Page 163 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

This test is sometimes conducted by a series test lamp and is called the ‘ground test’. It will only indicate if any
coil is grounded, and not the insulation resistance.
Growler test : A simple and most common method to test armature winding for short and open coils is by a
growler.

Growler : There are two types of growlers - 1) internal and 2) external growlers. An external growler is used for
testing small armatures and an internal growler for large DC armatures and AC motor stator windings.
External growler : An external growler, shown in Fig 3, is an electromagnetic device that is used to detect and
locate grounded, shorted and open coils in an armature.
This growler consists of a coil wound around an iron core and is connected to a 240 volt AC line. The core is
generally H shaped and cut out on top so that the armature will fit on it, as shown in Fig 4.

When an alternating current is applied to the growler coil, the voltage will be induced in the armature coils by
transformer action.

Fig 3 Fig 4

Internal growler : An internal growler, such as the one used for stators, may be used for armatures as well.
These are made with or without built-in feelers. The growler with a built-in feeler has a flexible blade attached
to the growler so that a hacksaw blade or similar instrument is not necessary. This type is especially desirable in
smaller stators that have no room for a separate feeler. Fig 5 shows an internal growler with a separate feeler,
used for large armatures.
Growler test for grounded coil : The armature to be tested is placed on the growler and then the growler is
switched ‘ON’. Place one lead of an AC milli-voltmeter on the top commutator bar and the other meter lead on
the shaft, as shown in Fig 6.

Fig 5 Fig 6

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CITS : Power - Electrician & Wireman - Lesson 86-92