GE Industrial Solutions Fan Assisted Cooling (FAC) Dry-Type Transformers - Manual (Page 6)

6
8.1 Loading
In general, dry type transformers are designed to operate continuously at their nameplate kVA rating. ANSI C57.96 provides
guidance for loading under unusual conditions including: 1. Ambient temperatures higher or lower than the basis for rating; 2. Short
term loading in excess of nameplate kVA with normal life expectancy and; 3. Loading that results in reduced life expectancy.
If the transformer is experiencing increased temperatures, the following load characteristics should be considered immediately:
•
Rigorous, frequent or multiple motor starting or impact loads for which a specific transformer for that application is required.
•
Over excitation of unit due to excessive supply line voltage.
•
Ambient temperatures above standard 40C maximum (30C average over 24 hours).
•
Harmonic distortions of the supply line voltage or currents.
•
Loads that are non-linear with harmonic distortion.
8.2 Over-excitation
Operation at voltages in excess of rating may cause core saturation, excessive core losses, overheating, abnormally high noise levels
and potential damage to fans. Special care should be taken where higher than rated primary voltage is anticipated. Most dry type
transformers incorporate primary taps to be able to match the supply voltage and are designed to reach rated temperature rise above
ambient air temperature when operated continuously at rated voltage, frequency and load.
WARNING
SERIOUS OVERHEATING RESULTING IN FIRE DAMAGE MAY RESULT IF THE UNIT IS OPERATED FOR
SUSTAINED PERIODS ABOVE RATED VOLTAGE OR CURRENT AND/OR AT OTHER THAN RATED FREQUENCY.
9.0 Troubleshooting
Problem: Circuit breaker (not three-phase disconnect included with unit) trips on start up
Possible causes:
Circuit breaker incorrectly sized for kVA rating of transformer.
Circuit breaker instantaneous trip (if applicable) set too low.
Supply voltage too high, over voltage being applied to transformer.
Supply voltage cables incorrectly connected to transformer secondary.
Transformer being reverse fed.
Primary ground cable connected to transformer secondary neutral bus.
Problem: Wrong secondary voltage or secondary voltage drifts
Possible causes:
Improper grounding.
Incorrect installation, review nameplate connection diagram.
Primary tap jumpers incorrectly installed.
Measurements must be taken with a true RMS meter.
Problem: Transformer noisy
Possible causes:
Transformer not installed per the recommended installation procedures outlined in this publication (paragraph 5.4).
Supply voltage to transformer higher than voltage rating of transformer.
Transformer overloaded.
Transformer enclosure panel screws not securely tightened.
Rubber isolation pads not installed.
Sound reverberating from reflecting surfaces.
Alarm is on (see below).
Problem: Transformer runs hot
Possible causes:
Overvoltage being applied to transformer.
Transformer being loaded at greater than nameplate kVA rating.
Higher than recommended (30C average / 40C maximum) ambient air.
Transformer enclosure ventilation openings obstructed or high content of dust and/or lint in transformer air ducts.
Clearance to walls (6.0”) not maintained.
Load contains large amount of harmonics.
Fans are obstructed, have been disconnected or are not working properly.
Problem: Alarm turns on
Possible causes:
Transformer is running over temperature limits (see above).