Dixième groupe de Vianden : problèmes particuliers posés par l'installation d'un groupe réversible de 200 MW : solutions adoptées

Directeur d'exploitation de l'usine hydro-électrique de Vianden, Société Electrique de l'Our, Luxembourg

Résumé

REASONS FOR THE EXTENSION (Figures 1-5). The Vianden pumped-storage station in Luxembourg is presently equipped with nine l00-MW sets with separate 70-MW pumps commissionned in 1964. Initially the power station was designed for a daily closed reversing cycle of 4 1/4 hours of generating and 8 hours of pumping and a yearly production of 1,350,000,000 kWh. In fact, the pumping period was progressively reduced to about 6 hours due to modifications of the load diagram, so that full use of the reservoirs can only be made by increasing the pumping capacity. CIVIL ENGINEERING ASPECTS (Figures 6-9). The new vertical reversible 200-MW unit, called the 10th machine, will be installed in a separate power station at a second location where the distance between the two reservoirs is relatively short (1,300 m). As the upper 63-m section of the pressure shaft was already constructed when the reservoirs were built, the works can be carried out without interferring with the operation of the present pumped storage station. The steel-lined pressure tunnel is in three sections (vertical, horizontal and inclined at 30°). As in the case of one machine, the per-unit costs of an access tunnel for the transport of the machinery exceed those of the lined pressure shaft, we were interested in placing the powerhouse as near as possible to the lower reservoir. Two solutions were studied, an underground power station (Figure 7) and a shaft power station (Figure 8), right beside the outlet in the Our valley. Finally, the latter type of construction was preferred for economic reasons. Its most important technical advantages are improved accessibility and more favourable hydraulic conditions due to the short length of the tailrace tunnel. STARTING FOR PUMPING OPERATION (Figures 10-15). For reasons of economy and simplification, a synchronous starting with partial voltage was selected. To reduce the voltage drop in the 220-kV system to the specified maximum value of 3 , a reactor is switched into the main circuit during running-up. Nevertheless the machine and the auxiliaries are designed in such a way that later on, when conditions in the system allow it, it is possible to go over to direct starting with full voltage. As shown in Figures 1l and 12, direct starting is possible with the filled pump-turbine, whereas starting with reduced voltage requires the dewatering of the impeller. In this case, filling is carried out after synchronization, simultanously from the draft side and from the head water. The damping winding which had to support current, of 45 kA during 30 sec is placed by solid poles with flexible copper connexions. By different constructive measures, it was possible to limit the temperature rise in the pole shoes to a maximum of 215 °C. AUTOMATISM (Figure 16). The control equipment transmits orders to the machine, protects the unit and informs the personnel of its state. Only the first of these functions is described in this article. In normal service, there are five types of set operation. These are standstill, turbine operation, pumping and synchronous condenser operation in both directions. Change-over from one of these final states to another is effected by 50 programmes which are subdivided into sequences and individual orders. For the execution of the programmes, four operation modes are possible : Remote automatic control used in normal service, local automatic control, semi-automatic and manual operation. The three latter modes of operation arc mainly used during tests or when the control apparatus is disturbed. Since there are no operating personnel on site, electronic components requiring no maintenance are used. except in those outlying parts of the equipment which are the most sensitive to interference. For data-logging, especially for the daily reports and the recording breakdowns, a small computer will be installed.