A Method and System for Assessing Contact Erosion Status Based on Dynamic Capacitance of Circuit Breaker Breaks

Abstract

This invention provides a method and system for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts, belonging to the field of power distribution switchgear testing technology. It includes: performing multiple opening and closing operations on the circuit breaker and using a dynamic capacitance measurement system to measure data during the opening and closing process. The data obtained in a single measurement includes contact voltage signal, circuit current signal, and travel signal. Based on the contact voltage signal and circuit current signal, the dynamic capacitance is calculated, and a curve is fitted between the dynamic capacitance and the travel signal. The capacitance drop value and the travel at the break point are calculated for each curve. A threshold for the rate of change of travel at the break point is set, and the range and degree of erosion are defined. Based on the correspondence between the capacitance drop value and the travel at the break point, the range of the rate of change of the capacitance drop value and the degree of erosion are calculated. When assessing the contact erosion status of the circuit breaker under test, the current dynamic capacitance and capacitance drop value are calculated to determine the current contact erosion status of the circuit breaker under test.

Description

Technical Field

[0001] This invention relates to the field of power distribution switchgear testing technology, and in particular to a method and system for evaluating the contact erosion state based on the dynamic capacitance of circuit breaker contacts. Background Technology

[0002] In circuit breakers, the contacts are the most easily worn components, directly affecting the circuit breaker's breaking capacity. During circuit breaker operation, the contacts can be eroded by electric arc. Severe erosion may cause pre-breakdown, re-breakdown, or even circuit breaker failure, leading to power accidents. Therefore, after being put into use, it is necessary to accurately assess the erosion status of the contacts and promptly investigate potential contact faults.

[0003] In existing technologies, marking contact erosion on the moving conductive rod of the vacuum interrupter is a common method. However, after the vacuum interrupter is assembled into the circuit breaker, it is generally located within the moving support of the main circuit of the circuit breaker. Especially after the adoption of solid sealing technology, it is difficult to observe the contact erosion marks of the vacuum interrupter. Existing vacuum circuit breakers with online monitoring devices, such as permanent magnet vacuum circuit breakers with online monitoring of contact erosion in the vacuum interrupter, use the monitoring point located on the insulating tie rod between the vacuum interrupter and the permanent magnet mechanism to indirectly detect the contact erosion. Since the contact erosion monitoring point is at the high-voltage end, it is easily affected by electromagnetic field interference from the high-voltage tester during live testing, resulting in insufficient testing accuracy and low safety. Summary of the Invention

[0004] In view of this, the present invention provides a method and system for evaluating the contact erosion state based on the dynamic capacitance of the circuit breaker break, which can quickly and accurately evaluate the erosion state of the contacts in the circuit breaker.

[0005] The technical solution adopted by the embodiments of the present invention to solve its technical problem is as follows:

[0006] A method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts includes:

[0007] Step S1: Perform multiple opening and closing operations on the circuit breaker, and use the dynamic capacitance measurement system to measure the data of the circuit breaker during the opening and closing process. The data obtained in a single measurement includes the circuit breaker's contact voltage signal, the circuit current signal of the measurement circuit, and the travel signal of the operating mechanism position in the feedback circuit breaker.

[0008] Step S2: Calculate the dynamic capacitance based on the break voltage signal and the circuit current signal, and further fit the curve of dynamic capacitance and stroke signal to obtain the dynamic capacitance-stroke curve corresponding to each opening and closing action.

[0009] Step S3: Calculate the capacitance drop value and the travel distance at the break point for each curve;

[0010] Step S4: Set the threshold for the rate of change of the stroke at the split point and define the threshold range and the degree of ablation corresponding to the range. Further, based on the threshold range for the stroke at the split point and the correspondence between the capacitor drop value and the stroke at the split point calculated in step S3, deduce the threshold range for the rate of change of the capacitor drop value and the degree of ablation corresponding to the range.

[0011] Step S5: When assessing the contact erosion status of the circuit breaker under test, measure the port voltage signal and loop current signal of the circuit breaker, and further calculate the current dynamic capacitance and capacitance drop value. Based on the capacitance drop value threshold range and the degree of erosion corresponding to the range, determine the current contact erosion status of the circuit breaker under test.

[0012] The dynamic capacitance measurement system includes an industrial control computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotational speed sensor, and a current transformer. The current transformer acquires the opening and closing coil control circuit of the circuit breaker and is used to acquire the opening and closing coil signals. The rotational speed sensor is coaxially connected to the shaft of the output crank arm of the circuit breaker. The measurement circuit consists of a high-frequency regulated power supply, a sampling resistor, and the circuit breaker connected in series. The voltage transformer samples the circuit voltage, and the sampling resistor provides the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotational speed sensor, and the industrial control computer. The industrial control computer is used to implement steps S2-S5.

[0013] Specifically, step S1 involves: starting the high-frequency regulated power supply to provide voltage to the circuit; the high-speed synchronous acquisition module receiving the circuit breaker's opening and closing coil signal as a trigger signal for data acquisition; continuously acquiring the break voltage signal, the circuit current signal, and the stroke signal of the rotation speed sensor; and outputting them to the industrial control computer.

[0014] Preferably, step S2, which involves curve fitting of dynamic capacitance and stroke for a single opening and closing operation, includes:

[0015] Step S21: Perform Discrete Short-Time Fourier Transform (STFT) on the break voltage signal and the loop current signal respectively. Define the non-stationary signal s(t) to represent the break voltage signal or the loop current signal. The STFT is defined as follows:

[0016]

[0017] In the formula, t is time, ω is the fundamental frequency, h(t) is the window function, and i is an imaginary number;

[0018] By using a window function to truncate the signal into different time periods n, the frequency f, fundamental voltage amplitude U(n), and fundamental current amplitude I(n) of the fundamental component of the signal in each time period are obtained by discrete short-time Fourier transform.

[0019] Step S22, calculate the dynamic capacitance C(n) of the circuit breaker under test:

[0020]

[0021] Step S23: Plot the travel versus time curve based on the travel signal, and further fit the dynamic capacitance-travel curve by time alignment. (Take the average value of this segment for n).

[0022] Preferably, in the dynamic capacitance-stroke curve:

[0023] The stroke at the dividing point is: the stroke value corresponding to the starting point of the dynamic capacitor-stroke curve;

[0024] The dividing point capacitance is: the capacitance value corresponding to the starting point of the dynamic capacitance-stroke curve;

[0025] The capacitance at the full opening point is the capacitance value when the contact moves to the fully open state, that is, the capacitance value at the end of the dynamic capacitance-stroke curve.

[0026] The capacitance drop value is the decrease in capacitance between contacts during the opening and closing process, which is equal to the capacitance at the point of initial opening minus the capacitance at the point of complete opening.

[0027] Preferably, step S4 includes:

[0028] Using the initial break point travel and initial capacitance drop value in the unablated state as comparison benchmarks: 0% is used as the first threshold for dividing the break point travel change rate threshold intervals, the break point travel change rate obtained after performing the full-capacity breaking number of circuit breakers is used as the fourth threshold, the average of two equal divisions between the first threshold and the fourth threshold is used as the second threshold and the third threshold, and 100% is used as the fifth threshold. Based on the five thresholds, five break point travel threshold intervals are divided.

[0029] Based on the circuit breaker breaking test results, the fourth threshold is determined to be 20%. Correspondingly, the range of the change rate of the rigid break point stroke relative to the initial rigid break point stroke in the unablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), and [20%, 100%].

[0030] Set the degree of erosion corresponding to the interval, and let the rate of change of the initial rigid point travel relative to the un-eroded state be located in the interval [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%], which respectively represent the degree of erosion of the circuit breaker as slight erosion, general erosion, severe erosion and very severe erosion.

[0031] Based on the dynamic capacitance-stroke curves, the rate of change of the capacitance drop value relative to the initial capacitance value in the un-burned state is located in the ranges [5%, 30%), [30%, 45%), [45%, 60%), and [60%, 100%], which respectively represent the degree of burn-off of the circuit breaker as slight burn-off, moderate burn-off, severe burn-off, and very severe burn-off.

[0032] Preferably, the break voltage signal is measured by a voltage transformer with a transformation ratio of 6:1.

[0033] Preferably, the loop current signal is sampled through a 200Ω non-inductive resistor.

[0034] Preferably, the stroke signal is measured using a rotary resistive speed sensor with a proportionality coefficient of 300mV / (° / s) and a range of ±120° / s.

[0035] Preferably, the rotational speed sensor is mounted on the shaft of the output crank arm of the circuit breaker operating mechanism by screws, and is also fixed to the wall of the operating mechanism housing by a universal bracket.

[0036] Preferably, the opening and closing coil current is measured by an ETCR007AD type clamp-type Hall current sensor with a proportional coefficient of 100mV / 1A and a range of 0mA to 50A. The clamp jaws are clamped in the circuit breaker opening and closing coil control circuit in the correct direction.

[0037] This invention provides a dynamic capacitance measurement system, comprising: an industrial control computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotational speed sensor, and a current transformer. The current transformer acquires signals from the opening and closing coil control circuit of a circuit breaker. The rotational speed sensor is coaxially connected to the shaft of the output crank arm of the circuit breaker. The measurement circuit consists of a high-frequency regulated power supply, a sampling resistor, and the circuit breaker connected in series. The voltage transformer samples the circuit voltage, and the sampling resistor provides the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotational speed sensor, and the industrial control computer. The dynamic capacitance measurement system is used to implement the aforementioned method.

[0038] As can be seen from the above technical solution, the contact erosion state assessment method based on the dynamic capacitance of a circuit breaker break provided in this embodiment of the invention is implemented based on a dynamic capacitance measurement system. First, the circuit breaker undergoes multiple opening and closing operations, and the dynamic capacitance measurement system measures the data during the opening and closing process. The data obtained from a single measurement includes the circuit breaker's break voltage signal, the measurement circuit's loop current signal, and the travel signal indicating the position of the operating mechanism in the feedback circuit breaker. Based on the break voltage signal and the loop current signal, the dynamic capacitance is calculated, and a curve between the dynamic capacitance and the travel signal is further fitted to obtain the dynamic capacitance corresponding to each opening and closing action. The method involves calculating the capacitance drop and the travel at the break point for each curve, setting a threshold for the rate of change of travel at the break point, defining threshold intervals and the corresponding ablation degree, and further, based on the threshold interval for the travel at the break point and the correspondence between the capacitance drop and the travel at the break point, deducing the threshold interval for the rate of change of capacitance drop and the corresponding ablation degree. When assessing the contact ablation state of the circuit breaker under test, the method measures the port voltage signal and loop current signal of the circuit breaker, and further calculates the current dynamic capacitance and capacitance drop. Based on the threshold interval for the capacitance drop and the corresponding ablation degree, the current contact ablation state of the circuit breaker under test is determined. By implementing the method of this invention, the ablation state of the contacts in a circuit breaker can be quickly and accurately assessed, maintaining power grid safety. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a contact erosion condition assessment system based on the dynamic capacitance of circuit breaker contacts.

[0040] Figure 2 This is a dynamic capacitance-time curve.

[0041] Figure 3 This is a dynamic capacitance-stroke curve.

[0042] Figure 4 A comparison chart of dynamic capacitance-stroke curves for different degrees of ablation.

[0043] Figure 5 This is a schematic diagram of the characteristic parameters.

[0044] Figure 6 Typical dynamic capacitance curves are shown for different ablation cycles.

[0045] Figure 7 This is a three-phase schematic diagram showing the change in the travel distance at the split point with the number of ablation cycles.

[0046] Figure 8 This is a schematic diagram showing how the capacitance at the break point changes with the number of ablation cycles.

[0047] Figure 9This is a schematic diagram showing how the capacitance at the fully open circuit breaker point changes with the number of ablation cycles.

[0048] Figure 10 This diagram illustrates how the capacitor drop value changes with the number of ablation cycles. Detailed Implementation

[0049] The technical solution and effects of the present invention will be further described in detail below with reference to the accompanying drawings.

[0050] A Method and System for Assessing Contact Erosion Status Based on Dynamic Capacitance of Circuit Breaker Breaks

[0051] This invention provides a method for assessing the contact erosion state based on the dynamic capacitance of circuit breaker contacts. Figure 1 The dynamic capacitance measurement system shown includes an industrial computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotational speed sensor, and a current transformer. The current transformer acquires the opening and closing coil control circuit of the circuit breaker and is used to acquire the opening and closing coil signals. The rotational speed sensor is coaxially connected to the shaft of the output crank arm of the circuit breaker. The measurement circuit consists of a high-frequency regulated power supply, a sampling resistor, and the circuit breaker connected in series. The voltage transformer samples the circuit voltage, and the sampling resistor provides the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotational speed sensor, and the industrial computer. The industrial computer is used to implement steps S2-S5 below.

[0052] The voltage signal at the circuit breaker break is measured using a voltage transformer with a 6:1 ratio; the circuit current signal is sampled using a 200Ω non-inductive resistor, which also limits the circuit current when the circuit breaker is closed, preventing short circuits; the travel signal is measured using a rotary resistive speed sensor with a proportionality coefficient of 300mV / (° / s) and a range of ±120° / s. The rotary speed sensor is screwed onto the shaft of the output crank arm of the circuit breaker operating mechanism and fixed to the operating mechanism housing wall using a universal bracket to prevent sensor movement during circuit breaker operation. During installation, ensure the shaft of the rotary speed sensor is concentric with the circuit breaker shaft; the opening and closing coil current is measured using an ETCR007AD type clamp-type Hall current sensor with a proportionality coefficient of 100mV / 1A and a range of 0mA~50A. The clamps are correctly positioned within the circuit breaker opening and closing coil control circuit.

[0053] The method steps for implementing the present invention include:

[0054] Step S1 involves performing multiple opening and closing operations on the circuit breaker and using a dynamic capacitance measurement system to measure data during the opening and closing process. Specifically, this involves starting a high-frequency regulated power supply to provide voltage to the circuit, using the high-speed synchronous acquisition module to receive the circuit breaker's opening and closing coil signals as trigger signals for data acquisition, continuously acquiring the break voltage signal, circuit current signal, and travel signal from the rotation speed sensor, and outputting the data to the industrial control computer. The data obtained in a single measurement includes the circuit breaker's break voltage signal, the circuit current signal of the measurement circuit, and the travel signal indicating the position of the operating mechanism in the circuit breaker.

[0055] Step S2: Calculate the dynamic capacitance based on the break voltage signal and the loop current signal, and further fit the curve of dynamic capacitance versus stroke signal to obtain the dynamic capacitance-stroke curve corresponding to each opening and closing action; in the dynamic capacitance-stroke curve:

[0056] The stroke at the dividing point is: the stroke value corresponding to the starting point of the stroke curve of the dynamic capacitor;

[0057] The breaking point capacitance is: dynamic capacitance—the capacitance value corresponding to the starting point of the stroke curve;

[0058] The capacitance at the full opening point is the capacitance value when the contact moves to the fully open state, that is, the capacitance value at the end of the dynamic capacitance-stroke curve.

[0059] The capacitance drop value is the decrease in capacitance between contacts during the opening and closing process, which is equal to the capacitance at the point of initial opening minus the capacitance at the point of complete opening.

[0060] Step S3: Calculate the capacitance drop value and the travel distance at the break point for each curve;

[0061] Step S4: Set the threshold for the rate of change of the stroke at the split point and define the threshold range and the degree of ablation corresponding to the range. Further, based on the threshold range for the stroke at the split point and the correspondence between the capacitor drop value and the stroke at the split point calculated in step S3, deduce the threshold range for the rate of change of the capacitor drop value and the degree of ablation corresponding to the range.

[0062] Step S5: When assessing the contact erosion status of the circuit breaker under test, measure the port voltage signal and loop current signal of the circuit breaker, and further calculate the current dynamic capacitance and capacitance drop value. Based on the threshold range of capacitance drop value and the degree of erosion corresponding to the range, determine the current contact erosion status of the circuit breaker under test.

[0063] Step S2, the process of curve fitting between dynamic capacitance and stroke for a single opening and closing operation, includes:

[0064] Step S21: Perform Discrete Short-Time Fourier Transform (STFT) on the break voltage signal and the loop current signal respectively. Define the non-stationary signal s(t) to represent the break voltage signal or the loop current signal. The STFT is defined as follows:

[0065]

[0066] In the formula, t is time, ω is the fundamental frequency, h(t) is the window function, and i is an imaginary number;

[0067] By using a window function to truncate the signal into different time periods n, the frequency f, fundamental voltage amplitude U(n), and fundamental current amplitude I(n) of the fundamental component of the signal in each time period are obtained by discrete short-time Fourier transform.

[0068] Step S22, calculate the dynamic capacitance C(n) of the circuit breaker under test:

[0069]

[0070] Step S23: Plot the travel versus time curve based on the travel signal (refer to...) Figure 2 Example), through time alignment, further fit the dynamic capacitance-stroke curve (reference). Figure 3 Example). During time alignment, the average value of n time intervals is taken.

[0071] The specific implementation of step S4 is as follows:

[0072] Using the initial break point travel and initial capacitance drop value in the un-burned state as comparison benchmarks: 0% is used as the first threshold for dividing the break point travel change rate threshold interval (representing the break point travel change rate threshold of the circuit breaker in the un-burned state), the break point travel change rate obtained after performing the full-capacity breaking number of circuit breakers is used as the fourth threshold (the full-capacity breaking number of circuit breakers is the rated short-circuit current breaking number specified by the manufacturer), the average of two equal divisions between the first and fourth thresholds is used as the second and third thresholds, and 100% is used as the fifth threshold. Based on the five thresholds, five break point travel change rate threshold intervals are divided.

[0073] Based on the circuit breaker breaking test results, the fourth threshold is 20%. Correspondingly, the range of the change rate of the stiff break point stroke relative to the initial stiff break point stroke in the unablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), and [20%, 100%].

[0074] Set the degree of erosion corresponding to the interval, and let the rate of change of the initial rigid point travel relative to the un-eroded state be located in the interval [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%], which respectively represent the degree of erosion of the circuit breaker as slight erosion, general erosion, severe erosion and very severe erosion.

[0075] Based on the dynamic capacitance-stroke curves, the rate of change of the capacitance drop value relative to the initial capacitance value in the un-burned state is located in the ranges [5%, 30%), [30%, 45%), [45%, 60%), and [60%, 100%], which respectively represent the degree of burn-off of the circuit breaker as slight burn-off, moderate burn-off, severe burn-off, and very severe burn-off.

[0076] Alternatively, the initial capacitance drop value in the un-ablated state can be used as a comparison benchmark: 0% is used as the first threshold for dividing the rate of change interval (representing the dynamic capacitance drop rate of change threshold of the circuit breaker in the un-ablated state), the dynamic capacitance drop rate obtained when the rated short-circuit current interruption number of the circuit breaker is executed is used as the fourth threshold, the average of two equal divisions between the first and fourth thresholds is used as the second and third thresholds, and 100% is used as the fifth threshold. Based on the five thresholds, five dynamic capacitance drop rate of change threshold intervals are divided, and the degree of ablation corresponding to each interval is further defined.

[0077] The following is a specific reference embodiment, please refer to it. Figures 2-10 :

[0078] Perform steps S1-S5 to calculate the typical circuit breaker tripping dynamic capacitance time curve under non-ablation conditions, as shown below. Figure 2 As shown, taking the moment of contact separation as time 0, the initial capacitance value of the dynamic capacitance curve is 33.07 pF. The capacitance value gradually decreases over time, and the rate of decrease also slows down, reaching 12.01 pF at 30 ms. After 30 ms, the capacitance value stops decreasing and exhibits fluctuations within a small range. Combined with the travel curve during the opening process, it can be seen that the contact travel has reached its maximum value of 150 mm at 30 ms, meaning the circuit breaker has completed the opening process, the contact opening distance has reached its maximum and it no longer moves, so the capacitance value stops decreasing. Based on the analysis in Section 3.1.2.1, the reason for the fluctuations in the capacitance curve is the non-integer cycle sampling of the signal.

[0079] Because the oscilloscope trigger time and the circuit breaker operating mechanism action time vary during each measurement, to facilitate subsequent comparative analysis, the horizontal axis of the dynamic capacitance-time curve is replaced with a dynamic capacitance-stroke curve, thus obtaining the curve of capacitance change with contact stroke during the opening process, as shown below. Figure 3As shown in the figure, the starting point of the dynamic capacitance-stroke curve corresponds to a stroke value of 37.97 mm, i.e., the stroke value at the point where the contact just separates. The maximum stroke is 150 mm. Therefore, the arc contact opening distance of the circuit breaker is calculated to be 150 - 37.97 = 112.03 mm. The product inspection report provided by the circuit breaker manufacturer shows an arc contact opening distance of 112 mm, which matches the calculated result.

[0080] Feature parameter extraction:

[0081] Based on the dynamic capacitance measurement results of the 0th erosion (no erosion), 16th erosion (moderate erosion), and 32nd erosion (severe erosion) of the C-phase erosion test of the circuit breaker, the comparison results of the dynamic capacitance-stroke curves under different erosion degrees are as follows: Figure 4 As shown, the overall shape of the dynamic capacitance curves does not change significantly with the degree of contact erosion, all exhibiting a rapid decrease in capacitance near the point of contact separation, followed by a gradual slowdown in the rate of decrease. With increasing erosion, the starting point of the dynamic capacitance curve shifts to the upper left, meaning the capacitance value at the starting point increases while the travel value decreases. The curves differ considerably near the starting point, but within a travel range greater than 40mm, the three curves nearly overlap, with only a slight difference in capacitance value at the fully open point.

[0082] Based on the above characteristics, in order to quantitatively analyze the variation law of the dynamic capacitance curve with the degree of ablation, the following four characteristic parameters are extracted from the dynamic capacitance-stroke curve (please refer to them together). Figure 5 ):

[0083] (1) Stroke at the starting point: The stroke value corresponding to the starting point of the dynamic capacitance-stroke curve, in mm;

[0084] (2) Capacitance at the starting point: Dynamic capacitance—the capacitance value corresponding to the starting point of the travel curve, in pF;

[0085] (3) Fully open point capacitance: The capacitance value when the contact moves to the fully open state, that is, the capacitance value at the end of the dynamic capacitance-stroke curve, in pF;

[0086] (4) Capacitor drop value: The decrease in capacitance between contacts during the opening process, equal to the capacitance at the opening point minus the capacitance at the fully opened point, in pF.

[0087] Dynamic capacitance parameter variation pattern:

[0088] Taking the dynamic capacitance curve measured by the C phase as an example, typical dynamic capacitance curves under different ablation cycles are as follows: Figure 6As shown, the curve shape did not change with the increase of ablation cycles. The starting point of the curve shifted significantly to the upper left, indicating that ablation caused a decrease in the stroke at the break point and an increase in the capacitance at the break point. In the section with a stroke greater than 40 mm, the curve split into three clusters, each cluster almost overlapping in the part with a stroke greater than 40 mm. The dynamic capacitance curves of the 10th, 18th, and 34th ablation cycles form the first cluster; the dynamic capacitance curves of the 2nd, 6th, 14th, 26th, and 30th ablation cycles form the second cluster; and the dynamic capacitance curve of the 22nd ablation cycle forms a separate cluster. The first cluster has the highest capacitance at the complete break point, followed by the second cluster, and the third cluster has the lowest. The distribution of the curve clusters is not significantly related to the number of ablation cycles, possibly due to the dispersion during measurement.

[0089] The characteristic parameters of the dynamic capacitance curves measured in the three-phase erosion test of the test circuit breaker were calculated to analyze the variation law of dynamic capacitance characteristics with the deterioration of contact erosion. The characteristic parameters were calculated by taking the average of five results for each group of dynamic capacitance tests to reduce random errors.

[0090] Just started the itinerary:

[0091] Figure 7 The curves show the variation of the three-phase contact travel of the test circuit breaker with the number of ablation tests. The ablation current for phase A was 10kA from tests 0 to 70, and 25kA from tests 71 to 103. The contact travel before ablation was 38.43mm, showing no significant change during tests 0-20, indicating that the ablation current was relatively small and the deterioration of the contacts was not yet significant. From tests 20 to 56, the ablation effect gradually accumulated, and the contact travel began to decrease, reaching 35.21mm after test 56. From tests 56 to 70, the contact travel fluctuated between 35.2 and 36.4mm. After test 70, the rate of decrease in contact travel increased significantly, indicating that the ablation effect of the 25kA current was more pronounced at this point. After test 103, the contact travel decreased to 30.22mm.

[0092] Phase B was ablated 70 times with a 20kA current. The initial travel at the break point before ablation was 36.48mm, which decreased to 30.83mm after 70 ablation cycles. The travel at the break point showed a certain degree of recovery during the 24th to 44th ablation cycles, possibly due to measurement error.

[0093] Phase C was ablated 34 times with a current of 30kA. The distance from the point of separation before ablation was 37.54mm. After the second ablation, it dropped rapidly to 34.11mm, and then maintained a relatively stable downward trend, dropping to 29.42mm after the 34th ablation.

[0094] In summary, during the ablation test, the travel distance at the break point of the three-phase arc-extinguishing chamber decreased with the increase of the number of ablation cycles. The travel distance at the break point of phase A decreased by 8.21 mm, that of phase B decreased by 5.65 mm, and that of phase C decreased by 8.12 mm.

[0095] The capacitor at the dividing point:

[0096] The calculated change in the three-phase breakpoint capacitance with the number of ablation cycles is as follows: Figure 8 As shown, the capacitance at the split point of phase A before ablation is 22.18 pF. During the 0th to 70th ablation cycles, the capacitance at the split point shows a certain upward trend, but the value fluctuates significantly, reaching a minimum of 19.5 pF and a maximum of 29.9 pF. During the 70th to 103rd ablation cycles, the upward trend of the capacitance becomes more pronounced, and the rate of increase accelerates, reaching 31.77 pF after the 103rd ablation cycle.

[0097] The initial capacitance of phase B before ablation was 24.21 pF. After the fourth ablation, it decreased to 21.45 pF, and then gradually increased with the number of ablation cycles, reaching 35.09 pF after 70 ablation cycles.

[0098] The capacitance at the split point of phase C before ablation was 26.87 pF. After the fourth ablation, it dropped to 22.94 pF. Subsequently, it fluctuated and increased with the number of ablations, reaching 31.15 pF after 34 ablations.

[0099] It can be seen that all three phases show an overall increasing trend in capacitance at the split point with increasing ablation cycles. After the ablation test, phase B showed the largest increase, rising by 10.88 pF. Phase A followed with an increase of 9.59 pF. Phase C showed the smallest increase, rising by 4.28 pF.

[0100] Fully tripped capacitor:

[0101] The change in capacitance at the fully open point with the number of ablation cycles is as follows: Figure 9 As shown, both phases A and C exhibit fluctuations within a certain range without a clear trend. Specifically, the capacitance at the fully open point of phase A fluctuates between 6.89 and 15.64 pF, while that of phase C fluctuates between 8.88 and 15.57 pF. Phase B's capacitance ranges from 9.26 to 14.97 pF, and after 36 ablation cycles, the value is generally higher than before, showing a slight increasing trend in capacitance with the number of ablation cycles.

[0102] Capacitor drop value

[0103] The variation of the three-phase capacitor drop value with the number of ablation cycles is as follows: Figure 10As shown, the capacitance of phase A increased from an initial 12.18 pF to 14.00 pF during the first 70 ablation cycles, with the rate of increase accelerating from 70 to 103 ablation cycles, reaching 18.93 pF after 103 ablation cycles. The capacitance of phase B before ablation was 13.11 pF, decreasing to 11.87 pF after 4 ablation cycles, then showing a stable upward trend from 4 to 70 ablation cycles, reaching 20.61 pF after 70 ablation cycles. Phase C slightly decreased from an initial 11.30 pF to 11 pF after 2 ablation cycles, then showed a stable upward trend from 2 to 34 ablation cycles, reaching 17.66 pF after 34 ablation cycles.

[0104] Overall, the capacitance drop values ​​of the three phases all showed a significant increase with the number of ablation cycles. Specifically, phase A increased by 6.75 pF after ablation, phase B increased by 7.5 pF, and phase C increased by 6.36 pF. The increase rates of the three phases were very similar.

[0105] Analysis of the variation law of dynamic capacitance parameters

[0106] Based on the above parameter variation patterns, it can be seen that, apart from the fully open capacitor, the three parameters of the just-opening point stroke, the just-opening point capacitance, and the capacitance drop value all show a clear trend of increasing or decreasing with the number of ablation cycles, which means that these three parameters are related to the degree of contact deterioration.

[0107] According to the definition of the breaking point travel, this travel is the contact travel when the arc contact has just completed one cycle. The circuit breaker's breaking speed is 4.5 m / s. The distance the contact travels in one cycle of the 50 kHz high-frequency power supply in this paper is approximately 0.09 mm, which can be ignored. Therefore, the breaking point travel is considered equal to the arc contact overtravel. The decrease in the breaking point travel means a decrease in the arc contact overtravel, i.e., a shortening of the effective contact length of the arc contact, indicating significant material loss at the arc contact tip under the action of arc erosion. Material loss will cause changes in the shape of the arc contact, leading to an increase in the degree of electric field distortion in the arc-extinguishing chamber and a decrease in the breaking capacity of the arc-extinguishing chamber. When the overtravel decreases to a certain extent, it will also cause the current to fail to transfer smoothly from the main contact to the arc contact for arc ignition during breaking, resulting in breaking failure.

[0108] The capacitance at the initial opening point shows an increasing trend with the number of ablation cycles, while the capacitance at the fully open point does not show a significant change with the number of ablation cycles. This is because the changes in the contacts caused by ablation can significantly affect the capacitance value between the contacts when the distance between the moving and stationary contacts is small. However, at the fully open point, the opening distance between the contacts reaches its maximum of 121mm. At this point, the distance between the contacts becomes the main factor affecting the capacitance, and the change in the contact tip has a negligible effect on the capacitance value. Figure 4The dynamic capacitance curves with different degrees of ablation show significant differences near the break point. The fact that the curves tend to overlap as the travel increases and the contact distance widens further confirms this. The fluctuation of several pF in capacitance at the fully open point is likely not caused by ablation but by measurement errors. During dynamic capacitance measurement, stray capacitance between conductors is treated as a fixed value, and two measurements are performed to correct for it. However, the relative positions of the conductors inevitably change between the two measurements, leading to alterations in stray capacitance and thus fluctuations in the measurement results.

[0109] The capacitance drop value is the difference between the capacitance at the breaking point and the capacitance at the fully open point. Compared to the fluctuating upward trend of the capacitance at the breaking point, the capacitance drop value shows a more stable upward trend with smaller fluctuations. This is because the random error introduced during stray capacitance correction acts on both the breaking point and fully open point capacitance values ​​simultaneously. The difference between the two parameters eliminates the influence of this random error, resulting in a more stable change and a more significant upward trend in the capacitance drop value. Furthermore, compared to the breaking point capacitance, the range and magnitude of the capacitance drop values ​​before and after ablation are more consistent across the three phases. Based on the calculation results of the energy-saving life formula in 2.2.2, the ablation degree of the three-phase arc-extinguishing chamber contacts is roughly the same. Therefore, it can be considered that the capacitance drop value can more reliably reflect the degree of contact ablation and deterioration.

[0110] Furthermore, ΔL and ΔC are calculated and denoted as the change in travel and capacitance at the separation point of the more severely eroded contact in a double-break circuit breaker, respectively. By definition, a change in ΔL exceeding 2mm, 4mm, 6mm, and 8mm is considered slight erosion, moderate erosion, severe erosion, and very severe erosion, respectively. Similarly, a change in ΔC exceeding 2pF, 4pF, 6pF, and 8pF is considered slight erosion, moderate erosion, severe erosion, and very severe erosion, respectively.

[0111] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for assessing the contact erosion state based on the dynamic capacitance of a circuit breaker break, characterized in that, include: Step S1: Perform multiple opening and closing operations on the circuit breaker, and use the dynamic capacitance measurement system to measure the data of the circuit breaker during the opening and closing process. The data obtained in a single measurement includes the circuit breaker's contact voltage signal, the circuit current signal of the measurement circuit, and the travel signal of the operating mechanism position in the feedback circuit breaker. Step S2: Calculate the dynamic capacitance based on the break voltage signal and the circuit current signal, and further fit the curve of dynamic capacitance and stroke signal to obtain the dynamic capacitance-stroke curve corresponding to each opening and closing action. Step S3: Calculate the capacitance drop value and the travel distance at the break point for each curve; Step S4: Set the threshold for the rate of change of the stroke at the split point and define the threshold range and the degree of ablation corresponding to the range. Further, based on the threshold range for the stroke at the split point and the correspondence between the capacitor drop value and the stroke at the split point calculated in step S3, deduce the threshold range for the rate of change of the capacitor drop value and the degree of ablation corresponding to the range. Step S5: When assessing the contact erosion status of the circuit breaker under test, measure the port voltage signal and loop current signal of the circuit breaker, and further calculate the current dynamic capacitance and capacitance drop value. Based on the threshold range of the capacitance drop value change rate and the degree of erosion corresponding to the range, determine the current contact erosion status of the circuit breaker under test. The dynamic capacitance measurement system includes an industrial control computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotational speed sensor, and a current transformer. The current transformer is located on the circuit breaker's opening and closing coil control circuit and is used to acquire the opening and closing coil signals. The rotational speed sensor is coaxially connected to the shaft of the circuit breaker's output crank arm. The measurement circuit consists of a high-frequency regulated power supply, a sampling resistor, and the circuit breaker connected in series. The voltage transformer samples the circuit voltage, and the sampling resistor provides the sampling circuit current to the high-speed synchronous acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotational speed sensor, and the industrial control computer. The industrial control computer is used to implement steps S2-S5. Step S1 specifically involves: starting the high-frequency regulated power supply to provide voltage to the circuit; the high-speed synchronous acquisition module receiving the circuit breaker's opening and closing coil signals as trigger signals for data acquisition; continuously acquiring the break voltage signal, the circuit current signal, and the stroke signal of the rotational speed sensor; and outputting these signals to the industrial control computer. In the dynamic capacitance-stroke curve: The stroke at the dividing point is: the stroke value corresponding to the starting point of the dynamic capacitor-stroke curve; The dividing point capacitance is: the capacitance value corresponding to the starting point of the dynamic capacitance-stroke curve; The capacitance at the fully open point is the capacitance value when the contact moves to the fully open state, i.e., the capacitance value at the end of the dynamic capacitance-stroke curve. The capacitance drop value is the decrease in capacitance between contacts during the opening and closing process, which is equal to the capacitance at the point of initial opening minus the capacitance at the point of complete opening.

2. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, Step S2, the process of curve fitting of dynamic capacitance and stroke for a single opening and closing, includes: Step S21: Perform Discrete Short-Time Fourier Transform (STFT) on the break voltage signal and the loop current signal respectively. Define the non-stationary signal s(t) to represent the break voltage signal or the loop current signal. The STFT is defined as follows: In the formula, t is time, ω is the fundamental frequency, h(t) is the window function, and i is an imaginary number; By using a window function to truncate the signal into different time periods n, the frequency f, fundamental voltage amplitude U(n), and fundamental current amplitude I(n) of the fundamental component of the signal in each time period are obtained by discrete short-time Fourier transform. Step S22, calculate the dynamic capacitance C(n) of the circuit breaker under test: Step S23: Plot the curve of stroke versus time based on the stroke signal, and further fit the dynamic capacitance-stroke curve by time alignment.

3. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 2, characterized in that, Step S4 includes: Using the initial break point travel and initial capacitance drop value in the unablated state as comparison benchmarks: 0% is used as the first threshold for dividing the break point travel change rate threshold interval; the break point travel change rate obtained after performing the full-capacity breaking number of circuit breakers is used as the fourth threshold; the average of two equal divisions between the first threshold and the fourth threshold is used as the second and third thresholds; and 100% is used as the fifth threshold. Based on the five thresholds, five break point travel change rate threshold intervals are divided. Based on the circuit breaker breaking test results, the fourth threshold is determined to be 20%. Correspondingly, the range of the change rate of the rigid break point stroke relative to the initial rigid break point stroke in the unablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), and [20%, 100%]. The ablation degree corresponding to the set interval is set so that the rate of change of the initial rigid break point travel relative to the unablated state is located in the intervals [5%, 10%), [10%, 15%), [15%, 20%), and [20%, 100%], which respectively represent the ablation degree of the circuit breaker as slight ablation, moderate ablation, severe ablation, and very severe ablation; according to each dynamic capacitance-travel curve, the rate of change of the capacitance drop value relative to the initial capacitance value in the unablated state is located in the intervals [5%, 30%), [30%, 45%), [45%, 60%), and [60%, 100%], which respectively represent the ablation degree of the circuit breaker as slight ablation, moderate ablation, severe ablation, and very severe ablation.

4. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, The break voltage signal is measured through a voltage transformer with a transformation ratio of 6:

1.

5. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, The loop current signal is sampled through a 200Ω non-inductive resistor.

6. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, The travel signal is measured using a rotary resistive speed sensor with a proportional coefficient of 300mV / (° / s) and a range of ±120° / s.

7. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, The rotational speed sensor is mounted on the shaft of the output crank arm of the circuit breaker operating mechanism by screws, and is also fixed to the wall of the operating mechanism box by a universal bracket.

8. The method for assessing contact erosion status based on the dynamic capacitance of circuit breaker contacts as described in claim 1, characterized in that, The opening and closing coil signal is measured by an ETCR007AD type clamp-type Hall current sensor with a proportional coefficient of 100mV / 1A and a range of 0mA to 50A. The clamp is positioned correctly in the circuit breaker opening and closing coil control circuit.

9. A dynamic capacitance measurement system, characterized in that, include: The system comprises an industrial control computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotational speed sensor, and a current transformer. The current transformer is located on the opening and closing coil control circuit of the circuit breaker and is used to acquire the opening and closing coil signals. The rotational speed sensor is coaxially connected to the shaft of the output crank arm of the circuit breaker. The measurement circuit consists of a high-frequency regulated power supply, a sampling resistor, and the circuit breaker connected in series. The voltage transformer samples the circuit voltage, and the sampling resistor provides the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotational speed sensor, and the industrial control computer. The dynamic capacitance measurement system is used to implement the method described in any one of claims 1-8.

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