AU2003200081B1 - Containment of high voltage power transformer internal explosions - Google Patents

Description

AUSTRALIA

Patent Act 1990 COMPLETE SPECIFICATION STANDARD PATENT No 2003200081 CONTAINMENT OF HIGH VOLTAGE POWER TRANSFORMER INTERNAL EXPLOSIONS By John Owen Williams The following statement is a full description of this invention, including the best method of performing it known to me.

DESCRIPTION

[001] This invention relates to the containment of high voltage power transformer intemrnal explosions in a secure gasket free contained volume of inert gas at atmospheric pressure, without discharging the explosive forces to atmosphere through bursting discs or pressure plate valves as with existing designs.

[002] This invention has been developed to overcome the problem of intemrnal explosions rupturing h.v power transformers tanks, resulting in the destruction of the transformer and surrounding equipments, cables/busbars by fire.

[003]This invention applies to h.v substation oil filled power transformers with or without conservator tanks, on-load tap changers and oil filled reactors.

[004] When the transformer is provided with a conservator, the conservator is slightly enlarged in diameter and length to form a sealed round pressure vessel where at least 80 percent of it's internal volume will be filled with an inert gas, while the remaining space is taken up by transformer oil.

[005] The conservator is supported by two large diameter pipes of between 100 and 300 mm ID (as an example) which connect from the bottom of the conservator to the side of the transformer tank and where each pipe is provided with a bursting disc at the pipe flange connections. The bursting discs allow the explosive force from a transformer internal explosion to send an oil surge through the Buchholz relay before rupturing the bursting discs and dissipating the explosive force in the conservator gas volume, by which time the Buchholz relay will have disconnected the supply voltage to the transformer.

[006]The conservator is mounted as low down and away from the transformer tank as the Buchholz connection will allow so as to reduce the head of oil above the bursting discs. When this is not possible, the bursting disc flange connections are moved closer to the conservator.

[007] The bursting discs are manufactured from an oil tolerant high grade insulating material and provided with a small oil pressure equalising hole in their centre.

[008] The conservator may also be provided with an oil level top up and drainage connection pipe and valves with ground level access. The one way valve prevents the oil draining while filling the conservator with oil. The one way valve is removed when the connection is being used as a drain, then the valve is sealed with a plug.

[009] The conservator is also provided with two sealing plug connections one to extract the air with a low vacuum and the other to insert an inert gas, both are sealed after the air has been replaced with an inert gas at atmospheric pressure.

[010] Extemrnally mounted bursting discs and pressure plate valves which discharge the explosive forces of a transformer intemrnal explosion to atmosphere are not used in conjunction with the absorption methods described in this invention.

[01 ]When a conservator is not fitted to the transformer, a steel skirt is welded to the underside of the tank top so as to fit neatly inside the tank. The bottom lip of the skirt is immersed in the transformer oil so as to provide a gasket less seal for the gas contents of the skirt. The trapped air within the skirt is removed with a low vacuum while being replaced by an inert gas at atmospheric pressure, the air outlet and gas inlet are then sealed with plugs, thus trapping the gas within the skirt for the life of the transformer.

[012] The depth of the skirt within the transformer tank will depend on the size of the transformer and would be in the region of 100 to 400 mm so as to provide an adequate gas cushion for any transformer internal explosion.

[013] A sight glass is installed on the inside surface of the skirt and another sight glass is installed on the outside of the tank wall so to line up with the skirt sight glass to determine oil levels.

[014] An oil level top up pipe is installed into the tank wall below the oil level so as to bypass the trapped inert gas; The pipe is sealed when not in use.

[015] Further characteristics and advantages of the present invention will become apparent from the following detailed description and the accompanied drawings, wherein: Figure 1 Shows a side view of the conservator, Buchholz relay connection and the large diameter conservator supporting and connecting pipe.

Figure 2 Shows an end view of the conservator, Buchholz relay connection and the large diameter conservator supporting and connecting pipes Figure 3 shows the large diameter pipe flange connection arrangement with the bursting disc.

Figure 4 shows a view of a transformer arrangement where a conservator is not used.

[016] With reference to the above figures, each part is generally designated with a reference numeral which is retained throughout this description and figures.

[017] With reference to Fig 1, the conservator 1 is mounted to the side of the transformer tank 2 with two large diameter pipes 3 which are joined together at the flange connection Fig 3, where the flange connection contains a bursting disc 40 with a hole at it's centre 41 for oil pressure equalisation.

[018] The explosive force of an internal explosion in the transformer tank sends an oil surge through the Buchholz relay 8 before rupturing the bursting disc/s 40 and allowing the full flow of the explosion to travel through the pipes 3 to the conservator 2 where the explosive forces are absorbed by the inert gas. During the collapse of the explosion, oil and gas will be drawn back into the transformer tank, but cannot contribute towards a secondary explosion because of the absence of air.

[019] The bursting discs Fig 3 allow a limited pressure build up in the transformer tank so as to ensure that the Buchholz relay surge element senses an oil surge, in order to trip the voltage supply to the transformer; The bursting discs are manufactured from an oil tolerant high grade insulating material.

[020] Transformer tank 2 in Fig 1 is tilted slightly so that pipe 6 for Buchholz relay 8 is at the highest point of the transformer lid so as to allow any gas that is generated by an intemal fault to quickly find it's way to the Buchholz relay.

[021] An isolating valve 7 in Fig 1 is mounted downstream of the Buchholz relay 8 by a distance of not less than five times the intemal I.D of the pipe, while the upstream isolating valve 9 is mounted not less than three times the pipe I.D from the Buchholz relay so as to ensure a turbulence free flow of oil through the relay during a transformer intemal explosion.

[022] The two large diameter pipes 3 supporting the conservator in Fig 1 2 are further strengthened by steel plates 14 and [023] The conservator is fitted with a combination low oil level switch and oil level gauge 13 which can be read from ground level and also by the substation PLC.

[024] With reference to Fig 3, This shows the pipe flange 43, gaskets 42 and bursting disc 40 arrangement at the joint of each large diameter pipe 3 in Fig 1 2 which connects the conservator to the transformer tank.

[025] Isolating valve 11 and the one way valve 12 in Fig 1 is used for topping up or draining conservator oil. The one way valve allows topping up of the oil level while preventing oil discharging, the one way valve is removed when the connection is used to drain oil from the conservator.

[026] The conservator in Fig 1 2 is constructed as a low pressure pressure vessel where all joins are welded so as to ensure a leak proof construction free from gasket sealing [027] With reference to figure 4, this shows a transformer tank arrangement when a conservator is not fitted. The tank top is shown in the raised position for clarity.

[028] The tank top is shown with a steel skirt 50 welded to it's under side so that it will fit neatly inside the tank 1 when lowered into position. The bottom edge of the skirt 51 is immersed below the transformer oil level 4 and is fitted with a sight glass 55 on it's inside surface so as to be clear of the tank side wall.

[029] A sight glass 54 is also fitted to the outside of the transformer tank wall so as to line up with the sight glass fitted to the skirt, for checking oil levels.

[030] Air is removed from under the skirt area when it is lowered into place by applying a small vacuum to one connection 10, while at the same time inserting an inert gas which will be cooler than the air at the other connection both are then sealed with a plug so as to trap the gas in the skirt at atmospheric pressure for the life of the transformer.

[031] An oil level top up connection pipe 53 is connected to the tank wall below the oil level and provided with a plug to seal the connection when not in use.

[032] The depth of the skirt 30 below the tank top will vary depending on the size and arrangement of the transformer tank and will be in the region of between 100 and 400 mm, while the depth that the bottom of the skirt is immersed in the oil will be around 40 mm so as to compensate for oil temperature differences.

[033] The bottom of the skirt 51 is shown when the tank cover is in place.

[034] Oil level 4 is shown with the tank cover in place and zero gas pressure within the skirt.

[035] Where technical features mentioned in any claim are followed by reference numbers, these reference numbers have been included for increasing the intelligibility of the claims and accordingly, such reference numbers do not have any limiting effect on the interpretation of each element identified by way of example by such reference number.

[036]This invention is susceptible of numerous modifications and variations, all of which are within the scope of this same inventive concept.

Claims (17)

1. Containment of h.v power transformer intemrnal explosions by absorbing them in a secure and contained volume of inert gas at atmospheric pressure without discharging the explosive force to atmosphere is achieved.

2. Containment of h.v power transformer intemrnal explosions in claim 1, by absorbing them within a secure volume of inert gas at atmospheric pressure in the conservator tank (when fitted), through two large diameter pipes 3 which connect between the side of transformer tank and the bottom of the conservator tank and where each pipe is fitted with a bursting disc Fig 3 at the connecting flanges, thus allowing the explosive forces from a transformer internal fault to be directed into the conservator tank.

3. Containment of h.v power transformer intemal explosions in claim 2, where the bursting disc/s Fig 3 allow an oil surge through the Buchholz relay before the bursting disc/s rupture from a transformer intemrnal explosion, thus ensuring that the power supply to the transformer is immediately disconnected.

4. Containment of h.v power transformer internal explosions in claim 2, where the conservator is constructed to form a fully welded gasket free low pressure pressure vessel where the completed assembly is pressure tested after manufacture.

Containment of h.v power transformer intemrnal explosions in claim 2 where the two large diameter pipes 3 connecting the side of the transformer tank to the bottom of the conservator tank are angled so as not to obstruct the flow of explosive forces from the transformer tank to the conservator, or to allow gases from a transformer intemrnal fault to bypass the Buchholz relay 8.

6. Containment of h.v power transformer internal explosions in claim 3, requires that the bursting discs Fig 3 be manufactured from an oil tolerant high grade insulating material and be provided with a small hole at their centre so as to equalise the oil pressure on both sides of the discs, as both pipes will be full of oil.

7. Containment of h.v power transformer internal explosions in claim requires that the conservator tank be mounted as low down and away from the transformer tank as allowable so as to reduce the head of oil above the bursting discs, or alternatively to locate the disc flange connection Fig 3 as close as possible to the conservator 2.

8. Containment of h.v power transformer internal explosions in claim 2, the conservator is fitted with an oil top up/drainage pipe connection with access at ground level and provided with a one way valve to prevent the discharge of oil when topping up the oil level in the conservator with a hand or electric pressure pump, the one way valve is removed when the connection is to be used for drainage.

9. Containment of h.v power transformer internal explosions in claim 2 when the transformer is fitted with an on-load tap changer, the tap changer tank is also be connected to the conservator with a large diameter pipe fitted with a bursting disc inserted at the joining flange.

Containment of h.v power transformer internal explosions in claim 1, also applies equally to oil filled reactors and similar equipment.

11. Containment of h.v power transformer internal explosions in claim 1, where the transformer in not fitted with a conservator, a metal skirt 50 is welded to the underside of the tank lid so that it fits neatly inside the transformer tank 1 with the bottom of the skirt 51 immersed in the transformer oil to form a secure and gasket free inert gas containment area, where the trapped air is removed with a low vacuum and replaced with an inert gas at atmospheric pressure which will be trapped there for the life of the transformer.

12. Containment of h.v power transformer internal explosions in claim 11, a sight glass is fitted on the inside of the skirt so as to be clear of the transformer tank intemrnal wall and another sight glass is installed on the transformer tank outside wall so as to line up with the internal sight glass to allow inspection of the oil levels.

13. Containment of h.v power transformer internal explosions in claim 11, the tank top is provided with valved air outlet and gas inlet connections which are sealed when the air has been removed and replaced with an inert gas at atmospheric pressure.

14. Containment of h.v power transformer internal explosions in claim 11, an oil level top up connection is provided which connects to the side of the transformer tank below the oil level, so as to bypass the gas volume. The top up connection is sealed when not in use.

Containment of h.v power transformer intemrnal explosions in claim 11, the depth of the skirt 51 from the tank top will vary with the size of transformer and would be around 100 to 400 mm in order to safely absorb intemrnal explosions. 7

16. Containment of h.v power transformer internal explosions in claim 11, is achieved without the use of bursting discs and/or pressure plate valves as intemrnal explosions are totally absorbed by the contained gas volume.

17. Containment of h.v power transformer internal explosions in claim 11, also applies to oil filled reactors and similar equipments. John Owen Williams 10 November 2002