1) Why did we perform the no-load operation experiment for the asynchronous moto
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Question
1) Why did we perform the no-load operation experiment for the asynchronous motor? 2) Why is the value of cos small at no-load? ( connected) Energy Analyzer (A connected) Energy analyzer Coso VA VAR U ICo W VA VAR coso 231 1.184 0.173 50.03 261.7 261.1 227.7 4.295 0059 95.36 226.7 920.3 225.2 1.249 0.275 7501 2753 274.2 224.5 4.322 0156 178.1 9595 929.7 222.2 1135 0.241 69.88 247.2 241.7 221.23.938 0.139 132.4 845.9 837.9 2 Table 1: Obtained values for No-Load Operation Of the 3-Phase asynchronous MotorExplanation / Answer
Answer 1) The efficiency of large motors can be determined by directly loading them and by measuring their input and ouput powers. For large motors it may be difficult to arrange loads for them. Moreover power loss will be large with direct loading tests. Thus no load test are performed on the motors. As the name suggested no load test is performed when rotor rotates with synchronous speed and there is no load torque. This test is similar to the open circuit test on trasformer. Actually, to achive synchronous speed in an induction motor or asynchronous motor is impossible.
The no load test give the information regarding no load losses such as core loss, friction loss and windage loss. Rotor copper loass at no load us very less that is vlaue is negligible. This test is also well know as runnig light test. This test is used to evaluate the resistance and impeadance of the magnetizing path of asynchronous motor.
The no laod test also give the information with respect to the exciting current.
Answer 2) The power factor ( cos) at no load is low because the magnetizing component of input current is a large part of the total input current of the motor. When the laod on the motor is increased, the in phase current supplied to the motor increases, but the magnetizing component of current remains the same. This means that the resultant line current is more nearly in phase with the voltage and the power factor is improved when the motor is loaded. Component with an unloaded motor which has its magnetizing current as a major component of the input current.
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