Three-phase generator

Scheme of a simple three-phase generator. The rotating permanent magnet creates a three-phase system with the external conductor voltages L1, L2 and L3 in the coils by induction.

Equivalent circuit diagram of the linked generator star

Graphical representation of three-phase alternating voltage with the three phases L1, L2 and L3, which are plotted once measured on the neutral conductor N and plotted once chained to one another.

The three-phase generator is a special form of the electrical generator , which induces three independent alternating voltages in the strands of its stator winding offset by 120 ° (see internal pole machine ). The three alternating voltages, i.e. the three-phase alternating voltage , have the same frequency , amplitude and a phase shift of 120 ° to one another. The three strands of the stator winding form a linked system. They are either connected in a star or a triangle . The star connection is used when a center conductor (neutral conductor) is required. The inventor of the three-phase generator was Friedrich August Haselwander .

commitment

Typical representatives of three-phase generators are the three-phase synchronous generator and the three-phase asynchronous generator . Three-phase synchronous generators are of great importance in large-scale power generation. They are used, for example, in steam power plants or hydropower plants . For the Finnish nuclear power plant Olkiluoto , Siemens manufactured what is currently (as of 2010) the largest generator, a three-phase synchronous generator with a nominal apparent power of 1,992 MVA. Three-phase asynchronous generators are used in the lower power range, for example in wind turbines and emergency power generators .

Induced tension

From and it follows for the induction voltage (induced string open circuit voltage ): ${\ displaystyle v = \ pi \ cdot d \ cdot n = \ pi \ cdot d \ cdot {\ tfrac {f} {p}}}$ ${\ displaystyle u _ {\ text {ind}} = B \ cdot l \ cdot v \ cdot z}$

{\ displaystyle {\ begin {aligned} U _ {{\ text {Str}}, 0} & = 2 \ cdot B \ cdot l \ cdot v \ cdot N_ {S} \\ & = 2 \ cdot B \ cdot l \ cdot \ pi \ cdot d \ cdot {\ frac {f} {p}} \ cdot N_ {S}, \ end {aligned}}}

wherein the speed , the circular constant , the rotor diameter , the rotor length , the rotational frequency , the number of pole pairs , the magnetic flux density , the conductor (an) number and the number of coil turns is. The product has to be doubled because with 3-phase alternating current (three-phase current) in the generator there are forward and return conductors (through which current flows) . ${\ displaystyle v}$ ${\ displaystyle \ pi}$ ${\ displaystyle d}$ ${\ displaystyle l}$ ${\ displaystyle n}$ ${\ displaystyle p}$ ${\ displaystyle B}$ ${\ displaystyle z}$ ${\ displaystyle N_ {S}}$ ${\ displaystyle B \ cdot l \ cdot \ pi \ cdot d \ cdot {\ tfrac {f} {p}} \ cdot N_ {S}}$