Baker D30R User Manual - page 54

Surge Test Applications 

12/3/2009 | 71-022 V6 

D30R 

54 

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Check for open test leads at the clip end. With heavy use, check test leads weekly to 

ensure there is no breakage. Check test leads by firmly grasping the boot and clip in one 

hand while pulling on the lead with the other. A broken lead will stretch. A good lead will 

not stretch. 

Form coils 

The surge test is a recommended for form coils. It can generate the turn-to-turn voltage 

needed to test these low impedance coils. 

Notes and tips for form coils 

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IEEE-522-1992 recommends a test voltage for vacuum pressure impregnation coils, 

before they are cured, of 60-80 percent of the test voltage of fully cured coils. 

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Currents required to test form coils often limit the maximum surge voltage. Placement of 

the coils into the stator iron or spare laminations has the effect of enabling the tester to 

produce a higher voltage drop across the coil for a given current level. 

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Caution

 should be exercised when testing form coils, since the laminations or stator core 

have induced voltage on them, which can provide a voltage path or ground. 

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Many formulas are used in calculating a test voltage for AC form-wound coils. These are 

generally based on experience and theoretical arguments about the distribution of 

voltage in a coil and the entire winding. Some of these formulas are difficult to apply 

because of the great diversity of coil specifications and characteristics. One popular 

formula (based on Paschen’s Law) states a minimum and maximum test voltage range: 

Minimum = Number of turns x 500 Volts 

Maximum = Winding operating voltage x 1.5 

The minimum voltage would be necessary to show a void in the turn insulation that would 

result in arcing. The maximum voltage value is based on the worst case distribution of a 

surge in the winding. Studies (IEEE-522-1992 and IEEE-587-1980) have shown that a very 

rapid surge from a lightning strike or contactor closing/opening may be distributed across the 

first coil of a winding. 

Three phase motors 

Wave patterns for three phase windings are compared in pairs. The storage capabilities of the 

digital tester, allows all three phases to be compared after reconnecting the test leads. The 

operator simply recalls any one of the previously tested leads.  For each test, check the display 

for a wave pattern, saving each waveform. Recall the waveform Summary from the digital 

tester’s memory for the wave patterns to be compared. If the three wave comparisons seen 

Fig 8-3: Open phase in a wye-connected motor