The science behind voltage rise in self-excited generators
Luciano Bertene
A self-excited generator is an electrical generator that can produce excitation or field current without the need for an external power source. Voltage increase is one of the critical processes in the operation of a self-excited generator. Voltage rise is the gradual increase in the generator output voltage from zero to its rated voltage during the starting phase. This happens due to the interaction between the magnetic field created by the generator's field winding and the armature current. Understanding the voltage rise process is crucial for the stable and efficient operation of self-excited generators and therefore represents an essential aspect of electricity generation.
Shunt Generator
When the shunt generator runs at a constant speed, there is an electromotive force created by residual magnetism at the main poles. This small electromotive force creates a field current that successively produces additional flux to amplify the initial residual change. This process continues and the generator accumulates the traditionally generated voltage according to the no-load characteristic, as shown in Fig.
A line through the origin usually represents the field resistance Rf. The two curves are often plotted on a single graph because they require an equivalent ordinate, which is shown in Fig.
From the point where the field circuit is inductive, there is a delay in the current rising as the field circuit switch closes. The rate at this current increases depending on the voltage available for improvement. Assume that the field current is I (= OA) at any time and grows at the rate di/dt. Then the following applies:
E Ó =IR F +Ldi/German
Where,
R F = Total resistance of the field circuit
L = field circuit inductance
Characteristics of a separately excited direct current generator
At one moment, the total electromotive force available in AC – the amount AB of the electromotive droplet iRf absorbs AC, and the remaining portion BC is available to overcome L di/dt. Because this excess voltage is available, it is possible for the field current to increase beyond the OA value. However, at point D, the available voltage is OM, which the drop I Rf absorbs. Consequently, the field current cannot increase any further and the generator stops working.
Finally, it must be said that the intersection of the no-load characteristic and the field resistance line determines the voltage increase of the generator. Fig. c, D is the intersection of the two curves. The generator can therefore create an OM voltage.
Series generator
In primary operation, when there is no current flow, a residual voltage is generated, especially with a shunt generator. Residual voltage can cause a current to flow through the entire circuit when the circuit is closed. There is an increase in voltage to a balance point equivalent to that of a shunt generator. The voltage rise graph is similar to that of the shunt generator, except that the current load current (instead of the field current in the shunt generator) is plotted on the X-axis.
DC shunt generator load distribution
Load sharing in DC generators is critical when multiple generators are connected in parallel to supply power to a common load. To achieve load distribution, sag control is often used. Each generator has a droop control device, such as an electronic or mechanical controller, that adjusts its field current or excitation to vary its speed and output voltage. The generator speed decreases as the load increases, causing the output voltage to decrease.
Connection Generator
When a compound generator uses its field flux in series and maintains its field flux in shunt, the machine is called a cumulative compound generator. The generator is said to be differentially coupled when the series field is inversely coupled so that its field flux opposes the shunt field flux.
The easiest way to increase voltage on a compound generator is to start it at idle. When inactive, only the shunt field is effective. As soon as the no-load voltage increases, the generator is charged. If the voltage increases under load, the series connection is cumulative. If the voltage drops significantly, it is a differential compound.
Conclusion
In summary, the increase in voltage in a self-excited generator is a fundamental process that ensures that the generator can produce electricity autonomously. The generator generates its magnetic field through a self-excitation mechanism, allowing it to start generating electricity without the need for an external source of excitation. We examine the different methods to achieve voltage increase, such as: B. Residual magnetism and use of capacitors in the excitation circuit. Understanding this phenomenon is critical to maintaining stable and reliable power generation in a variety of applications, from small portable generators to large power plants. By optimizing voltage generation techniques, we can improve the efficiency and performance of self-excited generators, contributing to a more resilient and sustainable electrical infrastructure.
