Abstract
The project concerns Phase Two of the design, construction and commissioning of a power plant of oscillating water column (OWC) type to be installed at Porto Cachorro, on the northern shoreline of the island of Pico, Azores, Portugal. Phase One, which was the object of contract JOU2-CT93-0314, concerned the plant basic studies, and the design and construction of the air chamber structure. The present project — Phase Two — concerns (i) the remaining civil engineering work, (ii) the design, construction and erection of the mechanical, electrical, control and monitoring equipment, and (iii) the commissioning and start up.
The partners include three universities, one government laboratory and four companies, two of which are utilities. The countries involved are Portugal, United Kingdom and Ireland.
The main objective of the project (phases One and Two) is to demonstrate the technical feasibility of OWC wave power plants by building one at a commercial scale. In addition, the plant was designed to provide a facility for testing power takeoff equipment, namely air turbines, generators, control equipment and valves.
The plant consists of a concrete structure standing on the rocky sea bottom, spanning a small gully where natural concentration of wave energy occurs. The oscillating water column has a 12´12m2 square cross-section. The plant’s power equipment is basically a horizontal-axis Wells turbo-generator set. Room has been left to install a second turbo-generator set for testing purposes. The plant is equipped with a relief valve whose purpose is to remove (positive and negative) pressure peaks in the air chamber and in this way avoid aerodynamic losses in the turbine due to rotor blade stalling.
The basic design of the plant, initiated in Phase One, was finalized. Results of the simulation of the power chain conversion (from wave to wire) were used to establish the specifications for the turbine and for the relief valve. A design value of 120 Pa m s -3 was adopted for the turbine damping coefficient, and 560 kW was adopted as turbine shaft (maximum instantaneous) power output (assuming a turbine maximum efficiency of 80%). An effective cross-sectional area of 0.8 m2 was adopted as an adequate design value for the relief valve.
The turbine, generator and the power electronics unit are located in a 10´12m2 turbine room behind the air chamber. Most of the remaining equipment (namely electrical, control and monitoring) is located in two rooms under the turbine room.
A major task of the civil contractor was the removal of boulders from the sea bed in front of the plant.
Some damage to the front wall of the structure was detected in summer 1997. Its most likely cause was defective underwater concreting in 1996 (as part of Phase One). Repair work was carried out in summer 1998.
The civil work, which included the construction of the equipment rooms and the roof of the chamber structure, was completed in August 1998.
The aerodynamic design of the Wells turbine was carried out in 1996. The turbine, ducts and two air valves were supplied by Applied Research and Technology Ltd (ART, Inverness, Scotland) in 1997.
The use of a variable speed electrical generator (750 to 1500 rpm) is one of the most important and innovative features of the plant. The development of the nonconventional electrical equipment (especially the power electronics and the control equipment) was a major task of the project. Practically the whole electrial equipment (conventional as well as non-conventional) was supplied by EFACEC Engenharia SA (Portugal).
The plant equipment was erected in summer 1998. An accident, due to flooding by sea water, occurred on 5th September 1998 when some of the conventional electrical equipment was being installed in the lower room of the plant. The damaged equipment (including the 630 kVA transformer and the general AC board) was later returned to factory for repair or replacement. This prevented the plant from becoming operational before the end of October 1998. The repaired equipment is expected to be re-erected in spring 1999. The plant is planned to be fully operational in summer 1999.