Squirrel Cage Growler test

[petronila]

Dear Friends,

We are performing Squirrel Cage rotor´s test with a Growler, we are interesting in to know about some tips in order to good result interpretation . The Squirrel Cage is placed on the growler and the current is meassured by an analog clamp.

¿How many amperes could desviate the current when we turn the rotor or we change the growler position?

¿Is this desviation related with the rated motor HP?

How many current desviation will be considered fair For a 300 UP TO 400 HP Motors ??

Thank you very much for the Inputs.

Petronila

 

[SteveKW]

It's an old book, but The Growler by Samuel Heller has a lot of information that may be helpfull!

 

[aolalde]

Hello Petronila.

We test cage rotors with a good size Growler (15”x14”x9”L). The excitation voltage AC 60 HZ is kept fixed at 60 Volts and the current changes depending on the rotor slots, size of the bars and rings and material (Al, Cu, or alloys). Currents as low as 20 amps and as high as 90 amps are developed.
90% of the rotors do not show current variation when rotated, however we allow up to 2 amps variation before a detail check for open or fractured bars is done.
While the rotor is energized we place a magnetic paper on the rotor surface to check the bar traces for fractures.
Another test that we make is Locked Rotor Single-Phase low voltage excitation of the motor stator winding, the rotor is rotated by hand and current variations recorded. I consider this last test better than the Growler Test but is limited to motors with a healthy stator winding.