CN212410659U

CN212410659U - Asymmetric current source in low-current grounding system

Info

Publication number: CN212410659U
Application number: CN202020020283.7U
Authority: CN
Inventors: 薛占钰; 邢进春
Original assignee: Baoding Yuxin Electrical Technology Co ltd
Current assignee: Baoding Yuxin Electrical Technology Co ltd
Priority date: 2020-01-06
Filing date: 2020-01-06
Publication date: 2021-01-26
Anticipated expiration: 2030-01-06

Abstract

The utility model discloses an asymmetric current source in undercurrent ground system, including the independent high voltage switch of double-phase or three-phase, select a return line as first return line, high voltage switch one side and arbitrary double-phase or three-phase in the first return line intersect in the junction point, another side connects the earth, the one-way wire impedance of junction point position to power outlet or the one-way wire impedance of junction point position to power outlet and the current-limiting impedance sum between junction point position to the earth can make the size of short-circuit current not trigger I section overcurrent protection of first return line; the time for turning on and off the high-voltage switch can enable the duration of the short-circuit current to be smaller than the current duration of II-segment overcurrent protection of the first return line. The interphase short-circuit current manufactured by the device is obviously different from the line load current and is easy to identify.

Description

Asymmetric current source in low-current grounding system

Technical Field

The utility model relates to a detection technology that single-phase earth fault took place for 10KV or 35KV undercurrent grounding system's of electric power system circuit particularly, relates to the asymmetric current source of characteristic current for the manufacturing detection among the undercurrent grounding system.

Background

At present, most power distribution networks in China adopt a low-current grounding system (also called a neutral point indirect grounding system), the power distribution system has multiple and complex branches, and when single-phase grounding faults occur in the systems, the fault points are very difficult to find due to the fact that fault current is small and fault characteristics are complex.

Chinese utility model patent 201020549446.7 discloses an asymmetric current source, including secondary control part, electron PT, relay and interchange high pressure vacuum contactor, electron PT passes through the changer and inserts secondary control part's input, and secondary control part's output connects the relay coil, and relay control exchanges high pressure vacuum contactor's coil, and three interchange high pressure vacuum contactor once inclines respectively with A, B, C three-phase connection, and the opposite side is established ties and is connect D high-voltage diode and R current-limiting impedance, and another termination ground of R current-limiting impedance. Utility model patent 201220448758.8 has simplified aforementioned patent, only adopts two interchange high pressure vacuum contactor can realize corresponding function. In the patent, when a certain phase has a ground fault, the voltages of the other two phases to ground are increased and detected by an electronic PT, then a secondary control part controls one of the alternating current high-voltage vacuum contactors connected with the non-fault phase to be closed, so that the phase circuit is also connected with the ground, thus, a phase-to-phase short circuit is formed with the fault phase to generate a short-circuit current, the short-circuit current can generate a half-wave current after being rectified by a high-voltage diode, the short-circuit current has obvious characteristics when the current is large, the short-circuit current can be identified by a fault indicator on the three-phase circuit, and a ground fault point can be judged according to a loop where the short-. Both of the above two methods for generating characteristic current require a current-limiting impedance to be connected in series to avoid large-area power failure caused by overcurrent protection triggered by short-circuit current. However, since the contact point of the single-phase ground is unpredictable, the impedance value of the impedance in the short-circuit current loop cannot be determined, if the series impedance is too small, the current limiting protection cannot be performed, and if the series impedance is too large, the short-circuit current is too small to be detected, which limits the application of the method. Also for the above reasons, the above two patents are not ideal in practical use and are difficult to popularize.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing an asymmetric current source among undercurrent ground system, the alternate short-circuit current that the device produced obviously is different from circuit load current, very easily discerns, does not have current-limiting impedance's dilemma selection problem to can not make short-circuit current too big and trigger circuit protection action.

In order to achieve the purpose, the utility model adopts the following technical scheme:

an asymmetric current source in a small current grounding system comprises a two-phase independent or three-phase independent high-voltage switch, an outgoing line in the small current grounding system is selected as a first outgoing line, one side of the high-voltage switch is intersected with any two phases or three phases in the first outgoing line at a wiring point, the other side of the high-voltage switch is connected with the ground, when one phase of a certain return line in the small-current grounding system has a grounding fault and a high-voltage switch of a certain non-fault phase of the first return line is closed and opened to generate short-circuit current, the sum of the one-way wire impedance from the wiring point position to the power outlet of the low-current grounding system or the one-way wire impedance from the wiring point position to the power outlet of the low-current grounding system and the current-limiting impedance from the wiring point position to the ground can ensure that the I-section overcurrent protection of the first return line is not triggered by the magnitude of the short-circuit current; the time for switching on and off the high-voltage switch can enable the duration of the short-circuit current to be smaller than the current duration of II-segment overcurrent protection of the first return line.

Preferably, the predefinable impedance is defined as the impedance of the single-phase wire from the terminal point to the power outlet of the low-current grounding system or the sum of the impedance of the single-phase wire from the terminal point to the power outlet of the low-current grounding system and the impedance value of the current-limiting impedance connected in series, and then the terminal point position is determined as follows:

(a) supposing that the first return line generates a metallic two-phase direct short circuit at the power outlet of the low-current grounding system, and defining the short-circuit current at the moment as a limit short-circuit current;

(b) and (b) serially connecting a hypothetical impedance in the short-circuit loop of the step (a), so that the magnitude of the short-circuit current is reduced to be less than or equal to 0.9 times of the current fixed value of the I-section overcurrent protection of the first return line from the limit short-circuit current, the impedance value of the hypothetical impedance is the impedance value of the preset impedance, then calculating the length of the wire to be serially connected according to the impedance value of the preset impedance and the impedance of the wire with the unit length, and determining the position of the wiring point accordingly, or determining the position of the wiring point according to the difference of the impedance value of the current limiting impedance subtracted from the impedance value of the preset impedance and the impedance value of the wire with the unit length.

Preferably, the outgoing line with the smallest overcurrent protection current constant value in the I section of the outgoing lines of the low-current grounding system is selected as the first outgoing line.

Preferably, the high-voltage switch is closed and opened for a time period which enables the short-circuit current not to exceed one period.

Preferably, the short-circuit current duration is shorter than a half period, or equal to a half period, or longer than a half period and shorter than a period.

Preferably, the high-voltage switch comprises a vacuum bulb, a fixed contact and a movable contact are arranged in the vacuum bulb, the fixed contact of two phases or three phases is connected with two phases or three phases of the low-current grounding system, the movable contact is connected with the ground, and the movable contact can be close to the fixed contact under the driving of the movable contact driving mechanism and can be far away from the fixed contact under the driving of the movable contact resetting mechanism.

Preferably, the moving contact driving mechanism is provided with a power source of a first electromagnetic coil or a first spring, and the moving contact resetting mechanism is provided with a power source of a second spring or a second electromagnetic coil.

Preferably, a voltage transformer is arranged to monitor the voltage of the first return line, the voltage transformer is connected with the control unit, and the control unit controls the moving contact driving mechanism and the moving contact resetting mechanism to act.

Preferably, each high-voltage switch is formed by connecting a first high-voltage switch and a second high-voltage switch in series, the first high-voltage switch is in an open state, and the second high-voltage switch is in a closed state.

The utility model has the advantages of, the device starts to make the characteristic current as big as possible from the size of short-circuit current and long harmony to in order to detect. Because the contact fault point is unpredictable, then the wire impedance and the ground impedance of the fault line of the string-in short-circuit loop just become impedance value unpredictable impedance, and the utility model discloses the I section overcurrent protection that can guarantee not triggering the circuit of impedance self can be predetermine to the string-in, like this in addition above-mentioned unpredictable impedance, certainly can not trigger I section overcurrent protection, utilize simultaneously the utility model discloses the short-circuit current who produces also is the artificial maximum safe electric current that can control the production ("safety" indicates not triggering I section overcurrent protection), simultaneously the utility model discloses the high-voltage switch closed off speed need satisfy make the length of time of short-circuit current not trigger II section overcurrent protection. Do not have to current size and time long solution problem for prior art, the utility model discloses specially from short-circuit current's size and time long manufacturing problem who sets out solution characteristic current, the characteristic current that produces can generally be bigger than normal load current tens times or even hundreds of times, is detected very easily, provides the prerequisite condition for promoting practical and feasible ground fault point detection.

Drawings

FIG. 1 is a schematic diagram of the method of the present invention;

FIG. 2 is a schematic diagram of the external structure of a high voltage switch used in the present invention;

fig. 3 is a schematic sectional view of a high-voltage switch used in the present invention;

fig. 4 is a graph showing the wave recording curve of each electrical parameter in the simulation under 10 KV.

Fig. 5 is a schematic diagram of the relevant circuit in the test of fig. 4.

Detailed Description

The present invention will be further explained with reference to the accompanying drawings by way of specific embodiments, in which the low current grounding system comprises a three-phase system in which the neutral point is not grounded or is grounded via an arc suppression coil and a high impedance.

As shown in fig. 1, in the low-current grounding system, a power source has multiple return lines, one of the return lines is selected as a first return line, and when one phase of one of the return lines in the multiple return lines has a ground fault (for example, phase a), the other two phases (phase B and phase C) except phase a in the first return line are defined as non-fault phases. The utility model relates to a following mode of connection: any two phases of A, B, C three phases of the 10KV first return line are respectively connected to one end of two 10KV ac high-voltage vacuum contactors (i.e. high-voltage switches) K1 and K2 (three independent ac high-voltage vacuum contactors may also be respectively connected to the three phases), for example, A, B two phases (hereinafter, A, B two phases are taken as an example), the connection point of the two ac high-voltage vacuum contactors and A, B two phases is a point O and a point P, and the other end is directly connected to the ground or a current-limiting impedance is connected in series between the other end and the ground. The length of the wire that is connected in series between the high voltage switch and the power supply is determined by setting the location of the termination point (i.e., point O, P) to a wire impedance equal to the wire impedance per unit length multiplied by the wire length. When one phase (if is A phase) of a certain return line has a ground fault, the B phase high-voltage switch in the first return line is actuated to conduct with the ground, and a short-circuit current is generated. The impedance in the short circuit loop comprises the impedance of a single-phase wire between a wiring point position and a power supply, the impedance of a wire between a grounding point and the power supply and the grounding impedance (the impedance and the grounding impedance are unpredictable impedances with impedance values, cannot be artificially determined and can only be determined according to the fact that each grounding fault occurs), and the impedance in the short circuit loop also comprises a current-limiting impedance (which can be connected in series with the current-limiting impedance or not) which is connected in series between a high-voltage switch and the ground, and the impedance of the single-phase wire between the wiring point position and the power supply and the current-limiting impedance are combined. Therefore, can adjust the impedance size of predetermineeing through adjustment wiring point position to can influence the short-circuit current size, the utility model discloses the method requires to predetermine the impedance and will all make short-circuit current size can not trigger I section overcurrent protection under various earth fault, can specifically realize through following method:

(a) assuming that the first return line is in a metallic two-phase direct short circuit at the power outlet, and defining the short-circuit current at this time as a limit short-circuit current (because the maximum short-circuit current is generated at this time);

(b) a hypothetical impedance is connected in series in the short-circuit loop of the step (a), so that the magnitude of the short-circuit current is reduced from the limit short-circuit current to be less than or equal to 0.9 times (equal to 0.9 times is the optimal choice, the required maximum short-circuit current is generated, the current is reduced when the current is less than 0.9 times, but the current is clearly distinguished from the normal load current of the line, and the smooth detection can be realized, for a transformer substation provided with a protection device which can ensure that the I-section overcurrent protection fixed value which is 0.95 times is still reliably operated, the number can be adjusted to 0.95, the impedance value of the hypothetical impedance is the impedance value of the presettable impedance, then the length of the lead which should be connected in series is calculated according to the impedance value of the presettable impedance and the impedance of the lead with the unit length, and the position of the junction point is determined accordingly (at this time, the current limiting impedance is not connected in series, the high-voltage switch is directly connected with the ground, and the impedance between the wiring point position and the ground is generally negligible, so that the operation is simpler, the cost of current-limiting impedance is saved and the wiring point position is the best choice), or the wiring point position is determined according to the difference of the preset impedance value minus the impedance value of the current-limiting impedance and the impedance of a lead with unit length (the current-limiting impedance is connected in series at the moment, the impedance value of the current-limiting impedance is generally used for abutting against the single-phase lead impedance of the wiring point position to a power supply, namely, compared with the condition that the current-limiting impedance is not connected in series, if the wiring point position is closer to the power supply, the reduced impedance of the lead can be used as the current-limiting; of course, there are other combinations of current limiting impedance and the single-phase wire impedance in order to control the short-circuit current).

In the above scheme, for the situation that the cable thickness, material, line length and the like of each outgoing line are basically consistent, the I-section overcurrent protection constant values of each outgoing line are basically equal, and one outgoing line can be selected as a first outgoing line; for the conditions that the cable conditions are different greatly and the I-section overcurrent protection constant values are not equal, the I-section overcurrent protection constant value is the smallest as the first return line, so that when the short-circuit current does not trigger the I-section overcurrent protection of the first return line, the overcurrent protection from the grounding point in the short-circuit loop to the lead of the power supply is definitely not triggered.

Meanwhile, the duration of the short-circuit current is controlled through the on-off time of the high-voltage switch, so that the duration is not more than the current duration of the II-stage overcurrent protection (the duration is more than one period). Preferably, the current duration may be shortened to no more than one cycle, such as less than half a cycle, equal to half a cycle, or more than half a cycle and less than one cycle. In order to improve the easy detectability of the current waveform, the current transient waveform not greater than half period may be a positive half-wave or a negative half-wave (including a zero point), i.e., all of the current transient waveform are greater than or equal to zero, or all of the current transient waveform are less than or equal to zero. The current is dozens of times of the normal load current, the characteristic is very obvious and is very easy to detect by a fault indicator on a line, so that the characteristic current has very practical value, and the technical defect that the current as large as possible cannot be produced under the condition of ensuring no tripping operation in the prior art is overcome.

The following description is provided for how a high-voltage switch can be set to generate an alternating current of no more than one cycle during the on/off process, and can be described in two embodiments:

1. the high-voltage switch comprises only one switch (for example, only one vacuum AC contactor or breaker is used for switching on and off the circuit)

For a mechanical switch with a moving contact and a fixed contact, the key point is to control the moving contact to pass through alternating current of no more than one period in the process from the time when the moving contact is close to the fixed contact and a circuit is conducted to the time when the moving contact is far from the fixed contact and the circuit is cut off. The high-voltage switch can generally adopt a structure as shown in fig. 2 and 3, and comprises a vacuum bubble 50, a static contact 51 and a moving contact 52 are arranged in the vacuum bubble 50, one end of the static contact 51 extends out of the vacuum bubble 50 and is connected with a three-phase line, and the moving contact 52 extends out of the vacuum bubble 50 and is connected with a moving contact driving mechanism and a moving contact resetting mechanism and is also connected with a grounding wire. The moving contact driving mechanism can drive the moving contact to move towards the fixed contact, and the moving contact resetting mechanism can drive the moving contact to be far away from the fixed contact. In one embodiment, the movable contact driving mechanism includes a connecting rod 53 having one end connected to the movable contact, the other end of the connecting rod 53 is connected to a side panel 541 of the metal angle plate 54 hinged to the base, the other side panel 542 of the metal angle plate 54 is substantially perpendicular to the panel 541 and can be attracted by the electromagnetic coil 55, and a pin 543 is provided at both ends of the connection between the panel 541 and the panel 542 and is hinged to the base 59 through the pin. When the electromagnetic coil 55 attracts the panel 542, the metal angle plate 54 rotates, and the panel 541 pushes the connecting rod 53 upward and further pushes the movable contact 52 toward the stationary contact. The connecting rod 53 is further sleeved with a spring 56, when the connecting rod 53 pushes the movable contact 52 to move towards the fixed contact 51, the spring 56 is compressed, and when the electromagnetic coil 55 is de-energized and the magnetic force of the electromagnetic coil disappears, the spring 56 pushes the panel 541 downwards, so that the connecting rod 53 moves downwards, and the movable contact 52 is separated from the fixed contact 51. And other moving contact driving mechanisms and moving contact resetting mechanisms for driving the moving contacts to be close to the fixed contacts and to be far away from the fixed contacts. The power source of the moving contact driving mechanism can be an electromagnetic coil or a spring, and the power source of the moving contact resetting mechanism can be a spring or an electromagnetic coil.

Referring to the above-mentioned high-voltage switch structure and referring to fig. 1, the voltage transformers PT 1, PT 3, PT 5 collect corresponding phase voltage signals and send the phase voltage signals to the control unit, i.e., the input terminals UA, UB, UC of the secondary control portion. The control unit is internally transmitted to the singlechip through a secondary PT and digital-to-analog conversion unit, finally, electromagnetic coils of moving contact driving mechanisms of two 10KV alternating-current high-voltage vacuum contactors K1 and K2 are controlled through a relay, a moving contact resetting mechanism of a high-voltage switch (alternating-current high-voltage vacuum contactor) is a spring, and after the electromagnetic coils of the moving contact driving mechanisms are de-energized, the spring drives the moving contact to move towards the original position. The speed of the moving contact close to the static contact is controlled by the power of an electromagnetic coil of the moving contact driving mechanism, and the speed of the moving contact far away from the static contact is controlled by adjusting the restoring force of the spring. When the electromagnetic coil of the moving contact driving mechanism is powered on, the moving contact is driven to move towards the fixed contact, the spring is stretched, the moving contact overcomes the restoring force of the spring, and when the electromagnetic coil of the moving contact driving mechanism is powered off, the moving contact is only subjected to the restoring force of the spring and is far away from the fixed contact under the action of the restoring force, and a circuit is cut off.

Specifically, the process of analyzing that the moving contact approaches the fixed contact, conducts the line, then leaves the fixed contact again and cuts off the line can include the following five stages: 1. the moving contact starts to move, namely the moving contact obtains acceleration from a state that the initial speed is zero and moves towards the direction of the static contact under the driving of the moving contact driving mechanism, and at the moment, the moving contact only does mechanical motion and does not conduct a circuit; 2. when the moving contact approaches the static contact to a certain degree, the line is conducted (at the moment, the phase of the voltage at two ends of the switch is a closing phase angle), the moving contact may just physically contact the static contact, and a certain distance may exist between the moving contact and the static contact, and only if the distance is small enough, the moving contact is no longer an insulation distance under the voltage condition at the moment; 3. the electromagnetic coil of the moving contact driving mechanism loses power, namely loses the acceleration close to the static contact, but still keeps the initial speed close to the static contact (if the static contact is contacted when losing power, the initial speed is not provided), and meanwhile, the restoring force of the spring starts to act independently to generate the acceleration far away from the static contact, and because the moving contact is still close to the static contact or is contacted yet to be separated at the moment, the circuit is still conducted; 4. the moving contact moves towards the direction far away from the static contact until the insulation distance between the moving contact and the static contact is reached, and at the moment, the circuit is cut off; 5. the moving contact moves further away when the insulation distance between the moving contact and the fixed contact is reached until the moving contact returns to the initial position.

To the utility model discloses, the key lies in the process in above-mentioned 2 nd to 4 th stage, because this process is the whole process that the circuit switched on to cutting off, also is the process that short-circuit current exists, and the time of this process also is short-circuit current's time, the utility model discloses it is long when requiring the alternating current of this process not to exceed II sections overcurrent protection's electric current, preferably not to exceed a cycle, more preferably not to exceed half cycle, to the electric power system of china, a cycle is 20 milliseconds promptly. Under the premise, the on-off time of the high-voltage switch can be further shortened, so that the current does not exceed a half cycle. The speed of the moving contact approaching the static contact and the speed of the moving contact far away from the static contact can be controlled by only adjusting the power of an electromagnetic coil of a moving contact driving mechanism of the alternating-current high-voltage vacuum contactor and the elastic force (such as the elastic coefficient of an adjusting spring) of a moving contact resetting mechanism spring, so that the on-off time of a circuit is controlled. The short-circuit current can not exceed a half period by adjusting the matching of the power of an electromagnetic coil of the moving contact driving mechanism and the restoring force of the moving contact resetting mechanism. If the power of the electromagnetic coil and the restoring force of the spring are given, the duration of the current can be controlled by adjusting the initial distance between the moving contact and the fixed contact.

When the asymmetric current source is used for single-phase earth fault detection, when one phase line of a certain return line has an earth fault, a voltage transformer detects that the fault phase voltage is reduced and the non-fault phase voltage is increased, and transmits a signal to a control unit, the control unit controls a driving electromagnetic coil of a non-fault alternating current high-voltage vacuum contactor to act through a relay to start driving a moving contact to approach a static contact, and when the moving contact approaches a conducting circuit, alternating voltages at two ends of a high-voltage switch, namely a voltage closing phase angle, can control the voltage closing phase angle to be 0-90 degrees, preferably 75-90 degrees. Because the magnitude of the current during conduction is determined by the magnitude of the voltage closing phase angle, when the voltage closing phase angle is 75-90 degrees, the current is larger and the detection is easier when the positive voltage rises to a higher voltage value. The following describes how to control the magnitude of the voltage closing phase angle by taking the control voltage closing phase angle as zero as an example: the movement of the moving contact needs to be coordinated with the change of the alternating voltage, and the design can be generally carried out according to the following principle that when a ground fault occurs and is detected by a control unit, the control unit firstly acquires the future zero crossing point moment of the alternating voltage of a circuit to be switched on where the high-voltage switch is located (the future zero crossing point moment can be acquired by a zero crossing and voltage period detection circuit, and the prior art), and can also determine the time delta t required by the alternating-current high-voltage vacuum contactor from the beginning of driving the moving contact to the line connection through a preliminary test_aSo that the control unit precedes the voltage zero crossing by Δ t_aWhen the electromagnetic coil of the alternating-current high-voltage vacuum contactor starts to act, the alternating voltage at two ends of the high-voltage switch just crosses a zero point when the moving contact and the static contact approach to a conducting circuit, namely, the voltage switching-on phase angle is zero. Before the zero crossing point, Δ t_aThe time of the step (a) is the preset time.

The method for controlling the voltage switching phase angle to be 75 degrees, 90 degrees and the like is similar to the method.

The above describes how to set the time when the movable contact drive starts to operate, but it is also important when the movable contact drive stops, from which point it acts as a spring to act alone and move the movable contact finally away from the stationary contact to break the circuit. The duration of the short-circuit current is determined by the time that the driven contact driving mechanism drives the moving contact to conduct the circuit and then stops acting on the moving contact, and then the moving contact resetting mechanism acts independently and enables the moving contact to leave the fixed contact to cut off the circuit. The control unit may be provided with a time Δ t from the time of issuing a closing command_bAfter the time, the electromagnetic coil of the movable contact driving mechanism loses power, and the spring acts independently immediately. The Δ t_bThe time can be determined by offline testing to ensure that the short circuit current does not exceed one cycle, such as by controlling the alternating current to be half a cycle or less.

Fig. 3 shows the wave-recording curves of the wave-recorder for a plurality of electrical parameters when the high-voltage switch is switched on and off under the conditions of small current and 10KV voltage, the test has been adjusted so that the voltage switching-on phase angle is zero and the current passing does not exceed one cycle. The curve a is a voltage change curve at two ends of the high-voltage switch, the curve c is a high-voltage switch voltage zero-crossing detection signal, the vertex of each peak on the curve c is a voltage zero-crossing point, and the high-voltage switch is seen to be in periodic change before being closed. When the high-voltage switch is closed to make the line start to conduct, the voltage across the high-voltage switch is zero (curve a), and the position of a dotted line L is seen, and at this time, the voltage coincides with the time point of the periodic zero crossing point of the voltage (the conclusion can be obtained by comparing curves a and c), which indicates that the voltage closing phase angle is zero, and the voltage of the high-voltage switch is always zero after a period of time, which indicates that the process is a process that the high-voltage switch continuously conducts current from the conducting line, and curve e is a current curve flowing through the high-voltage switch. The time on the abscissa of curve e corresponding to the dashed line M is the time when the current is zero, at which time the line is cut off and the voltage across the high-voltage switch starts to change again in a wave form (curve a). The portion of the curve e between the dashed line L and the dashed line M is the alternating current not exceeding one cycle, in particular the half-cycle alternating current plus the decay current of the half-cycle alternating current after flowing through the zero point. The reason for the generation of the decaying current may be that the moving contact is not far away from the static contact in the second half period of conduction to be able to cut off the circuit, and as the voltage is reversed, a reversed current is generated, but decays to zero quickly, so that the whole current does not exceed one period. If the spring restoring force increases such that the moving contact just leaves the stationary contact breaking circuit during the conducting half cycle, the current may be just half cycle. The half-cycle alternating current or the half-cycle alternating current plus the attenuation current is not more than one cycle of alternating current, the current value is large, the characteristics are obvious, and the detection is easy. Curve b in fig. 3 is a voltage curve of the electromagnetic coil of the movable contact driving mechanism of the high-voltage switch, and curve d is a voltage curve of the direct-current solid-state relay controlling the electromagnetic coil of the movable contact driving mechanism. Fig. 5 shows the relevant circuit for this experiment. The circuit further comprises an electromagnetic coil 87 of a moving contact driving mechanism, a current transformer 88, a voltage transformer 1, a secondary PT83, a zero-crossing detection circuit 86, a direct-current fixed relay 84 for controlling the electromagnetic coil 87, a direct-current Hall element 82 and a control device 85. Wherein, the secondary PT83 collects the high-voltage switch voltage corresponding to the curve a; the electromagnetic coil 87 of the moving contact driving mechanism corresponds to the curve b, and the zero-crossing detection corresponds to the curve c; the direct current solid relay corresponds to a curve d; the current transformer 88 is used to obtain the load current, curve e.

2. The high-voltage switch is formed by mutually matching two switches

The high-voltage switch is formed by connecting a first high-voltage switch and a second high-voltage switch in series, the first high-voltage switch is in an off state, the second high-voltage switch is in an on state, and the time length of the short-circuit current is controlled not to exceed a period through the time difference of closing the first high-voltage switch and opening the second high-voltage switch.

In order to control the duration of the current, the utility model patent ZL201921412022.3 requests to protect a switch structure for controlling the on-off of a single-phase line in a short time, and the content of this patent is used for solving the control of the duration of the short-circuit current in this patent in a manner of introducing the whole text, so that the duration of the short-circuit current is not more than the duration of the current of the II-section overcurrent protection, preferably not more than a cycle, preferably half a cycle, even shorter than half a cycle. When the voltage closing phase angle is just 90 degrees and the short-circuit current duration is a quarter cycle, short-circuit pulse currents with current values all larger than or equal to zero or all smaller than or equal to zero and large absolute values can be obtained, and the possibility of detection is further increased.

In addition, if the high-voltage power electronic switch is adopted, the response is very timely because the high-voltage power electronic switch does not have the mechanical motion of the alternating-current high-voltage vacuum contactor, the high-voltage power electronic switch can be directly conducted on a line at the zero crossing point of the voltage, and the line is cut off after one period (20 ms) or half period (10 ms). I.e. the best control mode of the electronic switch is that the voltage is conducted at zero crossing and the current is cut off at zero crossing.

The above embodiments are only a few descriptions of the concept and implementation of the present invention, and are not intended to limit the scope of the present invention.

Claims

1. An asymmetric current source in a small current grounding system comprises a two-phase independent or three-phase independent high-voltage switch, an outgoing line in the small current grounding system is selected as a first outgoing line, one side of the high-voltage switch is intersected with any two phases or three phases in the first outgoing line at a wiring point, the other side of the high-voltage switch is connected with the ground, it is characterized in that when one phase of a certain return line in the small-current grounding system has a grounding fault and a high-voltage switch of a certain non-fault phase of the first return line is closed and opened to generate short-circuit current, the sum of the one-way wire impedance from the wiring point position to the power outlet of the low-current grounding system or the one-way wire impedance from the wiring point position to the power outlet of the low-current grounding system and the current-limiting impedance from the wiring point position to the ground can ensure that the I-section overcurrent protection of the first return line is not triggered by the magnitude of the short-circuit current; the time for switching on and off the high-voltage switch can enable the duration of the short-circuit current to be smaller than the current duration of II-segment overcurrent protection of the first return line.

2. The asymmetric current source as claimed in claim 1, wherein the outgoing line with the smallest constant value of I-section overcurrent protection current is selected as the first outgoing line in the outgoing lines of the low-current grounding system.

3. The asymmetric current source of claim 1, wherein said high voltage switch is closed and open for a time such that said short circuit current does not exceed a period.

4. An asymmetric current source as claimed in claim 3, in which the short circuit current is shorter than half a period, or equal to half a period, or longer than half a period and shorter than one period.

5. The asymmetric current source as claimed in claim 1, wherein the high voltage switch includes a vacuum bulb, a static contact and a moving contact are disposed in the vacuum bulb, the static contact of two phases or three phases is connected to the two phases or three phases of the low current grounding system, the moving contact is connected to the ground, and the moving contact can be driven by the moving contact driving mechanism to approach the static contact and can be driven by the moving contact resetting mechanism to be away from the static contact.

6. The asymmetric current source of claim 5 wherein the motive power source for the movable contact drive mechanism is a first solenoid or a first spring and the motive power source for the movable contact return mechanism is a second spring or a second solenoid.

7. The asymmetric current source as claimed in claim 5 wherein a voltage transformer is provided to monitor the voltage of said first return line, the voltage transformer being connected to a control unit which controls the operation of said movable contact drive mechanism and movable contact reset mechanism.

8. The asymmetric current source of claim 1, wherein each said high voltage switch is comprised of a first high voltage switch in series with a second high voltage switch, said first high voltage switch being in an open state and said second high voltage switch being in a closed state.