FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2OO3
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A controller based apparatus for drying, based on microwave energy.
APPPLICANTS
Crompton Greaves Limited, CG House, 6th House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company.
INVENTOR
Nemade Janamejay Bhalchandra of Crompton Greaves Limited, Advanced Materials and Process Technology Centre, CG Global R&D Centre, Kanjur Marg (E), Mumbai, Maharashtra, India, and Chaudhari Sushil Ekanath of Crompton Greaves Ltd., Conition Monitoring & Diagnostic Centre, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India. ; both Indian National.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention :

FIELD OF THE INVENTION:
This invention relates to assemblies for drying.
Particularly, this invention relates to a controller based assembly for drying.
Still particularly, this invention relates to an intelligent controller based assembly for drying, based on microwave energy.
BACKGROUND OF THE INVENTION:
In high voltage equipment, condenser bushings are employed, the condensor bushings have a condenser core wound around a centre core. This condenser core is formed by alternate windings of an insulating layer (insulating paper) and a metal or an electrically conducting foil. The high voltage equipment may be switchgear equipment, or transformers or the like.
This insulated paper may further be impregnated with oil to improve its dielectric properties. In the method of winding, water is used to form a tight-fit of the insulating paper over the core. However, the induced water is a cause of concern as it reduces the insulation property. There is a need for drying the insulating paper before use, said heat and heating process be adequately defined to remove the water and moisture content, without any lapse.
Vacuum based heating is known in the art, where heating and continuous exposure to heat, by radiation, convection are used. However, none of the prior art methods provide an efficient process or assembly, said efficiency being in terms of the time involved and the power consumed. Another ill-

effect of using the systems of the prior art is that the uniformity of heat and moisture irradiation is never achieved. Layers of insulating paper, in the inner circumferences of the roll, are prone to retain moisture, even if the external circumferences are readily dried according to industry standards. Notwithstanding the amount of energy that is consumed, it has been observed that, merely increasing the time duration of drying or merely increasing the intensity of heat, does not render the insulating paper of the condenser bushings perfectly dry.
OBJECTS OF THE INVENTION:
An object of the invention is to provide an optimised drying process and assembly for drying insulating paper of condenser bushings.
Another object of the invention is to provide a uniform drying process.
Yet another object of the invention is to provide an improved drying process in relation to time involved and power consumed.
Still another object of the invention is to provide a better dried insulating paper of condenser bushing.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a controller based apparatus for drying condensor bushings containing moist insulating paper, based on microwave energy, said apparatus comprises:

a. chamber means adapted to hold said at least a single condenser
bushings with insulated paper, in its wound configuration;
b. vacuum enabling means adapted to create a vacuum in said chamber;
c. microwave radiating means adapted to expose said bushings, and
hence, said insulating paper, loaded in said chamber, with microwave
radiation;
d. turntable adapted to host the condenser bushings within said chamber;
e. rotary mechanism adapted to rotate said turntable, alternatively, in a
positive 180 degree cycle followed by a negative 180 degree cycle
with reference to a centre-point in order to appropriately dry said
insulating paper in the microwave environment;
f. first controller means adapted to provide temperature control inside
said microwave chamber; and
g. second controller means adapted to provide power control inside said
microwave chamber.
Typically, said chamber means is a microwave transparent material based chamber means.
Preferably, said chamber means is made of borosilicate glass, microwaveable glass or the like.
Typically, said first controller means is a time-based temperature controller adapted to define durations of times, in which the microwave radiating means is to be enabled or to be cut-off.

Typically, said first controller means includes temperature sensing means adapted to sense temperature in said chamber.
Typically, said first controller means includes temperature threshold defining means adapted to define temperature thresholds in order to control temperature in said chamber.
Typically, said second controller means includes power burst means adapted to defines bursts of power supply in relation to defined time periods in order to operate said microwave radiating means.
Typically, said second controller means includes temperature sensing means adapted to sense temperature in said chamber.
Typically, said second controller means includes temperature threshold defining means adapted to define power thresholds in order to control power to said microwave radiating means.
Typically, said apparatus includes synchronization means adapted to synchronise said first controller means and said second controller means.
Typically, said apparatus included an oil impregnation means adapted to impregnate said insulating paper with oil
Typically, said apparatus includes moisture traps in series between said chamber and said vacuum pump for trapping moisture.

BRIEF DESCRIPTON OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates a schematic of the apparatus;
Figure 2 illustrates a graphical curve of moisture removal versus microwave radiation time.
DETAILED DESCRIPTON OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a controller based apparatus for drying, based on microwave energy. Typically, said apparatus is adapted to dry insulating paper of condenser bushings.
Figure 1 illustrates a schematic of the apparatus;
In accordance with an embodiment of this invention, there is provided a chamber (10) means to hold said condenser bushings with insulated paper, in its wound configuration. Preferably, a plurality of such bushings is adapted to be fitted into said chamber.

Typically, said chamber means is a microwave transparent glass chamber. Preferably, it is borosilicate glass.
In accordance with another embodiment of this invention, there is provided a vacuum enabling means (12) adapted to create a vacuum in said chamber.
In accordance with another embodiment of this invention, there is provided a microwave radiating means (24) adapted to expose said bushings, and hence, said insulating paper, loaded in said chamber, with microwave radiation. This heating effect caused due to the microwave radiation provides an improved moisture removal quotient.
In accordance with yet another embodiment of this invention there is provided a turntable (16) adapted to host the condenser bushings within said chamber. In a conventional art which relates to microwave ovens, the turntable rotates in any direction to complete a full 360 degree circle. However, according to this invention, the turntable and its associated rotary mechanism (18) are characterised to rotate in a positive 180 degree cycle followed by a negative 180 degree cycle from the centre-point. This alternating partial rotation is adapted to appropriately dry the insulating paper in the microwave environment.
In accordance with still another embodiment of this invention, there is provided a first controller means (20) adapted to provide temperature control inside said microwave chamber. This time based temperature controller defines durations of times, in which the microwave radiation means is to be

enabled or to be cut-off. Pre-defined threshold heat measurements are used to sense and work the temperature controller means.
In accordance with an additional embodiment of this invention, there is provided a second controller means (22) adapted to provide power control inside said microwave chamber. This power controller means defines bursts of power supply in relation to defined time periods in order to operate said radiation means. The heating provided by virtue of microwave radiation will directly be proportional to the power provided by said power controller means. Pre-defined threshold power measurements are used to sense and work the power controller means.
Preferably, said first controller means and said second controller means cumulatively form a dual-mode controller means (20, 22).
The time controller means and power controller means, working synchronously, provides an optimised heating process, and thus a drying process, to relegate the need to continuously work a heating means. This leads to savings in power, cost, and time. The power and time characteristics may be pre-fed or may be intelligently computed based on sensors located for providing feedback and also on the load inside said chamber.
According to an exemplary embodiment of the working of this invention, it has been observed that initial moisture content of 7% was brought down to 0.5% using the method and assembly of this invention.

In accordance with yet an additional embodiment of this invention, there is provided an oil impregnation means adapted to impregnate said insulating paper with oil.
The invention will now be explained with respect to a non-limiting exemplary embodiment.
The glass chamber was made of Borosilicate glasses which are known to be microwave transparent. The Internal Diameter of the chamber was 120mm. It had two ports at the top. One was for connection to the vacuum pump and the other for oil impregnation.
The requirement was that a vacuum hose be connected to the sample (apparatus) at all times. This made it impossible to rotate the turntable continuously. Hence, the bottom motor of a kitchen microwave was replaced with a stepper motor and driver. This facilitated the elimination of twisting of the silicon pipe by limiting the rotation of the turntable in plus and minus 180° from the mean position. An electronic circuit, stepper motor with limit-switches mounted on it and mount on the microwave oven from the bottom was fabricated for the purpose.
The moisture sucked out of the glass chamber could have been dragged in the vacuum pump. Hence, two moisture traps were put in series between the glass chamber and the vacuum pump. Both traps were re-circulated with water at 4°C. Initially a third liquid nitrogen trap was used in order to confirm whether moisture was still remaining after the second trap. No

traces of any condensation proved that two traps were sufficient. The liquid nitrogen trap was hence not used further.
A rotary vacuum pump (Hindhivac, model No. ED 12) was used to create necessary vacuum. Vacuum levels were measured using a Bourdon tube gauge.
For all the experiments, around 15cm long sub-sized bushing samples were used. The winding pattern was exact same as 52kV condenser bushing and it included the aluminum foils at the same locations. Its thickness matched the thickness of the actual condenser bushing.
The experiments were conducted in 4 stages:
1. Pre-experimental trials;
2. Establishing cycle for microwave drying;
3. Microwave drying; and
4. Microwave drying followed by oil impregnation.
1. Pre-experimental trials:
The objective of these trials were to confirm that the sub-sized condenser bushing gets heated to the required temperature range of 110-120°C and that water from the same is removed. Various power settings were tried for various durations with vacuum on. Water was successfully collected in the moisture traps. The weight loss of the sample indicated that moisture was getting removed.
2. Establishing cycle for microwave drying

The objective of this stage was to determine the microwave power -radiation time cycle such that the samples are heated between 110 and 120°C and is maintained in that range. This temperature range is the same as that used for production cycles of drying.
A sub-sized condenser bushing was specially wound with 6 K-type thermocouples placed at various locations (across thickness and length). An additional thermocouple was stuck to the inside aluminum core to measure the inside temperature. This specially made sample was placed in the glass sample holder and thermocouple wires were removed through the hole provide for oil impregnation. The port was sealed and the thermocouples were then taken out from the microwave oven through the extra hole made and then connected to a temperature data logger.
It was observed that microwaves generated sparks at the thermocouple wires when there was vacuum applied to the glass sample holder. The experiment was thus conducted without vacuum application.
The following was the outcome of the experiment:
1. Heating cycle: At microwave power of 180W and radiation time of 30 minutes the temperature reaches gradually to 120°C.
2. Soaking cycle: Microwave power of 100W was required to maintain the temperature between 110 and 120°C.
This cycle was thus set and was practiced for rest of the further experiments.
3. Microwave drying:
Various experiments were conducted to prove that moisture was removed and the final moisture level in the sample. First approach was to measure the

condensed water in the moisture traps, however, it was proved to be prone to inaccuracies. The second approach of the weight loss (initial weight minus weight after radiation) of the samples was thus followed. During the Soaking Cycle, radiation was stopped every 30 minutes and weight was recorded. Table 1 illustrates was the outcome of the various stages of experiments.
Table 1

1 lime, minutes
0 Weight measured, gm
2088.3 Weight loss, gm
0.0
1 30 2060.0 28.3
-1
3 60 2055.0 5.0
4 90 2052.8 2.2
5 120 2051.3 1.5
6 150 2050.5 0.8
7 180 2050.0 0.5
Total 38.3
Figure 2 illustrates a graphical curve of moisture removal versus microwave radiation time.
The following is revealed by the curve of Figure 2:
1. Major amount moisture removal was taking place in first 90 minutes; and
2. The moisture removal decreased exponentially with time.

It may be noted that in these experiments the moisture was removed using a rotary pump (against a diffusion pump in production units). There is difference in the level of vacuum achieved by a rotary pump (10-2 mbar) and a diffusion pump (10-5 mbar).
Table 2 illustrates calculations.
Table 2

Weight of sample, gm 802.3
Weight of Al rod (approx), gm 250
Weight of paper, gm 552. 3
Weight loss after radiation, gm 38.3
Moisture removal, % 6.93
. _
Stage 4. Microwave drying followed by oil impregnation
The same procedure in stage 3 above was followed. Oil was impregnated
after the drying in hot condition. Oil flow was controlled manually so that

the oil level increased by approximately 25mm per hour. The sample was allowed to soak overnight after complete immersion.
Tan-S measurements were carried out on the sample (inside oil) (Equipment make: Doble Engineering Company). The value was found to be 0.47%
It was hence, inferred that:
A sub-sized (15cm long) and actual diameter (around 9.2cm) condenser
busings were dried using a modified microwave oven. Total heating time of
30 minutes and soaking time of 150 minutes were practiced under vacuum
generated by a rotary pump. Oil was impregnated in the dried sample.
Weight loss due to moisture removal of 38.2 gm in 802.3 gm was recorded,
which corresponds to 6.93%.
After oil impregnation the Tan-5 of the sample was found to be 0.47%
This proves that it is feasible to dry a condenser bushing using microwave
radiation instead of conventional thermal energy.

We claim,
1. A controller based apparatus for drying condensor bushings containing moist insulating paper, based on microwave energy, said apparatus comprising:
a. chamber means adapted to hold said at least a single condenser
bushings with insulated paper, in its wound configuration;
b. vacuum enabling means adapted to create a vacuum in said chamber;
c. microwave radiating means adapted to expose said bushings, and
hence, said insulating paper, loaded in said chamber, with microwave
radiation;
d. turntable adapted to host the condenser bushings within said chamber;
e. rotary mechanism adapted to rotate said turntable, alternatively, in a
positive 180 degree cycle followed by a negative 180 degree cycle
with reference to a centre-point in order to appropriately dry said
insulating paper in the microwave environment;
f. first controller means adapted to provide temperature control inside
said microwave chamber; and
g. second controller means adapted to provide power control inside said
microwave chamber.
2. An apparatus as claimed in claim 1 wherein, said chamber means is a microwave transparent material based chamber means.
3. An apparatus as claimed in claim 1 wherein, said chamber means is a glass chamber means.

. An apparatus as claimed in claim 1 wherein, said chamber means is a borosilicate glass chamber means.
. An apparatus as claimed in claim 1 wherein, said first controller means is a time-based temperature controller adapted to define durations of times, in which the microwave radiating means is to be enabled or to be cut-off.
. An apparatus as claimed in claim 1 wherein, said first controller means includes temperature sensing means adapted to sense temperature in said chamber.
An apparatus as claimed in claim 1 wherein, said first controller means includes temperature threshold defining means adapted to define temperature thresholds in order to control temperature in said chamber.
An apparatus as claimed in claim 1 wherein, said second controller means includes power burst means adapted to defines bursts of power supply in relation to defined time periods in order to operate said microwave radiating means.
An apparatus as claimed in claim 1 wherein, said second controller means includes temperature sensing means adapted to sense temperature in said chamber.

10.An apparatus as claimed in claim 1 wherein, said second controller means includes temperature threshold defining means adapted to define power thresholds in order to control power to said microwave radiating means.
11.An apparatus as claimed in claim 1 wherein, said apparatus includes synchronization means adapted to synchronise said first controller means and said second controller means.
12.An apparatus as claimed in claim 1 wherein, said apparatus includes an oil impregnation means adapted to impregnate said insulating paper with oil.
13.An apparatus as claimed in claim 1 wherein, said apparatus includes moisture traps in series between said chamber and said vacuum pump for trapping moisture.