Method and apparatus for isolating and switching lower voltage pulses from high voltage pulses in electrocrushing and electrohydraulic drills

Abstract

Method and apparatus for isolating and switching lower voltage pulses from high voltage pulses in electrocrushing and electrohydraulic drills. A transformer with a high permeability core acts as a magnetic switch or saturating inductor to switch high voltage pulses to initiate an electrocrushing arc and lower voltage pulses to sustain the arc. The transformer isolates the lower voltage components from the high voltage pulses, and switches to deliver the low voltage current when the core saturates. The transformer enables impedance matching to the arc during all stages of drilling. The saturation time of the transformer core is the time delay between initiation of delivering the high voltage pulse and initiation of delivering the lower voltage current.

Description

BACKGROUND OF THE INVENTION

Field of the Invention (Technical Field)

The field of the present invention is the supply of high voltage pulses to a drill bit in an electro-crushing or electrohydraulic drill.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

The present invention is a method of providing a high voltage pulse to an electrocrushing or electrohydraulic drill bit, the method comprising providing a transformer comprising a core comprising a saturating high relative permeability magnetic material, the transformer delivering a high voltage pulse to an electrocrushing or electrohydraulic drill bit to initiate arc formation in a substrate being drilled, isolating lower voltage electrical components from the high voltage pulse, saturating the transformer core, thereby lowering its relative permeability, and the lower voltage components delivering a lower voltage current through the transformer and to the electrocrushing or electrohydraulic drill bit for maintaining the arc in the substrate. The method preferably further comprises substantially matching an impedance of the arc both during and after arc formation. A pulse width of the high voltage pulse is preferably shorter than a saturation time of the transformer core. The method preferably further comprises actively resetting the transformer by bringing the magnetic material out of saturation. The magnetic material preferably comprises Metglas, Supermendur, or a ferrite. The lower voltage components preferably comprise at least one switch and at least one capacitor and preferably comprise sufficient capacitance to absorb current that leaks through the transformer while the high voltage pulse is being delivered. The method oprionally further comprises flowing a second current to a capacitor while the transformer delivers the high voltage pulse, integrating the second current over a desired time until a threshold charge level is reached, thereby initiating the saturating step, inverting the polarity of the capacitor, and initiating delivery of the lower voltage current. A saturation time of the transformer core is preferably the time delay between initiation of delivering the high voltage pulse and initiation of delivering the lower voltage current. The capacitor is preferably electrically connected in parallel to the transformer.

The present invention is also an apparatus for switching power for use in electrocrushing or electrohydraulic drilling, the apparatus comprising a transformer comprising a core, the core comprising a saturating high relative permeability magnetic material, a first circuit electrically connected to the transformer, the first circuit for delivering high voltage pulses to an electrocrushing or electrohydraulic drill bit, and a second circuit electrically connected to the transformer, the second circuit for delivering a lower voltage current to the drill bit. The apparatus preferably further comprises a reset circuit for resetting the transform by bringing the magnetic material out of saturation. The magnetic material preferably comprises Metglas, Supermendur, or ferrites. The second circuit preferably comprises at least one switch and and least one capacitor and preferably comprises sufficient capacitance to absorb current that leaks through the transformer while the high voltage pulse is being delivered. The apparatus preferably further comprises a capacitor for triggering the second circuit. The capacitor is preferably electrically connected in parallel to the transformer.

Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating certain embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

FIG. 1 is a diagram of solenoid-configuration linear inductor in accordance with an embodiment of the present invention.

FIG. 2A is a diagram of a linear magnetic switch in accordance with an embodiment of the present invention.

FIG. 2B is a diagram of a toroidal magnetic switch in accordance with an embodiment of the present invention.

FIG. 3 is an example electrocrushing saturating transformer circuit diagram in accordance with an embodiment of the present invention.

FIG. 4 is a picture of a high voltage pulse transformer in accordance with an embodiment of the present invention.

FIG. 5 is an embodiment of a schematic of a magnetic switch trigger for an electro-crushing drill switch.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

“Electrocrushing” is defined herein as the process of passing a pulsed electrical current through a mineral substrate so that the substrate is “crushed” or “broken”. One of the characteristics of the electro-crushing drilling process is very large disparity between the impedance of the bit before the arc is formed compared to the bit impedance after arc formation. The impedance of the arc during formation can be between approximately 150 and 500 ohms or even greater. The impedance of the arc after arc formation can be less than 10 ohms, and even lower with an electro-hydraulic system. If a single pulsed power system is used for the electro-crushing or electro-hydraulic system, then it will be significantly mismatched either during the arc formation stage or during the arc power loading stage. This mismatch creates a substantial reduction in efficiency. A spiker sustainer circuit (as disclosed in, for example, commonly owned U.S. Pat. No. 8,186,454, entitled “Apparatus and Method for Electrocrushing Rock”) was adapted to the electro-crushing technology as a very important invention to resolve this issue. With the spiker sustainer technology two separate circuits are used to manage power flow into the arc. The spiker circuit provides the high impedance high voltage pulse necessary to initiate arc formation inside the rock. As used throughout the specification and claims, the term “high voltage” means greater than approximately 30 kV. The sustainer circuit then provides a tow impedance high current pulse necessary to break the rock.

One of the issues in developing practical electro-crushing drills is isolating the high voltage spiker pulse needed to initiate conduction inside the rock from lower voltage sustainer components in the system. As used throughout the specification and claims, the term “lower voltage” means less than approximately 30 kV. However, those lower voltage components, such as a switch, need to conduct current into the arc after the high voltage pulse has initiated conduction. One tool for isolating the high voltage pulse from lower voltage components is a saturating inductor, also known as a magnetic switch. When the magnetic switch is in the high inductance state, that inductance blocks the high voltage pulse from the lower voltage components. The time scale for current to flow through the magnetic switch in the high inductance state is longer than the width of the high voltage pulse.V=L dl/dt

• • where V=the voltage of the pulse
  • L=the inductance of the magnetic switch
  • I=the current flowing through the magnetic switch

dl/dt=the rate of change of current through the magnetic switch with time.

Sufficient capacitance is incorporated into the lower voltage components to absorb the small amount of current that flows through the magnetic switch when in the high inductance state. The voltage pulse time scale is shorter than the time it takes sufficient current to flow through the magnetic switch to raise the voltage of the lower voltage capacitance above the design point.

To explain the saturation process of the present invention, consider a magnetic switch comprising coils of wire wound around cores of magnetic material to form a solenoid-configured inductor, as shown in FIG. 1, which shows the turns of wire, the connecting leads, and the space in the center to accommodate a high permeability core. FIG. 2A shows such a linear inductor with the core in place. The inductance of the linear magnetic switch is given by:L=μ_oμn²lA where μ_o=permeability of free space=8.85×10⁻¹² farads/meter,

• • μ=relative permeability (vacuum=1),
  • n=number of turns per meter,
  • l=length of the coil in meters, and
  • A=cross section area of the coil in square meters.

When the current flowing in the inductor creates sufficient voltage over a specific period of time (i.e. the voltage-time (v-t) product), the magnetic material goes from a high relative permeability (defined as approximately 2000-10,000) to nearly approximately 1.0 (i.e. saturation), thus significantly reducing the inductance of the magnetic switch and facilitating separation of the high voltage input lead from the output lead. The time for the magnetic switch to saturate is preferably longer than the pulse width of the high voltage pulse, thus isolating the lower voltage components from the high voltage pulse. In addition, the current required to saturate the switch preferably does not flow until the arc connection through the rock has been made, except for some small current flow from stray capacitance plus leakage current from when L is high. Then, as the lower voltage component current flows through the magnetic switch, it saturates and becomes a low inductance low impedance conduit for the lower voltage component to feed power into the arc. In some embodiments of the present invention the saturating magnetic switch is incorporated into the transformer that provides the high voltage pulse. In these embodiments the transformer preferably comprises a saturating magnetic material such that after the transformer has delivered the high voltage pulse, the transformer core saturates, enabling lower voltage components to feed current into the arc. The high permeability of the core prior to saturation provides the inductive isolation of the high voltage pulse from the lower voltage components. An alternate embodiment is the toroidal configuration as shown in FIG. 2B, comprising a wire wrapped around a toroid comprising a high permeability saturable magnetic material.

FIG. 3 shows an example circuit comprising transformer windings around the core K1 to provide the high voltage pulse and output windings to provide inductive isolation for the lower voltage components. When switch S1 closes, current flows from lower voltage capacitor C1 through the primary winding of the transformer, creating a high voltage pulse on capacitor C2, which is in turn connected to the bit in series with capacitor C3. As current flows through the bit from the establishment of the arc in the rock from the high voltage pulse, current flows from lower voltage capacitor C3 through the secondary windings of the transformer. The voltage-time product created by the flow of current from capacitor C3 through the bit and through the transformer saturates the transformer and hence provides the high current pulse to break the rock. FIG. 4 shows an embodiment of a typical high voltage pulse transformer, showing the black primary (lower voltage) windings and the secondary (high voltage) windings tapered for high voltage insulation and isolation. The core preferably comprises magnetic materials that have the desired saturation properties. This transformer is intended to be immersed in transformer oil for insulation. After the pulse is over, a reset circuit is often used to bring the transformer out of saturation and prepare it for the next pulse. Thus, a saturating transformer in accordance with the present invention enables the use of a high impedance high voltage spiker circuit to initially create conduction in the rock in conjunction with a lower voltage high current sustainer source to provide power into the arc to break the rock. The same piece of equipment, the saturating transformer, preferably provides both functions.

The core of magnetic material preferably comprises the capability of moving from high permeability to low permeability with the correct application of the voltage-time product in order for the transformer to possess the desired saturation properties. Magnetic materials suitable for the saturating transformer switch include ferrites, Metglas, Supermendur, and other similar magnetic materials with magnetic characteristics that facilitate saturation with the application of the correct voltage-time product.

Embodiments of the transformer magnetic switch of the present invention combine the functions of a pulse transformer and a high-voltage high current switch or diode that isolates the lower voltage components from the high voltage pulse. The transformer magnetic switch replaces the high voltage solid state diode or switch or gas switches that would be used to isolate the lower voltage components from the high voltage pulse and control the flow of current from the sustainer capacitor bank into the arc after arc formation. The switches require isolation from the high voltage pulse, said isolation is provided by the inductance of the secondary windings of the magnetic transformer switch. This is advantageous in the electro-crushing drill pulsed power circuit because such a switch is highly immune to damage from a fault in the circuit. For example, rock is very non-uniform, and the pulses delivered by the pulsed power system vary greatly from shot to shot during the drilling process. Occasionally a shot will produce very unusual current or voltage waveforms. If solid-state diodes were used for voltage isolation, they might be damaged by the unusual shot. A magnetic switch which functions as a diode, however, is very immune to damage from unusual events. In addition, the magnetic “diode” can be quite compact compared to high voltage solid-state diodes and their protection circuits.

Triggering

One of the difficulties with the spiker-sustainer circuit is electrical noise generated in the circuit from the spiker pulse. This electrical noise is often sufficient to trigger the sustainer switch, thus preventing proper control of the sustainer switch timing by the control system. In addition, the electrical noise is sometimes sufficient to damage the solid state trigger switches often used. Thus it is desirable to provide a noise immune trigger for turning on the sustainer switch in such a spiker-sustainer circuit without upsetting timing from electrical noise and without damage from electrical noise. An embodiment of such a trigger of the present invention is preferably configured for use with a saturating inductor, also known as a magnetic switch, as the switching element to trigger the sustainer switch. In embodiments of this invention, the saturating inductor (magnetic switch) is connected to the spiker output and conducts a small amount of current from the spiker output pulse through the magnetic switch to a ballast capacitor during the spiker pulse. This current flow, integrated over the desired time delay for sustainer ignition, will cause the magnetic switch to saturate creating a trigger pulse to turn on the sustainer switch.

The time for the magnetic switch to saturate is preferably designed to be the correct time delay between onset of the high voltage pulse and turning on the sustainer switch. After the trigger pulse is over, a reset circuit is often used to bring the magnetic switch out of saturation and prepare it for the next pulse. Thus, a magnetic switch in accordance with the present invention provides a trigger pulse to turn on the sustainer switch without susceptibility to electrical noise, either in timing upset or damage to components. The timing of the sustainer trigger pulse is preferably determined by passive components, and is not subject to upset from electrical noise. Once the timing of the sustainer trigger pulse has been set by the design of the magnetic switch, it will always be the same for a given spiker output voltage pulse profile.

FIG. 5 is a schematic of an embodiment of a magnetic switch trigger for an electro-crushing drill switch. Negative voltage signal 2, preferably the spiker output voltage of the pulse sent to the rock during the drilling process, is preferably reduced in magnitude through resistor array 6 and charges capacitor 3 through diode 4 in parallel with magnetic switch 1. When magnetic switch 1 saturates, it inverts the polarity of capacitor 3 to provide the required positive polarity to trigger (i.e. turn on) switch 5 through diode 7. Capacitor 8 is preferably used to manage the pulse shape going to switch 5.

Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.

Claims

1. A method of providing a high voltage pulse to an electrocrushing or electrohydraulic drill bit, the method comprising: providing a transformer comprising a core comprising a saturating high relative permeability magnetic material;the transformer delivering a high voltage pulse to an electrocrushing or electrohydraulic drill bit to initiate arc formation in a substrate being drilled;isolating lower voltage electrical components from the high voltage pulse;saturating the transformer core, thereby lowering its relative permeability; andthe lower voltage components delivering a lower voltage high current pulse through the transformer and to the electrocrushing or electrohydraulic drill bit for powering the arc in the substrate and saturating the transformer core.

2. The method of claim 1 further comprising substantially matching an impedance of the arc both during and after arc formation.

3. The method of claim 1 wherein a pulse width of the high voltage pulse is shorter than a saturation time of the transformer core, thus preventing transformer core saturation by the high-voltage pulse.

4. The method of claim 1 further comprising actively resetting the transformer by bringing the magnetic material out of saturation.

5. The method of claim 1 wherein the magnetic material comprises an amorphous metal alloy, a cobalt-iron alloy, or a ferrite.

6. The method of claim 1 wherein the lower voltage components comprise at least one switch and at least one capacitor.

7. The method of claim 1 wherein the lower voltage electrical components comprise sufficient capacitance to absorb current that leaks through the transformer while the high voltage pulse is being delivered.

8. The method of claim 1 wherein a saturation time of the transformer core is the time delay between initiation of delivering the high voltage pulse and initiation of delivering the lower voltage current.

9. The method of claim 6 wherein said at least one switch comprises a solid state switch, a solid state diode switch, a gas switch, or a magnetic switch.

10. An apparatus for switching power for use in electrocrushing or electrohydraulic drilling, the apparatus comprising: a transformer comprising a core and separate primary and secondary windings, said core comprising a saturating high relative permeability magnetic material;a first circuit electrically connected to said primary winding, said first circuit for delivering an electrical pulse to said primary winding;a second circuit electrically connected to said secondary winding, said second circuit comprising a first capacitor connected in parallel to said secondary winding, wherein a first end of said first capacitor and a first end of said secondary winding is electrically connected to an electrocrushing or electrohydraulic drill bit; anda second capacitor, wherein a first end of said second capacitor is electrically connected to a second end of said first capacitor and a second end of said secondary winding, and a second end of said second capacitor is electrically connected to said electrocrushinq or electrohydraulic drill bit;wherein said second capacitor is charged at a voltage lower than a voltage charging said first capacitor.

11. The apparatus of claim 10 further comprising a reset circuit for resetting said transform by bringing said magnetic material out of saturation.

12. The apparatus of claim 10 wherein said magnetic material comprises an amorphous metal alloy, a cobalt-iron alloy, or a ferrite.

13. The apparatus of claim 10 wherein said first circuit comprises at least one switch and at least one capacitor.

14. The apparatus of claim 10 wherein said second circuit comprises sufficient capacitance to absorb current that leaks through said transformer while a high voltage pulse is being delivered to said electrocrushing or electrohydraulic drill bit.

15. The apparatus of claim 13 wherein said at least one switch comprises a solid state switch, a solid state diode switch, a gas switch, or a magnetic switch.