A partial discharge detection circuit and detection method

Abstract

The present invention belongs to the technical field of insulation defect detection, and specifically relates to a partial discharge number detection circuit and detection method. In the detection circuit, the voltage signal of partial discharge is connected to a differential circuit, the output end of the differential circuit is respectively connected to the positive input end of the electronic switch tube Q4, Q5 and the voltage comparator P2, Q4, Q5 are respectively connected to the positive input end of the voltage comparator P1 and the negative input end of the voltage comparator P3, the output ends of P1, P2 and P3 are connected to the anode of the diode, and also include sampling capacitors C1, C2 and C3, Q1, Q2 and Q3 are connected to the cathode of the diode and the input end of the logic AND gate, the positive logic output end of the logic AND gate outputs the partial discharge number signal, and the negative logic output end of the logic AND gate is connected to Q1, Q2 and Q3 after a logic NOT gate delay. The present invention makes the collection of partial discharge number signals more accurate; the real-time performance is high; and the situation where multiple partial discharge number signals are superimposed together can be distinguished and counted.

Description

Technical Field

[0001] The invention belongs to the technical field of insulation defect detection, and in particular relates to a partial discharge frequency detection circuit and a detection method. Background Art

[0002] Partial discharge is a non-penetrating discharge phenomenon caused by local defects in insulating media. According to the degree of partial discharge, the partial discharge process can be divided into four stages: initiation, occurrence, development, and danger. Long-term partial discharge will cause the degradation of equipment insulation and even lead to insulation breakdown and equipment damage.

[0003] Taking common insulation defects as an example, there are bubbles doped in cross-linked polyethylene (cable insulation layer), and the bubble diameter is in the micrometer range. When the number of partial discharges of the insulating medium is detected, the number of bubbles cannot be known and the shape of the bubbles is not fixed, so the equivalent capacitance value and breakdown voltage of a single bubble cannot be known. The industry usually calls this model of parallel resistor-capacitor structure a partial discharge model. The number of insulation defects (equivalent capacitance of bubbles), capacitance value and breakdown voltage of the partial discharge model are unknown, and the starting discharge time of different insulation defects is short, which may cause the partial discharge signal to overlap and be difficult to distinguish. Therefore, the number of partial discharges in the prior art is difficult to accurately measure. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a partial discharge number detection circuit and detection method, which mainly solves the problem that the number of discharges is difficult to accurately detect during the partial discharge process. The technical solution adopted by the present invention is as follows:

[0005] A partial discharge frequency detection circuit, the partial discharge voltage signal V in The differential circuit is connected to the differential circuit, the output end of the differential circuit is respectively connected to the electronic switch tube Q4, Q5 and the positive input end of the voltage comparator P2, Q4, Q5 are respectively connected to the positive input end of the voltage comparator P1 and the negative input end of the voltage comparator P3, the output ends of P1, P2 and P3 are connected to the anode of the diode, the sampling capacitors C1, C2 and C3 are respectively connected to the electronic switch tubes Q1, Q2 and Q3 in parallel, Q1, Q2 and Q3 are connected to the cathode of the diode and the input end of the logic AND gate AND, Q1, Q2 and Q3 are connected to GND; Q2 is connected to Q4, Q5; or, Q2 is connected to Q4, Q1 is connected to Q5; the positive logic output end of the logic AND gate AND outputs the partial discharge number signal V out The negative logic output of the logic AND gate AND is connected to Q1, Q2 and Q3 after being delayed by the logic NOT gate NOT.

[0006] As a further preferred implementation, one end of the bidirectional Zener diode ZD is connected to GND, and the other end is connected to the output end of the differential circuit, Q4 and Q5 respectively.

[0007] As a further preferred embodiment, the electronic switch tube is an electronic component with a switch function.

[0008] A method for detecting the number of partial discharges, using the aforementioned partial discharge number detection circuit, comprises the following steps:

[0009] At t0, the product under test starts to discharge, and the partial discharge voltage signal V in In a very short time, it rises to the maximum value and reaches the moment t1. The partial discharge voltage signal V in During the rising process, the output voltage V d >0, the sampling capacitor C2 is charged, the electronic switch tubes Q4 and Q5 are turned on, and when V d >V hd When the sampling capacitor C1 is charged, after time t1, the partial discharge voltage begins to decrease, V d <0, the sampling capacitor C3 is charged, and after the logic gate AND operation, the positive logic output terminal of the logic gate AND outputs the partial discharge number signal V out is high level, and at the same time, the negative logic output terminal of the logic AND gate AND outputs a signal that is delayed by the logic NOT gate NOT for a time t del After that, at time t2, the electronic switches Q1, Q2, and Q3 are turned on to discharge the sampling capacitors C1, C2, and C3. out It returns to a low level and the electronic switches Q1, Q2, and Q3 are turned off.

[0010] Beneficial effects of the present invention:

[0011] 1. The present invention utilizes electronic switch tubes, voltage comparators, logic AND gates and logic NOT gates to make the collection of partial discharge frequency signals more accurate;

[0012] 2. The present invention uses a differential circuit to process the voltage signal of partial discharge, which has high real-time performance;

[0013] 3. The present invention can distinguish and count the situation where multiple partial discharge frequency signals are superimposed on each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of a partial discharge frequency sampling circuit in the prior art;

[0015] Figure 2 It is a sampling timing diagram of a partial discharge frequency sampling circuit in the prior art;

[0016] Figure 3It is a structural schematic diagram of a partial discharge frequency detection circuit according to a first embodiment of the present invention;

[0017] Figure 4 is a schematic structural diagram of a partial discharge frequency detection circuit according to a second embodiment of the present invention;

[0018] Figure 5 It is a schematic diagram of the working timing of the partial discharge number detection circuit according to the embodiment of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0020] like Figure 1 FIG. 1 is a schematic diagram of the structure of a partial discharge frequency sampling circuit in the prior art. The partial discharge voltage signal V in The positive input terminal of the voltage comparator P1 is connected to the anode of the diode D, the positive input terminal of the voltage comparator P1 is connected to the cathode of the diode D, and the input voltage of the negative input terminal of the voltage comparator P1 is the discharge voltage measurement threshold V hd The output terminal of the voltage comparator P1 outputs a partial discharge number signal V out , the electronic switch tube Q1 is connected in parallel with the sampling capacitor C1, the collector of Q1 is connected to the cathode of the diode D, the emitter of Q1 is connected to GND, the base of Q1 is connected to the clock pulse CLK, and GND is the 0 potential reference point. V in is the voltage signal of partial discharge, V out is the partial discharge frequency signal. Each time a partial discharge occurs, V out A pulse signal will be generated.

[0021] like Figure 2 FIG. 1 is a schematic diagram of the sampling timing of the partial discharge frequency sampling circuit in the prior art. Figure 1 , Figure 2 Taking the partial discharge sampling circuit structure and its working mode in the prior art as an example, when the clock pulse CLK is at a low level, the partial discharge voltage signal V in Sampling is performed when the voltage V C1 >V hd When the output V out When CLK is high, Q1 is turned on, C1 is discharged, and the output V out Restore to low level. Figure 2 As shown in the figure, when the local discharge process is entirely during the conduction period of Q1, the discharge process cannot be counted; when most of the local discharge process is during the conduction period of Q1, and when Q1 is turned off, when the voltage V on C1 C1 <V hdWhen Q1 is turned off, if multiple partial discharges occur, only one partial discharge will be output.

[0022] like Figure 3 FIG. 1 is a schematic diagram of the structure of a partial discharge frequency detection circuit according to the first embodiment of the present invention. Figure 3 For example, the structure of the partial discharge detection circuit is briefly described. For the convenience of description, the electronic switch tube uses an NPN transistor. A partial discharge detection circuit, the partial discharge voltage signal V in Connected to the differential circuit, the differential circuit detects V in The slope of the output differential circuit is V d , V in The slope is used to characterize that the partial discharge signal voltage is in the rising or falling stage. The slope in the rising stage is greater than zero, and the slope in the falling stage is less than zero. The partial discharge signal can be approximately regarded as a pulse signal with a very short rising edge. The output end of the differential circuit is respectively connected to the collector of the electronic switch tubes Q4 and Q5 and the positive input end of the voltage comparator P2. The emitters of the electronic switch tubes Q4 and Q5 are respectively connected to the positive input end of the voltage comparator P1 and the negative input end of the voltage comparator P3. The output ends of the voltage comparators P1, P2 and P3 are connected to the anode of the diode. The sampling capacitors C1, C2 and C3 are respectively connected in parallel with the electronic switch tubes Q1, Q2 and Q3. The collectors of the electronic switch tubes Q1, Q2 and Q3 are connected to the cathode of the diode and the input end of the logic AND gate AND. The emitters of the electronic switch tubes Q1, Q2 and Q3 are connected to GND. In addition, the collector of the electronic switch tube Q2 is connected to the bases of Q4 and Q5. The positive logic output end of the logic AND gate AND outputs the partial discharge number signal V out The negative logic output of the logic gate AND is connected to the base of the electronic switch tubes Q1, Q2 and Q3 after a delay through the logic gate NOT. One end of the bidirectional voltage stabilizing Zener diode ZD is connected to GND, and the other end is connected to the output end of the differential circuit, the collectors of Q4 and Q5 respectively. The function of ZD is to prevent the output voltage of the differential circuit from being too high and damaging the subsequent components.

[0023] like Figure 4 , which is a schematic diagram of the structure of the partial discharge number detection circuit of the second embodiment of the present invention. The difference from the first embodiment is that the collector of the electronic switch tube Q2 is connected to the base of Q4, and the collector of Q1 is connected to the base of Q5.

[0024] The electronic switch tubes in the embodiment of the present invention can be other electronic components with switch functions in addition to NPN. The function of the electronic switch tubes Q1, Q2, and Q3 is to maintain / discharge the capacitor voltage to identify a partial discharge, and the function of the electronic switch tubes Q4 and Q5 is to delay the action sequence, that is, first determine the occurrence of the partial discharge signal (voltage rise), and then determine Vin The slope of the discharge signal is checked to see whether it meets the standard of a true discharge signal (the voltage rise slope (rate) is large), and finally the voltage is judged to have dropped, and the whole process is regarded as one discharge.

[0025] The differential circuit in the embodiment of the present invention is a prior art, and a relatively common differential circuit structure can be used.

[0026] like Figure 5 FIG. 1 is a schematic diagram of the working timing of the partial discharge frequency detection circuit according to an embodiment of the present invention. Figure 3 , Figure 4 and Figure 5 Taking the example of the present invention, the working principle of the partial discharge detection circuit of the present invention is briefly described. A partial discharge detection method adopts the above-mentioned partial discharge detection circuit, and comprises the following steps:

[0027] At t0, the product under test starts to discharge, and the partial discharge voltage signal V in In a very short time, it rises to the maximum value and reaches the moment t1. The partial discharge voltage signal V in During the rising process, the output voltage V d >0, the sampling capacitor C2 is charged, the electronic switch tubes Q4 and Q5 are turned on, and when V d >V hd When the sampling capacitor C1 is charged, after time t1, the partial discharge voltage begins to decrease, V d <0, the sampling capacitor C3 is charged, and after the logic gate AND operation, the positive logic output terminal of the logic gate AND outputs the partial discharge number signal V out is high level, and at the same time, the negative logic output terminal of the logic AND gate AND outputs a signal that is delayed by the logic NOT gate NOT for a time t del After that, at time t2, the electronic switches Q1, Q2, and Q3 are turned on to discharge the sampling capacitors C1, C2, and C3. out The voltage signal V of the next partial discharge is restored to a low level, and the electronic switch tubes Q1, Q2, and Q3 are turned off. in When rising, repeat the above process (t3~t5).

[0028] Compared with the prior art solutions, the sampling method of the technical solution involved in the present invention depends only on the discharge pulse itself, and will not cause the "missing times" due to external synchronization signals. The collection is more accurate, and the result can reflect the phase information of the local discharge pulse. It has strong real-time performance and can distinguish and count the situation where repeated discharges are superimposed on each other, which greatly improves the accuracy of the measurement of the number of local discharges.

Claims

1. A partial discharge frequency detection circuit, characterized in that: Partial discharge voltage signal V in connected to a differential circuit, the output end of the differential circuit is respectively connected to the collector of the electronic switch tubes Q4 and Q5 and the positive input end of the voltage comparator P2, the emitters of the electronic switch tubes Q4 and Q5 are respectively connected to the positive input end of the voltage comparator P1 and the negative input end of the voltage comparator P3, the output ends of the voltage comparators P1, P2 and P3 are connected to the anode of the diode, the sampling capacitors C1, C2 and C3 are respectively connected to the electronic switch tubes Q1, Q2 and Q3 in parallel, the collectors of the electronic switch tubes Q1, Q2 and Q3 are connected to the cathode of the diode and the input end of the logic AND gate AND, and the emitters of the electronic switch tubes Q1, Q2 and Q3 are connected to GND; The collector of the electronic switch tube Q2 is connected to the base of the electronic switch tubes Q4 and Q5; the positive logic output terminal of the logic AND gate AND outputs the partial discharge number signal V out , the negative logic output end of the logic AND gate AND is connected to the base of the electronic switch tubes Q1, Q2 and Q3 after being delayed by the logic NOT gate NOT; one end of the bidirectional voltage stabilizing Zener diode ZD is connected to GND, and the other end is connected to the output end of the differential circuit and the collector of the electronic switch tubes Q4 and Q5 respectively; Alternatively, the collector of the electronic switch tube Q2 is connected to the base of the electronic switch tube Q4, and the collector of the electronic switch tube Q1 is connected to the base of the electronic switch tube Q5.

2. A partial discharge detection circuit according to claim 1, characterized in that: Electronic switch tubes are electronic components with switching functions.

3. A method for detecting the number of partial discharges, characterized in that: The partial discharge detection circuit according to claim 1 comprises the following steps: At t0, the product under test starts to discharge, and the partial discharge voltage signal V in In a very short time, it rises to the maximum value and reaches the moment t1. The partial discharge voltage signal V in During the rising process, the output voltage V d >0, the sampling capacitor C2 is charged, the electronic switch tubes Q4 and Q5 are turned on, and when V d >V hd When the sampling capacitor C1 is charged, after time t1, the partial discharge voltage begins to decrease, V d <0, the sampling capacitor C3 is charged, and after the logic gate AND operation, the positive logic output terminal of the logic gate AND outputs the partial discharge number signal V out is high level, and at the same time, the negative logic output terminal of the logic AND gate AND outputs a signal that is delayed by the logic NOT gate NOT for a time t del After that, at time t2, the electronic switches Q1, Q2, and Q3 are turned on to discharge the sampling capacitors C1, C2, and C3. out It returns to a low level and the electronic switches Q1, Q2, and Q3 are turned off.

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