High potential (hipot) testing procedures for motor and generator windings are usually performed with 50/60 Hz AC or DC as the power source. Hipot testing is a critical step in validating the quality of new windings. AC and DC hipot tests are also useful to understand the condition of aged insulation for machines in service. The disadvantage of the AC test at power frequency is when the size of the test set and/or complexity of the setup becomes problematic in motor repair and in the field. And the DC test stresses the end turns more. The very low frequency (VLF) test set has been successfully used to bridge the test gap between AC and DC hipot tests.

 Los procedimientos de prueba de alto potencial (hipot) para devanados de motores y generadores generalmente se realizan con 50/60 Hz CA o CC como fuente de alimentación. La prueba de Hipot es un paso crítico para validar la calidad de los devanados nuevos. Las pruebas hipot de CA y CC también son útiles para comprender el estado del aislamiento envejecido de las máquinas en servicio. La desventaja de la prueba de CA a frecuencia industrial es cuando el tamaño del equipo de prueba y / o la complejidad de la configuración se vuelven problemáticos en la reparación del motor y en el campo. Y la prueba de CC enfatiza más los giros finales. El equipo de prueba de muy baja frecuencia (VLF) se ha utilizado con éxito para cerrar la brecha de prueba entre las pruebas hipot de CA y CC.

The October 2012 Currents article titled "How to properly test AC stator and wound rotor windings" provides a thorough explanation on the proper application of insulation resistance, winding resistance, surge testing and high potential testing for stators and wound rotors. The article emphasizes that NEMA MG 1-2011 specifies AC and DC high potential (hi-pot) test levels for new windings and does not recommend repeated application of the high potential test. This is reinforced in EASA's Recommended Practice for the Repair of Rotating Electrical Apparatus (ANSI/EASA AR100-2010) which calls for reduced voltage levels for repeated tests should they be required. This article is intended to provide additional information on the high potential test performed on new windings. Specifically, it addresses the advantages of AC high potential testing for new, form coil stator windings. Topics discussed include: A real-world example Destructive test? Sizing the AC test set Example calculation Bibliographic references to additional reference materials

There is much discussion in the industry about how to properly electrically test AC stator and wound rotor windings. Topics include test voltage, procedure, frequency and when to perform the various tests. This article describes how the following standards address these questions:

• NEMA MG 1-2011
• (MG1) IEEE 43-2000
• (IEEE 43) IEEE 62.2-2004
• (IEEE 62.2) IEEE 522-2004
• (IEEE 522) IEEE 1068-2009
• (IEEE 1068) ANSI/EASA AR100-2010
• (AR100) CSA C392-2011 (C392)

These standards are regularly reviewed and coordinated, so some of the information may not match the old yellowed reference taped to your toolbox lid. These updated references should replace anything dated previous to the dates indicated on the standard. AR100 Section 4.3.1 lists the recommended tests for stator and wound rotor windings. They are insulation resistance (IR), winding resistance, growler, phase balance, surge comparison, polarity and ball rotation tests. This article covers the IR, winding resistance and surge tests. Noticeably absent from this list is the ever popular high potential (hi-pot) test. Topics covered also include: IR (or megohm) test Polarization index test Winding resistance test Surge comparison test Hi-pot test.

A frequent question that arises during repair or maintenance is how much voltage to apply when performing a high potential test. The test voltage for a new winding will be higher than that of a winding that has been in service, but what is the appropriate test voltage? Seeking answers to this question can sometimes lead to confusion. Our goal in this article is to clarify high potential testing and test voltages.