US3851287A - Low leakage current electrical isolation system - Google Patents
Low leakage current electrical isolation system Download PDFInfo
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- US3851287A US3851287A US00367584A US36758473A US3851287A US 3851287 A US3851287 A US 3851287A US 00367584 A US00367584 A US 00367584A US 36758473 A US36758473 A US 36758473A US 3851287 A US3851287 A US 3851287A
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- 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
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/32—Insulating of coils, windings, or parts thereof
- H01F27/324—Insulation between coil and core, between different winding sections, around the coil; Other insulation structures
- H01F27/325—Coil bobbins
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- 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
- H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
- H01F27/36—Electric or magnetic shields or screens
-
- 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
- H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
- H01F27/36—Electric or magnetic shields or screens
- H01F27/363—Electric or magnetic shields or screens made of electrically conductive material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F19/00—Fixed transformers or mutual inductances of the signal type
- H01F19/04—Transformers or mutual inductances suitable for handling frequencies considerably beyond the audio range
- H01F19/08—Transformers having magnetic bias, e.g. for handling pulses
- H01F2019/085—Transformer for galvanic isolation
Definitions
- the disclosed invention presents an isolated electrical distribution system which includes at least a pair of power lines for providing a source of alternating voltage, one of the lines being connected to electrical ground, which are connected across the primary winding of an isolation power transformer, and at least a second pair of lines, neither of which is connected to said ground potential, wired to an electrical outlet or load and connected across the secondary winding of the transformer
- the isolation transformer housed in a metal enclosure, includes a magnetic core, a primary winding formed in a coil, a secondary winding formed in a separate coil with the coils mounted on themagnetic core on one side of the primary, with the turns of one coil wound in a clockwise direction relative to the core and the windings of the other coil wound in a counterclockwise direction relative to the core; another secondary winding formed in a separate coil-and mounted on the core on the other side of the primary coil; and thin flat nonmagnetic metal shield members, each having a slot therethrough, are fitted over the magnetic core and sandwiched in between each of the two secondary
- This invention relates to hospital electrical distribution system and, more particularly, to high power low leakage current isolation transformer and hospital type isolated electrical supply system combinations.
- Electrical AC distribution systems provide AC power from a source located at the power company over electrical lines which distribute the power to consumers at different locations.
- Electrical transformers are included in such a distribution system.
- the transformer is a well known electrical component by which AC electrical energy is coupled or transformed from one circuit at the transformer input to another coupled to the output by electromagnetic induction.
- the transformer includes at least a primary winding made up of a coil of wire, a secondary winding, also a coil of wire, inductively coupled together, and located physically on an iron core, the magnetic properties of which enhance the inductive coupling between the windings.
- a source of alternating voltage coupled to the primary winding is transformed and coupled by means of electromagnetic induction into an alternating voltage that appears across the secondary winding.
- the relationship between the magnitude of voltage applied to the primary and the voltage appearing at the secondary is primarily a function of the turns ratio of the windings, the number of turns of wire in the coil which makes up the primary as compared to the secondary. This and other factors affecting the design and operation of transformers are well known and explained in readily available literature.
- transformers are that in which the turns ratio, the number of turns in the secondary winding as compared to the number of turns in the primary winding, is equal approximately to one or two, whereby a voltage applied to the input or primary winding of that transformer is the same voltage which is produced at the secondary winding, or double that of the primary winding.
- This type of transformer permits a coupling of voltages and current from one circuit coupled to the primary winding to a second circuit coupled to the secondary winding, with no direct or DC current path between each primary and secondary circuits.
- the transformer of this type serves to isolate electrically the first and second circuits and the transformer appropriately is referred to as an isolation transformer.
- isolation transformers have long found application for many different purposes as part of electrical AC distribution systems.
- One well-known and particularly critical application for isolation transformers is in combinationwith the electrical supply system of an operating room found in the modern hospital.
- the hospital operating room contains a special isolated electrical system.
- the power available from the electrical utility companies is brought into the hospital via two or more lines and fed into an isolation transformer of the operating room supply.
- One of the utility company lines is always grounded, i.e., connected in a direct current path with the earth.
- the output of the isolation transformer is thereupon fed to the numerous electrical distribution outlets found in the operating room. By connection to these outlets electrical and electronic instruments used in modern hospital operating rooms receive electrical power. Accordingly, isolation transformers must be capable of handling large amounts of AC power.
- the transformer primary and secondary windings are insulated from one another and from the magnetic iron core by isulating material. However even the best insulating material has some resistive leakage, however slight. And after years of service the insulation ages increasing resistive leakage current. In a transformer this insulation breakdown could permit noticeable resistive leakage currents between the primary and secondary windings and between each of those windings and the iron transformer core.
- a second cause of inherent leakage currents occurs due to electrostatic coupling.
- the inherent operation of the transformer at the 60-cycle frequencies usually found on the power lines relies upon magnetic induction action for coupling between the windings, it is apparent that there exists between the spaced electrically conductive materials of each of the primary and secondary windings and of the iron core some degree ofelectrical capacitance, however small.
- alternating current does effectively pass through capacitance; the larger the capacitance, the more current which can flow therethrough.
- this electrostatic coupling through distributed capacitance should be minimized.
- the leakage due to distributed capacitance is more predominant than that due to insulation resistance, resistive leakage.
- capacitive leakage current decreases to more than offset increased resistive leakage current.
- the transformers in all cases, should be of the isolating type and designed for low current leakage in the secondary winding.
- the capacitive current leakage of the secondary should not exceed 10 microamperes on units 5 KVA and smaller or 25 microamperes on units 15 KVA and larger. Transformers having higher current leakage values would limit the usable circuits in the total system.
- the present standard does not call for the isolating transformer to have an electrostatic shield between the primary and secondary windings, however most leading authorities have recommended the use of a shield. It seems likely that the new standards will require an isolating transformer with an electrostatic shield. From the practical viewpoint, it does complicate the problem of producing a low leakage transformer, as it represents an additional capacitive coupling to ground. It does, however, provide an additional margin of safety in preventing shorts between the primary and secondary. Perhaps an even greater contribution of the shield is that of providing a measure of protection against the coupling of harmonic distortions between the primary and secondary which might otherwise adversely effect sensitive electronic monitoring equipment.
- An electrostatic shield between the primary and secondary windings of the transformer reduces not only 60 cycle AC coupling but minimizes coupling of any high frequency AC signals such as radio frequency signals that in some way get onto the power lines.
- the location of such a metal member is visualized in connection with the physical arrangement of the transformer elements.
- Power transformers typically include the iron core which forms a closed magnetic circuit.
- the iron core is shaped into either the core" or shell" type, and contain different winding arrangements.
- the magnetic circuit resembles a rectangle, and the primary and secondary windings are generally placed on two opposed legs of top core.
- the primary and secondary may be split and a portion of each placed on each of the two opposed legs.
- the magnetic core configuration resembles a rectangle with a center leg down the middle.
- the transformer windings are placed on the center leg, essentially remaining within the confines of the window formed on each side of the center leg by the outer legs of the rectangle, hence the term shell.
- the primary and secondary windings are either formed one on ts of the other, termed double wound," or are separately wound and placed side by side.
- the primary and secondary windings may be split, that is, a coil on one leg includes a part of the secondary wound over a part of the primary winding in a double wound arrangement; a like coil arrangement is placed on the opposed leg and each of the remote portions of the same primary and secondary windings are placed in an electrical series circuit together. This latter arrangement is typical of the transformer in the aforecited Sorgel publication.
- a metal barrier or shield is used in those transformer structures where it is desired to form or provide an 1 electrostatic shield to prevent passage of high frequency electrical currents between parts.
- Such shields are commonly found in transformers of the double wound variety.
- the shielding is accomplished typically by placing a metal foil layer between the primary and overwound secondary windings grounding that shield.
- An isolated electrical distribution system includes at least a pair of lines having applied thereto an alternating voltage, one of the lines being connected to ground, connected to the primary winding of an isolation transformer, and at least a second pair of lines, neither of which is connected to said ground, connected to the secondary windingof said transformer and to an electrical outlet load.
- the high power isolation transformer is located in a metal enclosure, suitably iron, and includes amagnetic core, a primary winding formed in a coil, a secondary winding formed in two coils mounted side by side on the magnetic core with the primary winding coil sandwiched between.
- a pair of thin, flat, nonmagnetic metal shield members each having a slot therethrough, is fitted over the core; each one in between a respective secondary coil and the primary coil to form a physical barrier between said coils, and twin insulating spacers are provided between said metal shields and each said coils to form a closely packed sandwich of coils, spacers and shield.
- the coils are oriented with the turns of one of the secondary coils wound in a clockwise direction with respect to the core leg and the turns of the other secondary coil wound counterclockwise, with the primary coil having its turns in one or other of such direction.
- FIG. 1 illustrates one view of an embodiment of the invention.
- FIG. 2 illustrates a side view of the transformer construction used in the embodiment of FIG. 1.
- FIG. 3 illustrates a shield member used in the embodiment of FIG. 1.
- FIG. 4 illustrates a specific example of a magnetic lamination of the transformer used in the iron core of the transformer of FIG. 1.
- FIG. 5 illustrates schematically the transformer disclosed in FIG. 1 together with circuits for testing current leakage.
- FIG. 6a and FIG. 6b represent core type and double wound shell type isolation transformer constructions commercially used in prior art hospital type isolated electrical supply systems.
- FIG. 7 illustrates another embodiment of the invention.
- FIG. 8 schematically illustrates the transformer included in FIG. 7.
- FIGS. 9a through 1' illustrate various lamination configurations.
- FIG. 10 illustrates still another embodiment of the invention.
- FIG. 11 illustrates schematically the transformer cluded in the embodiment of FIG. 10.
- the top view of the transformer in FIG. 1 shows it to include a first coil winding 1 spaced side by side from a second coil winding 3 and mounted on the center leg 5 of a shell type transformer core.
- the magnetic iron core includes two side legs, 7 and 9, and front and back legs, 11 and 13, which, form two windows, one on each side of the center leg. A large number of these laminations are stacked up together to form a transformer iron core. Suitable openings, 15, extend through the stack of laminations to permit bolts, not illustrated, to clamp the individual laminations together mechanically into a single core.
- Winding 1 is of conventional construction and consists of a plurality of layers of electrical wire wound around and along the core in a given direction, clockwise or counterclockwise, with each layer separated from the next adjacent layer suitably by a layer of insulating material until the requisite number of turns in the winding are formed and to form a spool with a central passage through which leg 5 extends.
- the two electrical leads 23 and 25 extend from coil 1 with lead 25 connected to the start of coil 1 and going to the first turn in the first layer most proximate the core and electrical lead' 23, finish lead, is attached to the last turn of wire in the coil.
- Winding 3 is similarly wound upon insulation tube 22, only partially illustrated, and in this embodiment comprises the same number of turns and structure so that the turns ratio between coils l and 3 is one-to-one. Likewise coil 3 includes a start electrical lead 27 and a finish electrical lead 29.
- the winding 3 which serves as the secondary winding, may contain double the number of turns if a two-to-one turns ratio is desired to double the voltage at the secondary.
- a thin flat metal member 31 which is also fitted ove-r central leg 5, which is better discussed hereinafter in connection with FIG. 3.
- a pair of thin flat O-shaped insulating members 26 and 28 are fitted between metal member 31 and a respective one of the coils 1 and 3 to insure insulation therebetween. As is apparent, this forms a closely packed sandwich construction of coil 1,
- the secondary winding 3 is mounted on the center leg in a manner which is magnetically opposite to that of primary winding l.-That is, assuming the turns in the coil making up winding 1 are wound upon core tube 21 or leg 5 in a clockwise manner in the view of FIG. 1, the turns of the winding 3 appear from the same view to be wound around insulating tube 22 or leg 5 in a counterclockwise manner. This is accomplished typically by winding both coils in the same direction but reversing one of the coils relative to the other prior to building up the laminations and completing the magnetic core.
- a lead 33 electrically connects shield member 31 in circuit with the magnetic core at leg 7 to electrical ground potential as indicated by the symbol in the drawing.
- the electrical utility lines which are provided by the power company provide connection to an alternating voltage source.
- the source is represented as the 120-
- the dash lines 32 symbolically denote a six sided metal housing or enclosure in which the transformer and usually monitoring instruments, not illustrated, or other electrical components common to hospital distribution systems are installed.
- This enclosure sometimes referred to as a panel, usually contains a door or removable trim cover, is formed of 12 gauge steel.
- the enclosure is electrically grounded as illustrated in the figure.
- FIG. 2 illustrates a front side view of the transformer found in FIG. 1. Visible in this view is the iron core leg 13, coil 3, leads 27 and 29, the insulating tube 22 partially visible, O-shaped insulating spacer 28 and metal shield member 31. As is apparent the view of the structural arrangements from the other end of the transformer would appear to be a mirror image of FIG. 2. Note that member 31 completely obscures the coil I located on the other side.
- Member 31 is suitably of aluminum, is thin and flat but of a somewhat complicated geometry. This includes a central passage 32 through which the central leg 5 of the transformer of FIG. 1 ex- For convenience, where an element appears in an-' tends and two cutaway end portions 39 and 41 with which to hook over the side core legs 9 and 7 in FIG. I.
- a slot 34 extends through the member, between passage 32 and an outer edge of the member 31. This slot forms a gap and prevents a current path in the metal from encircling passage 24.
- the geometry is essentially a C-shaped member with a hat on the upper end of a pedestal at its bottom end, if analogy is appropriate. In its simplest form it is apparent that a simple C-shaped member, eliminating the ends which hook over core legs 9 and 7 of FIG. 1,
- passage 32 is larger in cross section than core leg 5, and in position on the leg the shield is placed so that the slot 34 is not bridged electrically by any part of the iron laminations which make up the center or outer core legs. This prevents the shield from acting as a single turn coil that is short-circuited.
- Other ways of maintaining slot 34 open are apparent to the reader.
- FIG. 4 illustrates two individual laminations, A and B, which are commonly referred to as E-I laminations which is, by way of example, used to construct the magnetic core of FIG. 1.
- E-I laminations which is, by way of example, used to construct the magnetic core of FIG. 1.
- the transformer core is built up by alternating the positions of E and I laminations so that the I of the next adjacent lamination would be situated over the back rib leg of the E lamination, A, and the next E lamination would be situated atop both the I lamination, 38, and the stems of the E with the stems facing the opposite direction. And thisis continued until the core is of the desired height. 1
- a transformer construction of the embodiment of FIG. 1 constructed according to the teachings of this invention included a stack of laminations having a height of 1% inches and length and width dimensions of 9% and II% inches, respectively.
- Coil l comprised approximately 78 turns of 9 sq. heavy armored Polythermaleze 2,000 wire and consisted of approximately four layers.
- The'insulating tube comprised Nomex, well I known insulating material, and the layer to layer insulation comprised Quintex I.
- a like construction was used for the secondary winding 3.
- the transformer is put together in the conventional way by first forming the coils on suitable coil winding equipment.
- the coils are oriented as previously described, and the metal layer is sandwiched in between.
- the magnetic lamination is built up by individually inserting E laminations through the coil,
- the operation of a transformer is well understood and need not be repeated here in detail.
- the voltage at the primary, volts in the example produces a current which induces a voltage in the secondary winding, equal approximately to the primary voltage multiplied by the turns ratio, which equals 1 in the example given and is also 120 volts AC..
- the transformer is schematically illustrated in FIG. 5 with its core 50 and shield 31' connected to ground.
- a source of alternating current, 49 is applied across the primary winding of the transformer and one end of the secondary winding is connected by means of a 500 ohm resistor, 51, to ground potential.
- a microvolt meter, 53 is connected in parallel with resistor 51 to measure the small voltages that will be generated by the small currents flowing through resistor 51.
- the measuring circuit and load resistor represented by the dashed lines is, instead, used.
- a line, 54 is connected between one side of each of the primary and secondary windings. This, in turn, is connected through a resistor, 57, suitably 500 ohms to ground, and a microvolt meter, 55, is connected across resistor 57 to measure voltages generated by leakage currents.
- a source of 60 cycle alternating current, 49 is connectedacross the primary winding as in the preceding test.
- the isolated distribution system of the invention primarily due to the transformer construction has substantially less leakage current in all measurable respects, whether from the primary winding to ground, the secondary winding to ground, and between the primary to secondary winding, and even though a shield is included. All of the leakage currents are substantially below those levels desired in a hospital supply type isolation system, namely 10 microamps. This is true even though the transformer includes. essentially, a shield member 31 in FIG. I which would normally be expected to increase the capacitive coupling to ground and increase individual winding to ground leakage current as the prior art teaches. Accordingly, it is believed that some effects do occur by sandwiching the shield in between side by side primary and secondary windings on the transformer core which, though unexplained, do provide unexpected and highly desirable results.
- FIG. 1 Prior Art Double-wound FIG. 6(1)) Voltage Drop Across 500 ohm Resistor Millivolts Invention FIG. 1
- a 250 VA, 60 Hz, 120 volt transformer constructed according to the teachings of the invention included a primary winding having 169 turns of wire and a secondary winding having I76 turns of wire, with the secondary winding mounted on the transformer core so that the turns of the winding were in the same clockwise direction, and with the shield grounded, and various leakage currents were measured as set forth in Row 2 of the chart hereinafter presented.
- the leakage currents set forth in Row 1 of the chart below presented were obtained.
- the primary to secondary leakage decreased from 0.82 microamps to 0.06 microamps measured between the winding starts, and decreased from 1.6 microamps to 0.19 microamps measured between winding finishes:
- FIG. 7 discloses another embodiment of the invention in which the transformer is of a slightly different configuration.
- a first coil of wire 70 forms a primary winding and consists of a suitable predetermined number of turns of wire which, by way of one specific example, can comprise 78 turns of9 sq. heavy armored Polythermaleze 2,000 wire wound in four layers, is mounted on center leg of magnetic core 5'; Coil 70 is wound with the turns in a clockwise direction as indicated by the arrow.
- a second coil of wire 73 forms a first secondary winding and is mounted at one end of leg 5' spaced from winding 70.
- a third coil of wire 75 forms a second secondary winding and this coil is mounted on leg 5 at the other end of primary winding 70.
- each of these secondary windings contains an equal number of turns of wire, with the number of turns in each coil being an integral multiple of those turns in the primary winding.
- the turns ratio of each secondary insulator 83 form a sandwich arrangement in between coils 73 and -70.
- insulator 85 is sandwiched in between the ends of coils and 75.
- these insulator elementsand shield elements are identical in construction with corresponding elements 26, 28 and 31 of the preceding embodiments and function in the same manner.
- Shield 81, shield 87 are joined by electrical wires 23' in common with core 7 'which in turn is connected to electrical ground potential as indicated by the symbol in the drawing
- the primary winding 70 includes two leads 27' and 29 connected to the ends of the coil. These are connected to a grounded AC line via leads 37' and 35.
- Secondary winding 73 includes two leads 91 and 93 connected to the start (St.) and finish (Fin.) ends ofthe secondary coil 73, respectively, and coil includes leads 95 and 97 connected to the finish and start ends of secondary winding 75, respectively.
- Secondary winding 73 is positioned on core 5 so that its windings are in the opposite winding direction as that of the other secondary coil 75. Otherwise stated, given winding 75 wound in a clockwise direction, winding 73 would have its windings running in a counterclockwise direction. In so doing, the positive phase of coil 75 is at the start lead 95 while the positive phase end of winding 73 is at the finish lead 93.
- the secondary windings are connected together so as to place themelectrically in parallel with electrical lead 98 connected between lead 97 of winding 75 and to lead 93 ofwinding 73 and lead 91 connected to lead 95 by lead 99.
- the full secondary voltage is produced by each of the two secondary windings and these are placed in parallel to provide the appropriate output voltage that appears across leads 98 and 99 which are conducted via leads 36' and 38, respectively, to outlet 40' and with each secondary coil seeing approximately one-half the current to the load. This is in contrast to the single secondary winding 3 in the embodiment of FIG. I. I I
- the dash lines 32' symbolically denote a six sided metal housing or enclosure in which the transformer and usually monitoring instruments or other electrical components, not illustrated, common to hospital distribution systems are installed.
- This enclosure sometimes referred to as a panel, usually contains a removable trim cover or door, and typically is of 12 gauge steel material.
- the enclosure is electrically grounded.
- FIG. 8 The construction of the transformer component of FIG. 7 is schematically indicated in FIG. 8 where identical numerals are used to denote the windings.
- secondary winding 75 has the turns wound in the direction oppositeto that of secondary winding 73.
- the symbol St.” located at one end of the respective windings symbolizes the start end of that winding with the unlabeled end being the finish end.
- the start end of winding 75 is connected to the finish end of winding 73 and the start end of winding 73 is connected electrically to the finish end of winding 75.
- the windings are in parallel so that full output voltage appears across each winding and each winding sees one-half the load current taken from terminals T1 and T2.
- Other conventional connections can be substituted as is apparent to the skilled reader.
- both of the secondary coils on the same side of the primary coil with a single shield fitted between one end of the primary winding and the most adjacent one of the secondary windings.
- a four coil arrangement is possible with two primary coils and two secondary coils.
- the two primary windings can be connected together in phase addition with the windings wound in opposite directions and likewise the two secondary coils are oriented on the core with the directions of turn winding contraclockwise and connected together in series additive phase.
- a shield and insulator arrangement would be placed between each coil set.
- FIGS. 9a through 9] illustrate some conventional configurations including FIG. 9a, the 2-U and I configuration; FIG. 9b, the stacked I configuration; FIG. 90, the two wound core configuration; FIG. 9a, the U-I lamination configuration; FIG. 9e, the CC or J] configuration; FIG. 9f, the long and short I configuration; FIG. 9g, a single wound core configuration; FIG. 9h, an FF configuration; and FIG. 91', a T-L configuration.
- FIGQl discloses another embodiment of the invention which contains a transformer similar in structure to the transformer incorporated in the embodiment of FIG. 7.
- the elements in the embodiment of FIG. 10 are the same as that previously described and discussed in connection with the embodiment of FIG. 7, they are similarly labeled with primed numerals. Further reference may be made to the preceding description of the embodiment of FIG. 7 for the description and construction of such corresponding elements.
- each of the secondary windings 73' and 75' operate as individual isolated sec ondaries.
- each of the turns of wire in the coil forming such secondary winding comprises an integral number of turns of wire.
- the dash lines 32" symbolically denote the six sided metal housing or enclosure, previously referred to in the preceding embodiments, in which the transformer and usually monitoring instruments, not illustrated, common to hospital distribution systems are installed.
- This enclosure sometimes referred to as a panel, usually contains a door and typically is of an iron material.
- FIG. 10 For convenience, a schematic illustration of the transformer of this embodiment is presented in FIG. 10. As is apparent, this schematic differs from th e .sc hematic of the transformer of FIG. 8 in that it omits the connection 98 joining the secondary windings inseries in FIG. 8 and each secondary winding in FIG. 1 0 is double the number of turns in FIG. 8.
- a somewhat different leakage current condition exists from that in the preceding cases.
- the leakage current between the aiding secondary and the primary winding is somewhat higher than that between the opposing secondary winding and primary.
- the leakage current between the opposing secondary and primary winding is relatively the same as in the preferred embodiment, and the leakage current between each secondary winding to ground are relatively equal.
- An isolated hospital electrical supply system with very low leakage current to electrical ground potential and low noise for transforming AC voltage from an electrically grounded source and providing ungrounded AC voltage so as to minimize the possibility of electrical shock of a patient who is in contact with said electrical ground of said grounded source and to minimize audible noise generation in the system comprising:
- At least a first pair of lines for providing low frequency alternating voltage from an electrical utility line, one of said lines being electrically connected to ground potential;
- an electrical outlet receptacle adapted for connection to electrical equipment
- isolation transformer located spaced from said outlet receptacle, said isolation transformer including:
- a first coil of wire containing a first predetermined number of turns, N,,, comprising a primary winding
- a second separate coil of wire containing a second predetermined number of turns, N comprising a first secondary winding
- a third separate coil of wire containing a third predetermined number of turns, N comprising a second secondary winding, said third coil of wire being substantially identical with said second coil of wire and said second and third predetermined number of turns of wire being the same;
- first and second nonmagnetic metal shields having a passage therethrough and a slot between said passage and anouter edge thereof;
- said first, second and third coil being electrically insulated from said core and mounted on said core side by side and closely adjacent one another with said second coil located adjacent one side of said first coil and with said third coil located adjacent the remaining side of said first coil;
- said second coil having the turns of wire therein wound in a clockwise direction as mounted on said core and said third coil having the turns of wire therein wound in a counterclockwise direction as mounted on said core;
- N llN is equal to a number less than 3 and at least 1
- the ratio, Vietnamese/N is equal to a number less than 3 and at least 1;
- said first shield mounted on said core sandwiched between one side of said first coil and said second coil and said second shield mounted on said core sandwiched between the remaining side of said first coil and said third coil;
- a steel walled enclosure for housing electrical components, including said transformer, said enclosure being connected to electrical ground potential;
- said transformer being located in said enclosure;
- An isolated hospital electrical supply system with very low leakage current to electrical ground potential and low noise for transforming AC voltage from a grounded source and providingungrounded AC voltage so as to minimize the possibility of electrical shock of a patient who is in contact with said electrical ground of said grounded source and to minimize audible noise generation in the system comprising:
- an isolation transformer located spaced from said outlet receptacle, said isolation transformer including: a core of magnetic material;
- a second separate coil of wire containing a second predetermined number of turns, N,,,, comprising a first secondary winding
- a third separate coil of wire containing a third predetermined number of turns, N comprising a second secondary winding, said third coil of wire being substantially identical with said second coil of wire and said second and third predetermined number of turns of wire being the same;
- first and second nonmagnetic metal shields having a passage therethrough and a slot between said passage and anouter edge thereof;
- said first, second and third coils being electrically insulated from one another and said core and mounted on said core side by side and closely adjacent one another with said second coil located adjacent one side of said first coil and with said third coil located adjacent the remaining side of said first coil;
- said second coil having the turns of wire therein wound in a clockwise direction as mounted on said core and said third coil having the turns of wire therein wound in a counterclockwise direction as mounted on said core;
- ratio sl/Np is equal to a number less I than 3 and at least 1;
- said first shield mounted on said core sandwiched between one side of said first coil and said second coil and said second shield mounted on said core sandwiched between the remaining side of said first coil and said third coil;
- a steel walled enclosure for housing electrical components, including said transformer, said enclosure being connected to electrical ground potential;
- said transformer being located in said enclosure
Abstract
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US00367584A US3851287A (en) | 1972-02-09 | 1973-06-06 | Low leakage current electrical isolation system |
CA201,722A CA1002621A (en) | 1973-06-06 | 1974-06-05 | Low leakage current electrical isolation system |
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US22487872A | 1972-02-09 | 1972-02-09 | |
US00367584A US3851287A (en) | 1972-02-09 | 1973-06-06 | Low leakage current electrical isolation system |
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Cited By (31)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3963975A (en) * | 1975-03-05 | 1976-06-15 | General Electric Company | Electromagnetically shielded electrical power supply with reduced common mode electromagnetic interference output |
US4201965A (en) * | 1978-06-29 | 1980-05-06 | Rca Corporation | Inductance fabricated on a metal base printed circuit board |
US4333900A (en) * | 1977-12-02 | 1982-06-08 | Chloride Electro Networks, Division Of Chloride, Inc., N. American Operation | Process for manufacture of high voltage transformers and the like |
EP0133661A2 (en) * | 1983-08-04 | 1985-03-06 | Siemens Aktiengesellschaft | Small transformer |
US4660014A (en) * | 1985-06-19 | 1987-04-21 | Jaycor | Electromagnetic pulse isolation transformer |
US4710707A (en) * | 1985-01-16 | 1987-12-01 | Zenith Electronics Corporation | High voltage electronic component test apparatus |
US4977491A (en) * | 1986-10-15 | 1990-12-11 | Electronique Serge Dassault | High frequency transformer with a printed circuit winding in particular for a very high voltage power supply |
US5025489A (en) * | 1987-05-14 | 1991-06-18 | Matsushita Electric Industrial Co., Ltd. | Transformer having shielding wall for driving a magnetron |
US5343143A (en) * | 1992-02-11 | 1994-08-30 | Landis & Gyr Metering, Inc. | Shielded current sensing device for a watthour meter |
US5546065A (en) * | 1991-09-13 | 1996-08-13 | Vlt Corporation | High frequency circuit having a transformer with controlled interwinding coupling and controlled leakage inductances |
US5656983A (en) * | 1992-11-11 | 1997-08-12 | Kabushiki Kaisha Toyoda Jidoshokki Seisakusho | Inductive coupler for transferring electrical power |
US5684341A (en) * | 1993-08-07 | 1997-11-04 | Magnet-Physik Dr. Steingroever Gmbh | Electromagnetic generator for fast current and magnetic field pulses, for example, for use in magnetic metal working |
US5777538A (en) * | 1995-04-25 | 1998-07-07 | Raychem Corporation | Apparatus comprising inductive and/or power transfer and/or multiplication components |
US5804892A (en) * | 1994-04-17 | 1998-09-08 | Ulrich Schwan | Transmission device |
US5844461A (en) * | 1996-06-06 | 1998-12-01 | Compaq Computer Corporation | Isolation transformers and isolation transformer assemblies |
US6143157A (en) * | 1995-11-27 | 2000-11-07 | Vlt Corporation | Plating permeable cores |
WO2004032159A1 (en) * | 2002-10-01 | 2004-04-15 | Delta Energy Systems (Switzerland) Ag | Coil form |
US20040217838A1 (en) * | 2003-04-29 | 2004-11-04 | Lestician Guy J. | Coil device |
US20050156701A1 (en) * | 2003-04-02 | 2005-07-21 | Duval Randall J. | Electrical reactor assembly having center taps |
US20050253678A1 (en) * | 2002-03-19 | 2005-11-17 | Daifuku Co., Ltd. | Composite core nonlinear reactor and induction power receiving circuit |
US20050280423A1 (en) * | 2004-06-21 | 2005-12-22 | Barbour Erskine R | Method and apparatus for measuring voltage in a power switching device |
US7028387B1 (en) * | 2003-03-26 | 2006-04-18 | Advanced Neuromodulation Systems, Inc. | Method of making a miniaturized positional assembly |
US7236086B1 (en) | 1993-06-14 | 2007-06-26 | Vlt, Inc. | Power converter configuration, control, and construction |
US20080117012A1 (en) * | 2006-11-22 | 2008-05-22 | Jurgen Pilniak | Winding assembly |
US20100039202A1 (en) * | 2008-08-18 | 2010-02-18 | Delta Electronics, Inc. | Magnetic element |
CN101656142B (en) * | 2008-08-21 | 2012-09-19 | 台达电子工业股份有限公司 | Magnetic component |
WO2016071098A3 (en) * | 2014-11-05 | 2016-06-30 | Epcos Ag | Inductive component |
US10304621B2 (en) * | 2017-01-24 | 2019-05-28 | Lear Corporation | Bobbin with electromagnetic interference shield for electromagnetic device |
US20200402696A1 (en) * | 2019-06-21 | 2020-12-24 | Panasonic Intellectual Property Management Co., Ltd. | Core |
US20210134511A1 (en) * | 2019-10-31 | 2021-05-06 | Delta Electronics (Shanghai) Co., Ltd | Transformer and power module including the same |
US11683900B2 (en) | 2019-10-31 | 2023-06-20 | Delta Electronics (Shanghai) Co., Ltd | Power conversion system |
Citations (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2114189A (en) * | 1937-10-15 | 1938-04-12 | Gen Electric | Transformer |
US2183355A (en) * | 1938-08-22 | 1939-12-12 | Jefferson Electric Co | Transformer construction |
US2229373A (en) * | 1939-09-25 | 1941-01-21 | Timken Axle Co Detroit | Shielded transformer and shield therefor |
US2343725A (en) * | 1941-04-24 | 1944-03-07 | Honeywell Regulator Co | Transformer |
US2547649A (en) * | 1948-12-08 | 1951-04-03 | Gen Electric | Electric induction apparatus |
US2652521A (en) * | 1949-08-22 | 1953-09-15 | Nu Way Corp | Shield for transformer coils |
US2815408A (en) * | 1955-10-14 | 1957-12-03 | Hafler David | Transformers |
US2904762A (en) * | 1954-05-20 | 1959-09-15 | Richard B Schulz | Shielded transformer |
US2914719A (en) * | 1957-09-13 | 1959-11-24 | Elcor Inc | Isolated power supply |
US3277416A (en) * | 1962-12-04 | 1966-10-04 | Taylor Instrument Co | Shielding arrangement for transformer |
US3287680A (en) * | 1963-06-18 | 1966-11-22 | Automatic Timing & Controls | Electrical device |
US3360754A (en) * | 1965-06-29 | 1967-12-26 | Wagner Electric Corp | Transformer having reduced differential impedances between secondary portions |
US3393388A (en) * | 1967-03-14 | 1968-07-16 | George V. Young | Windings having continuous shields therearound |
-
1973
- 1973-06-06 US US00367584A patent/US3851287A/en not_active Expired - Lifetime
Patent Citations (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2114189A (en) * | 1937-10-15 | 1938-04-12 | Gen Electric | Transformer |
US2183355A (en) * | 1938-08-22 | 1939-12-12 | Jefferson Electric Co | Transformer construction |
US2229373A (en) * | 1939-09-25 | 1941-01-21 | Timken Axle Co Detroit | Shielded transformer and shield therefor |
US2343725A (en) * | 1941-04-24 | 1944-03-07 | Honeywell Regulator Co | Transformer |
US2547649A (en) * | 1948-12-08 | 1951-04-03 | Gen Electric | Electric induction apparatus |
US2652521A (en) * | 1949-08-22 | 1953-09-15 | Nu Way Corp | Shield for transformer coils |
US2904762A (en) * | 1954-05-20 | 1959-09-15 | Richard B Schulz | Shielded transformer |
US2815408A (en) * | 1955-10-14 | 1957-12-03 | Hafler David | Transformers |
US2914719A (en) * | 1957-09-13 | 1959-11-24 | Elcor Inc | Isolated power supply |
US3277416A (en) * | 1962-12-04 | 1966-10-04 | Taylor Instrument Co | Shielding arrangement for transformer |
US3287680A (en) * | 1963-06-18 | 1966-11-22 | Automatic Timing & Controls | Electrical device |
US3360754A (en) * | 1965-06-29 | 1967-12-26 | Wagner Electric Corp | Transformer having reduced differential impedances between secondary portions |
US3393388A (en) * | 1967-03-14 | 1968-07-16 | George V. Young | Windings having continuous shields therearound |
Cited By (54)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3963975A (en) * | 1975-03-05 | 1976-06-15 | General Electric Company | Electromagnetically shielded electrical power supply with reduced common mode electromagnetic interference output |
US4333900A (en) * | 1977-12-02 | 1982-06-08 | Chloride Electro Networks, Division Of Chloride, Inc., N. American Operation | Process for manufacture of high voltage transformers and the like |
US4201965A (en) * | 1978-06-29 | 1980-05-06 | Rca Corporation | Inductance fabricated on a metal base printed circuit board |
EP0133661A2 (en) * | 1983-08-04 | 1985-03-06 | Siemens Aktiengesellschaft | Small transformer |
EP0133661A3 (en) * | 1983-08-04 | 1985-04-03 | Siemens Aktiengesellschaft | Small transformer |
US4652846A (en) * | 1983-08-04 | 1987-03-24 | Siemens Aktiengesellschaft | Small transformer with shield |
US4710707A (en) * | 1985-01-16 | 1987-12-01 | Zenith Electronics Corporation | High voltage electronic component test apparatus |
US4660014A (en) * | 1985-06-19 | 1987-04-21 | Jaycor | Electromagnetic pulse isolation transformer |
US4977491A (en) * | 1986-10-15 | 1990-12-11 | Electronique Serge Dassault | High frequency transformer with a printed circuit winding in particular for a very high voltage power supply |
US5025489A (en) * | 1987-05-14 | 1991-06-18 | Matsushita Electric Industrial Co., Ltd. | Transformer having shielding wall for driving a magnetron |
US5546065A (en) * | 1991-09-13 | 1996-08-13 | Vlt Corporation | High frequency circuit having a transformer with controlled interwinding coupling and controlled leakage inductances |
US5719544A (en) * | 1991-09-13 | 1998-02-17 | Vlt Corporation | Transformer with controlled interwinding coupling and controlled leakage inducances and circuit using such transformer |
US6653924B2 (en) * | 1991-09-13 | 2003-11-25 | Vlt Corporation | Transformer with controlled interwinding coupling and controlled leakage inductances and circuit using such transformer |
US5343143A (en) * | 1992-02-11 | 1994-08-30 | Landis & Gyr Metering, Inc. | Shielded current sensing device for a watthour meter |
US5656983A (en) * | 1992-11-11 | 1997-08-12 | Kabushiki Kaisha Toyoda Jidoshokki Seisakusho | Inductive coupler for transferring electrical power |
US5719546A (en) * | 1992-11-11 | 1998-02-17 | Kabushiki Kaisha Toyoda Jidoshokki Seisakusho | Inductive coupler for transferring electrical power |
US7236086B1 (en) | 1993-06-14 | 2007-06-26 | Vlt, Inc. | Power converter configuration, control, and construction |
US5684341A (en) * | 1993-08-07 | 1997-11-04 | Magnet-Physik Dr. Steingroever Gmbh | Electromagnetic generator for fast current and magnetic field pulses, for example, for use in magnetic metal working |
US5804892A (en) * | 1994-04-17 | 1998-09-08 | Ulrich Schwan | Transmission device |
US5777538A (en) * | 1995-04-25 | 1998-07-07 | Raychem Corporation | Apparatus comprising inductive and/or power transfer and/or multiplication components |
US5883392A (en) * | 1995-04-25 | 1999-03-16 | Raychem Corporation | Apparatus comprising inductive and/or power transfer and/or voltage multiplication components |
US6143157A (en) * | 1995-11-27 | 2000-11-07 | Vlt Corporation | Plating permeable cores |
US6165340A (en) * | 1995-11-27 | 2000-12-26 | Vlt Corporation | Plating permeable cores |
US5844461A (en) * | 1996-06-06 | 1998-12-01 | Compaq Computer Corporation | Isolation transformers and isolation transformer assemblies |
US20050253678A1 (en) * | 2002-03-19 | 2005-11-17 | Daifuku Co., Ltd. | Composite core nonlinear reactor and induction power receiving circuit |
US7265648B2 (en) * | 2002-03-19 | 2007-09-04 | Daifuku Co., Ltd. | Composite core nonlinear reactor and induction power receiving circuit |
US20090102593A1 (en) * | 2002-10-01 | 2009-04-23 | Jurgen Pilniak | Coil form |
US7429908B2 (en) | 2002-10-01 | 2008-09-30 | Det International Holding Limited | Coil form |
WO2004032159A1 (en) * | 2002-10-01 | 2004-04-15 | Delta Energy Systems (Switzerland) Ag | Coil form |
US20060125590A1 (en) * | 2002-10-01 | 2006-06-15 | Jurgen Pilniak | Coil form |
US20060132275A1 (en) * | 2002-10-01 | 2006-06-22 | Jurgen Pilniak | Coil form |
US7218198B2 (en) | 2002-10-01 | 2007-05-15 | Det International Holding Limited | Coil form |
US7028387B1 (en) * | 2003-03-26 | 2006-04-18 | Advanced Neuromodulation Systems, Inc. | Method of making a miniaturized positional assembly |
US20050156701A1 (en) * | 2003-04-02 | 2005-07-21 | Duval Randall J. | Electrical reactor assembly having center taps |
US7315231B2 (en) | 2003-04-02 | 2008-01-01 | Illinois Tool Works Inc. | Electrical reactor assembly having center taps |
US6954131B2 (en) * | 2003-04-02 | 2005-10-11 | Illinois Tool Works Inc. | Electrical reactor assembly having center taps |
US20040217838A1 (en) * | 2003-04-29 | 2004-11-04 | Lestician Guy J. | Coil device |
US20050280423A1 (en) * | 2004-06-21 | 2005-12-22 | Barbour Erskine R | Method and apparatus for measuring voltage in a power switching device |
US7550960B2 (en) | 2004-06-21 | 2009-06-23 | Abb Technology Ag | Method and apparatus for measuring voltage in a power switching device |
US20080117012A1 (en) * | 2006-11-22 | 2008-05-22 | Jurgen Pilniak | Winding assembly |
EP1926110A1 (en) * | 2006-11-22 | 2008-05-28 | DET International Holding Limited | Winding assembly and method of its manufacture |
US8022804B2 (en) * | 2006-11-22 | 2011-09-20 | Det International Holding Limited | Winding assembly |
US20100039202A1 (en) * | 2008-08-18 | 2010-02-18 | Delta Electronics, Inc. | Magnetic element |
US8054150B2 (en) * | 2008-08-18 | 2011-11-08 | Delta Electronics, Inc. | Magnetic element |
CN101656142B (en) * | 2008-08-21 | 2012-09-19 | 台达电子工业股份有限公司 | Magnetic component |
WO2016071098A3 (en) * | 2014-11-05 | 2016-06-30 | Epcos Ag | Inductive component |
US20170309393A1 (en) * | 2014-11-05 | 2017-10-26 | Epcos Ag | Inductive Component |
US10978242B2 (en) * | 2014-11-05 | 2021-04-13 | Epcos Ag | Inductive component |
US10304621B2 (en) * | 2017-01-24 | 2019-05-28 | Lear Corporation | Bobbin with electromagnetic interference shield for electromagnetic device |
US20200402696A1 (en) * | 2019-06-21 | 2020-12-24 | Panasonic Intellectual Property Management Co., Ltd. | Core |
US11798724B2 (en) * | 2019-06-21 | 2023-10-24 | Panasonic Intellectual Property Management Co., Ltd. | Core |
US20210134511A1 (en) * | 2019-10-31 | 2021-05-06 | Delta Electronics (Shanghai) Co., Ltd | Transformer and power module including the same |
US11683900B2 (en) | 2019-10-31 | 2023-06-20 | Delta Electronics (Shanghai) Co., Ltd | Power conversion system |
US11783987B2 (en) * | 2019-10-31 | 2023-10-10 | Delta Electronics (Shanghai) Co., Ltd | Transformer and power module including the same |
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