US2960672A - Transformer - Google Patents

Description

1960 J. KOWATSCHITSCH ETAL 72,960,672

TRANSFORMER Filed May 18, 1959 III III III] III/ II,

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INVENTORS JOSEF KOWATSCHITSCH a ALFRED LEHMANN AGENT United States PatentO TRANSFORMER Josef Kowatschitsch and Alfred Lehmann, Weiz, Styria,

Austria, assignors to Elin Aktiengesellschaft fiir elektrische Industrie, Vienna, Austria Filed May 18, 1959, Ser. No. 813,835

Claims priority, application Austria May 21, 1958 1 Claim. (Cl. 336-58) This invention relates to electrical transformers and more particularly to an exhaust valve ventilating gas bubbles resulting from tap changing under load.

It is a known method to protect the oil in a transformer tank or in its expansion tank above the tank by filling the space above the oil level with an inert gas, usually nitrogen, preventing in such a way the deterioration of the oil quality by absorption of oxygen, hydrogen and moisture from the outside air. In transformers being adjustable under load, furthermore, it is known to sep arate the oil in the transformer tank from the oil of the transfer switch as this latter oil may be contaminated by the effects of the switching arc (gas bubbles, contact burning off). If the on-load tap changers are incorporated in the transformer unit, as usual, the selector switch and the transfer switch are assembled into one tube-shaped unit which is sunk into the transformer tank. The transfer switch, however, is contained in a separate oil-tight enclosure to prevent communication of the transformer oil with the oil of the transfer switch. For the same purpose, the expansion tank contains a separate compartment for the expansion of the transfer switch oil. Gases due to the switching arc may escape through this compartment to the open. This contact of the transfer switch oil with the outside air, however, is disadvantagzous by two reasons. First of all, it is diflicult to seal the transfer switch compartment against the surroundlng transformer oil to a satisfying extent, because the gas pressure resulting from fluctuations in oil temperature (caused by load variations) may rise considerably so that an overflow of tank oil into the transfer switch compartment may always occur. Of late there is moreover a trend to protect also the transfer switch oil from absorption of oxygen, hydrogen and moisture from the outside air. Therefore, also the oil level in the expansion tank compartment belonging to the on load taps changer has been covered with an inert gas by providing an opening in the dividing wall of the expansion tank lying above the maximum oil level, enabling in such a way to access of the inert gas from the expansion tank compartment be'onging to the transformer tank to the oil level of the transfer switch. In doing so also the transfer switch oil is protected from the access of oxygen, hydrogen and moisture. Likewise the pressure differences between the transformer tank and the transfer switch compartment are equalized. It is a disadvantage, however, that in such a case the gas bubbles resulting from the switching are mix with the inert gas and soil it and influence the rate of pressure of the inert gas cushion.

Therefore it is the object of this invention to show a way for ventilating gas bubbles resulting from tap changing under load Without the above indicated disadvantages.

This invention will be better understood from the following description taken in connection with the accompanying drawing.

In the drawing Fig. 1 is a simplified view illustrating a transformer tank (partly represented only), its expansion 2,960,672 Patented Nov. 15, 1960 tank (likewise partly represented only) and the connecting pipes between the tank and the expansion tank. Fig. 2 shows the ventilating valve on an enlarged scale.

Referring now to the drawing and more particularly to Fig. 1 there is shown therein a transformer tank 1 receiving the active parts of the transformer 2 (core and windings) and the on-load tap changer consisting of selector switch 3 and transfer switch 4. As indicated, the transfer switch 4 is enclosed in a separate casing whilst the selector switch is surrounded by the transformer tank oil, as a rule. The expansion tank 5 is subdivided by a wall 6 into a compartment for the transformer tank oil and a smaller compartment for the transfer switch oil. 7 is the oil pipe from the expansion tank to the transformer tank and 8 is the oil pipe to the transfer switch casing. In accordance with this invention, an exhaust valve 9 is inserted into the latter. The wall 6 dividing the expansion tank has an opening above the highest oil level that might be reached. The space 10 of the expansion tank above the oil level is filled in known manner with an inert gas having a fluctuating pressure.

In Fig. 2 which shows the exhaust valve according to this invention in section on an enlarged scale, 11 indicates a float chamber. This float chamber is inserted into the oil pipe 8 to the transfer switch by flanges 12, 13, and that in such a manner that gas bubbles coming from the transfer switch casing gather in the upper part of the float chamber. 14 is a float the buoyant force of which in the oil is transmitted by an one-armed lever 15 to a valve disk 16. The latter is guided in a valve casing 18 fixed to the cover 17 of the float chamber 11 and cooperates with the valve case 19. An outlet connecting piece 21 is fitted to the valve case 19 by the screw cap 20. 22 is a guiding rod for the float and 23 an oil gauge atttched to the float chamber. As it is seen from the drawing, the buoyant force of the float is geared into a high contact pressure of the valve disk.

The operation of the exhaust valve according to this invention is as follows. Before a stepping action, the oil level in the float chamber may stand as high as indicated by the level marker (V) in Fig. 1). With such an oil level the float is subjected to a certain buoyant force. The latter acts in a geared rate upon the valve disk and closes the valve. Supposing that gas bubbles result from a stepping action, the gas bubbles will gather in the upper space of the float chamber and will depress the oil level. In doing so the buoyant force becomes lower. If the oil level has sunk sufliciently so that the weight of the swimmer exceeds the buoyant force the valve opens and lets out so many of the gathered gas bubbles that the oil level existing before the switching action is restored and the outlet valve closes again.

In this way it is avoided that gas bubbles resulting from switching reach the expansion tank compartment belonging to the transfer switch. Therefore, the cushion of inert gas may be common for both the expansion tank compartments without running the risk of deteriorating the inert gas and influencing the pressure in the gas cushion. Furthermore, in doing so equal pressure is reached in the transfer switch casing and in the transformer tank, and therefore, the difliculties with regard to the sealing of the transfer switch casing against the surrounding transformer oil are minimized. There is avoided, moreover, the loss of inert gas resulting from the blowoff of the mixture of the switching gas and the inert gas being necessary from time to time if the switching gas mixes with the protecting inert gas.

What is claimed as neW and desired to secure by Letters Patent of the United States is:

In combination a transformer tank including a transformer core and its windings, an on-load tap changer sunk in said transformer tank consisting of the selector switch and the transfer switch, the latter being enclosed in a sep arate casing, an expansion tank subdivided by a wall into one compartment for the transformer tank oil and one compartment for the oil of the transfer switch casing, the space over the oil levels in said expansion tank compartments being filled with an inert gas, oil pipes leading from the transformer tank and the transfer switch casing to the expansion tank, an exhaust valve being inserted into the oil pipe leading from the transfer switch casing to the expansion tank, for exhausting gas bubbles ascending 10 from the transfer switch casing, said exhaust valve con- References Cited in the file of this patent UNITED STATES PATENTS 2,915,720 Mueller Dec. 1, 1959 FOREIGN PATENTS 162,526 Austria Mar. 10, 1949

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