GE Industrial Solutions Dry-Type General Purpose Power Transformers - Manual (Page 3)

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CAUTION
ONLY EXPERIENCED AND QUALIFIED PERSONNEL SHOULD PERFORM INSTALLATION AND MAINTENANCE. NO
ATTEMPT SHOULD EVER BE MADE TO CHANGE THE TAPS OR MAKE CABLE CONNECTIONS WHILE THE
TRANSFORMER IS ENERGIZED.
TRANSFORMERS SHOULD BE INSTALLED IN SECURE, CONTROLLED ACCESS AREAS, NEVER IN AREAS SUBJECT
TO DELIBERATE, UNAUTHORIZED ACTS BY MEMBERS OF THE UNSUPERVISED PUBLIC. IF INSTALLED IN SUCH
AREAS, TAMPER RESISTANT ENCLOSURE SCREWS SHOULD BE USED.
5.1 Preparation
Remove any accumulation of dirt or dust by vacuuming, brushing or by blowing dry air on the unit. If moisture is evident by the
appearance of rust or mildew or moisture is visible on the insulation surfaces, the unit should be dried out by placing it in an oven
or by blowing heated air over it. In either case the temperature should not exceed 110C/230F. Insulation resistance tests of the type
used on liquid filled transformers are of little value on dry-type transformers. The nature of insulation used in dry type transformers
is such that megger readings are not reliable and may be misleading. Refer to ANSI/NEMA C57.12.91 paragraph 10.9 for
additional information.
5.2 Mounting and Placement
The only foundation necessary is a non-combustible flat surface strong enough to support the weight of the unit. Note that
permanent and effective grounding of the metal case in accordance with NEC is recommended as a safety precaution.
Free circulation of ambient air is essential for the proper operation of all ventilated dry-type transformers. The sides of the
transformer with ventilation openings require a minimum distance of six inches to adjacent noncombustible structures or equipment
to ensure proper circulation of air. Refer to enclosure assembly picture on last page.
CAUTION
GENERAL PURPOSE TRANSFORMERS SHOULD BE INSTALLED AT LEAST TWELVE INCHES FROM COMBUSTIBLE
MATERIALS, INCLUDING MOUNTING SURFACE UNLESS SEPARATED BY FIRE RESISTANT HEAT INSULATING
BARRIERS. SPECIFIC REQUIREMENTS ARE DESCRIBED IN NEC, SECTION 450-21. CHECK LOCAL CODES.
5.3 Ventilation
Dry-type general-purpose transformers are cooled by free circulation of surrounding air. They depend on air to enter at the bottom,
flow upward over the core and coil surfaces and exit through the openings near the top. These transformers will carry full-rated
loads continuously when the surrounding air does not exceed 30C/86F average, 40C/104F maximum and adjacent structures permit
free movement of cooling air.
The room in which dry-type transformers are located should be sized to permit locating transformers with sufficient spacing
between units and sufficient clearances to walls and other obstructions to permit the free circulation of air around each unit and to
minimize noise amplification. Sufficient space should also be maintained to permit routine inspection and maintenance.
Adequate ventilation is essential for the proper cooling of transformers. Clean dry air is desirable. Filtered air at or above
atmospheric pressure may reduce maintenance if dust or other contaminants present a problem. When transformers are located in
rooms or other restricted spaces, sufficient ventilation should be provided to hold the air temperature within established limits
(30C/86F average over 24 hours with a 40C/104F maximum) when measured near the transformer inlets.
5.4 Audible Sound Sources
The audible sound produced by transformers is due to the energizing of the core by the alternating voltage applied to the windings.
This creates vibrations whose fundamental frequency is twice the frequency of the applied voltage. The audible sound will be
present even under no load conditions. The vibrations producing audible sound can occur in the core, coil, mounting, housing, and
in the conduit. The transmission of sound from the transformer can be by various media such as air, metal, concrete, wood or any
combination. Amplification of audible sound can occur in a given area due to the presence of reflecting surfaces.