A Guide To Diagnostic Insulation Testing Above 1 kV
Why a 10 kV Insulation Tester?
Megger invented insulation testing before the beginning of the 20th century and has continued to lead the market in innovation and technological advancement. So, why did we develop a 10 kV model when all other suppliers stopped at 5 kV? The answer is in the IEEE standards. Megger developed a 10 kV unit to meet the new testing recommendations outlined by the IEEE. Megger has offered a 10 kV insulation resistance tester since 2001.
In March 2000, The IEEE-SA Standards Board approved a revision to IEEE Std 43-1974. The "IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery," Std 43-2000, emphasizes the need for upgrading current practices to accommodate changes and improvements in insulating materials and the value of higher voltage testing that reveals otherwise hidden flaws.
Following is a brief summary of the highlights of the standard:
- Test voltages up to 10 kV are recommended for windings rated greater than 12 kV.
- Both the Insulation Resistance test and the Polarization Index test are recommended.
- Test results should be compared to historical values to identify changes.
- In lieu of historical records, minimum acceptable values (based on the type of equipment) for both tests are indicated.
- Depending on the machine rating, the readings for one or both tests should exceed the minimum acceptable values.
- If the readings are below the minimum acceptable values, the winding is not recommended for an over voltagetest or for operation.
IEEE Std 43-2000 recommends a procedure for measuring insulation resistance of armature and field windings in rotating machines rated 1 hp, 750 W or greater and applies to synchronous machines, induction machines, dc machines and synchronous condensers. It does not apply to fractional horsepower machines. It also recommends the insulation test voltage (based on winding rating) and minimum acceptable values of insulation resistance for ac and dc rotating machine windings.
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