A switch cabinet partial discharge detection method using pulse injection

Abstract

A method for detecting partial discharge in switchgear using pulse injection, belonging to the field of fault detection, includes: connecting a Rogowski coil to the high-voltage incoming bushing of the switchgear; applying a pulse signal to the secondary side of the Rogowski coil, injecting the pulse signal into the high-voltage conductor of the switchgear; acquiring the pulse signal at the phase comparison aperture of a live indicator; sending the pulse signal to an oscilloscope to obtain the rise time of a standard pulse signal waveform; periodically applying a pulse signal to the secondary side of the Rogowski coil, with the oscilloscope acquiring the measured pulse signal again, and calculating the rise time of the measured pulse signal waveform; comparing the rise time of the measured pulse signal waveform with the rise time of the standard pulse signal waveform; if the rise time / wavefront time of the measured pulse signal waveform becomes slower or longer, a partial discharge fault is determined to have occurred inside the switchgear. By periodically and actively injecting pulse signals, the method determines whether corona discharge exists in the high-voltage conductor, thus performing active detection of partial discharge in the switchgear.

Description

Technical Field

[0001] This invention belongs to the field of testing and fault diagnosis of power equipment, and particularly relates to a method for determining the severity of thermal defects in gas-insulated switchgear. Background Technology

[0002] Switchgear is a key piece of equipment in power distribution networks, and its usage is increasing.

[0003] During the operation of the switchgear, the part most prone to partial discharge is the high-voltage conductor. Once the high-voltage conductor experiences partial discharge, it manifests as conductor corona discharge, which will generate a "corona" phenomenon around the high-voltage conductor.

[0004] During the operation of switchgear, insulation defects may occur. These defects can cause partial discharge under the influence of voltage. Corona discharge (also known as "partial discharge") at high-voltage conductors is the most common type of defect.

[0005] The invention patent with authorization announcement date of August 31, 2018, and authorization announcement number CN 104459499 B, discloses "an apparatus and method for measuring partial discharge of power capacitors". The apparatus includes a test equipment system, a CPU, and an oscilloscope. A capacitor test sample and a test sample are connected in parallel to the test equipment system. The test sample is composed of multiple unit capacitors of the same model as the capacitor test sample connected in series and parallel. The test equipment system uses a parallel resonant system to provide test power to the capacitor test sample and the test sample. The capacitor test sample and the test sample are respectively connected to the CPU through Rogowski coils. The CPU is connected to the oscilloscope. The current of the capacitor test sample and the test sample is measured through the Rogowski coils. The two measured signals are sent to the CPU for differential product calculation. The calculation result is output to the oscilloscope for display. This method avoids the uncertainty and external interference of ultrasonic measurement and can be used to measure the partial discharge of large-capacity power capacitor products. This technical solution is only applicable to the measurement of power capacitors, and can only be used for "offline" testing of partial discharge hazards in large-capacity power capacitor products. It cannot be used to monitor or detect "partial discharge" hazards or faults in online high-voltage equipment.

[0006] An invention patent with authorization announcement date of May 15, 2018, and authorization announcement number CN 105116306 B, discloses a "method and device for collecting electromagnetic interference for partial discharge detection in substations." The method includes collecting coupled electromagnetic interference signals of the measured electromagnetic interference using a UHF antenna and a transient ground voltage-capacitance sensor, and collecting conducted electromagnetic interference signals of the measured electromagnetic interference using a high-frequency Rogowski coil. The collected electromagnetic interference signals are then conditioned and output. The device includes an electromagnetic interference signal sensing unit and a signal conditioning unit. The electromagnetic interference signal sensing unit includes a UHF antenna and a transient ground voltage-capacitance sensor for collecting coupled electromagnetic interference signals, and a high-frequency Rogowski coil for detecting conducted electromagnetic interference signals. The output terminals of the UHF antenna, the transient ground voltage-capacitance sensor, and the high-frequency Rogowski coil are connected to the signal conditioning unit. This technical solution involves a relatively complex measurement system, and the signal processing unit's processing is cumbersome, requiring a computer unit with certain data processing capabilities. This is not conducive to on-site testing or low-cost monitoring of partial discharge.

[0007] In summary, the commonly used methods for detecting partial discharge in switchgear include ultra-high frequency (UHF) method, ultrasonic method, and transient ground wave method. The UHF method requires the sensor to be implanted inside the switchgear, which is not easy to install in the field. The ultrasonic method and transient ground wave method are performed on the outside of the switchgear, and their sensitivity is limited, so they cannot achieve accurate detection of partial discharge inside the switchgear.

[0008] In addition, the most crucial point is that the above monitoring schemes are all "passive reception" detection methods. They can only output relevant detection signals after a "partial discharge" fault occurs, and cannot actively check and test for potential "partial discharge" faults.

[0009] How to conveniently conduct low-cost, proactive on-site testing or monitoring of partial discharge is an urgent technical problem to be solved in actual substation operation and equipment management. Summary of the Invention

[0010] The technical problem to be solved by this invention is to provide a method for detecting partial discharge in switchgear using pulse injection. It utilizes the basic physical principle that the wavefront of a pulse slows down when it passes through a high-voltage conductor with corona discharge. By injecting high-frequency pulses into the high-voltage conductor of the switchgear and detecting the pulses at the phase-detection aperture of a live indicator, the pulse wavefront time is calculated. When the pulse wavefront time increases, it is determined that corona discharge exists in the high-voltage conductor. This method is used for the active detection of potential partial discharge hazards inside the switchgear.

[0011] The technical solution of this invention is: to provide a method for detecting partial discharge in switchgear using pulse injection, characterized in that:

[0012] 1) Connect a Rogowski coil to the high-voltage incoming bushing of the switchgear;

[0013] 2) During the operation of the switchgear, a pulse signal is applied to the secondary side of the Rogowski coil through a high-frequency pulse generator, and the pulse signal is injected into the high-voltage conductor of the switchgear by utilizing the coupling effect of the Rogowski coil.

[0014] 3) Acquire pulse current signals at the phase aperture of the charged display;

[0015] 4) The pulse current signal is sent to the oscilloscope. The oscilloscope acquires the pulse signal and calculates the rise time of the pulse signal waveform, which is stored as the wavefront time of the pulse waveform.

[0016] 5) When the switchgear is first put into operation or in normal condition, calculate the pulse waveform wavefront time under normal condition and use it as the standard waveform wavefront time.

[0017] 6) After the switchgear has been running for a period of time, a pulse signal is applied to the secondary side of the Rogowski coil again through a high-frequency pulse generator. The oscilloscope collects the pulse signal measured again and calculates the rise time of the measured pulse signal waveform.

[0018] 7) Compare the rise time / wavehead time of the measured pulse signal waveform with the rise time / wavehead time of the stored pulse waveform under normal conditions;

[0019] 8) If the rise time / wavehead time of the measured pulse signal waveform is slower or longer than that of the pulse waveform under normal conditions, it is determined that there is a corona discharge problem in the high-voltage conductor inside the switch cabinet, and a partial discharge fault or hidden danger has occurred.

[0020] Specifically, a Rogowski coil is connected to the high-voltage incoming bushing of at least one of the three phases (A, B, and C) of the switchgear.

[0021] Specifically, the high-voltage conductors of the switchgear include at least a high-voltage busbar and a copper busbar for the switchgear's incoming lines.

[0022] Specifically, pulse current signals are acquired at the phase-connection aperture of at least one of the three phases (A, B, and C) of the switchgear live indicator.

[0023] Furthermore, the rise time / wavehead time of the measured pulse signal waveform is compared with the rise time / wavehead time of the pulse waveform in the normal state stored. When the change in wavehead time between the two exceeds 10%, it can be determined that a partial discharge fault has occurred inside the switch cabinet.

[0024] The partial discharge detection method for switchgear using pulse injection described in this invention utilizes the basic characteristic that the wavefront of a pulse slows down when it passes through a high-voltage conductor with corona discharge. By injecting a high-frequency pulse signal into the high-voltage conductor of the switchgear, active partial discharge detection is performed. The pulse is detected at the phase-detection aperture of the live display, and the rise time / wavefront time or pulse wavefront time difference of the injected pulse signal is calculated. When the wavefront time of the pulse signal increases, it is determined that corona discharge exists in the high-voltage conductor, thus enabling active detection of partial discharge inside the switchgear.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1. The technical solution of the present invention involves injecting high-frequency pulses into the high-voltage conductor of the switchgear and detecting the pulses at the phase hole of the live display. The pulse wavefront time is calculated. When the pulse wavefront time increases, it is determined that there is corona discharge in the high-voltage conductor. This method is used for active detection of partial discharge hazards inside the switchgear.

[0027] 2. The technical solution of the present invention utilizes a Rogowski coil and a switchgear live indicator for partial discharge detection in switchgear, which has the characteristics of low cost and strong anti-interference ability;

[0028] 3. The technical solution of the present invention is not affected by strong electromagnetic interference on site, and can avoid the false alarms and missed alarms that are easy to occur in the detection device or sensor in the strong electromagnetic interference environment. It has low implementation cost, is easy to promote and implement. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the field testing system of the present invention;

[0030] Figure 2 This is a schematic diagram of two waveform changes according to the present invention;

[0031] Figure 3 This is a flowchart illustrating the method of the present invention.

[0032] In the figure, 1 is the switch cabinet shell, 2 is the high-voltage conductor of the switch cabinet, 3 is the bushing that introduces the high-voltage conductor into the switch cabinet, 4 is the high-frequency pulse generator, 5 is the Rogowski coil, 6 is the switch cabinet live indicator, 7 is the oscilloscope, 8 is the pulse signal waveform when there is no partial discharge of the high-voltage conductor in the switch cabinet, and 9 is the pulse signal waveform when there is partial discharge of the high-voltage conductor in the switch cabinet. Detailed Implementation

[0033] The invention will now be further described with reference to the accompanying drawings.

[0034] In the technical solution of this invention, the specific system components and their interconnections are as follows: Figure 1As shown, 1 is the switch cabinet housing, 2 is the high-voltage conductor of the switch cabinet, 3 is the bushing that introduces the high-voltage conductor into the switch cabinet, 4 is the high-frequency pulse generator, 5 is the Rogowski coil, 6 is the switch cabinet live display, and 7 is the oscilloscope.

[0035] like Figure 3 As shown, the technical solution of the present invention provides a method for detecting partial discharge in switchgear using pulse injection: a Rogowski coil is connected to the high-voltage incoming bushing of the switchgear, a high-frequency pulse current is applied to the secondary side of the Rogowski coil, and the pulse is injected into the high-voltage conductor of the switchgear by utilizing the coupling effect of the Rogowski coil; the high-frequency pulse current propagates along the high-voltage conductor, passes through the impedance of the energized display, and the pulse current signal is acquired at the phase hole of the energized display; the pulse wavefront time is calculated; when there is partial discharge in the high-voltage conductor, corona discharge will occur, which will cause the pulse wavefront time to slow down, and the partial discharge of the high-voltage conductor of the switchgear is detected by the change in the pulse wavefront time.

[0036] Specifically, in the technical solution of the present invention, during the operation of the switchgear, a pulse signal is applied to the secondary side of the Rogowski coil 5 by a high-frequency pulse generator 4. The rising edge of the pulse is 5ns (not limited to 5ns, mainly determined by the change of the wavefront). The Rogowski coil injects the high-frequency pulse into the high-voltage conductor (i.e., the high-voltage busbar or busbar copper busbar) through electromagnetic induction. The high-frequency pulse propagates along the high-voltage conductor.

[0037] The function of the live indicator installed on the switchgear is to indicate whether the high-voltage conductor is energized. It contains a capacitor voltage divider. The phase hole of the live indicator is short-circuited (i.e., electrically connected) to the low-voltage arm of the capacitor voltage divider.

[0038] Liveness indicators are typically installed in the incoming / outgoing line cabinets of high-voltage busbar sections. They are also commonly installed on incoming busbars, circuit breakers, main transformers, switch cabinets, GIS switchgear, and other places where it is necessary to display whether the equipment is energized. These devices can intuitively show whether the electrical equipment is currently energized, and can effectively prevent electrical misoperation.

[0039] The panel of the live indicator has three round holes for "phase verification" (short for "phase sequence verification"), which can indicate whether the phase is live.

[0040] For information regarding the working principle, module composition, or product structure of the live display, please refer to the relevant content disclosed in the utility model patents "High Voltage Live Display" with authorization announcement number CN201780325U, "High Voltage Live Display" with authorization announcement number CN 203275504 U, and "A High Voltage Live Display with Dual Protection Function" with authorization announcement number CN 207301168 U. It will not be described again here.

[0041] The panel of the live indicator has three round holes for "phase verification" (short for "phase sequence verification"), which can indicate whether the phase is live.

[0042] The technical solution of this invention sends the low-voltage arm signal into an oscilloscope through a phase aperture, and the oscilloscope acquires the propagated high-frequency pulse signal.

[0043] In practical use, a timed transmission method can be adopted, with the high-frequency pulse generator 4 generating a pulse signal once every day or several days. The signal is received through the phase detection hole of the switch cabinet's live display and sent to an oscilloscope to calculate the rise time (also known as "wave head time") of the pulse waveform.

[0044] When a partial discharge occurs in a high-voltage conductor, the corona signal causes the rise time of the pulse waveform flowing through the conductor to slow down. At this time, the signal received by the oscilloscope 7 will change. Based on the change in the wavefront time of the pulse waveform obtained at different times, it is possible to detect whether a partial discharge has occurred.

[0045] For example, if the injected high-frequency pulse waveform has a wavefront time of 5ns, and there is no partial discharge in the switchgear, the pulse signal wavefront received by the phase-detection aperture will be 5ns. Based on this, the length of the high-frequency pulse waveform wavefront time under normal switchgear conditions can be determined (also known as the standard high-frequency pulse waveform wavefront time, or simply the standard waveform wavefront time).

[0046] If the measured high-frequency pulse waveform wavefront time (hereinafter referred to as the measured signal wavefront time) is found to be slower (or longer), such as changing to 6ns, it is determined that a partial discharge has occurred inside the switch cabinet.

[0047] The greater the change in wavefront time between the measured signal wavefront time and the standard waveform wavefront time (or the greater the time difference), the stronger the corona phenomenon and the more severe the partial discharge.

[0048] Generally speaking, based on practical field experience, once the difference between the measured signal wavefront time and the standard waveform wavefront time exceeds 10%, it can be determined that internal partial discharge has occurred. Figure 2 As shown, 8 represents the pulse signal waveform when there is no partial discharge, and 9 represents the pulse signal waveform when there is partial discharge in the high-voltage conductor.

[0049] The technical solution of this invention breaks through the limitations of passive reception in previous detection methods such as ultra-high frequency and ultrasonic waves. By actively injecting pulses to detect partial discharge, and comparing the change (or time difference) of the wavefront time between the measured signal wavefront time and the standard waveform wavefront time, the defect of partial discharge can be actively detected. It has the advantages of good anti-interference performance, high detection sensitivity and low implementation cost.

[0050] This invention can be widely used in the field of active detection or monitoring of partial discharge defects in switchgear.

Claims

1. A method for detecting partial discharge in switchgear using pulse injection, characterized in that: 1) Connect a Rogowski coil to the high-voltage incoming bushing of the switchgear; 2) During the operation of the switchgear, a pulse signal is applied to the secondary side of the Rogowski coil through a high-frequency pulse generator, and the pulse signal is injected into the high-voltage conductor of the switchgear by utilizing the coupling effect of the Rogowski coil. 3) Acquire pulse current signals at the phase aperture of the charged display; 4) The pulse current signal is sent to the oscilloscope. The oscilloscope acquires the pulse signal and calculates the rise time of the pulse signal waveform, which is stored as the wavefront time of the pulse waveform. 5) When the switchgear is first put into operation or in normal condition, the pulse waveform wavefront time under normal condition is collected and calculated, and used as the standard waveform wavefront time. 6) After the switchgear has been running for a period of time, a pulse signal is applied to the secondary side of the Rogowski coil again through a high-frequency pulse generator. The oscilloscope collects the pulse signal measured again and calculates the rise time of the measured pulse signal waveform. 7) Compare the rise time / wavehead time of the measured pulse signal waveform with the rise time / wavehead time of the stored pulse waveform under normal conditions; 8) If the rise time / wavehead time of the measured pulse signal waveform is slower or longer than that of the pulse waveform under normal conditions, it is determined that there is a corona discharge problem in the high-voltage conductor inside the switch cabinet, and a partial discharge fault or hidden danger has occurred.

2. The method for detecting partial discharge in switchgear using pulse injection according to claim 1, characterized in that... A Rogowski coil is connected to the bushing of at least one of the three phases (A, B, and C) of the switchgear.

3. The method for detecting partial discharge in switchgear using pulse injection according to claim 1, characterized in that: The high-voltage conductors of the switchgear include at least a high-voltage busbar and a copper busbar for the switchgear's incoming lines.

4. The method for detecting partial discharge in switchgear using pulse injection according to claim 1, characterized in that... At least one of the three phases (A, B, and C) of the switchgear's live indicator is used to acquire pulse current signals.

5. The method for detecting partial discharge in switchgear using pulse injection according to claim 1, characterized in that: Compare the rise time / wavehead time of the measured pulse signal waveform with the rise time / wavehead time of the pulse waveform under normal conditions stored. If the change in wavehead time between the two exceeds 10%, it can be determined that a partial discharge fault has occurred inside the switchgear.

6. The method for detecting partial discharge in switchgear using pulse injection according to claim 1, characterized in that: The pulse injection method for partial discharge detection in switchgear utilizes the fundamental characteristic that the wavefront of a pulse slows down when it passes through a high-voltage conductor with corona discharge. It actively detects partial discharge by injecting a high-frequency pulse signal into the high-voltage conductor of the switchgear, and detects the pulse at the phase-detection aperture of the live indicator. The rise time / wavefront time or pulse wavefront time difference of the injected pulse signal is calculated. When the wavefront time of the pulse signal increases, it is determined that corona discharge exists in the high-voltage conductor, thus enabling active detection of partial discharge inside the switchgear.

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