4.4.3 Alternating current engines
Alternating current engines are relatively low power drive units. Above all, they are used in small electric devices and machines.
In the sanitary, heating and air-conditioning sector alternating current engines are e.g. used for circulation pumps, fans, etc. They are mostly being connected with single-phase alternating current (see diagram 47 below).
Very often a capacitor is necessary for starting assistance: Since a capacitor can store electric charges, it helps the engine to create a rotary field. The rotary field is bringing the engine rotor into a rotating movement (rotation).
Three-phase engines are above all used in big installations and for high performance engines. Three-phase engines do not need any capacitors for starting assistance since the three-phase current that is flowing through the windings of the engine produces a rotary field which is propelling the rotor.
Three-phase engines can be operated in y-connection or in delta connection. Up to a power of 3kW they are mostly connected in y-connection.
High-performance three-phase engines often start in y-connection (because of the smaller starting current) and then achieve their full engine performance in delta connection. The engine performance in y-connection reaches about only 1/3 of the engine performance in delta connection:
Diagram 47: Engine connections with protective grounding/earth PE
At the neutral point of the
y-connection (see diagram 48) the voltages neutralise themselves (U ± 0V). Each
string voltage is 230V. Between the string windings of the delta connection (see
diagram 49) the voltage is 400V.
|Diagram 48: Y-connection
||Diagram 49: Delta connection|