Insulation fault detection circuit and ungrounded system

Abstract

The present invention discloses an insulation fault detection circuit for an ungrounded system. The ungrounded system is provided with a first connection end and a second connection end connected to a main line, and the main line is connected to a plurality of branches, mainly including: at least one equipotential terminal; a first detection loop providing circuit coupled between the first connection end and the equipotential terminal, or / and, a second detection loop providing circuit coupled between the second connection end and the equipotential terminal; a plurality of insulation resistors coupled between one side of each branch and the equipotential terminal, or / and, a plurality of insulation resistors coupled between the other side of each branch and the equipotential terminal, or / and, an insulation resistor coupled between one side of the main line and the equipotential terminal, or / and, an insulation resistor coupled between the other side of the main line and the equipotential terminal; wherein: the insulation resistor can form a detection loop with the first / second detection loop providing circuit, wherein a leakage current for indicating an insulation fault can be generated on the detection loop.

Description

Technical Field

[0001] The present invention belongs to the field of insulation detection circuits, and in particular relates to an insulation fault detection circuit for an ungrounded system and an ungrounded system applying the insulation fault detection circuit. Background Art

[0002] Insulation detection and leakage protection are widely used in grounding systems, where the grounding system includes ordinary 220V single-phase AC systems or three-phase four-wire systems.

[0003] Figure 1 A grounding system is shown, which is provided with a ground terminal G, and a live terminal L and a neutral terminal N as outputs connected to the main circuit. L , I N is the main circuit current, where: several branches are drawn from the main circuit to connect and drive various loads, I L1 , I N1 The main circuit is equipped with a leakage current protection switch (LB0), while the branches are equipped with leakage current protection switches (LB1 and LB2). In a grounding system, both the main circuit and the branches are coupled to the ground terminal (G). When leakage currents (Iag and Ibg) flow to the ground terminal on the corresponding lines, the leakage current protection switches (LB0 and LB2) are turned off.

[0004] CN114430159A discloses a DC microgrid system with independent branch leakage detection and protection. Each branch is equipped with a leakage protector (which has the same function as the leakage protection switch). The leakage protector includes: a leakage current detection element, a tripping device, and an arc extinguishing device.

[0005] Alternatively, insulation resistance can be measured to determine whether an insulation fault exists in the system. For example, CN105356848A discloses an insulation impedance detection device for a multi-channel MPPT input photovoltaic inverter, and CN211905521U discloses an insulation impedance detection circuit and its application device. These devices calculate the insulation resistance using a combination of an external resistor and a relay. However, these technical solutions lack the ability to indicate the specific fault point. When the branch circuit is large, the inability to quickly determine the fault point affects system stability and maintenance efficiency.

[0006] Figure 2 This diagram illustrates an ungrounded system. Due to the lack of a ground terminal and the absence of a ground loop, leakage protection through leakage current detection is objectively impossible. Both the live terminal (L) and the neutral terminal (N) are suspended relative to the ground. The insulation resistances Rp and Rn between the live terminal (L) and the ground terminal are extremely high, both exceeding the Ω level. When insulation damage occurs, the insulation resistances Rp and Rn drop significantly, forming a leakage loop and generating leakage current.

[0007] In an ungrounded system, when a single-ended insulation fault occurs in the live or neutral wire, no leakage current will be generated, so leakage protection cannot be achieved by detecting leakage. Summary of the Invention

[0008] On the one hand, in order to realize insulation fault detection in an ungrounded system, the present invention provides an insulation fault detection circuit for being configured in the ungrounded system. By detecting insulation faults, protective measures can be taken before leakage actually occurs to realize leakage protection.

[0009] The ungrounded system is provided with a first connection end and a second connection end for connecting a load to form a power supply circuit. The first and second connection ends of the ungrounded system are connected to a trunk line, which is connected to a plurality of branches, and the load is usually connected to the branches.

[0010] The insulation fault detection circuit mainly includes a first detection loop providing circuit and / or a second detection loop providing circuit.

[0011] The first detection loop providing circuit includes a first switch circuit coupled between the first connection terminal and an equipotential terminal of the ungrounded system.

[0012] Preferably, the first detection loop providing circuit further includes a first current suppression circuit.

[0013] One end of the first switch circuit is connected in series with the first connection end of the ungrounded system and is connected to the main line of the ungrounded system. The first current suppression circuit is coupled in series between the other end of the first switch circuit and the equipotential end.

[0014] An insulation resistor Rni is coupled in series between one end of each branch of the ungrounded system and the equipotential terminal. A detection loop is formed along the first switch circuit, the first current suppression circuit, the equipotential terminal, and each insulation resistor Rni when the first switch circuit is closed.

[0015] For any branch, if an insulation failure occurs on one side of the series insulation resistor Rni in that branch, its resistance will decrease. Thus, when the first switching circuit is turned on, the leakage current generated in the branch with the insulation failure increases compared to the leakage current generated in a normal insulation state. According to Ohm's law, an increase in leakage current reflects a decrease in insulation resistance. This leakage current can be used to indicate an insulation failure and can be collected and read by a detection circuit, such as a sensor.

[0016] Furthermore, each branch of the ungrounded system is equipped with a leakage protection switch (LBi). The leakage protection switch (LBi) and the insulation resistor (Rni) are located in the same branch. When the leakage protection switch (LBi) detects that the leakage current in the circuit containing the insulation resistor (Rni) reaches or exceeds its operating current, the leakage protection switch (LBi) activates, cutting off the power supply to the branch.

[0017] The second detection loop providing circuit includes a second switch circuit coupled between the second connection terminal and an equipotential terminal of the ungrounded system.

[0018] Preferably, the second detection loop providing circuit further includes a second current suppression circuit.

[0019] One end of the second switch circuit is connected in series with the second connection end of the ungrounded system. The second current suppression circuit is coupled in series between the other end of the second switch circuit and the equipotential end.

[0020] One end of the second switch circuit is connected in series with the second connection end of the ungrounded system and is connected to the main line of the ungrounded system. The second current suppression circuit is coupled in series between the other end of the second switch circuit and the equipotential end.

[0021] An insulation resistor Rpi is coupled in series between the other end of each branch of the ungrounded system and the equipotential terminal. A detection loop is formed by sequentially following each insulation resistor Rpi, the equipotential terminal, the second current suppression circuit, and the second switch circuit. When the second switch circuit is closed, a detection loop is formed. Similarly, when the leakage protection switch LBi on a branch detects that the leakage current in the loop containing the insulation resistor Rpi reaches or exceeds its operating current level, the leakage protection switch LBi operates, cutting off power to that branch.

[0022] Furthermore, a leakage protection switch LB0 is provided on the main line connected to the ungrounded system. A first current suppression circuit is coupled in series between one side of the main line and the equipotential terminal, and / or a second current suppression circuit is coupled in series between the other side of the main line and the equipotential terminal.

[0023] An insulation resistor Rpa is coupled between the side of the main line connected to the first connection end of the ungrounded system and the equipotential terminal. A detection loop is formed along the insulation resistor Rpa, the equipotential terminal, the second current suppression circuit, and the second switch circuit. When the second switch circuit is turned on, a detection loop is formed. When the leakage protection switch LB0 on ​​the main line detects that the leakage current in the loop containing the insulation resistor Rpa reaches or exceeds its operating current level, the leakage protection switch LB0 activates, disconnecting the main line.

[0024] An insulation resistor Rpb is coupled between the side of the main line connected to the second connection end of the ungrounded system and the equipotential terminal. A detection loop is formed by sequentially following the insulation resistor Rpb, the equipotential terminal, the first current suppression circuit, and the first switch circuit. When the first switch circuit is turned on, a detection loop is formed. When the leakage protection switch LB0 on ​​the main line detects that the leakage current in the loop containing the insulation resistor Rpb reaches or exceeds its operating current level, the leakage protection switch LB0 activates, disconnecting the main line.

[0025] As described above, when an insulation fault occurs on either side of the main line or each branch line, the equipotential terminals and the first and second switch circuits that can be connected form a loop, allowing leakage current to form, thus achieving insulation fault detection. This overcomes the disadvantage of ungrounded systems that cannot detect leakage current due to the lack of ground connection.

[0026] The first and second switch circuits can be turned on or off according to settings, and the first and second switch circuits do not need to be normally closed, thereby having better flexibility.

[0027] When the first and second switching circuits are off or there is no insulation fault, no leakage current is generated, or the leakage current is very small. When each of the detection loops is formed, the parallel connection of the resistor between the positive and negative electrodes is equivalent to adding a low-frequency common-mode voltage to the entire system, which does not affect the operation of the ungrounded system and maintains normal and stable operation of the system.

[0028] In addition, compared with the leakage current that actually causes harm, the leakage current introduced by the operation of the first and second switching circuits can eliminate insulation faults before the leakage current that may cause harm is generated, thereby achieving pre-emptive protection.

[0029] Preferably, the equipotential terminal is grounded.

[0030] On the other hand, the present invention provides an ungrounded system equipped with the insulation fault detection circuit. By detecting insulation faults, protective measures can be taken before leakage actually occurs, thereby achieving leakage protection.

[0031] In summary, the present invention, by providing a first detection loop providing circuit and / or a second detection loop providing circuit, together with the insulation resistance of the branch and main circuits, forms a detection circuit. This allows for single-ended insulation fault detection in branches and main circuits, and localizes branch faults, facilitating the execution of protective actions and notification of maintenance personnel. Consequently, the present invention achieves insulation fault detection in ungrounded systems with advantages such as reliability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the existing AC grounding system.

[0033] Figure 2 Schematic diagram of an existing ungrounded system.

[0034] Figure 3 Schematic diagram of an ungrounded system and its insulation fault detection circuit in an embodiment.

[0035] Figure 4 FIG. 4 is a schematic block diagram of an insulation fault detection circuit according to an embodiment.

[0036] Figure 5 FIG. 4 is a schematic block diagram of an insulation fault detection circuit according to another embodiment.

[0037] Figure 6 Schematic diagram of the control connection between the control module and the first and second switch circuits in the embodiment.

[0038] Description of the figure number:

[0039] 100. Ungrounded system, 200. Trunk line, 300. Branch line, 400. Load.

[0040] 500. First detection loop providing circuit, 510. First switching circuit, 520. First current suppression circuit.

[0041] 600. Second detection loop providing circuit, 610. Second switching circuit, 620. Second current suppression circuit.

[0042] 700. Equipotential terminal, 800. Control module. DETAILED DESCRIPTION

[0043] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0044] like Figure 3 As shown, an ungrounded system 100 includes a first connection terminal L and a second connection terminal N, a main circuit 200 connected to the first connection terminal L and the second connection terminal N, and a plurality of branches 300. The number N of branches 300 satisfies N ≥ 1. In actual grid systems, there are many branches 300. As an example, two branches 300 are shown in the figure. Each branch 300 is connected to a corresponding load 400. In the figure, load 400 connected to one branch 300 is load 1, and load 400 connected to the other branch is load 2.

[0045] In general circuits, the first connection terminal L and the second connection terminal N correspond to the positive and negative poles. When used in a civil power grid, the first connection terminal L and the second connection terminal N correspond to the live and neutral wire terminals to connect the live and neutral wires.

[0046] In this embodiment, the insulation fault detection circuit mainly includes a first detection circuit providing circuit 500. Figure 4 As shown, the first detection loop providing circuit 500 includes a first switch circuit 510. Preferably, the first detection loop providing circuit 500 further includes a first current suppression circuit 520 connected in series with the first switch circuit 510.

[0047] The first detection loop providing circuit 500 is coupled between the main line 200 and the equipotential terminal 700 of the ungrounded system 100, wherein: one end of the first detection loop providing circuit 500 is connected to the side of the main line 200 connected to the first connection terminal L, and further connected to the positive electrode; the other end of the first detection loop providing circuit 500 is connected to the equipotential terminal 700.

[0048] An insulation resistor Rni is coupled between the side of any branch 300 of the ungrounded system 100 connected to the negative electrode and the equipotential terminal 700 .

[0049] When the first switch circuit 510 is closed, a closed loop is formed along the positive electrode, the first detection loop providing circuit 500, the equipotential terminal 700, the insulation resistor Rni, and the negative electrode. If an insulation fault occurs in the insulation resistor Rni on the branch 300 corresponding to this loop, a leakage current will be generated in this loop.

[0050] The first current suppression circuit 520 may be used to suppress the leakage current and improve safety.

[0051] In another embodiment, the insulation fault detection circuit mainly includes a second detection loop providing circuit 600. Figure 5 As shown, the second detection loop providing circuit 600 includes a second switch circuit 610. Preferably, the second detection loop providing circuit 600 further includes a second current suppression circuit 620 connected in series with the second switch circuit 610.

[0052] The second detection loop providing circuit 600 is coupled between the main line 200 and the equipotential terminal 700 of the ungrounded system 100, wherein: one end of the second detection loop providing circuit 600 is connected to the side of the main line 200 connected to the second connection terminal N, and then connected to the negative pole; the other end of the second detection loop providing circuit 600 is connected to the equipotential terminal 700.

[0053] An insulation resistor Rpi is coupled between the side of any branch 300 of the ungrounded system 100 connected to the positive electrode and the equipotential terminal 700 .

[0054] When the second switch circuit 610 is closed, a closed loop is formed along the positive electrode, the insulation resistor Rpi, the equipotential terminal 700, the second detection circuit providing circuit 600, and the positive electrode. If an insulation fault occurs in the insulation resistor Rpi on the branch 300 corresponding to this loop, a leakage current will be generated in this loop.

[0055] The second current suppression circuit 620 may be used to suppress the leakage current and improve safety.

[0056] In some embodiments, the insulation fault detection circuit includes a first detection loop providing circuit 500 and a second detection loop providing circuit 600 to detect insulation faults on both sides of the branch 300 .

[0057] The insulation resistors Rni and Rpi on different branches 300 are correspondingly and independently coupled to the first detection loop providing circuit 500 and the second detection loop providing circuit 600. When leakage current occurs in the loop of a branch 300, the leakage current can be sampled and detected by a detection device such as a sensor, and the branch 300 can be located for maintenance and treatment.

[0058] Back to Figure 3 As shown, further, a leakage protection switch is provided on the branch 300. The branch 300 where load 1 is located is provided with a leakage protection switch LB1, and the branch 300 where load 2 is located is provided with a leakage protection switch LB2.

[0059] In an actual circuit, the insulation resistors Rni and Rpi have relatively large resistance values, and when insulation failure occurs, the resistance values ​​decrease.

[0060] For example, if an insulation fault occurs on the negative side of load 2, the corresponding insulation resistor Rni decreases. Leakage protection switch LB2 detects this change by monitoring the leakage current. When the leakage current reaches a certain level, it cuts off the power to branch 300 where load 2 is located, implementing leakage protection. If an insulation fault occurs on the positive side of load 2, leakage protection switch LB2 also detects the leakage current and, when the leakage current reaches a certain level, shuts off the power supply.

[0061] In this embodiment, an insulation resistor Rpa is coupled between the side of the trunk line 200 connected to the first connection terminal L and the equipotential terminal 700. Figure 4 As shown, when an insulation fault occurs in the insulation resistance Rpa, a leakage circuit may be formed with the second detection circuit providing circuit 600 .

[0062] In some embodiments, an insulation resistor Rna is coupled between the side of the trunk line 200 connected to the second connection terminal N and the equipotential terminal 700. Figure 5As shown, when an insulation fault occurs in the insulation resistor Rna, it can form a leakage circuit with the first detection circuit providing circuit 500.

[0063] Furthermore, the trunk line 200 is provided with a leakage protection switch LB0, which can detect leakage current caused by a failure of either the insulation resistor Rna or the insulation resistor Rpa, and can perform power-off protection when the leakage current reaches a certain level.

[0064] Preferably, the first current suppression circuit 520 is a resistor Rp0, and the second current suppression circuit 620 is a resistor Rn0.

[0065] Preferably, the equipotential terminal 700 is a ground terminal.

[0066] In this embodiment, in the initial state, the first switch circuit 510 and the second switch circuit 610 are both in the off state, and no leakage circuit is formed. When the insulation fault detection circuit is in operation, the first switch circuit 510 and the second switch circuit 610 are alternately connected, or alternately connected at a certain time interval.

[0067] like Figure 3 As shown, the first switch circuit 510 is a switch S1 , and the second switch circuit 610 is a switch S2 .

[0068] The first switch circuit 510 and the second switch circuit 610 are preferably controlled switches.

[0069] Combine Figure 6 As shown, the first switch circuit 510 and the second switch circuit 610 are connected to a control module 800. The control module 800 can be a control system such as a PLC or a single-chip microcomputer. The control module 800 sends control signals / instructions to the first switch circuit 510 and the second switch circuit 610 to control their on / off states.

[0070] The first switch circuit 510 is closed for a period of time and then opens. The second switch circuit 610 is closed for a period of time after the first switch circuit 510 opens. The time when either switch circuit is closed is the detection window time. During this time, a loop is formed with the insulation resistance on one side of the main circuit 200 and the branch circuit 300.

[0071] In other embodiments, the first switch circuit 510 and the second switch circuit 610 are tested at intervals and in a cycle. For example, in terms of timing, within one cycle, the following actions are performed sequentially: the first switch circuit 510 is closed for 1 second, the first switch circuit 510 is opened for 4 seconds, the second switch circuit 610 is closed for 1 second, and the second switch circuit 610 is opened for 4 seconds. The closing and opening times of the first switch circuit 510 and the second switch circuit 610 can also be adjusted as needed.

[0072] From the end of the main line 200 connected to the ungrounded system 100 to the end of the main line 200 connected to the branch line, the following connections / couplings are provided in sequence: leakage protection switch LB0, first and second detection loop providing circuits 500 and 600, and insulation resistance.

[0073] like Figure 3 As shown, insulation damage occurs at point A of circuit 200, with an insulation resistance of Rpa. When switch S2 is closed, insulation resistance Rpa forms a loop with resistor Rn0 via ground, generating leakage current Iag. This leakage current Iag flows only through leakage protection switch LB0, not through LB1 or LB2, and therefore only triggers LB0.

[0074] like Figure 3 As shown, if insulation damage occurs at point B of branch 300, with an insulation resistance of Rnb, then while switch S1 is closed, insulation resistance Rnb forms a loop with resistor Rp0 via ground, generating leakage current Ibg. This leakage current Ibg flows only through leakage protection switch LB2, not through LB1 or LB0, and therefore only triggers LB2 to operate.

[0075] Take the leakage protection switch LB0 as an example. Under normal circumstances, Rp0 = Rn0. Let Ip be the operating current of the leakage protection switch. When the operating current Ip is generated, the insulation resistance drops to R0. The system voltage is U, and Rp0 = Rn0 = U / Ip-R0.

[0076] The leakage protection time is Tp, which is the working parameter of the leakage protection switch. It refers to the time between the occurrence of a fault and the execution of the switch action, which is generally within 0.1 seconds. For any switch circuit, the detection window time in the closed state is Tw, and the time in the open state between two adjacent detections is the interval time Tb. Preferably, it can be set to Tp < Tw, Tw < Tb. Further preferably, Tw = 2Tp ~ 3Tp, Tb = 10Tw ~ 100Tw, that is, on the one hand, the detection window time must be greater than the leakage protection time to ensure that the leakage protection can operate normally, and on the other hand, the detection window time does not need to be too long to avoid unnecessary leakage current loss. Preferably, the value of Tw is in the millisecond level, within 1 second; the interval time Tb is as long as possible on the one hand, and on the other hand, it does not affect safety due to being too long. The value of Tb is about several seconds to several minutes.

[0077] The embodiments of the present invention are only used to illustrate the present invention and do not limit the scope of the claims. Other substantially equivalent alternatives that can be thought of by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. An insulation fault detection circuit for an ungrounded system, wherein: The ungrounded system is provided with a first connection end and a second connection end for connecting a main line, wherein the main line is used to connect a plurality of branches; the plurality of branches are provided with a plurality of insulation resistors Rni coupled between one side of each branch and an equipotential terminal, or / and, a plurality of insulation resistors Rpi coupled between the other side of each branch and the equipotential terminal; or / and, the main line is provided with an insulation resistor Rna coupled between one side of the main line and the equipotential terminal, or / and, an insulation resistor Rpa coupled between the other side of the main line and the equipotential terminal; characterized in that the insulation fault detection circuit includes: At least one equipotential terminal; a first detection loop providing circuit coupled between the first connection terminal and the equipotential terminal, or / and a second detection loop providing circuit coupled between the second connection terminal and the equipotential terminal; The first detection loop providing circuit includes a first switch circuit; the second detection loop providing circuit includes a second switch circuit; The first switch circuit and the second switch circuit are connected to the control module, and the control module sends a control signal / instruction to the first switch circuit and the second switch circuit to control the on and off states of the two; The first switch circuit and the second switch circuit are switched to a closed state alternately or intermittently; When the first switch circuit is closed and connected, a closed loop is formed along the positive electrode, the first detection loop providing circuit, the equipotential terminal, the insulation resistors Rni / / Rna, and the negative electrode. If an insulation fault occurs in the insulation resistors Rni / Rna, a leakage current is generated in the loop. When the leakage protection switch LBi / LB0 detects that the leakage current in the loop where the insulation resistors Rni / Rna are located reaches or exceeds the level of its operating current, the leakage protection switch LBi / LB0 is activated to cut off the power supply of the branch / main circuit; When the second switch circuit is closed and connected, a closed loop is formed along the positive pole, the insulation resistor Rpi / Rpa, the equipotential end, the second detection circuit, and the positive pole. If there is an insulation fault in the insulation resistor Rpi / Rpa, a leakage current is generated in the loop. When the leakage protection switch LBi / LB0 detects that the leakage current of the loop where the insulation resistor Rni / Rna is located reaches or exceeds the level of its operating current, the leakage protection switch LBi / LB0 is activated to cut off the power supply of the branch / main circuit.

2. The insulation fault detection circuit according to claim 1, wherein: The equipotential terminal is grounded.

3. The insulation fault detection circuit according to claim 1, wherein: The first detection loop providing circuit further includes: a first current suppression circuit connected in series with the first switch circuit, or / and a second current suppression circuit connected in series with the second switch circuit.

4. The insulation fault detection circuit according to claim 3, wherein: The first current suppression circuit is a resistor Rp0, and the second current suppression circuit is a resistor Rn0.

5. The insulation fault detection circuit according to claim 1, wherein: The first switch circuit and the second switch circuit are switched to a closed state alternately or intermittently.

6. The insulation fault detection circuit according to claim 5, characterized in that: Define the detection window time as Tw, the interval time as Tb, and the cyclic detection period as 2*(Tw+Tb), where: In one of the cyclic detection cycles, the following are executed in sequence: the first switch circuit is closed for a time period of Tw, the first switch circuit is opened for a time period of Tb, the second switch circuit is closed for a time period of Tw, and the second switch circuit is opened for a time period of Tb.

7. The insulation fault detection circuit according to claim 6, characterized in that: The detection window time and interval time satisfy: Tw=2Tp~3Tp, Tb=10Tw~100Tw, wherein Tp is the time between the leakage protection switch detecting the occurrence of a fault and executing the switching action.

8. An ungrounded system, characterized in that: An insulation fault detection circuit according to any one of claims 1 to 7 is provided.

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