Banki
turbine-generator group on horizontal axis
Cross-flow turbine
The wheel blades are in steel and are directly welded
on the side plates. The hub is fixed on the turbine shaft by means of two conic
section pliers. The turbine shaft revolves on ball bearings external to the
turbine case and transmits the motion to the generator shaft by means of a revolution
multiplier, which is made up of a couple of pulleys with a cogged driving belt,
properly sheltered.
Turbine case and injector
The case consists of a welded assembly in sheet steel. A baffle for the manual
flow regulation is mounted inside the case. The injector is provided with a
small inspection door: the internal part of the injector and the wheel are easily
accessible for inspection and cleaning.
Feeding group
It connects the penstock to the turbine case. It consists of the introductor
tube, on which the floodgate for plant control is mounted, and the pressure
gauge connection. The introductor is provided with a DIN flanged fitting for
connection to the penstock.
Generator
Three-phase synchronous generators are used, from which it is possible to draw
single-phase energy. The rotating inductor is a 4-salient pole type. These generators
are characterised by the absence of brushes. The exciting current is supplied
by an auxiliary generator whose induced rotor is mounted on the same shaft of
the main generator. The excitation regulation is voltamperometric by "Compound"
system. The ball bearings of all generators are "water tight", hence, they require
no lubrication.
ELECTRIC CONTROL BOARD
The electric control board consists of a sheet hanging cabinet in which the different devices are contained.
The meters of the single-phase control board are: a voltmeter, a digital frequency-meter, an ammeter indicating the total current distributed by the generator, and a second ammeter indicating the current drawn by the consumers. In the three-phase control board, there are six ammeters, 3 of them indicating the input current on each phase and the other 3 the current drawn by the consumers.
The protections of the single-phase control board consist of a three-pole cicuit breaker, which protects the generator from possible short circuits on the consumer line, and an electronic voltage relay, operating a warning buzzer and a visual signal in the event the voltage variation exceeds the preset limits. In the three-phase control board, there is a three-pole circuit breaker and three electronic voltage relays, each of them being connected between one phase and neutral.
The terminal boards are used for connection of the wires of the generator, the consumer line and the electronic regulator. Isolation and size of the terminals are suitable for the voltages and sections of the wires normally used.
ELECTRONIC REGULATOR
The electronic regulator is made up of the control unit and the ballast resistances. The regulator cares to keep the voltage and frequency stable, as the absorption of the energy produced by the turbine-generator group remains constant. In fact, this group always works at full load and the regulator dissipates the energy produced by the plant and not utilised by the consumers on some ballast resistances. The exceeding energy may be dissipated in air or water by means of largely dimensioned dissipating elements, automatically connected or disconnected by the electronic control unit of the regulator.
ELECTRICAL CHARACTERISTICS OF THE PLANT
The micro-hydroelectric plant supplies standard 220V single-phase and 220/380V three-phase AC electric energy, at the frequency of 50Hz and 60Hz. The plant global efficiency (i.e. the ratio between the generated electric power and the available hydraulic energy) varies according to the distributed power and the conditions of use. However, the efficiency is always high compared to the involved powers.