Steps to find the Efficiency
- Determination of hot resistances of windings
- Determination of constant losses
Determination of hot resistances of windings
Determination of constant losses
i.e. voltage stamped on the nameplate. The speed of the motor is adjusted to the rated speed with the help of field regulator R as shown in figure (for more details please visit speed control of dc shunt motor).
Efficiency when running as a motor
Efficiency when running as a generator
Advantages of Swinburne’s test
- The power required to carry out the test is small because it is a no-load test. Therefore, this method is quite economical.
- The efficiency can be determined at any load because constant losses are known.
- This test is very convenient.
Disadvantages of Swinburne’s test
- It does not take into account the stray load losses that occur when the machine is loaded.
- This test does not enable us to check the performance of the machine on full-load. For example, it does not indicate whether commutation on full load is satisfactory and whether the temperature rise is within the specified limits.
- This test does not give quite accurate efficiency of the machine. It is because iron losses under actual load are greater than those measured. This is mainly due to armature reaction distorting the field.