Howard HI-102 Overhead Transformer - Manual (Page 25)

Document 2.4.95, Revision 0
May, 2013
25
Fluid-Filled Overhead Distribution Transformers
Magnex ™ Interrupter
The Magnex ™ interrupter and protective link, if
present, are accessible by removing the transformer
cover or handhole cover. Interrupters do not normally
require field adjustment. Defective interrupters
should be replaced. Refer to “Opening the
Transformer Tank” for instructions.
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.
Insulating Fluid
For transformers filled with mineral oil, refer to
IEEE Standard C57.106 Guide for Acceptance and
Maintenance of Insulating Oil in Equipment for
additional guidelines that should be observed when
testing or handling insulating fluid. For transformers
filled with natural ester fluids (such as Envirotemp
FR3 ™ ), refer to IEEE Standard C57.147 Guide for
Acceptance and Maintenance of Natural Ester Fluids
in Transformers for information. For transformers
filled with silicone fluid, contact the Howard Industries
Transformer Division for information.
Sampling 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 the sampling
recommendations provided by the manufacturer 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
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 greater.
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. 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.).
1. De-energize the transformer, and make sure the
tank and all terminals are effectively grounded.
2. Remove the cover or handhole cover, if provided,
as outlined in the “Opening the Transformer
Tank” section.
3. Use a clean, dry temporary storage container to
contain the fluid.
4. Place the pump discharge hose nozzle at the
bottom of storage container.
5. Pump slowly, and do not allow the fluid to splash
into the container, as this could introduce air and
moisture into the fluid.
6. Do not lower the insulating fluid below the top
of the core/coil clamp pan. Exposing coils could
allow moisture to contaminate coil insulation.
Filling with Fluid
When refilling the transformer with insulating
fluid, fill with the same type of fluid, following the
procedure outlined below. 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 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
contaminants 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. Place discharge hose at the bottom of the
transformer tank to prevent aeration and the
introduction of bubbles.
4. Pump and fill the transformer tank slowly.