Improve ventilation or relocate unit to cooler location.
Reduce load; reduce amperes by improving power factor with capacitors; check for circulating currents for paralleled transformers - different ratios or impedances; check for open phase in delta bank.
Change circuit voltage, taps.
If other than naturally cooled, check fans, pumps, valves and other units in cooling systems.
Winding failure - incipient fault
See "No voltage - unsteady voltage" below.
Test for exciting current and no-load loss; if high, inspect core, remove and repair; check core bolt, clamps and tighten; check insulation between laminations; if welded together, return to factory for repair or replacement.
High harmonic loads
Measure neutral current - replace with K-rated transformer
See "Hot transformer" above.
Metal part ungrounded, loose connection
Determine part and reason; check clamps, cores and parts normally grounded for loose or broken connections, missing bolts or nuts, etc.; tighten loose clamps, bolts, nuts; replace missing ones.
External parts and accessories in resonant vibration
Tighten items as above; in some cases, loosen to relieve pressure causing resonance and install shims.
Incipient fault - core or winding
See above under "Hot transformer."
No Voltage / Unsteady Voltage
Winding failure - lightning; overload; short-circuit from foreign object or low strength dielectric
Check winding; remove foreign object or damaged material; repair or replace parts of insulation materials.
Rust and paint deterioration
Weather, pollution, corrosive or salt atmosphere; overloads
Remove rust and deteriorated paint; clean surfaces; repaint with proper paints and sufficient coatings.
Excessive heating discoloration
If excessive heating discoloration occurs, check sizing, input voltage, or loading amps.
Hot neutral line
Too small neutral conductor: replace. Severe unbalance between phase: rebalance and equalize loads.
One leg of wye bank open
Check associated fuse. If blown, remove cause and replace. Check for open circuit in winding of transformer in bank. Measure odd harmonic amps with RMS meter.
Open neutral unbalanced loads
Check neutral connections. See "Hot neutral line" above.
Voltage high and unbalanced
Open neutral on wye bank ground in winding of one transformer in wye
Check neutral connections and load balance. Check values of voltages between phases and phase-to-ground voltages. Vector should indicate source of trouble.
No voltage - one phase of delta connected bank
Grounds on two legs of delta (delta collapse - loads "single phasing")
Remove grounds from at least one leg of delta source.
Overloads on two delta bank
Open in third transformer of bank; operating in open delta
Check fuses on supply to their bank; check winding of transformers in third transformer for continuity.
Low voltage on two phases on delta
Open in one phase of delta supply; two transformers now connected across one same phase
Check fuse on supply; check supply circuit back to source for open circuit.