Discharging a Capacitor
Charging a Capacitor
Electric FluxClosely Related Articles
Principle of DC Generator
Construction of DC Generator | Yoke Pole Armature Brushes of DC Generator
Characteristics of Series Wound DC Generator
Characteristic of Separately Excited DC Generator
EMF Equation of DC Generator
Parallel Operation of DC Generators
Self Excited DC Generators
Phasor Diagram for Synchronous Generator
DC Generators Performance Curves
Types of DC Generators
Characteristic of Shunt Wound DC Generator
Magnetization Curve of DC Generator
Applications of DC Generators
Alternator Synchronous Generator | Definition and Types of Alternator
Working Principle of Alternator
Construction of Alternator
Armature Reaction in Alternator or Synchronous Generator
Rating of Alternator
Derivation of Various Power Conditions in Alternators and Synchronous Motors
Induction Generator | Application of Induction Generator
Parallel Operation of Alternator
Motor Generator Set | M G Set
Types of Winding
Characteristic of Shunt Wound DC Generator
Magnetic or Open Circuit Characteristic of Shunt Wound DC GeneratorThis curve is drawn between shunt field current(Ish) and the no load voltage (E0). For a given excitation current or field current, the emf generated at no load E0 varies in proportionally with the rotational speed of the armature. Here in the diagram the magnetic characteristic curve for various speeds are drawn.
Due to residual magnetism the curves start from a point A slightly up from the origin O. The upper portions of the curves are bend due to saturation. The external load resistance of the machine needs to be maintained greater than its critical value otherwise the machine will not excite or will stop running if it is already in motion. AB, AC and AD are the slops which give critical resistances at speeds N1, N2 and N3. Here, N1 > N2 > N3.
Critical Load Resistance of Shunt Wound DC GeneratorThis is the minimum external load resistance which is required to excite the shunt wound generator.
Internal Characteristic of Shunt Wound DC GeneratorThe internal characteristic curve represents the relation between the generated voltage Eg and the load current IL. When the generator is loaded then the generated voltage is decreased due to armature reaction. So, generated voltage will be lower than the emf generated at no load. Here in the figure below AD curve is showing the no load voltage curve and AB is the internal characteristic curve.
External Characteristic of Shunt Wound DC GeneratorAC curve is showing the external characteristic of the shunt wound DC generator. It is showing the variation of terminal voltage with the load current. Ohmic drop due to armature resistance gives lesser terminal voltage the generated voltage. That is why the curve lies below the internal characteristic curve. The terminal voltage can always be maintained constant by adjusting the of the load terminal.
When the load resistance of a shunt wound DC generator is decreased, then load current of the generator increased as shown in above figure. But the load current can be increased to a certain limit with (upto point C) the decrease of load resistance. Beyond this point, it shows a reversal in the characteristic. Any decrease of load resistance, results in current reduction and consequently, the external characteristic curve turns back as shown in the dotted line and ultimately the terminal voltage becomes zero. Though there is some voltage due to residual magnetism.
We know, Terminal voltage
Now, when IL increased, then terminal voltage decreased. After a certain limit, due to heavy load current and increased ohmic drop, the terminal voltage is reduced drastically. This drastic reduction of terminal voltage across the load, results the drop in the load current although at that time load is high or load resistance is low.
That is why the load resistance of the machine must be maintained properly. The point in which the machine gives maximum current output is called breakdown point (point C in the picture).
Closely Related Articles Principle of DC GeneratorConstruction of DC Generator | Yoke Pole Armature Brushes of DC GeneratorCharacteristics of Series Wound DC GeneratorCharacteristic of Separately Excited DC GeneratorEMF Equation of DC GeneratorParallel Operation of DC GeneratorsSelf Excited DC GeneratorsHopkinson TestPhasor Diagram for Synchronous GeneratorDC Generators Performance CurvesTypes of DC GeneratorsMagnetization Curve of DC GeneratorApplications of DC GeneratorsMore Related Articles Alternator Synchronous Generator | Definition and Types of AlternatorWorking Principle of AlternatorConstruction of AlternatorArmature Reaction in Alternator or Synchronous Generator Rating of AlternatorDerivation of Various Power Conditions in Alternators and Synchronous MotorsInduction Generator | Application of Induction GeneratorParallel Operation of AlternatorMotor Generator Set | M G SetArmature Winding | Pole Pitch Coil Span Commutator PitchWave WindingWinding Factor | Pitch Factor | Distribution FactorLap Winding Simplex and Duplex Lap WindingFrog Leg Winding | Drum Winding | Gramme Ring WindingArmature Winding of AlternatorNew Articles Ring CounterDischarging a CapacitorCharging a CapacitorElectric PotentialParity GeneratorElectric Flux