Description:
TECHNICAL FIELD OF INVENTION
The present disclosure in general relates to an electricity distribution system. In particular, the present disclosure relates to a compact type of distribution transformer in the electricity distribution system.

BACKGROUND OF INVENTION
Distribution Transformer (DTR) is the medium voltage source of power for consumers in every utility, catering largely to the domestic and commercial sector. As the terminal conversion equipment DTRs are mostly located in public places and so safety, reliability and efficiency of these units are the major areas of concern for any distribution utility. The situation is more critical for utilities operating in urban areas where population density is very high.

Mineral insulating oil poses a serious threat of fire hazard. Therefore, the inventors is thus gradually moving toward installation of Dry type DTR. The figure 1 illustrates the dry type DTR from the low voltage (LV) side and the figure 2 illustrates the dry type DTR from the high voltage (HV) side. To take care of the temperature rise, dry type distribution transformer has larger physical dimension than its oil counterpart. As most of the DTRs are installed at congested locality within and surrounding a city, accommodating DTRs within the specified location is itself a challenging job.

This constraint is even more severe for the road side pole mounted DTRs as there is very limited space on the scaffolding to carry out any job. Moreover, pole dimension cannot be increased further due to site constraints.

Therefore, it is very important to limit the dimension of the DTRs within the specified values, otherwise it may restrict the space available on the scaffolding or increase height, both of which are not safe for the operating personnel. Over-dimension also increases the weight of the transformer which makes it unsuitable for installation at pole.

Further, due to predominating underground network, the DTRs have a number of compartments, that may include but not limited to High tension (HT) cable box, High tension (HT) fuse chamber, High tension (HT) isolator chamber, LT CFS box. All these compartments are connected to each other or with main tank by flanged joints, which make it vulnerable to (i) moisture ingress, and (ii) improper earthing.
Every bolted joint in the compartment has gasket which becomes brittle over the years. Although all these compartments are covered with canopies, these canopies become rusted or corroded gradually or even it can go missing. If it is not reported and attended in time, the gasketted joints become exposed to rain water, dust, sunlight etc. As no routine periodic cleaning is carried out, these different compartments become corroded with time, allowing rain water to enter HV compartments. The most vulnerable joint in this regard is that between High Tension Fuse Fixing Arrangement (HTFFA) chamber and High Tension (HT) cable box because High Tension (HT) cable terminating bushings are just beneath that joint. Rain water, if enters, will drop directly on that bushing leading to failure of HT bushing or cable termination. The figure 3 shows an image of the Corroded HT cable box that causes water accumulation inside.

Further, the DTR body is earthed at two separate points and continuity of earthing is maintained in all the compartments that includes but not limited to HV cable box, HTFFA chamber, LT CFS box etc. by separate copper strips connecting the two sides of every flanged joints. But over the service life of the transformer it is quite natural that these small copper strips go missing or detached which makes a compartment unearthed. It yields an unsafe condition for the operating personnel and also for the common public. The figure 4 shows an image of the copper strips across gaketted joints.

Moreover, since humidity is one of the killer factors for electrical plant and equipment, the DTRs installed in moisture prone area develops partial discharge between HT cable termination and side wall and cover of the cable box. This could have been avoided had the cable box been larger in size. But again it must not affect the overall dimension.

Thus, to summarize the drawbacks of the conventional DTR are as follows:
1. To avoid flashover at HT cable boxes, particularly in moisture prone, polluted & industrial areas, HT cable boxes were made larger so that higher electrical clearances could be achieved. But it had impact on overall dimension of the transformer which has limitation as mentioned earlier.

2. Another way of preventing the flashover in those locations are to cover the bare termination with non-adhesive tape inside HT cable boxes. This, no doubt reduces the electrical stress between phase to phase and phase to earth but with the age of the transformer this tape was getting loose and touched with that of other phases which initiates partial discharge and eventually causes a flashover.

3. Cable boot was also tried to cover the bare termination inside HT cable boxes but it eventually led to the origin of partial discharge between that boot and bare termination

4. Replacing the gaskets of the flange joints through which moisture ingress is possible is not feasible for every transformer at site.

Thus, in view of the above-mentioned drawbacks, there exists a need for improvements in this regard. A compact dry type transformer is the only solution to get all the benefits together – with larger electrical clearance & lesser overall dimension and much lesser chance of flashover than that in conventional one with same rating.

OBJECT OF THE INVENTION
An object of the invention is to provide a compact type of enclosure for a distributed transformer where all the bolted flange joints have been eliminated and all the compartments have been combined in such a way that they become a compact one with lesser footprint and weight, but with larger inner dimension.

Another object of the invention is to utilize the unutilized spaces as an extended part of the main tank of the DTRs.

Yet another object of the invention is to achieve lesser the winding temperature rise than the conventional one in spite the overall dimension being also lesser.

Still another object of the invention is to provide a compact dry type transformer to get all the benefits together – with larger electrical clearance and lesser overall dimension and much lesser chance of flashover than that in conventional one with same rating.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts in a simplified format that is further described in the detailed description. This summary is not intended to identify key or essential inventive concepts.

In accordance with the purposes of the invention, the present invention as embodied and broadly described herein provides a multi-winding distribution transformer. The invention achieves lesser winding temperature rise than the conventional one in spite of being the overall dimension also being lesser. Most interestingly phase to phase and phase to earth clearance inside HT cable box & HTFFA have also increased significantly with simultaneous reduction in overall dimension.

In one implementation, the present invention provides a compact distribution transformer having a lesser physical dimensions, implemented in an energy distribution system. The compact distribution transformer comprising:

a High Voltage (HV) side enclosure mounted on at least a pole; and
a Low Voltage (LV) side enclosure mounted on said pole;
wherein a main tank of said HV side and LV side enclosures being extended by using at least an unutilized space to incorporate plurality of ventilation louvers between said main tank and its extended portions, so that the heat generated inside said main tank can traverse into this extended portions and dissipate along the surface of one or more compartments.

In one implementation, the compartments are directly attached to said main tank.

In one implementation, the earthing at primary two points of the main tank enables continuity of earthing in said enclosures, to avoid the use of at least a bolted flange joints and separate copper strips for continuation of body earth in said compartments.

In one implementation, a preferable range for HV winding temperature rise is 95-100 deg C, and LV winding temperature rise is preferably in the range of 90-95 deg. C.

In one implementation, the top surfaces of each of said compartments said main tank includes a same level which creates ample and more convenient working space.

In one implementation, the overall reduction of 19% lesser footprint is achieved as all the flange joints have been eliminated.

In one implementation, at least a guard rail is fixed on top of said DTR for clamping safety harness for carrying out job on said mounted transformer ensuring safety of operating and maintenance persons.

According to various implementations of the present invention, the compact Distribution Transformer utilizes unoccupied spaces of conventional transformers more effectively so that effective surface area for heat dissipation increases keeping even lesser footprint than that of its conventional counterpart. In this compact DTR i) the loss has been reduced, (ii) the dimension has been minimized and (iii) the reliability has been enhanced successfully without affecting the temperature rise. Lower temperature rise and lower dimension - these two contradictory requirements have been met simultaneously. Another contradictory requirement is also met which is less overall dimension with more electrical clearance between individual High Voltage components.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
It is appreciated that the drawings provided in the present disclosure only illustrate application examples of the present disclosure and are therefore not to be construed as limiting its scope. The foregoing disclosure provides additional information with additional specificity and detail with the accompanying drawings, which are listed below for quick reference.

Figure 1: Illustrates a schematic view of a dry type DTR-view from the LV side. (Prior art).

Figure 2: Illustrates a schematic view of a dry type DTR-view from HV side. (Prior art).

Figure 3: Illustrates a schematic view of a corroded HT cable box that causes water accumulation inside. (Prior art).

Figure 4: illustrates a schematic view of a copper strip across gasketted joints. (Prior art).

Figure 5: illustrates a schematic view of unutilized spaces of the main tank. (Prior art).

Figure 6: illustrates a schematic view of a compact DTR - view from LV side, according to one implementation of the present invention.

Figure 7: illustrates a schematic view of a Compact DTR – LV CFS box, metering kiosk and CFS handle enclosure, according to one implementation of the present invention.

Figure 8: illustrates a compact DTR - view from HV side, according to one implementation of the present invention.

Figure 9: illustrates a compact DTR-HT FFA chamber and HT isolator chamber, according to one implementation of the present invention.

Figure 10: illustrates a compact DTR - side view, according to one implementation of the present invention.

Figure 11: illustrates a compact DTR-HV cable box, according to one implementation of the present invention.

Figure 12: a general arrangement diagram of a compact DTR according to the present invention.

Figure 13: illustrates the working space on top of transformer: a) conventional type according to a prior art, b) compact type according to the one implementation of the present invention.

It may be noted that the one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding of the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of the ordinary skilled in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION
It should be understood at the outset that although illustrative implementations of the present disclosure are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or in existence. The present disclosure should be in no way limited to illustrative implementations, drawings, and techniques, illustrated below, including the exemplary design and implementation illustrated and described herein, but may be modified within the scope of equivalents.

Unless otherwise defined, all terms and especially technical and/or scientific terms, used herein, may be taken to have the same meaning as commonly understood by one having an ordinarily skilled in the art.

Reference is made herein to some “implementation”. It should be understood that an implementation is an example of a possible embodiment of any features and/or elements presented in the foregoing claims. Some embodiments have been described for the purpose of illustrating one or more potential ways in which the specific features and/or elements of the foregoing claims fulfill the requirements of uniqueness, utility, and non-obviousness.

Present disclosure is an improved design of DTR by utilizing the vacant space in High Voltage (HV) & Low Voltage (LV) side. These spaces were left unutilized but included in overall dimension. The present invention serves the electricity distribution system where performance & reliability of distribution transformers are 2 major yardsticks. This invention also serves the purpose of mitigating installation-site constraints due to lack of space and safety related to common people, particularly in urban areas. Both power distribution utility and consumers can adopt this invention for most reliable, efficient and safe service with easy installation and no additional cost.

To combat the shortcomings of the conventional DTR, a new type of enclosure has been developed where all the bolted flange joints have been eliminated and all the compartments have been combined in such a way that they become a compact one with lesser footprint and weight, but with larger inner dimension. Basically, the space above the HT cable boxes that includes but not limited to both sides of the HT isolator chamber, both sides of the LT CFS box, were left unutilized. This spaces have been used as an extended part of the main tank.

These unused spaces of the conventional DTR have been utilized as extended part of main tank according to one implementations of the present invention. Louvers are fitted in between the main tank and its extended portions, so that the heat generated inside the main tank can traverse into this extended portions and dissipate along the surface of those enclosures.

In one implementation, reference is made to figure 6 which illustrates a view of compact DTR from Low Voltage (LV) side and all chambers closed.

In one implementation, reference is made to figure 7 which shows a view of compact DTR from Low Voltage (LV) side with metering kiosk, Combined Fuse switch (CFS) chamber and its handle enclosure are open.

In one implementation, reference is made to Figure 8 which shows a view of compact DTR from High Voltage (HV) side and all chambers closed.

In one implementation, reference is made to Figure 9 which shows a view of Compact DTR from High Voltage (HV) Side with fuse chamber and isolator chamber open.

In one implementation, reference is made to Figure 10 which shows a side view of compact DTR where main tank, High Tension (HT) cable box, extended compartment etc. are visible

In one implementation, reference is made to Figure 11 which shows a side view of compact DTR with HT cable box open.

In one implementation, reference is made to Figure 12 which shows dimensions of conventional DTR vis-a-vis compact DTR. The figure 12 the overall dimension of the conventional DTR is 1750mm (L) X 2400mm (W) X 1950mm (H) whereas for compact DTR the same dimension becomes 1650 mm(L) X 2200 mm(W) X 1750mm (H), wherein L: Length, W: Width, H: Height.

In one implementation, in compact DTR surface of the main tank has been extended by using some unutilized space. Internal ventilation louvers have been incorporated between actual main tank and those extended compartments.

In one implementation, as the extended hollow enclosures become a part of the main tank, a larger surface area of actual main tank and its surrounding parts can be utilized for heat dissipation which makes it possible to lower the temperature rise. The heat run test also confirms lower temperature rise as compared to its conventional counterpart of same rating. The following Table 1 shows the comparison of the temperature rise between the conventional DTR and the compact DTR.

Table-1
500 KVA DTR
HV winding temperature rise (deg C) above ambient LV winding temperature rise (deg C) above ambient
Conventional 109.58 98.63
Compact 98.61 92.58

In one implementation, by increasing the effective surface area, by utilizing the unused spaces and by eliminating all the flange joints between compartments, the overall dimension could be reduced for this newly developed compact DTR. According to one exemplary implementation, the overall dimension has been compared for a 500 KVA DTR with same manufacturer as shown in the table 2:

From the above tables 1 & 2, it is evident that the winding temperature rise is much lesser than the conventional one in spite of being the overall dimension also lesser. Most interestingly phase to phase and phase to earth clearance inside High Tension (HT) cable box and High Tension Fuse fixing arrangement (HTFFA) have also increased significantly with simultaneous reduction in overall dimension.

In one implementation, with the compact design, by utilizing the earlier gaps between the compartments, the size of the HT cable boxes also could be made larger. The clearances between HT cable termination to side wall and to cable box cover, i.e. phase to earth clearances have increased in both direction. As compared from the conventional DTR, the clearance between HT cable terminating clamp of R & B ph to side wall may increased to 235 mm from 160 mm and the clearance between HT termination and cable box cover may increase to 320 mm from 250 mm, according to one exemplary implementation of the present invention. It will lessen the chance of initiating partial discharge and other flashovers in HT cable.

Some of the noteworthy features of the present invention are as follows:

1) Reduced Footprint
19% lesser footprint than in conventional transformer of same rating as all the flange joints have been eliminated. This provides more working space surrounding the transformer. This will also ensure safety of the maintenance people.

2) Larger Electrical Clearance
Elimination of flange joints let us allow to make larger electrical clearances in HT cable box and HTFFA chamber which will have an impact on prevention of flashover.

3) No Water Ingress
As all the gasketted flange joints have been eliminated, chances of rain water ingress into the HT chamber is also eliminated which also reduces the chance of flashover.

4) Lower Operating Temperature
As the vacant space of the conventional transformer is utilized as added heat dissipating surface, lesser winding temperature rise is obtained which will further ensure the longer service life of the transformer than the conventional one of same rating.

5) Natural heating HV compartments
In this compact DTR all the compartments are directly attached to main tank unlike its conventional counterpart where these compartments are physically separated from main tank. Heat generated in winding can be directly transmitted to other compartments i.e. HT cable boxes, HT FFA chamber, LV CFS box through conduction and keeps the bushings and other insulators warm. It will restrict the moisture deposition on different insulating components which will ultimately prevent partial discharge or in worst case failure of the same.

6) Body earthing ensured
As there is no bolted flange joints in compact version of DTR, the requirement for separate copper strips for continuation of body earth in different chambers no longer exists. Earthing at primary two points of the main tank is sufficient to ensure earth.

7) Separate kiosk for CFS operating handle
CFS operating handle in conventional DTR remains outside of LT box and accessible to anybody. It may cause unwanted operation of CFS and also remained prone to theft. But in compact version this handle has been placed inside a separate lockable kiosk, making it inaccessible to common people, which will prevent any inadvertent operation.

8) More working space on top
During breakdown at site working personnel may have to work climbing on top of the transformer for opening inspection cover and carry out any job inside main tank. In this compact version, as shown in the figure 13, the top surfaces of all compartments including those extended ones for main tank have come at same level which creates ample and more convenient working space on top of the DTR, enhancing safety.

9) Safety guard rail
A guard rail is fixed on top of the DTR which will be used for clamping safety harness for carrying out job on a pole mounted transformer ensuring safety of operating and maintenance persons

10) Weight and cost
Considering its reduced dimension and footprint, though separate enclosures have been incorporated, the total weight remains same as that of conventional one and within the specified capacity. Manufacturing cost is also similar to the earlier ones.

Those skilled in the art will recognize other use cases, improvements, and modification to the embodiments of the present disclosure. All such improvements and other use-cases are considered within the scope of the concepts disclosed herein.
, Claims:1. A compact distribution transformer having a lesser physical dimensions, implemented in an energy distribution system, wherein the compact distribution transformer comprising:
a High Voltage (HV) side enclosure mounted on at least a pole; and
a Low Voltage (LV) side enclosure mounted on said pole;
wherein a main tank of said HV side and LV side enclosures being extended by using at least an unutilized space to incorporate plurality of ventilation louvers between said main tank and its extended portions, so that the heat generated inside said main tank can traverse into this extended portions and dissipate along the surface of one or more compartments.

2. The compact distribution transformer as claimed in the claim 1, wherein said compartments are directly attached to said main tank.

3. The compact distribution transformer as claimed in the claim 1, wherein earthing at primary two points of the main tank enables continuity of earthing in said enclosures, to avoid the use of at least a bolted flange joints and separate copper strips for continuation of body earth in said compartments.

4. The compact distribution transformer as claimed in the claim 1, wherein a preferable range for HV winding temperature rise is 95-100 deg C, and LV winding temperature rise is preferably in the range of 90-95 deg. C.

5. The compact distribution transformer as claimed in the claim 1, wherein top surfaces of each of said compartments said main tank includes a same level which creates ample and more convenient working space.

6. The compact distribution transformer as claimed in the claim 4, wherein overall reduction of 19% lesser footprint is achieved as all the flange joints have been eliminated.

7. The compact distribution transformer as claimed in the claim 1, wherein at least a guard rail is fixed on top of said DTR for clamping safety harness for carrying out job on said mounted transformer ensuring safety of operating and maintenance persons.