CN110780223A - Ground fault detection circuit and device - Google Patents
Ground fault detection circuit and device Download PDFInfo
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- CN110780223A CN110780223A CN201810758233.6A CN201810758233A CN110780223A CN 110780223 A CN110780223 A CN 110780223A CN 201810758233 A CN201810758233 A CN 201810758233A CN 110780223 A CN110780223 A CN 110780223A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
Abstract
The embodiment of the invention provides a ground fault detection circuit and a current or frequency conversion device. The ground fault detection circuit includes: the resistance voltage division branch circuit comprises a sampling resistor and at least one voltage division resistor, the first end of the at least one voltage division sampling resistor is correspondingly connected with at least one branch circuit in the circuit to be detected, the second end of the at least one voltage division resistor is connected with the first end of the sampling resistor in parallel, and the second end of the sampling resistor is grounded; the signal sampling branch circuit is connected with the sampling resistor and is used for collecting an electric signal on the sampling resistor; and the direct current component extraction branch is connected with the signal sampling branch and is used for extracting the direct current component of the electric signal acquired by the signal sampling branch. By adopting the technical scheme of the invention, the accurate detection of the ground fault can be realized under the conditions of lower cost and no influence of parasitic capacitance.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a ground fault detection circuit and a ground fault detection device.
Background
The working process of common electrical equipment such as a three-phase frequency converter and a converter in an IT (insulation terra system) system comprises a rectification link, a direct current bus link and an inversion link, when any point of the three links has an earth fault, the equipment is abnormal, and the equipment should send an alarm or a fault prompt, but because the normal operation of the equipment is not affected by a single-point earth fault, the earth fault is detected by detecting inter-phase voltage, current signals of a main loop and the like, whether the earth fault occurs or not is difficult to judge, the earth fault can be detected only by adopting precise special detection equipment, and the detection cost is high; moreover, parasitic capacitance, parasitic inductance, and the like generally exist in the system, and particularly, a longer cable adopted has a larger parasitic capacitance to the ground, and the parasitic capacitance to the ground causes false detection of the ground fault, so that the accuracy of ground fault detection is low.
Disclosure of Invention
In view of the above, an object of the present invention is to provide a ground fault detection circuit and a ground fault detection device, so as to solve the problems of the prior art that the ground fault detection cost is high and the ground fault detection accuracy is low due to parasitic capacitance.
To achieve the above object, an embodiment of the present invention provides a ground fault detection circuit, including: the circuit comprises a resistance voltage division branch circuit, a voltage detection circuit and a voltage detection circuit, wherein the resistance voltage division branch circuit comprises a sampling resistor and at least one voltage division resistor, the first end of the at least one voltage division resistor is correspondingly connected with at least one branch circuit in the circuit to be detected respectively, the second end of the at least one voltage division resistor is connected with the first end of the sampling resistor after being connected in parallel, and the second end of the sampling resistor is grounded; the signal sampling branch circuit is connected with the sampling resistor and is used for collecting an electric signal on the sampling resistor; and the direct current component extraction branch circuit is connected with the signal sampling branch circuit and is used for extracting the direct current component of the electric signal acquired by the signal sampling branch circuit.
In an exemplary embodiment of the ground fault detection circuit, the circuit to be detected includes a rectification circuit, a dc bus circuit, and an inverter circuit, which are connected in sequence; the first end of the at least one divider resistor is correspondingly connected with at least one of the input end of the rectifying circuit, the direct-current bus and the output end of the inverter circuit.
In an exemplary embodiment of the ground fault detection circuit, the number of the voltage dividing resistors is at least two; the first end of at least one of the two divider resistors is connected with the direct current bus circuit, and the first end of the at least one divider resistor is correspondingly connected with at least one of the input end of the rectifying circuit and the output end of the inverter circuit.
In an exemplary embodiment of the ground fault detection circuit, an input end of the rectification circuit is a three-phase input end, an output end of the inverter circuit is a three-phase output end, and the dc bus includes a positive dc bus and a negative dc bus; the first end of at least one of the at least two voltage-dividing resistors is correspondingly connected with at least one of the positive and negative direct-current buses, and the first end of at least one voltage-dividing resistor is correspondingly connected with at least one of the three single-phase input ends of the rectifying circuit and the three single-phase output ends of the inverter circuit respectively.
In an exemplary embodiment of the ground fault detection circuit, the circuit to be detected includes a rectification unit, a dc bus circuit, and an inverter circuit, which are connected in sequence, where the rectification unit includes a plurality of cascaded rectification circuits; the number of the voltage dividing resistors is at least two, the first ends of the at least two voltage dividing resistors are respectively and correspondingly connected with at least two of the input ends of the rectifying circuits, the direct current bus circuit and the output ends of the inverter circuit, wherein the at least two voltage dividing resistors have different direct current potential components, and the direct current potential components of the equivalent voltage dividing resistors of the at least two voltage dividing resistors are different from the direct current potential components of any one of the input ends of the rectifying circuits, the direct current bus and the output ends of the inverter circuit.
In an exemplary embodiment of the ground fault detection circuit, the dc component extracting branch comprises a low pass filter device connected to the signal sampling branch.
In an exemplary embodiment of the ground fault detection circuit, the signal sampling branch includes a voltage sampling branch, and the voltage sampling branch is connected to two ends of the sampling resistor and collects voltage data of two ends of the sampling resistor.
In an exemplary embodiment of the ground fault detection circuit, the signal sampling branch includes a current sampling branch, and the current sampling branch is connected in series to the first end or the second end of the sampling resistor and collects current data on the sampling resistor.
The embodiment of the invention also provides a ground fault detection device, which comprises any one of the ground fault detection circuits of the embodiments of the invention, and a processor, wherein the processor is connected with the direct current component extraction branch in the ground fault detection circuit, and judges whether the circuit to be detected has ground fault according to the direct current component of the electric signal extracted by the direct current component extraction branch.
In an exemplary embodiment of the ground fault detection apparatus, the processor determines that a ground fault occurs in the circuit to be detected when a variation of the dc component of the electrical signal within a preset time period reaches a preset threshold.
In an exemplary embodiment of the ground fault detection device, the ground fault detection device further includes: and the alarm is connected with the processor and sends alarm information when the processor judges that the circuit to be detected has a ground fault.
In an exemplary embodiment of the ground fault detection apparatus, the ground fault detection apparatus is a converter device or a frequency converter device.
According to the ground fault detection circuit and the ground fault detection device, the resistance voltage division branch connected between the circuit to be detected and the grounding terminal, the signal sampling branch for detecting the electric signal on the sampling resistor and the direct current component extraction branch for extracting the direct current component of the acquired signal are arranged, so that when the circuit to be detected has a ground fault, the electric signal in a loop formed by the grounding terminal with the fault and the resistance voltage division branch can be effectively detected, the direct current component of the electric signal is extracted, whether the circuit to be detected has the ground fault or not can be accurately judged according to the direct current component of the acquired electric signal and the like, the influence of parasitic capacitance on the ground fault detection is avoided, and the accuracy of the ground fault detection is improved; and ground fault detection can be carried out without adopting precise special detection equipment, and the precise detection of the ground fault is realized under the condition of using lower cost.
Drawings
The foregoing and other features and advantages of the invention will become more apparent to those skilled in the art to which the invention relates upon consideration of the following detailed description of a preferred embodiment of the invention with reference to the accompanying drawings, in which:
fig. 1 is a first structural diagram of a ground fault detection circuit according to an embodiment of the invention;
FIG. 2 is a first structural diagram of a circuit under test according to an embodiment of the present invention;
FIG. 3 is a diagram of the equivalent circuit of the DC component of FIG. 2;
fig. 4 is a schematic diagram illustrating a first application state of a ground fault detection circuit according to an embodiment of the invention;
fig. 5 is a second structural diagram of a circuit under test according to an embodiment of the present invention;
FIG. 6 is a diagram of the equivalent circuit of the DC component of FIG. 5;
fig. 7 is a schematic diagram illustrating a second application state of the ground fault detection circuit according to an embodiment of the invention;
fig. 8 is a schematic diagram illustrating a third application state of the ground fault detection circuit according to an embodiment of the present invention;
FIG. 9 is the ground circuit of FIG. 8;
fig. 10 is a dc component equivalent circuit diagram of fig. 9.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail by referring to the following examples.
Fig. 1 is a schematic structural diagram of a ground fault detection circuit according to an embodiment of the present invention, referring to fig. 1, the ground fault detection circuit according to the embodiment includes a resistance voltage-dividing branch, a signal sampling branch, and a dc component extraction branch, where the resistance voltage-dividing branch includes a sampling resistor R0 and at least one voltage-dividing resistor (n voltage-dividing resistors, R1 and R2 … Rn are shown in the figure), a first end of the at least one voltage-dividing resistor is respectively connected to at least one branch in a circuit to be detected, a second end of the at least one voltage-dividing resistor is connected to a first end of the sampling resistor after being connected in parallel, and a second end of the sampling resistor is grounded; the signal sampling branch is connected with the sampling resistor and used for collecting the electric signal on the sampling resistor; the direct current component extraction branch is connected with the signal sampling branch and extracts the direct current component of the electric signal acquired by the signal sampling branch.
The ground fault detection circuit of the embodiment of the invention is used for carrying out ground fault detection on a circuit to be detected in an IT system. In the ground fault detection circuit, a resistance voltage division branch is correspondingly connected with at least one branch in the circuit to be detected one by one through a first end of at least one voltage division resistor, and is grounded through a second end of a sampling resistor; that is, the resistive voltage dividing branch is connected between the ground terminal and at least one branch of the circuit to be tested. In the working process of the circuit to be detected, if the circuit to be detected does not have a ground fault, no current is generated in the resistance voltage division branch, the signal sampling branch cannot acquire a power-on signal of the sampling resistor, or the acquired current, voltage and other electrical signals are zero; if when the circuit to be detected has a ground fault, the branch circuit with the ground fault and the resistance voltage-dividing branch circuit form a loop, current is generated on the sampling resistor, voltage is arranged at two ends of the sampling resistor, and current signals on the sampling resistor, voltage signals at two ends of the sampling resistor and other electrical signals can be collected by the signal sampling branch circuit.
According to the electric signal collected by the voltage sampling branch circuit, such as whether the current signal or the voltage signal is zero or not, and the change of the current signal or the voltage signal, whether the circuit to be detected has the ground fault or not can be accurately judged; and for the direct current component, the parasitic capacitor is open, whether the circuit to be detected has the ground fault is judged by extracting the direct current component of the acquired electric signal and based on the extracted direct current component, so that the false detection of the ground fault caused by the grounding of the acquired alternating current signal through the parasitic capacitor is avoided, the influence of the parasitic capacitor is avoided, and the accuracy of the ground fault detection is improved.
And the resistance voltage division branch can be formed by common resistors, the signal sampling branch can adopt conventional current, voltage and other signal acquisition equipment, and the direct current component extraction branch can adopt conventional filtering equipment to realize the direct current component extraction function, so that the ground fault detection can be carried out without adopting more precise special detection equipment, and the precise detection of the ground fault is realized under the condition of using lower cost. For example, the dc component extraction branch may comprise a low pass filter device connected to the signal sampling branch.
In practical applications, at least one voltage-dividing resistor in the resistor voltage-dividing branches may be connected to branches having different voltage signals in the circuit to be tested, for example, to input terminals or output terminals of different devices in the circuit to be tested.
And the signal sampling branch can be a voltage sampling branch connected to two ends of the sampling resistor, and the voltage sampling branch acquires voltage data at two ends of the sampling resistor. The signal sampling branch circuit can also be a current sampling branch circuit which is connected in series with the first end or the second end of the sampling resistor so as to acquire current data on the sampling resistor. Here, the current sampling branch may be connected between the second end of the sampling resistor and the ground terminal, or may be connected between a connection end where the second ends of the at least one voltage-dividing resistor are connected in parallel and the first end of the sampling resistor.
According to an exemplary embodiment of the present invention, as shown in fig. 2, the circuit to be detected may include a rectifier circuit (AC/DC), a direct current bus circuit (DC bus), and an inverter circuit (DC/AC) connected in sequence, and when the ground fault detection circuit is used to detect a ground fault of the circuit to be detected, a first end of at least one voltage-dividing resistor may be correspondingly connected to at least one of an input end of the rectifier circuit, the direct current bus circuit, and an output end of the inverter circuit, respectively. In the figure, the AC at the input side of the rectifying circuit is an AC source and is equivalent to a power grid side or a power supply side; m on the output side of the rectifier circuit is a motor, which corresponds to the load side.
The electric energy transmitted in the circuit to be detected can be three-phase electricity, the input end of the rectifying circuit is a three-phase input end, the output end of the inverter circuit is a three-phase output end, and the direct current bus comprises a positive direct current bus and a negative direct current bus; when the ground fault circuit is connected with the circuit to be detected, the first end of at least one divider resistor can be correspondingly connected with at least one of three single-phase input ends, a positive direct-current bus, a negative direct-current bus and three single-row input ends of the inverter circuit in a one-to-one manner. Optionally, the number of the voltage dividing resistors is smaller than the number of branches with different voltage signals in the circuit to be detected.
In the circuit to be tested shown in fig. 2, A, B, C is any point on the input line corresponding to each of the three single-phase input ends of the rectifying circuit, D, E is any point on the positive and negative dc buses, and F, G, H is any point on the output line corresponding to each of the three single-phase output ends of the inverter circuit.
When connecting the ground fault detection circuit to the circuit to be detected, the first terminal of the voltage dividing resistor may be connected to any point in A, B, C, D, E, F, G, H.
In an optional embodiment, the ground fault detection circuit may only include one voltage-dividing resistor, and the first end of the voltage-dividing resistor may be connected to any one of points A, B, C or F, G, H, that is, the voltage-dividing resistor is connected to the input end of the rectifier circuit or the output end of the inverter circuit, so that when a ground fault occurs on the positive and negative dc buses (that is, the point D or E), an effective dc component may be extracted from the electrical signal extracted by the dc component extraction branch circuit based on the signal sampling branch circuit, and then the ground fault occurring on the positive and negative dc buses may be accurately determined. It is explained here that if a voltage dividing resistor is connected to the input terminal of the rectifier circuit, the dc component extraction branch cannot effectively extract the dc component of the electrical signal when a ground fault occurs at the input terminal of the rectifier circuit and the output terminal of the inverter circuit; and if the divider resistor is connected to the output end of the inverter circuit, when a ground fault occurs at the input end and the output end of the rectifier circuit and the output end of the inverter circuit, the direct current component of the electric signal cannot be effectively extracted by the direct current component extraction branch, so that ground fault detection cannot be accurately performed.
And, the first end of the divider resistor can also be connected to any point in D, E, that is, the divider resistor is connected to the positive and negative dc buses, so that when a ground fault occurs at the input end of the rectifier circuit (i.e., point A, B or point C) or the output end of the inverter circuit (i.e., point F, G or point H), the effective electrical signal dc component can be extracted through the dc component extraction branch, thereby accurately performing ground fault detection.
In an optional implementation manner, the ground fault detection circuit may include at least two voltage dividing resistors, when the ground fault detection circuit is connected to the circuit to be detected, the first end of at least one of the at least two voltage dividing resistors may be connected to the positive and negative dc buses, and the first end of the at least one voltage dividing resistor may be connected to the input end of the rectification circuit or the output end of the inverter circuit, so as to ensure that the dc component extraction branch can extract an effective dc component from the electrical signal collected by the signal sampling branch when any point in the rectification circuit, the dc bus circuit, or the inverter circuit has a ground fault, thereby improving the reliability of the ground fault detection performed by the ground fault detection circuit.
And if the ground fault detection circuit only comprises one divider resistor, and the connection part of the divider resistor and the circuit to be detected has ground fault, although a loop is formed, no voltage difference exists in the loop, the voltage data sampled by the voltage sampling branch circuit is zero, and the ground fault of the circuit to be detected cannot be judged; or, the connection of the voltage dividing resistor has an open circuit fault, and the voltage sampling branch cannot sample a voltage signal, so that the ground fault of the circuit to be detected cannot be judged. The ground fault detection circuit provided by the embodiment is provided with at least two divider resistors connected with different branches in the circuit to be detected, so that a loop can be formed by the plurality of divider resistors and the fault ground in the circuit to be detected, and at least one closed current loop is ensured to flow through the ground, thereby further improving the reliability of the ground fault detection circuit.
Specifically, the first end of at least one of the at least two voltage-dividing resistors may be connected to the positive and negative dc buses (i.e., points D or E), and the first end of the at least one voltage-dividing resistor may be connected to three single-phase input terminals of the rectifier circuit or three single-phase output terminals of the inverter circuit (i.e., at least one point A, B, C, F, G, H) in a one-to-one correspondence.
If only the dc component is considered, the circuit to be detected shown in fig. 2 may be equivalent to the circuit shown in fig. 3, the three-phase input end of the rectifying circuit and the three-phase output end of the inverting circuit are simplified to three-phase power transmission line diagrams in fig. 3, and the voltage source in fig. 3 is equivalent to a dc voltage source. If the negative pole (namely, point E) of the direct current bus is taken as a reference potential (zero potential) and the potential of the positive pole (namely, point D) of the direct current bus is taken as Vdc, the A, B, C three points are taken as alternating current voltage input sources, the direct current potential component of the three points relative to the point E is 0.5Vdc, and correspondingly, the direct current potential component of the F, G, H three points is also 0.5 Vdc. In case only the dc component is considered, these six points may be connected together, i.e. the circuit under investigation shown in fig. 3 may be equivalent to the circuit under investigation shown in fig. 4.
In the circuit system (including the circuit to be detected and the ground fault detection circuit) output in fig. 4, only three kinds of 0, 0.5Vdc and Vdc are provided in the circuit to be detected, which are respectively represented by three points X0, X1 and X2. The ground fault detection circuit includes two voltage-dividing resistors R1 and R2, the voltage-dividing resistor R1 is connected to the X1 (in actual operation, the first end of the voltage-dividing resistor R1 may be connected to any point of A, B, C, F, G, H whose dc potential component is 0.5 Vdc), and the voltage-dividing resistor R2 is connected to the X2 (in actual operation, the first end of the voltage-dividing resistor R2 may be connected to the point D whose dc potential component is Vdc). The ground fault detection circuit adopts a voltage sampling branch circuit as a signal sampling circuit, the voltage signal sampling branch circuit can acquire a voltage signal VR0 on a sampling resistor R0, and a direct current component extraction branch circuit can extract a direct current component of the voltage signal VR0 to obtain a voltage direct current component signal Vave _ R0 which is used for judging whether a ground fault occurs in the circuit to be detected.
It should be noted that, in the embodiment of the present invention, only the circuit to be detected shown in fig. 2 is taken as an example to illustrate the connection manner between the ground fault detection circuit and the circuit to be detected and the ground fault detection method in the embodiment of the present invention, but it should be clear to those skilled in the art that the specific connection manner of the rectification circuit, the dc bus circuit and the inverter circuit in the circuit to be detected in the embodiment of the present invention is not limited to that shown in fig. 2, and the ground fault detection circuit in the embodiment of the present invention is not limited to that for detecting a circuit system including the rectification circuit, the dc bus circuit and the inverter circuit.
For example, in some embodiments of the present invention, the circuit to be detected may also be a multi-unit circuit cascade structure, each unit circuit includes a rectifying circuit, a dc bus circuit, and an inverter circuit, which are connected in sequence, that is, each unit may be the circuit to be detected shown in fig. 2. For this situation, referring to this embodiment, a plurality of ground fault detection circuits are provided, and each unit circuit is connected to one circuit to be detected, and specifically, the first end of at least one voltage-dividing resistor in the ground fault detection circuit is correspondingly connected to at least one of the input end (including a three-phase input end), the positive and negative dc buses, and the output end (including a three-phase output end) of the rectifying circuit in each unit circuit, so that whether the circuit to be detected has a ground fault can be determined according to the dc component signal of the electrical signal obtained by each ground fault detection circuit, and the unit circuit having a ground fault can be determined.
For another example, in other embodiments of the present invention, the circuit to be detected may further include a rectifying unit, a dc bus circuit, and an inverter circuit, which are connected in sequence, where the rectifying unit includes a plurality of cascaded rectifying circuits, that is, an arrangement unit formed by a plurality of cascaded rectifying circuits is connected to the dc bus circuit and the inverter circuit. In view of this situation, the first end of at least one voltage dividing resistor in the ground fault detection circuit may be correspondingly connected to at least one of the input end (including the three-phase input end), the positive and negative dc buses, and the output end (including the three-phase output end) of each rectification circuit, according to the embodiment of the present invention.
In a specific application scenario, the ground fault detection circuit shown in fig. 1 may be connected to the circuit to be detected shown in fig. 5, so as to perform ground fault detection on the circuit to be detected.
The circuit to be detected shown in fig. 5 is a frequency conversion device in the prior art, a power input side of the frequency conversion device comprises a transformer, a plurality of sets of windings are arranged on a secondary side of the transformer, each winding is connected with a three-phase rectification circuit, and a plurality of rectification circuits are connected with a direct-current bus circuit and an inverter circuit in sequence after being cascaded.
The direct-current potential components of the three-phase output lines (namely, the three-phase input lines of the rectifying circuits) of the windings are the same, and the direct-current potential components of the inverter circuits are also the same. In fig. 5, a cascade structure of 6 rectifying circuits is shown, if the negative pole of the dc bus (i.e. point X0 in the figure) is used as a reference potential (zero potential) and the positive pole of the dc bus (i.e. point X12 in the figure) is used as Vdc, the dc potential components at points X0, X1, … … X11, and X12 at the input end and the output end of each rectifying circuit shown in the figure are respectively 0V, 0.5/6Vdc, 1/6Vdc … … 5.5.5/6 Vdc, and Vdc; the dc potential component of the output terminal X13 of the inverter circuit is 0.5 Vdc. The circuit of fig. 5 may be equivalent to the circuit shown in fig. 6 if only the dc component is considered. The dc potential component at the point X13 is the same as the dc potential component at the point X6, and when only the dc component is analyzed, the two points can be connected together, and the equivalent circuit diagram is shown in the circuit to be detected in fig. 7.
When the ground fault detection circuit shown in fig. 1 is connected to the circuit to be detected shown in fig. 5, the voltage-dividing resistors R1 and R2 … Rn may be connected to n points X0, X1, … … X12, and X13, respectively, in a one-to-one correspondence.
If n is 1, the connection point of the divider resistor R1 and the circuit to be detected is Xs, the direct current potential is Xs, the point Xg where the ground fault occurs in the circuit to be detected, and the direct current potential is Xg, the direct current voltage component Vave _ R0 on the R0 can be calculated according to the formula (1), where Rg is the resistance of the ground terminal where the ground fault occurs in the circuit to be detected.
The point Xs shown in fig. 7 is the same as the dc potential of the point X10, and the point Xg is the same as the dc potential of the point X2, and in practical applications, Xs may be the same as the dc potential of any point, that is, the first end of the voltage-dividing resistor R1 may be connected to any point of X0 to X12. Xg may also be the same as the dc potential of any point X0 to X12, i.e., any point in the circuit under test may have a ground fault.
If n is 2, the connection point of the circuit to be detected of the voltage division resistor R1 is Xs1, the direct current potential is Xs1, the connection point of the circuit to be detected of the voltage division resistor R2 is Xs2, the direct current potential is Xs2, the point Xg of the ground fault in the circuit to be detected, and the direct current potential is Xg, as shown in fig. 8.
Fig. 9 shows the circuit of fig. 8, which was analyzed by the superposition theorem for the circuit shown in fig. 9, in a first step, considering only the first dc voltage source xs2-xs1 in the figure, in which case R0 is connected in series with Rg, then in parallel with R1, and then in series with R2 as a whole. The current magnitude at R0 can be calculated by formula (2);
wherein the content of the first and second substances,
secondly, only considering the operation of a second direct-current voltage source xs1-xg, in this case, R1 is connected in parallel with R2 and then connected in series with R0 and Rg, and the current magnitude of R0 can be calculated by formula (3);
the total current can be calculated by formula (4);
as shown in equation (4), the circuit in fig. 9 can be equivalent to the circuit in fig. 10, and therefore, the dc component voltage at R0 can be calculated by equation (5).
As can be seen from the above-mentioned manner of calculating the dc component voltage at R0 when n is 2, if only the dc component in the circuit system is considered and the potential magnitude in the system can be divided into infinite segments (or divided into a plurality of segments), the dc component voltage calculation formula at R0 when n is 2 can be equivalently transformed into the dc component voltage calculation formula at R0 when n is 1. Therefore, in the case where n is 3 or 4 … n, the dc component voltage calculation method on R0 may be an equivalent conversion method of n-1 times, and finally an equivalent conversion is performed to the dc component voltage calculation formula on R0 when n is 1.
It should be noted that the number of branches in the circuit system is limited, and the number of voltage dividing resistors to be connected is limited. For the cases where n is 2 and 3 … n, if the final equivalence is that n is 1, if the dc potential of the equivalent voltage-dividing resistor is not the same as the dc potential of any branch in the circuit system (one line where the dc potentials of any point on the line are the same), when any point in the circuit system has a ground fault, the dc component voltage on R0 can be effectively calculated, so that accurate ground fault detection can be performed according to the calculated dc component without being affected by parasitic capacitance; if the final equivalence is the case where n is 1, the dc potential of the equivalent voltage-dividing resistor is the same as the dc potential of one branch in the circuit system, when the branch has a ground fault, the dc component voltage at R0 cannot be calculated, and thus ground fault detection cannot be accurately performed.
Therefore, in order to accurately detect the ground fault when the ground fault occurs at each point in the circuit system, the direct current potential on each branch in the circuit system and the resistance value of each divider resistor can be calculated in advance; and connecting the n voltage-dividing resistors with n branches with different voltage signals in the circuit system on the principle that the direct-current potential of the equivalent voltage-dividing resistor is different from the direct-current potential of each branch in the circuit system when the final equivalent is n equal to 1. For example, in the circuit system in fig. 5, n voltage dividing resistors are connected to n corresponding ones of the plurality of rectifier circuits, dc bus circuits, and inverter circuits, respectively, which have different dc potential components, and the dc potential component of the equivalent voltage dividing resistor of the n voltage dividing resistors is different from the dc potential component of any one of the input terminals of the plurality of rectifier circuits, dc bus circuits, and output terminals of the inverter circuits. If a branch circuit in the circuit system is a three-phase circuit, the direct-current potentials of the three single-phase circuits are the same, and when the voltage-dividing resistor is connected with the branch circuit, the voltage-dividing resistor can be connected with any point on any one of the three single-phase circuits.
In an actual application scenario, each voltage dividing resistor (including R1 and R2 … Rn) in the embodiment of the present invention may be implemented by a single resistor, or may be implemented by multiple resistors connected in series.
According to the ground fault detection circuit, the resistance voltage division branch connected between the circuit to be detected and the grounding terminal, the signal sampling branch for detecting the electric signal on the sampling resistor and the direct current component extraction branch for extracting the direct current component of the acquired signal are arranged, so that when the circuit to be detected has a ground fault, the electric signal in a loop formed by the grounding terminal with the fault and the resistance voltage division branch can be effectively detected, the direct current component of the electric signal is extracted, whether the circuit to be detected has the ground fault or not can be accurately judged according to the direct current component of the acquired electric signal and the like, the influence of parasitic capacitance on ground fault detection is avoided, and the accuracy of ground fault detection is improved; and ground fault detection can be carried out without adopting precise special detection equipment, and the precise detection of the ground fault is realized under the condition of using lower cost.
On this basis, an embodiment of the present invention further provides a ground fault detection apparatus, where the ground fault detection apparatus includes the ground fault detection circuit according to the foregoing embodiment of the present invention, and a processor connected to the dc component extraction branch in the ground fault detection circuit, and the processor is configured to obtain a dc component of an electrical signal extracted by the dc component extraction branch, and determine whether a ground fault occurs in the circuit to be detected according to the obtained dc component.
Specifically, the processor may determine whether the circuit to be detected has a ground fault according to whether the obtained dc component of the electrical signal is zero or a variation within a preset time period. For example, when the direct current component of the obtained current signal or voltage signal is zero, it is determined that the circuit to be detected has no ground fault; or when the variation of the obtained direct current component of the current signal or the voltage signal within the preset time reaches a preset threshold, determining that the circuit to be detected has a ground fault.
Optionally, the ground fault detection device of the embodiment of the invention may further include an alarm, and the alarm is connected to the processor, so as to send alarm information when the processor determines that the ground fault occurs in the circuit to be detected, and notify a worker to timely overhaul the circuit to be detected, thereby avoiding a major loss caused by the ground fault. For example, the alarm may be an audible and visual alarm device that sends an audible and visual alarm signal when the processor determines that the device to be detected has a ground fault, or a communication device that sends a WeChat or a short message, so as to send information indicating that the device to be detected has a ground fault to the communication device of the associated worker when the processor determines that the device to be detected has a ground fault.
In a practical application scenario, the ground fault detection apparatus according to the embodiment of the present invention may be a converter device (e.g., a three-phase converter) or a frequency conversion device (e.g., a three-phase frequency converter). That is, in the common devices such as the current transformer and the frequency converter, the ground fault detection circuit according to the embodiment of the present invention may be provided to integrate the ground fault detection function in the devices such as the current transformer and the frequency converter, so as to perform ground fault detection on the internal circuits of the devices such as the rectifier circuit, the dc bus circuit, and the inverter circuit, thereby being capable of timely and accurately detecting the ground fault occurring in the devices without being affected by the parasitic capacitance. Of course, the ground fault detection device of the embodiment of the invention may also be an independent device, which is used for being connected with a circuit to be detected in a device such as a current transformer or a frequency converter, and performing accurate ground fault detection on the device such as the current transformer or the frequency converter.
It should be noted that, according to the implementation requirement, each component described in the embodiment of the present invention may be divided into more components, and two or more components or parts of components may be combined into a new component to achieve the purpose of the embodiment of the present invention.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (12)
1. A ground fault detection circuit, comprising:
the circuit comprises a resistance voltage division branch circuit, a voltage detection circuit and a voltage detection circuit, wherein the resistance voltage division branch circuit comprises a sampling resistor and at least one voltage division resistor, the first end of the at least one voltage division resistor is correspondingly connected with at least one branch circuit in the circuit to be detected respectively, the second end of the at least one voltage division resistor is connected with the first end of the sampling resistor after being connected in parallel, and the second end of the sampling resistor is grounded;
the signal sampling branch circuit is connected with the sampling resistor and is used for collecting an electric signal on the sampling resistor;
and the direct current component extraction branch circuit is connected with the signal sampling branch circuit and is used for extracting the direct current component of the electric signal acquired by the signal sampling branch circuit.
2. The ground fault detection circuit according to claim 1, wherein the circuit to be detected comprises a rectification circuit, a dc bus circuit, an inverter circuit, which are connected in sequence;
the first end of the at least one divider resistor is correspondingly connected with at least one of the input end of the rectifying circuit, the direct-current bus and the output end of the inverter circuit.
3. The ground fault detection circuit of claim 2, wherein the number of the voltage dividing resistors is at least two;
the first end of at least one of the two divider resistors is connected with the direct current bus circuit, and the first end of the at least one divider resistor is correspondingly connected with at least one of the input end of the rectifying circuit and the output end of the inverter circuit.
4. The ground fault detection circuit of claim 3, wherein the input of the rectification circuit is a three-phase input, the output of the inverter circuit is a three-phase output, and the dc bus comprises positive and negative dc buses;
the first end of at least one of the at least two voltage-dividing resistors is correspondingly connected with at least one of the positive and negative direct-current buses, and the first end of at least one voltage-dividing resistor is correspondingly connected with at least one of the three single-phase input ends of the rectifying circuit and the three single-phase output ends of the inverter circuit respectively.
5. The ground fault detection circuit according to claim 2, wherein the circuit to be detected comprises a rectification unit, a direct current bus circuit and an inverter circuit which are connected in sequence, wherein the rectification unit comprises a plurality of cascaded rectification circuits;
the number of the voltage dividing resistors is at least two, the first ends of the at least two voltage dividing resistors are respectively and correspondingly connected with at least two of the input ends of the rectifying circuits, the direct current bus circuit and the output ends of the inverter circuit, wherein the at least two voltage dividing resistors have different direct current potential components, and the direct current potential components of the equivalent voltage dividing resistors of the at least two voltage dividing resistors are different from the direct current potential components of any one of the input ends of the rectifying circuits, the direct current bus and the output ends of the inverter circuit.
6. The ground fault detection circuit of claim 1, wherein said dc component extraction branch includes a low pass filter device connected to said signal sampling branch.
7. The ground fault detection circuit according to any one of claims 1 to 6, wherein the signal sampling branch comprises a voltage sampling branch, the voltage sampling branch is connected across the sampling resistor and collects voltage data across the sampling resistor.
8. The ground fault detection circuit according to any one of claims 1 to 6, wherein the signal sampling branch comprises a current sampling branch, the current sampling branch is connected in series with the first end or the second end of the sampling resistor and collects current data on the sampling resistor.
9. A ground fault detection apparatus, characterized in that the ground fault detection apparatus comprises the ground fault detection circuit according to any one of claims 1 to 8, and a processor, the processor is connected with a dc component extraction branch in the ground fault detection circuit, and judges whether a ground fault occurs in the circuit to be detected according to the dc component of the electrical signal extracted by the dc component extraction branch.
10. The ground fault detection device of claim 9, wherein the processor determines that a ground fault occurs in the circuit to be detected when a variation of the dc component of the electrical signal within a preset time period reaches a preset threshold.
11. The ground fault detection circuit of claim 9, wherein the ground fault detection device further comprises:
and the alarm is connected with the processor and sends alarm information when the processor judges that the circuit to be detected has a ground fault.
12. The ground fault detection device according to any one of claims 9 to 11, wherein the ground fault detection device is a current transformer or a frequency converter.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810758233.6A CN110780223A (en) | 2018-07-11 | 2018-07-11 | Ground fault detection circuit and device |
| PCT/EP2019/068317 WO2020011740A1 (en) | 2018-07-11 | 2019-07-09 | Ground fault detection circuit and device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810758233.6A CN110780223A (en) | 2018-07-11 | 2018-07-11 | Ground fault detection circuit and device |
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| CN110780223A true CN110780223A (en) | 2020-02-11 |
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| WO (1) | WO2020011740A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112462194A (en) * | 2020-11-09 | 2021-03-09 | 国网山东省电力公司东平县供电公司 | Fault finding device and method for distribution line |
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