Insulation state evaluation method and system for grading capacitor of ultra-high voltage GIS circuit breaker

Abstract

The application relates to a method and system for evaluating the insulation state of a grading capacitor of an extra-high voltage GIS circuit breaker, and relates to the technical field of high-voltage equipment detection. The method sets one built-in extra-high frequency sensor on each side of the extra-high voltage GIS circuit breaker, determines a standard electromagnetic pulse excited by a defect of the right grading capacitor, and names the standard electromagnetic pulse as a type II high-frequency electromagnetic pulse; determines a standard electromagnetic pulse excited by a defect of the left grading capacitor, and names the standard electromagnetic pulse as a type III high-frequency electromagnetic pulse; compares the monitored high-frequency electromagnetic original pulse with the type II and type III high-frequency electromagnetic pulses, and determines whether the insulation state of the grading capacitor is abnormal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage equipment detection, in particular to a method and system for evaluating the insulation state of a grading capacitor of an ultra-high voltage GIS circuit breaker. BACKGROUND

[0002] An ultra-high voltage GIS (Gas Insulated Switchgear) circuit breaker generally adopts a multi-break structure. In order to make the voltage borne by each break consistent during the opening and closing of the circuit breaker, a grading capacitor is connected in parallel between the breaks. The grading capacitor does not bear voltage during the closing of the ultra-high voltage GIS circuit breaker, but will bear a high voltage when there is a running standby. If the grading capacitor has defects, insulation breakdown may occur during the standby of the circuit breaker, causing a fault of the GIS circuit breaker.

[0003] Since the grading capacitor of the GIS circuit breaker is sealed inside the GIS tank, its appearance cannot be observed, and the insulation performance parameters of the capacitor cannot be detected by conventional test and detection methods. During the closing of the circuit breaker, there is no voltage difference across the capacitor, so the commonly used on-line detection methods such as ultra-high frequency and ultrasonic waves cannot detect the insulation state of the grading capacitor.

[0004] Since the grading capacitor of the circuit breaker will bear voltage in the standby state, and the strong impact vibration caused during the opening and closing of the circuit breaker is conducive to exciting the defects of the grading capacitor, the grading capacitor may generate occasional high-frequency electromagnetic pulses during the operation and in the short time thereafter. During the opening and closing of the circuit breaker, pre-breakdown and re-breakdown between the breaks will also excite high-frequency electromagnetic pulses. These high-frequency electromagnetic pulses are mixed together, making it difficult to screen out the pulses excited by the defects of the grading capacitor. SUMMARY

[0005] The purpose of the present application is to provide a method and system for evaluating the insulation state of a grading capacitor of an ultra-high voltage GIS circuit breaker.

[0006] In order to achieve the above purpose, in a first aspect, the present application provides a method for evaluating the insulation state of a grading capacitor of an ultra-high voltage GIS circuit breaker, the method comprising the following steps:

[0007] S1: arranging an in-built ultra-high frequency sensor on each side of the ultra-high voltage GIS circuit breaker;

[0008] S2: during the closing of the ultra-high voltage GIS circuit breaker, monitoring the high-frequency electromagnetic original pulses inside the ultra-high voltage GIS circuit breaker by using the in-built ultra-high frequency sensors on both sides;

[0009] S3: Determine the standard electromagnetic pulse excited by the defect of the right side voltage-sharing capacitor using the built-in ultra-high frequency sensor on both sides, and name it as the II type high-frequency electromagnetic pulse; determine the standard electromagnetic pulse excited by the defect of the left side voltage-sharing capacitor, and name it as the III type high-frequency electromagnetic pulse.

[0010] S4: Compare the high-frequency electromagnetic original pulse monitored in S2 with the II type and III type high-frequency electromagnetic pulses to determine whether the insulation state of the voltage-sharing capacitor is abnormal.

[0011] In an optional implementation, S1 includes:

[0012] The left side voltage-sharing capacitor is a distance a from the left side built-in ultra-high frequency sensor, and the right side voltage-sharing capacitor is also a distance a from the right side built-in ultra-high frequency sensor.

[0013] In an optional implementation, S2 includes:

[0014] The high-frequency electromagnetic pulse signal received by the built-in ultra-high frequency sensor is preprocessed, and the high-frequency component in the range of 300MHz-1500MHz in the high-frequency electromagnetic pulse signal is filtered and amplified.

[0015] In an optional implementation, S3 includes:

[0016] The pulse time-frequency characteristics of the II type and III type high-frequency electromagnetic pulses are determined respectively, and the pulse time-frequency characteristics are used as the standard for identifying the II type or III type high-frequency electromagnetic pulse.

[0017] In an optional implementation, the pulse time-frequency characteristics of the II type high-frequency electromagnetic pulse include: the peak-to-peak value of the electromagnetic signal is 700mV-900mV, the high-frequency component lasts for 500ns-600ns, and the wave head of the signal collected by the right side built-in ultra-high frequency sensor leads the wave head of the signal collected by the left side built-in ultra-high frequency sensor by a time difference △T.

[0018] In an optional implementation, △T satisfies the following relationship:

[0019] (1)

[0020] Wherein, L is the distance between the two built-in ultra-high frequency sensors, C is the propagation speed of the electromagnetic wave, and a is the distance between the signal source and the right side built-in ultra-high frequency sensor.

[0021] In an optional implementation, the pulse time-frequency characteristics of the III type high-frequency electromagnetic pulse include: the peak-to-peak value of the electromagnetic signal is 700mV-900mV, the high-frequency component lasts for 500ns-600ns, and the wave head of the signal collected by the left side built-in ultra-high frequency sensor leads the wave head of the signal collected by the right side built-in ultra-high frequency sensor by a time difference △T.

[0022] In an optional embodiment, S4 comprises:

[0023] counting the number N and the duration T of the type II and type III high-frequency electromagnetic pulses in the monitored high-frequency electromagnetic raw pulses in S2;

[0024] determining whether the insulation state of the grading capacitor is abnormal based on the number N and the duration T.

[0025] In an optional embodiment, determining whether the insulation state of the grading capacitor is abnormal based on the number N and the duration T comprises:

[0026] when N < 50 and T < 2 seconds, the insulation state of the grading capacitor is normal; when N ≥ 50 or T ≥ 2 seconds, the insulation state of the grading capacitor is attention, which can be monitored in operation; when N ≥ 1000 and T ≥ 5 seconds, the insulation state of the grading capacitor is abnormal, which needs to be repaired after power-off.

[0027] In a second aspect, the application provides a grading capacitor insulation state evaluation system for an ultra-high voltage GIS circuit breaker, which comprises:

[0028] two built-in ultra-high frequency sensors installed on both sides of the ultra-high voltage GIS circuit breaker for monitoring high-frequency electromagnetic raw pulses inside the ultra-high voltage GIS circuit breaker;

[0029] an ultra-high frequency amplification processing unit for pre-processing high-frequency electromagnetic pulse signals received by the built-in ultra-high frequency sensors;

[0030] a processor for comparing the monitored high-frequency electromagnetic raw pulses with type II and type III high-frequency electromagnetic pulses to determine whether the insulation state of the grading capacitor is abnormal; wherein the standard electromagnetic pulse excited by the right-side grading capacitor with defects is named as type II high-frequency electromagnetic pulse, and the standard electromagnetic pulse excited by the left-side grading capacitor with defects is named as type III high-frequency electromagnetic pulse.

[0031] Through the above technical solution, during operation of the ultra-high voltage GIS circuit breaker, the high-frequency electromagnetic raw pulses are monitored, the interference is removed by using the pulse time-frequency characteristics, and the abnormal high-frequency electromagnetic raw pulses excited by the grading capacitor are screened out, which are used for insulation state evaluation of the grading capacitor.

[0032] Other features and advantages of the application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0034] Figure 1 The flow chart of the insulation state evaluation method of the ultra-high voltage GIS circuit breaker grading capacitor based on high-frequency electromagnetic original pulse monitoring provided by the embodiments of the present application;

[0035] Figure 2 The internal structure of the ultra-high voltage GIS circuit breaker and the layout of the built-in ultra-high frequency sensor on both sides;

[0036] Figure 3 The high-frequency electromagnetic signal excited by the pre-breakdown and heavy breakdown of the breaking port of the ultra-high voltage GIS circuit breaker;

[0037] Figure 4 The high-frequency electromagnetic signal excited by the grading capacitor on the right side of the ultra-high voltage GIS circuit breaker;

[0038] Figure 5 The time delay of the high-frequency electromagnetic signal excited by the grading capacitor on the right side of the ultra-high voltage GIS circuit breaker;

[0039] Figure 6 The high-frequency electromagnetic signal excited by the grading capacitor on the left side of the ultra-high voltage GIS circuit breaker;

[0040] Figure 7 The time delay of the high-frequency electromagnetic signal excited by the grading capacitor on the left side of the ultra-high voltage GIS circuit breaker.

[0041] Legend: 1-built-in ultra-high frequency sensor; 2-grading capacitor. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the following will combine the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0043] In the description of the present application, it should be pointed out that the terms "in", "out" and the like indicate the position or location relationship based on the position or location relationship shown in the drawings, or the position or location relationship when the product of the application is usually placed, which is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0044] In the description of the present application, it should be pointed out that unless otherwise explicitly specified and limited, the terms "set", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0045] The present application provides a kind of based on high frequency electromagnetic original pulse monitoring ultra-high voltage GIS circuit breaker grading capacitor insulation state evaluation method (hereinafter referred to as: method), during ultra-high voltage GIS circuit breaker operation, by high frequency electromagnetic original pulse monitoring, interference is removed using pulse time-frequency characteristics, screening out the abnormal high frequency electromagnetic original pulse excited by grading capacitor, to be used for the insulation state evaluation of grading capacitor.

[0046] Specifically, please refer to Figure 1 Method comprises the following steps:

[0047] S1: set one built-in UHF sensor 1 on each side of the ultra-high voltage GIS circuit breaker.

[0048] The structure of the double-port ultra-high voltage GIS circuit breaker is shown in Figure 2 Set one built-in UHF sensor 1 on each side of the ultra-high voltage GIS circuit breaker, specifically, the left side grading capacitor 2 is a distance from the left side built-in UHF sensor 1 (also referred to as: 1# sensor), and the right side grading capacitor 2 is also a distance from the right side built-in UHF sensor 1 (also referred to as: 2# sensor), the two built-in UHF sensors 1 are apart by L meters, specifically, a can be 6.5 meters, and L can be 17.2 meters.

[0049] S2: during the closing process of the ultra-high voltage GIS circuit breaker, the built-in UHF sensor 1 on both sides is used to monitor the high frequency electromagnetic original pulse inside the ultra-high voltage GIS circuit breaker.

[0050] The high-frequency electromagnetic pulse signal received by the built-in UHF sensor 1 is preprocessed by the ultra-high frequency amplification processing unit, and the high-frequency components in the range of 300MHz-1500MHz are filtered and amplified. The ultra-high frequency amplification processing unit is connected with the high-frequency signal acquisition unit through a signal cable. In the present application, the sampling rate of the built-in UHF sensor 1 is not less than 2Gs / S, and the analog bandwidth is not less than 800MHz.

[0051] S3: Using the built-in UHF sensors 1 on both sides, the standard electromagnetic pulse excited by the defect of the right side voltage-sharing capacitor 2 is determined, which is named as the II type high-frequency electromagnetic pulse; the standard electromagnetic pulse excited by the defect of the left side voltage-sharing capacitor 2 is determined, which is named as the III type high-frequency electromagnetic pulse.

[0052] The pulse time-frequency characteristics of the I, II and III type high-frequency electromagnetic pulses are determined respectively, and the pulse time-frequency characteristics are used as the standard for identifying the I, II or III type high-frequency electromagnetic pulse.

[0053] During the closing process of the ultra-high voltage GIS circuit breaker, pre-breakdown may occur between the breaking points, which will also generate high-frequency electromagnetic pulses, which are named as the I type high-frequency electromagnetic pulse. The signals measured by the 1# sensor and the 2# sensor are as shown in Figure 3 .

[0054] It can be seen that the pulse time-frequency characteristics of the I type high-frequency electromagnetic pulse include: the peak-to-peak value of the electromagnetic signal measured by the 1# sensor is 900mV-1100mV, which can be 1000mV, the high-frequency component lasts for 700ns-900ns, which can be 800ns, and the tail has obvious low-frequency oscillation. The peak-to-peak value of the electromagnetic signal measured by the 2# sensor is 2800mV-3200mV, which can be 3000mV, the high-frequency component lasts for 900ns-1100ns, which can be 1000ns, and the tail also has obvious low-frequency oscillation. Since the number of pre-breakdown of the ultra-high voltage GIS circuit breaker is limited, the number of I type high-frequency electromagnetic pulses is usually less than 10.

[0055] During the closing process of the ultra-high voltage GIS circuit breaker, if the voltage-sharing capacitor 2 has a latent defect, a high-frequency electromagnetic signal will be excited under the excitation of strong impact vibration of the operating mechanism. If the right side voltage-sharing capacitor 2 has a defect, the standard electromagnetic pulse excited is as shown in Figure 4 , which is named as the II type high-frequency electromagnetic pulse in the present application.

[0056] As can be seen, the pulse time-frequency characteristics of Type II high-frequency electromagnetic pulses include: the peak-to-peak value of the electromagnetic signal measured by sensor #1 is 700mV~900mV, specifically 800mV; the high-frequency component lasts 500ns~600ns, specifically 550ns; and there is no low-frequency oscillation at the tail. The peak-to-peak value of the electromagnetic signal measured by sensor #2 is also 700mV~900mV, specifically 800mV; the high-frequency component lasts 500ns~600ns, specifically 550ns; and there is no low-frequency oscillation at the tail. The signals received by sensors #1 and #2 are similar; their wavefronts are unfolded as follows... Figure 5 As shown in the figure, the time difference ΔT between sensor #2 and sensor #1 is approximately 14 ns. Using formula (1):

[0057] (1)

[0058] Where L is the distance between sensor #1 and sensor #2, which is 17.2 meters, ΔT is the time difference between sensor #2 and sensor #1, which is about 14 ns, and C is the speed of electromagnetic propagation, which is 0.3 m / ns. It can be deduced that the distance between the signal source and sensor #2 is 6.5 meters, and it can be basically determined that the signal comes from the equalizing capacitor 2 on the right.

[0059] During the closing process of an ultra-high voltage GIS circuit breaker, if the equalizing capacitor 2 on the left side has a defect, the standard electromagnetic pulse generated will be as follows: Figure 6 As shown, this application refers to it as Class III high-frequency electromagnetic pulse.

[0060] As can be seen, the pulse time-frequency characteristics of Class III high-frequency electromagnetic pulses include: the signals received by sensors #1 and #2 are similar, with the measured peak-to-peak value of the electromagnetic signal being 700mV~900mV, specifically 800mV; the high-frequency component lasting 500ns~600ns, specifically 550ns; and no low-frequency oscillation at the wave tail. Its wavefront unfolds as follows... Figure 7 As shown in the figure, the time difference ΔT between sensor #1 and sensor #2 is approximately 14 ns. Using formula (1), where L is the distance between sensor #1 and sensor #2, which is 17.2 meters, ΔT is the time difference between sensor #1 and sensor #2, which is approximately 14 ns, and C is the speed of electromagnetic propagation, which is 0.3 m / ns, the distance between the signal source and sensor #1 can be calculated to be 6.5 meters. It can be basically determined that the signal comes from the equalizing capacitor 2 on the left.

[0061] S4: Compare the original high-frequency electromagnetic pulses detected in S2 with Class II and Class III high-frequency electromagnetic pulses to determine whether the insulation state of the equalizing capacitor 2 is abnormal.

[0062] In the closing process of the UHV GIS circuit breaker, if the II and III high-frequency electromagnetic pulses appear, it indicates that the insulation state of the grading capacitor 2 may be abnormal, and there may be a latent defect. Since the grading capacitor 2 will not bear voltage after the UHV GIS circuit breaker is closed, even if the grading capacitor 2 has a defect, it will not excite II and III high-frequency electromagnetic pulses again after being closed. Therefore, it is necessary to monitor again through high-frequency electromagnetic original pulses in the opening process of the UHV GIS circuit breaker.

[0063] In the opening process of the UHV GIS circuit breaker, if the grading capacitor 2 has a defect, under the excitation of the mechanism impact vibration, the UHV GIS circuit breaker will excite electromagnetic pulses, similar to the closing process. The defect of the grading capacitor 2 on the right corresponds to the II high-frequency electromagnetic pulse, and the defect of the grading capacitor 2 on the left corresponds to the III high-frequency electromagnetic pulse.

[0064] Therefore, first, the number N and the duration T of the II and III high-frequency electromagnetic pulses in the high-frequency electromagnetic original pulses monitored in S2 are counted; then, based on the number N and the duration T, it is determined whether the insulation state of the grading capacitor 2 is abnormal.

[0065] The application proposes that when N<50 and T<2 seconds, the insulation state of the grading capacitor 2 is normal; when N≥50 or T≥2 seconds, the insulation state of the grading capacitor 2 is attention, which can be monitored in operation; when N≥1000 and T≥5 seconds, the insulation state of the grading capacitor 2 is abnormal, and power-off maintenance is required.

[0066] In this way, by comprehensively considering the number and duration of the II and III high-frequency electromagnetic pulses excited in the opening and closing processes of the UHV GIS circuit breaker, a method for evaluating the dynamic insulation state of the grading capacitor is proposed.

[0067] Based on the same concept, the embodiment also proposes a UHV GIS circuit breaker grading capacitor insulation state evaluation system (hereinafter referred to as: system), which comprises:

[0068] Two built-in ultra-high frequency sensors 1 are installed on both sides of the UHV GIS circuit breaker for monitoring the high-frequency electromagnetic original pulses in the UHV GIS circuit breaker;

[0069] The ultra-high frequency amplification processing unit is connected with the two built-in ultra-high frequency sensors 1, and is used for pre-processing the high-frequency electromagnetic pulse signals received by the built-in ultra-high frequency sensors 1;

[0070] The processor is connected with the ultra-high frequency amplification processing unit, and is used for comparing the monitored high-frequency electromagnetic original pulse with the II and III high-frequency electromagnetic pulses to determine whether the insulation state of the grading capacitor 2 is abnormal; wherein, the standard electromagnetic pulse excited by the right grading capacitor 2 existing defects is named as the II high-frequency electromagnetic pulse; and the standard electromagnetic pulse excited by the left grading capacitor 2 existing defects is named as the III high-frequency electromagnetic pulse.

[0071] The ultra-high voltage GIS circuit breaker grading capacitor insulation state evaluation method and system provided by the embodiment has the following beneficial effects:

[0072] The pulse time-frequency characteristics of the high-frequency electromagnetic pulse excited by the grading capacitor 2 in the defect state are used to accurately identify whether the grading capacitor 2 exists defects, and the misjudgment caused by the high-frequency electromagnetic pulse of the pre-breakdown between the fracture is avoided, and the accuracy of identifying the defects of the grading capacitor 2 is improved.

[0073] It should be noted that the features in the embodiments of the present application can be combined with each other without conflict.

[0074] The above is only a preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating the insulation state of a grading capacitor of an ultra-high voltage GIS circuit breaker, characterized in that, The method comprises the following steps: S1: One built-in UHF sensor (1) is arranged on each side of the UHV GIS circuit breaker; S2: In the closing process of the UHV GIS circuit breaker, the built-in UHF sensors (1) on both sides are used to monitor the high-frequency electromagnetic original pulse inside the UHV GIS circuit breaker; S3: The built-in UHF sensors (1) on both sides are used to determine the standard electromagnetic pulse excited by the defect of the right side grading capacitor (2), which is named as the II type high-frequency electromagnetic pulse; and the standard electromagnetic pulse excited by the defect of the left side grading capacitor (2), which is named as the III type high-frequency electromagnetic pulse; S4: The high-frequency electromagnetic original pulse monitored in S2 is compared with the II type and III type high-frequency electromagnetic pulses to determine whether the insulation state of the grading capacitor (2) is abnormal; Wherein, the number N and the duration T of the II type and III type high-frequency electromagnetic pulses in the high-frequency electromagnetic original pulse monitored in S2 are counted, and based on the number N and the duration T, it is determined whether the insulation state of the grading capacitor (2) is abnormal; when N < 50 and T < 2 seconds, the insulation state of the grading capacitor (2) is normal; when N ≥ 50 or T ≥ 2 seconds, the insulation state of the grading capacitor (2) is attention, which can be monitored in operation; when N ≥ 1000 and T ≥ 5 seconds, the insulation state of the grading capacitor (2) is abnormal, which needs to be repaired after power off.

2. The method according to claim 1, characterized in that, S1 comprises: The left side grading capacitor (2) is a distance a from the left side built-in UHF sensor (1), and the right side grading capacitor (2) is also a distance a from the right side built-in UHF sensor (1).

3. The method according to claim 1, wherein S2 It comprises: The high-frequency electromagnetic pulse signal received by the built-in UHF sensor (1) is preprocessed, and the high-frequency component in the range of 300MHz-1500MHz in the high-frequency electromagnetic pulse signal is filtered and amplified.

4. The method according to claim 1, wherein S3 It comprises: The pulse time-frequency characteristics of the II type and III type high-frequency electromagnetic pulses are determined respectively, and the pulse time-frequency characteristics are used as the standard for identifying the II type or III type high-frequency electromagnetic pulse.

5. The method according to claim 4, characterized in that, The pulse time-frequency characteristics of the II type high-frequency electromagnetic pulse include: the peak-to-peak value of the electromagnetic signal is 700mV-900mV, the high-frequency component lasts for 500ns-600ns, and the wave head of the signal collected by the right side built-in UHF sensor (1) leads the left side built-in UHF sensor (1) by a time difference △T.

6. The method according to claim 5, characterized in that, △T satisfies the following relationship: (1) Wherein, L is the distance between the two built-in UHF sensors (1), C is the propagation speed of electromagnetic, and a is the distance between the signal source and the right side built-in UHF sensor (1).

7. The method according to claim 4, characterized in that, The pulse time-frequency characteristics of the III type high-frequency electromagnetic pulse include: the peak-to-peak value of the electromagnetic signal is 700mV-900mV, the high-frequency component lasts for 500ns-600ns, and the wave head of the signal collected by the left side built-in UHF sensor (1) leads the right side built-in UHF sensor (1) by a time difference △T.

8. An insulation condition evaluation system for a grading capacitor of an ultra-high voltage GIS circuit breaker, characterized in that, The system comprises: Two built-in UHF sensors (1) are installed on both sides of the UHV GIS circuit breaker, which are used to monitor the high-frequency electromagnetic original pulse inside the UHV GIS circuit breaker; The ultra-high frequency amplification processing unit is used for pre-processing the high-frequency electromagnetic pulse signal received by the built-in ultra-high frequency sensor (1); The processor is used for comparing the monitored high-frequency electromagnetic original pulse with the II and III high-frequency electromagnetic pulses to determine whether the insulation state of the grading capacitor (2) is abnormal; wherein the standard electromagnetic pulse excited by the defect of the right grading capacitor (2) is named as the II high-frequency electromagnetic pulse; the standard electromagnetic pulse excited by the defect of the left grading capacitor (2) is named as the III high-frequency electromagnetic pulse; the number N and the duration T of the II and III high-frequency electromagnetic pulses are counted, and based on the number N and the duration T, it is determined whether the insulation state of the grading capacitor (2) is abnormal; when N < 50 and T < 2 seconds, the insulation state of the grading capacitor (2) is normal; when N ≥ 50 or T ≥ 2 seconds, the insulation state of the grading capacitor (2) is attention, and the operation can be monitored; when N ≥ 1000 and T ≥ 5 seconds, the insulation state of the grading capacitor (2) is abnormal, and power-off maintenance is required.

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