Electrical Engineering ⇒ Topic : Testing of d.c machines
TESTING OF D.C. MACHINES
The following important performance tests are conducted on D.C. machines :
1. The magnetisation or open circuit test
2. The load characteristics
3.The determination of efficiency curve
4.The temperature rise test.
The method for determining efficiency can be divided into following three methods :
(1) Direct method. The direct tests can be used only on small machines.If brake is to be applied to a series motor, the brake must be tight before the motor is started, otherwise the armature may get damaged and fly to pieces.
(2) Indirect method. The simplest of the indirect tests is Swinburne test. This method may be applied to series motors, because the speed of a series motor being very high at no-load it is not possible to run a series motor on no-load.
(3) Regenerative method. Hopkinson's test (Back to back test). It is a regenerative test.The power taken from the supply is that required to overcome the losses only.
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