What is a DC Generator

In this article, we will discuss DC Generator (Direct Current Generator), an electrical machine that converts rotational mechanical energy into direct current electricity.

Definition of DC Generator

A DC generator, also called a direct current generator or a dynamo, is a type of rotating electrical machine that converts mechanical energy into dc electrical energy by utilizing the principle of electromechanical energy conversion.

The source of mechanical energy input to a dc generator can be a turbine or diesel engine.

Construction of DC Generator

The construction of a dc generator is shown in the following figure.

A DC generator has the following main parts:

(1). Stator – It is the stationary part of the dc generator. In a DC generator, the stator forms the magnetic field system of the machine.

(2). Armature – It is the rotating part of the dc generator, also called the rotor. It has a cylindrical armature core made up of silicon steel laminations.

(3). Armature Winding – It is a coil made up of copper wires. In a dc generator, the armature winding is provided on the rotor/armature. The voltage is generated in the armature winding. In a DC generator, there are two types of armature winding based on the construction namely, LAP Winding and Wave Winding.

(4). Yoke – It is the outer frame of the dc generator that provides the mechanical covering to internal parts of the generator. It also provides a low reluctance path to the stator magnetic field.

(5). Magnetic Poles and Pole Shoes – Magnetic poles are electromagnets used to produce a working magnetic field in the machine. The pole shoe is the front part of a magnetic pole which is mainly used to spread a magnetic field uniformly in the air gap.

(6). Commutator and Brushes – It is one of the most important parts of a dc generator. It is a cylindrical shaped part of the machine made up of copper segments and mounted on the rotor shaft with insulation between them. It acts as a mechanical rectifier to convert generated alternating current in the armature into direct current in the external circuit. The brushes are installed to make a connection between the stationary external circuit and the rotating commutator. Brushes are made up of carbon/graphite.

Working Principle of DC Generator

The working of a dc generator is based on the principle of electromagnetic induction, which says that whenever there is a relative motion between a conductor and a magnetic field, an emf is induced in the conductor. The magnitude of this induced emf is given by,

`\e=N (dϕ)/dt`

Where, e is the induced emf, N is the number of conductors/turns in the coil, and dϕ/dt is a time-varying magnetic field.

When the armature of a DC generator is rotated by a prime mover like a turbine, there will be a relative motion between the stator magnetic field and the armature winding. Due to this relative motion, an emf or voltage is induced in the armature winding. This generated emf is alternating in nature. Hence, a mechanical rectifier called a commutator is employed to convert this alternating emf into direct voltage. The carbon brushes are used to collect this voltage and supply it to the external circuit with a constant polarity.

Types of DC Generators

Based on the connection between armature winding and field winding, dc generators are classified into the following four types:

(1). Separately Excited DC Generator:

A separately excited dc generator is one which has a field winding excited from some external dc power supply. There is no direct connection between the field winding and armature winding.

(2). Series DC Generator:

A series dc generator is one in which the field winding and armature winding are connected in series with each other.

(3). Shunt DC Generator:

A shunt dc generator is another type of dc generator in which armature and field windings are connected in parallel with one another.

(4). Compound DC Generator:

A compound dc generator is a combination of both series and shunt generator, in which the series and shunt field windings are used simultaneously. Based on the connections of series and shunt windings, there are two types of compound dc generators namely short-shunt generators and long-shunt generators.

Advantages of DC Generators

The following are some major advantages of a dc generator:

• DC generators are simple to design and manufacture.
• A dc generator can also be used as a dc motor.
• DC generators can produce a consistent voltage with around 90% efficiency.
• DC generators can be designed in various sizes.

Disadvantages of DC Generators

The following are the major key disadvantages of dc generators:

• The output of a dc generator cannot be transformed by using a transformer.
• DC generators have higher mechanical losses.
• DC generators cannot be used to supply voltage over longer distances.
• DC generators require higher maintenance.

Applications of DC Generators

The following are some important applications of dc generators:

• DC generators are used to generate large dc voltages required to run dc motors.
• DC generators are also used in electroplating plants.
• DC generators are used to charge large batteries in industries.
• DC generators are also used to power dc welding machines.
• DC generators are also used as boosters in transmission lines.

Hence, this is all about DC generators, their types, construction, and applications. In conclusion, a DC generator is an electrical machine used for generating direct current electricity.