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Monday, April 4, 2011

LOAD CHARACTERISTICS OF SELF EXCITED DC SHUNT GENERATOR


LOAD CHARACTERISTICS OF SELF EXCITED
DC SHUNT GENERATOR

AIM:
To obtain internal and external characteristics of DC shunt generator.

APPARATUS REQUIRED:
S.No.
Apparatus
Range
Type
Quantity
1
Ammeter
(0-2)A
(0-20) A
MC
MC
1
1
2
Voltmeter
(0-300)V
MC
1
3
Rheostats
1200W, 0.8A
Wire Wound
2
4
Loading Rheostat
5KW, 230V
-
1
5
Tachometer
(0-1500)rpm
Digital
1
6
Connecting Wires
2.5sq.mm.
Copper
Few

PRECAUTIONS:
  1. The field rheostat of motor should be at minimum position.
  2. The field rheostat of generator should be at maximum position.
  3. No load should be connected to generator at the time of starting and stopping.

PROCEDURE:
  1. Connections are made as per the circuit diagram.
  2. After checking minimum position of DC shunt motor field rheostat and maximum position of DC shunt generator field rheostat, DPST switch is closed and starting resistance is gradually removed.
  3. Under no load condition, Ammeter and Voltmeter readings are noted, after bringing the voltage to rated voltage by adjusting the field rheostat of generator.
  4. Load is varied gradually and for each load, voltmeter and ammeter readings are noted.
  5. Then the generator is unloaded and the field rheostat of DC shunt generator is brought to maximum position and the field rheostat of DC shunt motor to minimum position, DPST switch is opened.


DETERMINATION OF ARMATURE RESISTANCE:

















PROCEDURE:
1. Connections are made as per the circuit diagram.     
2. Supply is given by closing the DPST switch.
3. Readings of Ammeter and Voltmeter are noted.
4. Armature resistance in Ohms is calculated as Ra = (Vx1.5) /I




TABULAR COLUMN:

S.No.
Voltage
V (Volts)
Current
I (Amps)
Armature Resistance
Ra (Ohms)












TABULAR COLUMN:
S.No.
Field Current
If (Amps)
Load Current
IL (Amps)
Terminal Voltage
(V) Volts
Ia = IL + If
(Amps)

Eg =V + Ia Ra (Volts)



















FORMULAE:
Eg          =          V + Ia Ra (Volts)                    
            Ia          =          IL + If (Amps)
Eg        :           Generated emf in Volts
V         :           Terminal Voltage in Volts
Ia          :           Armature Current in Amps
IL             :           Line Current in Amps
If          :           Field Current in Amps
Ra        :           Armature Resistance in Ohms

MODEL GRAPH:

                                   











RESULT:
Thus the load characteristics of self excited DC shunt generator is obtained.

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