 Myself, Mrs. Veena Sunil Patki, Assistant Professor, Department of Electronics Engineering, Vulturen Institute of Technology, Solapur, welcomes you for this session. At the end of this session, students can describe construction, characteristics and application of universal motor. Universal motor is a series wound DC motor having high starting torque and variable speed characteristics. It runs at dangerously high speed on no load and the input range is few watts to 2000 watts. Now let us discuss about the construction of universal motor. You can see in this diagram the stator which consists of the field winding having the field poles N and S. The winding is provided to create the magnetic field in the motor. And the second part is the rotor. Armature is nothing but the armature having the armature core that is laminated armature core is used with number of slots. In that slots the armature winding is provided and the commutator is given with that the winding connections are connected to the commutator and the brushes are there to provide the supply connection to the armature winding. Stator having the field winding to generate the magnetic field, the rotor armature winding with current through carbon brushes to generate the magnetic field and the brushes mechanical linking to power supply and the rotor windings and commutator and compensating winding. There are two types of the universal motor according to construction concentrated pole non compensating and second is the distributed field compensated type. So in first type non compensated type with concentrated poles in first diagram you can see the salient poles are provided and the laminated pole is there to reduce the eddy current losses because we are going to use these motors for AC or DC also. Can we use AC here that create the heat due to eddy current losses and generally to reduce the eddy current losses laminated part is used and the stator is there. So in second diagram you can see the armature that is nothing but the rotor is given and the armature winding and the field winding is connected in series. So the construction is same as the series DC motor. Another type is the compensated type with distributed field. So compensating winding is provided that is connected in series with the main field winding. So in first diagram you can see the compensating winding is given with the field winding. Generally that compensating winding is used to reduce the reactance voltage present in the armature when motor runs on AC supply because the reactance that is excel equal to 2 pi f L. So as the frequency increases the reactance drop or the reactance increases and due to that the voltage across that winding increases and that compensating winding is used to reduce that reactance voltage present in the armature and again we can reduce that by using less number of turns for that winding. In the second diagram you can see the armature main winding and compensating winding are connected in series and we can connect the single phase AC supply or the DC supply for that motor. So that is why the name universal motor is given because we can use this motor for AC and DC both also. Now let us discuss about the working of universal motor. You can see in this diagram the series field winding is there to create the magnetic field. N and S poles are created by using that winding that armature conductors are connected to the commutator through brushes we can connect the AC supply or DC supply. Now if we connect the DC supply for this motor the working is same as the DC motor. Whenever any current carrying conductor is placed in the magnetic field the mechanical force is created on that current carrying conductor. We can find out the direction of the motion or the force which is created on the current carrying conductor by using Fleming's left hand rule. That Fleming's left hand rule states that if we place three fingers middle finger four finger and thumb perpendicular to each other of the left hand then the four finger indicates the direction of the magnetic field middle finger indicates the direction of the current then thumb indicates the direction of the force which is created on the current carrying conductor. You can see the second diagram the conductor B is placed in the magnetic field the direction of the force is created on the current carrying is upward and the magnetic fluxes due to the main winding having the direction left side if we connect the AC supply to that motor the direction of the current through series field winding and the armature winding both are reversed for positive cycle and negative cycle. So the torque which is created on the current carrying conductor has the same direction so we can say the unidirectional torque is created due to positive cycle and negative cycle both. So here unidirectional torque is created due to AC supply. Now let us discuss about the speed load characteristics. So in this diagram you can see the graph the speed is inversely proportional to armature current speed is inversely proportional to torque also. So generally the gears are used to get the required speed for required load and generally these motors are run with the load at the starting because these motors runs with very large speed and you can see in the graph the power output is again directly proportional to the torque at the starting and then as the torque increases the power decreases and speed is very high at low load or we can say speed is very high at no load and as the torque increases speed decreases and the graph for AC and DC both are approximately same. Now pause the video and think about can a universal motor be used with either DC or AC yes answer is yes because the name is universal motor and these motors are run with AC or DC that is why the name is given as universal motor. Now let us discuss about the application of universal motor. Universal motors are used in various home appliances like vacuum cleaners, food mixers and domestic sewing machines etc. The higher rating universal motors are used in portable drill, blenders etc. These motors are also used for hair dryers, grinders, table fans and blowers, polishers and kitchen appliances. Number of advantages are there for the universal motors. The structure is simple, robust, having small size, portable motors are there and rotates more than 3000 to 20,000 rpm but the some disadvantages are there sparse occurring between brushes and commutator due to their imperfect contact leads to noise while running. As the result life of brushes is reduced and maintenance is required temperature results in limited lifetime and these are the disadvantages you can refer these books thank you.