US3894171A - Electrical transformers - Google Patents
Electrical transformers Download PDFInfo
- Publication number
- US3894171A US3894171A US417559A US41755973A US3894171A US 3894171 A US3894171 A US 3894171A US 417559 A US417559 A US 417559A US 41755973 A US41755973 A US 41755973A US 3894171 A US3894171 A US 3894171A
- Authority
- US
- United States
- Prior art keywords
- oil
- casing
- transformer
- degassing apparatus
- outlet
- 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 - Lifetime
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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
- H01F27/08—Cooling; Ventilating
- H01F27/10—Liquid cooling
- H01F27/12—Oil cooling
- H01F27/14—Expansion chambers; Oil conservators; Gas cushions; Arrangements for purifying, drying, or filling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D19/00—Degasification of liquids
- B01D19/0063—Regulation, control including valves and floats
Definitions
- the present invention aims at enabling transformer oil to be treated while the transformer is live, but obviating, or at least reducing, down-time of the transformer.
- the present invention provides an oilinsulated electrical transformer which is as claimed in the appended claims.
- a transformer casing 2 houses the windings and insulating oil of the transformer, electrical connection to the transformer windings being effected by means of insulating bushings 4.
- a conduit 6 leading through a valve 8 to a filter vessel 10 which 'is designed to remove from the oil at least a high proportion, if not all, of any solid particles in suspension in, or entrained by, the oil stream.
- the filtered oil stream passes along conduit 6 and through a flowcontrol valve 12 to the upper partof a vacuum treatment vessel 14, having a central compartment 16 in which are packed Raschig rings or other column fillers 17 over which the oil to be treated flows in a thin film.
- the oil is subjected to vacuum by means of a vacuum pump 18 driven by an electric motor 20.
- P0- sitioned in the lower part of vessel 14 is a level-sensing switch 22.
- the conduit 6 leading from the bottom of vessel 14 passes through an oil pump 24 and a permanent magnet filter 26 to a discharge valve 28. From valve 28 the treated oil passes through a valve 30 before reentering the interior of casing 2.
- control unit 32 which is connected to valve 8; motor a vacuum gauge 21; level-sensing switch 22, and pump 24.
- control unit 32 acts to open valve 8 when the level of contamination of the oil in chamber 2 reaches a chosen value. It is also effective to monitor the degree of vacuum in vessel 14 and to start the vacuum pump when the pressure in the interior of vessel 14 rises to too high a value. It is also effective to switch the vacuum pump off when the pressure in vessel 14 has fallen to a chosen minimum level.
- Control unit 32 is also effective to energise pump 24 when the level-sensing switch 22 indicates that there is sufficient volume of vacuum-treated and filtered oil in the bottom of the vessel 14.
- the discharge valve 28 can be operated either automatically or manually as need arises.
- the temperature of the contaminated oil to be treated is raised to about 4565C. At this temperature the surface tension of the oil is sufficiently low to allow any absorbed gases or vapours to be desorbed by the application of a suitable degree of vacuum in vessel 14.
- the oil is raised to this treatment temperature by the waste heat normally released by the transformer windings when it is operating. If the oil does not normally reach the desired treatment temperature, or if it falls below this temperature under adverse weather conditions, it is within the purview of the present invention to incorporate an auxiliary heater 34 in conduit 6 before filter 10.
- the heater In view of the relatively large mass of oil required to be treated, the heater will be of insufficient capacity to heat all the oil in casing 2 from ambient temperature to the treatment temperature, so that the major proportion of the heat necessary would be supplied by the transformer windings. This leads to a substantial reduction in the expense of the degassing equipment, in that the heater can be of very low rating compared with that necessary for existing mobile servicing units.
- the degree of contamination of the oil can be monitored either continuously or intermittently, and the results of the monitoring can be used to cause control unit 32 to switch on the treatment unit when the degree of contamination has risen to a specified level.
- control unit 32 it might be desirable in some circumstances to keep the treatment unit operating continuously so that any contaminants are removed more or less immediately after they appear in the oil.
- An oil insulated electrical transformer including a casing having an outlet permanently communicating its interior with vacuum degassing apparatus for treatment of the oil while the transformer is live, means for feeding oil to the degassing apparatus, and returning treated oil to the interior of the casing, either continually or intermittently, the degassing apparatus including a compartment containing packed column fillers over which the oil can flow in thin films, said compartment being connected to a vacuum pump, a control unit operatively connected between the compartment and vacuum pump to turn the vacuum pump on when the pressure in the compartment is above a chosen maximum; and to turn the pump off when the pressure is below a chosen minimum, a valve located at the outlet of the casing and controlling flow of oil from the interior of the casing, said control unit opening the valve when the contamination in the oil in the casing reaches a chosen level, and a second valve located at the inlet of the casing and controlling the flow of treated oil toward the interior of the casing.
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Transformer Cooling (AREA)
- Housings And Mounting Of Transformers (AREA)
Abstract
The cooling oil in large electrical transformers is purified, by having sorbed water and gases removed, by means of a vacuum treatment vessel permanently plumbed to the transformer. The desorbing treatment is carried out while the transformer is live, so that the oil needs little or no extra heat supplied before it can be treated.
Description
United States Patent [191 Kusay July 8, 1975 [54] ELECTRICAL TRANSFORMERS 3,675,395 7/1972 Baranowski 55/164 [75] Inventor: Roland Gregor Paul Kusay,
Blechingley, England Primary ExaminerSamih N. Zaharna [73] Ass1gnee: TheBntrsh Oxygen Compan Assistant ExaminerRichard W. Burks Lmmed London England Attorney, Agent, or FirmDennison, Dennison, 22 Filed: Nov. 20, 1973 Townshend & Meserole [21 Appl. No.: 417,559
[ 30] Foreign Application Priority Data [57] ABSTRACT Nov. 23, 1972 United Kingdom 54199/72 [52] Us Cl 174/14 R; 55/164. 55/190. The cooling oil in large electrical transformers is puri- 210/223; fied, by having sorbed water and gases removed, by [51] Int CL. Holb 9/06;BO1d 19/OO-.BO1d 39/00 means of a vacuum treatment vessel permanently [58] Field of Search u 55 /21 52 5 5 164 plumbed to the transformer. The desorbing treatment 55/189 190 210/222 174/121 R 15 is carried out while the transformer is live, so that the oil needs little or no extra heat supplied before it can [56] References Cited be treated- UNITED STATES PATENTS 2,340,898 2/1944 Race 55/189 X 2 Claims, 1 Drawing Figure tim ELECTRICAL TRANSFORMERS This invention relates to big electrical transformers of which the windings are immersed in a dielectric oil housed in a container.
The dielectric strength of such an oil is appreciably reduced by the presence in it of water, gas or particulate impurities. This leads to inefficient operation of the transformer as its losses increase with time as the oil becomes increasingly adulterated as water and gas from the atmosphere are absorbed by the oil. While solid impurities can be removed by filters having pores of appropriate size, absorbed gases and water vapour have to be removed by a desorption process.
It is known to treat electrical oils intermittently by coupling up the transformer container at chosen intervals to a mobile treatment unit employing filters, electrical or other heaters, and vacuum degassing apparatus. The treatment unit consumes a lot of power in heating the oil up to its treatment temperature, and takesa long time because of the care which has to be taken during the heating process to limit the temperature which the oil reaches so as to avoid thermally decomposing the oil. Immediately prior to the treatment, and during all the time that the treatment is taking place, the transformer is out of commission, and hence elaborate and expensive measures have to be taken to make up for this.
The present invention aims at enabling transformer oil to be treated while the transformer is live, but obviating, or at least reducing, down-time of the transformer.
Accordingly the present invention provides an oilinsulated electrical transformer which is as claimed in the appended claims.
The present invention willl now be described by way of example with reference to the accompanying drawing, which is a diagrammatic view of a transformer of the present invention.
A transformer casing 2 houses the windings and insulating oil of the transformer, electrical connection to the transformer windings being effected by means of insulating bushings 4.
Extending from the lower part of casing 2 is a conduit 6 leading through a valve 8 to a filter vessel 10 which 'is designed to remove from the oil at least a high proportion, if not all, of any solid particles in suspension in, or entrained by, the oil stream. The filtered oil stream passes along conduit 6 and through a flowcontrol valve 12 to the upper partof a vacuum treatment vessel 14, having a central compartment 16 in which are packed Raschig rings or other column fillers 17 over which the oil to be treated flows in a thin film. In so doing, the oil is subjected to vacuum by means of a vacuum pump 18 driven by an electric motor 20. P0- sitioned in the lower part of vessel 14 is a level-sensing switch 22.
The conduit 6 leading from the bottom of vessel 14 passes through an oil pump 24 and a permanent magnet filter 26 to a discharge valve 28. From valve 28 the treated oil passes through a valve 30 before reentering the interior of casing 2.
Associated with the apparatus is a control unit 32 which is connected to valve 8; motor a vacuum gauge 21; level-sensing switch 22, and pump 24.
By means which do not form part of the subjectmatter of the present application, and which are therefore not described in further detail, the control unit 32 acts to open valve 8 when the level of contamination of the oil in chamber 2 reaches a chosen value. It is also effective to monitor the degree of vacuum in vessel 14 and to start the vacuum pump when the pressure in the interior of vessel 14 rises to too high a value. It is also effective to switch the vacuum pump off when the pressure in vessel 14 has fallen to a chosen minimum level.
The discharge valve 28 can be operated either automatically or manually as need arises.
For the treatment process to be successful, it is necessary for the temperature of the contaminated oil to be treated to be raised to about 4565C. At this temperature the surface tension of the oil is sufficiently low to allow any absorbed gases or vapours to be desorbed by the application of a suitable degree of vacuum in vessel 14. In accordance with the present invention, the oil is raised to this treatment temperature by the waste heat normally released by the transformer windings when it is operating. If the oil does not normally reach the desired treatment temperature, or if it falls below this temperature under adverse weather conditions, it is within the purview of the present invention to incorporate an auxiliary heater 34 in conduit 6 before filter 10.
In view of the relatively large mass of oil required to be treated, the heater will be of insufficient capacity to heat all the oil in casing 2 from ambient temperature to the treatment temperature, so that the major proportion of the heat necessary would be supplied by the transformer windings. This leads to a substantial reduction in the expense of the degassing equipment, in that the heater can be of very low rating compared with that necessary for existing mobile servicing units.
The degree of contamination of the oil can be monitored either continuously or intermittently, and the results of the monitoring can be used to cause control unit 32 to switch on the treatment unit when the degree of contamination has risen to a specified level. However, it might be desirable in some circumstances to keep the treatment unit operating continuously so that any contaminants are removed more or less immediately after they appear in the oil.
The choice between these two conditions is made on considerations which do not effect the mode of operation of the present invention, and so will not be described further.
I claim:
1. An oil insulated electrical transformer including a casing having an outlet permanently communicating its interior with vacuum degassing apparatus for treatment of the oil while the transformer is live, means for feeding oil to the degassing apparatus, and returning treated oil to the interior of the casing, either continually or intermittently, the degassing apparatus including a compartment containing packed column fillers over which the oil can flow in thin films, said compartment being connected to a vacuum pump, a control unit operatively connected between the compartment and vacuum pump to turn the vacuum pump on when the pressure in the compartment is above a chosen maximum; and to turn the pump off when the pressure is below a chosen minimum, a valve located at the outlet of the casing and controlling flow of oil from the interior of the casing, said control unit opening the valve when the contamination in the oil in the casing reaches a chosen level, and a second valve located at the inlet of the casing and controlling the flow of treated oil toward the interior of the casing.
2. A transformer as claimed in claim 1, in which a filter vessel is located between the outlet of the casing a permanent magnet filter being located between the outlet of the oil pump and the inlet of the casing.
Claims (2)
1. An oil insulated electrical transformer including a casing having an outlet permanently communicating its interior with vacuum degassing apparatus for treatment of the oil while the transformer is live, means for feeding oil to the degassing apparatus, and returning treated oil to the interior of the casing, either continually or intermittently, the degassing apparatus including a compartment containing packed column fillers over which the oil can flow in thin films, said compartment being connected to a vacuum pump, a control unit operatively connected between the compartment and vacuum pump to turn the vacuum pump on when the pressure in the compartment is above a chosen maximum; and to turn the pump off when the pressure is below a chosen minimum, a valve located at the outlet of the casing and controlling flow of oil from the interior of the casing, said control unit opening the valve when the contamination in the oil in the casing reaches a chosen level, and a second valve located at the inlet of the casing and controlling the flow of treated oil toward the interior of the casing.
2. A transformer as claimed in claim 1, in which a filter vessel is locatEd between the outlet of the casing and the inlet of the degassing apparatus, an oil pump being located between the outlet of the degassing apparatus and the inlet of the casing, said the control unit energising the oil pump when the amount of treated oil in the degassing apparatus reaches a chosen level, and a permanent magnet filter being located between the outlet of the oil pump and the inlet of the casing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB5419972A GB1440190A (en) | 1972-11-23 | 1972-11-23 | Electrical transformers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US3894171A true US3894171A (en) | 1975-07-08 |
Family
ID=10470242
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US417559A Expired - Lifetime US3894171A (en) | 1972-11-23 | 1973-11-20 | Electrical transformers |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US3894171A (en) |
| DE (1) | DE2358072A1 (en) |
| GB (1) | GB1440190A (en) |
Cited By (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4234754A (en) * | 1978-02-28 | 1980-11-18 | Bicc Limited | Oil-filled electric cable installations comprising pressurizing oil tanks |
| US4280014A (en) * | 1979-02-27 | 1981-07-21 | Bicc Limited | Electric cable installations |
| US4358379A (en) * | 1980-11-21 | 1982-11-09 | Noboru Inoue | Process for refining electric insulating liquids |
| US4437082A (en) | 1982-07-12 | 1984-03-13 | Westinghouse Electric Corp. | Apparatus for continually upgrading transformer dielectric liquid |
| US4526677A (en) * | 1984-06-04 | 1985-07-02 | Rockwell International Corporation | Removal of polyhalogenated biphenyls from organic liquids |
| US5976226A (en) * | 1997-12-18 | 1999-11-02 | Bastian; Juergen | Means to ensure a minimum of gas content in liquids used for heat exchange and insulating purposes with complementary means for liquid expansion into vessels with variable volumes |
| WO2000007688A1 (en) * | 1998-08-03 | 2000-02-17 | Tokyo Electron Limited | Esrf coolant degassing process |
| US6217634B1 (en) * | 1999-08-27 | 2001-04-17 | Electric Power Research Institute, Inc. | Apparatus and method for monitoring and purifying dielectric fluids |
| GB2360953A (en) * | 2000-04-04 | 2001-10-10 | Oil Purification Systems Ltd | Oil cleaner for removing water and gases from oil |
| US6391096B1 (en) | 2000-06-09 | 2002-05-21 | Serveron Corporation | Apparatus and method for extracting and analyzing gas |
| US7409849B2 (en) * | 2003-11-22 | 2008-08-12 | Filmax, Inc. | Oil filtration system for plural phase power equipment tanks |
| CN103594227A (en) * | 2013-10-24 | 2014-02-19 | 国家电网公司 | Transformer high-voltage side incoming cable oil tank three-phase assembly |
| WO2015141612A1 (en) * | 2014-03-17 | 2015-09-24 | 国立大学法人東京大学 | Separation apparatus, fluid device, separation method, and mixing method |
| CN105140014A (en) * | 2015-09-24 | 2015-12-09 | 江苏宏源电气有限责任公司 | Method for oil injection of liquid immersed type distribution transformer |
| CN105185519A (en) * | 2015-07-29 | 2015-12-23 | 国网山东省电力公司电力科学研究院 | Online monitoring and purifying system for transformer oil |
| CN105223297A (en) * | 2015-11-20 | 2016-01-06 | 江苏有能电力自动化有限公司 | The degasser that a kind of novel transformer oil chromatography on-Line Monitor Device is special |
| CN105223277A (en) * | 2015-11-20 | 2016-01-06 | 江苏有能电力自动化有限公司 | A kind of novel transformer oil chromatography on-Line Monitor Device |
| CN105259260A (en) * | 2015-11-20 | 2016-01-20 | 江苏有能电力自动化有限公司 | Novel transformer oil chromatography online monitoring device with three-way valve |
| US10773192B1 (en) * | 2019-04-09 | 2020-09-15 | Bitfury Ip B.V. | Method and apparatus for recovering dielectric fluids used for immersion cooling |
| US11608217B1 (en) | 2022-01-01 | 2023-03-21 | Liquidstack Holding B.V. | Automated closure for hermetically sealing an immersion cooling tank during a hot swap of equipment therein |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4303783C2 (en) * | 1993-02-05 | 1997-03-27 | Aeg Tro Transformatoren Gmbh | Process for cleaning transformer oils and arrangement for carrying out the process |
| DE19501323C2 (en) * | 1995-01-19 | 2003-10-09 | Micafil Ag Zuerich | Process for drying the solid insulation of a transformer arranged in an electrical system |
| DE102014216280A1 (en) * | 2014-08-15 | 2016-02-18 | EnBW Energie Baden-Württemberg AG | Method for voltage-free maintenance of a stationary transformer station and mobile transformer station |
| CN105632707B (en) * | 2015-12-27 | 2017-08-01 | 国家电网公司 | A kind of transformer oil filter oil inlet and outlet commutating structure |
| CN109003786B (en) * | 2018-07-24 | 2021-08-31 | 国网福建省电力有限公司 | Intelligent microwave vacuum treatment device for transformer oil |
| CN109003787B (en) * | 2018-07-24 | 2021-08-31 | 国网福建省电力有限公司 | Intelligent microwave vacuum treatment method for transformer oil |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2340898A (en) * | 1941-11-29 | 1944-02-08 | Gen Electric | Electric apparatus |
| US3675395A (en) * | 1970-10-09 | 1972-07-11 | Keene Corp | Apparatus for the purification of oils and the like |
-
1972
- 1972-11-23 GB GB5419972A patent/GB1440190A/en not_active Expired
-
1973
- 1973-11-20 US US417559A patent/US3894171A/en not_active Expired - Lifetime
- 1973-11-21 DE DE2358072A patent/DE2358072A1/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2340898A (en) * | 1941-11-29 | 1944-02-08 | Gen Electric | Electric apparatus |
| US3675395A (en) * | 1970-10-09 | 1972-07-11 | Keene Corp | Apparatus for the purification of oils and the like |
Cited By (28)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4234754A (en) * | 1978-02-28 | 1980-11-18 | Bicc Limited | Oil-filled electric cable installations comprising pressurizing oil tanks |
| US4280014A (en) * | 1979-02-27 | 1981-07-21 | Bicc Limited | Electric cable installations |
| US4358379A (en) * | 1980-11-21 | 1982-11-09 | Noboru Inoue | Process for refining electric insulating liquids |
| US4437082A (en) | 1982-07-12 | 1984-03-13 | Westinghouse Electric Corp. | Apparatus for continually upgrading transformer dielectric liquid |
| US4526677A (en) * | 1984-06-04 | 1985-07-02 | Rockwell International Corporation | Removal of polyhalogenated biphenyls from organic liquids |
| US5976226A (en) * | 1997-12-18 | 1999-11-02 | Bastian; Juergen | Means to ensure a minimum of gas content in liquids used for heat exchange and insulating purposes with complementary means for liquid expansion into vessels with variable volumes |
| WO2000007688A1 (en) * | 1998-08-03 | 2000-02-17 | Tokyo Electron Limited | Esrf coolant degassing process |
| US6491742B1 (en) | 1998-08-03 | 2002-12-10 | Tokyo Electron Limited | ESRF coolant degassing process |
| US6217634B1 (en) * | 1999-08-27 | 2001-04-17 | Electric Power Research Institute, Inc. | Apparatus and method for monitoring and purifying dielectric fluids |
| GB2360953A (en) * | 2000-04-04 | 2001-10-10 | Oil Purification Systems Ltd | Oil cleaner for removing water and gases from oil |
| GB2360953B (en) * | 2000-04-04 | 2004-04-07 | Oil Purification Systems Ltd | Oil cleaner |
| US6391096B1 (en) | 2000-06-09 | 2002-05-21 | Serveron Corporation | Apparatus and method for extracting and analyzing gas |
| US7409849B2 (en) * | 2003-11-22 | 2008-08-12 | Filmax, Inc. | Oil filtration system for plural phase power equipment tanks |
| US20080295904A1 (en) * | 2003-11-22 | 2008-12-04 | Filmax, Inc. | Oil filtration system for plural phase power equipment tanks |
| CN103594227A (en) * | 2013-10-24 | 2014-02-19 | 国家电网公司 | Transformer high-voltage side incoming cable oil tank three-phase assembly |
| WO2015141612A1 (en) * | 2014-03-17 | 2015-09-24 | 国立大学法人東京大学 | Separation apparatus, fluid device, separation method, and mixing method |
| JPWO2015141612A1 (en) * | 2014-03-17 | 2017-04-06 | 国立大学法人 東京大学 | Separation apparatus, fluid device, separation method and mixing method |
| CN105185519B (en) * | 2015-07-29 | 2016-06-29 | 国网山东省电力公司电力科学研究院 | A kind of transformer oil on-line monitoring cleaning system |
| CN105185519A (en) * | 2015-07-29 | 2015-12-23 | 国网山东省电力公司电力科学研究院 | Online monitoring and purifying system for transformer oil |
| CN105140014A (en) * | 2015-09-24 | 2015-12-09 | 江苏宏源电气有限责任公司 | Method for oil injection of liquid immersed type distribution transformer |
| CN105223297A (en) * | 2015-11-20 | 2016-01-06 | 江苏有能电力自动化有限公司 | The degasser that a kind of novel transformer oil chromatography on-Line Monitor Device is special |
| CN105259260A (en) * | 2015-11-20 | 2016-01-20 | 江苏有能电力自动化有限公司 | Novel transformer oil chromatography online monitoring device with three-way valve |
| CN105223277A (en) * | 2015-11-20 | 2016-01-06 | 江苏有能电力自动化有限公司 | A kind of novel transformer oil chromatography on-Line Monitor Device |
| CN105223277B (en) * | 2015-11-20 | 2017-07-18 | 江苏有能电力自动化有限公司 | A kind of novel transformer oil chromatography on-Line Monitor Device |
| CN105223297B (en) * | 2015-11-20 | 2017-07-18 | 江苏有能电力自动化有限公司 | A kind of special degasser of novel transformer oil chromatography on-Line Monitor Device |
| US10773192B1 (en) * | 2019-04-09 | 2020-09-15 | Bitfury Ip B.V. | Method and apparatus for recovering dielectric fluids used for immersion cooling |
| US11772019B2 (en) | 2019-04-09 | 2023-10-03 | Liquidstack Holding B.V. | Method and apparatus for recovering dielectric fluids used for immersion cooling |
| US11608217B1 (en) | 2022-01-01 | 2023-03-21 | Liquidstack Holding B.V. | Automated closure for hermetically sealing an immersion cooling tank during a hot swap of equipment therein |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2358072A1 (en) | 1974-06-06 |
| GB1440190A (en) | 1976-06-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| AS | Assignment |
Owner name: POROUS ELEMENT HEATING LIMITED, HAVENSIDE, BOSTON, Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:BOC INTERNATIONAL LIMITED;REEL/FRAME:003847/0172 Effective date: 19810330 |
|
| AS | Assignment |
Owner name: COLOROLL (MARCH 1990) LIMITED Free format text: CHANGE OF NAME;ASSIGNOR:POROUS ELEMENT HEATING LIMITED;REEL/FRAME:005668/0126 Effective date: 19900820 Owner name: POROUS ELEMENT TECHNOLOGY LIMITED, BROOKHILL ROAD, Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:COLOROLL (MARCH 1990) LIMITED;REEL/FRAME:005668/0128 Effective date: 19910307 |