Separation of losses in DC machine using Swinburne’s test.

Experiment No.: – 07

Aim of the experiment: –

Separation of losses in DC machine using Swinburne’s test.

Apparatus Required: –

Sl. No.NameSpecificationQuantity
1DC Shunt MotorArm- 180V, Field- 180V1 no.
2TachometerDigital1 no.
3Voltmeter(0-150)V, PMMC1 no.
4Ammeter(0-5)A, PMMC1 no.
5Ammeter(0-2)A, PMMC1 no.
6Rheostat(0-80) ohm2 nos.
7Connecting wiresPVC Insulated copperAs per required

Circuit Diagram: –

Theory: –

Swinburn’s test is an indirect method (without loading) for finding out the efficiency of dc machine various losses occurring in dc machine can be classified as…

  • Constant Losses
  • Variable Losses.

Variable losses are directly proportional to the square of armature current or approximately load current where as constant losses are independent of load conditions.

In this method constant losses are determined experimentally by operation dc machine as motor running at no load.

Variable losses occurring on load are calculated from known specifications of the machine.

Let the voltage applied to the shunt motor be V volts and current flowing in the armature and shunt field no. Load conditions be Ia and Ish.
Then,
Input power to armature circuit = V x Ia watts.
Input power to shunt field circuit = V x Ish watts
Total input power to the motor = Wo = V (Ia + Ish)
Armature Cu losses at no Load = (Ia)2 R
Thus constant losses of machine = Wc = Wo – (Ia)2R watts
The Swinburne’s test should be performed at rated voltage and at rated speed.

Procedures: –

  1. Connect the dc motor as per circuit diagram.
  2. Ensure that the external resistance in field circuit is zero.
  3. Switch ON the de supply to the motor and start it with help of starter. In case the starter is not provided start the motor using rheostat.
  4. Adjust the speed of motor to rated value by varying resistance of the field circuit
  5. Record the readings of all instruments connected in circuit.
  6. To stop the motor, switch off the dc supply.

Precaution: –

  1. Ensure that the voltage applied to the motor is of rated voltage.
  2. Switch off the dc supply after the experiment.

Observation Table: –

Sl. No.Supply voltage
V (volts.)		Armature current
Ia (Amps.) 		Field current
Ish (Amps.) 		Armature Resistance
Ra (Ohm)		Speed N
(RPM)
1

Calculation:

\[\color\red{W_c}\;\color\green{\;=}\color\red{V}\;\color\green{X}\;\color\red{I_T\;-\;I_a^2}\;\color\green{X}\;\color\red{R_a}\] \[\color\red{I_T}\;\color\green{=}\;\color\red{I_a}\;+\;\color\red{I_{sh}}\]

Conclusion: –

To be written by student.

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