Owner's manual

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 eld 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 lled 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 uid. For transformers
lled with natural ester uids (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
lled with silicone uid, contact the Howard Industries
Transformer Division for information.
Sampling the Fluid
Before sampling the insulating uid, 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 uid test equipment.
Filtering the Fluid
The insulating uid can be ltered using a lter
press system. A lter press can remove particle
contaminants as well as small amounts of moisture.
Follow the operating instructions provided by the lter
press system manufacturer. Continue to lter the uid
until the dielectric test result is 26kV or greater.
When ltering any particular type of insulating uid,
make sure the lter press system is not contaminated
with any other type of uid. Contamination of the uid
may alter its chemical or physical characteristics and
could reduce its re point.
Removing or Lowering the Fluid
Should it be necessary to remove or lower the
insulating uid, the following procedure should be
used. Use clean pumps and hoses that have not
been contaminated by different types of uids.
Hoses must be designed for handling the particular
uid 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 uid.
4. Place the pump discharge hose nozzle at the
bottom of storage container.
5. Pump slowly, and do not allow the uid to splash
into the container, as this could introduce air and
moisture into the uid.
6. Do not lower the insulating uid below the top
of the core/coil clamp pan. Exposing coils could
allow moisture to contaminate coil insulation.
Filling with Fluid
When relling the transformer with insulating
uid, ll with the same type of uid, following the
procedure outlined below. Do not mix different types
of uids. Care should be taken to avoid introduction
of air bubbles during the lling process. After relling
is complete, allow 24 hours for dissipation of air
bubbles before energizing the transformer. Trapped
air bubbles can reduce the insulation value of the
uid and cause an internal ash-over.
1. Every storage container of transformer uid used
in the lling process should be visually inspected
and tested for water and other possible
contaminants before proceeding with the lling
process.
2. Pump from the bottom of storage container. To
prevent bubbles in the uid, 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 ll the transformer tank slowly.