Section 5—Operation

The standard dip and baked varnish process does not support the growth of fungus. The only concern when units are stored in high humidity areas is retaining the integrity of the insulation material. If units are properly maintained and cleaned at shut down prior to long periods of de-energization there should be no issue with fungus.

Humidity conditions are unimportant as long as the transformer is energized. However, follow the precautionary steps listed below if the transformer is de-energized, is allowed to cool to ambient temperature, and will exceed a shutdown of 12 hours (especially in high humidity conditions).

1. Place small strip heaters in the bottom of the unit shortly after shutdown to maintain the temperature of the unit a few degrees above that of the outside air.

2. Inspect the unit for evidence of moisture before returning it to service.

3. Check the insulation resistance. If evidence of moisture exists, or if the insulation resistance is less than 1 megohm, dry out the transformer by placing it in an oven or by blowing heated air over it.

The temperature rise on the enclosure exterior for ventilated transformers should not exceed 122°F (50°C), except as indicated in UL 1561.

Removing Temporary Braces

1. Remove any temporary braces. See Removing Temporary Braces.

2. Check bolted electrical connections. Refer to Making Electrical Connections for a detailed check list.

3. Remove excess dirt accumulations from the transformer windings and insulators to permit free circulation of air and to guard against the possibility of insulation breakdowns. Refer to Cleaning for a detailed check list.

4. Perform insulation resistance tests with an appropriate device. Refer to Insulation Resistance for a detailed instructions.

5. Perform a visual and mechanical check of the transformer and its surrounding environment. Refer to Performing Visual and Mechanical Checks for a detailed check list.

1. Follow all safety precautions and requirements for PPE as outlined in NFPA 70E and any other applicable standards and/or codes.

   1. Immediately de-energize the transformer if there is any indication of arcing (visual or audible) at any time during the initial start-up.

   2. Investigate and correct the cause of the arcing before re-energizing the unit.

2. Investigate and correct sources of excessive noise. When energized, the transformer will make some audible noise. Excessive mechanical noise, hums or rattles may be an indication of improperly installed or tightened hardware or enclosure parts.

3. Measure and verify the primary and secondary phase-to-phase and phase-to-ground voltages for all windings.

   1. Where applicable, measure and verify phase-to-neutral voltages, as well.

   2. Record and save the values for future reference.

      NOTE: Phase-to-phase, phase-to-ground and phase-to-neutral measurements will verify that the transformer is functioning per the nameplate voltages.
   3. Measure phase-to-ground voltages.
   4. Record and save the values for future reference.
      NOTE: Phase-to-ground voltages will verify that the unit has been installed correctly.

4. Move one tap at a time, or verify that the jumper lands per the wiring diagram as shown on the nameplate. See Phase Diagram, Tap Locations and Voltage Rating Marked on Nameplate.

   NOTE: Do not change taps while the transformer is energized.

   1. Adjust the transformer taps as necessary to match the actual voltage requirements.

   2. Ensure taps are cleaned of varnish or other insulating material.

5. Perform a phase rotation check with an appropriate device for loads that are phase sensitive (e.g., certain motor or drive applications).

   1. Follow the manufacturer’s instructions for the device.

   2. Correct phase rotation errors before energizing the transformer.