Electricité de France looked outside France when it decided to modernise speed governors at Beaucaire
At one time only two qualified suppliers shared the speed governor market in France, but times are changing. In an attempt to create a more competitive environment, Electricité De France (edf) has amended its rules in parallel with new EU directives and reorganisation of the European energy market. The company has developed an extensive qualification process comprising two phases:
•Qualification of companies capable of designing and manufacturing speed governors according to EDF’s specifications.
•Qualification of a company’s products on the basis of their suitability and operational capabilities.
After a long absence from the French market, Voith Hydro Heidenheim applied for qualification of its company and products. EDF led inspections of the company, incl#uding a review of its existing EN ISO9001 quality assurance system. After successful completion of phase one, Voith Hydro was invited to provide a quotation for modernising speed governors in France.
The first invitation to tender was for the modernisation of speed governors at Beaucaire on the Rhine, in the south of France. The Beaucaire powerhouse has six bulb turbines, sized at 35MW and 400m3/sec. The speed governing system was commissioned in the early 1970s, and it had been developing problems. The system was experiencing increasing levels of vibration, due to the non linear and closed loop effect of wear and tear in the loose piping supports and worn out pumps. The positioning system, including the actuators, the m#ain distributing valves, feedback levers and transducers were also contributing to the high levels of vibration. The timing capacitors which were used in the stabilising loops, derivative or integral loops, were also beginning to age — when these electrolytic capacitors become dry, due to age and heat conditions, the time constants will vary tremendously. Potentiometers, which were used to allow continuous setting of parameters, were also liable to failure.
The permanent heavy vibration in the whole system caused induced stresses in the oil piping support; what is more, the oil was heavily polluted, the synchronisation process had become very lengthy, and it had became increasingly difficult and expensive to obtain spare parts.
Voith Hydro was awarded the contract for the replacement in April 1998 and the first machine was commissioned in October 1998.
There were two main considerations during the modernisation: the modernisation of the governors themselves, including replacement of the analogue governors; and renovation of the support piping. The real challenge in modernising the governors was synchronising them with the modernisation of the power plant’s automation system as a whole, which included protectors and a new excitation system. EDF Hydro Engineering was responsible for this task.
The new speed governor selected by EDF is a Voith standard full digital VGC type for bulb units. One of its main characteristics is its ability to operate with non-Voith components such as the main distributing valve. These main distributing valves, already designed for hydraulic control, were not replaced: they were modified to correlate with Voith’s standards.
Many of the main oil pipes had been damaged by wear and tear, corrosion and vibrations in the supporting system: these were replaced by new ones. Critical supports were replaced by state-of-the-art versions whose much lower flexibility help reduce vibration. New hydraulic pumps were installed as spare parts were not economically available and the size of the pumps were not identical.
Before the modernisation, two different oil pressures were used for blade and wicket gate control, resulting in two separate circuits. Following the refurbishment there is a true redundant pump system, improving the availability of the whole machine. In addition low oil loss actuators replaced the existing actuators. The complete oil load has also been filtered in order to allow the machine to run without any trouble.
The existing transducers, which were subjected to wear and tear because of their associated transmission levers, were replaced by full linear versions, even for the long hub wicket gate servomotors control.
Keeping on schedule
Successful organisation played a part in ensuring that the modernised machine went back in operation on schedule. At Voith Hydro, a special team was assigned to the project after the contract award. During the customisation of the new speed governors, one of the main tasks of this team was to co-ordinate the site works, using French speaking supervisors.