FIELD OF THE INVENTION
The present invention relates to a safe and reliable method of cooling the
tank wall of High current Rectifier transformer. More particularly, the
invention relates to extend the use of an auxiliary cooling system to limit
the temperature magnetic wall of a high power rectifier transformer below
safe working temperature limit.
BACKGROUND OF THE INVENTION
A Rectifier transformer is a power transformer used in process industry
where very high current at low voltage D C is required for carrying out an
electrolytic process for extraction of metals and other chemicals. The
Rectifier transformer is a transformer that has at least one high voltage
winding and at least one low voltage secondary winding. Power is fed to
the Rectifier transformer (power transformer) at high voltage for example
11 kV ( or 33 kV or 66 or 132 kV or 220 kV ) and the power is evacuated
from the secondary winding which can have a voltage ranging from 45 volts
( or less ) up to a voltage of 1800 volt ( or more ). The current in the
secondary winding is in the range of 5 kilo Ampere up to 140 kilo Ampere.
This A C current from the Rectifier transformer may be routed through a
Transductor/IPT and fed to Diode/Thyristor Rectifiers for converting to D C
current.

The input HV winding current is normally few hundred amperes,
where as the LV current is in the magnitude of thousands of Ampere. To
handle such large LV winding current, the LV winding is subdivided in to a
number of parallel windings, each parallel winding having few turns of
multi-parallel wires. The termination of each parallel coil is made on
separate copper flats ( known as raisers or bus-bars ). These raisers are
further grouped into separate bunches and terminated on different epoxy
casted bushings. Each of the bus-bars and bus-bars bunches carry
thousands of amperes and set up their own magnetic field. As a result, the
magnetic tank wall adjacent to the raisers (bus-bars) and the bus-bar
bunches get heated to a very high temperature. The temperature of this
tank wall heats the adjacent oil and the temperature of the oil goes beyond
the safe working temperature limit. At this high temperature, gasification in
oil starts resulting in deterioration of the transformer oil deteriorating the
over all insulation system of the transformer.
The HV and LV winding (means for incoming and out going of power)
terminals of the transformer are taken out from the transformer tank and
connected to external circuits. Even though, there are a number of ways to
take out the terminations, the actual method of termination is decided
based on the applications and location of the Transformer as well as the
Rectifier. A C power from the LV winding (may be routed through
Transductor/IPT) is taken out through LV bushing is fed to the
Diode/Thyristor Rectifiers for converting to D C power required for the
process of electrolysis. The routing of this high current connections often
come very close to the tank. As a result the magnetic effect of

the high current in the connections, causes additional heating of the tank
including LV side tank wall causing additional problems .
Due to the heat generated by the raisers inside the tank and the external
connection (from transformer LV bushing to the D C Rectifiers ) the tank
and the LV side tank wall gets heated and increases the temperature of oil.
The adjacent insulations also starts deteriorating which could trigger failing
of the transformer. Due to this heat, the paintings on the wall starts
burning and paint gets peeled off. The peeled off paints floats in oil and
reaches unwanted places in winding causing choking of oil duct in winding
and other damages . The peeled bare surface of the tank wall gets rusted
owing to the moisture in oil and cause damage to oil . The temperature also
causes breaking of the epoxy bushing and gasket leading to oil leakage
from he tank. The hot oil leaked through the broken epoxy bushing and
gasket when flow over the over heated tank wall, generates a potential
danger of fire hazard.
To overcome the above problems, a method has been invented to cool the
magnetic tank wall of the transformer externally. Once the tank wall is
cooled there will be no over heating of the oil and all the associated
problems Viz. cracking of LV epoxy bushings, gaskets, oil leakage, fire
hazard, paint peeling and deterioration of oil and insulation are eliminated.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an auxiliary cooling
system to limit the temperature magnetic wall of a high power rectifier
transformer below safe working temperature limit.
Another object of the invention is to propose an auxiliary cooling system to
limit the temperature of magnetic wall of a high power rectifier transformer
below safe working temperature limit in which the temperature of the oil of
the Rectifier transformer is delimited below the safe working temperature
limit.
A still another object of the invention is to propose an auxiliary cooling
system to limit the temperature of magnetic wall of a high power rectifier
transformer below safe working temperature limit m which eliminates the
probability of cracking of LV bushing to prevent leakage of oil.
Yet another object of the invention is to propose an auxiliary cooling
system to limit the temperature of magnetic wall of a high power rectifier
transformer below safe working temperature limit which eliminates the
probability of fire hazard owing to flow of leaked oil over the over heated
tank wall of the transformer.
A further object of the invention is to propose an auxiliary cooling system
to limit the temperature of magnetic wall of a high power rectifier
transformer below safe working temperature limit which prevents paint
peeling and deterioration of the tank wall due to extra high temperature.

A still further object of the invention is to propose an auxiliary cooling
system to limit the temperature of magnetic wall of a high power rectifier
transformer below safe working temperature limit which restricts oil
contamination due to interaction of hot oil with peeled off surface of the
tank.
SUMMARY OF THE INVENTION
Accordingly, there is provided an auxiliary cooling system to limit the
temperature magnetic wall of a high power rectifier transformer below safe
working temperature limit, the transformer comprising at least a core
having high voltage (HV) windings, and low-voltage (LV) windings housed
in a tank made of magnetic steel, the tank being maintained full of oil to
keep the windings and the other associated accessories of the transformer
completely immersed in the oil the terminals of the LV and HV windings
are taken out from the tank for connection to the external circuits, the LV-
side of the transformer carries high current and routed through a plurality
of raisers for termination to several epoxy bushings, the magnetic field of
this high current generating high temperature on the LV-side magnetic
wall of the tank, the auxiliary cooling system comprising a plurality of
external coolers; an oil pipe circuit branched out of the main cooling pipe
of the transformer; and a plurality of box-type stiffeners provided along the
length of the tank wall.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows arrangement of LV coils and bus-bars ( raisers ) in a
Rectifier Transformer inside the tank.
Figure 2 - shows in a schematic diagram heating of tank wall due to the
magnetic field of the LV raisers inside the tank.
Figure 3 - shows schematically heating of a tank wall due to routing of the
LV connections outside the tank.
Figure 4 - Method of external cooling of the tank wall according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
The Rectifier transformer is the source of power in a process industry for
extraction of metals and chemicals by electrolysis. As shown in figure 1, the
transformer comprises HV and LV windings housed in a metallic container
known as tank (1). The LV side of the transformer carries several thousands
of current routed through a number of vertical copper/aluminum
raiser/bars (2) and terminated onto a plurality of epoxy bushings (3). The
magnetic field of the current generates very high temperature on the LV
side magnetic wall (4) of the tank (1).

As shown in Fig.3, the Connections (9) from LV winding are taken to the
Rectifiers (10) for generating D C power. The routing of the external bus-
bars (9) from the LV coil terminations (bushing) also creates high
temperature on the tank wall with stiffeners. The tank (1) of the
transformer is made of magnetic steel. The tank houses the transformer
comprising a core, a coil and the other associated equipments and it is full
of oil. The tank has to be made suitable for Pressure test, Vacuum test that
is essential for the safe working of the transformer during various
conditions of working. For this purpose the tank (1) is strengthened by
providing several hollow-box type stiffeners (5) as shown in Fig.l. The LV
side wall (4) of the Rectifier transformer is also provided with external
hollow stiffener (5) all along the length of the tank wall (4).
Heat is generated inside the transformer during working of the
transformer. This heat is cooled by providing a plurality of auxiliary coolers.
As shown in Fig.4, the oil in the transformer is cooled externally by
providing a group of external auxiliary coolers (6). Hot oil from the
transformer flows into the auxiliary coolers (6) and the cooled oil from the
auxiliary coolers (6) go into the transformer through main cooler pipe (7)
thereby maintaining the temperature of the oil inside the transformer
below the safe working limit. Oil thorough this branched pipe (8) flows
through the external stiffeners (5) and thereby removing the additional
heat caused due to the magnetic field of the LV raisers (2) carrying heavy
current. The hot oil from the stiffeners (5) enters the auxiliary coolers (6)
for dissipation of this additional heat.

In this method the tank wall gets cooled due to the magnetic heating of the
raisers (2) inside the tank wall. The additional heat generated on the tank
wall/stiffener due to the external routing of the LV bus bar also gets cooled
by this method.

WE CLAIM :
1. An auxiliary cooling system to limit the temperature magnetic wall of
a high power rectifier transformer below safe working temperature
limit, the transformer comprising at least a core having high voltage
(HV) windings, and low-voltage (LV) windings housed in a tank made
of magnetic steel, the tank being maintained full of oil to keep the
windings and the other associated accessories of the transformer
completely immersed in the oil the terminals of the LV and HV
windings are taken out from the tank for connection to the external
circuits, the LV-side of the transformer carries high current and
routed through a plurality of raisers for termination to several epoxy
bushings, the magnetic field of this high current generating high
temperature on the LV-side magnetic wall of the tank, the auxiliary
cooling system comprising a plurality of external coolers; an oil pipe
circuit branched out of the main cooling pipe of the transformer; and
a plurality of box-type stiffeners provided along the length of the
tank wall, the auxiliary cooler is simultaneously used permanently to
dissipate the loss generated inside the transformer during it's
working.

2. The system as claimed in claim 1, wherein temperature of the tank
wall is reduced by flow of cooled oil inside box stiffeners by
extending the use of the transformer cooler without providing any
additional cooling unit/system .

ABSTRACT

The invention relates to an auxiliary cooling system to limit the temperature
magnetic wall of a high power rectifier transformer below safe working
temperature limit, the transformer comprising at least a core having high voltage
(HV) windings, and low-voltage (LV) windings housed in a tank made of
magnetic steel, the tank being maintained full of oil to keep the windings and the
other associated accessories of the transformer completely immersed in the oil
the terminals of the LV and HV windings are taken out from the tank for
connection to the external circuits, the LV-side of the transformer carries high
current and routed through a plurality of raisers for termination to several epoxy
bushings, the magnetic field of this high current generating high temperature on
the LV-side magnetic wall of the tank, the auxiliary cooling system comprising a
plurality of external coolers; an oil pipe circuit branched out of the main cooling
pipe of the transformer; and a plurality of box-type stiffeners provided along the
length of the tank wall.