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Home / Download Center / Electrical Engineering Books and Technical Guides / Electricity generation, t&d guides / Detailed electrical design of a small hydropower plant (from turbine, generator to transformer)

Synchronous generator

Synchronous generator of natural air-cooled self ventilated with brush less excitation will be used. The generator shall be capable of delivering 10% continuous overload and must be designed to with stand the runaway speed of the turbine for 30 minutes without any detrimental effect.

Detailed electrical design of a small hydropower plant (from turbine, generator to transformer)
Detailed electrical design of a small hydropower plant (from turbine, generator to transformer) – photo credit: Peter Goldberg

The generator shall be star connected complete with stator, rotor, bearings, stator temperature detector, oil coolers for bearings, brush less excitation system, AVR and protection equipment.

The generator must be able to operate in parallel with other generator and with grid also.

The generator stator and rotor shall have class F insulation Class B temperature rise and designed for continuous operation at 10% overload with screen-protected enclosure.

The six terminals from three main windings shall be brought out to the terminal box. The generator neutral shall be directly or through resistor / transformer connected to earth through disconnecting link.

The generator shall be capable to operate with either leading or lagging power factor by control of excitation. The power factor commonly ranges between .80 and 1.0.

The synchronous generator will be capable to establish its own operating voltage and maintain frequency while operated isolated. Thus if interconnection to the power system is severed, the generator may continue supplying the station and local load.

Typical single line diagram for 2x25 KW hydro generator sets with one transformer for each unit
Typical single line diagram for 2×25 KW hydro generator sets with one transformer for each unit

Basic Parameters of generator

  • Rated output kVA
  • Rated terminal voltage kV
  • Power factor .8 to 1.0
  • Frequency 50 Hz
  • No. of phases 3
  • Speed RPM
  • Range of voltage variation + 10%
  • Range of frequency variation + 3%
  • Short circuit ratio > .8
  • Inertia constant > 1.0

Rated voltage of generator

Followings are recommended rated voltages for generators of different rated output.

  • Up to 500 KW 415 V
  • 501 to 2500 KW 3.3 KV
  • 2501 to 5000 KW 6.6 KV or 11 kV
  • More than 5000 KW 11 KV

Range of voltage variation

The generators are normally manufactured to + 5% voltage variation range. The voltage variations at the location of mini/small Hydro Power Station is very much higher to the range of say + 10% to + 15%.

The higher voltage variation range call for much higher sized machine and more pertinently, a special design machine. It is therefore desirable to use standard design machine and try to adopt means to deal with voltage variation in, for instance, by changing taps of transformer.

Speed of generator

The generators are manufactured having standard speed of 500, 750, 1000 or 1500 RPM. In case the speed of turbine is low than the speed of standard generator, gear/ belt drive may be used to match with the speed of standard generator.

The noise level of a generator must not exceed 90 dB when measured at a distance of 1.0 meter from any component of the generator.

Title: Detailed electrical design of small hydropower plant (from turbine, generator to transformer) – Alternate Hydro Energy Centre; Indian Institute Of Technology, Roorkee
Format: PDF
Size: 8.0 MB
Pages: 162
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Detailed electrical design of small hydropower plant (from turbine, generator to transformer)
Detailed electrical design of small hydropower plant (from turbine, generator to transformer)

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3 Comments


  1. G.Venkatesh
    Jan 23, 2019

    Why speed of turbine is low than the standard generator?


  2. G.Venkatesh
    Jan 23, 2019

    What happens when generator noise level exceed to 90db?


  3. YEOSHUA SAADA
    Jan 17, 2019

    Hello!
    This Hydro generator works at a mediocre performance. It would be possible to improve the yield by purifying the grid! Increasing real power by more than 10 %!

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