Objectives of Reduced Voltage Running up Test on 3 Φ IM.
Q. Describe the objectives of reduced voltage running up test on 3 Φ IM.
- Many induction motors are started with star – Delta starter where the applied voltage at starting is 1√3 times the rated voltage.
- To ascertain the ability of the motor to run at rated speed in both directions satisfactorily (when connected in star) this test is carried out.
- Also the rotor of a squirrel – cage motor sometimes refuses to start at all, particularly when voltage is low.
- This happens due to magnetic locking between stator and rotor teeth. This phenomenon is called cogging.
- The cage motors are also liable to harmonic torques and result is crawling.
- This test also reveals if the tendency of crawling is present, as well as noisy running and the presence of loose bars.
- The respective meters are connected as shown in the circuit diagram. The motor is started by giving rated voltage through auto transformer and no load speed is measured with tachometer.
- The motor is run in reverse direction by changing phase sequence and speed is noted down.
