CN111337849A - Novel leakage current measuring device and method - Google Patents
Novel leakage current measuring device and method Download PDFInfo
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- CN111337849A CN111337849A CN201811545653.2A CN201811545653A CN111337849A CN 111337849 A CN111337849 A CN 111337849A CN 201811545653 A CN201811545653 A CN 201811545653A CN 111337849 A CN111337849 A CN 111337849A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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Abstract
The invention provides a novel leakage current measuring device and a method thereof, which are characterized by comprising an A-phase current transformer, a B-phase current transformer, a C-phase current transformer, a zero line current transformer, an A-phase current transformer secondary line, a B-phase current transformer secondary line, a C-phase current transformer secondary line, a zero line current transformer secondary line, a measuring current transformer and a measuring terminal; the phase current transformer A, the phase current transformer B, the phase current transformer C and the zero line current transformer are respectively arranged on the phase A, the phase B, the phase C and the zero line of the line to be detected; the secondary line of the phase current transformer A, the secondary line of the phase current transformer B, the secondary line of the phase current transformer C and the secondary line of the zero line current transformer penetrate through the hole of the measuring current transformer. The invention calculates the leakage current of the original circuit by measuring the induced current of the current transformer, and solves the problem that the leakage current is difficult to measure by sleeving one transformer when the distance of the low-voltage 400V overhead circuit is too large.
Description
Technical Field
The invention relates to the problem of measuring leakage current of a low-voltage 400V overhead line, in particular to a novel leakage current measuring device and a method thereof.
Background
The current low-voltage 400V line leakage current measurement mode is as follows: if the circuit is a three-phase circuit, a current transformer is used for sheathing four wires of the A phase, the B phase, the C phase and a zero line together, and the measured current is the leakage current; if the circuit is a single-phase circuit, the live wire and the zero wire are sleeved together by using a current transformer, and the measured current is the leakage current. The method has certain difficulty in the actual operation process, namely, the phases of the 400V overhead line are very large in space and difficult to be sleeved together, and if a current transformer is sleeved on the overhead line, the current transformer needs to be very large and heavy, so that the line cannot bear the load.
The prior patent of 'external circuit breaker of electric energy meter' (patent number: 201620497112.7) also adopts a mode that four current transformers are respectively arranged on a line to measure the leakage current, but the mode adopted by the patent is that the amplitude and the angle of the current of each phase line at the same time are respectively collected by the four current transformers, and then the leakage current is directly calculated. The text is as follows:
"following use three-phase electric energy meter as an example, when explaining and adopting many current transformer the utility model discloses a theory of operation:
according to kirchhoff's law, leakage current is the vector sum of three-phase current and neutral current, namely when a three-phase four-wire distribution line normally operates, three-phase load is unbalanced, the line leakage current is zero at the moment, namely when a certain phase has a ground fault, the detected vector sum of three-phase current and neutral current is not zero and is equal to the ground fault current.
The controller of the electric operating mechanism respectively collects A, B, C, N vector current j of each phase through a current transformer: amplitude (I)A、IB、IC、IN) And angle (phi)A、φB、φC、φN) Each vector is decomposed into real parts (I)AI、IBI、ICI、INI) And imaginary part (jI)A、jIB、jIC、jIN) The method comprises the following steps:
I＝IAI+IBI+ICI+INI
J＝jIA+jIB+jIC+jIN
when a ground fault occurs, the leakage current amplitude I acquired by the current transformerPE：
IPE=√I2+J2≠0
If the current transformer has a transformation ratio of K, the earth fault current I is setO(d)：
IO(d)＝K×IPE
Setting value (setting value) I of leakage protection of external circuit breaker of electric energy meterZdGAccording to the following steps:
IO(d)≤1.3IZdG
to avoid malfunction, set value IZdGThe total leakage current of the line and the equipment is 2.5-4.0 times larger than that of the line and the equipment in normal operation, and the leakage current can be set according to field application conditions. ".
The invention adopts the method that a measuring current transformer is sleeved on the secondary wires of the four current transformers for direct measurement. The two methods are not essentially the same.
Disclosure of Invention
The invention provides a novel leakage current measuring device and a method thereof, which are characterized by comprising an A-phase current transformer, a B-phase current transformer, a C-phase current transformer, a zero line current transformer, an A-phase current transformer secondary line, a B-phase current transformer secondary line, a C-phase current transformer secondary line, a zero line current transformer secondary line, a measuring current transformer and a measuring terminal; the phase current transformer A, the phase current transformer B, the phase current transformer C and the zero line current transformer are respectively arranged on the phase A, the phase B, the phase C and the zero line of the line to be detected; the secondary line of the phase current transformer A, the secondary line of the phase current transformer B, the secondary line of the phase current transformer C and the secondary line of the zero line current transformer jointly penetrate through the hole of the measuring current transformer; the measuring current transformer is connected to a measuring terminal.
The phase current transformer A, the phase current transformer B, the phase current transformer C and the zero line current transformer are current transformers with the same model and the same specification.
The secondary line of the phase current transformer A, the secondary line of the phase current transformer B, the secondary line of the phase current transformer C and the secondary line of the zero line current transformer penetrate through the hole of the measuring current transformer in the same direction.
The phase A current transformer secondary line, the phase B current transformer secondary line, the phase C current transformer secondary line and the zero line current transformer secondary line are connected to the measuring terminal.
A common method for measuring leakage current of a low-voltage 400V three-phase line is to sleeve a current transformer on a three-phase line and a zero line, sleeve the four lines together, and calculate an induced current generated in the current transformer to obtain the leakage current. According to the basic principle of the current transformer, compared with the current of the original line, the induced current generated by the current transformer has the same current phase, and the current magnitude is in a multiple relation, and the multiple is determined by the model specification of the transformer. Therefore, when the secondary line of the phase current transformer of A phase, the secondary line of the phase current transformer of B phase, the secondary line of the phase current transformer of C phase and the secondary line of the zero line current transformer penetrate through the hole of the measuring current transformer, the induced current generated by the measuring current transformer is consistent with the phase of the leakage current of the original line, and the magnitude of the induced current is in a multiple relation. The leakage current of the original line can be obtained through simple calculation of the measuring terminal. The method provides a basis for the maintainers to judge the position of the line leakage current, and accelerates the speed of overhauling the leakage current fault.
The method provided by the invention is not only suitable for a low-voltage 400V three-phase line, but also suitable for a low-voltage 400V single-phase line, and only needs to change the installation of four current transformers on the A phase, the B phase, the C phase and the zero line into the installation of two current transformers on the live line and the zero line, and the others are unchanged.
The invention mainly solves the problem that the leakage current transformer is difficult to install on the low-voltage 400V overhead line because the distance between each phase line is large, and utilizes the principle of the current transformer to equivalently convert the original line into a secondary line of the current transformer which can be sleeved in a measuring current transformer, thereby realizing the measurement of the leakage current of the low-voltage 400V overhead line. The current transformers are already installed on each phase line of the existing low-voltage 400V line monitoring system, and the method can increase the leakage current measuring function in the system at lower cost.
Drawings
FIG. 1 is a schematic diagram of the current transformers installed at the input ends of the current Ia, Ib and Ic of the measurement terminals in the three-phase circuit according to the invention;
FIG. 2 is a schematic diagram of the output ends of the current transformers installed at the measurement terminals Ia, Ib and Ic of the three-phase circuit for measuring current in the invention;
FIG. 3 is a schematic diagram of the present invention in which the secondary side of the phase current transformer A, the phase current transformer B, the phase current transformer C and the zero line current transformer is not connected with a measuring terminal;
FIG. 4 is a schematic diagram of the present invention in a single phase circuit;
in the figure: the device comprises a phase current transformer A, a phase current transformer B, a phase current transformer C, a phase current transformer zero line, a.
Detailed description of the preferred embodiments
The invention provides a novel leakage current measuring device and a method thereof, which are characterized in that an A-phase current transformer 1, a B-phase current transformer 2, a C-phase current transformer 3, a zero line current transformer 4, an A-phase current transformer secondary line 5, a B-phase current transformer secondary line 6, a C-phase current transformer secondary line 7, a zero line current transformer secondary line 8, a measuring current transformer 9 and a measuring terminal 10 are adopted; the phase A current transformer 1, the phase B current transformer 2, the phase C current transformer 3 and the zero line current transformer 4 are respectively arranged on a phase A, a phase B, a phase C and a zero line of a line to be detected; the A-phase current transformer secondary wire 5, the B-phase current transformer secondary wire 6, the C-phase current transformer secondary wire 7 and the zero line current transformer secondary wire 8 jointly penetrate through a hole of the measuring current transformer 9; the measuring current transformer 9 is connected to a measuring terminal 10.
The phase current transformer 1 of A phase, the phase current transformer 2 of B phase, the phase current transformer 3 of C phase, the zero line current transformer 4 are the current transformers of the same model and the same specification.
The directions of the A-phase current transformer secondary line 5, the B-phase current transformer secondary line 6, the C-phase current transformer secondary line 7 and the zero line current transformer secondary line 8 penetrating through the hole of the measuring current transformer 9 must be consistent.
And the A-phase current transformer secondary wire 5, the B-phase current transformer secondary wire 6, the C-phase current transformer secondary wire 7 and the zero line current transformer secondary wire 8 are connected to a measuring terminal 10.
A common method for measuring leakage current of a low-voltage 400V three-phase line is to sleeve a current transformer on a three-phase line and a zero line, sleeve the four lines together, and calculate an induced current generated in the current transformer to obtain the leakage current. According to the basic principle of the current transformer, compared with the current of the original line, the induced current generated by the current transformer has the same current phase, and the current magnitude is in a multiple relation, and the multiple is determined by the model specification of the transformer.
The first embodiment is as follows:
IN the figure 1, an A-phase line current IA penetrates through an A-phase current transformer 1 to generate an induced current Ia, a B-phase line current IB penetrates through a B-phase current transformer 2 to generate an induced current Ib, a C-phase line current IC penetrates through a C-phase current transformer 3 to generate an induced current IC, a zero line current IN penetrates through a zero line current transformer 4 to generate an induced current IN, an A-phase current transformer secondary line 5, a B-phase current transformer secondary line 6, a C-phase current transformer secondary line 7 and a zero line current transformer secondary line 8 penetrate through a hole of a measuring current transformer 9, the measuring current transformer 9 generates an induced current I △ n and the induced current I △ n is introduced into a measuring terminal 10, and the measuring terminal 10 can calculate.
When the A-phase current transformer secondary wire 5, the B-phase current transformer secondary wire 6, the C-phase current transformer secondary wire 7 and the zero line current transformer secondary wire 8 penetrate through the hole of the measuring current transformer 9, the induced current generated by the measuring current transformer 9 is consistent with the phase of the leakage current of the original line, and the magnitude of the induced current is in a multiple relation. The leakage current of the original line can be obtained through simple calculation of the measuring terminal 10. The method provides a basis for the maintainers to judge the position of the line leakage current, and accelerates the speed of overhauling the leakage current fault.
Example two:
from fig. 2, when the measuring current transformer 9 is installed at the current output end of the measuring terminal 10, the measuring method is the same as the first embodiment as long as the access directions of the four wires are ensured to be the same.
Example three:
referring to fig. 3, when the secondary sides of the a-phase current transformer 1, the B-phase current transformer 2, the C-phase current transformer 3, and the zero line current transformer 4 are not connected to the measurement terminal 10, the measurement method is the same as the first embodiment as long as the access directions of the four wires are the same.
The method provided by the invention is not only suitable for a low-voltage 400V three-phase line, but also suitable for a low-voltage 400V single-phase line, and only four current transformers are required to be arranged on the A phase, the B phase, the C phase and the zero line from the graph shown in FIG. 4, and two current transformers are required to be arranged on the live line and the zero line, and the others are not changed. Because the A-phase current transformer 1, the B-phase current transformer 2, the C-phase current transformer 3 and the zero line current transformer 4 are current transformers with the same specification, taking the example that the A-phase current transformer 1 is arranged on a live wire:
IN the second diagram, a current IA on the live wire passes through the phase a current transformer 1 to generate an induced current IA, a current IN on the zero wire passes through the zero line current transformer 4 to generate an induced current IN, a secondary wire 5 of the phase a current transformer, a secondary wire 8 of the zero line current transformer passes through a hole of the measuring current transformer 9, the measuring current transformer 9 generates an induced current I △ n, the induced current I △ n is connected to the measuring terminal 10, and the measuring terminal 10 can calculate the leakage current on the original line.
The embodiments of the present invention are not limited to the above examples, and those skilled in the art should understand that any other modifications or equivalent substitutions without departing from the spirit and principle of the present invention should be considered as equivalent substitutions and all fall within the protection scope of the present invention.
Claims (3)
1.A novel leakage current measuring device and a method thereof are characterized in that an A-phase current transformer, a B-phase current transformer, a C-phase current transformer, a zero line current transformer, an A-phase current transformer secondary line, a B-phase current transformer secondary line, a C-phase current transformer secondary line, a zero line current transformer secondary line, a measuring current transformer and a measuring terminal are arranged;
the phase current transformer A, the phase current transformer B, the phase current transformer C and the zero line current transformer are respectively arranged on the phase A, the phase B, the phase C and the zero line of the line to be detected;
the secondary line of the phase current transformer A, the secondary line of the phase current transformer B, the secondary line of the phase current transformer C and the secondary line of the zero line current transformer jointly penetrate through the hole of the measuring current transformer;
the measuring current transformer is connected to a measuring terminal.
2. The apparatus and method according to claim 1, wherein the phase-a current transformer, the phase-B current transformer, the phase-C current transformer, and the zero-line current transformer are of the same type and the same specification.
3. The novel leakage current measuring device and method according to claim 1, wherein the secondary line of the A-phase current transformer, the secondary line of the B-phase current transformer, the secondary line of the C-phase current transformer, and the secondary line of the zero-line current transformer are connected to the measuring terminal.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811545653.2A CN111337849A (en) | 2018-12-18 | 2018-12-18 | Novel leakage current measuring device and method |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201811545653.2A CN111337849A (en) | 2018-12-18 | 2018-12-18 | Novel leakage current measuring device and method |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113075577A (en) * | 2021-02-18 | 2021-07-06 | 国家电网有限公司 | Residual current monitoring system and method for low-voltage alternating-current power supply system |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4683513A (en) * | 1986-04-07 | 1987-07-28 | Westinghouse Electric Corp. | Dual current transformer current sensing method and sensor |
| CN2746400Y (en) * | 2004-10-16 | 2005-12-14 | 邓加慧 | Electric energy metering connecting conductor |
| CN203881884U (en) * | 2014-05-22 | 2014-10-15 | 赖韵宇 | Power distribution network overhead line fault monitoring device |
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2018
- 2018-12-18 CN CN201811545653.2A patent/CN111337849A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4683513A (en) * | 1986-04-07 | 1987-07-28 | Westinghouse Electric Corp. | Dual current transformer current sensing method and sensor |
| CN2746400Y (en) * | 2004-10-16 | 2005-12-14 | 邓加慧 | Electric energy metering connecting conductor |
| CN203881884U (en) * | 2014-05-22 | 2014-10-15 | 赖韵宇 | Power distribution network overhead line fault monitoring device |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113075577A (en) * | 2021-02-18 | 2021-07-06 | 国家电网有限公司 | Residual current monitoring system and method for low-voltage alternating-current power supply system |
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Application publication date: 20200626 |