Understanding Generators and Motors: Principles and Initial Flashes

Generators and motors are two of the most fundamental components in electrical engineering, both based on the principles of electro-magnetic attraction and/or repulsion. This article aims to provide a deeper understanding of the starting principles of generators and motors, with a specific focus on the initial flashing of windings in DC generators. We will also explore common starting problems and how to overcome them.

Principles of Generators and Motors

Generators and motors operate on similar principles, but they function in opposite directions. Both rely on electro-magnetic forces to convert mechanical energy into electrical energy (in generators) or vice versa (in motors).

Generators: When a conductor is moved through a magnetic field, it induces an electromotive force (EMF), generating electricity. This is based on Faraday's law of induction. Motors: When an electrical current passes through a conductor placed in a magnetic field, it experiences a force that causes its motion. The principle here is the interaction between the current and the magnetic field.

Initial Flashes in Shunt DC Generators

When a shunt DC generator is first energized, there is no current in the field, hence no flux and residual flux. Without any flux, flux cutting and EMF induction do not occur, resulting in no voltage across the field winding, and hence no current in the field. In essence, a dead loop exists unless action is taken to initiate the process.

To break this loop, a process known as flashing the windings is employed. This involves briefly applying current to the field winding, which generates residual flux. This initial torque input facilitates flux cutting, leading to the induction of EMF. The induced EMF then causes more current to flow through the field winding, leading to increased flux and further EMF generation. This process continues until the system reaches a self-sustaining state where the generated flux is additive and continues to build up.

Understanding the Cycle

Let's break down the cycle more succinctly:

No current, no flux. No flux, no EMF. No EMF, no more current in the field winding. No current in the field winding, no flux. Flash the windings to generate residual flux. Initiate torque input to induce flux cutting and EMF. Induced EMF causes more current and more flux. A self-sustaining state occurs where flux and EMF continue to build up.

The cautionary note to remember is that the residual flux and generated flux must be additive. If they cancel each other out, the system will revert to the dead loop.

Common Starting Problems

Starting problems in generators can arise from various issues, such as insufficient voltage, mechanical faults, and overloaded conditions. These problems can disrupt the normal starting process and affect the overall performance of the generator.

Conclusion

Generators and motors are indispensable components in many applications, from power generation to industrial machinery. Understanding the starting principles and the initial flashing of windings is crucial for ensuring optimal performance. Whether in a shunt DC generator or a motor, the principles of electro-magnetic forces and the additive nature of flux are fundamental to their operation.

For a more detailed exploration, refer to standard books and consult with industry experts. By grasping these concepts, you can better diagnose and solve starting problems in generators and motors, ensuring reliable and efficient operation.