Machine Parts

                                               If we connect a load to the secondary of the transformer as shown in fig-1, the induced emf in the secondary, causes the current   to flow in the secondary winding. At the instant shown in the diagram, the source of power causes the upper terminal of the primary to be positive, and the instantaneous direction of current is given by . In accordance with Lenz’s law, the secondary induced emf and the current it causes must be in such a direction as to oppose the setting up of the flux . Application of the right hand rule will show that this secondary current direction is given by. We now have a magnetomotive force in   the secondary. , opposing that of the primary . It must be remembered, however, that the primary induced voltage   is always directly proportional to the flux , and is also equal to the impressed voltage , with all values now taken as the effective, or rms ones. Since the impressed voltage does not c

Phasing of a transformer :  Two dimensional vector is known as phasor.As the vector diagram of a transformer is drawn in phasor form and this is called the phasing of transformer. When load is applied to the secondary terminal the current that flows through the secondary terminal opposite to the primary current from lenz’s law.So flux is reduced,causes the induced emf in the primary winding is also reduced and therefore more current flows in the primary winding.This increased primary current will cause the flux to increase its original value.When more load current flow through secondary,the process is repeated. Phasor diagram with load : When load is connected the load current I 2 is   lagging E 2 .I 1 ̕   is the current that flows in the primary winding to balance the demagnetizing effect of I 2 .Since the flux remains constant I o   must be the same current that energizes the transformer at no load I 1 the actual current that   flows in the p

When a transformer primary is energized from a voltage source and the secondary is opened circuited, a small current will flow in the primary. This current is usually less than 5 percent of the rated full load value of the transformer. Since no current flows in the secondary winding . The primary may be considered as a coil with a large reactance due to the iron core. Thus causes a small current . But when load is applied to the secondary terminals. In accordance with Lenz’s law, the current that flows through the secondary winding must act in such a direction as to oppose the flux set up by the primary current. When the flux is momentarily reduced, the induced emf in the primary winding is also reduced and therefore more current flows, in the primary winding. When more load current flows in the secondary the primary current will again increase.flux