DC generator is the electrical machine that is used to convert mechanical energy into dc electrical energy by the principle of electromagnetic induction. There are two types of generators, AC generator and DC generator. In this article, we will learn about DC generator.
construction of dc generator
DC generator consist with different main parts like other DC machines.
Stator : stationary part of DC generator is called stator
Stator frame : outer portion of machine is known as frame or yoke that play very important role in the working of dc generators. It provide mechanical strength and protect from mechanical damage. It provide the support to pole core and provide low reluctance path for the magnetic flux.
Stator core : stator core of DC machine is made up of laminated silicon Steel where poles are present at inner portion. Structure of poles like it consist with pole core and pole shoe. Silicon Steel has high permeability and it provide lower reluctance path for the magnetic field lines.
And lamination is the arrangement of various thin metal sheets where each sheet laminated to each other. We provide lamination in the machine core to reduce electrical losses like eddy current loss.
Pole core : sarface of pole core remain curved , usually Pole core and pole shoe are made up of cast steel and Pole core has different features.
- Pol core provide support to the field coil or exciting coil
- it spreads the magnetic flux towards rotor periphery of the DC machine.
- pole core increases the cross section area of magnetic path so reluctance of magnetic path decreases and magnetic field line easily passes.
Field winding : field winding placed around the pole core that is also known as exciting winding , main purpose of field winding is to produce magnetic flux. Field winding is made up of enameld copper wire, enamel coating provides insulation and we use copper wire due to their good electrical conductivity.
Field coils are connected in series and develop opposite magnetic polarity between adjacent pole.
Armature : the rotating part of DC generator is called as armature.
slots are present at the outer portion of armature core were we place armature winding. There are two main purpose of armature core armature core houses the armature conductor in the slots and it provides an easy path for the magnetic flux.
armature is the rotating part of DC generator so there will be more chance of hysterosis loss that’s why it is designed of laminated Silicon Steel. Diameter of lamination Stamping of armature core is about 0.3 to 0.5 mm and each laminations insulated to each other by the coating of varnish. And insulated armature coil is placed in the slots of armature.
energy conversion take place where armature winding placed. in case of DC generator mechanical power converted in electrical power. There are two types of armature winding Lap winding and wave winding
in lap winding conductor arranged like number of parallel path is equal to the number of pole. And in case of wave winding conductors are divided into two parallel path with irrespective to the number of pole of the machine.
Commutator : commutator is the most important part of the DC generator it rotates with armature and it is made up of hard drawn bars. Each commutator segment connected to the end of the armature coil. It connect the rotating armature with external circuit through brush and it convert the induced AC voltage in DC voltage.
Brush : Carbon brushes are attached with commutator segment that is used to collect the current from armature conductor.
Working principle of DC generator
first of all we give DC supply in field winding that is also known as exciting winding. So due to DC current flowing in the inductive winding, constant magnetic field produces. To produce filled flux permanent magnets are also used instead of electromagnet but in large DC generator generally we prefer electromagnet.
since DC generator convert mechanical Input in to electrical energy so we use external prime mover to give mechanical input. As prime mover we can use IC engine , steam engine , water wheel , turbines etc.
suppose we are using IC engine as prime mover to rotate the rotor and generator shaft is coupleed with IC engine shaft , when IC engine operates then coupled shaft of DC generator also rotate and receives the mechanical energy produced by IC engine.
when armature of DC generator rotates then armature conductor cuts the constant magnetic field that produced by field winding due to DC supply.
when armature conductor cuts the stationery magnetic field than EMF induces in the armature conductor from Faraday’s law of electromagnetic induction .
according to this principle whenever changing magnetic field cuts the stationery conductor or variable conductor cuts the stationery magnetic field then in both of the case due to relative motion between conductor and magnetic field EMF induces in the conductor.
in case of DC generator armature conductor is variable and field flux is stationery stationery so due to relative motion between stationary field flux and variable armature conductor EMF induces in the armature conductor. Armature conductors are sort circulated so AC nature of current generates in the armature conductor. Initially AC current induces in the armature winding whose direction is determined by the flaming right hand rule.
and commutator converts the induced AC current in armature winding to the DC current in output of DC generator. Commutator behave like mechanical rectifier that converts induced AC into DC current. Carbon brushes that attached with the commutator , collect DC current and supply to the load. Thus dc generator generates the dc current.
Applications of dc generator
- separately excited DC generator and compound type Dc generators are usually used for providing power for lighting and general power distribution
- Dc generators are used for the battery charging in vehicles and other battery bank.
- differential compound wound DC generator is used for the AC welding because that have ability to provide large voltage drop and constant current.
- DC shunt generator is used for the excitation of alternator in different power plant like thermal power plant.
- in electrical distribution system DC series generator is used as boosters where it compensate the voltage drop in feeders.
Other Topics
- DC motor working
- Dynamic braking
- Plugging braking
- Lap winding and wave winding
- BLDC Motor
- Commutation in dc machine
- Video