Capacitance current measuring circuit of grounding system through phase-controlled arc suppression coil

Abstract

The utility model provides a capacitance current measuring circuit of a grounding system through a phase-controlled arc suppression coil, which comprises a phase-controlled arc suppression coil and a voltage source circuit, and is characterized in that the voltage source circuit is connected in parallel with a filtering winding of the phase-controlled arc suppression coil and is used for injecting voltage into the phase-controlled arc suppression coil; the power supply circuit comprises a capacitor Xcx, a transformer T2, a solid-state switch and an alternating-current power supply; the capacitor Xcx is used for dividing voltage and limiting voltage applied to the two ends of the filter winding induction coil; the capacitor Xcx is connected in series to one side of the transformer T2, the other side of the transformer T2 is connected in series with the solid-state switch, and one side of the solid-state switch is externally connected with an alternating current power supply. The voltage source circuit is introduced to be connected with the filtering winding of the phase-controlled arc suppression coil in parallel, voltage is injected into the phase-controlled arc suppression coil, the capacitive current of a grounding system can be accurately measured, the capacitor Xcx not only plays a role in voltage division, but also effectively limits the voltage applied to the two ends of an induction coil of the filtering winding, and therefore the voltage of the grounding system can be accurately measured. And the safety and the stability of the circuit are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the power grid detection technical field, specifically, it relates to a kind of capacitive current measurement circuit of phase-controlled arc suppression coil grounding system. BACKGROUND

[0002] Effective grasp of the basic data of distribution network to ground capacitance current, regular development of arc suppression coil device checking, it is an important work to ensure the safe and stable operation of distribution network.According to the relevant provisions of the electric power department, for the 6-20kV system not directly connected with generator, when single-phase ground fault occurs, if the power grid to ground capacitance current is less than or equal to 10A, neutral point ungrounded mode can be used;if the power grid to ground capacitance current is greater than 10A, neutral point through arc suppression coil grounding mode is suitable.Therefore, accurate measurement of medium voltage distribution network to ground capacitance current has important significance for reasonable selection of neutral point grounding mode and correct selection of arc suppression coil capacity.

[0003] Traditional measurement methods of capacitive current include single-phase metal grounding method, bias capacitor method, artificial neutral point method, neutral point external capacitor method, resonance method, two-point method, three-point method, impedance triangle method, etc.Single-phase metal grounding method is a direct and accurate measurement method, which is to artificially ground the medium voltage distribution network system through single-phase grounding switch.The disadvantage of this method is that the operation and wiring are complex, which may endanger the weak link of normal phase insulation to cause two-phase or three-phase ground short circuit and may endanger the safety of operating personnel;In addition, single-phase grounding of distribution network may also cause power failure.Indirect measurement methods such as neutral point external capacitor method are more convenient than direct methods, and can also accurately measure the power grid capacitance current, but still have some shortcomings:①Measurement still involves primary side, and safety is poor.②Since the measurement process involves primary equipment, the operation is still complex and inefficient. CONTENT OF THE UTILITY MODEL

[0004] In view of the defects in the prior art, the purpose of the present application is to provide a capacitive current measurement circuit of phase-controlled arc suppression coil grounding system, which injects a voltage into the primary measurement through filter winding, and changes the conduction angle of thyristor at the same time to realize the calculation of system capacitance, and the measurement process does not depend on the asymmetry of power grid, and testing is convenient.

[0005] In one aspect of the present application, a capacitive current measurement circuit of phase-controlled arc suppression coil grounding system is provided, which comprises a phase-controlled arc suppression coil, and further comprises a voltage source circuit connected in parallel with the filter winding of the phase-controlled arc suppression coil, for injecting voltage into the phase-controlled arc suppression coil;

[0006] The power supply circuit comprises capacitor Xcx, transformer T2, solid-state switch and alternating current power supply;

[0007] The capacitor Xcx is used for voltage division and limiting the voltage applied to the filter winding inductor;

[0008] The capacitor Xcx is connected in series to one side of the transformer T2, and the other side of the transformer T2 is connected in series to the solid-state switch, and one side of the solid-state switch is connected to the AC power supply.

[0009] Further, the voltage source circuit further comprises a voltage limiting resistor connected in parallel to the solid-state switch, for limiting the voltage of the solid-state switch.

[0010] Further, the solid-state switch uses a solid-state relay as the switch of the voltage source circuit.

[0011] Further, the voltage source circuit further comprises a frequency divider connected to the solid-state relay, for sampling the power frequency and controlling the on-off time of the solid-state relay.

[0012] Further, the frequency divider is a frequency divider for sampling the power frequency of 50Hz AC.

[0013] Further, the solid-state relay is a periodic relay with 2 seconds on and 80 seconds off.

[0014] Further, the transformer T2 is a double-winding transformer.

[0015] The turns ratio of the transformer T2 is 1:1.

[0016] Further, the phase type arc-extinguishing coil comprises a primary winding and a secondary winding; the secondary winding comprises a first secondary winding and a second secondary winding.

[0017] The primary winding is connected to the main circuit of the power grid.

[0018] The filter winding is connected in parallel across the first secondary winding, and the second secondary winding is connected to the thyristor control circuit.

[0019] Further, the filter winding comprises a capacitor Xc3, a reactance X13, a capacitor Xc5 and a reactance X15.

[0020] The capacitor Xc3 and the reactance X13 are connected in series, and the branch after series connection is connected in parallel across the first secondary winding.

[0021] The capacitor Xc5 and the reactance X15 are connected in series, and the branch after series connection is connected in parallel with the branch after series connection of the capacitor Xc3 and the reactance X13.

[0022] Further, the conduction angle of the phase control type arc-extinguishing coil ranges from 90° to 179°.

[0023] Compared with the prior art, the application has at least one of the following beneficial effects:

[0024] The application injects a voltage into the primary through a filter winding, and then changes the conduction angle of the thyristor at the same time of injection, to realize the calculation of the system capacitance. The measurement process does not depend on the asymmetry of the power grid, and the test is convenient. The midpoint voltage and current when the injected voltage is collected directly from the secondary side, avoids direct contact between personnel and the power grid, greatly improves the safety. BRIEF DESCRIPTION OF DRAWINGS

[0025] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0026] Figure 1 For an embodiment of the application, a capacitance current measurement circuit for a phase-controlled arc-extinguishing coil grounding system.

[0027] Figure 2 For an embodiment of the application, an equivalent circuit diagram of an injection type phase-controlled arc-extinguishing coil. DETAILED DESCRIPTION

[0028] The application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These all belong to the protection scope of the application.

[0029] Referring to Figure 1 Fig. 1 shows a capacitance current measurement circuit for a phase-controlled arc-extinguishing coil grounding system according to an embodiment of the application, which includes a phase-controlled arc-extinguishing coil and a voltage source circuit.

[0030] The voltage source circuit is connected in parallel with the filter winding of the phase-controlled arc-extinguishing coil, and is used to inject a voltage into the phase-controlled arc-extinguishing coil.

[0031] The power supply circuit includes a capacitor Xcx, a transformer T2, a solid-state switch and an alternating current power supply.

[0032] The capacitor Xcx is used for voltage division and limiting the voltage applied to the filter winding inductor. The capacitor Xcx is connected in series at one side of the transformer T2, the other side of the transformer T2 is connected in series with the solid-state switch, and one side of the solid-state switch is connected with the alternating current power supply.

[0033] The application realizes the function of injecting voltage into the phase-controlled arc-extinguishing coil by connecting the voltage source circuit in parallel with the filter winding of the phase-controlled arc-extinguishing coil, so that the capacitance current of the grounding system can be accurately measured. The capacitor Xcx not only plays a role in voltage division, but also effectively limits the voltage applied to the filter winding inductive coil, thereby improving the safety and stability of the circuit.

[0034] Specifically, during operation, the alternating current power supplies power to the transformer T2 through the solid-state switch, and the transformer T2 transmits the voltage to one side connected in series with the capacitor Xcx. The capacitor Xcx divides the voltage and limits the voltage across the inductive coil, ensuring that the circuit works within a safe range. At the same time, the voltage source circuit is connected in parallel with the filter winding of the phase-controlled arc-extinguishing coil, and the voltage is injected into the phase-controlled arc-extinguishing coil, thereby realizing accurate measurement of the capacitance current.

[0035] Referring to Figure 1 As shown in the figure, the filter circuit is connected in series with one side of a transformer T2 with a transformation ratio of 1:1 through an external capacitor Xcx; the other side of the T2 is connected in series with a solid-state switch and then an external 220V alternating current power supply; the 220V alternating current power supply is used to inject an external voltage, and the solid-state switch is used to control the injection of the voltage; the external capacitor Xcx functions as a voltage divider, limiting the voltage applied to the filter winding inductive coil, thereby limiting the primary neutral point voltage and preventing the neutral point voltage from being too high to affect the normal operation of the system.

[0036] Among them, according to Figure 2 As shown in the figure, if a voltage source is applied at L5, the midpoint voltage and current when directly sampling the injected voltage can be directly calculated when Us=0 (the midpoint voltage of the system is 0). The capacitance of the system (the equivalent system capacitance is not drawn, which should be connected across Us) can be directly calculated. Of course, when the midpoint voltage rises during injection, the system capacitance can also be calculated according to the existing state equation solution.

[0037] The injection equipment dedicated air switch is installed in the PK screen, which controls the power supply of all 220V injection equipment. The injection transformer is placed in the damping box, and the voltage source circuit is connected in parallel with the filter winding of the phase-controlled arc-extinguishing coil. The capacitance current is measured by injecting voltage into the phase-controlled arc-extinguishing coil.

[0038] In the application, in order to improve the calculation accuracy, the automatic injection control is realized by the combination of software and hardware, and the capacitance current value is given after 5 consecutive injections and taking the average, thereby improving the calculation accuracy and avoiding frequent adjustment caused by incorrect calculation results.

[0039] In some possible embodiments, the voltage source circuit further comprises a voltage-sensitive resistor connected in parallel with the solid-state switch, for limiting the voltage of the solid-state switch.

[0040] The solid state switch uses a solid state relay as a switch of the voltage source circuit.

[0041] In some specific embodiments, the voltage source circuit further comprises a frequency divider connected with the solid state relay, for sampling the power frequency to control the on-off time of the solid state relay.

[0042] The frequency divider is a frequency divider for sampling the power frequency of 50 Hz AC.

[0043] The solid state relay is a periodic relay with 2 seconds of conduction and 80 seconds of disconnection.

[0044] In the present application, a solid state relay used in a bridge is used as a switch of the control power supply, a frequency divider of model 4020 is used to sample the power frequency of 50 Hz AC as a clock, and the result of the frequency division is that the device is on for 2 seconds and off for 80 seconds. The voltage at both ends of the filter winding is sampled, and after single-phase grounding occurs, the system voltage rises to 30%, after which the distributor 4020 is reset to block the injection current. The circuit works all the time after power-on and is not controlled by the controller. The controller automatically identifies through software according to this characteristic.

[0045] During the on-off process of the solid state relay, overvoltage may occur at both ends of the solid state relay, which may cause the relay to break down. In order to prevent this phenomenon from occurring, a voltage-dependent resistor is connected in parallel at both ends of the solid state relay.

[0046] In some specific embodiments, the transformer T2 is a double-winding transformer; the turns ratio of the transformer T2 on both sides is 1:1. The primary side of the transformer T2 is completely electrically isolated from the secondary side.

[0047] In some specific embodiments, the phase type arc extinction coil comprises a primary winding and a secondary winding; the secondary winding comprises a first secondary winding and a second secondary winding.

[0048] The primary winding is connected with the main loop of the power grid.

[0049] Referring to Figure 1 As shown, the filter winding is connected in parallel at both ends of the first secondary winding, and the second secondary winding is connected to the silicon controlled rectifier control circuit.

[0050] Specifically, the filter winding comprises: a capacitor Xc3, a reactance X13, a capacitor Xc5 and a reactance X15; the capacitor Xc3 and the reactance X13 are connected in series, and the branch after the series connection is connected in parallel at both ends of the first secondary winding; the capacitor Xc5 and the reactance X15 are connected in series, and the branch after the series connection is connected in parallel with the branch after the series connection of the capacitor Xc3 and the reactance X13.

[0051] Specifically, the arc suppression coil body includes one primary winding and two secondary windings, the primary winding is connected in the main circuit of the power grid, the first secondary winding is connected to a filter circuit composed of multiple capacitors and inductors, the filter circuit includes capacitors Xc3, reactance X13, capacitor Xc5 and reactance X15 connected in parallel at both ends of the first secondary winding respectively, the second secondary winding is connected to a thyristor control circuit, a capacitor Xcx is connected after the filter circuit, and then connected to an isolation transformer T2 (secondary side); the right end (i.e. primary side) of the isolation transformer T2 is connected to a circuit including a varistor and a solid state switch, which is powered by an AC 220V.

[0052] Among them, the capacitor Xc3 and the reactance X13 are connected in series, and the capacitor Xc5 and the reactance X15 are connected in series, forming a 3rd harmonic filter branch and a 5th harmonic filter branch.

[0053] In some specific embodiments, the conduction angle of the phase-controlled arc suppression coil ranges from 90° to 179°.

[0054] In this application, first of all, the conduction angle of the arc suppression coil needs to be placed at the cutoff angle of 148°, at which point the inductance of the arc suppression coil is maximum, and the entire system is inductive, Lp and Lt are in series, and the inductive reactance is generally hundreds of Ω, which is much larger than the fundamental impedance of the filter winding (generally 2-3 Ω). From the injection side, it can be approximately considered that the primary is open circuit, so when the primary side is grounded, the voltage at the neutral point hardly threatens the injection side.

[0055] Secondly, assuming that the conduction angle is placed at the full conduction position of 90°, the three-phase circuit system is capacitive at this time. Since the impedance of the 1uf capacitor is approximately 300Ω, multiplied by the square of the transformation ratio, the impedance after conversion to the secondary side is very large, while the impedance of the 3rd and 5th windings to the fundamental wave (generally 2-3 Ω), so from the injection side, it can also be considered that the primary is open circuit. However, according to the simulation data of the actual parameters of the arc suppression coil by PSCAD software, when the cutoff angle changes from 90° to 179°, the measurement and calculation requirements of the instrument can be met.

[0056] Among them, a specific embodiment is:

[0057] 1) Field conditions:

[0058] Tianjin Petrochemical 220kV substation has four bus sections, each of which has two arc suppression coils. Among them, 34A and 35A two bus sections can be operated in parallel, 34B and 35B two bus sections can be operated in parallel, and four bus sections cannot be operated in parallel. Among them, 1# main transformer with 34A bus corresponds to 1#, 3# arc suppression coil; 2# main transformer with 35A bus corresponds to 2#, 4# arc suppression coil; 3# main transformer with 34B bus corresponds to 5#, 7# arc suppression coil; 4# main transformer with 35B bus corresponds to 6#, 8# arc suppression coil.

[0059] 2) Modification experiment

[0060] After the 2# arc suppression coil injection method experimental device was put into operation, the actual measurement value of the arc suppression coil was basically the same as the test value of the capacitance tester. When 34A and 35A two bus sections were operated in parallel, 1#, 3# arc suppression coil was out of operation, 2#, 4# injection method was used for testing, the actual measurement value was about 7.987uF, and the capacitance tester test result was about 7.93uF; when 35A bus was operated alone, the actual measurement value was about 3.616uF, and the capacitance tester test result was about 3.80uF. During the injection process, no abnormal situation such as flickering of the customer's lighting lamp was found, and the current test result was relatively recognized.

[0061] When 34A and 35A two bus sections are operated in parallel, if 1#, 3#, 2#, 4# four arc suppression coils are operated at the same time, due to the problem of communication of four arc suppression coils, the calculation of arc suppression coil is inaccurate, when four arc suppression coils work at the same time, 2#, 4# arc suppression coil control screen displays the calculated capacitance as 9.054uF, when 1#, 3# arc suppression coils are out of operation, 2#, 4# arc suppression coil control screen displays the calculated capacitance as 7.987uF.

[0062] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be combined in any combination without conflict.

Claims

1. A capacitive current measurement circuit for a phase-controlled arc suppression coil grounding system, comprising, a phase-controlled arc suppression coil, characterized in that, The voltage source circuit is connected in parallel with the filter winding of the phase-controlled arc-extinguishing coil, and is used for injecting voltage into the phase-controlled arc-extinguishing coil. The voltage source circuit comprises a capacitor Xcx, a transformer T2, a solid-state switch and an alternating current power supply. The capacitor Xcx is used for voltage division and limiting voltage applied to the filter winding induction coil. The capacitor Xcx is connected in series at one side of the transformer T2, and the other side of the transformer T2 is connected in series with the solid-state switch, and one side of the solid-state switch is connected with the alternating current power supply.

2. A capacitive current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 1, characterized in that, The voltage source circuit further comprises a voltage-dependent resistor connected in parallel with the solid-state switch, and used for limiting voltage of the solid-state switch.

3. A capacitive current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 1, characterized in that, The solid-state switch uses a solid-state relay as a switch of the voltage source circuit.

4. A capacitive current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 3, characterized in that, The voltage source circuit further comprises a frequency divider connected with the solid-state relay, and used for sampling power frequency and controlling on-off time of the solid-state relay.

5. A capacitive current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 4, characterized in that, The frequency divider is a frequency divider for sampling alternating current 50HZ power frequency.

6. A capacitance current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 4, wherein The solid-state relay is a periodic relay with 2 seconds of on time and 80 seconds of off time.

7. A capacitance current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 1, wherein The transformer T2 is a double-winding transformer. The transformation ratio of the transformer T2 is 1:

1.

8. A capacitance current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 1, wherein The phase-controlled arc-extinguishing coil comprises a primary winding and a secondary winding. The primary winding is connected with a main circuit of a power grid. The filter winding is connected in parallel at two ends of the first secondary winding, and the second secondary winding is connected to a thyristor control circuit.

9. A capacitance current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 8, wherein, The filter winding comprises a capacitor Xc3, a reactance X13, a capacitor Xc5 and a reactance X15. The capacitor Xc3 and the reactance X13 are connected in series, and the series branch is connected in parallel at two ends of the first secondary winding. The capacitor Xc5 and the reactance X15 are connected in series, and the series branch is connected in parallel with the series branch of the capacitor Xc3 and the reactance X13.

10. A capacitance current measurement circuit for a phase-controlled arc suppression coil grounding system according to claim 1, wherein, The on angle of the phase-controlled arc-extinguishing coil ranges from 90° to 179°.

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