1. Field of the Invention
The present invention relates generally to power supplies for generating high voltages. More particularly, the present invention relates to a high voltage power supply such used with neutron generating tubes in oil well logging equipment. Further, the invention relates to an arrangement of special capacitors utilized in both a series-parallel type fashion having a construction that maximizes the operations of such a multiplier used in these high voltage power supplies.
2. Related Art
Oil well logging devices which include neutron generating tubes are well known in the art. Such devices are sized to be lowered down an oil well bore and emit neutrons into the formation through which the bore passes. By detecting the radiation coming back from the formation, particularly the atoms in the formation that have been made radioactive by the emitted neutrons, the location of the oil bearing strata can be determined along the depth of the well. This indicates where the well casing should be perforated to allow oil to flow into the well.
The neutron generating tubes which are the heart of these logging devices require 100,000 volts or more to operate. Currently available logging devices generally use a Cockroft-Walton type series voltage multiplier circuit which include capacitors and rectifiers, which takes an AC voltage from a step up transformer and converts it to a high DC voltage by successively raising up the voltage in a step wise fashion to operate the neutron generating tube. Voltage multiplying circuits using capacitors and rectifiers are well known, with the Cockroft-Walton series multiplier type circuit being commonly used in the currently available logging devices. These currently available logging devices can generally operate satisfactorily up to about 150 degrees C. Beyond this point, excessive electrical leakage in the semiconductors (rectifiers) precludes efficient power conversion. The leakage currents in semiconductors generally increase exponentially with increases in temperature. Many of the deep oil wells currently being drilled have internal temperatures in the deeper parts of the well over 150 degrees C. and up to 175 degrees C. or greater. This presents a problem in logging the deeper portions of the wells because, as indicated, the presently used logging devices do not operate satisfactorily at these higher temperatures.
In addition, in order to provide the required 100 kV of operating voltage required by neutron generating tubes, a reasonable limit must be imposed on the number of stages present in a Cockroft-Walton series voltage multiplying circuit. Several reasons exist for this limit. One deals with the output voltage droop that occurs between no load and full load conditions which is proportional to the cube of the number of stages utilized. When the neutron tube is gated to be on, it is not uncommon to find the 100 kV dropping towards 80 kV as the power supply tries to feed into the load of the tube. A second problem that occurs is the generation of ripple voltage that rides on the high voltage output due to the incomplete conversion of AC to DC voltage. This unwanted electrical noise interferes with the acceleration voltage of the tube and is difficult to remove from the process. Unfortunately, the ripple voltage present on the high voltage output from a series multiplier is proportional to the square of the number of stages used in the multiplier.
Thus, there is currently a need for an improved oil well logging device that will operate at temperatures above 150 degrees C., for example.
The present invention is directed to a high voltage power supply, a voltage multiplier circuit, an oil well logging device, and methods for making and using high voltage power supply, a voltage multiplier circuit, an oil well logging device. For example, high voltage power supply can include an AC power source input configured to receive an AC output of desired voltage from an AC power source. The high voltage power supply can further include a voltage multiplier circuit. The voltage multiplier circuit can include a plurality of capacitors and a plurality of rectifiers. The voltage multiplier can be coupled to the AC power source input so as to provide a DC output voltage higher than the AC input from the AC output of the AC power source. The voltage multiplier circuit can be configured so that the voltage across each of a plurality of the plurality of capacitors is greater than the reverse voltage across any one of the rectifiers of the plurality of rectifiers. The dielectric of an AC side of the voltage multiplier can be tapered in such a fashion to have a smaller thickness at a first end and a larger thickness at a second end. The second end can be a relatively higher voltage end as opposed to the first end. And, the second end can be proximate to a high voltage output of the voltage multiplier circuit and the first end is proximate to an AC input of the voltage multiplier circuit.
The total output voltage of the high voltage power supply can appear across one of the capacitors. And, the reverse voltage across any of the rectifiers of the plurality of rectifiers can be low enough to allow the circuit to provide a desired output voltage at temperatures above 150 degrees C. where reverse diode leakage becomes problematic.
A plurality of the plurality of capacitors can be electrically connected in series-parallel and constructed with a common capacitor electrode, a plurality of individual capacitor electrodes, and dielectric material positioned between each individual capacitor electrode and the common electrode. And, the common capacitor electrode is an elongate piece of conductive material, the dielectric material is formed at least partially around the common electrode, and the individual capacitor electrodes are positioned around the dielectric material. The dielectric can be a ceramic material configured to fit around at least a portion of the common electrode. And, the individual capacitor electrodes can be formed by areas of metallization on the ceramic material.
The elongate piece of conductive material can be a cylinder of conductive material. And, the ceramic material can be formed as a closed end sleeve of ceramic material configured and sized to receive at least a portion of the common electrode therein. The dielectric can be a high temperature dielectric film material wrapped around at least a portion of the elongate piece of conductive material forming the common electrode. For example, the high temperature film material can include a Kapton polyimide film material.
The individual electrodes can include conductive material concentrically positioned around the dielectric material which can be concentrically formed around at least a portion of the elongate piece of conductive material forming the common electrode.
The plurality of the plurality of capacitors can be electrically connected in series-parallel and constructed with a common capacitor electrode, can be less than all of the capacitors of the plurality of capacitors, and the remaining capacitors of the plurality of capacitors can be individual separate capacitors connected in electrical series.
The plurality of capacitors can include two pluralities of capacitors. The plurality of capacitors of each of the two pluralities of capacitors can be electrically connected in parallel and constructed with a common capacitor electrode. The voltage multiplier circuit can be encapsulated in an electrical insulating material. And, the tapered dielectric region can increase AC feed capacitance at lower voltage stages.
The high voltage power supply can include internal metallic electrodes, wound within the dielectric structure that provides a factor of ten improvement in electrode surface area and capacitance value. And, higher numbered stages of the assembly can have more projected area to the common central electrode of the input voltage feed mitigating the losses in coupling inefficiencies as the thickness of the dielectric material is increased.
The high voltage power supply can have a full parallel multiplier which uses two tapered and graduated capacitor banks. Both AC and DC capacitors can include tapered capacitor arrangements. Both AC and DC capacitors can include tapered and graduated capacitor arrangements.
Additional features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention, and wherein:
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
Embodiments disclosed herein include a high voltage power supply which can be used in any situation where a high voltage power supply is needed. A specific application of the high voltage power supply is in connection with oil well logging devices which are lowered down an oil well while emitting pulses of neutrons into the formation through which the well extends to find the oil bearing strata intersected by the well. The specific example embodiments described herein are directed to this specific application, but the invention is not so limited. Section 1 of this Detailed Description discusses examples of oil logging devices within which the high voltage power supply may be implemented, Section 2 discusses examples of the Inventor's innovative voltage multiplier circuits, as included in the Inventor's previous patent applications, and Section 3 discusses several means for evening out the voltage generation per-stage in the Inventor's innovative high voltage power supply as newly introduced and claimed herein.
1. Examples of Oil Logging Devices within which the High Voltage Power Supply May be Implemented
Referring to
As indicated, the traditional logging devices as shown in
As shown in
In the embodiments shown, the invention is directed to the voltage multiplier circuit portion 18 of the high voltage power supply. The other parts of the high voltage supply and the oil well logging device in which the high voltage supply and the voltage multiplier circuit of the invention is shown, as an example of its use, generally remain the same as for the prior art shown in
2. Examples of the Inventor's Innovative Voltage Multiplier Circuits
As indicated, because in the parallel multiplier circuit topology the output voltage droop (load regulation) is proportional only to the number of stages (as opposed to the cube of the number of stages) while the ripple voltage is only a function of the capacitance used, independent of the number of stages (as opposed to the square of the number of stages), when using parallel multiplier circuits as opposed to the normally used Cockroft-Walton series multiplier circuits, the number of stages can be increased significantly compared to the number of stages used in the Cockroft-Walton series multiplier circuits. Therefore, to lessen the reverse voltage across the rectifiers to thereby increase the temperatures at which such circuits will operate satisfactorily, the number of stages used in the parallel circuits, such as the parallel circuit of
The use of the parallel multiplier circuits of the present invention in oil well logging equipment is possible with the use of a special high voltage capacitor construction of the invention.
Each common capacitor electrode 40 is coated with a dielectric material 42 having a high breakdown voltage. It has been found that a wrapping of multiple layers of a polyimide film material such as KAPTON or TEFLON film material around the common electrode, e.g., around the brass tube 40, provides a dielectric of sufficient breakdown voltage to be used satisfactorily in a 100,000 volt power supply. A single layer of the KAPTON film or tape, depending on the thickness, will withstand up to about 30,000 volts. A wrapping of four layers of such KAPTON film or tape will withstand well over 100,000 volts. While the KAPTON film or tape has been found satisfactory for use in building the capacitors, various other electrically insulating materials can be used, such as Teflon or other plastics, ceramics, aluminum oxide, reconstructed mica, etc. With the dielectric layer around the common electrode, the individual capacitors for a set of parallel capacitors can be easily constructed by forming individual electrodes of conductive material 44 on the dielectric material, such as by wrapping a conductive material, such as a conductive foil material or a conductive band, around the dielectric 42. Each separate electrode formed by conductive material 44 may be provided with a terminal connection 46 where the rectifiers 47 and 48 are connected in opposite orientations to the individual capacitor electrodes. Alternatively, the respective rectifiers can be attached, such as by soldering, directly to the conductive material forming the individual electrodes without provision of specific terminal configurations. Care must be taken particularly with the last capacitor toward the output 49 of a tube 40 that the dielectric coating 42 extends far enough beyond the conductive material 44 forming the individual capacitor electrode that there will be no arcing between the last individual capacitor electrode and the tube forming the common electrode. As shown, the dielectric material 42 can extend beyond the end of the tube 40 at the high voltage output end of a parallel capacitor set. Also, although the difference in voltage between adjacent capacitors is not high since the number of stages is large, the individual capacitor electrodes 44 must be kept far enough apart along the tube to prevent arcing between the individual capacitors electrodes 44. While shown as a cylindrical tube 40, the common capacitive electrode could take various other shapes and forms.
For a ten stage multiplier as shown in
As apparent from the circuitry shown in
With the parallel-series multiplier circuitry, again the voltage across each of the rectifiers is reduced from that present in a standard Cockroft-Walton series multiplier circuit so the multiplier circuitry works well at high temperatures above 150 degrees C., but the parallel capacitors have to be high voltage capacitors as almost the entire output voltage of the circuit appears across capacitor C10.
With the circuitry of
As apparent from the circuitry shown in
Either the parallel circuitry of
The AC power supply may provide an AC signal of various waveforms with various voltages. For Example, the AC power supply 14 may provide a 100 Vpp sinusoidal AC signal to the input (primary winding 15) of the step up transformer 16. With a ten stage multiplier circuit of the invention, the step up transformer may provide a ten kilovolt AC output to the input of the voltage multiplier circuit 18. The voltage multiplier circuit then increases the voltage to a 100,000 volt DC output that is connected to the neutron generator 12. With a twenty stage multiplier circuit of the invention, the step up transformer may provide a five kilovolt output to the input of the voltage multiplier circuit 18. The twenty stage voltage multiplier circuit then, again, increases the voltage to a 100,000 volt DC output that is connected to the neutron generator 12. Depending upon the output voltage needed, the available voltage supply, and the components used in the circuitry, various voltage supply signals can be used as input to the step up transformer and the step up transformer can provide various AC signals to the multiplier circuitry. Further, depending upon the AC voltage supply signal available, a step up transformer may not be necessary. If appropriate, the AC voltage supply may alone be the AC voltage source and be connected directly to the voltage multiplier circuit.
An alternative construction for a parallel set of capacitors for either a parallel or parallel-series voltage multiplier circuit is shown in
While the invention has been illustrated and described with respect to embodiments of the invention specifically designed for use in oil well logging applications, it should be realized that the invention can be used in any application where any high voltage DC is required. Further, with the arrangement of the rectifiers in the circuits as shown in the drawings, the high voltage DC output is a negative voltage which is needed for the neutron generating tubes. If used in a different application where a positive high voltage DC is needed, the polarity of the respective rectifiers is reversed.
With the parallel and parallel-series circuits for the voltage multiplier of the invention, the reverse voltage across the rectifiers is reduced over the reverse voltages that appear in a series circuit because many more stages may be used without having the problem of the N (number of stages) cubed droop problem or N squared ripple problems. This lower reverse voltage allows the higher temperature operation of the circuits due to reduced diode leakage. With such parallel and parallel-series circuits, the voltage across a plurality of the capacitors in the circuit is greater than the voltage across any one of the rectifiers in the circuit. Further, the entire output voltage will generally appear across one of the capacitors. Further, with the physical construction of sets of parallel capacitors along a common capacitor electrode where the common electrode is elongate, and with the individual capacitors arranged along the length of the common electrode, the stepped up voltages will appear on consecutive capacitors so that the stepped up voltages will increase linearly with respect to the physical spatial dimensions of the circuits. Further, with the parallel-series combination circuit, the series connection of the capacitors will provide a voltage increase across each individual capacitor which scales linearly along the spatial length dimension of the circuit.
3. Means for Evening Out the Voltage Generation Per-Stage in the Inventor's Innovative High Voltage Power Supply
It has been found by the Inventor of this application that while semiconductor rectifiers operating at high reverse voltages, i.e., the rectifiers are used to block high voltages, suffer excessive leakage currents at temperatures above 150 degrees C. with the danger of thermal runaway, but that such rectifiers, if operated at lower voltages, will operate satisfactorily up to and over 175 degrees C., the temperatures needed for operation in deep oil wells. Thus, if the voltages across the rectifiers can be reduced, the operating temperature for the circuits using such rectifiers can be increased. This can be achieved by increasing the number of stages used in a voltage multiplying circuit. In doing so the voltage generated by each stage can be reduced and consequently the reverse voltage across the rectifiers used in each stage can be reduced as well. However, as indicated above, the number of stages that can be included in the presently used Cockroft-Walton series multiplication circuits to provide the needed high output voltage without excessive output voltage droop and ripple is very limited. Therefore, it is generally not possible to increase the number of stages in such Cockroft-Walton multiplier circuits above eight stages without increasing the value of the stage capacitance. This is usually not easy to do because of size constraints within the geometry of the logging tool itself. It has been found by the Inventor of this patent application that in voltage multiplier circuits utilizing a parallel or combination parallel and series multiplication scheme, the voltage regulation (droop) and ripple does not scale as the cube and square of the number of stages used as it does in the Cockroft-Walton series multiplier circuits. In the parallel or combination parallel and series multiplier circuit topology, the output voltage regulation (droop) scales only as the number of stages (N) while the ripple voltage is only a function of the capacitance used, independent of the number of stages. Therefore, a much larger number of multiplying stages can be used to generate the needed high DC voltage output without serious output voltage droop and ripple. If such voltage multiplying circuits can be incorporated into oil well logging devices, such circuits can be used to provide the needed DC voltage to operate the neutron generating tube at the higher temperatures above 150 degrees C. However, when using a parallel or combination parallel and series voltage multiplier circuit, it is necessary to provide capacitors that will operate at high voltages up to the output voltage of the power supply, usually at least 100 kV. Providing high voltage capacitors that will physically fit into such circuits where the circuits have to fit into a cylindrical case with an outside diameter between one and one quarter inch and two inches (75 mm diameters are common), is very difficult. Standard 100 kV disc or mica construction high voltage capacitors do not fit in such small diameter spaces.
According to the teachings discussed in Section 2 of this specification, as well as in the previously referenced '015 patent application, a high voltage power supply which will operate at high temperatures in excess of 150 degrees C. and which can fit into an oil well logging tool can be made by utilizing a voltage multiplier circuit with a parallel or combination of parallel and series multiplication schemes. As a result, a much larger number of multiplying stages, for example ten, twenty, or even thirty stages, can be used in the circuits thereby reducing the reverse voltage drop across each semiconductor rectifier. The lower reverse voltage drop across the rectifiers reduce the leakage currents thereby reducing the power loss, minimizing internal power dissipation, and increasing system efficiency. This allows such circuits to operate at higher temperatures. In addition, by using lower AC input voltages to the multiplier, a simpler and more efficient step-up transformer may be utilized. Since the voltage regulation and ripple in such circuits does not scale as the cube and square of the number of stages used, better voltage regulation with less ripple is obtained. Because high voltage capacitors are required for such circuits, the invention uses a special novel and non-obvious construction of high voltage capacitors that will fit into the small diameters required by the oil well logging devices. By constructing the needed high voltage capacitors from a common capacitor electrode, such as formed by an elongate piece of conductive material, for example a length of cylindrical conductive material such as a length of metal tubing or rod, coated with a high voltage dielectric, such as several layers of a Kapton or other plastic film material wrapped around at least a portion of the cylindrical length or a ceramic material positioned around at least a portion of the cylindrical length such as sleeves of alumina positioned around the tube or rod, separate individual capacitor electrodes can be formed on and inside the layered dielectric with conductive material, such as with strips of conductive material wrapped concentrically with the tube or rod within the dielectric material. With this construction, a small diameter set of high voltage parallel capacitors can be constructed to fit within an oil well logging device. To insure mechanical integrity, the entire apparatus may be encapsulated within a high voltage container by a high temperature potting material and placed within a metal outer case.
At least three improvements have been discovered by the Inventor of this patent application that can be implemented individually or in combination with one another to allow an increase in gain of the parallel multiplier that uses a series stack of DC capacitors. They include (1): the usage of a tapered dielectric region to increase the AC feed capacitance at lower voltage stages; (2) the use of internal metallic electrodes, wound within the structure that allow a factor of ten improvement in electrode surface area and capacitance value, and (3) the scaling of the electrode design so that higher numbered stages have more projected area to the common central electrode of the input voltage feed—mitigating the losses in coupling inefficiencies as the thickness of the dielectric material is increased. These will now be discussed in detail starting with the third improvement first:
It has been found by the Inventor of this application that parallel multipliers consisting of large number of multiplying stages (15 or more) of the type discussed in the '015 patent application can allow lower voltages to be placed across rectifiers as compared to series voltage multipliers of the Cockroft-Walton type. This is because they do not suffer from the disastrous “cube effect” which relates the voltage regulation (droop in output voltage) to the cube of the number of multiplication stages used. They are however sensitive to the number of stages used and show a regulation that scales as a linear function of the number of stages used in the device. According to some embodiments it is important for all stages to supply their fair share of voltage, or as close to it as possible. In an effort to equalize out the voltage generation of all stages, it has been found that the higher numbered stages (those having the higher total DC voltage) do not always produce their full share, especially under load, due to diode capacitance, stray capacitance, and the gradual reduction in DC capacitor values with respect to ground as more stages are added due to increased dielectric thickness (higher voltage capability).
With the circuitry of
As shown in
Moreover, the scaling of the electrode design can be such that so that higher numbered stages (lower voltage stages near T2) have more projected area to the common central electrode of the input voltage feed—mitigating the losses in coupling inefficiencies as the thickness of the dielectric material is increased. For example, the distance between stages can be increased as shown in
For example,
Thus, in an effort to equalize out the voltage generation of all 18 stages, it has been found that the higher numbered stages (those having the higher total DC voltage) do not always produce their full share, especially under load, due to diode capacitance, stray capacitance, and the gradual reduction in DC capacitor values with respect to ground as more stages are added. For example, in a eighteen stage multiplier producing 100 kV of output voltage, it has been found by the Inventor that the first stage may be producing 8 kV while the 18th stage only produces 5 kV. Detailed SPICE analysis shows that this effect is due to the capacitance mentioned, with higher numbered stages taking the most hit. In the earlier patent application, the AC coupling capacitance of this type of multiplier is relatively small. It can, however, still transmit electrical energy to the DC capacitor of each stage, but it does so at lower and lower coupling values as one proceeds up the multiplier to higher numbered stages. To compensate for this effect, it is found by the Inventor of this application that an increase in coupling capacitance value will provide more voltage generation per stage. The Inventor of this application discovered that this is easily accomplished by two methods, both embodied in this new multiplier design. One feature is to increase dramatically the value of the AC feed capacitor by inserting the capacitor electrode during the roll-up procedure. This allows a tenfold increase in value of capacitance helping to minimize the uneven voltage distribution among stages as mentioned earlier. The second technique, a consequence of the first, is to place the lower number stage AC electrode at a smaller dielectric thickness, again maximizing the capacitance value. Third, another technique is to begin the electrode in positions that allow larger and larger projected area between the higher numbered electrode and the common electrode (brass tube). This maximizes the parallel voltage multiplier effectiveness by increasing the direct capacitance between the AC input to the multiplier and each stage. By having the higher number stages couple to the AC input with larger capacitance values, the droop effect mentioned earlier is minimized.
This has the effect of evening out the voltage generation per stage and prevents any one stage from carrying the brunt of the voltage generation. Basically, smaller capacitance at the lower stages and higher capacitance at the end allows less concentrated stress across the rectifying devices within the structure of the parallel-series multiplier. This is completely retrograde to techniques used to improve equalization in Cockroft-Walton series multipliers where larger capacitors are normally used at the lower stages to improve the voltage regulation.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
This application claims the benefit of, and priority to, U.S. Provisional Patent Application 61/453,448 filed on Mar. 16, 2011, the contents of which are hereby incorporated by reference herein. This patent application is related to U.S. patent application Ser. No. 12/397,015 filed Mar. 3, 2009 (the '015 patent application). This patent application is also related to U.S. patent application Ser. No. 12/490,041 filed Jun. 23, 3009, which issued on Dec. 27, 2011 as U.S. Pat. No. 8,085,561 (the '041 patent application). The contents of both the '015 patent application and the '041 patent application are hereby incorporated by reference herein. Both the '015 patent application and the '041 patent application, as well as this patent application, share the same inventive entity, Gary Hanington of Elko, Nev. (the Inventor).
Number | Date | Country | |
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61453448 | Mar 2011 | US |