How does DC Generator work? | What are the types of DC Generators?

What is a DC Generator?

A direct current generator or DC generator is an electrical device that converts mechanical energy into direct current. The output direct current is used to charge the battery or to run many other electrical devices.

DC Generator

DC generator generates electricity using Faraday’s law of electromagnetic induction. According to this law, when a conductor rotates in a magnetic field, the magnetic lines of force intersect. This process induces an electromagnetic force in the conductor due to that, DC power is produced. 

Working Principle of DC Generator

The DC generator works on Faraday’s laws of electromagnetic induction.

According to this law, as the conductor moves in a magnetic field, the e.m.f induces within the conductor. The magnitude of the induced electromagnetic force is calculated by using the generator e.m.f equation.

When the conductor is located within a closed lane, the induced current will flow in the lane.

DC Generator working

In this generator, the field coil generates the electromagnetic field, and the armature conductor is changed into the field. Therefore, the electromagnetically induced e.m.f generates within the armature conductor. Fleming’s right-hand rule uses to provide the induced current path.

Construction of DC Generator

You may use a DC generator as a DC motor without any improvement in the structure. The below-given structure represents the 4-pole DC generator.

It contains various components such as brushes, commutators, pole shoes, armature windings, armature cores, field winding, poles, and Yoke. The rotor and stator are the main parts of this generator.

DC Generator Parts

The DC generator has the following parts:

  1. Stator
  2. Rotor
  3. Armature Winding
  4. Yoke
  5. Poles
  6. Pole Shoe
  7. Commutator
  8. Brushes
  9. Yoke

DC generator parts

1) Stator

The stator provides a magnetic field where the conductor rotates. The stator contains two magnets facing each other with reverse polarities. These magnets usually install in the rotor area.

2) Rotor

The rotor of the DC motor consists of a slotted iron lamination with slots assembled to form a cylindrical armature core. The lamination reduces the eddy current losses.

3) Armature Winding

It is installed in a closed-circuit design. The windings connect in series to parallel to increase the total output current.

4) Yoke

The Yoke is the external construction of the DC generator. Steel or cast iron is used for the construction of the Yoke. The armature core slots usually use to hold the armature winding.

5) Poles

The pole holds the field winding. The field windings are twisted in series or parallel to the poles through armature winding.

6) Pole Shoe

The main function of the pole shoes is to spread the magnetic flux and stop the field coils from falling.

7) Commutator

This part of the DC generator acts as a rectifier, converting the alternating current to direct current in the armature winding. It contains copper segments; each copper segment protects the other segment with the help of a mica sheet. The commutator is usually installed on the machine shaft.

8) Brushes

With the help of a brush, you can secure the electrical connection between the external load circuit and the commutator.

9) Yoke

The yoke is the outer structure of the generator. Steel or cast iron uses to manufacture the Yoke. It provides the required mechanical force to transport the magnetic flux to the pole.

Read More: AC Generator Working and Types

Function of DC Generator

The main function of a DC generator is to convert the mechanical energy into direct current. The generator has a commutator that converts the alternating current into directing current. This commutator works as a reversing switch.

The electromotive force induced in the generator armature coil is alternating. Therefore, the armature coil current can also be AC. Therefore, a commutator uses to convert this AC into DC.

As the armature coil runs through the non-biased magnetic axis, the commutator can reverse the output current at just the right moment. Therefore, the battery or other load connected to the generator receives DC or unidirectional current.

The commutator ensures that the generator current always flows in one direction. The brush moves across the commutator to create a high-quality electrical connection between the load and the generator.

Types of DC Generators

The DC generator has the following major types:

  1. Separately excited generator
  2. Self-excited generator

1) Separately Excited Generator

In this type of DC generator, an autonomous external DC source uses to strengthen the field coils.

2) Self-Excited Generator

In these types of DC generators, the output current of the generator uses to strengthen the field coils. The induction of the first emf occurs due to its excellent magnetism within the field pole.

The resultant emf applies a small current to the field coil, which increases not only the emf but also the magnetic flux of the field. These types of DC generators are further divided into the following types:

  1. Series Wound: In this type of DC generator, the armature winding and field winding connects in series.
  2. Shunt-wound or Parallel Wound: In this type, the armature winding and field winding are attached in parallel with each other.
  3. Compound Wound: It is a combination of series and parallel windings.

Losses in DC Generators

The DC generator converts mechanical energy into electrical energy. During this energy conversion process, some parts of energy losses, i.e., not all input energy is transferred to the output. Following are the major energy losses in the DC generator:

1) Copper Loss

The copper loss occurs during the flow of current through the winding. In the case of a parallel wound DC generator, the filed copper loss is equal to Ish2Rsh and is almost stable. For the series wound generator, the field copper loss is equal to Ise2 Rise and almost constant.

The copper losses are further divided into the following types:

  1. Losses due to brush resistance
  2. Armature copper loss
  3. Loss of field copper winding

2) Iron Losses

Hysteresis losses and eddy current losses are caused due to the induced current in the armature. These losses are also referred to as magnetic losses or core losses.

3) Hysteresis Losses

The hysteresis losses occur due to the inversion of the armature core. Each section of the rotor core alternates under the north and south poles, achieving S and N polarity accordingly.

4) Eddy’s Current Loss

The armature core can block the flux during its rotation and induce an electromotive force within the outside of the core.

According to the law of electromagnetic induction, this electromotive force is very small but creates a large current at the core surface. This enormous current is called eddy current, and the loss is known as the eddy current loss.

The core losses of parallel and compound wound generators are stable due to their fairly constant field current. This loss mainly occurs between 20% and 30% of the full-load losses.

5) Stray Loss

This loss mainly takes place due to the combination of machine loss and core loss. The stray loss is also referred to as spin loss.

6) Mechanical Loss

The loss caused by friction between generator components is known as mechanical loss.

Advantages of DC Generator

  • It generates a large output current.
  • These generators have a high terminal load.
  • It is very simple to design.
  • They use to produce uneven output power.
  • The DC generator is highly consistent, with an efficiency rating between 85% to 95%.
  • These generators supply a reliable output.
  • They have a compact design and are lightweight.

Disadvantages of DC Generator

  • You can’t use a dc generator with a transformer.
  • These generators have more losses (such as eddy current, mechanical, copper, etc.) than AC generators. Therefore, they have low efficiency.
  • They require high maintenance.
  • They are costly.
  • High energy is lost during the transmission process.
  • The spark is generated while generating energy

 Applications of DC Generators

  • The series DC generators are used in arc lamps for booster, stable current generator, and lighting.
  • They are used to charge vehicle batteries.
  • The DC generators are used to supply power to DC welding machines.
  • The compound DC generators use to supply power to offices, lodges, hostels, etc.
  • Over compound, DC generators use to return the voltage drop within Feeders.
  • They use to supply power to the DC devices.

Difference between DC Generator and AC Generator

AC GeneratorDC Generator
AC generator changes the mechanical power into alternating current.  DC generator changes the mechanical energy into direct current.
It uses slip rings.It uses slip rings to change the AC power into DC power at the output terminal
It has simple construction and design.It has a little bit complex design than an AC generator due to slip rings and commutators.
It periodically reverses the direction of the electrical current.In this generator, the current runs only in one direction.
These generators don’t contain a commutator.This generator uses a commutator to ensure the current flow in one direction only.
It contains slip rings.It uses commutators.
It is more efficient due to low power losses.It is less efficient due to low power losses.
In an AC generator, the output current can be either induced in the rotor or in the stator.In a DC generator, the output current can only be induced in the rotor.
It has more cost than a DC generator.It is less expensive than an AC generator.

FAQ Section

What is a DC generator?

A DC generator is an electrical device that uses to transform mechanical power into electrical power.

What are the types of generators?

The generators have the following types:

  1. DC generator
  2. AC generator

What is the Yoke?

Yoke is the external structure of the DC generator.

What are the types of self-excited generators?

The self-excited generators have the following types:

  1. Compound generator
  2. Shunt generator
  3. Series generator

What are the types of DC generators?

  1. Separately excited generator
  2. Self-excited generator  

What are the parts of the DC generator?

  1. Stator
  2. Rotor
  3. Armature Winding
  4. Yoke
  5. Poles
  6. Pole Shoe
  7. Commutator
  8. Brushes
  9. Yoke

What is the difference between a DC generator and an AC generator?

The main difference is that the DC generator converts the mechanical power into the direct current, while the AC generator converts the mechanical power into an alternating current.

What is DC generator example?

The alternator of your car (i.e., the DC generator which recharges your car’s battery) is a most common example of the DC generator.

What is the output of DC generator?

The output frequency varies (mostly 50Hz to 60Hz). DC generators produce a low voltage than AC generators which is constant in amplitude and time i.e., the output frequency is zero.

What frequency is DC?

DC has a frequency of zero. Direct current is the current that moves in only one direction and has a constant strength.

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