A leakage current detection device and detection method for three-phase power line

Abstract

The present invention provides a leakage current detection device and detection method for a three-phase power line, and relates to the technical field of power grid fault monitoring. A voltage injection unit sequentially inputs an injection voltage different from the working phase angle of the phase line to each phase line by inductive coupling, and a current measurement unit measures the magnitude and phase angle of the corresponding signal current flowing through the neutral line by inductive coupling. A control unit extracts the magnitude of the signal current with the same phase angle as the injection voltage from the signal current measured by the current measurement unit, and calculates the leakage resistance of each phase line using the extracted signal current and the injection voltage on each phase line, and calculates the leakage current of each phase line based on the calculated leakage resistance and the working voltage of each phase line. The detection device of the present invention has a simple structure and can easily and accurately measure the leakage current of each phase line of the three-phase power line separately.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid fault monitoring, and more specifically, relates to a leakage current detection device and a detection method for a three-phase power line. Background Art

[0002] Usually, when the insulation layer of the wire is aged or damaged, the insulator will be damaged, causing the current to leak to the ground through the damaged part. If the human body touches the leakage point, there is a risk of electric shock, and excessive leakage current may also cause overheating due to electric arc and cause fire due to surrounding combustible materials.

[0003] Prior art CN110402396A discloses a leakage current detection device and method for detecting leakage current, including a leakage current detection unit for detecting leakage current flowing in a three-phase four-wire power line under test, wherein the three-phase four-wire power line under test is formed by connecting three phases in a star shape and grounding the neutral point to lead out a grounding wire; a voltage detection unit for detecting the voltage applied between any two phases of the power line under test; a phase difference detection unit for detecting the phase difference according to the leakage current and the voltage detected by the voltage detection unit; a resistance component leakage current calculation unit for calculating the resistance component leakage current caused by the insulation resistance to the ground contained in the leakage current flowing in the power line under test according to the phase difference and the leakage current; and judging whether the phase difference is within a prescribed range, and sending the phase difference detected by the phase difference detection unit to the judgment processing unit of the voltage detection unit when judging that the phase difference is not within the prescribed range. The voltage detection unit switches the phase receiving voltage detection in the power line under test according to the phase difference, and detects the voltage applied between the two phases after switching. The existing technology has the problem that the leakage current measurement of three-phase power lines is complicated and the leakage current of each phase line cannot be accurately measured separately. Summary of the invention

[0004] The object of the present invention is to provide a leakage current detection device and a detection method for a three-phase power line, which can easily and accurately measure the leakage current of each phase line of the three-phase power line separately.

[0005] To achieve the above object, on the one hand, the present invention provides a leakage current detection device for a three-phase power line, wherein the three-phase power line is formed by connecting three phase lines in a star shape and grounding the neutral point to lead out a zero line, comprising:

[0006] A voltage injection unit, used for inputting an injection voltage different from a working phase angle of the phase line to each phase line by means of inductive coupling;

[0007] A current measuring unit is arranged on the neutral line, and is used to measure the magnitude and phase angle of the signal current flowing through the neutral line by inductive coupling after the voltage injection unit applies an injection voltage to each phase line;

[0008] A control unit controls the voltage injection unit to sequentially input an injection voltage to each phase line, extracts the magnitude of a signal current having the same phase angle as the injection voltage from the signal current measured by the current measurement unit, calculates the leakage resistance using the extracted signal current and the injection voltage on each phase line, and calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line.

[0009] Furthermore, each phase line is provided with a voltage injection unit, and the control unit sequentially controls the voltage injection unit on each phase line to inject voltage into the corresponding phase line input.

[0010] Furthermore, the voltage injection unit includes a voltage source and a transformer, the transformer includes an iron core and a primary winding and a secondary winding wound on the iron core, the voltage source is connected in series with the primary winding, and each phase line can be respectively wound on the iron core to form a corresponding secondary winding.

[0011] Furthermore, the current measuring unit includes an ammeter and a current transformer, the current transformer includes an iron core and a primary winding and a secondary winding wound on the iron core, the ammeter is connected in series with the primary winding, and the neutral line is wound on the iron core to form the secondary winding.

[0012] Furthermore, the leakage resistance of each phase line is calculated by the following formula:

[0013]

[0014] in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line with the same phase angle as the injected voltage;

[0015] The leakage current of each phase line is calculated by the following formula:

[0016]

[0017] in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

[0018] On the other hand, the present invention provides a leakage current detection method for a three-phase power line, wherein the three-phase power line is formed by connecting three phase lines in a star shape and grounding the neutral point to lead out a zero line, comprising the following steps:

[0019] S1, the control unit controls the voltage injection unit to input an injection voltage different from the working phase angle of the phase line to each phase line in turn through inductive coupling;

[0020] S2, the current measurement unit measures the magnitude and phase angle of the signal current flowing through the neutral line by means of inductive coupling;

[0021] S3, the control unit extracts the magnitude of the signal current having the same phase angle as the injected voltage from the signal current measured by the current measuring unit, and calculates the leakage resistance of each phase line by using the extracted signal current and the injected voltage on each phase line;

[0022] S4. The control unit calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line.

[0023] Further, each phase line is provided with a voltage injection unit, and in the step S1, the control unit sequentially controls the voltage injection unit on each phase line to inject voltage into the corresponding phase line input.

[0024] Furthermore, the voltage injection unit includes a voltage source and a transformer, the transformer includes an iron core and a primary winding and a secondary winding wound on the iron core, the voltage source is connected in series with the primary winding, and each phase line can be respectively wound on the iron core to form a corresponding secondary winding.

[0025] Furthermore, the current measuring unit includes an ammeter and a current transformer, the current transformer includes an iron core and a primary winding and a secondary winding wound on the iron core, the ammeter is connected in series with the primary winding, and the neutral line is wound on the iron core to form the secondary winding.

[0026] Furthermore, in step S3, the leakage resistance of each phase line is calculated by the following formula:

[0027]

[0028] in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line with the same phase angle as the injected voltage;

[0029] In step S4, the leakage current of each phase line is calculated by the following formula:

[0030]

[0031] in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

[0032] The beneficial effects brought by the technical solution adopted by the present invention are as follows: the present invention sequentially inputs an injection voltage different from the working phase angle of the phase line to each phase line through the voltage injection unit by inductive coupling, the current measurement unit measures the magnitude and phase angle of the corresponding signal current flowing through the neutral line by inductive coupling, the control unit extracts the magnitude of the signal current with the same phase angle as the injection voltage from the signal current measured by the current measurement unit, and calculates the leakage resistance of each phase line by using the extracted signal current and the injection voltage on each phase line, and calculates the leakage current of each phase line based on the calculated leakage resistance and the working voltage of each phase line. The leakage current detection device for the three-phase power line of the present invention has a simple structure and is easy to detect the leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of an electrical circuit of a leakage current detection device for a three-phase power line provided by an embodiment of the present invention;

[0034] Figure 2 A system block diagram of a leakage current detection device for a three-phase power line provided by an embodiment of the present invention;

[0035] Figure 3 A flowchart of a leakage current detection method for a three-phase power line provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and effect of the present invention more clearly understood, the embodiments of the present invention will now be further described in conjunction with the accompanying drawings.

[0037] Embodiment 1

[0038] Figure 1 , 2 A schematic diagram shows a leakage current detection device for a three-phase power line provided by an embodiment of the present invention. The three-phase power line is connected in a star shape with the neutral point grounded.

[0039] The neutral line O is formed, and the detection device includes a voltage injection unit 10 , a current measurement unit 20 and a control unit 30 .

[0040] The voltage injection unit 10 can be respectively arranged on each phase line, that is, the voltage injection unit 10 can be respectively arranged on the A phase line, the B phase line, and the C phase line. Each voltage injection unit 10 inputs an injection voltage different from its working phase angle to each phase line according to the control of the control unit 30. For example, in a general three-phase power line, the phase angles of the A phase line, the B phase line, and the C phase line are 0 degrees, 120 degrees, and 240 degrees, respectively, so a voltage with a phase angle different from the working phase angle of each phase line can be injected, for example, a voltage with a phase angle of 60 degrees is injected into the A phase line, a voltage with a phase angle of 180 degrees is injected into the B phase line, and a voltage with a phase angle of 300 degrees is injected into the C phase line.

[0041] Each voltage injection unit 10 injects voltage into each phase line by inductive coupling, so that when the voltage injection unit 10 is set on each phase line, it can be installed without changing the circuit configuration of the power line. Specifically, each voltage injection unit 10 includes a voltage source 100 and a transformer 50, and the transformer 50 includes an iron core 120 and a primary winding 110 and a secondary winding 130 wound on the iron core 120. The voltage source 100 is connected in series with the primary winding 110, and each phase line, i.e., the A phase line, the B phase line, and the C phase line, is respectively wound on the iron core 120 to form a corresponding secondary winding 130.

[0042] The current measuring unit 20 is arranged on the neutral line O, and is used to measure the magnitude and phase angle of the signal current flowing through the neutral line after the voltage injection unit 10 applies the injection voltage to each phase line. The current measuring unit 20 measures the signal current by inductive coupling. Specifically, the current measuring unit 20 includes an ammeter 200 and a current transformer 40, and the current transformer 40 includes an iron core 220 and a primary winding 210 and a secondary winding 230 wound on the iron core 220. The ammeter 200 is connected in series with the primary winding 210, and the neutral line O is wound on the iron core 220 to form a secondary winding 230.

[0043] The control unit 30 controls each voltage injection unit 10 to sequentially input an injection voltage to each phase line, and then the control unit 30 receives the magnitude and phase angle of the corresponding signal current generated on the neutral line after the injection voltage is applied to each phase line from the current measuring unit 20. For example, the control unit 30 controls the voltage injection unit 10 on the A phase line to input the injection voltage of the 60-degree phase angle as described above to the A phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the A phase line from the current measuring unit 20. Similarly, the control unit 30 controls the voltage injection unit 10 on the B phase line to input the injection voltage of the 180-degree phase angle as described above to the B phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the B phase line from the current measuring unit 20. Similarly, the control unit 30 controls the voltage injection unit 10 on the C phase line to input the injection voltage of the 300-degree phase angle as described above to the C phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the C phase line from the current measuring unit 20. It should be understood that the order of inputting the injection voltage to the A-phase line, the B-phase line, and the C-phase line is not limited to the above order.

[0044] After measuring the magnitude and phase angle of the signal current corresponding to each phase line, the control unit 30 calculates the leakage resistance and leakage current of each phase line based on the magnitude and phase angle of the measured signal current. Specifically, the control unit 30 extracts the magnitude of the signal current having the same phase angle as the injected voltage from the signal current measured by the current measuring unit 20, and calculates the leakage resistance using the extracted signal current and the injected voltage on each phase line. Here, if the injected voltage of the present invention is input by inductive coupling as described above, the injected voltage can be calculated based on the voltage induction ratio of the transformer 50 and the voltage of the voltage source 100.

[0045] Here, the leakage resistance of each phase line is calculated by formula (1-1):

[0046]

[0047] in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line that has the same phase angle as the injected voltage, and k is A, B or C.

[0048] As described above, after calculating the leakage resistance of each phase line, the control unit 30 calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line. Here, the leakage current of each phase line is calculated by formula (1-2):

[0049]

[0050] in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

[0051] In the above embodiment, the injection voltage is sequentially input to each phase line, the magnitude and phase angle of the signal current on the neutral line corresponding to the injection voltage of each phase line are measured, and then the leakage resistance and leakage current of each phase line are calculated. Of course, the injection voltage can also be applied to one phase line, the magnitude and phase angle of the signal current are measured, and after the leakage resistance and leakage current are calculated, the leakage resistance and leakage current of other phase lines can be measured.

[0052] In the above embodiment, three voltage injection units 10 are installed on each phase line respectively. However, one voltage injection unit 10 may be prepared and connected to different phase lines in sequence to apply injection voltage to each phase line.

[0053] As configured above, an injection voltage having a phase angle different from that of the working voltage is input into each phase line in turn by inductive coupling, and the phase angle and magnitude of the corresponding signal current on the neutral line are measured by inductive coupling. The leakage current generated by each phase line can be measured in turn. The detection device is simple and can easily and accurately measure the leakage current of each phase line of the three-phase power line separately.

[0054] More specifically, according to relevant electricity safety standards in my country, for low-voltage lines where insulation resistance cannot be measured, it is stipulated that the leakage current should be kept below 0.5mA. However, in the digital industrial age, due to the large number of electronic and electrical equipment using switch-mode power supplies or inverters, when using ordinary leakage current meters to measure on most low-voltage lines, most of them will exceed 0.5mA, which will lead to the problem of judging them all as bad lines. In contrast, the present invention does not measure the resistive leakage current (resistive leakage current ILr + capacitive leakage current ILc), but measures the resistive leakage current (ILr), so that optimal leakage current management can be achieved and electric shock or fire accidents can be prevented.

[0055] Embodiment 2

[0056] Refer to the following Figure 3 , a leakage current detection method of a three-phase power line of the present invention is described, the three-phase power line is formed by three phase lines A phase line, B phase line, and C phase line through star connection and the neutral point is grounded to lead out the zero line O, including the following steps:

[0057] S1, the control unit 30 controls the voltage injection unit 10 to sequentially input an injection voltage different from the working phase angle of the phase line to each phase line through inductive coupling;

[0058] Specifically, voltage injection units 10 may be respectively provided on the A phase line, the B phase line, and the C phase line, and each voltage injection unit 10 inputs an injection voltage different from its working phase angle to each phase line according to the control of the control unit 30. For example, in a general three-phase power line, the phase angles of the A phase line, the B phase line, and the C phase line are 0 degrees, 120 degrees, and 240 degrees, respectively, so a voltage with a phase angle different from the working phase angle of each phase line can be injected, for example, a voltage with a phase angle of 60 degrees is injected into the A phase line, a voltage with a phase angle of 180 degrees is injected into the B phase line, and a voltage with a phase angle of 300 degrees is injected into the C phase line.

[0059] Each voltage injection unit 10 includes a voltage source 100 and a transformer 50. The transformer 50 includes an iron core 120 and a primary winding 110 and a secondary winding 130 wound on the iron core 120. The voltage source 100 is connected in series with the primary winding 110. Each phase line, namely, the A phase line, the B phase line, and the C phase line, is respectively wound on the iron core 120 to form a corresponding secondary winding 130.

[0060] The control unit 30 controls each voltage injection unit 10 to sequentially input an injection voltage to each phase line, and then the control unit 30 receives the magnitude and phase angle of the corresponding signal current generated on the neutral line after the injection voltage is applied to each phase line from the current measuring unit 20. For example, the control unit 30 controls the voltage injection unit 10 on the A phase line to input the injection voltage of the 60-degree phase angle as described above to the A phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the A phase line from the current measuring unit 20. Similarly, the control unit 30 controls the voltage injection unit 10 on the B phase line to input the injection voltage of the 180-degree phase angle as described above to the B phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the B phase line from the current measuring unit 20. Similarly, the control unit 30 controls the voltage injection unit 10 on the C phase line to input the injection voltage of the 300-degree phase angle as described above to the C phase line, and then receives the magnitude and phase angle of the signal current generated on the neutral line O by the injection voltage of the voltage injection unit 10 on the C phase line from the current measuring unit 20. It should be understood that the order of inputting the injection voltage to the A-phase line, the B-phase line, and the C-phase line is not limited to the above order.

[0061] S2, the current measuring unit 20 measures the magnitude and phase angle of the signal current flowing through the neutral line O by means of inductive coupling;

[0062] Specifically, the current measuring unit 20 includes an ammeter 200 and a current transformer 40 . The current transformer 40 includes an iron core 220 and a primary winding 210 and a secondary winding 230 wound on the iron core 220 . The ammeter 200 is connected in series with the primary winding 210 , and the neutral line O is wound on the iron core 220 to form a secondary winding 230 .

[0063] S3, the control unit 30 extracts the magnitude of the signal current having the same phase angle as the injected voltage from the signal current measured by the current measuring unit 20, and calculates the leakage resistance of each phase line by using the extracted signal current and the injected voltage on each phase line;

[0064] Specifically, the leakage resistance of each phase line is calculated by formula (1-1):

[0065]

[0066] in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line that has the same phase angle as the injected voltage, and k is A, B or C.

[0067] S4. The control unit 30 calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line.

[0068] Specifically, the leakage current of each phase line is calculated by formula (1-2):

[0069]

[0070] in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

[0071] In the above embodiment, the injection voltage is sequentially input to each phase line, the magnitude and phase angle of the signal current on the neutral line corresponding to the injection voltage of each phase line are measured, and then the leakage resistance and leakage current of each phase line are calculated. Of course, the injection voltage can also be applied to one phase line, the magnitude and phase angle of the signal current are measured, and after the leakage resistance and leakage current are calculated, the leakage resistance and leakage current of other phase lines can be measured.

[0072] In the above embodiment, three voltage injection units 10 are installed on each phase line respectively. However, one voltage injection unit 10 may be prepared and connected to different phase lines in sequence to apply injection voltage to each phase line.

[0073] The method described above inputs an injection voltage with a phase angle different from that of the working voltage into each phase line in turn by means of inductive coupling, and measures the phase angle and magnitude of the corresponding signal current on the neutral line by means of inductive coupling. The leakage current generated by each phase line can be measured in turn, and the leakage current of each phase line of the three-phase power line can be easily and accurately measured separately.

[0074] More specifically, according to relevant electricity safety standards in my country, for low-voltage lines where insulation resistance cannot be measured, it is stipulated that the leakage current should be kept below 0.5mA. However, in the digital industrial age, due to the large number of electronic and electrical equipment using switch-mode power supplies or inverters, when using ordinary leakage current meters to measure on most low-voltage lines, most of them will exceed 0.5mA, which will lead to the problem of judging them all as bad lines. In contrast, the present invention does not measure the resistive leakage current (resistive leakage current ILr + capacitive leakage current ILc), but measures the resistive leakage current (ILr), so that optimal leakage current management can be achieved and electric shock or fire accidents can be prevented.

[0075] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A leakage current detection device for a three-phase power line, wherein the three-phase power line is formed by connecting three phase lines in a star shape and grounding the neutral point to lead out a zero line, characterized in that: include: A voltage injection unit, used for inputting an injection voltage different from a working phase angle of the phase line to each phase line by means of inductive coupling; A current measuring unit is arranged on the neutral line, and is used to measure the magnitude and phase angle of the signal current flowing through the neutral line by inductive coupling after the voltage injection unit applies an injection voltage to each phase line; A control unit controls the voltage injection unit to sequentially input an injection voltage to each phase line, extracts the magnitude of a signal current having the same phase angle as the injection voltage from the signal current measured by the current measurement unit, calculates the leakage resistance using the extracted signal current and the injection voltage on each phase line, and calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line.

2. The detection device according to claim 1, characterized in that Each phase line is provided with a voltage injection unit, and the control unit sequentially controls the voltage injection unit on each phase line to inject voltage into the corresponding phase line input.

3. The detection device according to claim 1, characterized in that: The voltage injection unit includes a voltage source and a transformer. The transformer includes an iron core and a primary winding and a secondary winding wound on the iron core. The voltage source is connected in series with the primary winding. Each phase line can be wound on the iron core to form a corresponding secondary winding.

4. The detection device according to claim 1, characterized in that: The current measuring unit comprises an ammeter and a current transformer, wherein the current transformer comprises an iron core and a primary winding and a secondary winding wound on the iron core, the ammeter is connected in series with the primary winding, and the neutral line is wound on the iron core to form the secondary winding.

5. The detection device according to claim 1, characterized in that: The leakage resistance of each phase line is calculated by the following formula: in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line with the same phase angle as the injected voltage; The leakage current of each phase line is calculated by the following formula: in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

6. A method for detecting leakage current of a three-phase power line, wherein the three-phase power line is formed by connecting three phase lines in a star shape and grounding the neutral point to lead out a zero line, characterized in that: The steps include: S1, the control unit controls the voltage injection unit to input an injection voltage different from the working phase angle of the phase line to each phase line in turn through inductive coupling; S2, the current measurement unit measures the magnitude and phase angle of the signal current flowing through the neutral line by means of inductive coupling; S3, the control unit extracts the magnitude of the signal current having the same phase angle as the injected voltage from the signal current measured by the current measuring unit, and calculates the leakage resistance of each phase line by using the extracted signal current and the injected voltage on each phase line; S4. The control unit calculates the leakage current of each phase line based on the calculated leakage resistance and the operating voltage of each phase line.

7. The detection method according to claim 6, characterized in that Each phase line is provided with a voltage injection unit. In the step S1, the control unit sequentially controls the voltage injection unit on each phase line to inject voltage into the corresponding phase line input.

8. The detection method according to claim 6, characterized in that: The voltage injection unit includes a voltage source and a transformer. The transformer includes an iron core and a primary winding and a secondary winding wound on the iron core. The voltage source is connected in series with the primary winding. Each phase line can be wound on the iron core to form a corresponding secondary winding.

9. The detection method according to claim 6, characterized in that: The current measuring unit comprises an ammeter and a current transformer, wherein the current transformer comprises an iron core and a primary winding and a secondary winding wound on the iron core, the ammeter is connected in series with the primary winding, and the neutral line is wound on the iron core to form the secondary winding.

10. The detection method according to claim 6, characterized in that: In step S3, the leakage resistance of each phase line is calculated by the following formula: in, is the leakage resistance of the kth phase line, is the injected voltage on the kth phase line, It is the magnitude of the signal current corresponding to the kth phase line with the same phase angle as the injected voltage; In step S4, the leakage current of each phase line is calculated by the following formula: in, is the leakage current of the kth phase line, is the operating voltage of the kth phase line.

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