New York, NY IMG HI 58° LO 56° Home About Contact
IMG-LOGO
LOGO
Home Electrical and Electronics Electrical Machines 1 To conduct field’s test on a given two identical dc series machines and to determine the efficiency
Electrical Machines 1 Lab Experiments

To conduct field’s test on a given two identical dc series machines and to determine the efficiency

Sep 24 2023


Aim

To conduct field’s test on a given two identical dc series machines and to determine the efficiency

Apparatus Required:

S.no Name Range Type Quantity
1 Voltmeter (0-300)V MC 2nos
2 Ammeter (0-20)A MC 1nos
3 Ammeter (0-2)A MC 1no
4 Techometer (0-10,000) RPM Digital 1nos
5 Rheostat 400Ω, 1.7A Wire Wound 1no
6 Load box 230V,5KW/20A Resistive 1no
7 Connecting Wires (0-20)A *********** Required

Name plate details:-

Motor Generator

Voltage - 220V Voltage - 220V

Current -13.6A Current -13.6A

Speed - 1500 rpm Speed - 1300 rpm

Excitation type –series Excitation type - series

Circuit Diagram:

circuit-diagrams

To determine armature resistance:

circuit-diagram-1

To determine series field winding resistance:

circuit-diagram-2

Procedure:-

Open circuit test:

  1. Connect the circuit as per the circuit diagram.
  2. Ensure that dc series generator is electrically loaded to its rated current before starting.
  3. Give the supply to the dc series motor by closing DPST switch and start the motor with the help of 2- point starter.
  4. Note down the readings of voltage across armature and series field winding of dc series generator and terminal voltage across the load of dc series generator.
  5. Repeat step no:4, by decreasing electrical load till 30% of rated current is obtained.
  6. Switch off the supply by opening DPST switch.

To determine armature 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.

To determine series field winding 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.

Table1:

s.no Input Voltage V(volts) Armature current of motor I1(amps) Armature current of generator I2(amps) Motor voltage V1(volts) Generator voltage V2(volts) Input power Wi = V*I1(watts) Armature cu losses of motor Wcu,m = (I1) 2*Ra (watts) Armature cu losses of generato r Wcu,g = (I1) 2*Ra (watts) Motor field cu losses Wse,m = (I1)2*Rse (watts )
1 220 3.5 4 220 90 770 23.37 30.4 22.05
2 220 4 4.5 220 80 880 30.4 38.475 28.8
3 220 4 5 220 80 880 30.4 47.5 28.8
4 220 4.5 5.5 220 80 990 38.4 57.47 36.45
5 220 5 6 220 75 1100 47.5 68.4 45

Generator field cu losses Wse,g =( I1) 2*Rse (watts) Stray losses W s = Wi -(W cu,m+ W cu,g+ W se,g+ W se,m) (Watts) Total losses of motor Wm = W cu,m+ W se,m + W s/2 (Watts) Total losses of generator W g= W cu,g+ W se,g+ Ws/2 ( Watts) % efficiency of motor %ηm= (V1 I1- W m) *100 (V1 I1) % efficiency of generator %ηg = (V2I2) *100 (V2 I2+ Wg)
22.05 672.225 381.44 388.56 50.46 46.09
28.8 753.2 435.96 444.04 50.45 44.8
28.8 744.5 431.45 448.55 50.97 47.14
36.45 821.5 504.5 504.5 49.04 46.6
45 894.1 521.97 560.45 52.55 44.53

Table:3

V I R a=(V/I)

Table:2

V I R a=(V/I)

Model Graph

model-graph
model-graph-1

Calculations:

Input voltage V =___ volts

Voltage across series field and armature winding V1=____ volts

Armature current of dc series motor, I1 =____amps

Armature current of dc series generator I2 =____amps

Terminal voltage of dc series generator V2 =____ volts

Input power to the set Wi =V* I1 watts

Armature copper losses of motor Wcu,m =(I2) 2*Ra watts

Wcu,g =______watts

Generator field copper losses Wse,g = (I1) 2*Rse watts

Wse,g = ______ watts

Motor field copper losses Wse,m = (I1) 2*Rse watts

Wse,m = ______ watts

Stray losses Ws = Wi- {Wcu,m+ Wcu,g + Wse,g + Wse,m}Watts

Total losses of motor Wm= Wcu,m + Wse,m + W s/2 Watts

Total losses of generator W g = W cu,g+ W se,g+ W s/2 Watts

Percentage efficiency of motor %ηm= ((V1 I1 - Wm)/ V1 I1)*100

Percentage efficiency of generator %ηg= (V2I2)/ (V2 I2+ Wg)*100

Result: Field test is conducted on a given dc series machine and hence efficiency is calculated for motor and generator .

Precautions:

  1. Why we are always start the series motor on load only?
  2. Give me one application of the series motor?
  3. What is the relation between torque and load current?
  4. What is the necessity of doing fields test?








Related Categories

Electrical Machines 1 Lab Experiment list


Laboratory Experiment Categories

Subscribe

Get all latest content delivered to your email a few times a month.