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EMF Equation of DC Generator
Parallel Operation of DC Generators
Self Excited DC Generators
Working Principle of Alternator
Construction of Alternator
Alternator Synchronous Generator | Definition and Types of Alternator
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Armature Winding of Alternator
Winding Factor | Pitch Factor | Distribution Factor
Rating of Alternator
Derivation of Various Power Conditions in Alternators and Synchronous Motors
Phasor Diagram for Synchronous Generator
Armature Reaction in Alternator or Synchronous Generator
Principle of DC Generator
Construction of DC Generator | Yoke Pole Armature Brushes of DC Generator
Frog Leg Winding | Drum Winding | Gramme Ring Winding
Types of DC Generators
Characteristic of Separately Excited DC Generator
Characteristics of Series Wound DC Generator
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Applications of DC Generators
Magnetization Curve of DC Generator
DC Generators Performance Curves
Motor Generator Set | M G set
Wind Turbine | Working Types and History of Wind Turbine
Theory of Wind Turbine
Induction Generator | Application of Induction Generator
Magnetization Curve of DC Generator
Magnetization CurveMagnetization curve of a DC generator is that curve which gives the relation between field current and the armature terminal voltage on open circuit.
When the DC generator is driven by a prime mover then an emf is induced in the armature. The generated emf in the armature is given by an expression
is constant for a given machine.it is replaced by K in this equation.
Here, φ is the flux per pole, P is the no. of poles, N is the no. of revolution made by armature per minute, Z is the no. of armature conductors, A is no. of parallel paths. Now, from the equation we can clearly see that the generated emf is directly proportional to the product of flux per pole and the speed of the armature. If the speed is constant, then the generated emf is directly proportional to the flux per pole. It is obvious that, as the excitation current or field current (If) increases from its initial value, the flux and hence generated emf is increased with the field current.
If we plot the generated voltage on the Y axis and field current on the X axis then the magnetization curve will be as shown in figure below. Magnetization curve of a DC generator has a great importance because it represents the saturation of the magnetic circuit. For this reason this curve is also called saturation curve.
According to the molecular theory of magnetism the molecules of a magnetic material, which is not magnetized, are not arranged in definite order. When current passed through the magnetic material then its molecules are arranged in definite order. Up to a certain value of field current the maximum molecules are arranged. In this stage the flux established in the pole increased directly with the field currant and the generated voltage is also increased. Here, in this curve, point B to point C is showing this phenomena and this portion of the magnetization curve is almost a straight line. Above a certain point (point C in this curve) the nu-magnetized molecules become very fewer and it became very difficult to further increase in pole flux.This point is called saturation point. Point C is also known as the knee of the magnetization curve. A small increase in magnetism require very large field current above the saturation point. That is why upper portion of the curve (point C to point D) is bend as shown in figure.