Baker D30R User Manual - page 58

Surge Test Applications 

12/3/2009 | 71-022 V6 

D30R 

58 

5)

Begin the test by pressing the test button or footswitch and slowly raising the Output 

control to the desired test voltage level. Carefully observe the wave pattern for its 

reference shape. 

6)

Store this wave pattern as the “reference” wave pattern for this span on this particular 

armature. Recall the reference wave pattern to the display (Use Quick Store if desired). 

Note the peak voltage displayed on the screen. 

7)

Begin testing again using the same output voltage until the test wave pattern matches 

the reference wave pattern. 

8)

Rotate the armature slowly through 360 degrees so that all commutator segments are 

tested while observing the reference wave pattern. 

Note

:  It is recommended to release the test button (or footswitch) each time the armature is 

turned, but it is not necessary. Doing so minimizes the chance of marking the commutator. 

If the test button or footswitch is not released each time the armature is turned, the wave 

pattern will show regular shifts and flickers as the brushes move across one commutator bar 

to the next. This wave pattern movements should be ignored as long as the trace returns to 

the reference wave pattern and remains stable when the brushes are again centered on top 

of the bars. 

Determination of a fault 

If the insulation is weak or failing on a particular bar or coil of the armature, the test wave 

pattern will become unstable and Shift Left when the section that contains the fault passes 

through the “test area”. The test wave pattern will no longer match the reference wave 

pattern. This indicates shorted windings within the span. 

Usually, as soon as the bad bar is placed under the hot brush, the wave pattern will show the 

shift to the left as noted above. Thus, the bar directly below the hot brush is the faulty bar.  

Notes and tips for span testing armatures 

−

A test fixture can be used in place of using the motor’s brushes to make contact with the 

armature. 

−

Set the span between the fixture’s brushes to the desired number of commutator bars. 

Either the fixture can be moved around the commutator during testing, or the armature 

can be rotated. Procedures for testing and fault determination are the same. 

−

Always HiPot the armature to ground first. This gives an upper limit for the maximum 

voltage to apply when surge testing. 

−

The greater the span surge test voltage is, the more adequate the stress between bars is 

(ideally, 335 V according to Paschen’s Law). Voltage stress is measured by the 

differential or drop between each bar. For example, a 10 bar span with 1,000 V applied 

to it will result in a 100V stress between bars. If the span is lowered to 5 bars, 1,000 V 

applied to the span will result in 200 V between bars. 

−

Consider, however, that a ten bar span at 335 volts between bars would require a span 

test voltage of 3,350 V. This potential to ground at the first coil may be too high. A lower 

span test voltage is recommended if, for instance, the HiPot test was only to 2,200 V. 

−

It is advantageous to keep the span as low as possible to still get a reasonably good 

ringing wave on the display. However, lowering the span reduces the resistance and 

inductance of the load under test. The low inductive load may cause difficulty achieving 

the desired test voltage and a good ringing wave pattern on the screen. 

−

To simulate a fault, use an insulated screwdriver to temporarily short two commutator 

bars together that are in the “test area”. This shows the response of the wave pattern 

when a fault exists. It gives an indication of what the user should expect to see. 

−

Equalizer windings can separate the test wave pattern from the reference pattern seen 

during span tests. Thus, a good armature winding can appear to be bad. For example, a