THE TESTING TOOLS

A description with the five of the most useful tests to assess rotor and stator winding condition for motors rated 400 V and above is given which are: the current signature analysis (CSA); growler; IR test; polarization index (PI) test; and the surge tests. CSA monitoring has improved the means of detecting broken rotor bars as well as cracked short-circuit rings in the squirrel-cage induction (SCI) and is able to find certain mechanical problems. On the other hand, the growler is a simple offline test that can detect open-circuited bars in squirrel-cage rotor windings. As for IR test, it measures the resistance of the electrical insulation between the copper conductors and the core of the stator. Meanwhile, PI comes in as a variation of the IR test which is defined as the ratio of the IR measured after voltage has been applied for 10 min to the IR measured after 1 min. Finally, the surge voltage test has the only ability to directly find stator windings with deteriorated turn insulation by applying a high-voltage surge between turns.