Oil-immersed Transformer Gas Analysis

Abstract

A sampling and testing device for diagnosing a condition of a dielectric fluid in an electrical apparatus, e.g., an oil-immersed transformer, by sampling dielectric liquid from the apparatus and extracting dissolved gases from the sampled dielectric fluid and subjecting the extracted gases to analysis for composition so as to infer the condition of the dielectric liquid therefrom. The device employs a cylinder disposed as part of the electrical apparatus, said cylinder having an inlet valve to draw dielectric liquid samples by vacuum. Gases that may have been generated and dissolved in the sampled dielectric liquid because of local heating or electrical arcs and faults within the electrical apparatus, are liberated by creating partial vacuum in the cylinder, in a closed condition thereof. Gases so extracted are conveyed through a controllable gas outlet valve on the cylinder into a gas analyzer for analysis of gas-composition so as to infer the condition of the liquid dielectric therefrom. Dielectric liquid sampled from the electrical apparatus is returned thereto in a closed circuit. Said cylinder comprises a piston including a flange portion which is expediently provided with a plurality of apertures connecting opposite sidefaces of the flange portion, whereby, during an outward stroke of the piston, dielectric liquid is ejected out of the apertures forcibly thereby facilitating degasification of the dielectric sample within the cylinder.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a device for treating an insulated fluid, e.g., oil, contained in an oil-immersed electrical apparatus, e.g., transformer, by analyzing gas resolved in the oil.

In a case when an abnormal phenomenon such as arcing and local overheating are caused in electrical apparatus having a liquid dielectirc, e.g., an oil-immersed transformer, the insulating oil or solid insulation material in the vicinity of the source of said abnormal phenomenon is decomposed into gas. The thus produced gas is in such a state that it is resolved in the oil contained in the transformer during an initial period of the abnormal phenomenon. Therefore, if the dissolved gas is extracted out of the oil and is analyzed for its components, the nature and degree of the abnormal phenomenon or fault can be inferred therefrom. Accordingly, any necessary damage-protecting countermeasure can be taken before significant damage is caused to the transformer. The method of deducing the abnormal condition of the transformer from the components of the gas thus analyzed is considered a superior method for determining the condition of the transformer in order to make an early diagnosis of an internal fault.

Description of Prior Art

However, in the conventional method of analyzing the gas components, a quantity of oil necessary to extract dissolved gases for analysis, is sampled into an oil-sampling container out of the transformer at the site where the transformer is installed, and then the sampled oil is brought to a laboratory where the degasification and gas analysis are conducted on the oil, and the oil thus tested is abandoned.

This conventional method for gas analysis has however the following disadvantages: First, at the step of sampling the oil, it is required for the oil not to be in contact with the air as much as possible in order that the ambient air does not further contaminate the sample, or the oil in the transformer itself. Further, when it is required to detect variations in the composition of gas extracted at short intervals of time, the prior art conventional methods would not work since they employ laborious and time-consuming operations. Next, it is to abandon the used sample oil or degasfied oil after every test.

SUMMARY OF THE INVENTION

It is therefore an essential object of the present invention to provide a device adapted to sample out an amount of liquid dielectric, e.g., oil, for analysis from an electrical apparatus having a liquid dielectric, e.g., an oil-immersed transformer, by a simple operation within a short time. An exemplary electrical apparatus on which the device of the invention is applied is hereinafter referred to as an oil-immersed transformer.

Another object of the present invention is to provide a device for diagnosing the condition of the oil contained in an oil-immersed transformer, in which no oil is lost or wasted.

A further object of the present invention is to provide a device testing oil contained in an oil-immersed transformer, which device can be also used as a degasification device.

The foregoing objects and other objects are achieved by provision of a device, wherein dissolved gas obtained through digasification from the oil extracted sampled out of an oil-immersed transformer is analyzed, and the oil taken out from the transformer is circulated back to the same transformer.

The nature, utility and principle of the present invention will be more clearly understood from the following detailed description when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is a schematic diagram of a device for treating oil, according to the present invention, in which a cylinder device SD is shown by a cross-sectional view along its longitudinal axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawing, there is shown an oil-immersed transformer Tr having an oil-circulation system. In the oil-circulation system, oil is circulated from an oil outlet port provided on the transformer through a first check valve V.sub.1, a cylinder device SD, a second check valve V.sub.2, and an oil inlet port provided on the transformer leading to the inside of the transformer Tr. The cylinder device SD comprises a cylinder 13 and a piston valve 14, said cylinder 13 being provided with an oil-inlet port 11 and an oil-outlet port 12, both being located at the upper portion of the cylinder 13. The piston valve 14 is installed slidably inside of the cylinder 13. A gas outlet port 15 is provided at the center of the upper portion of the cylinder 13, said gas outlet port 15 being constructed so as to introduce the extracted gas contained in the transformer through a gas check valve V.sub.3 to a gas analyzer GC which may be a conventional type. The piston rod valve 14 comprises a piston portion 141 and a valve flange member 142, said piston rod portion 141 being adapted to form the lower part of the piston valve 14 and being made to be smaller in diameter, while said valve flange member 142 has a greater diameter substantially equal to the inside diameter of the cylinder 13. Sealing conditions are maintained between the cylinder 13 and the valve flange member 142, and between the cylinder 13 and the piston portion 141 by O-rings 16 and 17, respectively, said O-ring 16 being provided on the periphery of the valve flange member 142, while the other O-ring 17 being is arranged at an opening provided at the bottom of the cylinder 13. The piston valve 14 is provided with several apertures 143 which communicate the upper portion of the piston rod portion 141 with the upper surface of the valve member 142.

The operation and action for analyzing gas resolved in the oil contained in the transformer Tr will be hereinafter described in connection with the above-described device.

First of all, the gas check valve V.sub.3 is closed, and the check valves V.sub.1 and V.sub.2 are opened, and then the piston valve 14 is reciprocated by a piston driving mechanism (not shown) in axial directions as shown by arrow marks. As a result, oil is sucked into the cylinder 13 from the inside of the transformer Tr through the check valve V.sub.1 and oil-inlet port 11 when the piston valve 14 is moved downwardly; and the oil is pushed into the transformer through the oil-outlet port 12 and check valve V.sub.2 during the course in which the piston valve 14 is moved upwardly up to a position shown by dot-dash line P. Therefore, by repeating the reciprocating motion of the piston valve 14, oil in the transformer Tr can be circulated through a closed oil circulation path, namely, transformer Tr-check valve V.sub.1 - cylinder device SD - check valve V.sub.2 - transformer Tr. Even if the oil used for the previous test sill remains in the device SD before operation of the device, the oil can be replaced with the oil contained in the transformer Tr. When the device SD has been thus completely and newly filled with the oil, the piston valve 14 is stopped once at a certain position, for instance, the position shown by a dot-dash line P so that a certain amount of the oil is left inside the device SD, and then the check valves V.sub.1 and V.sub.2 are closed. Now, if the piston valve 14 is moved downwardly from the position P at the same time maintaining all the valves V.sub.1, V.sub.2 and V.sub.3 in closed states, a vacuum tends to be created above the oil surface on the piston valve 14 inside the cylinder 13. At the same time, pressure in a chamber B formed by the piston portion 141 of the piston valve 14 inside the cylinder 13 is increased, as a result of which the oil in the chamber B is ejected to the upper surface of the piston valve 14 through the apertures 143 and at the same time the gas contained in the oil is liberated into the vacuum. When the piston valve 14 has reached a predetermined lower limit position in the degasification process, the check valve V.sub.3 is opened, the piston valve 14 is moved to the position P thereby to introduce the extracted gas to the gas analyzer GC, and a part of the oil present on the piston valve is led through the apertures 143 to the chamber B. Then, if the piston valve 14 is pulled downwardly again, gas contained in the oil is discharged out, as apparent from the above-described operation. The reciprocatory operation of the piston and the valve operation is repeated as required thereby to introduce the extracted gas to the gas analyzer GC whereupon the gas analysis performed by well known method is indicated by an indicator, recorded by a recorder, or properly processed as required.

The oil sampling and degasification can be carried out even without apertures 143 provided on the piston valve 14, but provision of said holes 143 surely improves the degasification since they produce the agitation and an ejection action of the oil.

The gas analyzer GC may be formed integrally with the cylinder device SD, its driving mechanism and the check valves; or may be provided separately as shown in the drawing so that piping and connections may be arranged as required to suit particular requirements. It is preferable to replaceably arrange a filter made of silica gel in series with the check valve V.sub.3 in order to screen certain components still contained in the gas separated from the oil.

The piston valve 14 of the device SD may comprise a bellows construction. In this case, the sealing construction arrangement will become more simple.

The devices according to the present invention can be formed into one unit thereby to cause possibility of assembling said unit with the transformer. Moreover, since the cylinder device and the check valves may be a motor or electromagnetic type, it is possible to carry out automatically a series of operations from oil sampling to gas analyzing within a short period of time by merely depressing a start push button of the device. In addition to the above advantage, the device can be constructed relatively simple, as a consequence of which, when compared with the previously mentioned conventional method in which oil sampled into a oil-sampling container which is brought to the laboratory for test, the present invention provides a novel method which is greatly improved in serviceability and quickness. Moreover, the result of analysis of gas contained in the oil can be known immediately at the site where the transformer is installed, and therefore, according to the result of the gas analysis, any suitable necessary countermeasure can be taken without dealy in order to prevent damage to the transformer. It is one of the characteristic features of the cylinder device of the invention that it can manage the functions of oil-return sampling, degasification, and oil into the transformer by means of a simple construction. In particular, the oil in the transformer may be degassed and purified in case where the device is operated with the transformer.

It is intended that all matter contained in the foregoing description and in the drawing shall be interpreted as exemplary and illustrative only not as limitative of the invention.

Claims

I claim:

1. A sampling and testing device for diagnosing a condition of a dielectric liquid in an electrical apparatus, the electrical apparatus having an outlet and an inlet for allowing said liquid to pass out of and into said apparatus respectively, said device comprising in combination with said dielectric liquid containing electrical apparatus: cylinder means; closable liquid inlet valve means of said cylinder means, said liquid inlet valve means being connectable to said outlet of said electrical apparatus for letting in dielectric liquid from said electrical apparatus into said cylinder means; closable liquid outlet valve means of said cylinder means, said liquid outlet valve means being connectable to said inlet of the electrical apparatus for returning dielectric liquid from said cylinder means to the electrical apparatus; closable gas outlet valve means of said cylinder means; gas analyzer means connected to said closable gas outlet valve means; piston means operating within said cylinder means for selectively causing one of pressurization and vacuum within said cylinder means, so that when said closable gas outlet valve is closed, said piston means operates to cause said dielectric liquid to flow to and from said cylinder means to said electrical apparatus in a closed circuit through said liquid outlet valve means and said liquid inlet valve means and when said closable liquid outlet valve means said liquid inlet valve means and said gas outlet vavle means are closed in a state wherein a sample of dielectric liquid from said electrical apparatus remains in said cylinder means, said operating piston means causes vacuum in said cylinder means during an outward stroke thereof, thereby liberating dissolved gases from said sample of dielectric liquid said gas outlet valve means being opened to allow said liberated gases to be conveyed therethrough for analysis of composition in said gas analyzer during an inward stroke of said piston means.

2. A sampling and testing device as claimed in claim 1 wherein said piston means comprises a piston rod and a flange portion having at least one aperture through a thickness of the flange portion said aperture facilitating easier liberation and extraction of dissolved gases from said sampled liquid dielectric contained in said cylinder means during said outward stoke of said piston means.

3. A device for detecting abnormal conditions of an oil-immersed transformer having an oil-outlet port and an oil-inlet port, by extracting gas dissolved in the oil of the oil-immersed transformer and by analyzing the components of the extracted gas, comprising in combination with said oil-immersed transformer: a cylinder device having a cylinder provided with an oil-inlet port; an oil-outlet port and a gas-outlet port; piston means disposed in said cylinder; a gas analyzer connected to said gas-outlet port, said oil-inlet port and oil-outlet port being respectively connectable to said oil-outlet port and said oil-inlet port of the oil-immersed transformer through a first check valve and a second check valve, said gas-outlet port being connectable through a third check valve to the gas analyzer, wherein, when the first and second check valves are opened and the third check valve is closed said piston means reciprocally operates to circulate the oil of the transformer through said cylinder device and when the first, second and third check valves are closed said piston means reciprocally operates to provide partial vacuum in said cylinder so that the gas dissolved in the oil within said cylinder device is separated, and thereafter the third check valve is opened so that the gas separated in the cylinder is introduced to the gas analyzer by the movement of said piston means.

4. A device for detecting abnormal conditions of an oil-immersed transformer, as claimed in claim 3, in which said piston means comprises a flange portion which is in liquid-tight contact with an inside surface of said cylinder and a piston rod-portion smaller than said flange portion in diameter so as to form a space with an inside surface of the cylinder, said flange portion being provided with at least one aperture which penetrates therethrough thereby to communicate with said space inside of the cylinder.