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Real Power Reactive Power Apparent Power (1)   Real Power: (P)   Alternative words used for Real Power (Actual Power, True Power, Watt-full Power, Useful Power, Real Power, and Active Power) In a DC Circuit, power supply to the DC load is simply the product of Voltage across the load and Current flowing through it i.e., P = V I. because in DC Circuits, there is no concept of phase angle between current and voltage. In other words, there is no  Power factor  in DC Circuits. But the situation is Sinusoidal or AC Circuits is more complex because of phase difference between Current and Voltage. Therefore average value of power (Real Power) is P = VI Cosθ is in fact supplied to the load. In AC circuits, When circuit is pure resistive, then the same formula used for power as used in DC as P = V I.  You may also read about  Power Formulas in DC, AC Single Phase and and AC Three Phase Circuits . Real Power formulas: P = V I                                        (In DC c

Commutation in DC Machine or Commutation in DC Generator or Motor The  voltage  generated in the armature, placed in a rotating  magnetic field , of a  DC generator  is alternating in nature. The  commutation in DC machine  or more specifically  commutation in DC generator  is the process in which generated alternating  current  in the  armature winding  of a dc machine is converted into direct current after going through the commutator and the stationary brushes. Again in  DC Motor , the input DC is to be converted in alternating form in armature and that is also done through commutation. This transformation of current from the rotating armature of a DC machine to the stationary brushes needs to maintain continuously moving contact between the commutator segments and the brushes. When the armature starts to rotate, then the coils situated under one pole (let it be N pole) rotates between a positive brush and its consecutive negative brush and the current flows through this c

Definition of Magnetic Saturation Magnetic Saturation of Iron Now if we try to work with flux density above this limit, the iron exhibits higher reluctance compared to that at low flux density. As a result the said iron or steel does not behave like good  conductor  of magnetic flux. At that situation much more mmf is required to drive the flux through the same iron core. More mmf means more ampere turn in the case of electromagnetic, hence this situation should avoid. Relation between Reluctance and Flux Density In the above figure it is seen that, when flux density is within limit, the reluctance of the magnetic path is quite low but when it crosses certain value such as 2 Tesla as shown here, the reluctance of the same magnetic path is sharply increased. To avoid the undesirable effect of the  magnetic saturation , the size of the iron core suitably chose for a particular engineering application. Generally volume of the iron or steel core of magnetic path in a machine is so chose

The Voltage generated in the armature, placed in a rotating Magnetic Field, of a DC generator is alternating in nature. The commutation in DC machine or more specifically commutation in DC generator is the process in which generated alternating  current  in the  armature winding  of a dc machine is converted into direct current after going through the commutator and the stationary brushes. Again in  DC Motor , the input DC is to be converted in alternating form in armature and that is also done through commutation. This transformation of current from the rotating armature of a DC machine to the stationary brushes needs to maintain continuously moving contact between the commutator segments and the brushes. When the armature starts to rotate, then the coils situated under one pole (let it be N pole) rotates between a positive brush and its consecutive negative brush and the current flows through this coil is in a direction inward to the commutator segments. Then the coil is short ci

In a  DC machine , two kinds of magnetic fluxes are present; 'armature flux' and 'main field flux'. The effect of armature flux on the main field flux is called as  armature reaction . MNA And GNA EMF is induced in the  armature conductors  when they cut the magnetic field lines. But, there is an axis (or, you may say, a plane) along which armature conductors move parallel to the flux lines and, hence, they do not cut the flux lines at the moment. MNA (Magnetic Neutral Axis) may be defined as the axis along which no emf is generated in the armature conductors as they move parallel to the flux lines. Brushes are always placed along MNA because reversal of current in the armature conductors takes place along this axis. GNA (Geometrical Neutral Axis) may be defined as the axis which is perpendicular to the stator field axis. Armature Reaction The  effect of armature reaction  is well illustrated in the figure below. Consider, no current is flowing in the armatur

Where Compensating windings and Interpoles are Used? In small generators, the effects of armature reaction are reduced by actually mechanically shifting the position of the brushes. The practice of shifting the brush position for each current variation is not practiced except in small generators. In larger generators, other means are taken to eliminate armature reaction. Compensating Windings or Interpoles are used for this purpose. Compensating Windings The cross-magnetizing effect of armature reaction may cause trouble in d.c. machines subjected to large fluctuations in load. In order to neutralize the cross magnetizing effect of armature reaction, a compensating winding is used. The compensating windings consist of a series of coils embedded in slots in the pole faces. These coils are connected in series with the armature. The series-connected compensating windings produce a magnetic field, which varies directly with armature current. Because the compensating windings are