WO2012156990A2

WO2012156990A2 - Air restoring breather

Info

Publication number: WO2012156990A2
Application number: PCT/IN2012/000341
Authority: WO
Inventors: Anil Sahadeo MHALA
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-05-10
Filing date: 2012-05-10
Publication date: 2012-11-22
Anticipated expiration: 2013-11-10
Also published as: WO2012156990A3

Abstract

Disclosed herein is a moisture free air restoring breather for oil filled transformer wherein air exhaled by the transformer is reutilized for next breathing cycle, said air restoring breather comprising a cylindrical transparent polycarbonate container, a desiccant filled in said polycarbonate container, a flexible air bag to store the air exhaled by the transformer, a cylindrical metallic container enclosing the said air bag and an oil cup.

Description

AIR RESTORING BREATHER

FIELD OF THE INVENTION:

The present invention relates to transformer breathers for oil filled transformers which reutilizes the moisture free air exhaled by the transformer for the next breathing cycle, the air being demoisturised during previous breathing cycle.

BACKGROUND OF THE INVENTION:

A transformer breather is an accessory of an oil filled transformer which is attached to oil conservator tank. It serves as a breathing point of the transformer. When the load on the transformer increases, the oil is heated up which in turn expands and goes back to the conservator tank i.e. an oil tank above the transformer. The expanded oil pushes air out of the conservator tank through the breather containing desiccant. When the oil cools down as a result of reduction in transformer load, it retracts and sucks the fresh air from the atmosphere. The desiccant absorbs the moisture from this air being inhaled by the transformer. In this way, the 'breathing' takes place.

The transformer oil used in the breather is highly refined mineral oil that is stable at high temperature. It helps to cool the transformer and has excellent electrical insulating properties.

For an oil transformer, moisture constitutes a hazard not only to the insulating qualities of the oil but also to the insulations that are immersed in the oil.

The destructive effects of water include:

• Expansion of the paper insulation, altering the mechanical pressure of the transformer clamping system.

• Loss of insulating ability (Dielectric Breakdown Voltage)

• Accelerating paper aging i.e-., triggering decomposition of the fibers in the paper

• Increased corrosion of the core¾nd tank It has been observed that insulating paper with 2% moisture content ages three times faster than one with 1 % moisture and thirty times faster with 3% moisture .It is thus easy to see the importance of maintaining low moisture levels within a transformer to ensure a long and trouble free service life.

The temperature of oil varies with the change in loading on transformer and change in ambient temperature resulting in change in volume of oil. This change in oil volume results in breathing by transformer. The transformer breathes through an opening provided to the oil conservator tank. Desiccant breather is provided at this opening to absorb the moisture from the air being breathed by the transformer.

There are many desiccant (Silica gel etc.) breathers available in market. These conventional breathers absorb the moisture from air during each breathing cycle. After certain number of breathing cycles, the desiccant reaches its limit to absorb the moisture because of which the desiccant has to be replaced or reconditioned on a frequent basis. It is very cumbersome yet important activity for maintaining the dielectric strength of ^'" transformer oil.

Japanese patent JP 60251608 teaches a device to monitor the hygroscopic capacity of silica gel in a breather easily at any optional time and place by a method wherein a humidity sensor and a humidity level measuring instrument connected thereto are provided in a vent pipe. A breather containing silica gel therein is connected to a conservator provided on the upper part of a transformer and a vent pipe while a humidity sensor is provided in the vent pipe and the humidity sensor is connected to a humidity level measuring instrument externally provided through the intermediary of a wiring. In a monitor with such a constitution, humidity of air running into the vent pipe through the breather is measured by the humidity sensor while the humidity level measuring instrument will transmit signals to direct the replacement of silica gel whenever the humidity level reaches the level preliminarily specified informing of the time of silica gel replacement. As such, the patent teaches of a humidity sensing method and thus an indicator of the hydroscopic capacity of desiccating silica gel. It does not teach any device or method that helps to prolong the life of the desiccant. British Application GB 1199941relates to a transformer breather comprises a glass container for desiccant, e.g. coloured silica gel through which air passes only when a change in pressure in the transformer housing is sufficient to allow the air stream to pass through an oil seal constituted by glass container filled with oil to level. As air in the housing expands, air passes through expanded metal guard, through space, through the oil seal, out through openings and perforated plates into the desiccant in container, and thence through perforated plate to the atmosphere. On contraction the air stream is reversed and the desiccant removes moisture from the air which passes to the interior of the housing. When the desiccant is exhausted, container is replaced without dismantling the entire assembly by loosening wing nuts, so allowing two adjacent rods to be slid out of slots in the edge of plate in which they are located. This patent teaches a system for simpler replacement of the desiccant with a desiccant capacity monitoring mechanism. The said invention fails to teach any method for reutilization of dry air.

A dehydrating breather for an oil-filled transformer, the desiccant is regenerated by heating while air is being expelled from the transformer is taught by British patent GB1072528. The desiccant or air being expelled may be heated by the transformer oil to supply all or part of the required heat or heating may be achieved using either the transformer-oil or an independent heat source (e.g. electrical) operated by a pressure switch Which will be actuated by the increase in gas pressure caused by a restricted outlet valve. Air is admitted from the atmosphere through valve and leaves thereto through valve. The space surrounding the desiccant container and inlet contains oil which passes to and from the transformer via passage and to and from the conservator tank via passage. When the oil in the transformer is being heated, heated oil passes from the transformer to the conservator tank and in the passage heats the desiccant and the inlet, while air is expelled from the conservator tank and passes to the atmosphere at after regenerating the desiccant. When the transformer oil cools, relatively cool oil returns to the transformer from the conservator tank, thus sucking air in at valve through the cooled desiccant to be thus dried. The oil jacket is omitted, and expelled air is heated by passage through a coil in transformer oil before entering breather to regenerate the desiccant therein. In air passages to desiccant directly by tube to and from the space at the top of transformer Conventional oil cooling tube passes through the charge and the circulation of oil there through when the transformer becomes heated is sufficient to heat the desiccant for the regeneration thereof.

As seen from the prior art, the present state of the art leaves a lot of room for improvement in devices/systems to provide a long term, simple and cost effective solution that requires minimum servicing.

Summary of Invention:

The present invention discloses an air restoring breather for oil filled transformer where dried air exhaled by the transformer is reutilized for next breathing cycle, the air restoring breather comprising a cylindrical transparent polycarbonate container, a desiccant filled in the polycarbonate container, an air bag to store the air exhaled by the transformer, a cylindrical metallic container enclosing the air bag,and an oil cup.

The present invention provides moisture free air to the oil filled transformer during breathing in process. It restores the same dry air for next breathing cycles. The present invention also provides a breather with minimum serviceability.

The air restoring breather achieves so by reutilising the previously dried air, without introducing any external moisture. As the same dry air is reused, the desiccant lasts for a much longer time compared to that of the conventional breather.

BRIEF DESCRIPTION OF DRAWINGS:

Fig 1 illustrates the air restoring breather. Detailed description of the Invention:

The present invention discloses an air restoring breather for oil filled transformer wherein dried air exhaled by the transformer is reutilized for next breathing cycle, said air restoring breather comprising a cylindrical transparent polycarbonate container, a desiccant filled in said polycarbonate container, a flexible air bag to store the air exhaled by the transformer, a cylindrical metallic container enclosing said air bag, and an oil cup. In the present invention, air exhaled by the transformer enters the desiccant filled polycarbonate container through gateway (A), which exists between the said container and transformer oil conservator tank, from where it flows through the desiccant to the bottom of said polycarbonate container to reach the two gateways (B) and (C) ahead. The gateway (B) is dipped in oil filled in transparent oil cup (5) which is present at the bottom of the polycarbonate container whereas the gateway (C) exists between the polycarbonate container and the air bag and consists of four holes. The exhaled air has to overcome the resistance of this oil seal at gateway(B) in order to escape to the external atmosphere. On the other hand, said gateway (C) allows easy flow of exhaled air from said polycarbonate container into the said air bag.

The said air bag is selected such that the resistance offered by it during inflation or deflation is less than the resistance offered by the oil seal to the air flow. The volume of the air bag is selected depending upon maximum change in volume of transformer oil during regular loading variations. The air bag is enclosed in a metallic container to prevent any physical damage to the air bag.

Further, the desiccant filled in the polycarbonate container is any hygroscopic substance, hence dries the atmospheric air upon entering into the polycarbonate container.

The present invention is now described in detail with respect to figures and embodiments. The preferred embodiment can be understood by referring to Fig. 1 .

According to the preferred embodiment, an air restoring breather for oil filled transformer is disclosed; where air exhaled by the transformer is stored and reutilised for next breathing cycles. The air restoring breather comprises of an air bag(4) which stores the air exhaled by the transformer to reutilise it in next breathing cycles , a cylindrical transparent polycarbonate container(2), a desiccant(3) filled in the said polycarbonate container, a cylindrical metallic container(9) enclosing the air bag(2) to provide physical protection to the air bag(4) and an oil cup(5).

The container(2) has three openings or gateways (A), (B) & (C). The gateway (A) exists between polycarbonate container(2) and transformer oil conservator. The gateway (B) exists between the polycarbonate container(2) and external atmosphere and is dipped in oil filled in transparent oil cup (5). Thus gateway (B) is sealed with oil(7) filled in the transparent oil cup(5). The gateway (C) exists between the polycarbonate container(2) and the air bag(4) and consists of four holes allowing air to escape in all directions. The gateway (C) communicates air between the polycarbonate(2) container and said air bag(4). An air opening (8) is provided in the oil cup(5). The air bag(4) is enclosed in a metallic container(9) to prevent any physical damage to the air bag.

In the preferred embodiment, the desiccant(3) is filled in the polycarbonate container(2) with metal flanges at top(l) and bottom(6). The desiccant can be silica gel.

The present invention performs its functions in the following manner:

During exhalation, air can flow through two paths:

Path 1 : Conservator tank— A~3~B~7~8~.External Atmosphere

Air exhaled from conservator tank enters the desiccant Silica Gel(3) through gateway (A) and then it has to overcome the resistance of oil seal(7) at gateway (B) to escape to the external atmosphere through opening(8) provided in the oil cup(5). This path is followed by the air when the air bag(4) is completely full.

Path 2: Conservator tank— A-3--C— Air Bag (4)

Air exhaled from conservator tank enters the desiccant Silica gel(3) through gateway (A) and then enters the air bag(4) through gateway (C). This path is followed by the air till the air bag(4) is completely full .

Similarly during inhalation, air can flow through same paths in reverse direction.

Path 1 reversed: External Atmosphere~8— 7— B— 3— A— Conservator tank

This path is followed by the air when the air bag(4) is empty.

Path 2 reversed: Air Bag (4)— C— 3— A— Conservator tank This path is followed by the air till the air bag(4) is completely empty. Breathing cycles of Air restoring breather are as follows:

Cycle 1 :

Breathing in

When load on a transformer reduces, the temperature of oil falls down resulting in reduction of volume of oil. So the transformer starts breathing in. Initially, there is no air in the air bag(4). As the air bag(4) is empty, air cannot flow through path 2 reversed i.e. air bag to conservator. Thus air flow takes place through reversed path 1 i.e. external atmosphere to the conservator tank. This air is demoisturised by the desiccant(3) placed in container(2). Thus dry air enters the conservator tank.

Breathing out

When the load on transformer increases, the temperature of oil also increases resulting in expansion of oil. The transformer breathes out. As the air bag(4) is empty, it easily allows the air to get accumulated inside it. The oil seal(7) offers more resistance than flexible air bag(4). Hence the air exhaled by the transformer follows path 2 & is stored in the air bag(4).

Cycle 2:

Breathing in

During the next breathing in cycle, the air from the air bag(4) is drawn in, as the oil seal(7) at gateway (B) provides more resistance to the atmospheric air. Thus the air stored in the previous cycle is re-supplied to the transformer. Since the air is already dry, there is no consumption of the desiccant.

The same breathing cycle is followed by the breather. Since dried air is reutilised during next breathing stages thereby enhancing the life of the desiccant by not consuming it until the fresh atmospheric air enters the breather. In the preferred embodiment, the air bag(4) is selected such that the resistance offered by the air bag during inflation or deflation is less than the resistance offered by said oil seal to the air flow. In other embodiments, the volume of the air bag(4) can be selected depending on the maximum change in volume of transformer oil during daily loading variations.

For example, for a 990KVA transformer containing 880 litres of oil & load variation from 55% to 70%, the maximum change in transformer oil volume is observed as 8-10 litres. The ambient temperature being 23°C minimum and 34°C maximum. Thus volume of air bag (4) can be selected as 10 litres or 10,000 cm³.

Critical cases:

Volume of air breathed by transformer is not equal to the volume of air bag.

If volume of air breathed by transformer is less than the volume of air bag (4), the working of "Air restoring breather" will remain the same as discussed above.

But, if the volume of air breathed by transformer is more than the volume of air bag (4), say about 10% more, the air bag (4) will be full with 90% of the air exhaled. Since the bag is full, its resistance to the flow of air becomes more than the oil seal (7). Thus the remaining 10% of air escapes to the external atmosphere through oil cup opening (8) preventing the air bag (4) from excess pressure.

If the bag (4) is punctured, the breather will no more store the air and the "air restoring breather" will start working as a "conventional breather". After certain number of breathing cycles, the colour of desiccant will change indicating problem with the air bag (4). The colour of the desiccant Silica gel (3) can be monitored periodically, for healthiness of the air bag (4).

The "Air Restoring Breather" enables an oil filled transformer with conservator tank to work as hermetically sealed transformer without exerting excess air pressure inside the transformer. The Air Restoring Breather can be retrofitted on the transformer without any outages. With proper volume of air bag selected, the efficiency of Air Restoring Breather becomes several folds than that of conventional one for the same amount of desiccant used. The desiccant thus need not be changed very often reducing the time and expenditure incurred for servicing the breather. The transformer breather for oil filled transformer of the current invention can be used for electrical transformer and any such devices which need dehydrated air for breathing purpose.

Claims

I claim,

1. A moisture free air restoring breather for oil filled transformer wherein air exhaled by the transformer is reutilized for next breathing cycle, said moisture free air restoring breather comprising:

a. an air bag(4) to store the air exhaled by the transformer and to reutilize the previously dried air during the exhalation,

b. a cylindrical transparent polycarbonate container(2),

c. a desiccant(3) filled in said polycarbonate container(2),

d. a cylindrical metallic container(9) enclosing said air bag(4), and e. a transparent oil cup(5).

2. The moisture free air restoring breather as claimed in claim 1, wherein the gateways on said polycarbonate container(2) for airflow / breathing comprises: a. gateway (A) to communicate air between said polycarbonate container and conservator tank;

b. gateway (B) to communicate air between said polycarbonate container and. external atmosphere;

c. gateway (C) to communicate air between said polycarbonate container and said air bag.

3. The moisture free air restoring breather as claimed in claim I, wherein an opening(8) is provided in the transparent oil cup(5) to inhale air from or exhale air to atmosphere.

4. The moisture free air restoring breather as claimed in claim 2, wherein said gateway (A) exists between said polycarbonate container(2) and transformer oil conservator tank.

5. The moisture free air restoring breather as claimed in claim 2, wherein said gateway (B) exists between said polycarbonate container(2) and external atmosphere.

6. The moisture free air restoring breather as claimed in claim 5, wherein said gateway (B) is sealed with oil filled in said transparent oil cup(5).

7. The moisture free air restoring breather as claimed in claim 2, wherein said

gateway (C) exists between said polycarbonate container and said air bag.

8. The moisture free air restoring breather as claimed in claim 2, wherein said

gateway (C) comprises four holes to allow air to escape in all directions within said air bag(4).

9. The moisture free air restoring breather as claimed in claim 1, wherein said

desiccant(3) is any hygroscopic substance.

10. The moisture free air restoring breather as claimed in claim 1 , wherein the

resistance offered by said air bag(4) during inflation or deflation is less than the _. ■^■■! resistance offered by said oil seal(7) to the air flow.

11. The moisture free air restoring breather as claimed in claim 1 , wherein the volume

of said air bag(4) is proportional to maximum change in volume of transformer oil during regular loading variations.

12. The moisture free air restoring breather as claimed in any of preceding claim,

wherein said air bag(4) is enclosed in a metallic container(9) to prevent any physical damage to said air bag(4).

13. The moisture free air restoring breather according to any of preceding claim,

wherein the air is exhaled through a path 1 when said air bag(4) is full.

14. The moisture free air restoring breather as claimed in claim 13, wherein said path

1 of the air flow is from said conservator tank to said desiccant through said gateway (A), thereby overcoming resistance of said oil sea!(7) at said gateway (B) to escape to the external atmosphere though said opening(8) provided in said oil cup(5).

15. The moisture free air restoring breather as claimed in any of the claims 1 to 12, wherein the air is exhaled through a path 2 till said air bag(4) is completely full.

16. The moisture free air restoring breather as claimed in claim 15, wherein said path 2 of the air flow is from said conservator tank to said desiccant(3) through said gateway (A) thereby entering said air bag(4) through said gateway (C).

17. A breathing cycle of a moisture free air restoring breather claimed in any of the preceding claims comprising:

a. inhaling via reversed path 1 when an air bag(4) is completely empty;

b. exhaling via path 2 till the an air bag(4) is completely full;

c. inhaling via reversed path 2 till the an air bag(4) is completely empty; d. exhaling via path 1 when an air bag(4) is completely full.

18. The breathing cycle of a moisture free air restoring breather as claimed in claim

17, wherein the air is demoisturised during all steps (a), (b), (c), and (d) by a desiccant(3) filled in said polycarbonate container(2).

19. The breathing cycle of a moisture free air restoring breather as claimed in claim

18, wherein the dried air is reutilized in steps (b) and (c) thereby not consuming and enhancing the life of said desiccant(3).