Losses in DC Machines
It is well-known that “Energy neither can be made nor it can be destroyed, it must be transferred from one form to another form” . A direct current (DC) machine converts mechanical energy into electrical energy. During this procedure, the entire input power is not converted into output power. Some of the input power is squandered in various forms. The types of losses may differ from one equipment to the next. As the temperature rises, these losses reduce the machine’s efficiency. There are four major forms of energy loss in a DC machine.
Copper losses
- Copper losses are winding losses that occur as the current flows through the windings. These losses occur due to resistance in the winding. In a DC machine, there are just two windings: armature and field winding.
- In this fashion, copper losses are classified into three types: armature losses, field winding losses, and brush contact resistance losses. Copper losses are proportional to the square of the current passing through the winding
Armature Copper Losses
- Armature copper loss = Ia2 Ra.
- Where Ia represents armature current and Ra represents armature resistance.
- These losses represent around 30% of the total full load losses.
Field Winding Copper Losses
- In a DC machine, the field winding copper loss =[Tex] I_f^2 R_f.[/Tex]
- where [Tex]I_f[/Tex] denotes the field resistance and [Tex]R_f[/Tex] represents the field current.
- The theoretical losses are roughly 25%, but in practice, they are constant.
Brush Contact Resistance Loss in DC Machine.
Brush contact losses are due to resistance between the outer layer of the brush and the commutator. It’s everything but losses that can be calculated individually since it’s a collection of variable losses. Overall, it contributes to both types of copper loss. As a result, they are taken into account when calculating the losses listed earlier.
Core or Iron Losses
As the iron core of the armature rotates in a magnetic field, certain losses occur in the core, known as center losses. These losses are essentially constant since machines normally run at the same pace. These losses are classified into two types: eddy current and hysteresis losses.
Hysteresis Loss in a DC Machine
Hysteresis losses occur in the armature winding as the core’s polarization reverses. When the core of an armature is subjected to a magnetic field, it undergoes a full magnetic reversal. After a full half electrical revolution, the section of the armature under the S-pole is replaced by a corresponding piece under the N-pole, and the magnetic lines are reversed to reverse the attraction within the core. The continual process of magnetic reversal in the armature consumes some energy, known as hysteresis losses. The degree of loss is determined by the iron’s grade and volume.
The frequency of magnetic reversal is f = P N / 120.
Where,
P = number of poles.
N = Speed (rpm)
Construction And Working of a DC Generator
In 1831, Michael Faraday, a British physicist, devised the electromagnetic generator. The primary function of this device is to convert mechanical energy to electrical energy. There are several types of mechanical energy sources available, including hand cranks, internal combustion engines, water turbines, and gas and steam turbines. The generator provides capacity for all electrical power networks. An electric motor should be able to perform the generator’s converse function. The basic purpose of the motor is to convert electrical energy into mechanical energy. Generators and motors have many properties.
Table of Content
- DC Generator
- Construction of a DC generator
- Workings
- Types
- Losses in DC Machines
- Characteristics of DC Generator
- Characteristics of DC Series Generator
- Characteristics of DC Shunt Generators
- External Load Characteristics of the DC Compound Generator
- Efficiency of a DC Generator