FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Composites with increased PD resistivity and a method of preparation therefore.
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, WorJi, Mumbai 400 030, Maharashtra, India, an Indian Company

INVENTOR
D'melo Dawid, Chaudhari Lokesh Kisan, Jaiswal Rajendra, Sharma Ramavatar; al! of Crompton Greaves Ltd, AMPTC, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India; all Indian Nationals.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of the Invention:
This invention relates to the field of composites for MVITs.
Particularly, this invention to composites with increased PD resistivity and a method of preparation therefor.
Background of the Invention:
Electrical treeing is a phenomenon, due to which electrical breakdown may occur in an electrical or electronic item. An insulator is subject to electrical treeing depending upon the material used to build the insulator and the quantum of electrical stresses to which it is applied.
This pre-breakdown phenomenon of electrical treeing is caused due to partial discharge in the material. It progresses due to stressed dielectric insulation and spreads through the entire mechanism material. The ultimate result of electrical treeing is the formation of a conductive path through the electrical insulator resulting in the catastrophic electrical failure of the insulation.
In order to avoid the phenomenon of treeing, a better material is needed which is more resistant to the negative effects of partial discharge, thereby providing better life to an insulator.
Till date the information and patents dealing with the increase in the PD resistivity of composites use an epoxy resin matrix.

Epoxies used in these applications are, in general, hot cured i.e. they need to be heated in order to cause the cure followed by a post-curing process. There is a need to save this energy spent in curing.
Objects of the Invention:
An object of the invention is to provide an insulation material with increased PD resistivity.
Summary of the Invention:
According to this invention, there is provided a method of preparation of a composite formulation with increased PD resistivity, said method comprises the steps of:
- selecting nano-particles and unsaturated polyester diluted with reactive diluents in pre-defined amounts;
- dispersing said selected nano-particles in said unsaturated polyester matrix using a combination of mechanical agitation and ultrasonication, thereby discharging resin;
- mixing micro-fillers and colouring agent in pre-defined concentrations using a mechanical agitation system; and
- mixing a curing agent of pre-defined quantity to obtain a formulation.
According to an embodiment of this invention, there is provided a method of preparing a product from said composite formulation as claimed in claim 1 wherein, said method comprises the steps of:
- casting said formulation in the mold encapsulating the assembled electrical
apparatus;

- curing at ambient temperatures after which they are de-moulded;
- stabilizing at ambient temperature and pressure; and
- post-curing at pre-defined temperature and duration
Typically, said step of selecting nano-particles includes the step of selecting 0.1 to lOphr by weight of said nano-particles.
Typically, said includes the step of placing said selected nano-particles and said selected unsaturated polyester in the ultrasonicator fitted with a mechanical agitator,
Typically, said agitation is at 500 to 1000 RPM.
Typically, said ultrasonicator frequency ranges from 15 to 45kHz.
Typically, said ultrasonication coupled with mechanical agitation is carried out for 3 to 12 hours depending on the nature of the particle and concentration.
Preferably, said nano-particles used in the composition are selected from a group consisting of silica, alumina, montmorillonite, talc, silicon carbide, magnesium oxide, calcium carbonate, magnesium carbonate, magnesium oxide.
Preferably, said resin used is a standard unsaturated polyester resin based on diacids and diols such as maleic anhydride, phthalic anhydride, propylene glycol, ethylene glycol.

Preferably, said diluents are selected from a group of diluting agents consisting of styrene, butyl aery late, and ethyl aery late.
Preferably, said fillers are a mixture of silica, titanium dioxide, aluminium trihydroxide, alumina, calcium carbonate.
Preferably, said accelerators are cobalt based organometallic compounds.
Typically, said step of mixing is carried out for 0.5 to 1.0 hours.
Typically, said step of mixing of the curing agent with the composition is carried out at 30-35°C.
Typically, said step of mixing of the curing agent with the composition is carried out at a pressure of 250 to 300mbar.
Typically, said step of casting is carried out at reduced pressures, ranging from about 125 - 150mbar.
Typically, said step of curing is carried for 3-5 hours.
Typically, said step of stabilizing is carried for 24 hours.
Typically, said step of post-curing is carried at 80°C.
Typically, said step of post-curing is carried for 4 hours.

According to this invention, there is provided a composite formulation, with increased PD resistivity, comprising:
- 100 parts by weight of unsaturated polyester resins having solid content 30 to 50%;
- 0.1 to 2.0 parts by weight of nano-particle;
- 0 to 90 parts by weight thermally pretreated filler and coloring agent;
- 0.5 to 3.0 parts coupling agent;
- 0.5 to 2 parts by weight initiator; and
- 0.1 to 0.7 parts by weight accelerator.
Detailed Description of the Invention:
According to this invention, there is provided a composite with increased PD resistivity and a method of preparation therefor.
The proposed composition is a mixture of micro and nano-materials with a high micro-filler level. The use of large amounts of micro-filler leads to a cost advantage as they are more economical as compared to the resin. On the other hand the use of high micro-filler contents leads to a high viscosity of the mix; this results in difficulties in handling as well as dispersion of the nano-filler in the resin matrix, to result in the properties which are desired.
In accordance with an embodiment of this invention, there is provided a first step selecting nano-particles and unsaturated polyester in pre-defined amounts.

Preferably, the amounts range from about 0.1 to lOphr. They are then placed in the ultrasonicator fitted with a mechanical agitator.
In accordance with an embodiment of this invention, there is provided a second step of dispersing the nano-particles in the unsaturated polyester matrix using a combination of mechanical agitation and ultrasoni cation. Typically, the RPM of the agitation is maintained between about 500 to 1000 and the ultrasonicator used has a frequency ranging from about 15 to 45kHz.
Typically, the duration of the ultrasoni cation coupled with mechanical agitation that is carried out is about 3 to 12 hours depending on the nature of the particle and concentration. After which the resin is discharged.
Preferably, the nano-particles used in the composition could be chosen from a group consisting of silica, alumina,montmorillonite, talc, silicon carbide, magnesium oxide, calcium carbonate, magnesium carbonate, and the like.
Preferably, the resin used is a standard unsaturated polyester resin which is based on diacids and diols such as maleic anhydride, phthalic anhydride, propylene glycol, ethylene glycol, and the like.
If a highly concentrated solution i.e. master batch e.g. 10 phr, is prepared then the required amount is taken with some pure unsaturated polyester resin and re-dispersed at the same frequency for 0.5 to 2 hours.

In accordance with another embodiment of this invention, there is provided a third step of diluting the unsaturated polyester with a reactive diluents. Preferably, the diluents is styrene or any other suitable diluting agent such as butyl aery late, ethyl acrylate, and the like.
In accordance with another embodiment of this invention, there is provided a fourth step of using mixing micro-fillers and colouring agent in pre-defined concentrations using a mechanical agitation system.The fillers used would be a mixture of silica, titanium dioxide, aluminium trihydroxide, alumina, calcium carbonate, and the like.
The accelerators used in the composition are cobalt based organometaJlic compounds such as cobalt naphthanate, cobalt octate, and the like. Preferably, this mixing is carried out for 0.5 to 1.0 hours.
In accordance with another embodiment of this invention, there is provided a fifth step of mixing a curing agent of pre-defined quantity to obtain a formulation Preferably, the mixing of the curing agent with the composition is carried out at 30-35°C and at a pressure of 250 to 300mbar.
In accordance with another embodiment of this invention, there is provided a sixth step of casting the formulation in the mold encapsulating the assembled electrical apparatus.
Preferably, the casting is carried out at reduced pressures, ranging from about 125 - 150mbar. Once the casting is carried out the products are allowed to cure at

ambient temperatures for about 3-5 hours after which they are de-moulded. The products are then allowed to stabilize for about 24 hours at ambient temperatures and pressure followed by post-curing at about 80°C for about 4 hours.
In the present invention, a room temperature cured unsaturated polyester system is used. This results in an energy saving as well as a process which is not as demanding. The post-curing step in the case of the unsaturated polyester is carried out at 80°C.
The use of an unsaturated polyester as compared to an epoxy resin results in a different polymer-filler interaction. This leads to a difference in the compatibility and the dispersion levels of the nano-particles or fillers in the polymer matrix, thus affecting the level of performance of the resultant composites. For example, it has been reported that the increase in the nano-particle concentration to the polymer matrix would result in an increase in the PD resisitivity of the sample, however, in the case of unsaturated polyester samples it was seen that an optimum value was below 2.0 phr of nano-particle with reference to the polymer.
The general formulation of the composition would be:
100 parts by weight of unsaturated polyester resins having solid content 30 to 50%;
0.1 to 2.0 parts by weight of nano-particle,
0 to 90 parts by weight thermally pretreated filler and coloring agent;
0.5 to 3.0 parts coupling agent
0.5 to 2 parts by weight initiator and
0.1 to 0.7 parts by weight accelerator;

We claim,
1. A method of preparation of a composite formulation with increased PD resistivity, said method comprising the steps of:
- selecting nano-particles and unsaturated polyester diluted with reactive diluents in pre-defined amounts;
- dispersing said selected nano-particles in said unsaturated polyester matrix using a combination of mechanical agitation and ultrasonication, thereby discharging resin;
- mixing micro-fillers and colouring agent in pre-defined concentrations using a mechanical agitation system; and
- mixing a curing agent of pre-defined quantity to obtain a formulation.
2. A method of preparing a product from said composite formulation as claimed in
claim 1 wherein, said method comprising the steps of:
- casting said formulation in the mold encapsulating the assembled electrical apparatus;
- curing at ambient temperatures after which they are de-mouided;
- stabilizing at ambient temperature and pressure; and
- post-curing at pre-defined temperature and duration.
3. A method as claimed in claim 1 wherein, said step of selecting nano-particles
includes the step of selecting 0.1 to lOphr by weight of said nano-particles.
4. A method as claimed in claim 1 wherein, said includes the step of placing said selected nano-particles and said selected unsaturated polyester in the ultrasonicator fitted with a mechanical agitator.
5. A method as claimed in claim 1 wherein, said agitation is at 500 to 1000 RPM.
6. A method as claimed in claim 1 wherein, said ultrasonicator frequency ranges from 15 to 45kHz.
7. A method as claimed in claim 1 wherein, said ultrasonication coupled with mechanical agitation is carried out for 3 to 12 hours depending on the nature of the particle and concentration.
8. A method as claimed in claim 1 wherein, said nano-particles used in the composition are selected from a group consisting of silica, alumina, montmorillonite, talc, silicon carbide, magnesium oxide, calcium carbonate. magnesium carbonate, magnesium oxide.
9. A method as claimed in claim 1 wherein, said resin used is a standard unsaturated polyester resin based on diacids and diols such as maleic anhydride, phthalic anhydride, propylene glycol, ethylene glycol.
10. A method as claimed in claim 1 wherein, said diluents are selected from a group of diluting agents consisting of styrene, butyl acrylate, and ethyl acrylate.

11. A method as claimed in claim 1 wherein, said fillers are a mixture of silica, titanium dioxide, aluminium trihydroxide, alumina, calcium carbonate.
12.A method as claimed in claim 1 wherein, said accelerators are cobalt based organometallic compounds.
13.A method as claimed in claim 1 wherein, said step of mixing is carried out for 0.5 to 1.0 hours.
14. A method as claimed in claim 1 wherein, said step of mixing of the curing agent with the composition is carried out at 30-35°C.
15. A method as claimed in claim 1 wherein, said step of mixing of the curing agent with the composition is carried out at a pressure of 250 to 300mbar.
16. A method as claimed in claim 1 wherein, said step of casting is carried out at reduced pressures, ranging from about 125 - 150mbar.
17.A method as claimed in claim 1 wherein, said step of curing is carried for 3-5 hours,
18. A method as claimed in claim 1 wherein, said step of stabilizing is carried for 24 hours.
19. A method as claimed in claim 1 wherein, said step of post-curing is carried at 80°C.

20. A method as claimed in claim 1 wherein, said step of post-curing is carried for 4 hours.
21 .A composite, with increased PD resistivity, comprising:
- 100 parts by weight of unsaturated polyester resins having solid content 30 to 50%;
- 0.1 to 2.0 parts by weight of nano-particle;
- 0 to 90 parts by weight thermally pretreated filler and coloring agent;
- 0.5 to 3.0 parts coupling agent;
- 0.5 to 2 parts by weight initiator; and
- 0.1 to 0.7 parts by weight accelerator.