C3G - C4G

Model: C3G - C4G
Power: Up to 3.400 kW
Voltages: Up to 690 V
Frame: 250 ± 710
Poles: From 4 to 16 poles (over contact Marelli Motori)
Cooling: IC 01
IP: IP 23. Available up to IP 56
Enclosure: ODP – Open Drip Proof Motors. 
Main Applications:
Cross-Flow turbines, Francis turbines, Kaplan turbines, Pelton turbines, Turgo turbines
Sector: Hydropower

Asynchronous generators

An induction machine is capable to work as a motor or as a generator depending on the rotating speed. Below the synchronous speed the machine will act as a motor. At synchronous speed, the line supplies reactive power and machine losses, but no torque or power is generated. Above the synchronous speed the machine act as a generator. Induction generators works in the stable region between the no-load condition and maximum torque region. If the speed of the generator increases, the breaking torque reaches a max value of torque (breakdown torque) that it can operates before the operating conditions become unstable.

Certificates and testing
Test Certificate supplied with the machine. Material certificates in accordance with EN 10204 : 2001 can be supplied.

Main components

Rigid frame, rugged welded steel fabrication (EN 10025 - S235 JR). Frame is provided with side ribs to increase the strength. Generators for continuous duty operation are designed to meet vibration levels per IEC 60034-14, ISO 10816-1 and BS 5000-3.

Made of grey cast-iron (EN 1561 – GJL 200) up to 500 frame size asynchronous generators. Made of hot-rolled structural steel (EN 10025 – S235 JR) from size 560 and above.

Made in carbon steel (EN 10083 – 2 C40 – TN) up to 450 frame and hot-rolled structural steel from 500 frame (EN 10025 – S355 JR). Cylindrical shaft with key. The shaft can be designed to install the flywheel, the brake or the specific client’s requirements (hollow shaft).

Main terminal box
Usually mounted on top can be located on the sides of the frame. Made of cold-rolled formable steels EN 10025 – S235JR.An oversized terminal box can be supplied according to customer requirements.

Internal Fan
Made of aluminum alloy up to 400 frame.Made of hot-rolled structural steel above (EN 10025 – S235 JR).

Cooling System
IC 01 as per IEC60034-6Free circulation.Internal air is flowing by a fan mounted on the shaft of the asynchronous generators at the driven side. The cooling air is taken on the ND-end, the air outlet is on the D-end. On request for variable speed application an external ventilation unit can be supplied to get the IC 06 cooling type.

Degree of protection  IP 23 as per IEC60034-5.The series can be supplied with air inlet filters to achieve the IP 44 rating. Higher IP is available on request with different construction (TEFC, TEAAC, TEWAC)

IM B3, V1 and V10 as per IEC60034-7.

Technical data

Stator/Rotor core
Laminated and enamel-insulated on both sides to minimise eddy-current losses. The stator winding is made of flat copper or round copper wire depending on the machine size. The completely wound stator pack with housing is thereby impregnated in an epoxy-resin VPI. The subsequent heat treatment hardens the resin.

Short circuit rotor type. Depending on machine size, the rotor construction is either a solid shaft or welded ribbed shaft. The rotor winding can be either a pressure die cast aluminum or a copper bar construction.Full shaft or drilled shaft according to turbine type. The rotor is dynamically balanced with half a key.

Asynchronous generators are supplied with rolling bearing as standard. The theoretical lifetime of bearings, L10h according to ISO 281/1 standard, of standard horizontal construction generators, without external forces (radial and / or axial) is in excess of 50.000 hours. On request, the lifetime of bearings, L10h can be in excess of 100.000 hours. Usually locating bearing is on the D end side and floating bearing on the ND end side on horizontal machines. Both bearings are fitted with a regreasing system. The used grease is removed through a valve locked in the outer bearing cover. Where special design is requested the proper types and sizes of bearings are selected according to customer requirements, turbine type and loads and confirmed by proven calculations. Using cylindrical roller bearings high radial forces can be supported at the generator shaft end. Radial forces below the minimum value can lead to bearing damages within a few hours. Rolling bearings are lubricated with grease or oil; sliding bearings are lubricated with internal oil or with oil circulated by an external lubrication unit specially developed for hydro generators.

Impregnation system
Stator is VPI treated with an unsaturated polyester amide resin which is polymerised in an oven.

Insulation system
Low voltage. Stator: F class insulated with a synthetic enamel. (H class insulation available on request)

Protective treatments
Dedicated protective enamel is applied on the winding.

Operating conditions

Parallel operations
The most common operation for the asynchronous generators is connected with the electrical grid.ì In this case the generator takes the necessary reactive power from the mains, and additional excitation systems are not necessary. 

The mains maintains voltage and frequency so that separate regulators are not necessary.

Isolated operations
When using asynchronous generators in isolated operation, the excitation is realized through the parallel connection of a capacitor bank. Its dimensioning depends on the generator power and on the generator parameters. The operating mode is considerably more expensive than the parallel operation with the mains and is only used for lower outputs. When compared to a synchronous generator, the induction generator has several advantages:

  • No voltage regulator is required, nor the exciter. Voltage and frequency are controlled by the electrical grid.
  • Exciter is not required. Reactive power is provided by the grid.
  • Simple construction; no brushes, diodes, or collector rings.
  • Lower maintenance costs.

Optional features

  • RTD’s on winding, beraings and air / water circuit
  • flanged shaft or special shaft end on both sides
  • increase protection degree up to IP 56
  • speed measurement (encoder or tachogenerators)
  • vibration sensors
  • special bearings
  • dedicated design for variable speed applications
  • anticondensation heaters
  • flywheel
  • hydraulic brake
  • oil lube system
  • filters on air inlet / outlet
  • other options available on request.