FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
PROVISIONAL SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
Compact Transmission Tower for Electric Power System
APPLICANTS
Name: CROMPTON GREAVES LIMITED
Nationality: Indian Company
Address: CG House, Dr Annie Besant Road, Prabhadevi,
Mumbai 400030, Maharashtra, India
INVENTOR
Name: Raghavan Venkatesh
Nationality: Indian National
Address: Crompton Greaves Ltd, Switchgear-6 & Power Quality Business Unit, D2, MIDC, Waluj, Aurangabad 431136, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification describes the invention:

FIELD OF INVENTION
This invention relates to a compact transmission tower for electric power systems. This invention is also related to electric power systems for voltages above 66 kV with compact transmission towers.
BACKGROUND OF THE INVENTION
With increasing electrification and increasing voltage levels used for electric power transmission it has become a necessity to compact the transmission towers as to reduce the right of way and increase the power density.
Most transmission towers are manufactured with lattice structures made of treated steel members designed as main load bearing structure and to provide adequate clearances amongst phase conductors of as multiphase power system and between the phase conductors and earth. The high voltage phase conductors are strung on outdoor insulators, which are made of a series of disc insulators. The disc insulators are made of ceramic or glass. The suspension insulators made with a string of disc insulators is supported on the metallic structure and supports the phase conductors. The typical construction of a conventional transmission tower of this type is shown in figure 1. These towers are large in size and are very heavy. These towers also are very tall as to accommodate the minimum ground clearances required.
In one type of compact transmission tower, the string insulators made of ceramic /glass disc insulators are replaced with polymeric composite long rod suspension insulators.
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Typical construction is as shown in figure 2. These types of towers are smaller than towers made with conventional disc insulators, but are more expensive due to the high cost of polymeric composite insulators. These towers though are shorter than conventional towers, due to shorter suspension insulators, still are tall as the ground clearances required are fairly large considering the length of the suspension insulator.
In another type of compact transmission tower, the tower is constructed from insulated pultruded composites, enabling closer spacing of conductors and creation of a smaller tower structure and weighing less than the weight of a steel structure with same power transmitting capabilities (US patent 5,247,774 and 5,749,198). One variation of the design the suspension insulators are eliminated by providing silicone rubber sheds to extended rods, which are integral part of the main structure. Though the towers are compact, these are very expensive as a large number of tower support members are constructed with insulated pultruded members. The second variant where the suspension insulators are replaced by silicone sheath insulated pultruded extended support arm is more expensive due to the silicone sheaths.
An object of the invention is to provide a compact transmission tower for electric power system with reduced tower height and compact right of way.
Another object of the invention is to provide a compact transmission tower where energy is transmitted more effectively due to lower inductive reactance of the phase conductors.
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Another object of the invention is to provide a compact transmission tower with integral capacitive voltage dividers for voltage measurement.
Another object of the invention is to provide a compact transmission tower with integral transient suppressors made of resistance and capacitances to reduce the switching and lightning over voltages appearing on the transmission lines.
DESCRIPTION OF INVENTION
According to the invention there is provided a compact electric power transmission tower comprising of a lattice steel structure as the main leg member and the extended support arms made out of a special formulation of outdoor polymeric resin. The extended support arms is made by a method of casting of a polymer concrete insulating material under vacuum and vibration to achieve the desired electrical and mechanical properties.
The polymer concrete material is made of a special formulation comprising of a base polymer made of polyester, Acrylic or epoxy resin systems or a combination of such resin systems. Suitable catalysts such as methyl ethyl ketone peroxide or benzoyl peroxide or combinations of such catalysts are used in suitable proportions to create an exothermic reaction to polymerize the unsaturated system, which acts as a binder.
The resin is filled with appropriate filler materials such as graded silica, aluminum tri hydrate, Titanium Dioxide, clay, fly ash, chopped glass strands, glass fiber, Kevlar fibers,
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carbon fibers etc. in selected proportions to achieve the desired electrical, mechanical, thermal, physical and chemical properties.
The composition and the proportion of various materials is so chosen to achieve the desired electrical, mechanical, thermal, chemical and physical properties.
Special additives such as wetting & coupling agents such as Silane, UV stabilizers, plasticizers, accelerators such as cobalt solutions, are added to improve the mechanical and outdoor weathering properties.
Typical composition by weight comprises of resin system in the proportion of 10% to 30%, coupling/wetting agents in the proportion of 0.1% to 2%, Graded silica in the portion of 50% to 80%, alumina trihydrate in the portion of 1% to 30%, Titanium dioxide in he portion of 0.1% to 10%, and reinforcing elements such as glass fibers etc in the proportion of 0.01% to 20%. Additional filler materials such as fly ash, clay etc. are added in proportion of 0.005% to 30% to get the required properties depending upon the application and specific property requirements.
The polymer concrete slurry is cast into desired shapes, which include the required electrical clearances and profiles (sheds) to enhance the outdoor electrical performance.
The casting is done under a vacuum with a pressure level in the range of 5 mm to 740 mm of Hg , in controlled temperature of 10°C to 75°C and the slurry is poured into a
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mound kept in vacuum, with pressure in the range of 5 mm to 740 mm of Hg, and controlled temperature in the range of 10°C to 75°C and is vibrated with an amplitude of 0.01 mm to 5 mm of vertical displacement with a frequency of 0.01 Hz to 400 Hz. The choice of process parameters such as Vacuum (pressure) level, temperature and vibration are controlled to get the desired properties and depends upon the shape and size of castings. The pouring rate of the slurry into the moulds is at a controlled rate of 0.1 kG to 10 kG per minute.
The polymeric reaction is exothermic and the temperature increase due to the exothermic reaction itself is used to complete the polymerization and cure the resin system. The temperature of the exothermic reaction is dependant upon the ambient temperature, resin system, proportion of various elements of the polymer concrete slurry, total mass of casting, material of mould etc. and is controlled to get the desired properties by controlling the proportion of various elements and the ambient temperature as to maintain the temperature in the range of 45°C to 120°C. This temperature range is adequate to completely cure the resin system without any additional heat input and is also low enough to be compatible with all materials used in the system for embedding or casting.
The mould is made of steel, aluminum, FRP or silicone rubber. The mould is preassembled with the metal parts to be cast into the polymer concrete. Suitable mould release agents are applied to the mould to facilitate easy mould release.
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According to an embodiment of the invention, the extended support arms are cast with reinforcing insulating components such as FRP rods, glass fibers, glass fiber woven mats etc. as to increase the mechanical strength of the support member.
According to another embodiment of the invention, the cast support structure in or many of the support arms has embedded capacitor elements as to increase the capacitive reactance of the phase conductors and thus reduce the inductive reactance of the phase conductor.
According to another embodiment of the invention, the integrally cast capacitor elements are configured as capacitive voltage dividers to facilitate measurement of phase to ground voltages.
In prior art, wherein the high voltage phase conductors are supported on a suspension insulator made of string of disc insulators, which is suspended from a steel structure. The steel structure provides the basic mechanical support and is designed to provide adequate electrical clearances between phase conductors and also between phase conductors and ground.
This design has the draw back that the height of the tower has to be high to satisfy the required ground clearances considering the length of the suspension insulator. This also suffers from the poor efficiency of the string insulator due to non-linear voltage distribution across the string of disc insulators. The total height of the string insulator is
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also more due to the metal parts such as pin and cap associated with the ceramic disc insulators. The structure is also very heavy due to the weight of the string insulator and the basic structure itself.
In prior art compact electrical transmission tower using polymer composite suspension insulator. The towers in this case are shorter due to the shorter length of the composite suspension insulators. The towers are also lighter due to the lower weight of the suspension insulator and the basic steel structure being smaller. The disadvantage associated with this type of design is that the suspension insulator is more expensive than string of disc insulators. Though the height of tower required to maintain required ground clearances are smaller, compared to the designs with string of disc insulators, this does required a minimum tower height as dictated' by the required ground clearances and height of the suspension insulators. Here also the voltage distribution
In the other type of compact electrical power transmission tower made with pultruded composite sections, the cost is high as steel members in the main leg structure are replaced by more expensive polutrded insulating composites. Also this does not reduce the height of the tower substantially as the height of the suspension insulators needs to be taken into considering while meeting the required ground clearances. In the version where the support arm is replaced by pultruded composites covered by silicone rubber sheaths, the cost is much more due to the use of expensive silicone rubber sheaths. Also in this case the voltage distribution across (along the insulating member) is non-uniform leading to a lower efficiency, necessitating a longer insulating member.
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The invention is superior than the prior art designs as this eliminates the need for suspension / string insulators and thus makes the tower shorter in height due to the elimination of consideration of height of suspension insulators, which is not required in this case.
The support arm itself is made out of an outdoor insulating material and supports the high voltage phase conductors and thus does not require and additional suspension insulators. Also since the insulating material used for making the support structure has outdoor weathering properties, this does not requires any additional sheathing with composite rubbers such as Silicone or EPDM.
In another embodiment, the support structure is manufactured with additional internal reinforcing elements such as glass fibers, glass fiber rods, glass mats etc. This enhances the strength of the support structure and facilitates supporting larger weights.
In another embodiment of the invention, discrete capacitor elements connected in series are embedded in one or more members of the of the support arm. These capacitor elements provide for capacitive reactive reactance to compensate for the inductive reactive reactance of the phase conductors. To increase the capacitive reactance these capacitors elements can be embedded in all the members of the support arm.
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In another embodiment of the invention, the capacitors embedded in the support arm are configured as capacitive voltage dividers to facilitate voltage measurement.
A high voltage electric power transmission tower comprising of a vertical support structure made of steel members and the extended support arm made of a outdoor polymer concrete material with arrangements for supporting multiphase phase conductors.
A high voltage electric power transmission tower as per the construction of this invention, is provided with an internal reinforcing elements in the cast support arm to enhance the mechanical strength.
A compact electric power transmission tower, in accordance with the present invention, where in the insulating cross arms have embedded capacitors in them to increase the capacitive reactance and/or compensate for inductive reactance of the phase conductors, A compact electric power transmission tower, in accordance with the present invention, wherein the embedded capacitors in the support arms are configured as capacitive voltage divider to facilitate measurement of voltage on the phase conductors.

Dated this 30th day of March 2007

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