MXPA98008783A - Density sensor to monitor the leak rate in the casing of an electrical apparatus with an improved reliability - Google Patents

Abstract

Gas escape rate monitor The heat radiator and upper temperature shield reduce the effects of solar heating so that more accurate pressure density measurements can be taken.

Description

DENSITY DETECTOR TO MONITOR A LEAK PROPORTION OF AN ELECTRICAL EQUIPMENT WITH A RELIABILITY IMPROVED Description of the invention The invention is concerned with a density detector for monitoring a leakage rate of an electrical equipment enclosure filled with pressurized gas, comprising a fixing leg mounted to the exterior in a thickness of the enclosure and communicating with the dielectric gas. An example of application of such detector is constituted by a generator or network circuit breaker mounted in a shielded enclosure or a metal enclosure post, the enclosure contains SF6 sulfur hexafluoride under a pressure of a few bars. The pressure detector is fixed in the enclosure to the outside and allows to monitor the leakage rate of the dielectric gas out of the enclosure by comparing density readings made during the use of the circuit breaker. Minimum leaks are unavoidable, the density tends, after several years of use, towards a lower threshold value of which the operation of the circuit breaker or the equipment is no longer safe. It is then necessary to proceed with an injection of dielectric gas in order to return the value of the density to a nominal value, for example equal to 3.5 bars. The step of the active threshold in REF: 28724 general, "an alarm in order to cause an intervention in the circuit breaker to proceed to the injection of the dielectric gas." The density detector includes a pressure detector and a temperature detector arranged inside of the fixing leg to communicate with the dielectric gas and a measuring head to calculate the density of the gas for all pairs of pressure values P and temperature T acquired at the same time Figure 21 of Figure 1 reports a conducted experiment with the aid of a detector of the type to be described hereinafter.The shielded enclosure is installed in the outdoor use site, which corresponds in an important way to the sites of use of such electrical equipment. in a longitudinal direction that is empirically oriented according to a direction from east to west of the site of use.The density detector is fixed at one end of the envelope, in such a way that it is not exposed to solar radiation more than in the afternoon. The graph 21 of the density calculated for each reading of pressure and temperature values acquired at the same time show two different behaviors of the detector. "" A first behavior is characterized by a flat evolution 21A of the density around the nominal value equal to 3.5 bars and corresponds to readings of pressure and temperature pairs made during the day and in the absence of radiation • » remarkable solar A second behavior, which corresponds to readings made during the day and in the presence of notable solar radiation, is characterized by a daily 2-B variation of the density, during which the density is initially higher than the nominal value, then lower, the point of The transition between positive and negative variations corresponds remarkably to the zenith of the sun. The actual density of SF6 in the envelope remains constant and equal to its nominal value, as shown by the flat evolution reproduced for each day of the readings made in the absence of notable solar radiation. The daily variation of the density in the presence of a remarkable sun represents in reality a measurement artifact. An artifact as such does not prevent monitoring the the leakage rate of the envelope, insofar as it is not easy to retain more than the readings made in the absence of notable solar radiation for the calculation of the density. However, a problem arises when the amplitude of the daily variation of the calculated value of the density during days of remarkable sunlight is less than the density threshold, denoted as 20 in Figure 1. This is particularly the case when the density of the gas contained in the envelope approaches that of the threshold after several years of use, due to leaks inevitable minimums. The passage of the active threshold then an alarm generated by a negative variation of the density calculated by the density detector during the days of remarkable sunshine, which is considered untimely to the extent that the density threshold will not actually be reached before several weeks or several months The object of the invention is a density detector for monitoring a leakage ratio of an enclosure of an electrical equipment having an improved reliability, as opposed to the passage of a density threshold. The basic idea of the invention is to transform the measurement device of the density detector into density variations of values always equal to or greater than the nominal value, in order to prevent any risk of untimely passage of the density threshold. The object of the invention is a density detector for monitoring the leakage rate of a housing of electrical equipment filled with a dielectric gas under pressure, comprising a fixing leg mounted to the outside in the thickness of the enclosure and communicating with the dielectric gas. , characterized in that a radiator is arranged around the fixation leg of the density detector.When ensuring a thermal exchange between the fixation leg of the density detector and the environment of the enclosure, which generally consists of atmospheric air, the radiator modifies the thermal equilibrium of the temperature detector and the dielectric gas in such a way that it transforms the variations it is negative and then positive of the calculated density, during the days of sunny notable to only positive variations. As a result, all risk of the untimely passage of a density threshold due to a measuring device generated by readings made in the presence of a remarkable sunlight is eliminated. It will be noted that the only positive variations of the density calculated by the detector according to the invention, during readings made in the presence of a remarkable sunlight, are still limited in amplitude against a leak that will be detected by the detector of "density with a Likewise, the amplitude of the positive variations has no detrimental effect on the passage of a higher threshold of the density of the envelope Other features and advantages of the invention will appear from the reading of the description illustrated by the drawings. 1 shows two graphs of density readings made with the aid of a density detector without a radiator and, on the other hand, with the aid of a detector according to the invention.

Figure 2 is a schematic view of an enclosure of an electrical equipment on which a density detector according to the invention is fixed. Figure 3 is an enlarged view of a density detector according to the invention. The invention is concerned with a density detector for monitoring a leakage ratio of an enclosure of an electrical equipment filled with a dielectric gas under pressure, comprising a fastening leg mounted to the outside in the thickness of the enclosure and communicating with the enclosure. dielectric gas. A density sensor 5 and an enclosure 3 of the dielectric equipment are shown in FIG. 2. The electrical equipment is for example a mains circuit breaker or a generator circuit breaker or a metal enclosure post and is arranged in enclosure 3 in which the dielectric gas 7, for example SF6 is injected at a pressure of about 3.5 bars. The enclosure 3 has a central body 3C of cylindrical shape and is closed by two opposite covers 3A and 3B screwed to the central body 3C. The density detector 5, equally visible in figure 3, is of a known type and schematically comprises a cylindrical fixing leg 5B assembled from a measuring head 5A and ends at the other end in a threaded tube 5C to be screwed into a duct 9 formed in the thickness from enclosure 3 and to communicate with the dielectric gas. The density detector is mounted * to the outside in the enclosure and tightened by means of a 5D bolt. A pressure sensor and a temperature sensor are housed in the fixing leg 5A and reach out of the threaded tube 5C through a protective tube 5E and communicate with the dielectric gas 7 contained in the conduit 9 of the envelope 3. The two pressure and temperature sensors are connected to the measuring head 5A of the density detector to which a signal representative of the detected pressure P and the detected temperature T is fed respectively. An integrated electronic circuit in the measuring head 5A allows determine a density valueFor each pair of pressure and temperature values "detected simultaneously, with the help of a dielectric gas state equation, each value of the density is transmitted to a monitoring unit, which compares it with a lower threshold value and with a higher threshold value and which triggers an alarm in the event that one of the thresholds is exceeded by a density value In accordance with the invention, a radiator is arranged around the fixing leg of the density detector. In FIGS. 2 and 3 a radiator 11 is shown which is "composed of two parts HA and 11B each having four identical fins 11C for increasing the heat exchange surface between the radiator and the ambient air. The two parts HA and 11B have a semi-cylinder 11D in depression to be mounted adhered around the cylindrical fixing leg 5B with the help of two mounting screws 13 and 15 that traverse the two parts 11A and 11B by means of two holes or holes 13A, 13B and 15A, 15B. In figure 2, it is shown that the radiator 11 is mounted around the fixing leg 5B while it is in contact with the pressure screw 5D to influence the thermal exchanges that take place between the temperature detector and the dielectric gas contained in the duct 9. Figure 1 shows a graph 23 of density values calculated by the density detector according to the invention, from each pair of pressure and temperature values detected simultaneously. The graph 21 described above is also shown. On the one hand, it is seen in 23 that "the radiator does not modify the behavior of the detector for readings of values carried out in the absence of noticeable solar radiation." This first result allows the density detector according to the invention to be used to monitor a ratio of leakage of the envelope by not retaining more than the readings made during the day and in the absence of noticeable solar radiation.On the other hand, it is seen that the second behavior of the density detector is modified by the readings made in the presence of remarkable sunlight, in the sense wherein the density values provided by the detector according to the invention are always equal to or greater than "the actual value of the density, with a variation 23B increasing in the morning and a decreasing variation after noon. An explanation among others is proposed to explain the behavior of the density detector according to the invention. It is known that the measurement of the temperature simultaneously with that of the pressure allows, by a temperature compensation, to release pressure drops that do not result in a loss of mass or leakage of the dielectric gas out of the shell, but only a contraction of the dielectric gas under the effect of a decrease in its temperature. However, the "temperature compensation of the pressure is not valid except on the condition that the decrease in temperature is quite large compared to the temperature deviation that inevitably exists between the temperature measured by the temperature detector and the actual temperature of the temperature. dielectric gas in which this detector is submerged and in the vicinity of which the pressure sensor measures the pressure.If the temperature measured by the temperature detector is higher than the actual dielectric gas temperature, the density detector calculates, when compensating the pressure measured by the measured temperature, a density value less than the actual density, and if the measured temperature is lower than the actual dielectric gas temperature, the density detector calculates a density value by compensating the temperature. greater than the real density In the experiment reported in Figure 1, the temperature detector exchanges heat with the gas and with the fixation leg of the detector, which is mounted in the thickness of the enclosure. In this way, a thermal equilibrium between the detector and the dielectric gas is influenced by the fixing foot and by the enclosure. In the absence of sunlight, the enclosure and the fixation leg have only a negligible influence on the thermal equilibrium of the dielectric gas and the temperature detector, so that the measured temperature is sufficiently close to the actual temperature of the dielectric gas. what the density detector calculates a density value that is remarkably true to the real value, it is expected that under these conditions, the radiator placed around the fixing leg and in the vicinity of the enclosure does not provide any thermal effect other than by itself This is what can be observed in graphs 21A and 23A for readings made during the day and in the absence of noticeable sunlight.In the presence of remarkable sunlight, the fixation foot and the enclosure alter the thermal equilibrium between the temperature detector and the dielectric gas in a different way according to the period of the day considered.In the mornings, the density detector is submerged in the shade, so that the fixing leg and consequently the temperature detector with which it is in contact, heat up faster than the dielectric gas that absorbs the heat that gives the envelope itself exposed to solar radiation. The heating rate of the detector and the fixing leg is still reduced by the presence of the radiator, which evacuates the heat given by the dielectric gas into the ambient air. Where it results that the temperature measured psr the temperature detector is lower than the actual temperature of the dielectric gas, leads to the density detector to provide a density value greater than the actual value, the deviation is accentuated by the presence of the radiator, as shown by the positive variations of the graphs 21B and 23B of figure 1. After noon, the detector that is introduced to the shadow is progressively exposed to solar radiation. Its temperature, as well as that of the temperature detector with which it is in contact, soon rises faster than that of the dielectric gas, due to the difference in thermal inertia between the dielectric gas, the fixing leg and the detector. The result of this is that the density detector provides a density value that is lower than the value of the real density, as shown in figure 21. In the presence of the radiator, the temperature rise of the fixing leg and of the detector is diminished by the evacuation in the ambient air, of the heat provided by the envelope itself exposed to solar radiation.The heating of the fixation leg and of the detector is diminished by the radiator so that the temperature of the latter does not reach It is higher than the actual temperature of the dielectric gas during the afternoon.The density provided under these conditions remains equal to or greater than the actual density, as can be seen in Figure 23B, In accordance with an advantageous embodiment of the invention, the The density detector is provided with a cover for protection against solar radiation, and in FIGS. 2 and 3, a fixed cover 17, constituted, for example, of a metallic reflector material, is fi the radiator 11, - "by means of screws 13 and 15, to reflect the solar radiation reaching the detector and a part of the solar radiation reaching the enclosure near the conduit 9 on which it is mounted. The screws 13 and 15 are preferably made of a low heat conducting material, for example Nylon, to thermally insulate the radiator cover. In this embodiment, it is observed that the cover reinforces the effect of the radiator, insofar as the density values calculated from readings made "in the presence of a remarkable sunlight are superior to those of the density detector provided in absence Therefore, it is considered to optimize the number of fins of the radiator to obtain a behavior of the density detector in the presence of the cover, remarkably equivalent to a behavior in the absence of the cover. Finally the orientation of the envelope according to a direction from east to west of the installation site represents an exposure to solar radiation that is more unfavorable than any other orientation, so that the results of figure 1 constitute an example of application particularly interesting but not limiting of the density detector according to the invention. It is noted that, in relation to this date, the best method known by the applicant, to bring the said invention into practice, is the conventional one for the manufacture of the objects to which it relates. preceding, property is claimed as contained in the following

Claims (3)

1. Claims 1. A density detector for monitoring a leakage ratio of an enclosure of an electrical equipment filled with a dielectric gas under pressure, comprising a clamping leg mounted to the outside in the thickness of the enclosure and communicating with the dielectric gas , characterized in that a radiator is arranged around the fixing leg of the density detector.
2. 2. The density detector according to claim 1, characterized in that a cover is disposed above the radiator.
3. 3. The density detector according to claim 2, characterized in that the cover is fixed to the radiator by means of screws made of a material that is not very hot.