Patent Grant
8299879
The present invention generally relates to power supplies and more particularly to a power supply containing a transformer using an internal load.
In a particular application of this invention, an electrode furnace (EF) enables rapid heating of a sample material used to create gases. These gases are then analyzed for their composition using a variety of scientific methods. The EF operates by generating a high current which is passed through a conductive crucible. Current is conducted through the crucible using electrode contacts. The current heats the crucible and any sample material therein. As used herein, the term electrode defines an electromechanical connection between a conductive material and a load.
Prior art systems have used large mains-frequency (50 Hz-60 Hz) power supplies to generate the high currents necessary to rapidly produce enough heat to drive off gases in the sample material. These types of linear power supplies require a large iron core transformer making them bulky and difficult to integrate into the EF. Although higher frequency switching supplies can be used for reducing the transformer size, these types of switching supplies often have problems when delivering a high current to the load. This is primarily due to the stray inductance created by the flexible lead wire used to connect the transformer with the electrode, the electrode inductance, and the transformer leakage inductance. The stray inductance results in an impedance that increases with frequency and is in series with the crucible resistance. At normal mains input frequencies of 50 Hz-60 Hz, the stray inductance contributes an insignificant amount of inductive reactance to the system. Therefore, the transformer secondary circuit impedance is dominated by the crucible resistance at 50 Hz or 60 Hz. At frequencies normally utilized by switching power supplies, the inductive reactance created by the stray inductance can be many times that of the crucible resistance.
A conventional EF utilizes 50 Hz-60 Hz power transformers and large copper conductive braided straps to create a mechanically flexible high current connection from the transformer to the electrodes. The flexible braids are required for allowing the electrodes to be separated for cleaning and inserting a new crucible for each analysis. The EF furnace uses a set of electrodes for delivering over 1100 Amps to a crucible. The magnetic loop created by the flexible leads connecting the transformer secondary to the electrodes produces substantial amounts of magnetic field that can couple into nearby objects. These magnetic fields can create interference with devices such as CRT monitors resulting in distortion of picture quality by altering the display position at the main frequency or one of its harmonics.
Often, the use of braid conductor at frequencies utilized by switching power supplies is not practical due to skin effect and large eddy currents resulting in extremely high temperatures in the connections. The high temperatures increase oxidation of the braid material further increasing its resistance. Moreover, the transformer's primary wires can also experience localized heating due to the large magnetic field created by the secondary current. In prior art devices, the high secondary current loop encircles only one side of the transformer creating magnetic fields that are not homogeneous over the entire structure. This often creates eddy current heating of the transformer's primary wires. The heated primary wire warms the transformer core. The added losses lower the amount of power the transformer can deliver before exceeding the transformer maximum operating temperature.
From a mechanical perspective, the size and weight of the 50 Hz-60 Hz transformer used in connection with thick copper braids result in increased package size and greater shipping cost. Although electronic solutions are known in the art for increasing the operating frequency to reduce transformer size, methods for reliably making such an electro-mechanical structure at the higher frequencies had not been realized. The problems involve realizing a flexible mechanical structure that minimizes inductance and loss of the high current secondary while providing reliable electrical contacts. The structure must allow repetitive insertion and removal of a crucible. Cleaning of the electrode assembly is also a requirement.
Alternative applications of using standard 50 Hz-60 Hz methods include using rigid bus bars and contacts to complete the electrical circuit. This includes using a conventional transformer high current secondary connected with conventional electrodes. This solution suffers from many of the problems outlined in previous paragraphs. Still further alternatives to the construction include the use of high current flexible conductors in the form of an S-bent conductive sheet. In this solution, the transformer is remote from the electrodes and the S-bent sheet is used to make the connections between the transformer secondary and the electrodes. A disadvantage to this type of arrangement includes excess inductance along with many problems as discussed previously.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a transformer using an internal load. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
The present invention provides a novel solution to a transformer's localized primary wire heating that involves encasing a transformer in a conductive housing or shield producing a more homogeneous magnetic field and providing the same magnetic coupling for each primary winding. The shield also serves as a portion of the secondary circuit eliminating the need for flexible secondary leads connected to the electrodes. The invention solves the inductance and loss issues of a conventionally mounted power transformer while providing a large surface area for a high current sliding contact. The size and weight of the total system is reduced while simplifying the design by combining the transformer secondary conductor with the conductive housing and the electrode assemblies. It also minimizes power losses to where mechanical structure efficiency is over 98% in view of the low resistance provided by the highly conductive materials used in its construction. Losses are further minimized by the short current path of the conductive housing.
The crucible is in physical contact with the first electrode and second electrode allowing a substantially large amount of current to be applied through the crucible with minimal electrical losses in the electrode structure. This allows the crucible to be heated to very high temperatures in order to evolve and/or expel gases from a sample material contained therein. These gases can then escape from a port where they can be used for various types of testing and analysis. A conductor is also positioned between the first electrode and the second electrode forming a circular current path through the first electrode, the conductive crucible or load, the second electrode, the conductor and then returning to the first electrode forming an electrical circuit. This current path is positioned so it passes through a transformer core window creating a high current secondary circuit magnetically coupled to the transformer core and primary winding. As will be evident to those skilled in the art, the conductor may consist of a single or multiple conductors arranged to form a connection between the first electrode and second electrode.
As seen in
When assembled, the second conductor assembly 217 is arranged such that it passes through the center of transformer core assembly 219 and forms an electrical connection to the top of the canister assembly 207. The canister assembly 207 is multifunctional serving to provide a conductive housing or path for current to flow in the secondary circuit and as a shield to close or seal the electromagnetic structure of the design. The canister assembly is typically manufactured of a metallic material for providing shielding and electrical conductivity. All of the magnetic fields created by the secondary current flow are contained within the shielded structure of canister assembly 207, the first conductor 201 and the second conductor assembly 217 as will be described herein.
The interior of the canister assembly 207 contains a surface (not shown) for allowing insertion of the brush contact 205, which forms a high current contact. The closed circuit formed by the brush contact 205, first conductor 201, crucible 211, second conductor assembly 217, and canister assembly 207 form a single turn secondary winding coupled to transformer core assembly 219. The sliding brush contact 205 allows for movement and opening of first conductor 201. This facilitates the removal and installation of the crucible 211 for adding analytical materials inside the crucible 211 as well as any cleaning of the electrode surfaces of first conductor 201 and second conductor 217. The transformer core assembly 219 includes primary leads 221 that pass through apertures 223 in the canister assembly 207. The primary leads connect with an inverter or other power electronics (not shown). An inverter or power electronics are used for creating a predetermined excitation voltage required for driving the electrode furnace assembly 200.
The second electrode probe 225 passes through hole 227 in the second conductor assembly 217 and into an area of the second conductor assembly 217 near the electrode contact (not shown) made with crucible top 215. Similarly, the first electrode probe 229 passes through the second conductor assembly 217 by means of hole 231 for making an electrical connection on first conductor 201 near first electrode 209. The second electrode probe 225 and first electrode probe 229 provide an instrument for various load measurements and/or the voltage at the crucible 211. The second conductor assembly 217 further contains a port 233 for the collection of gases escaping from the crucible 211 and/or the samples contained therein (not shown). The port 233 passes through the second conductor assembly 217 to a region located above the crucible top 215. As will be evident to those skilled in the art, both the second conductor 217 and first conductor 201 can be cooled if necessary by conventional means such as, but not limited to, heat pipes, liquid, convection, forced air or any combination of these cooling techniques.
One advantage of the invention is the incorporation of the load or crucible into the transformer structure. This arrangement has the effect of eliminating the need for a secondary winding in the transformer assembly or other connections between the load and the secondary winding. Moreover, the invention provides easy installation and removal of the load through the use of a sliding contact formed using brush contact 205 and the interior (not shown) of the canister assembly 207. In use, the first conductor 201 and/or the second conductor assembly 217 can engage a sliding contact for allowing the first electrode 209 and/or second electrode (not shown) to adjust position in the canister assembly 217. This allows for a variety of different size loads to remain in contact with the first electrode 209 and the second electrode (not shown). Although the use of a brush contact 205 is described herein, other methods of creating a sliding or adjustable contact for allowing opening of the canister and/or changing load dimensions can also be used. The sliding or adjustable contact can include but is not limited to clamps, split rings, knife edge contacts, or screw assemblies. Use of alternative methods for achieving a mechanically flexible structure are also within the scope of the invention.
In the case of using the invention in EF applications, the load is the conductive crucible 211. Many difficulties can arise when creating systems for use with such high power. These difficulties include heat dissipation and electromagnetic field generation. The details as described herein illustrate a particular application of the invention with regard to an EF application. The descriptions as provided herein are not intended to limit the scope of this invention but are merely described with regard to a particular application. These descriptions serve to highlight the design solutions used in the present invention for creation of an EF application. Those skilled in the art will further recognize that other applications of the invention can include but are not limited to the heat treatment of materials, fluid heating, gas heating, and/or the melting and formation of various materials.
The transformer core assembly 323 includes at least one core 325 that is made of ferrite or other magnetic materials that is inserted within the interior of the canister assembly 317. The transformer core assembly 323 is positioned so that the second conductor 313 passes through the window forming a magnetic transformer assembly or structure. The window of the magnetic structure is comprised of an area that a winding would pass through in order to couple magnetic energy between the core and the winding. The transformer core assembly 323 further contains a primary winding (not shown) with leads passing through the canister assembly 317 for connection to a power source (not shown). The inside surface 327 of canister assembly 317 is designed to accept the conducting brush contact 311 which forms a sliding electrical contact. When the first conductor 301 is inserted into the canister assembly 317, the load 307 forms an electrical current path between first conductor 301 and second conductor 313.
In addition, the brush contact 311 forms an electrical contact between the first conductor 301 and the canister assembly 317. The complete electrical current path of first conductor 301, load 307, second conductor 313, cover 315, canister assembly 317, and brush contact 311, which is in contact with both first conductor 301 and canister assembly 317, passes through the window of transformer core assembly 323. This provides a magnetic coupling to the primary winding (not shown). The load 307 is internal to the transformer structure and the brush contact 311 allows for easy opening and closing of the structure. This in-turn allows for the replacement of the load 307 after use as well as the cleaning of electrodes 303 and 319. The brush contact 311 also allows for different size loads to be installed in the assembly since brush contact 311 forms a sliding contact with canister assembly inside surface 327. Further, the sliding contact formed by brush contact 311 allows for expansion and contraction of load 307. When used in an EF application, second conductor 313 may include a channel 329 for collection of gases from the load 307. First conductor 301, canister assembly 317, and second conductor 313 could be manufactured from any suitable conductive material capable of passing substantially high currents with minimal power loss. The canister assembly 317 and first conductor 301 surround the load 307, second electrode 317, first electrode 303, transformer core assembly 323 and the primary winding (not shown). The canister assembly 317, second conductor 313 and first conductor 301 form a conductor positioned between the first electrode 303 and second electrode 319.
By way of example, for the EF application, twenty-four (24) turns forming the primary were utilized to achieve the desired magnetic operating point and turns ratio. Those skilled in the art will further recognize that a “turn” is counted when it passes through the window of the magnetic material. In the case of a toroid, the window is the center hole of the structure. Due to the large currents involved, the primary winding can consist of multiple parallel wires or conductive ribbon to increase the surface area and minimize losses. To create a uniform field and minimize leakage inductance, the primary windings are evenly distributed over the core surface in a single layer. The connection leads 407A, 407B are affixed to the primary windings for connection to the power electronics (not shown) providing the required voltage and current. In view of the structural nature of the invention as described herein, the transformer core assembly 400 does not have a wound secondary. However, the insertion of the second conductor assembly in the window of the transformer core along with the canister assembly, load and first conductor operate to create a single turn secondary with high current handling capabilities.
Thus, the transformer using an internal load offers many advantages over the prior art by reducing the size and complexity of a system when compared to conventional 50 Hz-60 Hz systems. In this particular application of an electrode furnace, the transformer using an internal load decreases overall weight, size, electromagnetic emissions, and circuit losses when compared to previous art. In view of the new transformer geometry and configuration, the secondary winding on the transformer and the associated flexible leads are eliminated as current is generated by magnetic coupling to the second conductor. The overall structure provides a closed or self shielded current path by using the canister structure to complete the electrical circuit for a brush contact, first conductor, load, and second conductor. Substantially low external electromagnetic fields are realized since the transformer and secondary circuit is shielded. The brush contact allows a movable high current contact that can slide inside the canister for providing adjustability in load size and thermal expansion. In addition, the brush contact allows separation of the first conductor from the second conductor assembly for electrode cleaning and installation or removal of a load. Another advantage of this architecture is the minimization of stray inductance due to the closed field structure and minimized current path lengths. Since secondary currents flow over the entire enclosure surface area, power losses are minimized. This creates a transformer assembly that can be driven by higher frequency switching supplies allowing for power factor correction and reduction in harmonic distortion when compared to prior art systems employing conduction angle or phase controlled chopper technologies.
Moreover, the present invention works to reduce the overall parts count over a conventional mounted power transformer by combining analytical functions of the first and second electrodes with the transformer construction. This eliminates the need for high current secondary windings, and eliminates flexible wire or strap connections between the transformer and the electrodes. Further, the present invention provides for lower power losses than can be obtained by a conventionally mounted transformer operating at frequencies utilized in switching power supply systems. Finally, lower primary winding losses in the transformer occur since all windings experience a similar magnetic field pattern due to the symmetrical shielding and current path provided by the canister structure. Thus, when used in combination with switching power supplies, the present invention provides a compact system that has superior performance over a conventional 50 Hz-60 Hz transformer design or a switching system using conventional connection means.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2455875 | Peterson et al. | Dec 1948 | A |
| 2469162 | Gehman et al. | May 1949 | A |
| 3146351 | Adams et al. | Aug 1964 | A |
| 3162829 | Wildy et al. | Dec 1964 | A |
| 3436709 | Schapira et al. | Apr 1969 | A |
| 3480896 | Neuman | Nov 1969 | A |
| 3500274 | Matsuura et al. | Mar 1970 | A |
| 3629759 | Douglas et al. | Dec 1971 | A |
| 4837544 | McDougal | Jun 1989 | A |
| 5214403 | Bogaerts et al. | May 1993 | A |
| 6084354 | Kohmura et al. | Jul 2000 | A |
| 6173611 | Laughlin | Jan 2001 | B1 |
| 6194834 | Seiler et al. | Feb 2001 | B1 |
| 6680575 | Ushio et al. | Jan 2004 | B1 |
| 6731076 | Gerhard et al. | May 2004 | B1 |
| 7772780 | Pokharna et al. | Aug 2010 | B2 |
| 20030175156 | Ford | Sep 2003 | A1 |
| 20080157696 | Pokharna et al. | Jul 2008 | A1 |
| 20080204180 | Aboumrad et al. | Aug 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 55-125610 | Sep 1980 | JP |
| 55-125610 | Sep 1980 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20120206229 A1 | Aug 2012 | US |
