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Oil
Cooled Transformer :
TECHNICAL
FEATURES :
Manufacturing standards :
UPTO 3000 KVA, 11/22/33 KV CLASS.
Core
:
The Core is build up from interleaved low
loss cold rolled, grain oriented Silicon
Steel laminations. Individual stampings
are coated on both sides with an insulating
material, which is both oil and temperature
resistant. The core limbs are securely bound
with heavy duty webbed cotton taps and the
yokes are firmly clamped between steel channels,
all cores have mitered joints. Top and bottom
clamps are secured to each other by means
of tie rods which serve the dual purpose
of securing the windings in place and of
transfering the load from the bottom to
the top clamps when the core and windings
are lifted. This prevents tensile stresses
being set up in the core legs which could
adversely affect the iron losses.
Windings
:
Transformer windings are designed to meet
three fundamental requirements such as mechanical,
tharmal and electrical. They are cylindrical
in shape and are assembled concentrically.
T he low-tension windings are of the helical
type, single or multilayer, using flat copper
strips, depending upon the size and current
rating of the transformer.The high-tension
winding consist of paper covered round and
strips conductors depending upon the current
rating of the transformer. For higher capacity
continuous disc windings are used. The windings
are rigidly supported by pressboard washers
and spacers. Interlayer cooling ducts are
provided to ensure that the temperature
gradient between windings and oil and hence
the hot spot temperature is minimised and
high life expectancy is achieved. Insulation
between layers and turns is based upon the
impulse test level of the voltage class
of the windings as specified in IS 2026.
Completed. Core coil assemblies are dried
prior to impregnation with transformer oil.
WINDING
CONNECTIONS :
Tappings and leads are run in multi paper
covered flexible conductors in press board
half tubes, the phase leads being separated
from he tapping leads by adequate barriers.
These tubes are rigidly based to ensure
that clearances between leads and tank sidewall
are maintained when the transformer is fixed
in position. Low voltage leads being of
larger cross section are sufficiently robust,
so supports are provided wherever necessary.
INSULATION
and IMPREGNATION :
The principal components of insulation are
pre-fabricated from pressboard sheet. All
items subjected to compression in services
are preshrunk and the slight recovery in
dimensions after preshrink age is compensated
for windings during final drying of the
completed transformer. The oil used for
impregnation complies with IS 335 and every
consignment received at works is tested
before entry is permitted into the storage
tanks.
SHORT
CIRCUIT STRENGTH :
In order to prevent deformation when subject
to short circuit force, solid blocks and
insulation, backed by substantial supporting
frames,are utilized. The axial end thrust
under fault condition is minimised by ensuring
that design dimensions are closely adhered
during manufacturing procedure. Transformers
are designed and constructed n such a way
that they are capable of withstanding the
effect of short circuit testing. Our transformers
have been type tested at
CPRI and ERDA.
TAPPINGS
:
For the range of transformer covered in
this Catalogue, tappings are provided on
the H. T. Windings at ±5% in steps
of ±2.5%. Other tapping ranges can
be supplied on request. Tap selection is
effected by means of an off circuit-tapping
switch operated by an external handle. Tappings
leads are brought away from the coils by
the means of paper insulated conductors.
They are arranged in such a manner that
the ampere-turn balance is maintained throughout
the tapping range. ON LOAD TAP CHANGRES
are also provided depending upon customer’s
requirement.
TERMINATIONS
:
All bushings are of high quality porcelain
or Epoxy complying as per IS 2099.
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