Hydroelectric systems

PELTON TURBINE-GENERATOR GROUP ON VERTICAL AXIS

Pelton wheel
The wheel buckets are in stainless steel, obtained by precision casting. This system ensures high accuracy and good finishing. The buckets are fixed to the disk-hub by TIG welding without added material. The disk-hub is in stainless steel, too, and is directly splined to the generator shaft.

Turbine case
It is made up of two cylinders in welded steel forming the feeding line to the nozzles. The internal cylinder is used to gather and convey the water into the wast trap. Furthermore, it fixes and supports the turbine-generator group by means of brackets welded on the cylinder external surface. A coupling ring, to be installed in the bedplate, is supplied to secure the turbine-case. The nozzles are pressed in special long-lasting plastic material. Their maximum number is 6.

Feeding group
Its function is to connect the penstock to the turbine case and consists of the introductor tube, on which the floodgate for plant control is mounted, the pressure gauge connection, the pressure gauge and the pressure water side plug (by-pass).

Generator
Three-phase, synchronous, permanent magnet generators are used. The ball bearings of all generators are "water tight", hence, they require no lubrication. The generator is separated from the turbine by a special shield preventing any contact with water. Under normal operation conditions, the generator is star-connected and supplies, at no-load, a 240V voltage at a revolution of 1500 rpm. The highest revolution number is 3000 rpm. The choice of such a voltage is justified by the possibility of using small section wires (3 x 1,5 / 2,5 sq/mm.) for the electric line from generator to regulator (normally installed inside the house), thus having negligible losses even when the electric line must be some hundred meters long. Depending on head and flow, the generator will work at voltages and frequencies other than the nominal ones; therefore, never connect the consumers directly to the generator. The efficiency of our permanent magnet generators is approx 0.85.

ELECTRONIC REGULATOR

The regulator, which is an electronically controlled electrodynamic type, keeps the voltage stable by means of a constant load system: the turbine and generator always work at full load because the energy not utilised by the consumers is dissipated on some ballast resistances.

The regulator is made up of the following main parts:

• The transformer, a three-phase type, reduces the generator voltage to a suitable value to get 24V DC and makes the turbine suitable for a vast range of heads H and flows Q.
• The rectifier is made of selenium plates. Selenium has been preferred to the more modern silicon because it ensures higher efficiency at such low voltages. Furthermore, selenium is much less vulnerable to atmospheric discharges.
• The electronic control of power transistors is realised on a printed circuit. Its components have been chosen by keeping in mind the highest realiability. Besides the control and operating signals of the power transistors, other signals are available for operating valves, boiler, etc. Some LED diodes indicate the regulator working phases.
• The power transistors are silicon, the quality and size being chosen to grant the maximum reliability.
• The resistances for the dissipation of the energy in excess are designed to ensure a low temperature even at full load, hence, a total reliability.
• The instruments ammeter and voltmeter, are mobile coil type, class 1.5. The pointer and the scale ensure an easy and accurate reading of the indicated values.
• The terminal board for the connection of the input and output wires is easily accessible. Isolation and size of the terminals are suitable for the voltages and sections of the wires being used. A special shunter enables to check, during installation and inspection, the power of the micro-hydroelectric plant without any need of loads or external instruments. All the above mentioned components are contained in a wall hanging cabinet in steel plate, accurately painted. The cabinet is designed to make all components easily accessbile for checking and replacements on the spot.