CA1149901A - Leak detector for vaporization cooled transformers - Google Patents
Leak detector for vaporization cooled transformersInfo
- Publication number
- CA1149901A CA1149901A CA000349247A CA349247A CA1149901A CA 1149901 A CA1149901 A CA 1149901A CA 000349247 A CA000349247 A CA 000349247A CA 349247 A CA349247 A CA 349247A CA 1149901 A CA1149901 A CA 1149901A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- heat exchanger
- coolant
- transformer
- tank
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/40—Structural association with built-in electric component, e.g. fuse
- H01F27/402—Association of measuring or protective means
- H01F2027/406—Temperature sensor or protection
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- Housings And Mounting Of Transformers (AREA)
Abstract
LEAK DETECTOR FOR VAPORIZATION COOLED TRANSFORMERS
ABSTRACT OF THE DISCLOSURE
A vaporization cooled transformer of the type comprising a transformer tank in combination with a heat exchanger employs temperature sensing means in both the tank and the heat exchanger for sensing a predetermined temperature differential to indicate the presence of air in the transformer. When the tem-perature differential exceeds a predetermined range, an alarm and a transformer disconnect relay become actuated. The temperature differential sensor can also be calibrated to provide excess moisture indication above a threshold moisture content caused by the saturation of the molecular sieve water scavenger within the transformer assembly.
ABSTRACT OF THE DISCLOSURE
A vaporization cooled transformer of the type comprising a transformer tank in combination with a heat exchanger employs temperature sensing means in both the tank and the heat exchanger for sensing a predetermined temperature differential to indicate the presence of air in the transformer. When the tem-perature differential exceeds a predetermined range, an alarm and a transformer disconnect relay become actuated. The temperature differential sensor can also be calibrated to provide excess moisture indication above a threshold moisture content caused by the saturation of the molecular sieve water scavenger within the transformer assembly.
Description
LEAK DETECTOR FOR VAPORIZATION COOLED TRANSFORMERS
Canadian patent application Serial No.
313,355 filed October 13, 1978l discloses a vaporization cooled transformer wherein a vaporizable , fluid is used for providing both cooling facility and dielectric capability to transformer cores and windings. An effective liquid level gage for sensing the quantity of coolant is known. The liquid , level gage adequately provides shutoff facility when a vaporizable fluid such as trichlorotrifluoroethane leaks out of the transformer tank. The aforementioned vaporization cooled transformer utilizes a quantity of molecular sieve material in the vapor path between the transformer tank and the heat exchanger as a water scavenger to remove any moisture that may be released from the cellulosic insulation materials during transformer operation. Since the insulating material continuously release water vapor to the transformer interior over the operating life of the transformer, a sufficient quantity of the molecular sieve material is employed to provide for adequate water adsorption throughout the ; operating life of the transformer. In the event that the sieve material becomes saturated, excess moisture can occur within the transformer and behave as an ideal gas under certain temperature conditions. The excess moisture under these conditions can cause corrosion ~9~o~
Canadian patent application Serial No.
313,355 filed October 13, 1978l discloses a vaporization cooled transformer wherein a vaporizable , fluid is used for providing both cooling facility and dielectric capability to transformer cores and windings. An effective liquid level gage for sensing the quantity of coolant is known. The liquid , level gage adequately provides shutoff facility when a vaporizable fluid such as trichlorotrifluoroethane leaks out of the transformer tank. The aforementioned vaporization cooled transformer utilizes a quantity of molecular sieve material in the vapor path between the transformer tank and the heat exchanger as a water scavenger to remove any moisture that may be released from the cellulosic insulation materials during transformer operation. Since the insulating material continuously release water vapor to the transformer interior over the operating life of the transformer, a sufficient quantity of the molecular sieve material is employed to provide for adequate water adsorption throughout the ; operating life of the transformer. In the event that the sieve material becomes saturated, excess moisture can occur within the transformer and behave as an ideal gas under certain temperature conditions. The excess moisture under these conditions can cause corrosion ~9~o~
- 2 -of ihe heat exchanger.
When leaks develop ~hrough openings occurring within Ihe heat exchanger or tank assemly a negative internal pressure within the heat exchanger or tank 5 assembly allows a substantial quantity of ambient air to enter through the lea~ openings. The presence of a quantity of atmospheric air within the heat exchanger can be detrimental to the transformer operation. One ; long-term deleterious effect is the premature saturation 10 of the molecular sieve material due to the presence of substantial quantities of water vapor present within the admitted air.
Short-term deleterious effects which can occur due to the presence of the admitted air include 15 both an overpressure condition caused by reduced heat ,~: exchanger efficiency as well as coolant loss by the ;,; excape of the vaporizable coolant out through the leak openings. The heat exchanger efficiency is decreased because the presence of the trapped air within the heat 20 exchanger headers and cooling tubes prevents the , vaporized coolant from entering into these areas during the condensation periods of the vaporization-condensation cycle. The loss in cooling efficiency in ~.
iurn causes the transformer to operate at a higher 25 temperature causing further increases in pressure until ; an overpressure mechanism becomes energized and the transformer becomes automatically disconnected.
The purpose of this invention is to provide , means for sensing the differences in temperature that 30 exist between the heat exchanger and the transformer tank to determine the presence of admitted air within the heat exchanger assembly as well as the presence of excess moisture.
Temperature sensing means are installed 35 both in the heat exchanger ~nd the transformer tank in ' 90~ ~
When leaks develop ~hrough openings occurring within Ihe heat exchanger or tank assemly a negative internal pressure within the heat exchanger or tank 5 assembly allows a substantial quantity of ambient air to enter through the lea~ openings. The presence of a quantity of atmospheric air within the heat exchanger can be detrimental to the transformer operation. One ; long-term deleterious effect is the premature saturation 10 of the molecular sieve material due to the presence of substantial quantities of water vapor present within the admitted air.
Short-term deleterious effects which can occur due to the presence of the admitted air include 15 both an overpressure condition caused by reduced heat ,~: exchanger efficiency as well as coolant loss by the ;,; excape of the vaporizable coolant out through the leak openings. The heat exchanger efficiency is decreased because the presence of the trapped air within the heat 20 exchanger headers and cooling tubes prevents the , vaporized coolant from entering into these areas during the condensation periods of the vaporization-condensation cycle. The loss in cooling efficiency in ~.
iurn causes the transformer to operate at a higher 25 temperature causing further increases in pressure until ; an overpressure mechanism becomes energized and the transformer becomes automatically disconnected.
The purpose of this invention is to provide , means for sensing the differences in temperature that 30 exist between the heat exchanger and the transformer tank to determine the presence of admitted air within the heat exchanger assembly as well as the presence of excess moisture.
Temperature sensing means are installed 35 both in the heat exchanger ~nd the transformer tank in ' 90~ ~
- 3 -vaporization cooled transformers. The temperature differential between the heat exchanger and the tank is sensed to determine when a predetermined temperature differential is exceeded. The excess temperature ~; 5 differential indicates the presence of ambient air or excess moisture within the transformer. Alarm indicating means ana transformer disconnect relays are -~ actuated when the temperature differential exceeds the predetermined range.
Figure 1 is a graphic representation of the coolant vapor pressure of a vaporization cooled trans-, former as a function of transformer loading for contours P of ambient air temperature;
Figure 2 is a front section view of a 15 vaporization cooled transformer containing the leak detection means according to the invention;
Figure 3 is a top section view of the heat -~ exchanger of Figure 2 through the plane 3-3;
Figure 4 is an enlarg~d section view of the '~ 20 lower header within the embodiment of Figure 1 with the temperature sensor connected to the end of the header;
" Figure 5 is a side section view of a vertically ,~l arranged heat exchanger as an alternative to the hori-~, zontally arranged heat exchanger of Figure 2;
Y 25 Figure 6 is a graphic representation of the ¢,~ relation between temperature and time for the embodiment of Figure 2 in the absence of a leak;
Figure 7 is a graphic representation of the relation between temperature and time for the embodiment 30 of Figure 2 in the presence of a leak;
Figure 8 is a graphic representation af the temperature differential between the temperatures depicted in Figures 6 and 7 as a function of time;
Figures 9A - 9C are diagrammatic representa-35 tions of the temperature separation which occurs within , '',,;
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the side, front and bottom section views of a portion of a heat exchanger at 25% transformer loading;
, Figures lOA - lOC are diagrammatic representa-tions of the temperature separation which occurs within .- 5 the side, front and bottom section views of a portion of : a heat exchanger at 75~ transformer loading;
.- Figures llA - llC are diagrammatic representa-.- tions of the temperature separation which occurs within the side, front and bottom sections of a portion of z 10 a heat exchanger at 100% transformer loading;
.~ Figure 12 is a front section view of a vapori-zation cooled transformer containing a further arrange-ment of the leak detection means of the invention;
. Figure 13 is a graphic representation of the . 15 relation between temperature and time for the embodiment of Figure 12 in the absence of a leak;
Figure 14 is a graphic representation of the relation between temperature and time for the embodiment of Figure 12 in the presence of a leak;
~,;, 20 Figure 15 is a graphic representation of the temperature differential between the temperatures : depicted in Figures 13 and 14 as a function of time; and , Figure 16 is a diagrammatic representation of , the temperature separation which occurs within a vaporization cooled transformer depicted in a partial section front view having vertical cooling tubes and containing the leak detection means according to the invention.
Figure 1 shows the relationship between vaporized coolant pressure and transformer loading existing within a vaporization cooled transformer for various ambient temperatures. It can be seen that the coolant vapor pressure within the transformer at low conditions of loading and low ambient temperatures can be quite low. A standard atmospheric pressure , ' . , ' ~: ' , :
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~9~ 5D-5602 _ 5 _ line P is included at 15 pounds per square inch absolute (PSIA) for comparison purposes. Pressures ; beneath the standard atmospheric pressure line P are considered as negative pressures for the purposes of this disclosure.
Figure 2 contains a vaporizati~n cooled transformer 10 as described within the aforementioned Canadian Patent application. The vaporization ; cooled transformer 10 comprises a transformer tank 11 and a heat exchanger 12 wherein the transformer windings 13, core 14, and bushing 15 are cooled by means of vaporizable coolant 16. The coolant becomes vaporized by the heat generated by the trans-former core and the windings and the vaporized coolant 16' enters up into the intake manifold 17 within the heat exchanger by means of intake pipe 18 in the direction indicated by arrow B. A plurality of headers 19 are connected to the intake manifold and in turn are connected with a plurality of inclined cooling tubes 20 ' 20 connecting between the intake manifold 17 and return - manifold 21. The condensed coolant droplets 16" return to the transformer tank from the return manifold by means of return pipe 22. An expansion tank 23 is provided for the expansion of the vaporized coolant and is connected with the intake manifold by means of connector pipe 24. Any coolant vaporizing within the expansion tank returns to the transformer tank by means of expansion return pipe 25. Located between the transformer tank 11 and intake pipe 18 is a molecular sieve container 26 consisting of a quantity of molecular sieve material 27 within housing 28 which contains a plurality of apertures 29 for retaining the molecular sieve material while permitting the transport of the coolant. Upon becoming vaporized, coolant 16' transmits out from the transformer tank through opening 30 in the ' , -,,~, ! ~ i, ., , '~
.
.
, ~l~s~al direction indicated by arrow A.
As previously discussed, the presence of a ; leak in any portion of the heat exchanger 12 or tank 11 causes an influx of ambient air into the heat exchanger assembly. During transformer operation the admitted air siabilizes within heat exchanger headers 19 after a period of extended use and settles in lowest header 19' within the intake manifold. The presence of a quantity of admitted air within any of the headers 19 prevents vaporized coolant 16' from en~ering those headers and their associated cooling tubes 20 so that the headers and cooling tubes remain at a somewhat lower temperature than the remaining cooling tubes and headers. This is -~
i~ because the vaporized coolant is prevented from con-densing and transmitting its heat of vaporization within the "air locked" headers and cooling tubes. The ' air locked condition also occurs when fans are employed to increase the cooling efficiency of the heat exchanger.
The insertion of a temperature sensor 31 such as a ~hermocouple, within the lowest header 19' and a sensor 32 within the transformer tank provides one means for sensing the temperature of the lowest header 19' and of the coolant within the transformer tank at any given time. Connecting the thermocouples 31, 32 , 25 by means of electrical connectors 33, 34 to a differential - temperature gage 35 allows the temperature difference between the header and the transformer tank to be - rapidly determined. Once the temperature differential ; is determined a direct readout is provided by indicator 36 in order for an operator to monitor the temperature differential while the transformer is operating. A
terminal 37 is provided on the differential temperature gage in order io provide an output signal for connecting to an audio-visual alarm device and to a circuit breaker relay for interrupting input power to the transformer - , .;
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when a predetermined temperature differential is ; exceeded.
The temperature sensor 31 can be connected to - heai exchanger 12, which is horizontally arranged, by connection through the side of the lowest header l9' as indicated in Figure 3 or by connection through the end of the lowesc header l9' as shown in Figure 4.
The-temperature sensor 31 can be located at the botiom of heat exchanger 12 of Figure 5 by connecting ' 10 through the side of lowest header l9' which is higher than enirance pipe 18 as indicated.
For normal operating conditions and in the absence of any leaks the temperature of the interior surface of the header or tube being moniiored is ' 15 approximately the same temperature as the temperature of the vaporized coolant 16' within the associated header or tube. A series of tests were performed on a 1000 Kva transformer within a 31C ambient. Figure 6 shows the temperatures from time of startup at a relatively high load value of 15380 watts. As shown, the temperatures of the coolant in the tank A and the coolant vapor in the lowes~ header B, are approximately equal. The temperature of the lowest header is about 3C less due to thermocouple errors and conduction , 25 heat loss through the header. It had previously been concluded that upon transformer startup, coolant in the tank would heat up in the vicinity of sensor 32 (Figure 2) before hot coolant vapor could move through the heat exchanger to sensor 31. However, the coolant vapor rapidly reaches sensor 32 so that sensor 32 stays approximately at the same temperature as sensor 31 during the startup cycle. This is indicated by the near equal temperature conditions for both A and B.
A quantity of air admitted to the transformer resulted in the temperatures A and B shown in Figure 7.
.
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~9~1 When the air was admitted into the transformer, the load had to be reduced to 9770 watts in order not to damage ihe windings. For this load value the steady state pressure measured 8.6 psig. For the iemperature values shown in Figure 6 the pressure measured 5.3 -psig at the higher load value. As the transformer containing the admitted air is further loaded, the temperature of sensor 32 begins to rise. However, due to the air leak, the temperature of sensor 31 remains :10 constant for the first 30 minutes. The temperature difference ~ To is 6.7C after 15 minutes. The temperature difference ~ Tl is 18.8C after one hour.
The leak detector can therefore give an early indication of the presence of a leak before a dangerous over pressure develops. The temperature of sensor 31 begins to heat up after one hour, possibly due to the hot vapor in the heat exchanger intermixing with the admitted air. However, the lowest header remains at a lower temperature due to the air leak. At steady state conditions the temperature difference ~ T2 was still approximately 13.4C.
Figure 8 is a graphic representation of the temperature differential occurring between sensors 31 and 32 with and without a leak. An alarm can be connected to terminal 37 on the temperature gage 35 in Figure 2 and preset above approximately 6C to allow for sensor errors and load deviation. Temperature differentials above preset values of from 0 to 10C would operate the alarm to give an audible and visual indica-tion of the presence of a leak.
The leak detector which comprises the combinationof temperature gage 35 and sensors 31 and 32 can have a direct reading visual scale, an audible alarm, or a ivisual and audible signaling mechanism, depending on transformer location and operator preference.
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_ g _ The leak detector can also be electrically coupled with a transformer disconnector relay.
Figures 9 through 11 depict the location of ihe hot vapor and cooler air in a 750 Kva transformer for loads of 3600, 9000, and 12000 watts. The 12000 watts value represents the approximate full load rating and the 9000 watt and 3600 watt values represent 75%
and 25% load values respectively. As shown in Figures 9A - 9C for 25% loading and Figures lOA - lOC for 75%
loading, the lowest row of cooling tuhes 20' are partially cold at 25% loading and entirely hot at the higher 75% rating. When the loading is increased to 100% the lowest row of cooling tubes has a well defined cool region as shown in Figures llA - llC.
When loads are less than 100%, the increase in coolant vapor pressure, which occurs in the presence of a leak, is not as detrimental as full load conditions and can be withstood until the load conditions increase ; further to 100%.
As shown in Figure 12, sensor 31 may be located in the highest header 19"~ An additional sensor 31' can be located within expansion tank 23 and connected to gage 35 by conductor 38 for use in combination with sensor 31 so that an indication can be received from 25 either sensor 31 or sensor 31' relative to sensor 32.
Under leak conditions at full load, temperature increases were sensed at sensor 32 while the tempera-tures at 31 and 31' decreased to lower levels. Tem-perature differentials in excess of the 6C setting are ' 30 sufficient to cause standard overpressure gages to become energized at high loads and to cause the transformers to be automatically shut down by standard auxiliary relay equipment. This occurs since pressures generated in excess of the standard overpressure gage setting of 15 psig can cause damage to the heat ' :
exchanger assembly. It is to be noted that pressure increases within the heat exchanger assembly and the transformer tank during operation cause a corresponding increase in the boiling temperature of the coolant so ; 5 that the transformer operates at a higher temperature.
The temperatures monitered at sensor 32 within the transformer tank and sensor 31' within the ;~
expansion tank, are shown at C and D respectively in ~ Figure 13 for transformer operation in the absence of a - 10 leak. The same temperatures monitered, when air was admitted are shown in Figure 14. Ii is to be noted that a differential occurs similar to that described earlier for the header mounted sensor 31 of Figure 2.
This differential is shown in Figure 15 under both regular and leak conditions over a period of time.
Intentionally forming leaks of various sizes at different locations within the horizontal heat exchanger assemblies of Figures 2 and 12 confirmed the fact that the admitted air generally settles in the lowest header on the intake manifold side of the heat exchanger assembly. The reason for the settling of the admitted air in the lowest header within the intake manifold is not at this time well understood. It is noted however, that regardless of where the leak occurs most of the admitted air does in fact locate within the lowest header within the intake manifold.
There is also a temperature differential occurring within the lowest cooling tubes 20' associated with , the lowest header 19' relative to the temperature of the coolant within the transformer tank.
The leak detector of this invention can be used with other heat exchanger designs. Figure 16 depicts a vertical type heat exchanger 12 described in afore-mentioned Canadian patent application Serial No.
313,355 filed October 13, 1978. Air leaking into this .
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heat exchanger 12 consisting of vertical tubes 20-segregates in upper header 40' as well as within the upper region of expansion chamber 41 and cooling tubes 20. Sensor 31 may op~ionally be located within upper header 40' or wiihin expansion iank 41.
Since the remainder of the cooling tubes and headers are hot relative to the top end portions of the tubes and headers it is to be clearly understood that sensor 32 can be connected to the hot portions ~ 10 of the headers and cooling tubes as well as to the -~ transformer tank. An auxiliary sensor 32' connected to the hot portion of one of the headers 40 can provide . a temperature differential relative to sensor 31 in the colder region of the heat exchanger.
Sensor 32 may be mounted within coolant 16 in tank 11, in the hot vapor space above the coolant as shown in Figures 2 and 12, or within the main vapor ; supply pipe 18 to the heat exchanger. Sensor 32 can also be located within the hot portion of one of the ; 20 headers 40 or cooling tubes 20 in the heat exchanger for providing a temperature differential relative to sensor 31.
The leak detector of the invention also provides effective high moisture indication. When the molecular sieve material ~ in Figure 2 becomes inopera-tive due to excessive moisture within the transformer, the excess water vapor behaves as a noncondensable gas - and segregates in a manner similar to the admitted air ~i in the presence of a leak and provides the same hot and cold regions indicated earlier in Figures 9 - 11.
Although thermocouples are used as the tem-perature sensors within the transformer tank and the heat exchanger assembly, other temperature sensing means such as thermistors, resistive elements and direct reading thermometers can also be employed.
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It is to be understood that the pressure within both the heat exchanger and ~he transformer tank can increase for a variety of reasons. This invention :` is directed to means for determining the presence of a leak either within the heat exchanger assembly or the transformer tank above the coolant liquid level that is not readily detectable until the transformer becomes energized. The presence of admitted air within `:~ the transformer tank, for example, can cause serious dielectric problems immediately upon transformer startup.
The admitied air is not determinable with standard type pressure sensing means either within the tank or heat exchanger assembly. A sufficient quantity of admitted air will immediately indicate a temperature lS differential between sensor 31 located within the heat exchanger and sensor 32 within the transformer tank before any dielectric breakdown problems can ocaur within the transformer windings during startup conditions.
Although the leak detector of the invention is directed to vaporization cooled transformers, this . is by way of example only. The invention finds appli-y~ cation wherever heat exchangers and vaporization ~;~ cooled e1ectrical1y heated e1ements may be employed.
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Figure 1 is a graphic representation of the coolant vapor pressure of a vaporization cooled trans-, former as a function of transformer loading for contours P of ambient air temperature;
Figure 2 is a front section view of a 15 vaporization cooled transformer containing the leak detection means according to the invention;
Figure 3 is a top section view of the heat -~ exchanger of Figure 2 through the plane 3-3;
Figure 4 is an enlarg~d section view of the '~ 20 lower header within the embodiment of Figure 1 with the temperature sensor connected to the end of the header;
" Figure 5 is a side section view of a vertically ,~l arranged heat exchanger as an alternative to the hori-~, zontally arranged heat exchanger of Figure 2;
Y 25 Figure 6 is a graphic representation of the ¢,~ relation between temperature and time for the embodiment of Figure 2 in the absence of a leak;
Figure 7 is a graphic representation of the relation between temperature and time for the embodiment 30 of Figure 2 in the presence of a leak;
Figure 8 is a graphic representation af the temperature differential between the temperatures depicted in Figures 6 and 7 as a function of time;
Figures 9A - 9C are diagrammatic representa-35 tions of the temperature separation which occurs within , '',,;
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the side, front and bottom section views of a portion of a heat exchanger at 25% transformer loading;
, Figures lOA - lOC are diagrammatic representa-tions of the temperature separation which occurs within .- 5 the side, front and bottom section views of a portion of : a heat exchanger at 75~ transformer loading;
.- Figures llA - llC are diagrammatic representa-.- tions of the temperature separation which occurs within the side, front and bottom sections of a portion of z 10 a heat exchanger at 100% transformer loading;
.~ Figure 12 is a front section view of a vapori-zation cooled transformer containing a further arrange-ment of the leak detection means of the invention;
. Figure 13 is a graphic representation of the . 15 relation between temperature and time for the embodiment of Figure 12 in the absence of a leak;
Figure 14 is a graphic representation of the relation between temperature and time for the embodiment of Figure 12 in the presence of a leak;
~,;, 20 Figure 15 is a graphic representation of the temperature differential between the temperatures : depicted in Figures 13 and 14 as a function of time; and , Figure 16 is a diagrammatic representation of , the temperature separation which occurs within a vaporization cooled transformer depicted in a partial section front view having vertical cooling tubes and containing the leak detection means according to the invention.
Figure 1 shows the relationship between vaporized coolant pressure and transformer loading existing within a vaporization cooled transformer for various ambient temperatures. It can be seen that the coolant vapor pressure within the transformer at low conditions of loading and low ambient temperatures can be quite low. A standard atmospheric pressure , ' . , ' ~: ' , :
~ ,.
~9~ 5D-5602 _ 5 _ line P is included at 15 pounds per square inch absolute (PSIA) for comparison purposes. Pressures ; beneath the standard atmospheric pressure line P are considered as negative pressures for the purposes of this disclosure.
Figure 2 contains a vaporizati~n cooled transformer 10 as described within the aforementioned Canadian Patent application. The vaporization ; cooled transformer 10 comprises a transformer tank 11 and a heat exchanger 12 wherein the transformer windings 13, core 14, and bushing 15 are cooled by means of vaporizable coolant 16. The coolant becomes vaporized by the heat generated by the trans-former core and the windings and the vaporized coolant 16' enters up into the intake manifold 17 within the heat exchanger by means of intake pipe 18 in the direction indicated by arrow B. A plurality of headers 19 are connected to the intake manifold and in turn are connected with a plurality of inclined cooling tubes 20 ' 20 connecting between the intake manifold 17 and return - manifold 21. The condensed coolant droplets 16" return to the transformer tank from the return manifold by means of return pipe 22. An expansion tank 23 is provided for the expansion of the vaporized coolant and is connected with the intake manifold by means of connector pipe 24. Any coolant vaporizing within the expansion tank returns to the transformer tank by means of expansion return pipe 25. Located between the transformer tank 11 and intake pipe 18 is a molecular sieve container 26 consisting of a quantity of molecular sieve material 27 within housing 28 which contains a plurality of apertures 29 for retaining the molecular sieve material while permitting the transport of the coolant. Upon becoming vaporized, coolant 16' transmits out from the transformer tank through opening 30 in the ' , -,,~, ! ~ i, ., , '~
.
.
, ~l~s~al direction indicated by arrow A.
As previously discussed, the presence of a ; leak in any portion of the heat exchanger 12 or tank 11 causes an influx of ambient air into the heat exchanger assembly. During transformer operation the admitted air siabilizes within heat exchanger headers 19 after a period of extended use and settles in lowest header 19' within the intake manifold. The presence of a quantity of admitted air within any of the headers 19 prevents vaporized coolant 16' from en~ering those headers and their associated cooling tubes 20 so that the headers and cooling tubes remain at a somewhat lower temperature than the remaining cooling tubes and headers. This is -~
i~ because the vaporized coolant is prevented from con-densing and transmitting its heat of vaporization within the "air locked" headers and cooling tubes. The ' air locked condition also occurs when fans are employed to increase the cooling efficiency of the heat exchanger.
The insertion of a temperature sensor 31 such as a ~hermocouple, within the lowest header 19' and a sensor 32 within the transformer tank provides one means for sensing the temperature of the lowest header 19' and of the coolant within the transformer tank at any given time. Connecting the thermocouples 31, 32 , 25 by means of electrical connectors 33, 34 to a differential - temperature gage 35 allows the temperature difference between the header and the transformer tank to be - rapidly determined. Once the temperature differential ; is determined a direct readout is provided by indicator 36 in order for an operator to monitor the temperature differential while the transformer is operating. A
terminal 37 is provided on the differential temperature gage in order io provide an output signal for connecting to an audio-visual alarm device and to a circuit breaker relay for interrupting input power to the transformer - , .;
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when a predetermined temperature differential is ; exceeded.
The temperature sensor 31 can be connected to - heai exchanger 12, which is horizontally arranged, by connection through the side of the lowest header l9' as indicated in Figure 3 or by connection through the end of the lowesc header l9' as shown in Figure 4.
The-temperature sensor 31 can be located at the botiom of heat exchanger 12 of Figure 5 by connecting ' 10 through the side of lowest header l9' which is higher than enirance pipe 18 as indicated.
For normal operating conditions and in the absence of any leaks the temperature of the interior surface of the header or tube being moniiored is ' 15 approximately the same temperature as the temperature of the vaporized coolant 16' within the associated header or tube. A series of tests were performed on a 1000 Kva transformer within a 31C ambient. Figure 6 shows the temperatures from time of startup at a relatively high load value of 15380 watts. As shown, the temperatures of the coolant in the tank A and the coolant vapor in the lowes~ header B, are approximately equal. The temperature of the lowest header is about 3C less due to thermocouple errors and conduction , 25 heat loss through the header. It had previously been concluded that upon transformer startup, coolant in the tank would heat up in the vicinity of sensor 32 (Figure 2) before hot coolant vapor could move through the heat exchanger to sensor 31. However, the coolant vapor rapidly reaches sensor 32 so that sensor 32 stays approximately at the same temperature as sensor 31 during the startup cycle. This is indicated by the near equal temperature conditions for both A and B.
A quantity of air admitted to the transformer resulted in the temperatures A and B shown in Figure 7.
.
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~9~1 When the air was admitted into the transformer, the load had to be reduced to 9770 watts in order not to damage ihe windings. For this load value the steady state pressure measured 8.6 psig. For the iemperature values shown in Figure 6 the pressure measured 5.3 -psig at the higher load value. As the transformer containing the admitted air is further loaded, the temperature of sensor 32 begins to rise. However, due to the air leak, the temperature of sensor 31 remains :10 constant for the first 30 minutes. The temperature difference ~ To is 6.7C after 15 minutes. The temperature difference ~ Tl is 18.8C after one hour.
The leak detector can therefore give an early indication of the presence of a leak before a dangerous over pressure develops. The temperature of sensor 31 begins to heat up after one hour, possibly due to the hot vapor in the heat exchanger intermixing with the admitted air. However, the lowest header remains at a lower temperature due to the air leak. At steady state conditions the temperature difference ~ T2 was still approximately 13.4C.
Figure 8 is a graphic representation of the temperature differential occurring between sensors 31 and 32 with and without a leak. An alarm can be connected to terminal 37 on the temperature gage 35 in Figure 2 and preset above approximately 6C to allow for sensor errors and load deviation. Temperature differentials above preset values of from 0 to 10C would operate the alarm to give an audible and visual indica-tion of the presence of a leak.
The leak detector which comprises the combinationof temperature gage 35 and sensors 31 and 32 can have a direct reading visual scale, an audible alarm, or a ivisual and audible signaling mechanism, depending on transformer location and operator preference.
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_ g _ The leak detector can also be electrically coupled with a transformer disconnector relay.
Figures 9 through 11 depict the location of ihe hot vapor and cooler air in a 750 Kva transformer for loads of 3600, 9000, and 12000 watts. The 12000 watts value represents the approximate full load rating and the 9000 watt and 3600 watt values represent 75%
and 25% load values respectively. As shown in Figures 9A - 9C for 25% loading and Figures lOA - lOC for 75%
loading, the lowest row of cooling tuhes 20' are partially cold at 25% loading and entirely hot at the higher 75% rating. When the loading is increased to 100% the lowest row of cooling tubes has a well defined cool region as shown in Figures llA - llC.
When loads are less than 100%, the increase in coolant vapor pressure, which occurs in the presence of a leak, is not as detrimental as full load conditions and can be withstood until the load conditions increase ; further to 100%.
As shown in Figure 12, sensor 31 may be located in the highest header 19"~ An additional sensor 31' can be located within expansion tank 23 and connected to gage 35 by conductor 38 for use in combination with sensor 31 so that an indication can be received from 25 either sensor 31 or sensor 31' relative to sensor 32.
Under leak conditions at full load, temperature increases were sensed at sensor 32 while the tempera-tures at 31 and 31' decreased to lower levels. Tem-perature differentials in excess of the 6C setting are ' 30 sufficient to cause standard overpressure gages to become energized at high loads and to cause the transformers to be automatically shut down by standard auxiliary relay equipment. This occurs since pressures generated in excess of the standard overpressure gage setting of 15 psig can cause damage to the heat ' :
exchanger assembly. It is to be noted that pressure increases within the heat exchanger assembly and the transformer tank during operation cause a corresponding increase in the boiling temperature of the coolant so ; 5 that the transformer operates at a higher temperature.
The temperatures monitered at sensor 32 within the transformer tank and sensor 31' within the ;~
expansion tank, are shown at C and D respectively in ~ Figure 13 for transformer operation in the absence of a - 10 leak. The same temperatures monitered, when air was admitted are shown in Figure 14. Ii is to be noted that a differential occurs similar to that described earlier for the header mounted sensor 31 of Figure 2.
This differential is shown in Figure 15 under both regular and leak conditions over a period of time.
Intentionally forming leaks of various sizes at different locations within the horizontal heat exchanger assemblies of Figures 2 and 12 confirmed the fact that the admitted air generally settles in the lowest header on the intake manifold side of the heat exchanger assembly. The reason for the settling of the admitted air in the lowest header within the intake manifold is not at this time well understood. It is noted however, that regardless of where the leak occurs most of the admitted air does in fact locate within the lowest header within the intake manifold.
There is also a temperature differential occurring within the lowest cooling tubes 20' associated with , the lowest header 19' relative to the temperature of the coolant within the transformer tank.
The leak detector of this invention can be used with other heat exchanger designs. Figure 16 depicts a vertical type heat exchanger 12 described in afore-mentioned Canadian patent application Serial No.
313,355 filed October 13, 1978. Air leaking into this .
.; , .
:
-1~9~
heat exchanger 12 consisting of vertical tubes 20-segregates in upper header 40' as well as within the upper region of expansion chamber 41 and cooling tubes 20. Sensor 31 may op~ionally be located within upper header 40' or wiihin expansion iank 41.
Since the remainder of the cooling tubes and headers are hot relative to the top end portions of the tubes and headers it is to be clearly understood that sensor 32 can be connected to the hot portions ~ 10 of the headers and cooling tubes as well as to the -~ transformer tank. An auxiliary sensor 32' connected to the hot portion of one of the headers 40 can provide . a temperature differential relative to sensor 31 in the colder region of the heat exchanger.
Sensor 32 may be mounted within coolant 16 in tank 11, in the hot vapor space above the coolant as shown in Figures 2 and 12, or within the main vapor ; supply pipe 18 to the heat exchanger. Sensor 32 can also be located within the hot portion of one of the ; 20 headers 40 or cooling tubes 20 in the heat exchanger for providing a temperature differential relative to sensor 31.
The leak detector of the invention also provides effective high moisture indication. When the molecular sieve material ~ in Figure 2 becomes inopera-tive due to excessive moisture within the transformer, the excess water vapor behaves as a noncondensable gas - and segregates in a manner similar to the admitted air ~i in the presence of a leak and provides the same hot and cold regions indicated earlier in Figures 9 - 11.
Although thermocouples are used as the tem-perature sensors within the transformer tank and the heat exchanger assembly, other temperature sensing means such as thermistors, resistive elements and direct reading thermometers can also be employed.
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It is to be understood that the pressure within both the heat exchanger and ~he transformer tank can increase for a variety of reasons. This invention :` is directed to means for determining the presence of a leak either within the heat exchanger assembly or the transformer tank above the coolant liquid level that is not readily detectable until the transformer becomes energized. The presence of admitted air within `:~ the transformer tank, for example, can cause serious dielectric problems immediately upon transformer startup.
The admitied air is not determinable with standard type pressure sensing means either within the tank or heat exchanger assembly. A sufficient quantity of admitted air will immediately indicate a temperature lS differential between sensor 31 located within the heat exchanger and sensor 32 within the transformer tank before any dielectric breakdown problems can ocaur within the transformer windings during startup conditions.
Although the leak detector of the invention is directed to vaporization cooled transformers, this . is by way of example only. The invention finds appli-y~ cation wherever heat exchangers and vaporization ~;~ cooled e1ectrical1y heated e1ements may be employed.
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Claims (24)
1. A method for determining leaks in vaporization cooled transformers of the type consisting of a transformer tank containing a transformer core and winding assembly, a condensable coolant, and a heat exchanger, comprising the steps of:
sensing the temperature of the condensable coolant within said transformer tank;
sensing the temperature within a portion of said heat exchanger;
determining the temperature differential between said heat exchanger and said coolant; and providing an indication when a predetermined temperature differential is exceeded, said excess temp-erature differential thereby indicating the presence of ambient air within said transformer.
sensing the temperature of the condensable coolant within said transformer tank;
sensing the temperature within a portion of said heat exchanger;
determining the temperature differential between said heat exchanger and said coolant; and providing an indication when a predetermined temperature differential is exceeded, said excess temp-erature differential thereby indicating the presence of ambient air within said transformer.
2. The method of claim 1, wherein the temperature sensing means is selected from the group consisting of thermocouples, resistors, and thermistors.
3. The method of claim 1, wherein the heat exchanger includes an expansion tank and wherein the temperature measurement is made within a portion of the expansion tank.
4. The method of claim 1, wherein the heat exchanger includes a plurality of headers and cooling tubes and wherein the step of measuring the heat exchanger temperature comprises determining the temperature within at least one of the cooling tubes.
5. The method of claim 4, wherein the cooling tubes are vertically arranged and wherein the temperature is measured at a top portion of the cooling tubes.
6. The method of claim 1, wherein the predetermined temperature differential comprises from 0°
to 10°C.
to 10°C.
7. The method of claim 1, wherein the coolant comprises a chlorinated fluorocarbon.
8. The method of claim 7, wherein the fluorocarbon comprises a trichlorotrifluoroethane.
9. The method of claim 1, wherein the heat exchanger includes a plurality of headers and cooling tubes and wherein the step of measuring the heat exchanger temperature comprises measuring the temperature of at least one of the headers.
10. The method of claim 9, wherein the headers are horizontally disposed in a vertical array and wherein the temperature measurement is made on the lowest header in the array.
11. The method of claim 1 including the step of providing an output signal when said predetermined temperature differential is exceeded for activating alarm and transformer disconnect means.
12. A leak detector for vaporization cooled transformer comprising in combination :
a transformer tank containing a transformer core and winding within a condensable collant;
a heat exchanger assembly operatably coupled with said transformer tank for receiving said coolant in vapor form and returning said coolant in condensed form;
a quantity of molecular seive material inter-mediate said tank and said heat exchanger;
temperature sensing means within the heat exchanger for measuring the temperature of a portion of the heat exchanger;
temperature sensing means within the transformer tank for measuring the temperature of the coolant within the transformer tank; and a differential temperature gage electrically connected with said heat exchanger temperature sensing means and said coolant temperature sensing means for sensing the temperature differential between said temperature sensing means and for providing an output signal when the temperature differential exceeds a predetermined temperature differential said excess temp-erature differential thereby indicating the presence of ambient air within said transformer.
a transformer tank containing a transformer core and winding within a condensable collant;
a heat exchanger assembly operatably coupled with said transformer tank for receiving said coolant in vapor form and returning said coolant in condensed form;
a quantity of molecular seive material inter-mediate said tank and said heat exchanger;
temperature sensing means within the heat exchanger for measuring the temperature of a portion of the heat exchanger;
temperature sensing means within the transformer tank for measuring the temperature of the coolant within the transformer tank; and a differential temperature gage electrically connected with said heat exchanger temperature sensing means and said coolant temperature sensing means for sensing the temperature differential between said temperature sensing means and for providing an output signal when the temperature differential exceeds a predetermined temperature differential said excess temp-erature differential thereby indicating the presence of ambient air within said transformer.
13. The leak detector of claim 12, wherein the heat exchanger comprises a plurality of horizontally extending headers arranged in a vertical array and wherein the heat exchanger temperature sensing means is connected to one of said headers.
14. The leak detector of claim 12, wherein the heat exchanger comprises a plurality of horizontally extending headers in a vertical array and a plurality of inter-connecting horizontally extending cooling tubes arranged in a corresponding vertical array and wherein the heat exchanger temperature sensing means is connected to one of the cooling tubes in the array.
15. The leak detector of claim 12, wherein the temperature sensing means is connected to the lowest header in the array.
16. The leak detector of claim 12, wherein the heat exchanger temperature detecting means is connected to the lowest cooling tube in the array.
17. The leak detector of claim 12, wherein the coolant temperature sensing means is in said coolant within the transformer tank.
18. The leak detector of claim 12, wherein the coolant temperature sensing means is above said coolant within the transformer tank.
19. The leak detector of claim 12, wherein the temperature sensor is selected from the group consisting of thermocouples resistors, and thermistors.
20. A method for determining leaks in vaporization cooled transformers of the type consisting of a transformer tank containing a transformer core and winding assembly, a condensable coolant, and a heat exchanger, comprising the steps of :
sensing the temperature in a first portion of said heat exchanger; and sensing the temperature in a second portion of said heat exchanger to determine a temperature differential between said first and second portions; and sensing the temperature of the condensable coolant in said temperature tank; and to determine when the temperature differential between said heat exchanger and said coolant exceeds a predetermined differential upon the presence of a leak,
sensing the temperature in a first portion of said heat exchanger; and sensing the temperature in a second portion of said heat exchanger to determine a temperature differential between said first and second portions; and sensing the temperature of the condensable coolant in said temperature tank; and to determine when the temperature differential between said heat exchanger and said coolant exceeds a predetermined differential upon the presence of a leak,
21. The method of claim 20, wherein the first portion of the heat exchanger is hotter than the second portion.
22. The method of claim 21, wherein the heat exchanger comprises at least one header and at least one cooling tube and wherein the first portion includes one of the headers.
23. The method of claim 22, wherein the second portion includes one of the cooling tubes.
24. An excess moisture detector for vaporization cooled transformers comprising:
a transformer tank containing a condensable coolant and having an opening in the top;
a heat exchanger assembly connected to the top of said transformer tank for receiving said coolant in vapor form and returning said coolant in condensed form to the tank;
a quantity of moisture absorbing material in an apertured container located intermediate the heat exchanger and the tank for removing moisture from the coolant, said moisture absorbing material being moisture saturated due to excessive moisture within said trans-former;
temperature sensing means within a portion of the heat exchanger to determine the temperature within said heat exchanger;
temperature sensing means within the tank to determine the temperature of the coolant within the tank; and indicating means for determining the differences in the heat exchanger temperature and the coolant temperature and for providing an indication when a predetermined temperature differential is exceeded thereby detecting that said moisture absorbing material has become inoperative due to the presence of excess moisture.
a transformer tank containing a condensable coolant and having an opening in the top;
a heat exchanger assembly connected to the top of said transformer tank for receiving said coolant in vapor form and returning said coolant in condensed form to the tank;
a quantity of moisture absorbing material in an apertured container located intermediate the heat exchanger and the tank for removing moisture from the coolant, said moisture absorbing material being moisture saturated due to excessive moisture within said trans-former;
temperature sensing means within a portion of the heat exchanger to determine the temperature within said heat exchanger;
temperature sensing means within the tank to determine the temperature of the coolant within the tank; and indicating means for determining the differences in the heat exchanger temperature and the coolant temperature and for providing an indication when a predetermined temperature differential is exceeded thereby detecting that said moisture absorbing material has become inoperative due to the presence of excess moisture.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000349247A CA1149901A (en) | 1980-04-03 | 1980-04-03 | Leak detector for vaporization cooled transformers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000349247A CA1149901A (en) | 1980-04-03 | 1980-04-03 | Leak detector for vaporization cooled transformers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1149901A true CA1149901A (en) | 1983-07-12 |
Family
ID=4116641
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000349247A Expired CA1149901A (en) | 1980-04-03 | 1980-04-03 | Leak detector for vaporization cooled transformers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1149901A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107063581A (en) * | 2017-06-01 | 2017-08-18 | 北京京能未来燃气热电有限公司 | Valves leakage detection means and detection method |
-
1980
- 1980-04-03 CA CA000349247A patent/CA1149901A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107063581A (en) * | 2017-06-01 | 2017-08-18 | 北京京能未来燃气热电有限公司 | Valves leakage detection means and detection method |
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