WO2020011740A1 - Ground fault detection circuit and device - Google Patents
Ground fault detection circuit and device Download PDFInfo
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- WO2020011740A1 WO2020011740A1 PCT/EP2019/068317 EP2019068317W WO2020011740A1 WO 2020011740 A1 WO2020011740 A1 WO 2020011740A1 EP 2019068317 W EP2019068317 W EP 2019068317W WO 2020011740 A1 WO2020011740 A1 WO 2020011740A1
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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
Definitions
- spurious capacitance, spurious inductance, etc. generally exists in a system, and especially use of a long cable leads to relatively high spurious capacitance to ground. Such spurious capacitance to ground will lead to incorrect ground fault detection, decreasing the accuracy of ground fault detection.
- Figure 1 is a first structural diagram for a ground fault detection circuit according to an embodiment of the present invention ;
- the signal sampling branch may be a voltage sampling branch connected to both ends of the sampling resistor, and the voltage sampling branch collects voltage data on both ends of the sampling resistor.
- the signal sampling branch may further be a current sampling branch collected in series to a first end or second end of the sampling resistor to collect current data on the sampling resistor.
- the current sampling branch may be connected between the second end of the sampling resistor and the grounding terminal, or may be connected between a connecting terminal connected in parallel to the second end of at least one voltage-dividing resistor and the first end of the sampling resistor.
- electric energy transferred in the circuit to be detected may be three-phase electric power
- the input end of the rectification circuit is a three-phase input end
- the output end of the inversion circuit is a three-phase output end
- the DC bus comprises a positive DC bus and a negative DC bus.
- the first ends of at least one voltage-dividing resistor may be connected by one-to-one correspondence to at least one of the three single-phase input ends of the three-phase input ends of the rectification circuit, the positive and negative DC buses, and at least one of the three single-phase output ends of the inversion circuit.
- the number of voltage-dividing resistors is smaller than the number of branches that have different voltage signals in the circuit to be detected.
- the DC component extraction branch cannot effectively extract a DC component of an electric signal
- the voltage-dividing resistor is connected to the output end of the inversion circuit, when a ground fault occurs at the input end and output end of the rectification circuit and the output end of the inversion circuit, the DC component extraction branch also cannot effectively extract a DC component of an electric signal, making it impossible to accurately detect the ground fault .
- a ground fault detection circuit In a ground fault detection circuit according to the present embodiment, at least two voltage-dividing resistors are disposed and connected to different branches in the circuit to be detected so that a loop is formed by the plurality of voltage-dividing resistors and the faulty grounding terminal of the circuit to be detected. This ensures that at least one closed current loop passes through the ground, thereby further improving the reliability of the ground fault detection circuit.
- the circuit to be detected has only three types of DC components: 0, 0.5 V dc , and V dc , respectively represented by three points X0, XI, and X2.
- the ground fault detection circuit comprises two voltage-dividing resistors: Ri and R 2 .
- the first end of at least one voltage-dividing resistor of the ground fault detection circuit may be correspondingly connected to at least one of the input end (including the three-phase input end) of the rectification circuit in each unit circuit, the positive and negative DC buses, and the output end (including the three-phase output end) of the inversion circuit.
- the DC component signals of the electric signals obtained by each ground fault detection circuit whether a ground fault has occurred in the circuit to be detected can be determined and the unit circuit in which the ground fault has occurred can be determined.
- the negative electrode of the DC bus (namely, point X0 in the figure) is used as a reference potential (zero potential) and the potential of the positive electrode of the DC bus (namely, point X12 in the figure) is V dc
- the DC potential components of points X0, XI, ...XI 1, and X12 at the input ends and output ends of each rectification circuit shown in the figure are 0 V, 0.5/6 V dc , 1/6 V dc ...5.5/6 V dc , and V dc , respectively;
- the DC potential component of output end X13 of the inversion circuit is 0.5 V dc .
- the circuit shown in Figure 5 can be considered equivalent to the circuit shown in Figure 6. Since point X13 and point X6 have the same DC potential component when only DC components are analyzed, the two points can be connected, and the equivalent circuit diagram is the circuit to be detected as shown in Figure 7.
- the voltage-dividing resistors in an embodiment of the present invention may be implemented by using a single resistor or by using a plurality of resistors connected in series.
- a ground fault detection circuit by means of a resistance voltage dividing branch disposed between a circuit to be detected and a grounding terminal, a signal sampling branch for detecting an electric signal on a sampling resistor, and a DC component extraction branch for extracting a DC component from a collected signal, can, when a ground fault occurs in the circuit to be detected, effectively detect an electric signal in a loop formed by the faulty grounding terminal and the resistance voltage dividing branch, and extract the DC component of the electric signal, thereby accurately determining whether a ground fault has occurred on the basis of the DC component of the collected electric signal, preventing spurious capacitance from affecting the ground fault detection, and improving the accuracy of the ground fault detection; in addition, since ground fault detection can be performed without any high-precision special detection device, ground faults can be accurately detected at relatively low costs.
- the processor can determine whether a ground fault has occurred in the circuit to be detected. For example, when the DC component of the obtained current signal or voltage signal is zero, the processor determines that no ground fault has occurred in the circuit to be detected; alternatively, when the variation in the DC component of the obtained current signal or voltage signal within a preset time period has reached or exceeded a preset threshold, the processor determines that a ground fault has occurred in the circuit to be detected.
- a ground fault detection device further comprises an alarm device that is connected to the processor; when the processor detects a ground fault in the circuit to be detected, the alarm device gives an alarm prompting repair of the circuit to be detected in a timely manner, thereby preventing the ground fault from causing a major damage.
- the alarm device may be an audio-visual alarm device for giving an audio-visual alarm when the processor detects a ground fault in the device to be detected, or a communication device capable of sending a WeChat message or short message, which, when the processor determines that a ground fault has occurred in the device to be detected, sends a message to an associated communication device of a member staff, indicating that a ground fault has occurred in the device to be detected.
- a ground fault detection device may be a current-transforming device (for example, a three-phase current transformer) or a frequency-transforming device (for example, a three-phase frequency transformer) .
- a ground fault detection circuit may be disposed to integrate a ground fault detection function in the current transformer or frequency transformer, thereby detecting ground faults in circuits in devices, such as rectification circuits, DC bus circuits, and inversion circuits; thus, ground faults in devices can be detected in a timely manner and accurately without being affected by spurious capacitance.
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- General Physics & Mathematics (AREA)
- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
An embodiment of the present invention provides a ground fault detection circuit and a current-transforming or frequency-transforming device. The ground fault detection circuit comprises: a resistance voltage dividing branch, the resistance voltage dividing branch comprising a sampling resistor and at least one voltage-dividing resistor, the first ends of the at least one voltage-dividing resistor being respectively and correspondingly connected to at least one branch in a circuit to be detected, the second ends of the at least one voltage-dividing resistor being connected in parallel and then connected to the first ends of the sampling resistor, the second ends of the sampling resistor being grounded; a signal sampling branch, connected to the sampling resistor, for collecting an electric signal on the sampling resistor; and a DC component extraction branch, connected to the signal sampling branch, for extracting a DC component of an electric signal collected by the signal sampling branch. With the technical solution of the present invention, a ground fault can be accurately detected at a low cost and without being affected by spurious capacitance.
Description
Specification
Ground Fault Detection Circuit and Device
Technical Field
The present invention relates to the technical field of electric power and electronics, in particular to a ground fault detection circuit and device.
Background Art
A three-phase frequency transformer, a current transformer, and other electrical devices that are commonly found in an isolation terra (IT) system each undergo a ratification step, a DC bus step, and an inversion step when operating. In the case of a ground fault at any point in any of the three steps, an abnormality arises in the device and the device should give an alarm or point out the fault. However, since a single-point ground fault generally does not affect the normal operation of a device, it is difficult to determine whether a ground fault has occurred by detecting a ground fault using methods such as detecting an interphase voltage and a current signal of the main loop, and a ground fault can be detected only by using a high-precision special device, incurring high detection costs. Moreover, spurious capacitance, spurious inductance, etc. generally exists in a system, and especially use of a long cable leads to relatively high spurious capacitance to ground. Such spurious capacitance to ground will lead to incorrect ground fault detection, decreasing the accuracy of ground fault detection.
Summary of the Invention
An objective of the present invention is to provide a ground fault detection circuit and device for solving the problems with the prior art that the costs of ground fault detection are high and the accuracy of ground fault detection is relatively low due to spurious capacitance.
In order to achieve the above-mentioned objective, an embodiment
of the present invention provides a ground fault detection circuit, comprising: a resistance voltage dividing branch, the resistance voltage dividing branch comprising a sampling resistor and at least one voltage-dividing resistor, the first ends of the at least one voltage-dividing resistor being respectively and correspondingly connected to at least one branch in a circuit to be detected, the second ends of the at least one voltage-dividing resistor being connected in parallel and then connected to the first ends of the sampling resistor, the second ends of the sampling resistor being grounded; a signal sampling branch, connected to the sampling resistor, for collecting an electric signal on the sampling resistor; and a DC component extraction branch, connected to the signal sampling branch, for extracting a DC component of an electric signal collected by the signal sampling branch.
In an exemplary embodiment of the ground fault detection circuit, the circuit to be detected comprises a rectification circuit, a DC bus circuit, and an inversion circuit that are connected in sequence; the first ends of the at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the input end of the rectification circuit, the DC bus, and the output end of the inversion circuit.
In an exemplary embodiment of the ground fault detection circuit, the number of the voltage-dividing resistors is at least two, a first end of at least one voltage-dividing resistor of the at least two voltage-dividing resistors is connected to the DC bus circuit, and the first ends of at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the input end of the rectification circuit and the output end of the inversion circuit.
In an exemplary embodiment of the ground fault detection circuit, the input end of the rectification circuit is a three-phase input end, the output end of the inversion circuit is a three-phase
output end, and the DC bus comprises a positive DC bus and a negative DC bus; the first ends of at least one voltage-dividing resistor of the at least two voltage-dividing resistors are respectively and correspondingly connected to at least one of the positive DC bus and the negative DC bus, and the first ends of at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the three single-phase input ends of the rectification circuit and the three single-phase output ends of the inversion circuit.
In an exemplary embodiment of the ground fault detection circuit, the circuit to be detected comprises a rectification unit, a DC bus circuit, and an inversion circuit that are connected in sequence, the rectification unit comprising a plurality of cascade 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 to at least two of the input ends of the plurality of rectification circuits, the DC bus circuit, and the output end of the inversion circuit that have different DC potential components, and the DC potential component of an equivalent voltage-dividing resistor of the at least two voltage-dividing resistors is different from the DC potential component of any one of the input end of the rectification circuit, the DC bus, and the output end of the inversion circuit.
In an exemplary embodiment of the ground fault detection circuit, the DC component extraction branch comprises a low-pass filter element that is connected to the signal sampling branch.
In an exemplary embodiment of the ground fault detection circuit, the signal sampling branch comprises a voltage sampling branch that is connected to both ends of the sampling resistor to collect voltage data on both ends of the sampling resistor.
In an exemplary embodiment of the ground fault detection circuit
the signal sampling branch comprises a current sampling branch that is connected in series to a first end or second end of the sampling resistor to collect current data on the sampling resistor .
An embodiment of the present invention further provides a ground fault detection device that comprises the ground fault detection circuit according to any one of the above-mentioned embodiments of the present invention and a processor that is connected to the DC component extraction branch in the ground fault detection circuit to determine whether a ground fault has occurred in the circuit to be detected on the basis of the DC component of the electric signal extracted by the DC component extraction branch.
In an exemplary embodiment of the ground fault detection device, the processor determines that a ground fault has occurred in the circuit to be detected when the variation in the DC component of the electric signal within a preset time period has reached or exceeded a preset threshold.
In an exemplary embodiment of the ground fault detection device, the ground fault detection device further comprises an alarm device that is connected to the processor, for giving an alarm when the processor determines that a ground fault has occurred in the circuit to be detected.
In an exemplary embodiment of the ground fault detection device, the ground fault detection device is a current-transforming or frequency-transforming device.
A ground fault detection circuit and device according to an embodiment of the present invention, by means of a resistance voltage dividing branch, a signal sampling branch for detecting an electric signal on a sampling resistor, and a DC component extraction branch for extracting a DC component from a collected signal, that are disposed between a circuit to be detected and
a grounding terminal, can, in case of a ground fault in the circuit to be detected, effectively detect an electric signal in the loop formed by the faulty grounding terminal and the resistance voltage dividing branch and extract the DC component of the electric signal, thereby accurately determining whether a ground fault has occurred on the basis of the DC component of the collected electric signal, preventing spurious capacitance from affecting the ground fault detection, and improving the accuracy of the ground fault detection; in addition, since ground fault detection can be performed without any high-precision special detection device, ground faults can be accurately detected at relatively low costs.
Brief Description of the Drawings
A preferred embodiment of the present invention will be described in detail below with reference to the drawings to make the above-mentioned and other characteristics and benefits of the present invention clearer to those of ordinary skill in the art. In the drawings,
Figure 1 is a first structural diagram for a ground fault detection circuit according to an embodiment of the present invention ;
Figure 2 is a first structural diagram for a circuit to be detected provided in an embodiment of the present invention;
Figure 3 is an equivalent circuit diagram for the DC component in Figure 2;
Figure 4 is a first application status schematic diagram for a ground fault detection circuit according to an embodiment of the present invention;
Figure 5 is a second structural diagram for a circuit to be detected provided in an embodiment of the present invention; Figure 6 is an equivalent circuit diagram for the DC component in Figure 5;
Figure 7 is a second application status schematic diagram for a ground fault detection circuit according to an embodiment of the present invention;
Figure 8 is a third application status schematic diagram for a ground fault detection circuit according to an embodiment of the present invention;
Figure 9 is the ground loop in Figure 8; and
Figure 10 is an equivalent circuit diagram for the DC component in Figure 9.
Specific Embodiment
In order to further clarify the objective, technical solution, and benefits of the present invention, the present invention will be described below in greater detail with respect to an embodiment .
Figure 1 is a structural diagram for a ground fault detection circuit according to an embodiment of the present invention. As shown in Figure 1, a ground fault detection circuit according to the present embodiment comprises a resistance voltage dividing branch, a signal sampling branch, and a DC component extraction branch, the resistance voltage dividing branch comprising a sampling resistor R0 and at least one voltage-dividing resistor (n voltage-dividing resistors, namely, Ri, R2...Rn, are shown in the figure) , the first ends of the at least one voltage-dividing resistor being respectively and correspondingly connected to at least one branch in the circuit to be detected, the second ends of the at least one voltage-dividing resistor being connected in parallel and then connected to the first ends of the sampling resistor, the second ends of the sampling resistor being grounded; the signal sampling branch is connected to the sampling resistor to collect an electric signal on the sampling resistor; and the DC component extraction branch is connected to the signal sampling branch to extract a DC component of an electric signal collected by the signal sampling branch.
A ground fault detection circuit according to the present embodiment is used to detect any ground faults in a circuit to be detected in an IT system. In a ground fault detection circuit,
the resistance voltage dividing branch, by the first ends of at least one voltage-dividing resistor, is connected to at least one different branch in the circuit to be detected by one-to-one correspondence, and is grounded by a second end of the sampling resistor; in other words, the resistance voltage dividing branch is connected between the input end and at least one branch of the circuit to be detected. When the circuit to be detected operates, if no ground fault has occurred in the circuit to be detected, no current is generated in the resistance voltage dividing branch, the signal sampling branch can collect no electrical signal on the sampling resistor, or the collected electric signal, for example, a current or voltage signal, is zero; if a ground fault has occurred in the circuit to be detected, a loop is formed by the branch in which the ground fault has occurred and the resistance voltage dividing branch, a current is generated on the sampling resistor, a voltage is generated on both ends of the sampling resistor, and the signal sampling branch can collect a current signal on the sampling resistor, a voltage signal on both ends of the sampling resistor, and other electric signals.
Based on the electric signal collected by the voltage sampling branch, for example, whether the current signal or voltage signal is zero and variation in the current signal or voltage signal, it can be accurately determined whether a ground fault has occurred in the circuit to be detected. In addition, in terms of a DC component, spurious capacitance is open-circuit; it is determined by means of the DC component of the collected electric signal and based on the extracted DC component, whether a ground fault has occurred in the circuit to be detected; thus, incorrect ground fault detection due to grounding of the collected AC signal by spurious capacitance is prevented and the ground fault detection remains unaffected by spurious capacitance, thereby improving the accuracy of the ground fault detection.
Further, the resistance voltage dividing branch can be composed
of common resistors, a conventional current, voltage, etc., a signal collection device can be used as the signal sampling branch, and a conventional filter device can be used as the DC component extraction branch to implement the function of DC component extraction. Thus, ground fault detection can be performed without any high-precision special detection device, and ground faults can be accurately detected at relatively low costs. For example, the DC component extraction branch may comprise a low-pass filter element that is connected to the signal sampling branch.
In actual application, at least one voltage-dividing resistor in the resistance voltage dividing branch may be respectively connected to branches that have different voltage signals in the circuit to be detected, for example, being connected to input ends or out ends of different components in the circuit to be detected .
Further, the signal sampling branch may be a voltage sampling branch connected to both ends of the sampling resistor, and the voltage sampling branch collects voltage data on both ends of the sampling resistor. The signal sampling branch may further be a current sampling branch collected in series to a first end or second end of the sampling resistor to collect current data on the sampling resistor. Herein, the current sampling branch may be connected between the second end of the sampling resistor and the grounding terminal, or may be connected between a connecting terminal connected in parallel to the second end of at least one voltage-dividing resistor and the first end of the sampling resistor.
According to an exemplary embodiment of the present invention, as shown in Figure 2, the circuit to be detected may comprise a rectification (AC/DC) circuit, a DC bus circuit, and an inversion (DC/AC) circuit that are collected in sequence. When the ground fault detection circuit is used to detect any ground faults in the circuit to be detected, the first ends of at least
one voltage-dividing resistor may be respectively and correspondingly connected to at least one of the input end of the rectification circuit, the DC bus circuit, and the output end of the inversion circuit. In the figure, the AC on the input side of the rectification circuit is an AC source, equivalent to the grid side or power supply side, and the M on the output side of the rectification circuit is a motor, equivalent to the load side.
Herein, electric energy transferred in the circuit to be detected may be three-phase electric power, the input end of the rectification circuit is a three-phase input end, the output end of the inversion circuit is a three-phase output end, and the DC bus comprises a positive DC bus and a negative DC bus. When the ground fault detection circuit is connected to the circuit to be detected, the first ends of at least one voltage-dividing resistor may be connected by one-to-one correspondence to at least one of the three single-phase input ends of the three-phase input ends of the rectification circuit, the positive and negative DC buses, and at least one of the three single-phase output ends of the inversion circuit. Optionally, the number of voltage-dividing resistors is smaller than the number of branches that have different voltage signals in the circuit to be detected.
In the circuit to be detected as shown in Figure 2, A, B, and C are respectively arbitrary points in the input lines to which each of the three single-phase input ends of the rectification circuit correspond, D and E are respectively arbitrary points in the positive and negative DC buses, and F, G, and H are respectively arbitrary points in the output lines to which each of the three single-phase output ends of the inversion circuit correspond .
When the ground fault detection circuit is connected to the circuit to be detected, the first end of the voltage-dividing resistor may be connected to any one of points A, B, C, D, E,
F, G, and H.
In an alternative embodiment, the ground fault detection circuit may comprise only one voltage-dividing resistor, and the first end of the voltage-dividing resistor may be connected to any one of points A, B, C, F, G, and H . In other words , the voltage-dividing resistor is connected to the input end of the rectification circuit or the output end of the inversion circuit so that when a ground fault occurs in the positive or negative DC bus (namely, at point D or E) , a valid DC component can be extracted by the DC component extraction branch on the basis of an electric signal extracted by the signal sampling branch, thereby accurately determining that a ground fault has occurred in the positive or negative DC bus. It should be noted that if the voltage-dividing resistor is connected to the input end of the rectification circuit, when a ground fault occurs at the input end of the rectification circuit or the output end of the inversion circuit, the DC component extraction branch cannot effectively extract a DC component of an electric signal, and if the voltage-dividing resistor is connected to the output end of the inversion circuit, when a ground fault occurs at the input end and output end of the rectification circuit and the output end of the inversion circuit, the DC component extraction branch also cannot effectively extract a DC component of an electric signal, making it impossible to accurately detect the ground fault .
Further, the first end of the voltage-dividing resistor may also be connected to point D or point E. In other words, the voltage-dividing resistor is connected to the positive and negative DC buses so that when a ground fault occurs at the input end of the rectification circuit (namely, point A, B, or C) or the output end of the inversion circuit (namely, point F, G, or H) , an electric signal DC component can be effectively extracted by the DC component extraction branch to accurately detect the ground fault .
In an alternative embodiment, the ground fault detection circuit may comprise at least two voltage-dividing resistors; when the ground fault detection circuit is connected to the circuit to be detected, the first ends 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 is connected to the input end of the rectification circuit or the output end of the inversion circuit. This ensures that when a ground fault occurs at any point in the rectification circuit, the DC bus circuit, or the inversion circuit, the DC component extraction branch can extract a valid DC component from an electric signal collected by the signal sampling branch, thereby improving the reliability of the ground fault detection circuit in ground fault detection.
Further, if the ground fault detection circuit comprises only one voltage-dividing resistor and a ground fault occurs where the voltage-dividing resistor and the circuit to be detected are connected, although a loop is formed, no voltage difference exists in the loop and the voltage data sampled by the voltage sampling branch is zero, making it impossible to determine that a ground fault has occurred in the circuit to be detected; alternatively, an open-circuit fault occurs where the voltage-dividing resistor is connected, and the voltage sampling branch is unable to sample a voltage signal; consequently, it cannot be determined that a ground fault has occurred in the circuit to be detected. In a ground fault detection circuit according to the present embodiment, at least two voltage-dividing resistors are disposed and connected to different branches in the circuit to be detected so that a loop is formed by the plurality of voltage-dividing resistors and the faulty grounding terminal of the circuit to be detected. This ensures that at least one closed current loop passes through the ground, thereby further improving the reliability of the ground fault detection circuit.
Specifically, the first end of at least one voltage-dividing resistor of the at least two voltage-dividing resistors may be connected to the positive or negative DC bus (namely, point D or E) , and the first ends of at least one voltage-dividing resistor may be connected by one-to-one correspondence to the three single-phase input ends of the rectification circuit or the three single-phase output ends of the inversion circuit (namely, at least one of points A, B, C, F, G, and H) .
If only DC components are considered, the circuit to be detected as shown in Figure 2 may be equivalent to the circuit shown in Figure 3. In Figure 3, the three-phase input end of the rectification circuit and the three-phase output end of the inversion circuit are simplified as three-phase power line legends. The voltage source shown in Figure 3 is equivalent to a DC voltage source. If the potential of the negative electrode of the DC bus (namely, point E) is used as a reference potential (zero potential) and the potential of the positive electrode of the DC bus (namely, point D) is Vdcr and points A, B, and C are AC voltage input sources, then the DC potential component of the these three points relative to point E is 0.5 Vdc and accordingly the DC potential component of the three points F, G, and H is also 0.5 Vdc · If only DC components are considered, these six points can be connected; in other words, the circuit to be detected as shown in Figure 3 can be considered equivalent to the circuit to be detected as shown in Figure 4.
In the output circuit systems (including the circuit to be detected and the ground fault detection circuit) in Figure 4, the circuit to be detected has only three types of DC components: 0, 0.5 Vdc, and Vdc, respectively represented by three points X0, XI, and X2. The ground fault detection circuit comprises two voltage-dividing resistors: Ri and R2. Voltage-dividing resistor Ri is connected to XI (in actual operation, the first end of voltage-dividing resistor Ri may be connected to any one of points A, B, C, F, G, and H that have a DC potential component of 0.5
Vdc) and voltage-dividing resistor R2 is connected to X2 (in actual operation, the first end of voltage-dividing resistor R2 may be connected to point D that has a DC potential component of Vdc) · The ground fault detection circuit uses a voltage sampling branch as a signal sampling branch; the voltage sampling branch may collect voltage signal VR0 on resistor R0; the DC component extraction branch may perform DC component extraction on voltage signal VR0 to obtain voltage DC component signal Vave-Ro f°r determining whether a ground fault has occurred in the circuit to be detected.
It should be noted that in the present embodiment, only the circuit to be detected as shown in Figure 2 is used as an example to describe the ground fault detection circuit according to an embodiment of the present invention, the method for connecting the ground fault detection circuit, and the ground fault detection method. However, it should be clear to those of ordinary skill in the art that a specific method for connecting a rectification circuit, a DC bus circuit, and an inversion circuit in the circuit to be detected according to an embodiment of the present invention is not limited to that shown in Figure 2 and that a ground fault detection circuit according to an embodiment of the present invention is also not limited to detection of a circuit system that comprises a rectification circuit, a DC bus circuit, and an inversion circuit; in another embodiment, with reference to the present embodiment, a ground fault detection circuit according to an embodiment of the present invention is connected to any other circuit to detect a ground fault.
For example, in certain embodiments of the present invention, a circuit to be detected may further be a cascade structure of multiple unit circuits, each unit circuit comprising a rectification circuit, a DC bus circuit, and an inversion circuit that are connected in sequence; in other words, each unit can be the circuit to be detected as shown in Figure 2. In such a case, with reference to the present embodiment, a plurality of
ground fault detection circuits may be disposed, and each unit circuit may be connected to one circuit to be detected. Specifically, the first end of at least one voltage-dividing resistor of the ground fault detection circuit may be correspondingly connected to at least one of the input end (including the three-phase input end) of the rectification circuit in each unit circuit, the positive and negative DC buses, and the output end (including the three-phase output end) of the inversion circuit. Thus, based on the DC component signals of the electric signals obtained by each ground fault detection circuit, whether a ground fault has occurred in the circuit to be detected can be determined and the unit circuit in which the ground fault has occurred can be determined.
Another example is that, in some other embodiments of the present invention, the circuit to be detected further comprises a rectification unit, a DC bus circuit, and an inversion circuit that are connected in sequence, the rectification unit comprising a plurality of cascade rectification circuits; in other words, a rectification unit composed of a plurality of cascade rectification circuits is connected to a DC bus circuit and an inversion circuit. In such a case, with reference to the present embodiment, the first end of at least one voltage-dividing resistor of the ground fault detection circuit may be correspondingly connected to at least one of the input end (including the three-phase input end) of each rectification circuit, the positive and negative DC buses, and the output end (including the three-phase output end) of the inversion circuit.
In a specific application scenario, the ground fault detection circuit shown in Figure 1 may be connected to the circuit to be detected as shown in Figure 5 to perform ground fault detection on the circuit to be detected.
The circuit to be detected as shown in Figure 5 is a frequency-transforming device in the prior art; the power input
side of the frequency-transforming device comprises a transformer; the transformer is secondarily provided with a plurality of windings, and each winding is connected to one three-phase rectification circuit; the plurality of rectification circuits are cascaded and then connected to a DC bus circuit and an inversion circuit in sequence.
The DC potential components of the three-phase output lines of each winding (namely, the three-phase input lines of each rectification circuit) are the same, and the DC potential components of the inversion circuit are also the same. Figure 5 shows a cascade structure of six rectification circuits. If the negative electrode of the DC bus (namely, point X0 in the figure) is used as a reference potential (zero potential) and the potential of the positive electrode of the DC bus (namely, point X12 in the figure) is Vdc, the DC potential components of points X0, XI, ...XI 1, and X12 at the input ends and output ends of each rectification circuit shown in the figure are 0 V, 0.5/6 Vdc, 1/6 Vdc...5.5/6 Vdc , and Vdc, respectively; the DC potential component of output end X13 of the inversion circuit is 0.5 Vdc. If only DC components are considered, the circuit shown in Figure 5 can be considered equivalent to the circuit shown in Figure 6. Since point X13 and point X6 have the same DC potential component when only DC components are analyzed, the two points can be connected, and the equivalent circuit diagram is the circuit to be detected as shown in Figure 7.
When the ground fault detection circuit shown in Figure 1 is connected to the circuit to be detected as shown in Figure 5, voltage-dividing resistors Ri, R2...Rn are connected by one-to-one correspondence to n of points X0, XI, ...X12, and X13.
If n = 1, the point connecting voltage-dividing resistor Ri and the circuit to be detected is Xs and has a DC potential of xs, and the point at which the ground fault occurred is Xg in the circuit to be detected and has a DC potential of xg, then the
DC potential component Vave_Ro on R0 can be obtained by equation (1) , wherein Rg indicates the resistance of the grounding terminal of the circuit to be detected that had a ground fault .
In Figure 7, points Xs and X10 have the same DC potential, and points Xg and X2 have the same DC potential . In actual application, Xs may have the same DC potential as that of any other point; in other words, the first end of voltage-dividing resistor Ri may be connected to any one of points X0 to X12. Xg may also have the same DC potential as that of any one of points X0 to X12; in other words, a ground fault may occur at any point in the circuit to be detected.
Suppose n = 2, the point connecting voltage-dividing resistor Ri and the circuit to be detected is Xsi and has a DC potential of xsi , the point connecting voltage-dividing resistor R2 and the circuit to be detected is Xs2 and has a DC potential of xs2, and the point at which the ground fault occurred is Xg in the circuit to be detected and has a DC potential of xg, as shown in Figure 8.
Figure 9 is the ground loop in Figure 8, and the circuit shown in Figure 9 is analyzed according to the principle of superposition. In the first step, only the operation of the first DC voltage source xs2 - xsi in the figure is considered. In this case, Ro and Rg are connected in series and then are connected to Ri in parallel, before being integrally connected to R2 in series. The current on R0 may be calculated by equation (2) :
wherein
in the second step, only the operation of the second DC voltage source xsi - xg is considered; in this case, Ri and R2 are connected in parallel and then are integrally connected to Ro and Rg in series; thus, the current on R0 may be calculated by equation (3) :
The total current may be calculated by equation (4) :
It is known from equation (4) that the circuit in Figure 9 can be considered equivalent to the circuit in Figure 10. Therefore, the DC component voltage on R0 may be calculated by equation (5) :
From the above-mentioned method for calculating the DC component voltage on R0 when n = 2, it can be known that if only the DC components in the circuit system are considered and the potential in the system can be subdivided infinitely (or subdivided multiple times), then the equation for calculating the DC component voltage on R0 when n = 2 may be equivalently transformed into an equation for calculating the DC component voltage on R0 when n = 1. Therefore, in cases where n = 3, 4...n, for the method of calculating the DC component voltage on R0, a method using equivalent transformation by n - 1 times may also be adopted and ultimately equivalently transformed into the equation for calculating the DC component voltage on R0 when n = 1.
It should be noted that since the number of branches in the circuit system is limited, the number of voltage-dividing resistors to
be connected is limited. In cases where n = 2, 3...n, if it is ultimately equivalent to the case where n = 1 and the DC potential of the equivalent voltage-dividing resistor is different from the DC potential of any branch (a line in which the DC potentials at any points are the same) in the circuit system, then when a ground fault occurs at any point in the circuit system, the DC component voltage on R0 can be effectively calculated; thus, without being affected by spurious capacitance, ground fault detection can be accurately performed on the basis of calculated DC components. If it is ultimately equivalent to the case where n = 1 and the DC potential of the equivalent voltage-dividing resistor is the same as the DC potential of a branch in the circuit system, then when a ground fault occurs in the branch, the DC component voltage on R0 cannot be calculated and consequently the ground fault cannot be detected accurately.
Therefore, in order to accurately detect a ground fault regardless of the point at which it occurred, the DC potentials on each branch in the circuit system and the resistance values of each voltage-dividing resistor may be calculated in advance; then, n voltage-dividing resistors are correspondingly connected to n branches in the circuit system so that given the principle whereby the DC potential of the equivalent voltage-dividing resistor, when it is ultimately equivalent to the case where n = 1, is different from any DC potential of each branch in the circuit system, the n voltage-dividing resistors are connected to the n branches that have different voltage signals in the circuit system. For example, for the circuit system shown in Figure 5, n voltage-dividing resistors are correspondingly connected to n of a plurality of rectification circuits, DC bus circuits, and inversion circuits that 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 ends of the plurality of rectification circuits, DC bus circuits, and output ends of the inversion circuits. If a branch
in the circuit system is a three-phase power line, then the DC potentials of the three single-phase power lines are the same; when a voltage-dividing resistor is to be connected to the branch, the voltage-dividing resistor may be connected to any point on any one of the three single-phase power lines.
In an actual application scenario, the voltage-dividing resistors (including Ri, R2...Rn) in an embodiment of the present invention may be implemented by using a single resistor or by using a plurality of resistors connected in series.
A ground fault detection circuit according to an embodiment of the present invention, by means of a resistance voltage dividing branch disposed between a circuit to be detected and a grounding terminal, a signal sampling branch for detecting an electric signal on a sampling resistor, and a DC component extraction branch for extracting a DC component from a collected signal, can, when a ground fault occurs in the circuit to be detected, effectively detect an electric signal in a loop formed by the faulty grounding terminal and the resistance voltage dividing branch, and extract the DC component of the electric signal, thereby accurately determining whether a ground fault has occurred on the basis of the DC component of the collected electric signal, preventing spurious capacitance from affecting the ground fault detection, and improving the accuracy of the ground fault detection; in addition, since ground fault detection can be performed without any high-precision special detection device, ground faults can be accurately detected at relatively low costs.
On this basis, an embodiment of the present invention further provides a ground fault detection device. The ground fault detection device comprises the ground fault detection circuit according to any one of the above-mentioned embodiments of the present invention and a processor that is connected to the DC component extraction branch in the ground fault detection circuit; the processor is configured to obtain the DC component of an
electric signal extracted by the DC component extraction branch and, on the basis of the extracted DC component, determine whether a ground fault has occurred in the circuit to be detected.
Specifically, based on whether the DC component of the obtained electric signal is zero, or its variation within a preset time period, the processor can determine whether a ground fault has occurred in the circuit to be detected. For example, when the DC component of the obtained current signal or voltage signal is zero, the processor determines that no ground fault has occurred in the circuit to be detected; alternatively, when the variation in the DC component of the obtained current signal or voltage signal within a preset time period has reached or exceeded a preset threshold, the processor determines that a ground fault has occurred in the circuit to be detected.
Optionally, a ground fault detection device according to an embodiment of the present invention further comprises an alarm device that is connected to the processor; when the processor detects a ground fault in the circuit to be detected, the alarm device gives an alarm prompting repair of the circuit to be detected in a timely manner, thereby preventing the ground fault from causing a major damage. For example, the alarm device may be an audio-visual alarm device for giving an audio-visual alarm when the processor detects a ground fault in the device to be detected, or a communication device capable of sending a WeChat message or short message, which, when the processor determines that a ground fault has occurred in the device to be detected, sends a message to an associated communication device of a member staff, indicating that a ground fault has occurred in the device to be detected.
In an actual application scenario, a ground fault detection device according to an embodiment of the present invention may be a current-transforming device (for example, a three-phase current transformer) or a frequency-transforming device (for
example, a three-phase frequency transformer) . In other words, in a conventional device, for example, a current transformer or a frequency transformer, a ground fault detection circuit according to an embodiment of the present invention may be disposed to integrate a ground fault detection function in the current transformer or frequency transformer, thereby detecting ground faults in circuits in devices, such as rectification circuits, DC bus circuits, and inversion circuits; thus, ground faults in devices can be detected in a timely manner and accurately without being affected by spurious capacitance. Certainly, a ground fault detection device according to an embodiment of the present invention may also be a standalone device that can be connected to a circuit to be detected in a device, for example, a current transformer or a frequency transformer, to accurately detect a ground fault in a device, for example, a current transformer or a frequency transformer.
It should be pointed out that based on implementation needs, various components of an embodiment of the present invention may be divided into more components, or two or more components or parts of components may be combined into a new component, to achieve the objective of the embodiment.
The above-described embodiment is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made without departing from the spirit or principle of the present invention shall fall within the protection scope of the present invention.
Claims
1. A ground fault detection circuit, characterized in that it comprises :
a resistance voltage dividing branch, the resistance voltage dividing branch comprising a sampling resistor and at least one voltage-dividing resistor, the first ends of the at least one voltage-dividing resistor being respectively and correspondingly connected to at least one branch in a circuit to be detected, the second ends of the at least one voltage-dividing resistor being connected in parallel and then connected to the first ends of the sampling resistor, the second ends of the sampling resistor being grounded;
a signal sampling branch, connected to the sampling resistor, for collecting an electric signal on the sampling resistor;
and a DC component extraction branch, connected to the signal sampling branch, for extracting a DC component of an electric signal collected by the signal sampling branch.
2. The ground fault detection circuit as claimed in claim 1, characterized in that the circuit to be detected comprises a rectification circuit, a DC bus circuit, and an inversion circuit that are connected in sequence;
the first ends of the at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the input end of the rectification circuit, the DC bus, and the output end of the inversion circuit.
3. The ground fault detection circuit as claimed in claim 2, characterized in that the number of the voltage-dividing resistors is at least two;
a first end of at least one voltage-dividing resistor of the at least two voltage-dividing resistors is connected to the DC bus circuit, and the first ends of at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the input end of the rectification circuit and the output end of the inversion circuit.
4. The ground fault detection circuit as claimed in claim 3, characterized in that the input end of the rectification circuit is a three-phase input end, the output end of the inversion circuit is a three-phase output end, and the DC bus comprises a positive DC bus and a negative DC bus;
the first ends of at least one voltage-dividing resistor of the at least two voltage-dividing resistors are respectively and correspondingly connected to at least one of the positive DC bus and the negative DC bus, and the first ends of at least one voltage-dividing resistor are respectively and correspondingly connected to at least one of the three single-phase input ends of the rectification circuit and the three single-phase output ends of the inversion circuit.
5. The ground fault detection circuit as claimed in claim 2, characterized in that the circuit to be detected comprises a rectification unit, a DC bus circuit, and an inversion circuit that are connected in sequence, the rectification unit comprising a plurality of cascade 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 to at least two of the input ends of the plurality of rectification circuits, the DC bus circuit, and the output end of the inversion circuit that have different DC potential components, and the DC potential component of an equivalent voltage-dividing resistor of the at least two voltage-dividing resistors is different from the DC potential component of any one of the input end of the rectification circuit, the DC bus, and the output end of the inversion circuit.
6. The ground fault detection circuit as claimed in claim 1, characterized in that the DC component extraction branch comprises a low-pass filter element that is connected to the signal sampling branch .
7. The ground fault detection circuit as claimed in any one of claims 1 to 6, characterized in that the signal sampling branch comprises a voltage sampling branch that is connected to both ends of the sampling resistor to collect voltage data on both ends of the sampling resistor.
8. The ground fault detection circuit as claimed in any one of claims 1 to 6, characterized in that the signal sampling branch comprises a current sampling branch that is connected in series to a first end or second end of the sampling resistor to collect current data on the sampling resistor.
9. A ground fault detection device, characterized in that the ground fault detection device comprises the ground fault detection circuit as claimed in any one of claims 1 to 8 and a processor that is connected to the DC component extraction branch in the ground fault detection circuit, and determines whether a ground fault has occurred in the circuit to be detected based on the DC component of the electric signal extracted by the DC component extraction branch.
10. The ground fault detection device as claimed in claim 9, characterized in that the processor determines that a ground fault has occurred in the circuit to be detected when the variation in the DC component of the electric signal within a preset time period has reached or exceeded a preset threshold.
11. The ground fault detection circuit as claimed in claim 9, characterized in that the ground fault detection device further comprises :
an alarm device, connected to the processor, for giving an alarm when the processor determines that a ground fault has occurred in the circuit to be detected.
12. The ground fault detection device as claimed in any one of
claims 9 to 11, characterized in that the ground fault detection device is a current-transforming or frequency-transforming device .
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201810758233.6A CN110780223A (en) | 2018-07-11 | 2018-07-11 | Ground fault detection circuit and device |
| CN201810758233.6 | 2018-07-11 |
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| WO2020011740A1 true WO2020011740A1 (en) | 2020-01-16 |
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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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| US20140008970A1 (en) * | 2012-07-09 | 2014-01-09 | Honda Motor Co., Ltd. | Ground fault detecting device for an ungrounded circuit |
| JP2018009875A (en) * | 2016-07-13 | 2018-01-18 | 株式会社ケーヒン | Ground fault detection device |
| CN107797018A (en) * | 2017-11-03 | 2018-03-13 | 中车大连电力牵引研发中心有限公司 | Diesel locomotive grounded inspection circuit, device and method |
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| JP2004212376A (en) * | 2002-11-11 | 2004-07-29 | Matsushita Electric Works Ltd | Leakage detecting device |
| JP5415480B2 (en) * | 2011-06-02 | 2014-02-12 | 中国電力株式会社 | Ground fault detection device, program |
| CN102830283A (en) * | 2011-06-13 | 2012-12-19 | 中兴通讯股份有限公司 | Insulating detection device and detection method for direct-current power supply |
| US20150168473A1 (en) * | 2013-12-18 | 2015-06-18 | Enphase Energy, Inc. | Method and apparatus for ground fault detection |
| JP2017146197A (en) * | 2016-02-17 | 2017-08-24 | 株式会社ケーヒン | Ground fault detector |
| JP6725349B2 (en) * | 2016-07-13 | 2020-07-15 | 株式会社ケーヒン | Ground fault detector |
| CN106199343A (en) * | 2016-10-13 | 2016-12-07 | 国网四川省电力公司电力科学研究院 | A kind of power system DC power supply monitor and monitoring method |
| CN206583996U (en) * | 2016-11-25 | 2017-10-24 | 上海荣威塑胶工业有限公司 | Ground detection device and pond system |
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| CA1195384A (en) * | 1981-03-31 | 1985-10-15 | Arno Eichmann | Method and apparatus for determining leakage impedance of an ac power supply system |
| JP2923572B2 (en) * | 1990-05-31 | 1999-07-26 | 株式会社日立製作所 | Change width detector |
| US20140008970A1 (en) * | 2012-07-09 | 2014-01-09 | Honda Motor Co., Ltd. | Ground fault detecting device for an ungrounded circuit |
| JP2018009875A (en) * | 2016-07-13 | 2018-01-18 | 株式会社ケーヒン | Ground fault detection device |
| CN107797018A (en) * | 2017-11-03 | 2018-03-13 | 中车大连电力牵引研发中心有限公司 | Diesel locomotive grounded inspection circuit, device and method |
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