CN109991563B - Current transformer disconnection detection method and measurement device - Google Patents
Current transformer disconnection detection method and measurement device Download PDFInfo
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- CN109991563B CN109991563B CN201810000852.9A CN201810000852A CN109991563B CN 109991563 B CN109991563 B CN 109991563B CN 201810000852 A CN201810000852 A CN 201810000852A CN 109991563 B CN109991563 B CN 109991563B
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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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/02—Testing or calibrating of apparatus covered by the other groups of this subclass of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating
Abstract
The invention discloses a method for detecting disconnection of a current transformer. The output signal of the current transformer is sent to an A/D port of the microprocessor after passing through the current signal conditioning circuit; the microprocessor carries out A/D sampling with the sampling point interval time of T0 on the output voltage signal of the current signal conditioning circuit, and calculates a current measurement value and a direct current voltage component V0 according to sampling data; between two adjacent sampling points of the A/D sampling, the microprocessor injects a direct current pulse level with the pulse width of T1 to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit through an I/O port of the microprocessor, and extracts a direct current voltage component V1 within the time T1, wherein T1 is less than T0; and finally, judging whether the current transformer is disconnected by the microprocessor: if V1 is larger than V0, the current transformer is judged to be disconnected; if not, the current transformer is judged to be normal. The invention also discloses a measuring device. The invention can effectively improve the accuracy of current sampling and the disconnection detection of the current transformer, and has simpler structure.
Description
Technical Field
The invention relates to a current transformer disconnection detection method and a measuring device with a current transformer disconnection detection function.
Background
With the development of modern power electronics and computer technology, people put forward more new requirements on the functions, performance and reliability of intelligent electrical appliances. The circuit breaker is an important element in a low-voltage power distribution system, has more and more abundant integrated functions, and provides various selectable protection functions and abundant measurement and maintenance functions besides the traditional three-stage protection. The intelligent controller is used as a central component of the circuit breaker and is the core for realizing the intellectualization of the circuit breaker. The current measurement is the basis for realizing various measurements and protections of the circuit breaker, and the accuracy of the current measurement determines the performance indexes of the various measurements and protections. The current transformer is a basic element for realizing current measurement and protection of the intelligent circuit breaker, has an irreplaceable position in current measurement and relay protection for a long time, and generally consists of a measurement coil and an energy coil. In a low-voltage distribution system, the whole current transformer is sleeved on a main loop bus of a circuit breaker, and the voltage output by a measuring coil in a sensing manner is in direct proportion to primary current in numerical value and is used as online parameter measurement and protection signal input of an intelligent controller; the energy coil induces self potential as one of the working power supplies of the intelligent controller. The current transformer in the intelligent circuit breaker has long running time and complex environment, and must have good reliability to ensure the normal work of the circuit breaker. Once a current transformer breaks down, the measurement of the power parameters of the circuit breaker is influenced slightly, and the circuit breaker can malfunction in severe cases. Therefore, the method ensures the current measurement accuracy of the circuit breaker and monitors the working state of the current transformer, and becomes an important measure for improving the working performance and reliability of the intelligent circuit breaker.
In the prior art, most of intelligent circuit breakers do not have the function of detecting the disconnection of a current transformer, and a few circuit breakers with the function of detecting the disconnection of the current transformer are generally superposed with a continuous direct-current voltage component between the current transformer and a current signal conditioning circuit, and then the direct-current voltage component of the output voltage of the current signal conditioning circuit is extracted through a Microprocessor (MCU) and compared with a preset reference value: when the two are the same, the current transformer is normal; when the two are different, the current transformer is disconnected. For example, in patent 201210461813, a digital-to-analog converter (DAC) generates a continuous dc voltage, which is superimposed on the current signal conditioning circuit, and the microprocessor determines whether the current transformer is disconnected by detecting the output voltage of the current signal conditioning circuit. According to patent 201110059748, a ground resistor is added between the current transformer and the current signal acquisition circuit, and the microprocessor determines whether the current transformer is disconnected by detecting the output voltage of the current signal conditioning circuit. In the technology, the direct current components for detecting the disconnection of the current transformer are all fixed voltages and are always superposed on the current signal conditioning circuit, so that the accuracy of current measurement is influenced to a certain extent. In addition, the current signal conditioning circuit usually includes electronic components such as a resistor, a capacitor, and an operational amplifier, and because of the influence of factors such as temperature drift of the electronic components and offset voltage variation of the operational amplifier, the dc voltage component output by the current signal conditioning circuit is often an indeterminate value, which makes it difficult to preset an accurate reference voltage in the microprocessor as a reference value for detecting and judging the disconnection of the transformer, and is easy to cause misjudgment of the disconnection of the current transformer.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for detecting the disconnection of a current transformer and a measuring device with the function of detecting the disconnection of the current transformer, which are not influenced by factors such as temperature drift of electronic elements, offset voltage change of an operational amplifier and the like, can effectively improve the accuracy of current sampling and the disconnection detection of the current transformer and have simpler structure.
The invention specifically adopts the following technical scheme to solve the technical problems:
a current transformer disconnection detection method is characterized in that an output signal of a current transformer is sent to an A/D port of a microprocessor after passing through a current signal conditioning circuit; the microprocessor carries out A/D sampling with the sampling point interval time of T0 on the output voltage signal of the current signal conditioning circuit, and calculates a current measurement value and a direct current voltage component V0 in A/D sampling data according to the A/D sampling data; between two adjacent sampling points of the A/D sampling, the microprocessor injects a direct current pulse level with the pulse width of T1 to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit through an I/O port of the microprocessor, and performs A/D sampling on the output voltage of the current signal conditioning circuit within time T1, and extracts a direct current voltage component V1 from the direct current pulse level, wherein T1 is less than T0; and finally, the microprocessor judges whether the current transformer is disconnected or not by comparing the V0 with the V1: if V1 is larger than V0, the current transformer is judged to be disconnected; if not, the current transformer is judged to be normal.
The following technical scheme can be obtained according to the same invention concept:
a measuring device has a current transformer disconnection detection function and comprises a current signal conditioning circuit and a microprocessor, wherein the current signal conditioning circuit comprises an integrating circuit and a signal processing circuit, and an output signal of the current transformer is sent to an A/D port of the microprocessor after passing through the integrating circuit and the signal processing circuit; one I/O port of the microprocessor is connected with one output end of the current transformer and the input end of the current signal conditioning circuit, and the other output end of the current transformer, the grounding end of the current signal conditioning circuit and the grounding end of the microprocessor are connected; the microprocessor carries out A/D sampling with the sampling point interval time of T0 on the output voltage signal of the current signal conditioning circuit, and calculates a current measurement value and a direct current voltage component V0 in A/D sampling data according to the A/D sampling data; between two adjacent sampling points of the A/D sampling, the microprocessor injects a direct current pulse level with the pulse width of T1 to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit through an I/O port of the microprocessor, and performs A/D sampling on the output voltage of the current signal conditioning circuit within the time T1, and extracts a direct current voltage component V1 from the direct current pulse level, wherein T1 is less than T0; and finally, the microprocessor judges whether the current transformer is disconnected or not by comparing the V0 with the V1: if V1 is larger than V0, the current transformer is judged to be disconnected; if not, the current transformer is judged to be normal.
Preferably, the dc voltage component V0 is extracted from the most recent a/D sample point data prior to injection of the dc pulse level. Alternatively, the dc voltage component V0 is an average value of dc voltage components extracted from a plurality of a/D sampling point data.
Further, the device also comprises a protection circuit for protecting the I/O port of the microprocessor, the protection circuit comprises resistors R1 and R2 and a diode D1, one end of the output signal of the current transformer is connected with one end of a resistor R1, the other end of the resistor R1, one end of a resistor R2 and the cathode of a diode D1 are connected and then connected to the I/O port of the microprocessor, the anode of the diode D1 and the other end of the resistor R2 are connected in a common ground mode, and the relations between the resistors R1 and R2 and the internal resistance Ri of the current transformer meet the following requirements: ri < R2 < R1.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention utilizes the I/O port of the microprocessor to directly inject the test signal for detecting the broken line of the circuit breaker to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit, does not need an additional test signal generating circuit, is used for judging that the reference voltage of the broken line of the current transformer is not influenced by factors such as temperature drift of electronic elements, offset voltage change of an operational amplifier and the like, and the test signal is directly controlled by the microprocessor, so that the injection of the test signal can avoid the A/D sampling of the current signal, thereby effectively improving the accuracy of the current sampling and the broken line detection of the current transformer and having simpler structure.
Drawings
FIG. 1 is a block diagram of the working principle of the measuring device of the present invention;
FIG. 2 is a schematic block diagram of a preferred embodiment of the measuring device of the present invention;
FIG. 3 is a schematic diagram of a protection circuit;
FIG. 4 is a detection flow chart of the current transformer disconnection detection;
fig. 5 is a sample example of the current transformer measurement coil output signal.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings:
the working principle of the measuring device of the invention for realizing the disconnection detection of the current transformer is shown in figure 1, and the working principle comprises the following steps: the current transformer comprises an integrating circuit for restoring an output signal of the current transformer, a signal processing circuit for amplifying the output signal of the current transformer, and a microprocessor for processing the output signal of a current signal conditioning circuit (comprising the integrating circuit and the signal processing circuit) and controlling the superposition of direct-current voltage components; one output end of the current transformer is sent into the signal processing circuit after passing through the integrating circuit, the microprocessor carries out A/D conversion and processing on the output voltage of the current signal conditioning circuit, and the other output end of the output signal of the current transformer is connected with the grounding end of the current signal conditioning circuit and the grounding end of the microprocessor; the microprocessor outputs a direct current voltage component through the I/O port and superimposes the direct current voltage component on an output signal of the current transformer.
In order to further protect the I/O port of the microprocessor, a preferred embodiment of the present invention is to add a protection circuit for protecting the I/O port of the microprocessor as shown in fig. 2, where the output signal of the measuring coil of the current transformer is restored by the integrating circuit to a signal current and then sent to the signal processing circuit, and the processed signal is sent to the a/D port of the microprocessor for sampling. The output signal of the measuring coil is connected with the I/O port of the microprocessor after passing through the protection circuit, and the protection circuit can prevent negative voltage of the measuring signal from damaging the I/O port of the microprocessor. When the disconnection detection is carried out, the I/O port of the microprocessor sends out a test pulse level outwards, the test pulse level is superposed to the output signal end of the measuring coil after passing through the protection circuit, and the microprocessor compares direct current components collected by the A/D ports before and after the pulse level is sent out to judge whether the current transformer is disconnected.
Fig. 3 shows a preferred embodiment of the protection circuit. As shown in fig. 3, the protection circuit includes resistors R1, R2 and a diode D1, one end of the output signal of the current transformer is connected with one end of the resistor R1, the other end of the resistor R1, one end of the resistor R2 and the cathode of the diode D1 are connected and then connected to the I/O port of the microprocessor, the anode of the diode D1 and the other end of the resistor R2 are connected in common, and the relationship between the resistors R1, R2 and the internal resistance Ri of the current transformer satisfies: ri < R2 < R1.
The specific process of the invention when detecting the disconnection of the current transformer is shown in fig. 4, and comprises the following steps:
firstly, a microprocessor carries out 16-point or 32-point A/D sampling on the output voltage of a current signal conditioning circuit in each period, the interval time of sampling points is T0, a current measurement value is calculated according to A/D sampling data, and a direct current voltage component V0 in the k-point A/D sampling data is extracted as a preset reference value; the dc voltage component V0 is preferably extracted from the a/D sampled data at the nearest sample point prior to the injection of the dc pulse level; alternatively, the dc voltage component V0 is an average value of dc voltage components extracted from a plurality of a/D sampling point data.
Secondly, as shown in fig. 5, between two adjacent sampling points of the a/D sampling, the microprocessor controls the I/O port to send a test pulse level outwards, where the pulse width of the test pulse is T1, and T1< T0, that is, the microprocessor controls the I/O port to output a dc voltage component, which is superimposed to one end of the output signal of the current transformer; assuming that the current transformer measures a sinusoidal voltage signal with a coil output signal of 50Hz, one period is 20ms, and the a/D sampling of the microprocessor is 16 points, i.e. the sampling interval T0=20/16=1.25 ms. In order to avoid that the test level applied in the disconnection detection affects the normal current sampling, the test level needs to be sent out in the time of T0 between two adjacent sampling points, and the pulse width T1< T0, preferably 0.5ms in the embodiment.
Thirdly, in the time T1 when the test level is sent out, the microprocessor samples the output voltage of the current signal conditioning circuit and extracts the direct current voltage component V1.
Fourthly, comparing the direct-current voltage components V0 and V1 by the microprocessor, judging whether V1 is larger than V0, and if so, judging that the current transformer is disconnected; if not, the current transformer is judged to be normal.
In conclusion, the invention utilizes the I/O port of the microprocessor to directly inject the test signal for detecting the disconnection of the circuit breaker to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit, does not need an additional test signal generating circuit, is used for judging that the reference voltage for detecting the disconnection of the current transformer is not influenced by factors such as temperature drift of electronic elements, offset voltage change of an operational amplifier and the like, can effectively improve the accuracy of the disconnection detection of the current transformer, and has simpler structure. On the other hand, the test signal of the disconnection detection is directly controlled by the microprocessor, and the injection of the test signal can be enabled to avoid the A/D sampling of the current signal through simple software setting, so that the accuracy of the current sampling data is effectively improved.
Claims (7)
1. A current transformer disconnection detection method is characterized in that an output signal of a current transformer is sent to an A/D port of a microprocessor after passing through a current signal conditioning circuit; the method is characterized in that the microprocessor carries out A/D sampling with the sampling point interval time of T0 on an output voltage signal of the current signal conditioning circuit, and calculates a current measurement value and a direct current voltage component V0 in A/D sampling data according to the A/D sampling data; between two adjacent sampling points of the A/D sampling, the microprocessor injects a direct current pulse level with the pulse width of T1 to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit through an I/O port of the microprocessor, and performs A/D sampling on the output voltage of the current signal conditioning circuit within time T1, and extracts a direct current voltage component V1 from the direct current pulse level, wherein T1 is less than T0; and finally, the microprocessor judges whether the current transformer is disconnected or not by comparing the V0 with the V1: if V1 is larger than V0, the current transformer is judged to be disconnected; if not, the current transformer is judged to be normal.
2. The method of claim 1 wherein the dc voltage component V0 is extracted from the most recent a/D sample point data prior to injecting the dc pulse level.
3. The method of claim 1, wherein the dc voltage component V0 is an average of dc voltage components extracted from a plurality of a/D sample point data.
4. A measuring device has a current transformer disconnection detection function and comprises a current signal conditioning circuit and a microprocessor, wherein the current signal conditioning circuit comprises an integrating circuit and a signal processing circuit, and an output signal of the current transformer is sent to an A/D port of the microprocessor after passing through the current signal conditioning circuit; the microprocessor is characterized in that one I/O port of the microprocessor is connected with one output end of a current transformer and the input end of a current signal conditioning circuit, and the other output end of the current transformer, the grounding end of the current signal conditioning circuit and the grounding end of the microprocessor are connected; the microprocessor carries out A/D sampling with the sampling point interval time of T0 on the output voltage signal of the current signal conditioning circuit, and calculates a current measurement value and a direct current voltage component V0 in A/D sampling data according to the A/D sampling data; between two adjacent sampling points of the A/D sampling, the microprocessor injects a direct current pulse level with the pulse width of T1 to the connecting point of the output end of the current transformer and the input end of the current signal conditioning circuit through an I/O port of the microprocessor, and performs A/D sampling on the output voltage of the current signal conditioning circuit within the time T1, and extracts a direct current voltage component V1 from the direct current pulse level, wherein T1 is less than T0; and finally, the microprocessor judges whether the current transformer is disconnected or not by comparing the V0 with the V1: if V1 is larger than V0, the current transformer is judged to be disconnected; if not, the current transformer is judged to be normal.
5. The apparatus of claim 4 wherein the dc voltage component V0 is extracted from the most recent a/D sample point data prior to injecting the dc pulse level.
6. The apparatus of claim 4, wherein the DC voltage component V0 is an average value of DC voltage components extracted from a plurality of A/D sample point data.
7. The apparatus of claim 4, further comprising a protection circuit for protecting the I/O port of the microprocessor, wherein the protection circuit comprises resistors R1 and R2 and a diode D1, one end of the output signal of the current transformer is connected to one end of the resistor R1, the other end of the resistor R1, one end of the resistor R2 and the cathode of the diode D1 are connected and then connected to the I/O port of the microprocessor, the anode of the diode D1 and the other end of the resistor R2 are connected in common, and the resistors R1 and R2 and the internal resistance of the current transformer Ri satisfy the following relationship: ri < R2 < R1.
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| CN201810000852.9A CN109991563B (en) | 2018-01-02 | 2018-01-02 | Current transformer disconnection detection method and measurement device |
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| CN201810000852.9A CN109991563B (en) | 2018-01-02 | 2018-01-02 | Current transformer disconnection detection method and measurement device |
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| CN109991563B true CN109991563B (en) | 2020-12-29 |
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| CN112881946B (en) * | 2021-01-15 | 2021-09-24 | 常熟开关制造有限公司(原常熟开关厂） | Double-core current transformer disconnection detection method and device and circuit breaker |
| CN112904265B (en) * | 2021-03-18 | 2022-05-13 | 浙江聚创智能科技有限公司 | Second winding open circuit detection circuit of zero sequence current transformer |
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| CN1506694A (en) * | 2002-12-09 | 2004-06-23 | 淄博科汇电气有限公司 | Broken wire detecting method for voltage transformer |
| CA2688975A1 (en) * | 2007-02-26 | 2008-09-04 | Elster Electricity Llc | A system and a method for detecting the presence of an unsafe line condition in a disconnected power meter |
| JP4673698B2 (en) * | 2005-08-08 | 2011-04-20 | 日立電線株式会社 | Wire breakage detection method and apparatus |
| EP2466322B1 (en) * | 2010-12-17 | 2013-09-11 | ABB Research Ltd. | Method and apparatus for transformer diagnosis |
| CN105807174A (en) * | 2014-12-30 | 2016-07-27 | 施耐德电器工业公司 | Current transformer broken line detection method in power transmission and distribution system protection |
| CN106383292A (en) * | 2016-10-09 | 2017-02-08 | 中国电力科学研究院 | Current transformer disconnection judgment method based on fault escape |
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2018
- 2018-01-02 CN CN201810000852.9A patent/CN109991563B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1506694A (en) * | 2002-12-09 | 2004-06-23 | 淄博科汇电气有限公司 | Broken wire detecting method for voltage transformer |
| JP4673698B2 (en) * | 2005-08-08 | 2011-04-20 | 日立電線株式会社 | Wire breakage detection method and apparatus |
| CA2688975A1 (en) * | 2007-02-26 | 2008-09-04 | Elster Electricity Llc | A system and a method for detecting the presence of an unsafe line condition in a disconnected power meter |
| EP2466322B1 (en) * | 2010-12-17 | 2013-09-11 | ABB Research Ltd. | Method and apparatus for transformer diagnosis |
| CN105807174A (en) * | 2014-12-30 | 2016-07-27 | 施耐德电器工业公司 | Current transformer broken line detection method in power transmission and distribution system protection |
| CN106383292A (en) * | 2016-10-09 | 2017-02-08 | 中国电力科学研究院 | Current transformer disconnection judgment method based on fault escape |
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