Contact ablation state evaluation method and system based on breaker fracture dynamic capacitance

Abstract

The invention provides a contact ablation state evaluation method and system based on breaker fracture dynamic capacitance, and belongs to the technical field of power distribution switch device detection. Comprising the steps that multiple switching-on and switching-off operations are carried out on the circuit breaker, a dynamic capacitance measurement system is used for carrying out data measurement on the circuit breaker in the switching-on and switching-off processes, and data obtained through single-time measurement comprise fracture voltage signals, loop current signals and stroke signals; calculating dynamic capacitance based on the fracture voltage signal and the loop current signal, and fitting a curve of the dynamic capacitance and the stroke signal; calculating a capacitance drop value and a rigid separation point stroke of each curve; setting a rigid separation point stroke change rate threshold value, defining an interval and an ablation degree, and calculating a capacitance drop value change rate interval and an ablation degree based on a corresponding relation between the capacitance drop value and the rigid separation point stroke; when the contact ablation state of the to-be-tested circuit breaker is evaluated, the current dynamic capacitance and the capacitance drop value are calculated, and the current contact ablation state of the to-be-tested circuit breaker is judged.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution switch device detection, and in particular to a contact ablation state evaluation method and system based on circuit breaker break dynamic capacitance. Background Art

[0002] In a circuit breaker, the contact is the most easily worn component and will directly affect the circuit breaker's breaking capacity. During the operation of the circuit breaker, the contact will be burned by the arc. If the burning is serious, it may cause the circuit breaker to break down or break down again, or even cause the circuit breaker to fail to operate, resulting in an electrical accident. Therefore, after the circuit breaker is put into use, it is necessary to accurately evaluate the burning of the contact and promptly troubleshoot the potential faults of the contact.

[0003] In the prior art, it is a common method to provide a contact burn mark on the moving conductive rod of the vacuum arc chamber. However, after the vacuum arc chamber is assembled on the circuit breaker, it is generally located in the moving bracket of the main circuit of the circuit breaker. Especially after the solid sealing technology is adopted, it is difficult to observe the contact burn mark of the vacuum arc chamber. In the existing vacuum circuit breakers with online monitoring devices, such as permanent magnet vacuum circuit breakers with online monitoring of contact burn in the vacuum arc chamber, the monitoring point is located on the insulating pull rod between the vacuum arc chamber and the permanent magnet mechanism, which is used to indirectly detect the contact burn. Since the contact burn monitoring point is at the live high-voltage end, it is easily interfered by the electromagnetic field of the high-voltage test during live detection, resulting in insufficient test accuracy and low safety. Summary of the invention

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

[0005] The technical solution adopted by the embodiment of the present invention to solve the technical problem is:

[0006] A contact ablation state assessment method based on circuit breaker break dynamic capacitance, comprising:

[0007] Step S1, 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 of the circuit breaker, wherein the data obtained from a single measurement includes a break voltage signal of the circuit breaker, a loop current signal of the measurement loop, and a travel signal of the position of the operating mechanism in the feedback circuit breaker;

[0008] Step S2, calculating the dynamic capacitance based on the break voltage signal and the loop current signal, and further fitting a curve of the dynamic capacitance and the stroke signal, so as to obtain a dynamic capacitance-stroke curve corresponding to each opening and closing action;

[0009] Step S3, calculating the capacitance drop value and the stroke of the split point of each curve;

[0010] Step S4, setting a threshold value of the stroke change rate of the split point and defining a threshold interval and a degree of ablation corresponding to the interval, and further calculating a threshold interval of the capacitance drop value change rate and a degree of ablation corresponding to the interval based on the threshold interval of the split point stroke and the corresponding relationship between the capacitance drop value and the stroke of the split point calculated in step S3;

[0011] Step S5, when evaluating the contact ablation state of the circuit breaker to be tested, measuring the port voltage signal and the loop current signal of the circuit breaker, and further calculating the current dynamic capacitance and the capacitance drop value, and determining the current contact ablation state of the circuit breaker to be tested based on the capacitance drop value threshold interval and the ablation degree corresponding to the interval;

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

[0013] The step S1 specifically includes: starting the high-frequency voltage-stabilized power supply to provide voltage to the circuit, the high-speed synchronous acquisition module receives the opening and closing coil signal of the circuit breaker as a trigger signal for executing data acquisition, continuously collects the break voltage signal, the circuit current signal, and the travel signal of the rotation speed sensor, and outputs them to the industrial computer.

[0014] Preferably, the step S2 performs a curve fitting process of dynamic capacitance and stroke for a single opening and closing of the switch, including:

[0015] Step S21, discrete short-time Fourier transform is performed on the break voltage signal and the loop current signal respectively, and a non-stationary signal s(t) is defined to represent the break voltage signal or the loop current signal. The short-time Fourier transform STFT is defined as:

[0016]

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

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

[0019] Step S22, calculating the dynamic capacitance C(n) of the circuit breaker to be tested:

[0020]

[0021] Step S23, draw a curve of travel and time according to the travel signal, and further fit the dynamic capacitance-travel curve by time alignment. (corresponding to n, take the average value of this section)

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

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

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

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

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

[0027] Preferably, step S4 includes:

[0028] The initial break point stroke and the initial capacitance drop value in the un-ablated state are used as comparison benchmarks: 0% is used as the first threshold for dividing the break point stroke change rate threshold interval, the break point stroke change rate obtained after executing the full capacity breaking times of the circuit breaker is used as the fourth threshold, two equally divided averages are taken between the first threshold and the fourth threshold as the second threshold and the third threshold, 100% is used as the fifth threshold, and five break point stroke threshold intervals are divided based on the five thresholds;

[0029] According to the circuit breaker breaking test results, the fourth threshold value is 20%. Accordingly, the interval of the change rate of the rigid breaking point stroke relative to the initial rigid breaking point stroke in the non-ablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%);

[0030] Set the ablation degree corresponding to the interval, so that the change rate of the just-break point stroke relative to the initial just-break point stroke in the non-ablated state is in the interval [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%), which respectively represent the ablation degree of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation;

[0031] According to each dynamic capacitance-stroke curve, it is found that the change rate of the capacitance drop value relative to the initial capacitance value in the non-ablated state is in the range of [5%, 30%), [30%, 45%), [45%, 60%), [60%, 100%), which respectively correspond to the degree of ablation of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation.

[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 travel signal is measured using a rotary resistive speed sensor, the sensor scale factor is 300mV / (° / s), and the measuring range is ±120° / s.

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

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

[0037] The present invention provides a dynamic capacitance measurement system, comprising: an industrial computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotation speed sensor, and a current transformer. The current transformer collects signals from a circuit breaker opening and closing coil control circuit and is used to collect opening and closing coil signals. The rotation speed sensor is coaxially connected to a rotating shaft of an output crank arm of the circuit breaker. The measurement circuit is composed of a high-frequency voltage-stabilized power supply, a sampling resistor, and a circuit breaker in series. The voltage transformer samples a circuit voltage. The sampling resistor is used to provide a sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotation speed sensor, and the industrial computer. The dynamic capacitance measurement system is used to implement the above method.

[0038] It can be seen from the above technical scheme that the contact ablation state assessment method based on the dynamic capacitance of the circuit breaker break provided by the embodiment of the present invention is implemented based on a dynamic capacitance measurement system. First, the circuit breaker is opened and closed for multiple times, and the dynamic capacitance measurement system is used to measure the data during the opening and closing process of the circuit breaker, wherein the data obtained by a single measurement includes the break voltage signal of the circuit breaker, the loop current signal of the measurement loop, and the stroke signal of the operating mechanism position in the feedback circuit breaker; the dynamic capacitance is calculated based on the break voltage signal and the loop current signal, and the curve of the dynamic capacitance and the stroke signal is further fitted, so as to obtain the dynamic capacitance corresponding to each opening and closing action. Capacitance-travel curve; calculate the capacitance drop value and the stroke of the just-break point of each curve; set the threshold value of the stroke change rate of the just-break point and define the threshold interval and the degree of ablation corresponding to the interval, and further based on the just-break point stroke threshold interval and the correspondence between the capacitance drop value and the just-break point stroke, deduce the capacitance drop value change rate threshold interval and the degree of ablation corresponding to the interval; when evaluating the contact ablation state of the circuit breaker to be tested, measure the port voltage signal and loop current signal of the circuit breaker, and further calculate the current dynamic capacitance and capacitance drop value, and determine the current contact ablation state of the circuit breaker to be tested based on the capacitance drop value threshold interval and the degree of ablation corresponding to the interval. By implementing the method of the present invention, the ablation state of the contacts in the circuit breaker can be quickly and accurately evaluated to maintain the safety of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the contact erosion status assessment system based on the dynamic capacitance of the circuit breaker break.

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

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

[0042] Figure 4 Comparison of dynamic capacitance-stroke curves at different ablation degrees.

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

[0044] Figure 6 This is a typical dynamic capacitance curve under different ablation times.

[0045] Figure 7 It is a three-phase schematic diagram of the change of the stroke of the rigid point with the number of ablation times.

[0046] Figure 8 This is a schematic diagram of the change of the capacitance of the rigid point with the number of ablation times.

[0047] Fig. 9Schematic diagram of the change of capacitance at the complete disconnection point with the number of ablation times.

[0048] Fig.10 The figure shows the change of capacitance drop value with the number of ablation times. DETAILED DESCRIPTION

[0049] The technical scheme and technical effects of the present invention are further elaborated in detail below in conjunction with the accompanying drawings of the present invention.

[0050] Contact erosion state assessment method and system based on circuit breaker break dynamic capacitance

[0051] The present invention provides a contact ablation state evaluation method based on the dynamic capacitance of a circuit breaker break. Figure 1 The dynamic capacitance measurement system shown is implemented, and the dynamic capacitance measurement system includes an industrial computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotation speed sensor, and a current transformer. The current transformer collects the opening and closing coil control circuit of the circuit breaker and is used to collect the opening and closing coil signal. The rotation speed sensor is coaxially connected to the rotating shaft of the output arm of the circuit breaker. The measurement circuit is composed of a high-frequency voltage-stabilized power supply, a sampling resistor, and a circuit breaker in series. The voltage transformer samples the circuit voltage, and the sampling resistor is used to provide the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotation speed sensor, and the industrial computer; the industrial computer is used to implement the following steps S2-S5;

[0052] The voltage signal of the breaker is measured by a voltage transformer with a transformation ratio of 6:1; the loop current signal is sampled by a 200Ω non-inductive resistor. The sampling resistor also plays the role of limiting the loop current when the circuit breaker is closed to avoid power short circuit; the travel signal is measured by a rotary resistor speed sensor, the sensor proportional coefficient is 300mV / (° / s), and the range is ±120° / s. The rotation speed sensor is installed on the shaft of the output crank arm of the circuit breaker operating mechanism by screws, and is fixed to the wall of the operating mechanism box by a universal bracket to avoid the sensor shaking when the circuit breaker is actuated. During installation, it should be noted that the axis of the rotation speed sensor is concentric with the circuit breaker shaft; the closing and opening coil current is measured by the ETCR007AD clamp-type Hall current sensor, the sensor proportional coefficient is 100mV / 1A, the range is 0mA~50A, and the jaws are clamped in the circuit breaker closing and opening coil control circuit in the correct direction.

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

[0054] Step S1, perform multiple opening and closing operations on the circuit breaker, and use the dynamic capacitance measurement system to measure the data during the opening and closing process of the circuit breaker, specifically: start the high-frequency voltage-stabilized power supply to provide voltage to the circuit, the high-speed synchronous acquisition module receives the opening and closing coil signal of the circuit breaker as a trigger signal for executing data acquisition, and continuously collects the break voltage signal, the loop current signal, and the travel signal of the rotation speed sensor and outputs them to the industrial computer. Among them, the data obtained from a single measurement includes the break voltage signal of the circuit breaker, the loop current signal of the measurement loop, and the travel signal of the operating mechanism position in the feedback circuit breaker;

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

[0056] The stroke of the split point is: the stroke value corresponding to the starting point of the dynamic capacitance-stroke curve;

[0057] The capacitance at the split point is: dynamic capacitance - the capacitance value corresponding to the starting point of the stroke curve;

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

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

[0060] Step S3, calculating the capacitance drop value and the stroke of the split point of each curve;

[0061] Step S4, setting a threshold value of the stroke change rate of the split point and defining a threshold interval and a corresponding ablation degree of the interval, and further calculating a threshold interval of the capacitance drop value change rate and a corresponding ablation degree of the interval based on the stroke threshold interval of the split point and the corresponding relationship between the capacitance drop value and the stroke of the split point calculated in step S3;

[0062] Step S5, when evaluating the contact ablation state of the circuit breaker to be tested, the port voltage signal and the loop current signal of the circuit breaker are measured, and the current dynamic capacitance and the capacitance drop value are further calculated, and the current contact ablation state of the circuit breaker to be tested is determined based on the capacitance drop value threshold interval and the ablation degree corresponding to the interval;

[0063] Step S2 is a process of performing a curve fitting of dynamic capacitance and stroke for a single opening and closing of the switch, including:

[0064] Step S21, discrete short-time Fourier transform is performed on the break voltage signal and the loop current signal respectively, and a non-stationary signal s(t) is defined to represent the break voltage signal or the loop current signal. The short-time Fourier transform STFT is defined as:

[0065]

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

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

[0068] Step S22, calculating the dynamic capacitance C(n) of the circuit breaker to be tested:

[0069]

[0070] Step S23, draw a curve of travel and time according to the travel signal (refer to Figure 2 Example), through time alignment, the dynamic capacitance-travel curve is further fitted (reference Figure 3 Example). During the time alignment process, the average value of n time periods is taken.

[0071] The specific implementation of step S4 is:

[0072] The initial just-trip point stroke and the initial capacitance drop value in the un-ablated state are used as comparison benchmarks: 0% is used as the first threshold value for dividing the just-trip point stroke change rate threshold interval (representing the just-trip point stroke change rate threshold value of the circuit breaker in the un-ablated state), the just-trip point stroke change rate obtained after executing the full-capacity breaking times of the circuit breaker is used as the fourth threshold value (the full-capacity breaking times of the circuit breaker is the rated short-circuit current breaking times specified by the factory), two equally divided averages are taken between the first threshold value and the fourth threshold value as the second threshold value and the third threshold value, 100% is used as the fifth threshold value, and five just-trip point stroke change rate threshold intervals are divided based on the five threshold values;

[0073] According to the circuit breaker breaking test results, the fourth threshold is 20%. Accordingly, the interval of the change rate of the rigid breaking point stroke relative to the initial rigid breaking point stroke in the non-ablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%);

[0074] Set the ablation degree corresponding to the interval, so that the change rate of the just-break point stroke relative to the initial just-break point stroke in the non-ablated state is in the interval [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%), which respectively represent the ablation degree of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation;

[0075] According to each dynamic capacitance-stroke curve, it is found that the change rate of the capacitance drop value relative to the initial capacitance value in the non-ablated state is in the range of [5%, 30%), [30%, 45%), [45%, 60%), [60%, 100%), which respectively correspond to the degree of ablation of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation.

[0076] In addition, the initial capacitance drop value in the non-ablated state can also be directly used as a comparison benchmark: 0% is used as the first threshold for dividing the change rate interval (representing the dynamic capacitance drop value change rate threshold of the circuit breaker in the non-ablated state), the dynamic capacitance drop value change rate obtained when the rated short-circuit current breaking times of the circuit breaker are executed is used as the fourth threshold, and two equal averages between the first threshold and the fourth threshold are taken as the second threshold and the third threshold, and 100% is used as the fifth threshold. Five dynamic capacitance drop value change rate threshold intervals are divided based on the five thresholds, and the degree of ablation corresponding to each interval is further defined.

[0077] A specific reference embodiment is given below, please refer to it. Figure 2-Figure 10 :

[0078] Execute steps S1-S5 to calculate the typical circuit breaker opening dynamic capacitance time curve under the non-ablation state as follows: Figure 2 As shown. Taking the moment when the arc contacts separate as the zero moment, the initial capacitance value of the dynamic capacitance curve is 33.07pF. The capacitance value gradually decreases with time, and the rate of decrease also slows down with time, decreasing to 12.01pF at 30ms. After 30ms, the capacitance value no longer continues to decrease, showing the characteristics of fluctuations in a small range. Combined with the stroke curve during the opening process, it can be seen that the contact stroke has reached the maximum value of 150mm at 30ms, that is, the circuit breaker has completed the opening process, the contact opening distance has reached the maximum and no longer moves, so the capacitance value no longer continues to decrease. Combined with the analysis in Section 3.1.2.1, the reason for the fluctuation of the capacitance curve is the non-integer period sampling of the signal.

[0079] Since the trigger time of the oscilloscope and the action time of the circuit breaker operating mechanism are dispersed in each measurement, in order to facilitate the subsequent comparative analysis, the horizontal axis of the dynamic capacitance-time curve is replaced by the dynamic capacitance-stroke curve, that is, the curve of the change of capacitance with the contact stroke during the opening process is obtained, such as Figure 3As shown. It can be seen that the starting point of the dynamic capacitance-stroke curve corresponds to the stroke value, that is, the stroke value of the contact just opening point is 37.97mm, and the maximum stroke is 150mm. The arc contact opening distance of the circuit breaker is calculated to be 150-37.97=112.03mm. The product factory inspection report provided by the circuit breaker manufacturer shows that the arc contact opening distance is 112mm, which is consistent with the calculation result.

[0080] Feature parameter extraction:

[0081] According to the dynamic capacitance measurement results of the 0th ablation (no ablation), the 16th ablation (moderate ablation), and the 32nd ablation (severe ablation) of the circuit breaker C phase ablation test, the dynamic capacitance-stroke curve comparison results under different ablation degrees are as follows: Figure 4 As shown. It can be seen that with the change of the degree of contact ablation, the overall shape of the dynamic capacitance curve has not changed significantly, and all show the characteristics of a rapid decrease in capacitance near the contact opening point, and then a gradual slowdown in the rate of decrease. As the degree of ablation increases, the starting point of the dynamic capacitance curve shifts to the upper left, that is, the capacitance value at the starting point increases, and the stroke value at the starting point decreases. The curves are quite different near the starting point, and within the range of stroke greater than 40mm, the three curves tend to overlap, and the capacitance value at the complete opening point has only a small difference.

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

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

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

[0085] (3) Full opening point capacitance: the capacitance value when the contact moves to the full opening state, that is, the capacitance value at the end point of the dynamic capacitance-travel curve, in pF;

[0086] (4) Capacitance drop value: The drop in capacitance between contacts during the opening process, equal to the capacitance at the opening point minus the capacitance at the full opening point, unit: pF.

[0087] Dynamic capacitance parameter change rules:

[0088] Taking the dynamic capacitance curve measured by phase C as an example, the typical dynamic capacitance curves under different ablation times are as follows: Figure 6As shown. It can be seen that with the increase in the number of ablations, the shape of the curve has not changed. The starting point of the curve is obviously shifted to the upper left, that is, the ablation causes a decrease in the stroke of the just-break point and an increase in the capacitance of the just-break point. In the part where the stroke is greater than 40mm, the curve is divided into three clusters of curves, and each cluster of curves almost overlaps in the part where the stroke is greater than 40mm. The dynamic capacitance curves of the 10th, 18th, and 34th ablations are the first cluster, and the dynamic capacitance curves of the 2nd, 6th, 14th, 26th, and 30th ablations are the second cluster, and the dynamic capacitance curve of the 22nd ablation is a separate cluster. The first cluster of curves has the highest capacitance at the complete gate-off point, followed by the second cluster, and the third cluster is the lowest. The distribution of each cluster of curves has no obvious relationship with the number of ablations, which may be caused by the dispersion during measurement.

[0089] The characteristic parameters of the dynamic capacitance curve measured in the three-phase ablation test of the test circuit breaker are calculated respectively to analyze the change law of the dynamic capacitance characteristics with the contact ablation degradation. The characteristic parameter calculation takes the average value of the five results of each group of dynamic capacitance tests to reduce random errors.

[0090] Just split the itinerary:

[0091] Figure 7 The curve of the change of the three-phase just-break point stroke of the test circuit breaker with the number of ablation tests. The ablation current of phase A from 0 to 70 is 10kA, and the ablation current from 71 to 103 is 25kA. The just-break point stroke without ablation is 38.43mm, and there is no obvious change from 0 to 20 ablation, indicating that the ablation degradation of the contact is not obvious at this time due to the small ablation current. In the 20th to 56th ablation, the ablation effect gradually accumulates, and the just-break point stroke begins to decrease until it drops to 35.21mm after the 56th ablation. In the 56th to 70th ablation, the just-break point stroke fluctuates within 35.2 to 36.4mm. After the 70th ablation, the rate of decrease of the just-break point stroke increases significantly, indicating that the ablation effect of the 25kA current is more significant at this time. After 103 ablation, the just-break point stroke drops to 30.22mm.

[0092] Phase B was ablated 70 times with a 20kA current. The stroke of the split point before ablation was 36.48 mm, and it dropped to 30.83 mm after 70 ablation. The stroke of the split point rose to a certain extent during the 24th to 44th ablation, which may be caused by measurement errors.

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

[0094] In summary, in the ablation test, the stroke of the three-phase arc extinguishing chamber just breaking point decreased with the increase of the ablation times. The stroke of the just breaking point of phase A decreased by 8.21mm, the stroke of the just breaking point of phase B decreased by 5.65mm, and the stroke of the just breaking point of phase C decreased by 8.12mm.

[0095] Capacitance at the split point:

[0096] The calculated change of the capacitance value of the three-phase rigid-dividing point with the number of ablation times is as follows: Figure 8 As shown. When phase A was not ablated, the capacitance value at the split point was 22.18pF. During the 0th to 70th ablation, the capacitance value at the split point showed a certain upward trend, but the value fluctuated greatly, reaching a minimum of 19.5pF and a maximum of 29.9pF. During the 70th to 103rd ablation, the capacitance value increased significantly, and the rate of increase accelerated, reaching 31.77pF after 103rd ablation.

[0097] The capacitance value of the B phase at the split point was 24.21 pF before ablation, which decreased to 21.45 pF after the fourth ablation, and then gradually increased with the increase in the number of ablation times, reaching 35.09 pF after 70 ablation times.

[0098] The capacitance value of the C phase at the split point was 26.87 pF before ablation, which decreased to 22.94 pF after the fourth ablation, and then increased with the increase in the number of ablation times, reaching 31.15 pF after the 34th ablation.

[0099] It can be seen that the three phases all show a trend of increasing capacitance at the split point as the number of ablation times increases. After the ablation test, the increase in phase B is the largest, increasing by 10.88pF. The increase in phase A is second, increasing by 9.59pF. The increase in phase C is the smallest, increasing by 4.28pF.

[0100] Full trip point capacitance:

[0101] The change of capacitance value at the complete disconnection point with the number of ablation times is as follows: Fig. 9 As shown. Both phase A and phase C show the characteristics of fluctuation within a certain range, with no obvious change trend. The capacitance value of phase A at the complete disconnection point fluctuates within the range of 6.89 to 15.64 pF, and that of phase C fluctuates within the range of 8.88 to 15.57 pF. The variation range of phase B is within 9.26 to 14.97 pF, and the values ​​after 36 ablations are generally higher than those before 36 ablations, showing a trend of the capacitance value slightly increasing with the number of ablations.

[0102] Capacitance drop value

[0103] The variation law of the three-phase capacitance drop value with the number of ablation times is as follows Fig.10As shown. Phase A increased from the initial 12.18pF to 14.00pF during the 0th to 70th ablation, and the rate of increase increased during the 70th to 103rd ablation, rising to 18.93pF after the 103rd ablation. The capacitance drop value of phase B was 13.11pF before ablation, and dropped to 11.87pF after 4 ablations. It showed a steady upward trend during the 4th to 70th ablation, and rose to 20.61pF after 70th ablation. Phase C slightly dropped from the initial 11.30pF to 11pF after 2 ablations, and then showed a steady upward trend during the 2nd to 34th ablation, and rose to 17.66pF after the 34th ablation.

[0104] In general, the capacitance drop values ​​of the three phases all show a pattern of increasing significantly with the increase in the number of ablation times. Phase A increased by 6.75pF after ablation, phase B increased by 7.5pF, and phase C increased by 6.36pF. The increase ranges of the three phases are very close.

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

[0106] Based on the variation patterns of the above parameters, it can be seen that, except for the fully disconnected capacitance, the three parameters of the just disconnected point stroke, the just disconnected point capacitance and the capacitance drop value all show an obvious pattern of rising or falling with the increase of the number of ablation times, which means that these three parameters are related to the degree of contact deterioration.

[0107] According to the definition of the just-breaking stroke, the stroke is the contact stroke when the arc contact just breaks one cycle. The circuit breaker opening speed is 4.5m / s. The distance that the contact moves in one cycle of the high-frequency power supply 50kHz in this article is about 0.09mm, which can be ignored. It is considered that the just-breaking stroke is equal to the arc contact overstroke. The decrease in the just-breaking stroke means the decrease in the arc contact overstroke, that is, the shortening of the effective contact length of the arc contact, indicating that the arc contact end material has been significantly lost under the action of arc ablation. Material loss will cause the shape of the arc contact to change, resulting in 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 overstroke decreases to a certain extent, it will also cause the current to fail to transfer smoothly from the main contact to the arc contact when breaking the current, resulting in a breaking failure.

[0108] The capacitance at the just-opening point shows an upward trend with the number of ablation times, while the capacitance at the fully-opening point does not show an obvious change pattern with the number of ablation times. The reason is that the contact changes caused by ablation can significantly affect the capacitance value between the contacts when the distance between the moving and static contacts is small, while the opening distance between the contacts reaches the maximum at the fully-opening point, which is 121mm. At this time, the distance between the contacts becomes the main factor affecting the capacitance, and the influence of the change in the contact end on the capacitance value can be ignored in comparison. Figure 4The dynamic capacitance curves of different ablation degrees have obvious differences near the just-opening point, and the characteristic that the curves tend to overlap as the stroke increases and the contact distance increases also confirms this point. The fluctuation of several pF in the capacitance at the fully-opening point may not be caused by ablation but by the error introduced by the measurement. When measuring dynamic capacitance, the stray capacitance between the wires is taken as a fixed value, and two measurements are performed to correct the stray capacitance between the wires. In fact, the relative position of the wires will inevitably change between the two measurements, resulting in a change in the stray capacitance, which in turn causes fluctuations in the measurement results.

[0109] The capacitance drop value is the result of the difference between the capacitance at the just-breaking point and the capacitance at the fully-breaking point. Compared with the fluctuation and rise of the capacitance at the just-breaking point, the capacitance drop value shows a more stable upward trend and a smaller fluctuation. The reason is that the random error introduced during the correction of stray capacitance acts on both the capacitance value at the just-breaking point and the capacitance value at the fully-breaking point. The difference between the two parameters eliminates the influence of the random error, so the change of the capacitance drop value parameter is more stable and the upward trend is more significant. At the same time, compared with the capacitance at the just-breaking point, the change range and increase amplitude of the three-phase capacitance drop value before and after ablation are relatively consistent. According to the calculation results of the life formula of the power saving in 2.2.2, the degree of ablation of the contacts of the three-phase arc extinguishing chamber is roughly the same, so it can be considered that the capacitance drop value can more reliably reflect the degree of ablation and degradation of the contacts.

[0110] Further, ΔL and ΔC are calculated and recorded as the separation point travel change and separation point capacitance change of the more severely ablated break contact in the double-break circuit breaker. It can be stipulated that when the ΔL change exceeds 2mm, 4mm, 6mm and 8mm, the circuit breaker is considered to be slightly ablated, generally ablated, severely ablated and very severely ablated respectively. When the ΔC change exceeds 2pF, 4pF, 6pF and 8pF, the circuit breaker is considered to be slightly ablated, generally ablated, severely ablated and very severely ablated respectively.

[0111] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for evaluating the contact ablation state of a circuit breaker based on the dynamic capacitance of the circuit breaker, characterized in that: include: Step S1, 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 of the circuit breaker, wherein the data obtained from a single measurement includes a break voltage signal of the circuit breaker, a loop current signal of the measurement loop, and a travel signal of the position of the operating mechanism in the feedback circuit breaker; Step S2, calculating the dynamic capacitance based on the break voltage signal and the loop current signal, and further fitting a curve of the dynamic capacitance and the stroke signal, so as to obtain a dynamic capacitance-stroke curve corresponding to each opening and closing action; Step S3, calculating the capacitance drop value and the stroke of the split point of each curve; Step S4, setting a threshold value of the stroke change rate of the split point and defining a threshold interval and a degree of ablation corresponding to the interval, and further calculating a threshold interval of the capacitance drop value change rate and a degree of ablation corresponding to the interval based on the threshold interval of the split point stroke and the corresponding relationship between the capacitance drop value and the stroke of the split point calculated in step S3; Step S5, when evaluating the contact ablation state of the circuit breaker to be tested, measuring the port voltage signal and the loop current signal of the circuit breaker, and further calculating the current dynamic capacitance and the capacitance drop value, and determining the current contact ablation state of the circuit breaker to be tested based on the capacitance drop value threshold interval and the ablation degree corresponding to the interval; The dynamic capacitance measurement system includes an industrial computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotation speed sensor, and a current transformer. The current transformer collects signals from the opening and closing coil control circuit of the circuit breaker and is used to collect signals from the opening and closing coil. The rotation speed sensor is coaxially connected to the rotating shaft of the output crank arm of the circuit breaker. The measurement circuit is composed of a high-frequency voltage-stabilized power supply, a sampling resistor, and a circuit breaker in series. The voltage transformer samples the circuit voltage. The sampling resistor is used to provide the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotation speed sensor, and the industrial computer. The industrial computer is used to implement steps S2-S5. The step S1 specifically includes: starting the high-frequency voltage-stabilized power supply to provide voltage to the circuit, the high-speed synchronous acquisition module receives the opening and closing coil signal of the circuit breaker as a trigger signal for executing data acquisition, continuously collects the break voltage signal, the circuit current signal, and the travel signal of the rotation speed sensor, and outputs them to the industrial computer.

2. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The step S2 performs a curve fitting process of dynamic capacitance and stroke for a single opening and closing of the switch, including: Step S21, discrete short-time Fourier transform is performed on the break voltage signal and the loop current signal respectively, and a non-stationary signal s(t) is defined to represent the break voltage signal or the loop current signal. The short-time Fourier transform STFT is defined as: Where t is time, ω is fundamental frequency, h(t) is window function, and i is an imaginary number; The signal is cut into different time periods n by using a window function, and the frequency f, fundamental voltage amplitude U(n), and fundamental current amplitude I(n) corresponding to the fundamental component of the signal in each time period are obtained by discrete short-time Fourier transform; Step S22, calculating the dynamic capacitance C(n) of the circuit breaker to be tested: Step S23, drawing a curve of travel and time according to the travel signal, and further fitting a dynamic capacitance-travel curve through time alignment.

3. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 2, characterized in that: In the dynamic capacitance-travel curve: The stroke at the break point is: the stroke value corresponding to the starting point of the dynamic capacitance-stroke curve; The capacitance at the break point is: the capacitance value corresponding to the starting point of the dynamic capacitance-stroke curve; The full opening point capacitance is: the capacitance value when the contact moves to the fully open state, that is, the capacitance value at the end point of the dynamic capacitance-travel curve; The capacitance drop value is: the drop in capacitance between the contacts during the opening and closing process, which is equal to the capacitance at the opening point minus the capacitance at the complete opening point.

4. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 3, characterized in that: Step S4 includes: The initial break point stroke and the initial capacitance drop value in the un-ablated state are used as comparison benchmarks: 0% is used as the first threshold for dividing the break point stroke change rate threshold interval, the break point stroke change rate obtained after executing the full capacity breaking times of the circuit breaker is used as the fourth threshold, two equally divided averages are taken between the first threshold and the fourth threshold as the second threshold and the third threshold, 100% is used as the fifth threshold, and five break point stroke change rate threshold intervals are divided based on the five thresholds; According to the circuit breaker breaking test results, the fourth threshold value is 20%. Accordingly, the interval of the change rate of the rigid breaking point stroke relative to the initial rigid breaking point stroke in the non-ablated state is divided into [0%, 5%), [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%); The ablation degree corresponding to the interval is set, and the change rate of the just-break point stroke relative to the initial just-break point stroke in the non-ablated state is in the interval [5%, 10%), [10%, 15%), [15%, 20%), [20%, 100%), which respectively correspond to the ablation degree of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation; according to each dynamic capacitance-stroke curve, it is obtained that the change rate of the capacitance drop value relative to the initial capacitance value in the non-ablated state is in the interval [5%, 30%), [30%, 45%), [45%, 60%), [60%, 100%), which respectively correspond to the ablation degree of the circuit breaker as slight ablation, general ablation, severe ablation and very severe ablation.

5. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The break voltage signal is measured by a voltage transformer with a transformation ratio of 6:

1.

6. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The loop current signal is sampled through a 200Ω non-inductive resistor.

7. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The travel signal is measured using a rotary resistive speed sensor, the sensor proportional coefficient is 300mV / (° / s), and the range is ±120° / s.

8. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The rotation speed sensor is mounted on the rotating shaft of the output crank arm of the circuit breaker operating mechanism through screws, and is fixed to the wall of the operating mechanism box through a universal bracket.

9. The contact ablation state assessment method based on circuit breaker break dynamic capacitance according to claim 1, characterized in that: The opening and closing coil current is measured by a ETCR007AD clamp-type Hall current sensor, the sensor proportional coefficient is 100mV / 1A, the range is 0mA~50A, and the jaws are clamped in the circuit breaker opening and closing coil control loop in the correct direction.

10. A dynamic capacitance measurement system, characterized in that: include: An industrial computer, a high-speed synchronous acquisition module, a measurement circuit, a voltage transformer, a rotation speed sensor, and a current transformer. The current transformer collects signals from the opening and closing coil control circuit of the circuit breaker and is used to collect the opening and closing coil signals. The rotation speed sensor is coaxially connected to the rotating shaft of the circuit breaker output crank arm. The measurement circuit is composed of a high-frequency voltage-stabilized power supply, a sampling resistor, and a circuit breaker in series. The voltage transformer samples the circuit voltage. The sampling resistor is used to provide the sampling circuit current to the acquisition module. The high-speed synchronous acquisition module is connected to the voltage transformer, the sampling resistor, the rotation speed sensor, and the industrial computer. The dynamic capacitance measurement system is used to implement the method described in claims 1-9.

Images