Date: 0101-01-01T00:00:00+00:00
Keywords: Alternative Energy

Generators

Omagh College

Principles

• All based on induction

• Electro or permanent magnets

• Power = speed x torque

• Direct or indirect grid connection

• Mostly without slip rings (less
maintenance)

Synchronous machines

Rotating stator field keeps rotor speed constant

Asynchronous machines

Rotating stator field turns the rotor with a certain slip

Torque curve

The steep part of the curve explains how an asynchronous generator can keep the rotor speed almost constant Pole number

• 2 = 3000 rpm

• 4 = 1500 rpm

• 8 = 750 rpm etc

• Some machines can change number of poles, and so optimise the rotor speed

• Multipole generators may be connected directly to the propeller

3-phase generators
are used in almost all
wind turbines

• Permanent Magnet Generators directly coupled to the main shaft are common on small wind turbines.

• Produces ”wild” AC current (variable frequency)

• A few manufacturers use brushless DC generators

Direct grid
connection with
asynchronous
generator (larger
machines)

Indirect grid
connection with
syncronous or
asynchronous
generator (smaller
machines)

Power quality issues (Grid)

• Voltage surges (if cut-in is not soft enough)

• Increased voltage level in weak grids

• Reactive power consumption

• Noise from electronic controls

• Same impact as corresponding motor load