Gas separation: apparatus – Apparatus for selective diffusion of gases – Membrane to degasify liquid
Reexamination Certificate
2000-06-09
2002-05-21
Bushey, C. Scott (Department: 1724)
Gas separation: apparatus
Apparatus for selective diffusion of gases
Membrane to degasify liquid
C096S413000, C096S417000, C073S019020, C073S023420
Reexamination Certificate
active
06391096
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to apparatus and methods for removing dissolved gases from liquid and for routing the removed gases to analytical instruments for analysis. More particularly, this invention is embodied in apparatus and method for extracting gases dissolved in electrical insulating oils, and for detecting and analyzing those gases.
BACKGROUND OF THE INVENTION
The electric power industry has for many years recognized that certain electrical and thermal phenomena that occur in oil-insulated electrical apparatus can lead to the generation of a number of “fault gases.” These phenomena occur in equipment such as oil filled transformers (both oil-filled and gas-blanketed types), load tap changers, current transformers and bushings and the like. The presence of fault gases may be a measure of the condition of the equipment. As such, detection of the presence of specific fault gases in electrical apparatus, and quantification of those gases can be an important part of a preventative maintenance program.
The presence of fault gases in oil-blanketed transformers and other devices has well documented implications relating to the performance and operating safety of the transformer. There is a substantial body of knowledge available correlating the presence of gases with certain, identified transformer conditions and faults. It is therefore beneficial to monitor the condition of dielectric fluids in electric equipment as a means to maximize performance, and at the same time minimize wear and tear on the equipment, and to thereby minimize maintenance costs and down time. Thus, information relating to the presence or absence of certain fault gases in transformer oil can lead to greatly increased efficiency in the operation of the transformer.
As an example, it is known that the presence of some kinds of fault gases in transformer oil can be indicative of transformer malfunctioning, such as arcing, partial or corona discharge. These conditions can cause mineral transformer oils to decompose generating relatively large quantities of low molecular weight hydrocarbons such as methane, and some higher molecular weight gases such as ethylene and ethane. Such compounds are highly volatile, and in some instances they may accumulate in a transformer under relatively high pressure. This is a recipe for disaster. Left undetected or uncorrected, these volatile gases can lead to an increased rate of degradation, and even to catastrophic explosion of the transformer. Transformer failure is a significantly expensive event for an electric utility, not only in terms of down time and the costs of replacement equipment, but also in terms of the costs associated with lost power transmission. On the other hand, by closely monitoring dissolved gases in transformer oil, the most efficient operating conditions for a given transformer can be actively monitored and the transformer load may be run at or near a maximized peak. Moreover, when dangerous operating conditions are detected the transformer can be taken off line for maintenance.
Despite the known need for reliable equipment to monitor gas in oil, designing equipment has been problematic for a variety of reasons. There have been many attempts to solve the problems associated with transformer gas-in-oil monitoring, but none of them ideal. Some electrical utilities routinely sample transformer oil in the field, extract gas sample aliquots and return the samples to laboratories to run dissolved gas analysis, often with laboratory GCs. Sometimes portable field GCs can be used, as well. But these methods do not give real-time analysis and may result in data that is not a true measure of actual, ongoing operating conditions. Moreover, physical sampling cannot be done on a continuous, ongoing basis, and instead requires scheduled visits. Sample analysis and historical data are thus based on widely intermittent sampling protocols rather than continuous sampling. But an intermittent sampling protocol may entirely miss a substantial transient transformer fault. That is, it is unlikely that the timing of an intermittent sampling will correlate with a specific fault event. Moreover, it is well known that each transformer tends to have a unique set of operating conditions and tends to run under certain conditions unique to that transformer. In essence, each transformer has a set of normal operating conditions that are unique to that unit. Knowledge of a transformer's normal operating conditions allows for accurate prediction and analysis of when a certain out-of-normal condition is a true fault condition or an event that might be expected. With periodic sampling it is all but impossible to develop an accurate operating profile for each transformer.
One practical result of such difficulties in such sampling and other factors has been that, out of safety and maintenance concerns, many commercial power transformers are run at loads that are significantly less than the transformer is capable of handling. Alternately, transformers are run at loads closer to their operating maximum without sufficient information about the existence of possible dangerous conditions, which could lead to catastrophic failure. This protocol for operating transformers is inefficient, expensive and in some cases dangerous.
Mechanical/vacuum and membrane extraction methods and apparatus for degassing transformer oil are also well known in the art. As one example, U.S. Pat. No. 5,659,126 discloses a method of sampling headspace gas in an electrical transformer, analyzing such gases according to a temperature and pressure dependent gas partition function, and based on the derived analysis predicting specific transformer faults. An example of a gas extraction apparatus that relies upon a membrane for extraction of gas from transformer oil is disclosed in U.S. Pat. No. 4,112,737. There, a probe having a plurality of membrane tubes is inserted directly into transformer oil in the transformer housing. The material used for the membrane is impermeable to oil, but gases dissolved in the oil permeate through the membrane into the hollow interior of the tubes. A portable analytical device such as a portable gas chromatograph is temporarily connected to the probe so that the test sample is swept from the probe into the analytical device for analysis.
Although these devices have provided benefits, there are numerous practical problems remaining to the development of reliable apparatus for extraction, monitoring and analysis of fault gases in transformer oils. Many of these problems relate to the design of reliable fluid routing systems that are redundant enough to provide a relatively maintenance free unit. Since transformers are often located in exceedingly harsh environmental conditions, fluid routing problems are magnified. This is especially true given that the instruments needed to reliably analyze the gases are complex analytical instruments.
Many chemical analytical instruments rely upon controlled and accurate fluid flow through the instrument during analytical processing. Such instruments include machines designed to perform chemical analysis of various types, purify samples and to perform monitoring of various aspects of laboratory and commercial processing. To name just a few of the types of analytical instruments in which precise fluid flow is a critical part of the functioning of the machines, there are gas chromatographs (GCs) of numerous types, spectrophotometers of many kinds, and many other similar instruments. Gas chromatographs, for example, rely upon accurate control and processing of known quantities of fluid flowing through separation columns during the analytical processing. Without accurate control of fluid flow, analytical results are compromised.
In a GC the fluid is in the form of gas. Samples of fluid under test are typically under the control of control devices such as pumps, valves, pressure transducers and pressure regulators. The control devices help in the acquisition of samples, and the isolation, handling and separation of the samples dur
Bushnell Raymond
Waters Thomas
Bushey C. Scott
Ipsolon LLP
Serveron Corporation
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