Items to Inspect
Points to be checked
Remedial Action
Frequency
Dielectric Fluid Level
Check dielectric fluid level gauge. Note that the
fluid level gauge has a notation as to the expected
level when the unit has an average internal fluid
temperature of 25 °C. A reading above this zone
is normal when at full operating temperature and
does not indicate that the transformer is operating
at a temperature higher than the nameplate rating.
If the dielectric fluid level is below the nominal
level, check transformer for signs of a leak. If a
leak is observed, repair immediately. If no leak
is observed, add oil to bring level to nominal
operating level.
Annual
Fluid Temperature
Check liquid temperature gauge for elevated
temperature. Reset the drag hand if one exists.
Compare temperature to that of similar units. Note
that the maximum top fluid temperature as noted
by the draghand is a function of the maximum
loading on the hottest day. A rule of thumb for a
typical maximum reading would be nameplate rated
temperature rise minus 10 °C plus the maximum
ambient peak experienced in the area.
Example: 65 °C - 10 °C + 40 °C = 95 °C. Similar
units should be within 3 °C of each other at the
same location.
If temperature is elevated compared to other
similar transformers, have unit serviced
immediately to determine source of elevation.
Annual
Fusing
If bayonet fuses have been extracted, fluid might be
present from that activity and may not be indicative
of a leak.
Annual
Cable Connections
If there are signs of overheating, check for loose
connections or discolored spades (paddles).
The tin plating will achieve a rainbow coloring
if a particular terminal is experiencing an over
temperature condition.
Tighten any loose connections immediately.
Any damage or discoloration that is observed
should be addressed immediately by a qualified
technician.
Annual
Bushings
Check condition of the HV and LV bushings.
Observe for any indication of dirt, breakage, general
damage, heat damage or flashover. Note that
excess dielectric grease from the separable dead
front connectors can liquefy from the heat and
appear like an internal fluid leak.
If the bushings are dirty, clean them
immediately. Any damage that is observed
should be addressed immediately by a qualified
technician.
Annual
Cubicle Padlock
Check that all cubicles are locked.
Replace any missing locks immediately.
Annual
LV Bushing Cantilever
Check for excessive cable weight or stiff cable
conductors putting upward or downward pressure
on the bushings due to pad settling.
Immediately adjust cable/conductor position to
eliminate pressure.
Annual
Pressure Relief Valve
Check for dirt, debris and operation.
Replace immediately if damage. Clean if dirty or
clogged with debris.
Annual
Lightning Arresters
Check for damage or breakage and an intact and
tight ground connection.
Replace damaged arresters and tighten or
secure any lose ground connections.
Annual
Dissolved Gas Analysis
Items to Inspect
Points to be checked
Remedial Action
Frequency
Oil Sample
Take an oil sample and send it to a third party
tester to check dissolved gas levels.
Compare dissolved gas analysis results to the
baseline result. Look for abrupt changes in
dissolved gas levels. Any abrupt changes should
be investigated immediately.
Annual
27
Three-phase pad-mounted compartmental type installation and maintenance instructions
MN202001EN August 2015
