Document 2.4.128, Revision 3
October, 2017
24
Network Transformer Instruction Manual
Other Accessory Devices
Other accessories devices, such as a gauges and
valves typically require no maintenance except for
replacement in the event of malfunction or damage.
Sampling and Testing the Fluid
Before sampling the insulating fluid, de-energize
the transformer and make sure all bushings and
terminals are effectively grounded. Samples should
be drawn from the bottom of the tank. Refer to
ASTM D923
Standard Practices for Sampling
Electrical Insulating Liquids
for recommended
sampling procedures. Also refer to any sampling
recommendations supplied by the fluid test
equipment manufacturer.
It is recommended that a fluid sample be drawn
annually and tested for dielectric strength. Dielectric
strength should measure at least 26 kV.
Filtering the Fluid
Insulating fluids such as mineral oil, R-Temp or
seed-based fluids can be filtered using a filter
press system. A filter press can remove particle
contaminants as well as small amounts of moisture.
Follow the operating instructions provided by the
filter press system manufacturer.
Continue to filter the fluid until the dielectric test
result is 26kV or better. When filtering any particular
type of insulating fluid, make sure the filter press
system is not contaminated with any other type
of fluid. Contamination of the fluid may alter its
chemical or physical characteristics and could
reduce its fire point.
Removing or Lowering the Fluid
Should it be necessary to remove or lower the
insulating fluid, the following procedure should be
used.
1. De-energize the transformer and make
sure the tank, bushings, and terminals are
effectively grounded.
2. If cover removal is required, remove cover
as outlined in the
“Opening the Transformer
Tank”
section.
3. Use a clean, dry temporary storage container
to contain the fluid.
4. Use clean pumps and hoses that have not
been contaminated by different types of
fluids. Hoses must be designed for handling
the particular fluid in the transformer (As an
example, rubber hoses should not be used
with mineral oil.).
5. Connect the pump intake line to the drain
valve at the bottom of the transformer tank.
6. Place the pump discharge line nozzle at the
bottom of storage container.
7. Pump slowly and do not allow the fluid to
splash into the container, as this will introduce
air and moisture into the fluid.
8. Do not lower the insulating fluid below top
of core/coil clamp pan unless absolutely
necessary. Exposing coils may allow moisture
to contaminate coil insulation.
Filling with Fluid
When refilling the transformer with insulating fluid, fill
with the same type of fluid. Do not mix different types
of fluids. Care should be taken to avoid introduction
of air bubbles during the filling process. After refilling
is complete, allow 24 hours for dissipation of air
bubbles before energizing the transformer. Trapped
air bubbles can reduce the insulating value of the
fluid and cause an internal flash-over.
1. Every storage container or tote of transformer
fluid should be visually inspected and tested for
WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY AND MAY ALSO RESULT IN
DAMAGE TO THE EQUIPMENT.
• Release internal pressure before opening the
tank. Personnel should wear eye and skin
protective equipment when using the pressure
relief valve to relieve tank presure. Hot fluid
may be expelled.
• Never allow anyone to enter the transformer
tank until an analysis of the air inside the tank
indicates at least 19.5% oxygen.
• Whenever someone is inside the tank, a
person should be stationed outside the tank
to ensure the safety of the person inside the
tank.
