Electrical & electronic design :Dr.K.Michailidis
THE VERTICAL SHAFT DARRIEUS TYPE
VARIABLE SPEED WIND GENERATOR
KA 140 (140 kW) OF SKYROS ISLAND
A BRIEF DESCRIPTION ( by
Prof.emer.N.Athanassiadis, Dr.Eng.K.Michailidis )
The Vertical axis Darrieus type wind generator KA
140, was designed in the Laboratory of Aerodynamics of the NTUA during
the year 1987-89 and was manufactures in Greece. This WTG is the subject
of Demonstration Project WE/209/85/IIE of the EEC Directorate General
XVII for Energy, with contractors the PPC of Greece and the NTUA.
The manufacturing of the WT as well as its preliminary
factory tests were completed in June 1995.
From June 1995 the unit is ready and stored in
the manufacturer's depot. Since then the manufacturer (BIOKAT industrial
LtD) waits the order from PPC to transport and install the unit in Skyros
island near the WTG OA/100 kW, which is installed and in service since
Nov.1991. After the installation of the KA 140, so that entailing the fulfilment
of the terms of the contract with the manufacturer, the unit will
belong PPC.
The main dimensions and the figure of the WTG
KA140 are as follows :
Darrieus type rotor, with vertical shaft 26m
height and maximum arc distance of each one of the two blades, in the middle
of their Darrieus curve from the rotor axis, 9.6m. The aerodynamic section
of the blade is constant along its length, of NACA 0015 type, with a chord
of 714 mm.
The rotor shaft is formed from steel tube of
914 mm diameter and a length of 26 m. It will be supported on a heavy type
spherical roller thrust bearing which is based on the top-cover of a specially
formed steel structure and it is kept in its vertical position by a "cover
bearing assembly" supported in its place by three suitable tensioned cables
in a tetrahedron edges arrangement, anchored on three concrete blocks.
The rotating movement of the rotor will be transmitted
by an intermediate shaft to the low speed shaft of the gear box. The gearbox
is of 90o degrees angle transmission type, it has a speed ratio 1:32.611
and its horizontal high speed shaft is connected to the generator through
a flexible coupling.
The disc of the two hydraulic brake systems is
fixed on the low speed shaft of the gearbox. There are two pairs of brake
callipers which constitute the service braking assembly (hydraulically
applied/spring retracted) and two pairs of brake callipers which form the
fail-safe braking system (spring applied / hydraulically retracted).
The generator is of a DC type with independent
excitation, 184 kW at 1595 RpM. Its cooling is achieved by a close circuit
air/air exchanger system.
The innovation in the design of this unit is
that it is able to work at variable speed according to the wind conditions,
by means of an AC/DC converter placed electrically between the 3 phase
AC, 50 Hz electric network and the DC generator.
The speed is controlled through a digital controller,
controlling the armature voltage. The speed reference and the whole control
operation is achieved by a PLC which acts on the converter side that
controls the voltage of the above mentioned circuit, enabling thus the
generator to run at variable speed. Through this action it is possible
to obtain the best efficiency that can be achieved according to the wind
conditions and the ability of the electric network to absorb the related
power.
The PLC acts as a very capable operator but incomparably
faster than a human operator. In such a manner PLC will be able to start
the unit from zero speed (the generator acts as a motor), increasing
the speed from working conditions from about 30 to 48 RpM for the rotor,
and monitoring the best possible efficiency and the safest possible operation
of the system.
According to the aerodynamic characteristics
of the rotor blades we estimate that the max. electric power of the KA140
will be 140 kW.
This page has been visited 
times.
Home