 Myself, Mrs. Veena Sunilpatki, Assistant Professor, Department of Electronics Engineering, Valkan Institute of Technology, Solapur, welcome you for this session. At the end of this session, students can describe and draw the construction of DC machine and types of generator. DC generator is the machine which converts mechanical energy into electrical energy. It is based on the principle of production of dynamically induced EMF according to Faraday's law. When we rotate the conductors in magnetic field, EMF is induced in that conductors. For this, here the magnetic field is required and rotating conductors are required. Now let us see about the construction of DC generator. To create the magnetic field, poles are used and to rotate the conductors, armature used. So these are the parts of DC machine, yoke, field poles, pole shoes, armature core, armature winding, commutator, brushes and shaft. Let us discuss about this one by one. Yoke is the outer part of the machine. It acts as a frame of machine. It provide mechanical support for field poles and field winding. It has low reluctance for magnetic flux and cast iron is used for small machine and cast steel is used for large machine. Now let us see about the field poles and pole shoes. You can see here these are the field poles which create the magnetic field in the machine. So this is the core, on that core the winding is placed and the large cross section is provided due to that it has the low reluctance. This is the former, over there the winding is placed. So here when the current flows through that coil, you can see the magnetic field is created around that coil and due to this circular shape that magnetic field is spread out uniformly over the armature core. Now let us see about the armature. Armature is the part of the DC generator which holds the armature conductors and this is the cylindrical shape. You can see here and has the low reluctance and drum shaped and this armature is the laminated using circular sheets and to reduce the ED current losses in this armature core generally the sheets are used and we can wound the armature winding in these slots. You can see here this is the armature and the armature winding is placed. So there are two types of armature windings. One is the lap winding and another is the wave winding. So here the lap winding and wave winding is bounded. So in for this lap winding, number of parallel paths equal to number of poles, equal to number of brushes. This lap winding is suitable for high current, low voltage machines like welding plants. For this wave winding, number of parallel paths equal to 2. This winding is suitable for high voltage and low current machine like generators used for lighting. Now let us discuss about the commutator. This commutator is very important in DC generator because when we rotate the conductors in magnetic field, EMF induced in that conductors is having the nature AC. So this commutator is used to convert that AC into DC current. So cylindrical structure is there and is built up of wedge shaped segments of high conductivity. So copper segments are used for that. That copper segments are separated with each other by using insulation, mica insulation. The brushes are used which are connected to commutator. So this is the part of commutator and the brushes are connected over there. So you can see here actually the armature winding is placed on the armature. That winding is connected to the commutator and then commutator is connected to the brushes through which we can collect the induced EMF in the armature winding. This commutator converts AC into DC and these brushes are connected here and the springs are used to maintain the pressure between commutator part and the brushes. So generally the carbon material is used for these brushes. Then shaft is used for mechanical link between prime mover and armature. That shaft is connected to the prime mover when that prime mover rotates, armature rotates and the EMF is induced in that armature conductors. Bearing are used for the smooth rotation. Now pause the video and think what is the use of commutator in DC generator? So what is the answer? In DC generator commutator is used to convert AC into DC. Because the nature of induced EMF in the rotating conductors in magnetic field is the AC. So we can convert that AC into DC by using commutators. So these are the types of DC generators. Basically DC generators has the two types self-excited DC generator and separately excited DC generator. So in DC generator you can see here the field winding is separated from the armature winding. So this is the armature, here the armature winding is placed. That armature winding is separated from the field winding. For this self-excited DC generator these are the three types shunt, series and compound. In this shunt generator field winding and the armature winding both are connected in parallel with each other. In this series DC generator field winding is connected in series with the armature winding. So you can see here the field winding and the armature winding both are connected in series. And for compound DC generator again there are two types long shunt and short shunt compound generator. Long shunt compound generator the field winding is connected in series with the armature winding and this series combination is then connected in parallel with the field winding. And for short shunt compound generator armature winding and the field winding both are connected in parallel and this parallel combination is connected in series with the field winding. So these are the types of DC generator. You can refer the books Electrical Engineering by B. L. Thareja, Principles of Electrical Machines by V. K. Mehta and Rohit Mehta. Thank you.