Device for detecting short-circuited turns in coil

Abstract

The invention relates to a device for detecting short-circuited turns in a coil. In one example, a coil includes a spool of a wire having a first end and a second end for winding onto a former to form the coil; a current source arranged to pass a current through a length of wire between the first end and the second end; a first conductive connector for electrically connecting a first end of the wire to a current source; a second conductive connector for electrically connecting a second end of the wire to a current source; and a voltmeter for measuring the resistance between the first end and the second end to identify a drop in resistance between the first conductive connector and the second conductive connector indicative of the generation of a short-circuit turn. The current provided from the current source to the length of wire is modulated in synchronization with the measurements made by the voltmeter. Measurements obtained by the voltmeter are averaged over a plurality of modulation periods to determine a measurement of an effective resistance between the first conductive connector and the second conductive connector at frequencies above 0 Hz.

Description

[0001] Individuals who are male or female are included in the term, regardless of grammatical usage. Technical Field

[0002] The example implementations described herein relate to a device for detecting short-circuited turns in a coil—such as those generated during the winding of a superconducting magnet coil. Background Technology

[0003] Superconducting magnets are made by winding coils of superconducting wire. Typically, such wires consist of multiple fine superconducting filaments sheathed with copper or other normally conductive materials. The wires used usually have a circular or rectangular cross-section. Using wires with rectangular cross-sections allows for higher packing densities. The wires typically have an insulating coating. This can be in the form of a braided fabric, such as polyester braid, polyethylene terephthalate tape, varnish, etc.

[0004] The chosen insulating coating must be able to withstand cooling to temperatures as low as 4K and may also need to withstand immersion in liquid refrigerants at that temperature. The insulating coating must be thin because superconducting magnet coils can contain thousands of turns and must have the smallest possible diameter to reduce wire costs and allow the finished system containing the coil (such as a magnetic resonance imaging (MRI) system) to be as small and lightweight as possible.

[0005] In use, the superconducting coil is cooled below its transition temperature, thus having zero resistance. Current then flows through the superconducting filament, rather than through the normally conductive sheath.

[0006] When a coil is wound, a short circuit can occur between adjacent turns. In some known cases, metal burrs or particulate contaminants can damage the insulation, leading to a short circuit. In other cases, the transition of conductors from one layer of the coil to the next can cause increased stress on the insulation coating of the involved turns, which can lead to damage and short circuit formation. This is particularly problematic for rectangular cross-section conductors, as the corners of the conductors can create particularly high stress points on the insulation. Another possible defect associated with rectangular cross-section conductors is twisting in the conductor. Twisting will create high-voltage points between adjacent turns, which can lead to a short circuit.

[0007] When the coil is in a stable superconducting state, the presence of short-circuited turns does not cause problems. Current flows through the superconducting filament, and the presence of a resistive short circuit between adjacent turns does not cause the current to deflect to a perceptible degree. However, during ramping—that is, during the introduction or removal of current from the superconducting coil—the presence of short circuits between adjacent turns does cause problems. It is known that at least some quenches occurring during ramping are caused by short-circuited turns. It is also known that some magnets cannot be raised to a magnetic field due to quenches caused by short circuits. These quenches have the characteristic of being consistently triggered under the same current.

[0008] The change in current in the coil will cause an induced voltage on each turn, which is controlled by the ratio V = L·(dI / dt). This voltage will appear on the copper sheath at the short circuit point, causing current to flow through the short circuit and heating the coil at that point.

[0009] Without expecting to be bound by any particular theory, the problem caused by a short-circuited turn can be explained as follows: The short-circuited turn provides a current loop that is tightly magnetically coupled to the rest of the coil. This is the electrical equivalent of a transformer. If the coil has 2000 turns, and one of them is short-circuited, this is equivalent to a transformer with a turns ratio of 1999:1. Any fluctuation in the current within the coil will result in an induced voltage on the short-circuited turn, and will induce a current change of 1999 times in the opposite direction. This large current flowing through the resistive sheath material at the short circuit causes heating, which rapidly leads to quenching in the superconducting coil. In a typical MRI system, several superconducting coils are arranged such that a quench in one coil will quickly propagate to the other coils.

[0010] A loss of quench is undesirable because it causes the superconducting coil to lose its magnetic field and release a significant amount of heat. The liquid coolant is consumed and may be lost during use. The released heat must be removed, and the magnet may be damaged. At the very least, the system in which the coil forms part will be unusable for a considerable period.

[0011] Therefore, it is important to detect the presence of short-circuited turns in the coil before it is built into the system. If a defect (such as a short-circuited coil) is discovered in the coil after it has been assembled into a product (such as an MRI system), replacing the coil or the entire system can be very expensive.

[0012] Existing techniques for detecting short-circuited turns involve measuring the room-temperature resistance of the entire coil and comparing it to a theoretical value. This has been found to be sufficient for detecting short-circuited layers, but not sensitive enough for detecting individual short-circuited turns.

[0013] Several attempts have been made in the past to detect short-circuited turns during winding. For example, in known processes, the resistance of each layer of turns is measured once it is completed. For accuracy, a four-wire arrangement is preferably used, in which current flows through the entire coil while the resulting voltage is measured between adjacent layers.

[0014] However, because a short-circuited turn can be one of a hundred or more turns on the same layer, and its resistance is much less than 1Ω, it has been found difficult to identify. The effects of temperature variations between and within the coils make detecting abnormally low resistance (indicating a short-circuited turn) quite challenging. The measurement process is time-consuming, tedious, and error-prone for the operator. Summary of the Invention

[0015] To address the aforementioned difficulties, an innovative device for continuously monitoring the resistance of a coil during winding is proposed. A spool of wire (e.g., a superconducting wire) is provided, with both the first and second ends of the wire being accessible. The first end of the wire on the spool is wound onto a coil forming device while the first end remains accessible. Winding continues from the spool onto the forming device, while the resistance between the first and second ends of the wire is monitored. If a sudden drop in voltage is detected on the wire, this indicates the formation of a short-circuit turn. An alarm can be triggered when a short-circuit turn is detected. By providing continuous monitoring of the coil resistance, a short-circuit coil is detected as soon as it is wound. The short-circuit turn can be unwound and rewound to eliminate the short circuit.

[0016] Figure 1An overview of the apparatus for detecting short-circuit turns is schematically shown. A superconducting wire 10 is wound from a spool 12 onto a coiler 14 to form a coil. A slip ring 16 can be positioned on the axis of the spool to provide electrical contact between the wire 10 on the spool 12 and a current source 20 (e.g., a power supply). Similarly, the first wound end of the wire wound on the coiler 14 is made accessible. A current I flows from the current source 20 through current lead 26, through slip ring 18, through wire 10, through slip ring 16, and through return current lead 28. This current allows the resistance of the circuit to be measured and recorded by a data logger, such as a voltmeter 22. To measure only the portion of the circuit including slip rings 16, 18 and wire 10, voltage sensing leads 30, 32 are provided from slip rings 16, 18 to the data logger or voltmeter 22. The use of the four leads 26, 28, 30, 32 allows for a more accurate measurement of the resistance of interest. The voltage input to data logger 22 is high impedance, thus drawing a negligible current through voltage sensing leads 30, 32. A small resistor can be placed within current source 20 or data logger 22 to sense the value of current I as the voltage across the series resistor. Therefore, data logger 22 is provided with the current value through the wires and the voltage value across the wires and slip rings, based on which data logger 22 can calculate a continuously updated resistance value.

[0017] The data logger or voltmeter 22 and the current source 20 can be connected to the controller 60 via a wired or wireless signal connection 61. Therefore, the controller 60 can be configured to control the current source to output current I and to receive voltage readings from the data logger or voltmeter 22. Furthermore, the controller 60 can be configured to control a winding motor (not shown) configured to wind the wire 10 from the spool 12 onto the coil former 14 to form a coil. For example, the controller 60 can be configured to control the current source 20 to supply power to the winding motor. However, the controller 60 can also be configured to directly control the winding motor via a wired or wireless signal connection.

[0018] Figure 2 An embodiment of the equivalent circuit model for a device used to detect short-circuited turns in a coil is shown. Current source 20 is modeled as current source I, data logger 22 is shown as voltmeter DMM1, and wire 10 is shown as equivalent resistance R1. Equivalent resistances R3, R5, R7, and R9 representing the resistance of the fixed connection between current source 20 and data logger 22, and equivalent resistances R2, R4, R6, and R8 of the terminal connection leads that connect this fixed connection to slip rings 16 and 18 are also shown. The equivalent resistances are series resistances in the current supply and sensing voltage signal paths.

[0019] In this example, the nominal output of the current source is shown as 100mA. The resistance R1 of the coil of wire 10 is nominally shown as 100Ω. The equivalent resistances R3, R5, R7, and R9, representing the fixed connections, are nominally shown as 1Ω, while the equivalent resistances R2, R4, R6, and R8 of the terminal connection leads are nominally shown as 100mΩ.

[0020] use Figure 2 Determining the following from the circuit model depicted in the diagram may be difficult: when is the drop in the measured voltage sudden enough to be caused by a short-circuit turn? Figure 3 A representative dataset 40 is shown, illustrating the resistance measured at data logger 22 when wire 10 is wound into a coil. As illustrated, the resistance does not present a constant value when wire 10 is wound into a coil. Rapid changes in resistance are observed, as indicated at 42. These rapid changes are attributed to measurement noise, such as noise from slip rings, current sources, or other electromagnetic interference. Quantization noise is also introduced by the digital data logger. Long-term changes in the measured resistance, as indicated at 44, are attributed to thermal changes in wire 10. Sudden and permanent decreases in resistance, as indicated at 46, can be used to indicate the formation of a short-circuit turn.

[0021] Small reductions in the measured resistance (e.g., from a small short-circuit portion of the coil) are important to allow these to be corrected for. However, when the noise component being measured is large, for example, on the same order of magnitude as the change in resistance caused by a short-circuited turn, it can be difficult to determine when a short-circuited turn has occurred. That is, if the change in resistance is small compared to the noise component in the measurement, it can be difficult to determine whether there is a real change in the measured resistance or whether the measurement indicates an induced noise spike. In addition to the problems associated with failing to detect a short circuit as described above, a false indication of the presence of a short circuit can lead to wasted time and effort trying to correct problems that do not actually exist.

[0022] In a first aspect, an apparatus for detecting a short-circuited turn in a coil is provided. The apparatus includes a spool for receiving a conductor having a first end and a second end for winding onto a formwork to form a coil; a current source arranged to allow current to flow through a section of the conductor between the first and second ends; a first conductive connector for electrically connecting the first end of the conductor to the current source; a second conductive connector for electrically connecting the second end of the conductor to the current source; a voltmeter arranged to measure the resistance between the first and second ends of the conductor to identify a decrease in resistance between the first and second conductive connectors indicating the occurrence of a short-circuited turn; and a controller arranged to modulate the current supplied from the current source to the section of the conductor in synchronization with the measurement performed by the voltmeter, and to average the measurement results obtained by the voltmeter over multiple modulation cycles to determine a measurement result of the effective resistance between the first and second conductive connectors at a frequency above 0 Hz.

[0023] In one example, the device includes a controller arranged to implement the methods described herein within the device.

[0024] By using a modulated current source, the voltage on an unknown resistive component of the wire is measured as the wire is wound onto the formwork. The voltage is modulated at the same frequency as the current and can be reconstructed into a stable signal, where electrical interference does not affect the average voltage measurement and therefore does not lead to incorrect determinations related to short-circuit turns.

[0025] In one example, the innovative device includes a winding motor configured to wind a wire onto a forming device. A controller is configured to continuously determine an effective resistance measurement based on modulated current and voltmeter measurements during winding under the operation of the winding motor. In another example, the controller is configured to control the winding motor to unwind the wire from the spool and wind the wire onto the forming device.

[0026] Continuous measurements are required to immediately determine when a short-circuit turn occurs, enabling immediate corrective action. However, the winding motor can be a significant source of electrical noise and is typically located near the conductor during winding. This makes accurate measurements challenging. Furthermore, the winding motor generally generates a series of random or quasi-random alternating frequencies of noise. Such noise is out of sync with the modulation of the current source and voltage measurements, and the average sum over multiple alternating modulation cycles will be zero. Additionally, it should be understood that another source of electrical noise in resistance measurements is the voltage induced in the coils and spools due to the asymmetric magnetism of the winding machine structure. It has been found that the frequency of this induced noise is directly related to the rotational speed of the coils and spools, and therefore directly related to the winding speed. The amplitude of this noise increases with increasing winding speed.

[0027] In one embodiment of the innovative device, the controller is configured to modulate the current supplied by the current source to a section of wire in sync with the measurement performed by the voltmeter, and to average the measurement results obtained by the voltmeter over multiple modulation cycles to determine the effective resistance measurement result at a frequency between a lower threshold frequency above 0 Hz and an upper threshold frequency above the lower threshold frequency.

[0028] According to another embodiment of the innovative device, the controller is configured to determine the electrical noise in the conductor and, based on the frequency characteristics of the measured electrical noise, control the current source and voltmeter to operate at a modulation frequency that results in an effective resistance measurement in a frequency window corresponding to relatively low electrical noise.

[0029] Electrical noise can be determined via a voltmeter and a current source. For example, a controller can be configured to control a current source to allow current to flow through a conductor and to receive voltage measurements from a voltmeter. The controller can be configured to determine electrical noise based on the current flowing through the conductor and the voltage measurements received from the voltmeter. In particular, the controller may include a processing unit configured to determine electrical noise based on the current flowing through the conductor and the voltage measurements received from the voltmeter.

[0030] According to an embodiment of the innovative device, the controller is configured to determine electrical noise in the conductor to determine one or more minimum electrical noise values, and to control a current source and a voltmeter to operate at a modulation frequency that results in an effective resistance measurement obtained within a frequency window corresponding to one of the minimum electrical noise values.

[0031] In one embodiment of the innovative device, the controller is configured to determine electrical noise in the conductor and identify noise frequency bands corresponding to one or more of the following: mains noise; current source 1 / f noise; winding motor noise; and harmonics of any of the aforementioned noises.

[0032] According to the invention, the controller is configured to control the current source and the voltmeter to operate at the modulation frequency, such that effective resistance measurement results are obtained in a frequency window outside the identified electrical noise band.

[0033] Specifically, the controller can be configured to identify noise frequency bands based on the determined electrical noise. The electrical noise can be determined according to the above embodiments.

[0034] In another embodiment of the innovative device, the controller is configured to modulate the current supplied to a section of wire in sync with the measurement performed by the voltmeter, so as to allow the determination of the effective resistance measurement at a frequency within a window frequency that falls between a lower threshold frequency above 20 Hz and an upper threshold frequency below 40 Hz.

[0035] According to the implementation, the controller of the innovative device is configured to modulate the current supplied to a section of wire in sync with the measurement performed by the voltmeter, allowing the determination of effective resistance measurements within a frequency window centered at 30 Hz, for example, at 30 Hz. This has been found to be a low-noise region far removed from mains noise, winding motor noise, 1 / f noise, and their significant harmonics, for the typical wound arrangement of superconducting coils used in magnetic resonance imaging.

[0036] In another embodiment of the innovative device, the controller is configured to determine electrical noise in the conductor using a current source and voltmeter connected to the conductor as described above, precisely before winding begins, within the initialization time window, and / or during the initial phase of winding (e.g., within the startup time window), or at the initial phase of winding before a short-circuit turn is detected. For example, the initialization time window can be on the order of seconds, particularly less than 30 seconds. In another example, the startup time window can be on the order of seconds, particularly less than 30 seconds.

[0037] In such an implementation, the modulation frequency can be determined based on the electrical noise conditions that are prevalent at or near the start of winding.

[0038] According to another embodiment of the innovative device, in order to wind the second wire into the coil, the controller is configured to control the current source and the voltmeter to operate at a modulation frequency that results in an effective resistance measurement obtained within a frequency window corresponding to relatively low electrical noise, based on the electrical noise determined from winding the first wire into the coil.

[0039] For example, the controller can be configured to determine electrical noise in a first conductor wound into the coil via an innovative device. Based on the frequency characteristics of the determined electrical noise in the first conductor, the controller can control a current source and a voltmeter to operate at a modulation frequency that results in an effective resistance measurement obtained within a frequency window corresponding to relatively low electrical noise.

[0040] In a preferred embodiment, the innovative device includes a storage unit configured to store characteristic information of measured electrical noise originating from winding a first wire into a coil. The storage unit may include a local data storage device (i.e., a hard disk drive, solid-state drive, flash drive, etc.), a network storage device, a cloud storage device, etc.

[0041] The controller is configured to use stored characteristic information of the measured electrical noise to determine the modulation frequency to be used when the second conductor is wound into the coil for detecting short-circuited turns of the second conductor. Preferably, the second conductor is different from the first conductor.

[0042] At a specific winding location, or when using a certain type of winding motor, the typical noise environment is likely to remain largely consistent over time. This means that once the characteristics of the measured electrical noise are determined for the first winding operation, the same characteristics can be reused at the same location or when using the same type of winding motor.

[0043] In one implementation of the innovative device, the current source connection and the voltmeter connection are switched in a phase-locked manner.

[0044] According to one implementation, the controller is configured to modulate the current supplied from a current source to a section of wire via switch-mode modulation.

[0045] For example, modulation may include square wave modulation. In one example, modulation may include synchronous modulation of the current and gating of voltage measurements. In another example, modulation is performed according to a square wave pattern. In yet another example, modulation may include supplying current to the conductor in the form of a trapezoidal wave. That is, a modified square wave in which the current rises at a rate different from a simple step change. Modulation may also include a sequence of current inputs in the alternating direction to the coil. For example, a controller may be configured to modulate a current source by switching current source connections. In one example, modulating a measurement performed by a voltmeter includes modulating the voltmeter connection. In a preferred embodiment, the controller is configured to switch the current source connection and the voltmeter connection synchronously with each other.

[0046] Square wave modulation advantageously enables resistance measurement across different frequency bands without requiring analog multipliers or other relatively complex circuitry. The controller (e.g., hardware and / or software controller) can be implemented to synchronously drive the current source and record data readings from the voltmeter.

[0047] As another advantage, the controller integrated with the current source and voltmeter can perform data logging of the measured voltage, followed by averaging and / or other post-filtering of the data, and can be connected to an alarm and / or winding motor driver to create an integrated device for detecting short-circuited turns and reacting by stopping the winding.

[0048] According to the implementation of the innovative device, the controller and / or the controller's processing unit are configured to average the measured voltage over multiple modulation cycles to determine the effective resistance.

[0049] For example, the controller can be configured to average the measured voltage over three or more modulation cycles. The controller can also be configured to average the measured voltage over a period of more than 3 seconds (e.g., 6 seconds, 9 seconds, or about 12 seconds). Furthermore, the controller can be configured to perform low-pass filtering on the measured voltage to determine the effective resistance. In one example, the controller can be configured to perform median average filtering on the measured voltage to determine the effective resistance.

[0050] According to another embodiment of the innovative device, the modulation provided via the controller includes analog multiplication, such as sine wave multiplication. It is also conceivable that the controller and / or its processing unit are configured to perform bandpass filtering on the modulated voltage signal to determine the effective resistance.

[0051] In one implementation, the controller is configured to provide modulation frequencies on the order of tens of hertz, such as 20 Hz, 30 Hz, or up to 100 Hz.

[0052] According to an embodiment, the innovative device includes an output device. The output device can be configured to provide acoustic, visual, and / or tactile signals. For example, the output device can be configured to output noise, melody, commands, graphics, video, and / or vibration. Preferably, the output device is configured to provide an output or alarm signal to notify the operator of a short-circuit detection.

[0053] The controller is configured to control the output device to generate an alarm signal to alert the operator of the occurrence of a short circuit.

[0054] In a preferred embodiment, the innovative device is configured to wind a superconducting wire into a superconducting coil and detect short-circuit turns in the superconducting coil.

[0055] Although several exemplary embodiments have been described, those skilled in the art will understand that various changes and modifications can be made without departing from the scope of the invention as defined in the appended claims. Attached Figure Description

[0056] To better understand the invention and to illustrate how embodiments of the invention can be implemented, reference will now be made by way of example to the accompanying drawings, in which:

[0057] Figure 1 , Figure 2 and Figure 3 An innovative device for detecting short-circuited turns in a coil, an equivalent circuit model for such a device, and an example of the coil's resistance output measured during winding are shown respectively.

[0058] Figure 4A representative example of the frequency characteristics of electrical noise measured in a wire when wound into a coil is shown;

[0059] Figure 5 The steps of an example embodiment of a method for detecting a short-circuited turn in a coil, according to an exemplary embodiment, are shown;

[0060] Figure 6 An equivalent circuit model for detecting short-circuited turns in a conductor using a method according to an example implementation is shown;

[0061] Figure 7 It shows the effect of switching with Figure 6 The equivalent circuit model corresponding to a part of the circuit;

[0062] Figure 8 It shows Figure 7 Representative traces of voltage and current measured in the circuit; and

[0063] Figure 9 An implementation of an innovative device for detecting short-circuited turns in a coil is shown. Detailed Implementation

[0064] This invention is particularly applicable to the detection of short-circuited turns in superconducting magnet coils. Similar problems with short-circuited turns exist in the production of other wound components (e.g., electric motors, generators, and transformers). However, these components operate at relatively low currents and are relatively inexpensive compared to superconducting magnet coils. While the device of this invention can be applied to detect short-circuited turns in such wound components, it can be found that simply discarding or rewinding the faulty unit is more economical.

[0065] In such as reference Figure 1 , Figure 2 and Figure 3 In the systems described, operators may be required to visually monitor in a manner similar to... Figure 2 The dataset, presented graphically or shown as a sequence of numerical resistance values, is used to identify resistance changes indicating short-circuit turns. Alternatively, the controller 60 or data logger 22 is programmed to identify sudden decreases in resistance, such as... Figure 2 As shown at point 46. However, in all such cases, when measuring resistance at DC (i.e., 0 Hz), the effects of electrical noise in the signal may mask the drop of interest or may identify a false indication. This is especially true when the interference noise spectrum has high amplitude at low frequencies.

[0066] In a typical coil, there can be 1500 turns. The resistance change caused by a short-circuited turn may only represent 0.05% of the measured resistance. Short-circuited turns can be detected independently of the actual resistance value using slope and amplitude thresholds. For example, a resistance decrease greater than 10 mΩ occurring within 10 seconds or less can be selected as a suitable threshold. Any decrease in resistance exceeding a predetermined rate of change threshold can be considered an indication of a short-circuited turn. The percentage change, as well as the threshold determination of the rate of change and the amount of change, can be compromised by electrical noise in the measurement.

[0067] Figure 5 An embodiment of a method for detecting short-circuited turns in a superconducting wire to be wound into a superconducting coil using an innovative device 1 is shown. The method is performed using a spool 12 with a wire having a first end and a second end, for winding onto a former 14 to form a coil. In step S110, current is introduced via a current source through a section of the wire 10 between the first and second ends. A first conductive connector (e.g., a slip ring connector) allows the first end of the wire 10 to be electrically connected to the current source 20. A second conductive connector (e.g., a slip ring connector) allows the second end of the wire 10 to be electrically connected to the current source 20.

[0068] In step S120, a data logger, specifically a voltmeter 22, is used to measure the resistance between the first and second ends of the wire 10.

[0069] In step S130, the controller 60 or the processing unit 62 of the controller 60 processes the measured voltage to identify a decrease in resistance between the first conductive connector and the second conductive connector, indicating a short-circuit turn.

[0070] Steps S110 and S120 may include modulating the current supplied from the current source 20 to a section of conductor 10 in synchronization with the measurement performed by the voltmeter 22, and averaging the measurement results obtained by the voltmeter 22 over multiple modulation periods to determine the measurement result of the effective resistance between the first conductive connector and the second conductive connector at a frequency outside the frequency range of the induced noise voltage in the conductor 10. Suitably, the modulation includes switch-mode modulation, which involves gating the voltage measurement according to a square wave pattern in synchronization with gating the current supplied from the current source 20.

[0071] Preferably, steps S110 and S120 are performed while the winding motor is used to wind the wire 10 onto the forming device 14, so that the effective resistance measurement results can be continuously determined based on the modulated current and voltmeter measurement results.

[0072] In an optional step S140, the controller 60 may generate an alarm signal to alert the operator of the occurrence of a short circuit turn.

[0073] Figure 4This demonstrates how the noise floor of voltage measurements via voltmeter 22 can be determined from the different components of device 1 and the different components surrounding device 1.

[0074] The noise line for the power supply unit "PSU" indicates the noise limit under quiet conditions (e.g., when the winding machine is not winding and therefore no winding motor is operating, but current source 20 is operational).

[0075] The induced noise line represents the induced noise in the coil caused by magnetic induction from the metal parts of the winding machine during rotation.

[0076] The winding noise line represents the interference generated in the coil by the current in the winding motor and the magnetic field of the winding machine. In a typical system, this is the main noise source and is proportional to the winding speed of the winding machine. Measurement results indicate that the amplitude of the winding noise decreases at higher frequencies, as shown. That is, although higher harmonic components exist, their amplitude decreases as the order increases.

[0077] The innovative device described in this paper aims to convert normal resistance measurements at 0 Hz into synchronous resistance measurements at an experimentally determined minimum noise level of 30 Hz. Approximately 30 Hz is the frequency window where interference noise is minimized. This eliminates the effect of winding noise peaks in the 2 Hz to 15 Hz bandwidth. For example, a noise signal within a given bandwidth window B will be modulated by a modulation frequency M and converted into a component at frequency M+ / -B. Figure 4 In the example implementation related to the noise characteristic curves shown, with a modulation frequency of 30Hz, a 2Hz interference signal will be converted to 30+ / -2, thus becoming 28Hz and 32Hz. This pattern is repeated for other interference bandwidths of the winding motor and other interference sources.

[0078] Figure 6 An example of an equivalent circuit model for innovative device 1 is shown, enabling synchronized modulation of current supply and measurement. Power supply 20 is modeled as a current source I1, data logger 22 is shown as a voltmeter, and the coil of the wire 10 to be wound is shown as an equivalent resistance R3 in series with a winding noise source N, which is the cause of the noise voltage component V1. Equivalent resistances R1, R2, R4, and R8, representing the resistance of the fixed connection between current source 20 and data logger 22, are also shown. The equivalent resistance is the series resistance in the current supply and sensing voltage signal path. The nominal value of the output of current source 20, shown as I1, is 100mA. The resistance R3 of the coil of wire 10 is nominally shown as 100Ω. The equivalent resistances R1, R2, R4, and R8, representing the resistance of the fixed connection, are nominally shown as 1Ω.

[0079] To modulate the current I1 supplied from the current source 20, four switches S1, S2, S7, and S8 are arranged in pairs on the input and output sides of the current source 20. The current source 20 is configured in an H-bridge configuration such that when S2 and S7 are closed, current is supplied to the coil of the conductor 10 in one direction, and when S1 and S8 are closed, current is supplied to the coil of the conductor 10 in the other direction. That is, when S2 and S7 are closed, current flows to the first end of the coil of the conductor 10, and when S1 and S8 are closed, current flows to the second end of the coil of the conductor 10. When one pair of switches is closed, the other pair is open. A controller 60 (not shown) or a modulator controls the timing of the opening and closing of the switches according to the modulation frequency.

[0080] To modulate the voltage measurement at voltmeter 22, four switches S3, S4, S5, and S6 are similarly arranged in pairs on the input and output sides of voltmeter 22. Voltmeter 22 is configured in an H-bridge configuration such that when S4 and S5 are closed, the voltage across the coil of conductor 10 is measured in one direction (i.e., with the first end of the conductor coil as the positive terminal). When S1 and S8 are closed, the voltage across the coil of conductor 10 is measured in the other direction (i.e., with the second end of the conductor coil as the positive terminal). When one pair of switches is closed, the other pair is open. A controller 60 (not shown) or a modulator controls the timing of the opening and closing of the switches according to a modulation frequency. The operation of the switches at the input / output of voltmeter 22 is synchronized with the operation of the switches at the input / output of current source 20 to achieve a modulation effect that eliminates the influence of winding noise on the measured voltage.

[0081] Figure 7 An equivalent circuit model of the innovative device 1, comprising the current source 20, switches S2 and S7, and the coil of conductor 10, is shown when switches S2 and S7 are closed. At this time, the change in current flow in the coil of conductor 10 is resisted by the build-up of the magnetic field in the coil. This is represented by the inductance L1 in the equivalent circuit model. In a typical example coil of the conductor, L1 can have a value of 10H.

[0082] like Figure 8 As shown in the lower trace, based on the operation of the associated switch and current source, current source 20 can output a trapezoidal output current. By controlling the timing of the opening and closing of the switch via controller 60 according to the above embodiment, the resistance and inductance of a typical MRI coil are modeled, thereby generating a current such as... Figure 8 The upper trace in the diagram shows the coil voltage. Figure 8 In the examples, representative values ​​are given below.

[0083]

[0084] In addition to switching the synchronous current source 20 and voltmeter 22 to provide a modulation effect for noise cancellation, the reading of voltmeter 22 of interest is acquired during the stable voltage portion of each switching cycle to avoid the effects of switching transients at the beginning of each cycle. This can be performed, for example, as post-processing in controller 60 or data logger 22.

[0085] As the modulation frequency increases, the induced voltage used to boost the current in the inductor also needs to increase. To keep the maximum induced voltage in the measurement system around 100V (which is prudent for safety), the maximum coil current can be reduced accordingly. In the example above, with a modulation frequency of 30Hz and a maximum voltage of 100V, the maximum coil current is approximately 40mA.

[0086] As will be understood, the production cost of superconducting coils, such as those used in MRI magnets, is very high. Once the coil is installed into a finished MRI system, the value of the device increases significantly again, but it can become inoperable due to a single short-circuited turn within the coil. Therefore, it is crucial to identify even very small short circuits at the earliest possible opportunity so that the coil can be repaired or discarded before being installed into the MRI system.

[0087] For example, if a short circuit is caused by contaminant particles, the contaminants can be removed and the turns rewound. If a short circuit is caused by high pressure between rectangular conductor turns at the transition between layers, a supplementary insulating material, such as a polyester sheet, can be placed between the turns. More simply, the insulation on the conductor may be defective, causing a short circuit between turns. If the short circuit occurs near a planned conductor joint, the joint can be performed in advance to avoid using the damaged conductor section.

[0088] Figure 9 Another embodiment of the innovative device 1 is shown. In the depicted example, the controller 60 includes a processing unit 62 configured to process measurement data received from the voltmeter 22 via the signal connection 61. Specifically, the processing unit 62 may be configured to determine electrical noise based on the current flowing through the wire 10 and the voltage measurement received from the voltmeter 22. However, it is also conceivable that the processing unit 62 may be configured to process the measured voltage to identify a decrease in resistance between the first conductive connector and the second conductive connector indicating a short circuit. In another example, the processing unit 62 may be configured to:

[0089] -Average the measured voltage over multiple modulation cycles to determine the effective resistance.

[0090] Perform a low-pass filter on the measured voltage to determine the effective resistance.

[0091] - Perform median averaging filtering on the measured voltage to determine the effective resistance, and / or

[0092] Perform bandpass filtering on the modulated voltage signal to determine the effective resistance.

[0093] like Figure 9 The depicted innovative device 1 may include a storage unit 80 configured to store characteristic information of measured electrical noise originating from winding a first conductor into a coil. A controller 60 may be configured to use the stored characteristic information of the measured electrical noise from the first conductor to determine a modulation frequency, wherein the modulation frequency is used when winding a second conductor into the coil for detecting short-circuit turns in the second conductor. In the depicted example, the storage unit 80 forms part of the controller 60. However, the storage unit 80 may also represent a network storage device and / or cloud storage device connected to the controller 60 via a wired or wireless signal connection.

[0094] The innovative device 1 may also include an output device 70. In the depicted example, the output device 70 includes a speaker configured to provide noise or instructions that alert the operator to the detection of a short-circuit turn. Preferably, the controller 60 and / or processing unit 62, according to the above embodiment, are configured to detect the short-circuit turn based on current flowing through the wire 10 via the current source 20 and voltage measurements obtained via the voltmeter 22. The controller 60 may be configured to output a control signal to the output device 70 via a wired or wireless signal connection 61 to control the output device 70 to generate an alarm signal. The alarm signal may be configured to alert the operator if a short-circuit turn has been detected.

[0095] By using the innovative device 1 described herein, the impact of electrical noise on the accurate detection of short-circuit turns is reduced, including when short-circuit turns are continuously monitored and detected during coil winding.

[0096] Although the invention has been described with reference to certain exemplary embodiments given by way of example only, many modifications and variations will be apparent to those skilled in the art.

[0097] For example, while the use of a controller or data logger has been described, any equivalent device can be used to implement a suitable modulation scheme and calculate and monitor the resistance of the wire as it is wound. The resistance can be calculated in real time, or the current and voltage values ​​can be stored and the corresponding resistance value calculated later. In the described example, both current and voltage are measured. This has the advantage of not requiring an accurate and constant current, as the resistance can be calculated as the instantaneous ratio of voltage to current.

[0098] All features and / or steps of any method or process disclosed in this specification (including any appended claims, abstract, and drawings) may be combined in any combination except where at least some of such features and / or steps are mutually exclusive.

[0099] Unless otherwise expressly stated, each feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by an alternative feature for the same, equivalent, or similar purpose. Therefore, unless otherwise expressly stated, each disclosed feature is merely one example of a general set of equivalent or similar features.

[0100] This invention is not limited to the details of the foregoing embodiments. The invention extends to any novel feature or any novel combination thereof disclosed in this specification (including any appended claims, abstract, and drawings), or to any novel step or any novel combination thereof in any method or process so disclosed.

Claims

1. An apparatus (1) for detecting short-circuited turns in a coil, the apparatus comprising a spool (12) for receiving a wire (10) having a first end and a second end for winding onto a forming device (14) to form the coil; A current source (20) is arranged to allow current to pass through a section of wire between the first end and the second end; A first conductive connector (18) is used to electrically connect a first end of the wire to the current source; A second conductive connector (16) is used to electrically connect the second end of the wire to the current source; A voltmeter (22), arranged to measure the resistance between the first and second ends of the conductor, to identify a decrease (46) in the resistance between the first and second conductive connectors, indicating the occurrence of a short-circuit turn; and A controller (60) is arranged to modulate the current supplied from the current source to the conductor segment in synchronization with the measurement performed by the voltmeter, and to average the measurement results obtained by the voltmeter over multiple modulation cycles to determine the measurement results of the effective resistance between the first conductive connector and the second conductive connector at a frequency above 0 Hz.

2. The apparatus (1) according to claim 1, comprising a winding motor configured to wind the wire (10) onto the forming device (14), wherein, The controller is configured to continuously determine the effective resistance measurement results based on the modulated current and voltage meter measurements during winding under the operation of the winding motor.

3. The apparatus (1) according to claim 2, wherein, The controller is configured to modulate the current supplied by the current source (20) to the conductor segment in sync with the measurement performed by the voltmeter (22), and to average the measurement results obtained by the voltmeter (22) over multiple modulation cycles to determine the effective resistance measurement results at frequencies between a lower threshold frequency above 0 Hz and an upper threshold frequency above the lower threshold frequency.

4. The apparatus (1) according to any one of claims 1, 2 or 3, wherein, The controller is configured to determine electrical noise in the conductor and, based on the frequency characteristics of the measured electrical noise, control the current source and the voltmeter to operate at a modulation frequency that results in an effective resistance measurement within a frequency window corresponding to relatively low electrical noise.

5. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to determine electrical noise in the conductor to determine one or more electrical noise minimums, and to control the current source (20) and the voltmeter (22) to operate at a modulation frequency that results in an effective resistance measurement obtained in a frequency window corresponding to one of the electrical noise minimums.

6. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to measure electrical noise in the conductor and identify noise frequency bands corresponding to one or more of the following: Mains noise; Current source 1 / f noise; winding motor noise, and harmonics of any of the aforementioned noises; as well as The current source (20) and the voltmeter (22) are controlled to operate at the modulation frequency so that the effective resistance measurement result is obtained in a frequency window outside the identified electrical noise band.

7. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to modulate the current supplied to the conductor segment in sync with the measurement performed by the voltmeter, so as to allow the determination of the effective resistance measurement result at a frequency within a window frequency that falls between a lower threshold frequency above 20 Hz and an upper threshold frequency below 40 Hz.

8. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to modulate the current supplied to the section of conductor (10) in sync with the measurement performed by the voltmeter (22) to allow the determination of effective resistance measurement results within a frequency window centered at 30 Hz, for example at 30 Hz.

9. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to determine electrical noise in the conductor using the current source (20) and the voltmeter (22) connected to the conductor (10) as described above, before winding begins and / or during the initial winding phase before a short-circuit turn is detected.

10. The apparatus (1) according to any of the preceding claims, wherein, In order to wind the second conductor into the coil, the controller (60) is configured to control the current source (20) and the voltmeter (22) to operate at a modulation frequency that results in an effective resistance measurement obtained in a frequency window that corresponds to relatively low electrical noise based on the electrical noise determined from winding the first conductor into the coil.

11. The apparatus (1) according to any preceding claim, comprising a storage unit configured to store characteristic information of measured electrical noise, the measured electrical noise originating from winding a first wire into a coil, wherein, The controller is configured to use stored characteristic information of the measured electrical noise to determine the modulation frequency to be used when the second conductor is wound into the coil for detecting the short-circuit turns of the second conductor.

12. The apparatus (1) according to any of the preceding claims, wherein, The controller is configured to modulate the current supplied from the current source to the conductor segment via switch-mode modulation, for example via modulation of the current according to a square wave pattern and gating of voltage measurements.

13. The apparatus (1) according to any of the preceding claims further includes an output device, wherein, The controller is configured to control the output device to generate an alarm signal to alert the operator of the occurrence of a short circuit.

14. The apparatus (1) according to any of the preceding claims, wherein, The coil includes a superconducting magnet coil.

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