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Publication numberUS3821605 A
Publication typeGrant
Publication dateJun 28, 1974
Filing dateAug 10, 1972
Priority dateAug 10, 1972
Also published asCA1022607A1, DE2337864A1
Publication numberUS 3821605 A, US 3821605A, US-A-3821605, US3821605 A, US3821605A
InventorsPendrak J
Original AssigneeWestinghouse Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Remote transformer monitoring system
US 3821605 A
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Description  (OCR text may contain errors)

111] 3,821,605 June 28, 1974 1 REMOTE TRANSFORMER MONITORING SYSTEM [75] Inventor: Johnny M. Pendrak, Athens, Ga.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

221 Filed: Aug. 10,1972 211 Appl. No.: 279,567

[52] U.S.Cl 317/14 R, 317/14 G, 317/14H [51] Int. Cl. H'IlZh 7/04 [58] Field 01 Search. 340/151, 256; 317/28, 14 G,

317/14 R, 14 H, 14 .1, 15, 28 B, 29 B, 28 R,

1/1969 Wagner 317/14 R 5/1972 Levy 340/256 Primary Examiner-J. D. Miller Assistant Examiner-Patrick R. Salce Attorney, Agent, or Firm-J. R. Hanway ABSTRACT Apparatus for detecting and controlling transformer conditions at a remote location. Detecting sensors and activating controllers are located within the transformer for detecting certain existing conditions of the transfonner and for applying control signals for changing the transformer conditions. Signals from the detectmg sensors are transmitted to a remote monitoring [56] References Cited station where they are processed and displayed. Signals are originated at the remote monitoring station UNITED STATES PATENTS and transmitted to the activating controllers to change 2,773,146 12/1956 Saver 317/14 G the transformer conditions 3,195,015 7/1965 Astleford 3l7/l4 H 3,253,260 5/1966 Hawley 340/151 14 Claims, 5 Drawing Figures a. |24 126- my I22 I30 I30 I30 |30 f ,137 (,52 ,l38 I DETECTOR ACTlVATOR TRANSFORMER CODER IDENTIF'ER %%%%%ER TR A'lvsMwTER I36 ,140 PROGRAMED MANUAL tlt ssess (I34 TRANSFORMER MNNTENANCE INDICATOR midi ($812 AND ALARM PATENTEUJUNZ am 3 2 05 EMT l W ENCODER TRANSMITTER DECODER- RECEIVER PATENTEDJUNZB I974 SHEET Q 0F A MANUAL CONTACT ACTIVATOR CONTACT POSITION DETECTOR REMOTE CONTACT ACTIVATOR m W N N000 ERIT GT H RNS E D 3 7 W L T WGEV Q RU A PRESSURE DETECTOR CONTROL ACT I VATOR EMERGENCY DECODER- RECEIVER ENCODER- vTRANSMITTER PATE'IITEEIIIIIIMII 3.821.605

SHEEF I BF A I8 v I W ig 5 56 8 I00 Hg WW, I

low I22 I24, Ige- I30 I30 I30 I30 FIGS 13? (,Is2 ,138 I 3255322 EN C'XSEE IDENTIF'ER RECEIVER TRANSMITTER ,I3C i ,I4O PROGRAMED AUTOMATIC 'w ACTI\ /ATOR TOR I CON TROI CONTROL TRANSFORMER MAINTENANCE STATUS INDICATOR INDICATOR ANO ALARM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical inductive apparatus and, more specifically, to remote monitoring and controlling systems for transformers.

2. Description of the Prior Art Transformers used in power distribution systems are generally associated with protective devices which prevent or limit damage to the transformer and its associated apparatus. Distribution transformers of the completely self-protected type include a lightning arrester to protect the distribution system from lightning surges. The completely self-protected transformer also includes a circuit breaker on the secondary or lowvoltage side and a fuse link ora full range currentlimiting fuse or a fuse link in series with a full or partial range current-limiting fuse on the primary or highvoltage side.

The completely self-protected transformer is protected against excessive damage by its protective devices. The secondary breaker disconnects the transformer from its load if the current becomes dangerously high. The current limiting fuse, the protective link, or the combination of both disconnects the transformer from the distribution feeder line if dangerously high current is drawn by a faulty transformer.

With the presently available protective devices in a distribution transformer, activation of a protective device to limit system damage causes a power outage. A signal light is mounted on the transformer enclosure to provide visual indication of when the secondary circuit breaker is about to trip. That is, the signal light is turned on at a lower overload current than that required to trip the breaker. The signal light remains on until reset even though the load current is later reduced to a satisfactory level. When line crews see an illuminated signal light, they are thereby given notice that a moderate overload condition has occurred. Repeated observations of an illuminated signal light usually indicates that the transformer should be replaced with a higher capacity transformer. The signal light also gives a quick and accurate visual indication of where a tripped breaker is located when a power outage occurs.

The completely self-protected transformer also includes an emergency control mechanism which effectively changes the rating of the circuit breaker. The emergency control mechanism may be moved from its normal position to an overload position to allow the resetting of a tripped breaker. The rating of the circuit breaker may be increased by the emergency control mechanism for a short period of time until the bimetallic strip in the circuit breaker has cooled sufficiently to allow setting of the rating of the circuit breaker at its normal position. This usually permits quicker restoration of service after a power outage. In some situations, the emergency control may be set to increase the capacity of the breaker and thus permit operation of the transformer with higher than normal overload current. While this procedure detrimentally affects the life of the transformer, the loss in some transformer life is sometimes justified when a power outage can be prevented.

The versatility of the completely self-protected distribution transformer is only limited by the necessity of visual observation and normal control of the transformer adjustments and switches. It is desirable, and, it is an object of this invention, to provide transformer apparatus in which the condition thereof may be monitored at a remote location. It is also desirable, and it is a further object of this invention, to provide a transformer monitoring system which can respond to the monitored information and remotely control the transformer adjustments and switches according to a predetermined program.

SUMMARY OF THE INVENTION The secondary circuit breaker of the distribution transformer is connected to activator and detector devices which control and monitor the status of the circuit breaker. A pressure detector is also used to monitor the pressure of the liquid coolant in the transformer and therefore monitor the pressure of the gases above the liquid. Activator devices are included which may open and close the circuit breaker contacts from local or remote locations, adjust the emergency control mechanism, and reset the signal light. Detector devices are included which monitor the signal light, the emergency control mechanism, and the circuit breaker contacts, as well as the coolant pressure. The detected information is sent to a remote monitoring station which provides visual or audible indications of the status of the detected transformer variables. Activator control signals are originated at the remote monitoring station by manual means or automatically by programmed means and sent back to the transformer to correct any undesirable condition detected at the transformer by the monitor. Various combinations of activator and detector devices may also be used.

BRIEF DESCRIPTION OF THE DRAWINGS I Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. l is a cut-away view of a distribution transformer including activators and detectors according to this invention;

FIG. 2 is a schematic diagram illustrating the transformer conditions which are detected and activated according to this invention;

FIG. 3 is a view showing activating and detecting devices connected to a circuit breaker according to a specific embodiment of this invention;

FIG. 4 is a schematic diagram illustrating activator and detector connections according to a specific embodiment of this invention; and

FIG. 5 is a block diagram illustrating an overall transformer monitoring and controlling system constructed according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar elements in all figures of the drawings.

Referring now to the drawings, and FIG. l in particular, there is shown a pole-type completely selfprotected distribution transformer 10. The transformer 10 includes an enclosure 12 with a lightning arrester l4 and a primary bushing 16 mounted thereon. The bushing 16. includes a current-limiting fuse or fusible link 18 and a protective link 20 which protect the primary distribution system from internal transformer faults.

Secondary bushings, such as the bushing 22, are attached to the enclosure 12. A signal light 24 is mounted on the enclosure 12 and is electrically connected to terminals on a circuit breaker 26. A core and coil assembly 28 is secured inside the enclosure 12 with the circuit breaker 26 attached thereto. Required winding leads, such as the lead 30, extending from the coil to appropriate bushings.

The circuit breaker 26 includes two sets of contacts each connected in series with a secondary winding lead. A three-phase transformer would have a circuit breaker with three sets of contacts. The contacts are opened or tripped by a bimetallic strip through which the contact current passes. A circuit breaker having thermally responsive bimetallic elements and suitable for use with this invention is described in US. Pat. No. 2,686,242, which is assiged to the same assignee as is this invention.

Activators and detectors are attached to the circuit breaker 26 and are electrically connected through the .plug 31 and the cable 34 to an encoder-transmitter 36 and to a decoder-receiver 38. A pressure detector 40 detects the pressure of the liquid coolant 42 contained within the transformer enclosure 12. An emergency control activator 44 may be remotely controlled to change the amount of current necessary to open the contacts of the circuit breaker 26. A remote contact activator 46 may be remotely controlled to open or close the contacts of the circuit breaker 26. A manual contact activator 48 mechanically trips the contacts of the circuit breaker 26 when a handle 50 is turned to move the linkage 52.

' The detectors and the remotely controlled activators are linked to a remote monitoring station which processes the detected information and issues appropriate control signals. The function of the detectors and activators illustrated in FIG. 1, and of additional detectors and activators not illustrated in'FlG. 1, is described in greater detail hereinafter in this description.

' FIG. 2 is a schematic diagram of a transformer having desired activators and detectors contained therein. The enclosurev 12 encloses the core and coil assembly 28 which has a current-limiting fuse 18 in a lead of the primary winding 56. The circuit breaker 26 is connected in the circuit of the secondary winding 58.

The desired activators and detectors are shown in block form with dashed lines indicating either an electrical or a mechanical connection to the circuit breaker 26. The manual contact activator Al provides means for manually changing the position of the circuit breaker contacts. The activator Al may be a mechanical linkage connecting the circuit breaker contacts to an externally mounted handle, an electrical switch which controls a motor connected to the circuit breaker contacts, or any other suitable activator device.

The remote contact activator A2 provides means for remotely changing the position of the circuit breaker contacts. The activator A2 may be a motor or solenoid which is connected to the circuit breaker contacts, or any other suitable activator device. The signal light reset activator A3 provides means for remotely resetting the signal light. The signal light reset activator A3 may be a solenoid or motor which disengages the signal light contacts, limit means which limits the movement of the remote contact activator A2 to the amount necessary to reset the signal light contacts, or any other suitable activator device.

The emergency control activator A4 provides means for recalibrating or resetting the rating of the circuit breaker 26. With the circuit breaker 26 described by this invention, adjusting screws provided on the outside of the circuit breaker 26 effectively change the position of the bimetallic strips inside the circuit breaker housing. By turning the adjustment screws, more or less movement of the bimetallic strips is necessary to trip the breaker contacts. Turning the adjustment screws may be accomplished with a solenoid or motor which is electrically connected to the adjustment screws. The emergency control position detector Dl provides means for detecting the position of the emergency control adjustment. That is, determining whether the circuit breaker 26 is adjusted to trip at its normal current or at an overload value above the normal value. The detector D1 may be a switch which is closedby the movement of the activator A4 when the emergency control is set at the overload position.

The contact position detector D2 provides means for detecting the position of the contacts of the circuit breaker 26. That is, determining whether the contacts are open or closed. The detector D2 may be a switch which is activated by the mechanical movement of the contacts, an electrical connection to the contacts which detects a change in voltage across the contacts when-they change position, or any other suitable detector device. The signal light detector D3 provides means for detecting if the signal light 24 is illuminated. A convenient detector arrangement is an electrical connection to the signal light voltage. An illuminated signal light indicates that an overload condition has occurred in the transformer. If only remote indications are desired, the external lamp of the signal light 24 may be omitted from the transformer components.

The pressure detector D4 provides means for detecting the pressure of the coolant in the transformer. Pressure detection is desirable since the transformer tank will withstand only a fixed amount of pressure. Although the pressure of the coolant is proportional to the temperature of the coolant, pressure detection is more reliable since pressure distribution is usually much more uniform than temperature distribution. The pressure detector D4 may be a switch which is activated when the coolant pressure reaches a predetermined value.

The information signals from the detectors D1, D2,

- D3 and D4 are applied to an encoder-transmitter 36 from which they are tranferred to a remote monitoring station. Activating signals from the remote monitoring station are applied to the decoder-receiver 38 from which appropriate control signals are applied to the activators A2, A3 and A4.

FIG. 3 illustrates a specific embodiment'of the invention wherein the circuit breaker 26 has detectors and activators connected thereto. The circuit breaker 26 includes the contact handles 60 and 62 which may be moved to open and close the circuit breaker contacts. The handles 60 and 62 are mechanically interconnected by a rod 64 to which a lifter link 66 is attached. The linkage 68 is pivoted on pin 70 and is attached to the lifter link 66 and to the wheel 72. The motor 74 rotates the wheel 72 when it is desired to change the position of the breaker contacts. Because of the eccentric connection of the linkage 68 to the wheel 72, the motor may move the handles 60 and 62 in two directions without reversing the direction of rotation of the motor 74, although a reversible motor may be used.

The signal light 24 is activated when the contacts 76 and 78 are electrically connected together within the housing of the circuit breaker 26. US. Pat. No. 2,686,242 discloses a suitable arrangement for connecting the contacts 76 and 78 together when the current flowing through the circuit breaker 26 is excessive.

The emergency control adjusting screws 80 and 82 are connected to crank arms 84 and 86, respectively. When the solenoid 88 is activated, the rod 90 is moved substantially in an axial direction to rotate the adjusting screws 80 and 82. The position of the adjusting screws 80 is detected by the switch 92. When the rod 90 is extend ed from the solenoid 88, the button 94 is depressed and the switch 92 is activated. The secondary leads 96 and 98 conduct the secondary winding current through the circuit breaker 26.

FIG. 4 illustrates a schematic diagram of a transformer constructed according to a specific embodi ment of this invention. The circuit breaker 26 includes the individual circuit breaker contact structures 1100 and 102 which each include a bimetallic strip through which the secondary currents flow. The terminal pairs across which the activator and detector signals are applied are denoted with the activator and detector symbols Al, A2, A3, A4, D1, D2, D3 and D4 according to FIG. 2.

The motor 74 opens and closes the circuit breaker 26 from remotely originated signals. The handle I04 may be utilized to locally and manually activate the circuit breaker 26. Conductors 106 and 108 which are connected to the breaker contact structure W2 provide means for electrically detecting the position of the circuit breaker 26. When the circuit breaker 26 is closed, negligible voltage will develop across the conductors I06and 1108. When the circuit breaker 26 is opened, a voltage develops across the conductors 1106 and 1108 through the resistor 110.

The switch 112 activates the signal light 241 and is mechanically connected to the bimetallic strips of the circuit breaker 26. When a predetermined amount of load current flows through either bimetallic strip, the switch 112 is closed. Thus, the signal light 24 is turned on and a voltage is detected across the signal light 241. The solenoid 114 may be activated to open the switch 112 to reset the signal light 24.

Solenoid 116 activates the emergency control feature of the circuit breaker 26 by mechanical coupling to the bimetallic strips. When the emergency control is activated, switch 118 closes to detect the position of the emergency control. Similarly, the pressure switch 120 is closed when the coolant pressure reaches a predetermined value.

The value of the voltages provided by the detectors in this embodiment is substantially equal to one-half the voltage of the secondary winding 58. Other arrangements may be used, such as a separate control circuit winding, to provide the control voltages.

FIG. 5 shows the transformer 10 in association'with a plurality of other transformers, such as transformers.

receiver device il3tl which processes the activating and detecting signals between the transformer and the remote monitoring station 1128. Transfer of the signal from the transformer to the remote monitoring station may be accomplished by telephone lines, power line carrier systems, radio signals, or any other suitable means.

The remote monitoring station I28 provides the equipment necessary to utilize the intelligence information signals from the transformers. Detector signals are applied to the detector decoder-receiver 132 which processes the signals to the proper form for application to the transformer status indicator 1134 and to the programmed automatic activator control 136. The transfonner identifier 137 processes unique coded information signals transmitted from each transformer by its associated transmitter-receiver device into the proper form for application to the transformer status indicator 1134.

The transformer status indicator 1134 may be a cathode ray tube on which the information is displayed in printed words. For example, a typical display would be TRANSFORMER 237-SIGNAL LIGHT ON. The station indicator 134 may also be an arrangement of panel lights wherein each light represents a particular transformer status. It is within the contemplation of this invention that other means of indication and identification may be used, for example, a print-out device, such as a typewriter.

The information signals are applied to a computer or a programmed automatic activator control I136 which processes the received information and sends appropriate predetermined signals to the activator encodertransmitter 113%. The activator encoder-transmitter 138 sends the desired activating signals to a particular identified transformer. The manual activator controll40 may be used to send desired activating signals in response to observations of the status indicator 1134. The manual activator control 1140 may comprise an arrangement of push-buttons and/or switches.

The transformer status indicator 1134 indicates which transformer is being monitored. This is accomplished by means of a code which is assigned to identify each separate transformer. It also indicates the status of the breaker contacts of the emergency control, and of the signal light, and the pressure of the coolant. The automatic activator control 136 may be programmed to originate activating signals in response to the detected information. For example, the program may be such that after a predetermined number of signal light indications, the maintenance indicator and alarm 142 would be activated to alert personnel to make the proper replacements or changes in the transformer system. The program may be such that an open circuit breaker will be reset only once automatically. The program may be such. that the emergency control will be activated to a higher load current position to prevent the tripping or opening of the circuit breaker as long as the pressure of the coolant is below a predetermined value.

In general, the transformer management philosophy of the electric utility company will determine the type of program by which the transformers will be controlled. Since numerous changes may be made in the above-described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A transformer comprising an enclosure, a core and coil assembly positioned in the enclosure, a circuit breaker assembly positioned in the enclosure, said circuit breaker assembly having open and closed contact positions and having emergency control means with normal and overload settings, overload responsive means positioned in the enclosure, said overload responsive means having normal and overload conditions, position means for detecting the position of said circuit breaker assembly, condition means for detecting the condition of said overload responsive means, transfer means for transferring electrical signals corresponding to the detected information from said position means and said condition means to the exterior of said enclosure, said electrical signals being electrically measurable from the exterior of said enclosure, switching means for switching said emergency control means between the normal and the overload settings in response to signals from a remotemonitoring station, and means for detecting information about the setting of said emergency control means.

2. The transformer apparatusof claim 1 including means for resetting the .overload responsive means to its normal condition in response to signals from a remote monitoring station.

3. The transformer apparatus of claim 1 wherein the emergency control means includes rotatable adjusting screws, and the means for activating the emergency control means includes a solenoid having an output shaft, said output shaft being eccentrically coupled to the adjusting screws.

4. A transformer comprising an enclosure, a core and coil assembly positioned in the enclosure, a circuit breaker assembly positioned in the enclosure, said circuit breaker assembly having open and closed contact positions, overload responsive means positioned in the enclosure, said overload responsive means having normal and overload conditions, position means for detecting the position of said circuit breaker assembly, condition means for detecting the condition ofsaid overload responsive means, transfer means for transferring electrical signals corresponding to the detected information from said position means and said condition means to the exterior of said enclosure, said electrical signals being electrically measurable from the exterior of said enclosure, and driving means for moving the circuit breaker assembly between the open and closed positions in response to signals from a remote monitoring station, said driving means including a motor having a rotating shaft, circuit breaker contact handles connected to the circuit breaker contacts, a pivoted linkage having first and second ends, the first end of said linkage being coupled to the circuit breaker contact handles, and the second end of said linkage being eccentrically coupled to the motor shaft.

5. The transformer apparatus of claim 3 wherein the means for detecting information about the position of the emergency control means includes a switch which is controlled by the position of the solenoid output shaft. 6

6. A transformer monitoring system comprising means for detectinginformation about the status of predetermined transformer variables, activating means for changing the status of predetermined transfomier variables, encoding and transmitting means for transferring the detected information to a remote monitoring station, the remote monitoring station including means for receiving and decoding the detected information, means for indicating at the remote monitoring station the status of the detected transformer variables, and means for sending control signals to said activating means from the remote monitoring station.

7. The transformer monitoring system of claim 6 wherein the detected predetermined transformer variables include the position of the contacts of a circuit breaker in the transformer and the condition of an overload responsive means in the transformer.

8. The transformer monitoring system of claim 6 wherein the activated transformer variables include the position of circuit breaker contacts in the transformer.

9. The transformer monitoring system of claim 6 wherein the detected predetermined transformer variables include the position of emergency control means in the transformer.

10. The transformer monitoring system of claim 6 wherein the activated transformer variables include the position of emergency control means in the transformer.

11. The transformer monitoring system of claim 6 wherein the activated transformer variables include the condition of overload responsive means in the transformer.

12. The transformer monitoring system of claim 6 wherein the detected predetermined transformer variables include the pressure of coolant inside the transformer.

13. The transformer monitoring system of claim 6 wherein the remote monitoring station includes means for identifying the transformer being monitored when more than one transformer is included in the system, and programmable automatic activating means which receives the detected information and controls the activating signals.

14. A transformer monitoring system for monitoring a plurality of transformers, each of said transformers including a circuit breaker assembly having pen and closed contact positions, overload responsive means having normal and overload conditions, emergency control means having normal and overload positions, means for detecting information about the position of the contacts of the circuit breaker assembly, the condition of the overload responsive means, the position of the emergency control means, and the pressure of coolant in the transformer, means for transferring the detected information to a remotely located monitoring station, said monitoring station including means for identifying the transformer from which detected information is received, means for indicating the detected information, programmed means which originates a control signal corresponding in a predetermined manner to the detected information, means for transferring the control signal to activating means located in a transformer, said activating means being constructed to change the position of the breaker contacts, the condition of the overload responsive means, and the position of the emergency control means according to the nature of the control signal originated by said programmed means.

i t i t I.

' UNITED STATES PATENTQOFFICE .QERTIFICATE OF CORRECTION Patent No.3,821,'605 Dated June 28, 197

Inventor (s) Johnny M. Pendr'ak It is certified that e rror appears in the above-identified patent and that said Letters Patent are hereby corrected as mhawn below:

Column 8, line 4H, cancel "pen" and substitute Signed ma mauled this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. Attesting Officer C MARSHALL DANN Commissioner of Patents U'COMM-DC 0870-980 FORM Po-1050 (o-o9) W 0.. OOVININIIY "INTI" OIHCI UNITED STATES PATENTQOFFICE v .QER'HFICATE 0F CORRECTION Patent; No 3,821,605 Dated June 28 197 4 Inventor (a) Johnny M. Pendrak It is certified that epror appears in the above-identified patent and that said Letters Patent are hereby con-acted as ehown below:

Column 8, line a l, cancel "pen" and substitute Signed and sealed this 5th day of November 1974.

(SEAL) Attest: 7

McCOY M. GIBSON JR. C. MARSHALL DANN Arresting Officer Conunissioner of Patents UlCOMM-DC DWI-F60 I Ill novllmllm IIIIYII. omcl nu o-ul-lu FORM Po-ioso (10-69)

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4124835 *Mar 26, 1976Nov 7, 1978Cahill Jr William JRemotely controlled utility service interrupter system and apparatus
US4218716 *Oct 14, 1977Aug 19, 1980General Electric CompanyProgrammable fault detecting relay for a transformer
US4249170 *Oct 9, 1979Feb 3, 1981Westinghouse Electric Corp.Annunciator
US4654806 *Mar 30, 1984Mar 31, 1987Westinghouse Electric Corp.Method and apparatus for monitoring transformers
US6494617Apr 30, 1999Dec 17, 2002General Electric CompanyStatus detection apparatus and method for fluid-filled electrical equipment
US6727821 *Mar 11, 2002Apr 27, 2004Perseus 2000, LlcApparatus and method for predicting an overload trip for an electrical power transformer
US8484150Feb 26, 2010Jul 9, 2013General Electric CompanySystems and methods for asset condition monitoring in electric power substation equipment
WO2000067019A1 *Apr 25, 2000Nov 9, 2000Gen ElectricStatus detection apparatus and method for fluid-filled electrical equipment
Classifications
U.S. Classification361/37, 340/646
International ClassificationH02H1/00, H02H3/04, H02H7/04, H01F27/00, H02H3/02, H01F27/40
Cooperative ClassificationH01F27/402, H02H7/04, H02H1/0061, H01F2027/404, H02H3/04
European ClassificationH01F27/40A, H02H3/04, H02H1/00E, H02H7/04
Legal Events
DateCodeEventDescription
Jun 7, 1990ASAssignment
Owner name: ABB POWER T&D COMPANY, INC., A DE CORP., PENNSYLV
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:WESTINGHOUSE ELECTRIC CORPORATION, A CORP. OF PA.;REEL/FRAME:005368/0692
Effective date: 19891229