System and method for partial discharge detection band extension via input signal aliasing

Abstract

A partial discharge detection screen includes a voltage divider configured to reduce a reflected signal. A buffer connected to the voltage divider. The buffer attenuates frequencies in the reflected signal that are higher than an upper cutoff frequency. An analog-to-digital converter connected to the buffer. The analog-to-digital converter receives frequency components in the reflected signal that are higher than an upper cutoff frequency, and the analog-to-digital converter converts the reflected signal from an analog domain to a digital domain. A filter connected to the analog-to-digital converter. The filter attenuates frequency components in the reflected signal that are lower than a lower cutoff frequency. A comparator connected to the filter. The comparator compares a voltage of the reflected signal with a reference voltage. A counter connected to the comparator. The counter increases counts when the voltage of the reflected signal is higher than the reference voltage.

Description

[0001] This application is a divisional application of an application filed on August 25, 2016, with application number "201610728547.2" and invention name "Partial discharge detection band extension by input signal aliasing". Background Art

[0002] Partial discharge refers to the localized dielectric breakdown of the electrical insulation system of a device (such as a motor) when the insulation system is subjected to high voltage. The breakdown is caused by one or more cracks, holes, or inclusions in the insulation system. Partial discharge causes small but significant damage to the device, indicating that the insulation system is beginning to fail, which may lead to catastrophic damage in the future. For this reason, it is best to detect partial discharge so that the insulation system can be repaired or replaced before such damage occurs.

[0003] In order to detect partial discharge, a partial discharge detection board is connected to the device, and when the device is subjected to a certain voltage, the partial discharge detection board is adapted to analyze the signal from (for example, reflected from) the device to determine whether the device is experiencing partial discharge. The partial discharge detection board includes an analog-to-digital converter (ADC) that samples the signal at a sampling frequency of, for example, 100 MHZ. The ADC cannot distinguish signal portions above the Nyquist frequency (for example, 50 MHZ in this example). Therefore, a conventional partial discharge detection board includes an anti-aliasing filter to remove frequency components above the Nyquist frequency. Summary of the invention

[0004] The present invention discloses a partial discharge detection screen. The detection screen includes a voltage divider configured to reduce the voltage of a reflected signal. A buffer is connected to the voltage divider. The buffer attenuates frequency components in the reflected signal that are higher than an upper cutoff frequency. An analog-to-digital converter is connected to the buffer. The analog-to-digital converter receives the portion of the reflected signal that is above the upper cutoff frequency, and the analog-to-digital converter converts the reflected signal from an analog domain to a digital domain. A filter is connected to the analog-to-digital converter. The filter attenuates frequency components in the reflected signal that are lower than a lower cutoff frequency. A comparator is connected to the filter. The comparator compares the voltage of the reflected signal with a reference voltage. A counter is connected to the comparator. When the voltage of the reflected signal is higher than the reference voltage, the counter increases the count.

[0005] In another embodiment, the detection screen includes a voltage divider configured to reduce the voltage of the reflected signal. The voltage divider does not include a capacitor or an inductor. A buffer is connected to the voltage divider. The buffer attenuates frequency components in the reflected signal that are higher than an upper cutoff frequency. An analog-to-digital converter is connected to the buffer. An anti-aliasing filter is not provided between the voltage divider and the analog-to-digital converter. The analog-to-digital converter receives frequency components in the reflected signal between the Nyquist frequency of the analog-to-digital converter and the upper cutoff frequency, and the analog-to-digital converter converts the reflected signal from the analog domain to the digital domain. A filter is connected to the analog-to-digital converter. The filter attenuates frequency components in the reflected signal that are lower than a lower cutoff frequency. A comparator is connected to the filter. The comparator compares the voltage of the reflected signal with a reference voltage. A counter is connected to the comparator. When the voltage of the reflected signal is higher than the reference voltage, the counter increases the count.

[0006] The present invention also discloses a method for detecting partial discharge. The method includes transmitting an electric pulse to a device. The electric pulse reflects off the device to generate a reflection signal. A voltage divider is used to reduce the voltage of the reflection signal. A buffer is used to attenuate one or more frequency components in the reflection signal that are higher than an upper cutoff frequency. An analog-to-digital converter is used to convert the reflection signal from an analog domain to a digital domain. The analog-to-digital converter receives a frequency component between the Nyquist frequency of the analog-to-digital converter and the upper cutoff frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present teaching and, together with the description, help explain the principles of the present teaching. In the drawings:

[0008] Figure 1 A schematic diagram of a system for detecting partial discharge according to an embodiment is shown.

[0009] Figure 2 A flow chart of a method for detecting partial discharge according to an exemplary embodiment is shown.

[0010] It should be noted that some details in the drawings have been simplified and are made to facilitate understanding of the embodiments rather than retain strict structural accuracy, detail, and scale. DETAILED DESCRIPTION

[0011] Reference will now be made to the details of embodiments of the present invention, examples of which are illustrated in the accompanying drawings. For convenience, the same reference numerals are used throughout the drawings to represent the same components. In the following description, with reference to the accompanying drawings which form a part of the specification and are illustrated in the specification, the present teachings may be implemented in one or more detailed example embodiments.

[0012] Further, although the broad ranges of numerical ranges and parameters set forth herein are approximate; the numerical values ​​set forth in the detailed examples are as accurate as possible. However, any numerical value inherently includes certain necessary errors, which are caused by the standard deviation found in the testing equipment. In addition, all ranges disclosed herein are to be understood to encompass any and all sub-ranges included therein.

[0013] Figure 1 A schematic diagram of a system 100 for detecting partial discharge according to one embodiment is shown. The system 100 is used to test a device 110. The device 110 includes three conductors 112, 114, 116, each corresponding to a different electrical phase. Each conductor 112, 114, 116 is at least partially surrounded by an electrical insulation 118. The device 110 includes an electric machine or a portion of an electric machine. For example, the device 110 includes an assembled electric machine (for example, with a rotor in place), a stator with a rotor removed (for example, for preventive maintenance), a new electric machine undergoing quality inspection, a single-form winding coil (the coil is designed to withstand high voltage), a DC interpoles, or any combination of the foregoing.

[0014] The system 100 includes an impulse discharge board 120 connected to the device 110. The impulse discharge board 120 is configured to provide high voltage electrical pulses to the device 110, one conductor 112, 114, 116 at a time. For example, the impulse discharge board 120 provides a plurality of electrical pulses to the first conductor 112 to determine a voltage at which the insulation 118 surrounding the first conductor 112 experiences a partial discharge. Then, the impulse discharge board 120 provides a plurality of electrical pulses to the second conductor 114 to determine a voltage at which the insulation 118 surrounding the second conductor 114 experiences a partial discharge, and so on.

[0015] The system 100 also includes a partial discharge detection screen 130. The partial discharge detection screen 130 is connected to the device 110, the impulse discharge screen 120, or both. The partial discharge detection screen 130 includes an input terminal 132 configured to receive a signal reflected from the device 110. The partial discharge detection screen 130 also includes a voltage divider 134 connected to the input terminal 132. The voltage divider 134 is a resistive divider including two or more (two are shown: 136, 138) resistors. In at least one embodiment, the voltage divider 134 does not include a capacitor or an inductor; thus, the voltage divider has little or no capacitive reactance or inductive reactance.

[0016] The partial discharge detection screen 130 further includes a buffer 140 connected to the voltage divider 134. The buffer 140 is an operational amplifier (op-amp) or includes an operational amplifier. In one embodiment, the buffer 140 is a unity-gain buffer. The partial discharge detection screen 130 further includes an analog-to-digital converter (ADC) 142 connected to the buffer 140. The ADC 142 includes an oscillator (for example, a crystal oscillator) 144 that sets the clock rate of the ADC 142. As will be disclosed in more detail below, the partial discharge detection screen 130 does not include an anti-aliasing filter.

[0017] The partial discharge detection screen 130 also includes a first bus 146 connected to the analog-to-digital converter 142. For example, the first bus 146 is a 12-bit bus with digitized data. The partial discharge detection screen 130 further includes a field programmable gate array (FPGA) 150 connected to the bus 146. The field programmable gate array 150 includes a filter 152. The filter 152 is a high-pass, finite impulse response (FIR) filter. In one example, the filter 152 is a 100-pole finite impulse response filter. In more detail, the filter 152 is connected to an input terminal (for example, a negative input terminal) of the comparator 158. A reference voltage source 160 is connected to another input terminal (for example, a positive input terminal) of the comparator 158. The field programmable gate array 150 also includes a counter 162 connected to an output terminal of the comparator 158.

[0018] The partial discharge detection screen 130 further includes a second bus 164 connected to the field programmable logic gate array 150. In more detail, the second bus 164 is connected to the counter 162. For example, the second bus 164 is an 8-bit bus. A microcontroller 166 is connected to the second bus 164.

[0019] Figure 2 A flow chart of a method 200 for detecting partial discharge according to one embodiment is shown. As at 202, the method 200 includes transmitting one or more electrical pulses from the impulse discharge screen 120 to the device 110. In more detail, a plurality of electrical pulses are transmitted from the impulse discharge screen 120 to the first conductor 112 of the device 110.

[0020] The electrical pulses are transmitted at a frequency of about 1 pulse per second to about 20 pulses per second. For example, the electrical pulses are transmitted at 5 pulses per second. The electrical pulses have a voltage of about 1V to about 15KV. Each of the electrical pulses has a duration of less than about 100 nanoseconds. Each electrical pulse reflects off the device 110 (for example, the conductor 112 or the insulating portion 118 near the conductor 112), generating a reflected signal in the form of one or more wavelets. The reflected signal has a duration of less than about 500 nanoseconds.

[0021] The method 200 then includes receiving the reflected signal at the input 132 of the partial discharge detection screen 130, as at 204. The method 200 then includes reducing the voltage of the reflected signal using a voltage divider 134 in the partial discharge detection screen 130, as at 206. Because the voltage divider 134 is a resistor divider, it attenuates the reflected signal without limiting the frequency spectrum. This allows a wider frequency range to pass through the buffer 140 and the analog-to-digital converter 142 compared to a voltage divider 134 having a capacitive or inductive component. For example, when the voltage divider includes a capacitor, the voltage divider 134 acts as a high-pass filter that removes low frequencies.

[0022] As at 208, the method 200 then includes buffering the reflected signal from the remainder of the partial discharge detection screen 130 (for example, the analog-to-digital converter 142 and the field programmable logic gate array 150) using the buffer 140. This protects the components of the partial discharge detection screen 130 "downstream" of the buffer 140 from high voltage surges that could damage the components.

[0023] As at 210, the method 200 also includes attenuating frequency components of the reflected signal that are higher than an upper cutoff frequency using a buffer 140. In more detail, the buffer 140 acts as a low pass filter that attenuates frequency components of the reflected signal that are higher than the upper cutoff frequency. The upper cutoff frequency is from about 100 MHz to about 500 MHz or from about 200 MHz to about 300 MHz. In one example, the upper cutoff frequency is about 235 MHz. Thus, in this example, the portion of the reflected signal above 235 MHz is removed from the reflected signal using the buffer 140.

[0024] As at 212, the method 200 then includes converting the reflected signal from an analog signal to a digital signal using the analog-to-digital converter 142. This includes sampling the reflected signal at a predetermined frequency determined by the oscillator 144. The predetermined frequency is about 30 MHz to about 500 MHz. In one example, the predetermined frequency is about 100 MHz.

[0025] As mentioned above, the partial discharge detection screen 130 does not include an anti-aliasing filter (for example, connected to the buffer 140 and the analog-to-digital converter 142 and positioned between the latter two). As a result, the analog-to-digital converter 142 receives frequency components of the frequency reflection signal that are above the Nyquist frequency and below the upper cutoff frequency (for example, 235 MHz). If the reflection signal contains data indicating that the device has experienced a partial discharge at the voltage of the electrical pulse that generated the reflection signal, the data is distributed between the different frequencies of the reflection signal. In some embodiments, at least some of these frequencies are above the Nyquist frequency and are removed using an anti-aliasing filter. Thus, by removing / omitting the anti-aliasing filter, the partial discharge detection screen 130 is able to sense a larger portion of the total discharge by amplifying the sensed reflection signal using frequencies above the Nyquist frequency, thereby enabling the strength / magnitude of the discharge to be measured more accurately.

[0026] As at 214, the method 200 then includes transmitting the reflected signal to the field programmable logic array 150 in the digital domain using the first bus 146. More specifically, the reflected signal is transmitted to a filter 152 (for example, a high pass filter) in the field programmable logic array 150. In addition to the reflected signal, the filter 152 also receives an electrical pulse transmitted from the impulse discharge screen 120, which has a frequency of about 0 MHz to about 10 MHz. The electrical pulse does not include information related to potential partial discharge in the device 110. Therefore, as at 216, the method 200 also includes attenuating frequency components of the reflected signal less than the lower cutoff frequency using the filter 152. The lower cutoff frequency is higher than or equal to the frequency of the electrical pulse to remove the electrical pulse. In one example, the lower cutoff frequency is between about 10 MHz and about 30 MHz (for example, 20 MHz). As a result, the reflected signal portion between about 20 MHz and about 235 MHz passes through the filter 152.

[0027] As at 218, the method 200 then includes comparing the voltage of the reflected signal with a reference voltage using the comparator 158. For example, the reference voltage is from about 5 mV to about 50 mV or from about 10 mV to about 20 mV. When the voltage of the reflected signal is higher than the reference voltage, it indicates that the device (for example, the conductor 112 and / or the electrical insulation 118) has experienced a partial discharge in response to the electrical pulse that generates the reflected signal. When the voltage of the reflected signal is less than the reference voltage, it is classified as noise and no partial discharge is determined to have occurred.

[0028] As at 220, the method then includes the counter 162 increasing the count when the comparator 158 indicates that the voltage of the reflected signal is greater than or equal to the reference voltage. As at 222, the output signal of the counter 162 is transmitted to the microcontroller 166 using the second bus 164. In addition, as at 224, the reflected signal portion output from the filter 152 (for example, having a frequency from about 20 MHz to about 235 MHz) is also transmitted to the microcontroller 166 using the second bus. This is used to visually represent the waveform of the reflected signal.

[0029] The present teaching has been described in one or more embodiments, and variations and / or modifications may be made to the described examples without departing from the spirit and scope of the claims. In addition, although the present teaching has described only certain features of one of the multiple embodiments, these features may be used in combination with one or more other features of other embodiments because they may be desirable and advantageous for some given or special functions. In addition, whether the terms "including", "having", "with" or variations of these terms are used in the specification or claims, they are intended to be inclusive, similar to the term "comprising". Further, in the specification and claims, the term "about" means that the listed values ​​may vary somewhat, as long as such changes do not cause the method or structure to be inconsistent with the described embodiment. The terms "couple, connect, connection, in connection with, connecting", "coupled, connected" mean "directly connected to..." or "connected to..." through one or more intermediate components or parts". Finally, "exemplary" means that the specification is used as an example and does not mean that it is ideal.

[0030] After considering the specification and embodiments disclosed in this teaching, other embodiments of this teaching will be obvious to those skilled in the art. The specification and embodiments are intended to be exemplary only, and the true scope and spirit of protection are indicated in the claims attached to this teaching.

Claims

1. A partial discharge detection system, comprising: a surge discharge screen configured to couple to the device and provide an electrical surge to the device; A partial discharge detection screen configured to couple to the device and receive a reflected signal from the device, wherein the reflected signal is caused in part by a partial discharge in the device, the partial discharge detection screen comprising: a voltage divider configured to reduce the voltage of the reflected signal, wherein the voltage divider does not include a capacitor or an inductor; a buffer connected to the voltage divider, the buffer attenuating frequency components of the reflected signal that are higher than an upper cutoff frequency; an analog-to-digital converter coupled to the buffer, wherein the partial discharge detection screen does not include an anti-aliasing filter, such that the analog-to-digital converter receives a portion of the reflected signal above a Nyquist frequency of the analog-to-digital converter and up to the upper cutoff frequency, and wherein the analog-to-digital converter converts the reflected signal from an analog domain to a digital domain; a filter connected to the analog-to-digital converter, wherein the filter attenuates frequency components of the reflected signal that are less than a lower cutoff frequency; a comparator connected to the filter, wherein the comparator compares the voltage of the reflected signal with a reference voltage, and a counter connected to the comparator, wherein the counter increases a count when the voltage of the reflected signal is higher than the reference voltage; Wherein, when the counter increments, it is determined that the device has experienced a partial discharge in response to the electrical pulse.

2. The partial discharge detection system according to claim 1, wherein: The upper cut-off frequency is 200 MHz to 300 MHz, and wherein the lower cut-off frequency is 10 MHz to 30 MHz.

3. The partial discharge detection system according to claim 2, wherein: The upper cut-off frequency is higher than the sampling frequency of the analog-to-digital converter.

4. The partial discharge detection system according to claim 1, wherein: The partial discharge detection screen also includes a microcontroller connected to the counter, wherein the microcontroller receives: an output of the counter; and a portion of the reflected signal output from the filter.

5. The partial discharge detection system according to claim 1, wherein: By not having an anti-aliasing filter in the partial discharge detection system, the partial discharge detection screen is able to sense a greater proportion of partial discharges than conventional systems by amplifying the reflected signal using frequencies above the Nyquist frequency, thereby allowing the intensity of partial discharges to be measured more accurately.

6. A method for detecting partial discharge, comprising: transmitting an electrical pulse to a device, wherein the electrical pulse reflects off the device to produce a reflected signal; Using a voltage divider to reduce the voltage of the reflected signal; attenuating frequencies of the reflected signal greater than an upper cutoff frequency using a buffer and converting the reflected signal from an analog domain to a digital domain using an analog-to-digital converter, wherein the analog-to-digital converter receives a portion of the reflected signal between a Nyquist frequency of the analog-to-digital converter and the upper cutoff frequency, wherein the voltage divider, the buffer, and the analog-to-digital converter are not connected to an anti-aliasing filter; wherein a filter is used to attenuate frequencies in the reflected signal that are less than a lower cutoff frequency; and the comparator is used to compare a voltage of the reflected signal with a reference voltage; and a counter increases a count in response to the voltage of the reflected signal being higher than the reference voltage; Wherein, when the counter increments, it is determined that the device has experienced a partial discharge in response to the electrical pulse.

7. The method according to claim 6, wherein: Converting the reflection signal from the analog domain to the digital domain includes sampling the reflection signal at a sampling frequency of the analog-to-digital converter, wherein the sampling frequency is less than the upper cutoff frequency.

8. The method according to claim 6, wherein: The lower cut-off frequency is greater than the frequency of the electrical pulse.

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