The present invention relates to a process for manufacturing high voltage terminal insulator for A.C. motors. More particularly, the invention relates to insulators for motors used in highly inflammable environments viz. petrochemical plants, oil refineries gas pipe lines,etc. These terminal insulators should be flame proof, explosion proof and able to withstand high fault currents.
Background of the Inventions
Existing terminal insulators for AC motors are basically inorganic based ceramic insulators. The electrical rating of these insulators is limited to only 6.6 kV, 300 MVA fault level currents. These insulators are fragile in nature and need careful handling. Their mechanical strength is weak and while assembling on the AC motors, chances of breakage are more. Process cycle for making these insulators takes long duration because it involves various steps like moulding, firing at temperatures of about 850 degree centigrade, pre stage machining, sintering and final machining to the required dimensions. Dimensional
tolerance is poor and there is high shrinkage while
manufacturing. Density of ceramic insulator is.3.69 gm/cm3.
Some of the important properties of ceramic insulators are given below.
Rating 6.6 kV,300 MVA fault level
Nominal insulation level 7 kV
Proof voltage 13 kV
Impulse .voltage 60 kV
Partial discharge inception
& extinction voltages 4.2 kV
Short time current rating 26 k A, 0.25 sec
Continuous current rating 240 Amp
Max temperature rise 100 degree C
Type of protection Flame proof and Explosion proof
Summary of the Inventions
The main object of the present invention is to overcome the drawbacks in the conventional ceramic insulators like poor impact strength, poor dimensional tolerance and higher cost of manufacture. This object is achieved by making the insulators for AC motors from essentially organic and inorganic based materials. Brominated epoxy resin, an organic material is used with inorganic fillers like Aluminium trihydrate and Silica.
The present invention thus provides a process for manufacturing high voltage terminal insulators for AC motor*, comprising the steps of mixing brominated epoxy resins with inorganic fillers in a first chamber; keeping a hardner material
in second chamber maintaining said first and said second chamber
under vacuum at a temperature of about 650C blending the filler
mixed brominated epoxy resins with said hardner for making a homogenous material; providing a sleeve in the center of a mould, and a ring for fixing the insulator to the motor terminal box; moulding said homogeneous material in the mould into an insulator
of required dimensions; curing the mould with the material under
pressure at a temperature of about 1400C; keeping the cured
insulator in an air circulating oven at a temperature of about
1300C for further curing and cohesive bonding of resin and the
hardner, and inserting a copper rod through the insulator for
providing electrical connection between the motor and the power
supply.
Brief Description of the Drawings
The present invention will now be described with help of the accompanying drawings wherein
Fig. 1 shows geometry and shape of the insulator;
Fig. 2 shows the sleeve of the terminal insulator;
Fig. 3 shows the mild steel ring of the terminal insulator;
Figs. 4(a), 4(b) show the copper rod used with the terminal insulator;
Fig. 5 shows the epoxy body of the insulator in cross section.
Detailed Description of the Inventions
Brominated epoxy resin in thoroughly mixed with filler*,like aluminium trihydrate and silica powder for about 8 hours in a chamber which is maintained under vacuum of 5 tor and at a temperature of about 65 degrees C. The vacuum maintained is of 5 tor. A hardner is also kept in another chamber maintained under the same conditions. This operation of maintaining the vacuum and temperature in both the chambers for about 8 hours is necessary to remove any dissolved gases present in the materials. After this operation, the filler mixed resin and the hardner are blended to get a homogeneous material.
The hardner used is carboxylic acid anhydride. For 100 parts by weight of brominated epoxy resin, 135 parts each of fillers aluminium trihydrate and silica powder are added and 65 parts by weight of carboxylic acid anhydride is used. For moulding of this material into an insulator of the present invention a mould is fabricated from MS material to the required dimensions of the insulator shown in Fig. 1.
As shown in Fig. 2, a sleeve 2 comprising a brass tube 21 and glass fabric 22 is arranged at the center of the mould. These are placed in position to achieve the required reinforcement and the mechanical strength.
A steel ring cm •how in Fig. 3 in also provided • an interface between the terminal box of the motor and the insulator a« shown in Fig. 1, so that the insulator gets tightly fixed with the terminal box of the motor.
The homogenous material which will be in semi-solid state, is pumped into the mould under pressure of 3 atm. The temperature of the mould is constantly maintained at about 1400C and pressure of 3 atm. Under these conditions of temperature and pressure, the material is kept in the mould for 4 hours for curing.
The cured insulator is then removed from the mould and kept in an air circulating oven at a temperature of 130 degrees C for 8 hours. This operation of further curing is necessary to help in a cohesive bonding of the resin and the hardner.
A copper rod 3, as shown Fig. 4, which is not an integral part of the epoxy body insulator 5 is inserted through the insulator to serve as an electrical connection between the motor and the power supply. The said copper rod has fasteners to connect for the power supply at one end and provision for
connecting cables from motor at the other end. Since the copper
rod 3 is not an integral part of the insulator, this arrangement
facilitates easy assembly, maintenance and replacement.
Crocs section of this new product i.e. the epoxy body terminal insulator for high voltage AC motors is shown in Fig. 9.
The process of manufacturing terminal insulators described hereinabove using the described composition of materials results in a new insulator capable of meeting the requirements of higher rating AC motors. The new terminal insulator of the present invention is flameproof and explosion proof. Apart from the improved electrical properties, another added feature of this new
insulator is that, it has a less weight to volume ratio. Density
of epoxy terminal insulator is 2.0 gm/cm . Laboratory tests
carried out show that the terminal insulator of the present invention has the following properties.

Rating
Nominal insulation level Proof voltage impulse voltage Partial discharge inception
& extinction voltages insulation resistance Short time current rating Continuous current rating Max temperature rise

11 kV,S00 MVA fault level
12 kV
28 kV
75 kV
7 kV
10,000 Mega Ohms
44 k A,0.25 sec
400 Amps
100 degrees C

Type of protection Flame proof and Explosion
proof
Size 110 mm dim X 256 mm
Weight 4 kg
The invention may be embodied in other specific form without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

WE CLAIM:
1. A process for manufacturing high voltage terminal insulators for AC motors, comprising the steps of:
(a) mixing brominated epoxy resins with inorganic fillers in a first chamber;
(b) keeping a hardner material in a second chamber;
(c) maintainig said first and said second chamber under
vacuum at a temperature of about 650C;
(d) blending the filler mixed brominated epoxy resins
with said hardner for making a homogeneous material;
(e) providing a sleeve in the center of a mould, and a
ring for fixing the insulator to the motor terminal box;
(f) moulding said homogeneous material in the mould into an
insulator of required dimensions;
(g) curing the mould with the material under pressure at a
temperature of about 1400C; and
(h) keeping the cured insulator in an air circulating oven
at a temperature of about 1300C for further curing and cohesive
bonding of resin and the hardner.
2. The process as claimed in claim 1, wherein said fillers are aluminium trihydrate and silica powder.
3. The process as claimed in claims 1 and 2, wherein the vacuum maintained in the chambers is of 5 torr.
4- The process as claimed in the preceding claims, wherein said hardner is carboxylic acid anhydride.
5. The process as claimed in the preceding claims wherein
for 100 parts by weight of brominated epoxy resin, 135 part each
of aluminium trihydrate and silica powder, and 65 parts by weight
of carboxylic acid anhydride are used.
6. The process as claimed in the preceding claims, wherein
said mould is fabricated from MS material to the required
dimensions.
7. The process as claimed in claim 1 wherein said homogenous
material of filler mixed brominated epoxy resins blended with
said hardner is pumped into the mould under pressure of about 3
atmosphere.
8. The process as claimed in the preceding claims, wherein
said sleeve provided in the center of the mould comprises a brass
tube and a glass fabric for giving required reinforcement and
mechanical strength to the insulator.
9. The process as claimed in the preceding claims, wherein a
copper rod is inserted through the insulator for providing
electrical connection between the motor and the power supply.
10. The process as claimed in claim 9, wherein said copper rod
inserted through the brass tube of the sleeve of the insulator is
provided with fasteners for connecting the power supply at one end and the motor terminal at the other end.
11. A process for manufacturing high voltage terminal insulators for AC motors, substantially as herein described and illustrated in the accompanying drawings.