, the digital controls and new mechanical systems, including speed sensor gear, linear displacement transducer and retrofitted valves improve speed and precision. As with earlier projects, GE completed the upgrade on time and actually cut commissioning time significantly. With two weeks per unit as the norm, GE took just five days to commission the first unit, and just three days for subsequent units.
The refurbished controls reduced typical start-up time from standstill to stable synchronous speed by approximately 40 percent. This enables faster connection to the grid, helping Genesis Energy pick up peak loads which carry higher margins. Also, with remote monitoring and control capabilities, Genesis Energy can allocate fewer in-house resources to supervise the generators.
Regarding completion of the upgrade, Ian Meredith of Genesis Energy said, "The retrofits are performing extremely well and helped us achieve our goal to improve performance. We're also pleased with the knowledge and skill displayed by the GE engineers who completed the upgrade with a minimum of downtime, keeping costs low."
An indirect benefit occurred during commissioning when a GE engineer noticed a malfunctioning pressure relief valve that was not targeted for replacement. If undetected, this situation could have caused overspeed during a high load rejection, with extensive mechanical damage to the turbine, bearings, and generator.
Benefits of GE's Woodward digital-based 505H Hydro-governors and mechanical controls: