Howard HI-104 Single-Phase Pad Transformer - Manual (Page 31)

Document 2.4.96, Revision 0
March, 2013
31
Single-Phase Pad-Mounted Compartmental-Type Distribution Transformers
dard C57.12.90 Test Code for Liquid-Immersed
Distribution, Power, and Regulating Transformers for
more information about design sound levels and fac-
tory sound testing.
Low-Voltage Circuit Breaker
The low-voltage circuit breaker is inaccessible (ex-
cept in the double-door style transformer) and typi-
cally requires no maintenance.
Magnex Interrupter
The Magnex Interrupter typically requires no mainte-
nance except for replacement in the event of mal-
function or damage.
Other Accessory Devices
Other accessory 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 from a remote location 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 recom-
mended sampling procedures. Also, refer to any
sampling recommendations provided by the manu-
facturer of the fluid test equipment.
Filtering the Fluid
The insulating fluid can be filtered using a filter press
system. A filter press can remove particle contami-
nants 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
results satisfy the requirements of IEEE Standard
C57.106 for mineral oil, IEEE Standard C57.147 for
natural ester fluids and IEEE Standard C57.212 for
transformers filled with less-flammable high mo-
lecular weight hydrocarbon insulating fluid (such as
R-Temp). When filtering any particular type of insu-
lating fluid, make sure the filter press system is not
contaminated with any other type of fluid. Contami-
nation 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 insu-
lating fluid, the following procedure should be used.
Use clean pumps and hoses that have not been
contaminated by other 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.).
1. De-energize the transformer, and make sure the
tank and all terminals are effectively grounded.
2. If cover removal is required, follow the procedure
outlined in the “Opening the Transformer Tank”
section.
3. Connect the pump inlet hose to the drain valve at
the base of the transformer tank. In the case of a
double-door style transformer, the inlet hose can
be inserted through the cover-mounted handhole
and placed at the bottom of the tank.
4. Use a clean, dry temporary storage container to
contain the fluid.
5. Place the pump discharge hose nozzle at the bot-
tom of storage container.
6. Pump slowly, and do not allow the fluid to splash
into the container, as this will introduce air and
moisture into the fluid.
7. Do not lower the insulating fluid below the top of
the core/coil clamp pan, as exposing coils could
allow moisture to contaminate coil insulation.
Filling with Fluid
When filling 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 intro-
duction of air bubbles during the filling process. After
filling is complete, allow 24 hours for dissipation
of air bubbles before energizing the transformer.
Trapped air bubbles can reduce the insulation value
of the fluid and cause an internal flash-over.
1. Every storage container of transformer fluid used
in the filling process should be visually inspected
and tested for water and other possible contami-
nants before proceeding with the filling process.
2. Pump from the bottom of storage container. To
prevent bubbles in the fluid, do not allow air to
enter the pump intake.
3. Connect the pump discharge hose to the drain
valve at the base of the transformer tank to