Direct Current Generator

Introduction

Direct current generator produces electric current by the process of electromagnetic induction. The electromagnetic force gives rise to the electromagnetic field. In an electromagnetic field, the electric field and the magnetic field are intertwined. Electromagnetic force determines electromagnetic phenomena. Electromagnetic force is the interaction between charged particles. Lorentz's force is also known as the electromagnetic force.

The electromotive force refers to the amount of work required by a battery pack to move charged particles through an electrical circuit. An electromagnetic field is a natural field caused by the motion of an object which is electrically charged. It affects the behavior of nearby electrified objects. Electric fields are caused by stationary charges and moving charges (currents)they also associated with a magnetic field.

EMI

• Electromagnetic induction (EMI) refers to the generation of voltage between two ends of a conductor when it is subjected to a changing magnetic field.

• Faraday discovered in 1831 that when a magnetic field relative to a coil of wire changes, an electric force is induced in it.

• Faraday showed that whenever there is relative motion between a conductor and a magnetic field, an electric force is induced in the conductor. Such an electric force is called electromotive force and the phenomenon is called electromagnetic induction.

• An inductor induces a current in the electromotive conductor. This current is called induced current.

• Electricity is generated for household and industrial use using the principle of electromagnetic induction.

Direct Current Generator

• Mechanical energy is converted into electrical energy in a generator. If the electrons travel at a uniform speed and in the same direction, the current is called direct current.

• A DC generator is used to generate a continuous constant direct current.

• As in an AC generator, a winding coil fitted with a rotating shaft rotates between the terminals of an electromagnet.

• A DC generator is a slightly modified form of an AC generator. All parts are the same in both.

Principle and Working

• When a coil of electric wire rotates in a magnetic field, a voltage is created across the conductor ends of the coil, and a current flows. This is the basic principle of the generator. It is called electromagnetic induction.

• A split ring commutator is used instead of slip rings to generate direct current (DC). Two semi-circular metal pieces S₁ and S₂ are separated by an insulator.

• When the commutator coil to which the rotating shaft is attached rotates, it rotates with it.

• Part S₁ touches brush B₁ in the first half-cycle. In the second half-cycle, part S₂ touches brush B₁.

• As the direction of motion of each armature of the winding coil changes, the brushes are arranged to touch a specific split ring area.

• One brush is positive and the other negative. Hence the current supplied to the external circuit is unidirectional in nature but its value changes.

• One brush is always in constant contact with the upward armature and the other with the downward armature.

• Hence, the current in the external circuit will flow in a unidirectional direction. This type of generator is called a direct current generator.

Formula

EMF induced in the generator E_g=rate of change of flux

$$\mathrm{E_g=\frac{d \phi}{dt}}$$

$$\mathrm{d\phi=ϕ(total\: flux)\times total\: pole (P)}$$

$$\mathrm{dt=\frac{60}{N}}$$

$$\mathrm{∴ E_g=ϕ_p \frac{ N}{60}}$$

$$\mathrm{N=speed\: of\: armature\: in\: r.p.m}$$

There is a total Z number of conductors in an armature. The total number of conductors in series in a DC generator is $\mathrm{\frac{z}{A}}$

$$\mathrm{Total\: emf\: induced\: E_g=ϕ_p \frac{ NZ}{60A}}$$

A=Number of parallel paths in which Z number of conductors are divided

Solved Examples

1.Calculate the E_g value by a 4 pole lap winding armature with 60 slots and 10 conductors per slot when driven at 1500 r.p.m. (ϕ=0.04 Wb)

$$\mathrm{E_g=ϕP\frac{ NZ}{60A}}$$

$$\mathrm{Pole (P)=4}$$

$$\mathrm{Number\: of\: conductors\: (Z)=10\times 60=600}$$

$$\mathrm{N=1500\: r.p.m}$$

$$\mathrm{ϕ=0.04\: Wb}$$

$$\mathrm{A=P=4}$$

$$\mathrm{E_g=ϕP\frac{NZ}{60A}=[\frac{0.04×600×1500}{60}]\times (\frac{4}{4})}$$

$$\mathrm{E_g=600\: volts}$$

Conclusion

Electromagnetic force determines electromagnetic phenomena. Electromagnetic force is the interaction between charged particles. Electromagnetic induction (EMI) refers to the generation of voltage between two ends of a conductor when it is subjected to a changing magnetic field. If the electrons travel at a uniform speed and in the same direction, the current is called direct current. A DC generator is used to generate a continuous constant value direct current. A DC generator is a slightly modified form of an AC generator. All parts are the same in both.

FAQs

1. How Alternating current is converted into a Direct current?

Alternating current is converted into Direct current by using rectifiers. This process is called rectification. Mostly p-n junction diodes are used as rectifiers. Current flows in one direction when it is allowed by the diode. This property is very useful for the rectification process.

2. Difference between AC and DC

Difference between AC and DC generator

AC	DC
Electric power can be maintained between two long-distance places.	Electric power will be lost in between the long travel. So it cannot be used in long-distance power supplies
Washing machine and fans work on AC . It is widely used in kitchen and household electrical equipments.	Batteries of cell phones and flashlights work on DC. Electric Scooters also work on DC. Mostly used in electronic equipment.
The Average Frequency of AC is 50 Hz to 60 Hz.	There is no frequency for DC. It has a zero frequency.

3. Explain about Loggerhead sea turtles

Loggerhead sea turtles return to the beach years after their birth to lay their eggs. In a study, turtles are said to use a method called geomagnetic localization to locate their natal beaches. These turtles can remember the strength of the magnetic field in different places on Earth. This memory enables them to return home.

4. Properties of EM field

• Ampere's law states that a change in magnetic field creates an electric field. Electric motor works based on this law.

• Electromagnetic waves have volume space (free space) with zero electric charge or current, that is the value of density is zero. These waves are taken by Maxwell’s equations.

5.Describe Magnetic Resonance Imaging (MRI)

It is a non-invasive medical test that helps doctors diagnose and treat abnormalities in the chest, head, pelvis and abdomen. A current is passed and a strong magnetic field is created. This magnetic field generates radio frequency pulses and transmits them to the computer. The computer gives an image of the internal organs with the doctor can treat the internal organs.

6.Define the thermal effect of current

The potential difference between its two electrodes drives electrons through the resistor, creating a current. As current flows the battery must continue to expand its energy. Part of the energy is converted into useful work. The remaining energy is wasted by heating it. If the circuit is made up entirely of resistance, the source’s energy is constantly wasted as heat. This is called the thermal effect of current.