Can a shunt generator self-excite in forward rotation? Can it self-excite in reverse rotation?

Before discussing the self-excitation of a shunt generator, we first need to understand the basic principle and structure of a shunt generator. A shunt generator is a device that converts mechanical energy into electrical energy using the principle of electromagnetic induction. It is mainly composed of a rotor, a stator, an excitation system, and a cooling system. Among them, the excitation system is a key component of a shunt generator, which provides the required magnetic field for the generator.

There are many excitation methods for shunt generators, among which the most common is the shunt excitation method. In the shunt excitation method, the excitation winding is connected in parallel with the output winding of the generator, and the output current of the generator provides current to the excitation winding, thereby generating a magnetic field. This excitation method has the advantages of simple structure, low cost, and easy maintenance, so it has been widely used in industrial production.

Next, let's discuss the self-excitation of shunt generators. Self-excitation means that the generator generates electrical energy through its own magnetic field without an external power supply. For shunt generators, they can be self-excited during forward rotation. This is because during forward rotation, the relative motion between the rotor and stator of the generator will generate an induced current, which will flow through the excitation winding, thereby generating a magnetic field. However, for shunt generators, can they be self-excited during reverse rotation?

First, we need to clarify what is reverse rotation. In a shunt-excited generator, reverse rotation means that the generator's rotor rotates in the opposite direction relative to the stator. In this case, the relative motion direction between the generator's rotor and stator changes, which affects the generation of induced current and the strength of the magnetic field.

During the reversal process, the relative motion direction between the rotor and stator of the generator changes, which causes the direction of the induced current to change. Since the excitation winding of the shunt generator is connected in parallel with the output winding, the change in the induced current will affect the current of the excitation winding. In some cases, this change may cause the current of the excitation winding to decrease, thereby reducing the strength of the magnetic field. If the strength of the magnetic field decreases to a certain extent, the generator may not be able to generate enough electrical energy to maintain the self-excitation state.

However, this does not mean that the shunt generator cannot be self-excited during reversal. In fact, whether the generator can be self-excited depends on many factors, such as the parameters of the excitation winding, the load condition of the generator, the relative speed between the rotor and the stator, etc. Under certain specific conditions, the generator can still achieve self-excitation even during reversal.

For example, if the parameters of the excitation winding are properly designed, the current of the excitation winding will not decrease significantly even during the reversal process, thereby ensuring the strength of the magnetic field. In addition, if the load of the generator is small, then during the reversal process, the change in the induced current has less effect on the current of the excitation winding, which also helps to achieve self-excitation. In addition, if the relative speed between the rotor and the stator is kept within a certain range during the reversal process, the self-excitation ability of the generator may be improved.

In summary, for a shunt-excited generator, whether it can be self-excited during reversal depends on many factors. Under certain specific conditions, the generator can still achieve self-excitation. However, since the relative movement direction between the rotor and stator of the generator changes during the reversal process, this may have an adverse effect on the self-excitation ability of the generator. Therefore, in practical applications, we need to optimize the excitation winding parameters, load conditions, etc. of the generator according to specific working conditions and requirements to improve the self-excitation ability of the generator.