FIELD OF THE INVENTION
The present invention relates an insulation arrangement inside the Current transformers that is regularly manufactured for use in electric sub-stations for power generation and transmission and distribution.
The invention also relates to the method of insulation comprising disposition of the insulating material used in the core-coil assembly of the current transformer.
BACKGROUND OF THE INVENTION
Electric power is the most common form of energy which can be generated, transmitted and utilized for different applications in Industry and Society. However, it is important to provide adequate safety and security to the system for different types of fault. During fault conditions, the current in the transmission lines go to a very high value which can damage the associated equipment (like transformers) in the sub-station. On such events, it is important to isolate the equipment from the line and protect from damaging.
It is also important that the energy generated and transmitted are to be regulated so as to determine the conditions of overload and take precautionary action before the system could be damaged owing to the overload.
It is also important to measure the flow of energy so as to determine the revenue, which is essentially the basis of viability of establishing a power generating or transmitting system. The arrangement of CT mounting in a sub¬station is shown in figure-2.
Current transformers are used to achieve the above requirements. Like a normal power transformer, the current transformer has a primary and secondary windings and core. However, the construction and assembly of the current transformer is totally different.
In the case of Current Transformer, the core is a ring core in the shape of a toroidal. Thin strips of Silicon steel around 0.27 mm thick are rolled to form a

ring core as shown in figure-3. The width and the height of the ring core is the cross sectional area of the core which is the path for the flow of magnetic flux in the core which in turn decides the magnetization current, knee point voltage (core saturation parameter), accuracy class etc. A typical dimension of the ring core could be stated as inner diameter - 200 mm, outer diameter - 450 mm, height - 100 mm. The inner diameter of the ring core should be sufficient enough for the primary line conductor to pass through it.
From Figure 2, it can be shown that the current transformer is connected in series with the line terminal of the equipment. So, the CT primary has the voltage and current of the line terminal. All the current flowing through the equipment necessarily flows through the current transformer. For the purpose, a conductor is spaced in the CT, through which the line current flows. This conductor is known as CT Primary. So, like any power transformer the power supply is connected to the CT primary. The secondary windings of the CT are wound on ring core of the CT, The current in the CT secondary is inversely proportional to the CT ratio. For a CT ratio of 1000: 1 the secondary current in the CT will be 1/1000 of the CT primary current. For a CT connected to a 220 kV, 150 MVA transformer, the CT with turn ratio 1000:1 primary current will be 393 Ampere and the CT secondary current will be 0.393 Ampere. The no of turns in the secondary winding is directly proportional to the turn ratio. So, for a turn ratio of 1000 :1, the no of turns in the secondary winding will be 1000. So, the CT primary is a conductor simply carrying the current passing through ring core of the CT and the CT secondary winding has very large number of turns wound over the core with very thin conductor of very less cross section. The CT primary current is typically 400 Amp (for the referred example). Whereas the CT secondary current is typically around 0.4 Ampere (FIG-6).
The core along with the primary conductor is housed in the same chamber and isolation is provided with cellulose insulating materials, While the CT is processed, these insulating materials are to be dried thoroughly for achieving the desired parameter (as shown in Figure 7).

These cellulose based insulations are hygroscopic in nature. These insulations absorb moisture from the atmosphere which need to be removed for the required performance on the CT. For the purpose, the core coil assembly are subjected to vacuum and drying process. By virtue of heating and vacuum, the moisture absorbed/trapped/embedded in the insulation are removed. Since the insulation is very thick, it takes more time and effort for their removal from the insulation.
The water molecules in the insulation also initiates partial discharge in the insulation which gradual increases that could lead to burning of the insulation and failure of the equipment.
Hence there is always a long felt need to develop an improved and better isolation/insulation so that the current transformer can function properly and have increased life span and also can safeguard to the damage owing to the overload.
The present subject matter meets the long felt need by proving an insulation device and methodology for current transformer for giving the desired result.
SUMMARY OF THE INVENTION:
An insulation device for the current transformers comprising: - multiple number of secondary windings placed on the ring core; - a primary conductor or winding passes through the inner diameter of the ring core; - multiple numbers of composite layers where at least one/or two oil ducts embedded in the said layers; - layers of cellulose papers are provided over the primary conductor and core of the current transformers; characterized in that the oil ducts infuse oil to provide better insulation with said cellulose paper in lower depth of insulation and in high voltage.

OBJECTS OF THE INVENTION
It is therefore the principal object of the present invention to provide a novel insulation device of a current transformer to reduce the drying and processing time of core-coil assembly,
Another object of the present invention to provide a novel method of insulation in CT, where the temperature of the insulating material has reduced and thereby provide better longevity of the insulation.
Yet another object of the invention to provide a novel insulation device which is durable, simple and provide high quality
Yet another object of the invention is to provide a method of insulation in CT which facilitate in revenue generation by increasing the viability of the system for power generation, transmission and use.
Further object of invention is to provide insulation apparatus in CT-serves faster manufacturing of current Transformer.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
Figure 1 illustrates the suggested insulation arrangement of the CT
Figure 2 illustrates the location of the Current Transformer in the sub-station
Figure 3 illustrates the core of the Current Transformer
Figure 4 illustrates the core along with the Secondary winding inside transformer tank of the Current Transformer

Figure 5 illustrates a Live Tank Current Transformer Figure 6 illustrates a Dead Tank Current Transformer
Figure 7 illustrates a conventional Dead Tank Current Transformer as per
exiting art
DETAILED DESCRIPTION OF THE INVENTION:
The present subject matter generally relates to a novel insulation device and a methodology of a current transformers which are in regular use in electric substation to generation power and transmission thereof.
The present method of insulation is also uses oil ducts (1) apart from the cellulose paper, so that the drying time and removal of moisture is improved substantially. The total insulation is embedded together in number of stipulated layers.
In accordance with the present method, the insulation provided are divided into no of stipulated layers with oil ducts (1) between them. This arrangement improves the drying time and moisture is removed very fast in comparison to the case where the total insulation is embedded together.
Generally, two types of current transformer (CT) are available, based upon their design and construction -
i. Live tank
ii. Dead tank
In both the type of CT, multiple no. of secondary windings (3) are provided depending upon the scope of activity viz. metering, Earth fault protection, Differential protection etc.
Fig 5 illustrates the Live tank type CT wherein the core and winding of the CT is isolated from the high voltage. In this condition, the tank is mounted on the top of a large insulator, and the insulator is mounted on the grounded metal base tank.

Figure 6 illustrates the Dead tank type CT, wherein the tank (5) houses the core and winding assembly. The winding assembly is kept in at the CT base, is placed on the foundation.
These secondary windings (3) comprises of very thin conductor (current being very small) and very high no. of turns dependent upon the turn ratio and they are wounded directly on the ring core (shown in figure - 4). A minor insulation is provided between these secondary windings (3) and core. The terminals of these secondary windings (3) are routed up to the base of the tank (5) and terminated on the epoxy terminal block for connecting to external metering and/or protection circuits. The routing of these secondary terminal are to be isolated from the very high line voltage.
Figure 3 and 4 illustrates the core of current transformers where the CT is connected in series with the transformer. All the incoming (PI) and outgoing (P2) connection through the transmission line passes through the CT, so that the CT primary is at a potential of the transmission line. The CT primary travels through the inner diameter of the ring core of the CT to provide the necessary magnetization to the core and thereby results in developing power in the secondary terminals by virtue of magnetic induction. The low voltage secondary winding are placed on the core of the CT. The secondary terminal are connected to very low voltage circuitry of protection relay and metering.
The primary (4) and secondary windings (3) of the CT are at two substantially different potential level and when both of them are needed to be separated, a substantially improved isolation is required. The insulation comprises of multiple or large number of composite layers of cellulose paper wound over each other covering the CT primary conductor and also the core of the CT.
The secondary windings (3), placed on the ring core need to be isolated from the primary conductor (4), which warrants provision of heavy insulation between them.

The cellulose insulation are hygroscopic in nature and it absorbs moisture from the surrounding. The CT is exposed to ambient atmosphere during manufacturing. The moisture absorbed has derogatory effect on the insulating properties of the insulations. The moisture will reduce the break down voltage, increase the Tan Delta value, create hot spots, accelerate ageing, initiate partial discharge and initiate carbonization in the insulation.
In accordance with the present embodiment as illustrated at figure- 1, apart from using layers of cellulose papers (2), the device for insulation also provides at least one or two oil ducts (1) layers in between, and the total thickness of the insulation is sub-divided into two or more composite layers. Thus, the thickness of the insulation subjected to drying reduces to 1/3 of the original insulation. The oil from the ducts can be used as a potential insulation and also reduces the total original thickness of cellulose insulation in a way adding to the factor of safety.
Figure 1 illustrates clearly the presence of at-least plurality of oil ducts (1) in the core of the CT. One oil duct can reduces depth to 24 mm for a composite requirement of 48 mm of insulating depth and the depth may be further reduced to 16 mm with provision of 2 oil ducts (1) in it. Thus, with the novel insulation assembly, with provision of one or two oil ducts (1) it takes substantially less time to penetrate and dry insulation thickness of 24 mm or 16mm as compared to that for a composite 48mm.
Further, the combination of oil and paper insulation provides more factor of safety as compared to insulating paper alone.
The drying out of the CT assembly is very important. The drying out of the CT is done through application of vacuum and heating. By application of vacuum, the moisture is dragged out from the depth of insulation. Hot fumes of vaporized solvent is applied into the insulation, which penetrated up to the insulation and dries the insulation provided on Primary. So, the thickness (depth) of insulation has a direct relation to the heating time and dried quality

of the insulation. When the thickness of insulation is high, time for penetration is also high.
Another embodiment of the present invention provides the primary turn (conductor), which passes through the inner diameter of the ring core. The primary winding (4) is at full line potential (33 kV or 66 kV or 132 kV or 220 kV or 400 kV) being directly connected to the transmission line as stated in figure-2. The ring core carries the magnetizing flux and kept is at ground potential. The core is at ground potential and the secondary windings (3) are at very low potential being the source of the signals whereas the CT primary is at line voltage (33 kV or 66 kV or 132 kV or 220 kV or 400 kV or higher).
According to the present subject matter the provision of using at least plurality of oil ducts (1) by sub-dividing the insulation provides two specific advantages.
At first, the drying and processing is easier because the drying solvent and vacuum sees lesser depth of insulation and secondly the voltage withstand level of the oil and paper combination is higher gives substantially higher safety margin for the CT.
Further, the temperature of the insulation in CT reduces as the oil irrigates the insulation at an intermediate depth and the heat is removed faster from the insulation, thereby reducing the temperature of the hottest zone in the insulation. This reduction in temperatures reduces the ageing of the insulation resulting enhanced life of the CT.
In accordance with the another embodiment of the present invention, there is provided a method for providing insulation in current transformers comprising at least multiple composite layers which further comprises one or two oil ducts (1) along-with layers of cellulose papers (2) between them for removal of moisture. The drying is performed through application of vacuum and solvents and the temperature is substantially reduced due to faster removal of heat. The drying is performed through application of vacuum and temperature or solvents

in a lesser time. Also the temperature of insulation is substantially reduced due to faster removal of heat.
The Non-limiting advantages are given below:
i. The new insulation assembly (figure-1) in CT provides a time efficient solution to the manufacturing time cycle of the CT as compared to the existing method of arrangement is as shown in figure 6
ii. The new method of insulation (figure-1) saves cost of the product owing to lesser processing time
iii. The new method of insulation reduces the hot spot temperature of the insulation preserving the property of the insulation for a longer time enhancing the life of CT and reducing the replacement cost of CT
iv. The new method of insulation provides more reliability for the supply of electric power by virtue of longer life of the CT
v. The enhance life of CT increases the tariff of the electric power enhancing more viability of the system for power generation and transmission system.
The existing method of arrangement is as shown in figure-6.
Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/device of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

WE CLAIM:
1. An insulation device for the current transformers comprising:
- multiple number of secondary windings (3) placed on the ring core;
- a primary conductor or winding (4) passes through the inner diameter of the ring core;
- multiple numbers of composite layers where at least one/or two oil ducts (1) embedded in the said layers;
- layers of cellulose papers (2) are provided over the primary conductor and core of the current transformers;
characterized in that the oil ducts (1) infuse oil to provide better insulation with said cellulose paper in lower depth of insulation and in high voltage.
2. The insulation device for the current transformers, wherein said primary and secondary windings (3) are isolated electrically.
3. The insulation device for the current transformers, wherein said primary and secondary windings (3) are kept at two different potential level.
4. The insulation device for the current transformers, wherein a space is
provided among said composite layers for flow of drying solvent and oil.
5. The insulation device for the current transformers, wherein the terminals of
said secondary winding are routed at the base of the tank (5) and terminated on
the epoxy terminal block for connecting to external circuits.
7. A method for providing insulation in current transformers comprising at least multiple composite layers which further comprises one or two oil ducts (1) along with layers of cellulose papers (2) between them for removal of moisture; the drying is performed through application of vacuum and solvents and the temperature is substantially reduced due to faster removal of heat.

8. The method of providing insulation in current transformers wherein said solvent is used in form of hot fumes.
9. The method of providing insulation in current transformers wherein the hot fumes of solvent penetrates to the insulation and eventually dried on it.
10. The method of for providing insulation in current transformers wherein the
said drying process utilizes low depths of insulation.