Generac Power Systems 5413 Section Insulation Resistance Tests, Effects of Dirt and Moisture

Section 3

Insulation Resistance Tests

Effects of Dirt and Moisture

Moisture and dirt are detrimental to the continued good operation of any generator set.

If moisture is allowed to remain in contact with the Stator and Rotor windings, some of the moisture will be retained in voids and cracks of the winding insula- tion. This will result in a reduced Insulation resistance and, eventually, the unit’s AC output will be affected.

Insulation used in the generator is moisture resistant. However, prolonged exposure to moisture will gradu- ally reduce the resistance of the winding insulation.

Dirt can make the problem worse, since it tends to hold moisture Into contact with the windings. Salt, as from sea air, contributes to the problem since salt can absorb moisture from the air. When salt and moisture combine, they make a good electrical conductor.

Because of the detrimental affects of dirt and mois- ture, the generator should be kept as clean and as dry as possible. Rotor and Stator windings should be tested periodically with an insulation resistance tester (such as a megohmmeter or hi-pot tester).

If the Insulation resistance is excessively low, drying may be required to remove accumulated moisture. After drying, perform a second insulation resistance test. If resistance is still low after drying, replacement of the defective Rotor or Stator may be required.

Insulation Resistance Testers

Figure 3-1 shows one kind of hi-pot tester. The tester shown has a “Breakdown” lamp that will glow during the test procedure to indicate an insulation breakdown in the winding being tested.

Figure 3-1. – One Type of Hi-Pot Tester

*DANGER! INSULATION RESISTANCE TESTERS SUCH AS HI-POT TESTERS AND

MEGOHMMETERS ARE A SOURCE OF HIGH AND DANGEROUS ELECTRICAL VOLTAGE. FOLLOW THE TESTER MANUFACTURER’S INSTRUCTIONS CAREFULLY. USE COMMON SENSE TO AVOID DANGEROUS ELECTRICAL SHOCK

Drying the Generator

GENERAL:

If tests indicate the insulation resistance of a winding is below a safe value, the winding should be dried before operating the generator. Some recommended drying procedures include (a) heating units and (b) forced air.

HEATING UNITS:

If drying is needed, the generator can be enclosed in a covering. Heating units can then be installed to raise the temperature about 15°-18° F (8°-10° C) above ambient temperature.

FORCED AIR:

Portable forced air heaters can be used to dry the generator. Direct the heated air into the generator’s air intake openings. Remove the voltage regulator and run the unit at no-load. Air temperature at the point of entry into the generator should not exceed 150° F. (66° C.).

Cleaning the Generator

GENERAL:

The generator can be cleaned properly only while it is disassembled. The cleaning method used should be determined by the type of dirt to be removed. Be sure to dry the unit after it has been cleaned.

NOTE: A shop that repairs electric motors may be able to assist you with the proper cleaning of generator windings. Such shops are often expe- rienced in special problems such as a sea coast environment, marine or wetland applications, min- ing, etc.

USING SOLVENTS FOR CLEANING:

If dirt contains oil or grease a solvent is generally required. Only petroleum distillates should be used to clean electrical components. Recommended are safe- ty type petroleum solvents having a flash point greater than 100° F. (38° C.).

*CAUTION!: Some generators may use epoxy or polyester base winding varnishes. Use sol-

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