SKF AWAIV-12, Руководство пользователя

Страница: 147 / 250

• Slight variations in magnetic properties of the tested device can result in similar coils
not comparing identically. An example of this is synchronous pole pieces, one of
which is making better magnetic contact with the rotor than the comparing pole. For
this reason, it is recommended that devices like pole pieces be evaluated individually
and not compared.
• Paschen’s Law states that a voltage greater than 375 V is required to initiate an arc
between two conductors in air. This would suggest a minimum voltage for surge
testing to be greater than 375 V per turn. Because of the sometimes non-linear
distribution of the surge pulse, it is recommended to use a minimum surge potential
of 500 V per turn when testing a two-terminal device.
• Shunt coils often have a small error in turns count. Some mismatch or separation of
patterns should be acceptable. If the wave patterns are very close in shape and
remain stable during the test, the coils are generally acceptable. In addition, winding
tolerances on single coils may allow for differences in turns count, which causes a
slight, steady separation. The operator should investigate whether this condition is
acceptable or not.
• Many two-terminal devices have very high turns count. The waveform displayed is
similar to that of an open circuit. In this case, the coil’s impedance is too high to be
tested. Double check for poor connections and test lead breakage to see if these
conditions may be causing the apparent open condition.
SKF Static Motor Analyzer—Baker AWA-IV User Manual 133
Motor testing theory and reference