European Power Station
Key Benefits
- Reassurance from using professional, expert supplier
- Work completed according to schedule and costings
- Excellent on and off-site facilities
Background
Quartzelec tendered in partnership with a leading European Service Provider for the refurbishment of an entire turbine-generator-exciter power train, driving one of the station’s units at a European based dual coal and oil ¬ red power station. The Quartzelec tender was successful against others on the basis of best value and least outage time.
The Project
A major part of the refurbishment project was to ¬fit the latest design of endwinding retaining ring. The high-stress, high-energy nature of generator retaining rings makes it essential that defects are detected early to avoid propagation and catastrophic failure. They can also be exposed to corrosive agents such as water (from leakage or condensation) or nitrates (produced by oxidation of nitrogen by ozone from the corona effect). An 18% manganese /18% chromium alloy is acknowledged as the latest standard, being more robust and offering greater longevity than the alloy previously employed.
The project started with shipping one of the station’s existing spare rotors – weighing a massive 55 tonnes – to Quartzelec’s Rugby workshop, which is equipped specifically for the maintenance and repair of large rotating machines. In order to determine the viability of the 25-year old unit, it was completely stripped down prior to undergoing a total overhaul, including fitting the new endwinding retaining rings – a process facilitated by use of a heat blanket to heat up the ring to enable it to be shrink-fitted in place.
Another important element of the refurbishment was the redesign and retrofit of the inter-pole connection. These connections tend to suffer from stress cracks and to eliminate this, the replacement – designed using ¬finite element analysis and made at Quartzelec’s Rugby workshop – uses an omega design, laminated copper construction.
Following the rotor overhaul, it was balanced and over speed tested, and delivered back to site and fitted into Unit 2 in place of the existing rotor during the major overhaul. This involved complete disassembly of the generator, removing the rotor, cleaning and decontamination, undertaking a series of highly specialized HV and mechanical checks on cooling systems for leakages or blockages (hydrogen for the rotor, water for the stators), checking the integrity of the stator insulation system plus tightness of stator bars, and a host of other component inspections and tests, all necessary to determine suitability for continued operation. The replacement process took eight weeks, with a total of twelve specialists on site. Refurbishment of the replacement rotor including testing and delivery took approximately four months. These timescales were within customer expectations and contractual requirements.
The existing rotor from Unit 2 underwent a similar refurbishment process before being installed in Unit 1 during that unit’s major outage a few months later.
Tests performed:
- Doppler flow
- Tan delta
- Partial discharge
- Wedge tightness
- Rotor pressure
- Pressure and vacuum tests
- Hydrogen leakage
- IR & PI
- RSO
Outcome
“Quartzelec is fast becoming the preferred partner for large 2 pole generator refurbishments, providing all the expertise of an OEM with the benefit of more competitive project costings".
Steve Cooper
Rotating Machines, Manager, Power Generation, Quartzelec's Rugby Engineerin