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Electrical Machines 1 Lab Experiments

To conduct load test on a given dc compound generator when acts as Cumulative & Differential compound generator

Sep 24 2023


Aim

To conduct load test on a given dc compound generator when acts as

  1. Cumulative compound generator
  2. Differential compound generator and to draw the characteristics

Apparatus Required:

S.no Name Range Type Quantity
1 Ammeter (0-20)A MC 2nos
2 Ammeter (0–2.5)A MC 1 no
3 Voltmeter (0-300)V MC 2nos
4 Tachometer (0-10,000)rpm Digital 1no
5 Rheostat 400Ω, 1.7A Wire wound 2nos
6 Connecting wires (0-20)A - Required
7 Load box 230V,5KW/20A Resistive 1 no.

Name plate details:-

Motor Generator

Voltage - 220V Voltage - 220V

Current -19A Current -13.6A

Speed - 1500 rpm Speed - 1500 rpm

Excitation type –compound Excitation type –compound

Circuit diagram:

circuit-diagram

(ii) To find armature resistance:

diagram

(iii)To find series field resistance:

diagram-1

Procedure:-

  1. Make the connections as per the circuit diagram.
  2. Keep the motor field rheostat in minimum position and generator field rheostat in maximum position.
  3. Keep the field winding in cumulative mode i.e. current flows from z to zz in Shunt field winding, from y to yy in series field winding.
  4. Give the dc supply to the circuit and start the motor with the help starter.
  5. Bring the motor to rated speed by varying the field rheostat in the motor circuit.
  6. Adjust the generator voltage to the rated value by using field rheostat of generator.
  7. Increase the load in steps and note down the values of terminal voltage, load current and field current.
  8. Increase the load till rated current is obtained.
  9. Interchange the field winding y and yy for differential mode and conduct experiment in above procedure

To determine armature and field resistance:

  1. Connect the circuit as per the circuit diagram.
  2. Switch on dc supply
  3. Increase the load and note down the voltage and current.

Tabular column

Table1 :Cumulative Mode

Terminal Voltage (Volts) Load Current (IL) Field Current (If) Ia= IL+ If(amp) Eg= V + Ia(Ra+R se)(volts)
220 0 0.75 0.75 222.7
220 1.6 0.76 2.36 228.09
220 4 0.75 4.76 237.13
220 6 0.74 6.74 244.26
220 7.5 0.74 8.24 249.2
220 10 0.74 10.74 258.6
220 11 0.7 11.7 262.2

Table2: Differential Mode:

Terminal Voltage (Volts) Load Current (IL) Field Current (If) Ia= IL+ If(amp) Eg= V + Ia(Ra+R se)(volts)
220 0 0.8 0.8 222.8
210 1.5 0.75 2.25 218.1
170 3.4 0.7 4.1 204.7
173 4.5 0.65 5.15 193.3
150 5 0.56 5.36 100.1

Table2: Armature Resistance

V(volts) I(amp) R a= (V/I) (ohms)

Table3:Series field winding Resistance

V(volts) I(amp) R se= (V/I) (ohms)

Model graph:

cultivate-mode
differential-mode
test-load-on-compound-generator

Result:Internal and external characteristics of dc compound generator (both cumulative and differential) are drawn by conducting load test on it.

Viva voce

  1. What is Armature reaction?
  2. What is the basic principle of generator?
  3. What are the types of compound generators?
  4. What are the applications of compound generators?
  5. What are the applications of compound generators?








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