Methods of excitation of DC machines and their classification

The current flowing in the excitation coil of the main poles creates a magnetic flux ... DC electric machines must differ in the method of excitation and the circuit for turning on the excitation coil.

DC generators can be run with independent, parallel, series and mixed excitation. It should be noted that the use of DC generators as power sources is now very limited.

Excitation winding A DC generator with an independent excitation receives power from an independent source - a direct current network, a special pathogen, a converter, etc. (Fig. 1, a). These generators are used in high power systems where the excitation voltage must be chosen different from the generator voltage, in systems motor speed controlpowered by generators and other sources.

The value of the excitation current of powerful generators is 1.0-1.5% of the generator current and up to tens of percent for machines with a power of the order of tens of watts.

Rice. 1.Schemes of DC generators: a — with independent excitation; b — with parallel excitation; c — with consistent excitement; d — with mixed excitation P — consumers

I have a G generator with parallel excitation, the excitation coil is connected to the voltage of the generator itself (see Fig. 1, b). Armature current Az is equal to the sum of load currents Azn and excitation current Azv: AzAz = AzNS + Azv

Generators are usually made for medium power.

Winding excitation generator of series excitation connected in series to the armature circuit and flowing from the armature current (Fig. 1, c). The self-excitation process of the generator is very fast. Such generators are practically not used. At the very beginning of the development of the power sector, a power transmission system with series-connected generators and series-excitation motors.

The generator with mixed excitation has two excitation windings — a parallel ORP and a series ORP usually with the inclusion of consonants (Fig. 1, d). The parallel winding can be connected before the series winding («short shunt») or after it («long shunt»). The MMF of a series winding is usually small and is only intended to compensate for the armature voltage drop under load. Such generators are now also practically not used.

Excitation circuits for DC motors are similar to those for generators. DC motors usually high power independently excited... In parallel field motors, the field winding is supplied from the same power source as the motor.The excitation coil is connected directly to the power source voltage so that the influence of the voltage drop in the starting resistance is not affected (Fig. 2).

Rice. 2. Schematic of a DC motor with parallel excitation

Mains current Integrated circuit composed of armature current Azi and excitation current Azv.

A series excitation electrical circuit is similar to the diagram in fig. 1, c. Due to the series winding, the load torque increases more than in parallel excitation motors, while the rotation speed decreases. This property of the motors determines their wide use in traction drives of electric locomotives: in highway electric locomotives, urban transport, etc. The field winding voltage drop at rated current is a few percent of the rated voltage.

Mixed excitation motors, due to the presence of a series winding, have to some extent the properties of series excitation motors. Currently, they are practically not used. Parallel excited motors are sometimes made with a stabilizing (series) winding connected in line with the parallel field winding to provide quieter operation at peak loads. The MDS of such a stabilizer coil is small — a few percent of the main MDS.