CN112578177A - Device and method for measuring current signal of feeder terminal in wide range - Google Patents
Device and method for measuring current signal of feeder terminal in wide range Download PDFInfo
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- CN112578177A CN112578177A CN202011518626.3A CN202011518626A CN112578177A CN 112578177 A CN112578177 A CN 112578177A CN 202011518626 A CN202011518626 A CN 202011518626A CN 112578177 A CN112578177 A CN 112578177A
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- current
- circuit
- main control
- current transformer
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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
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
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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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
Abstract
The invention relates to a device for measuring current signals of a feeder terminal in a wide range, which comprises a three-phase current input circuit and a three-phase voltage input circuit, wherein the signal output ends of the three-phase current input circuit and the three-phase voltage input circuit are connected with the signal input end of an AD conversion circuit; the three-phase current input circuit comprises a first current transformer and a second current transformer. The invention also discloses a measuring method of the device for measuring the current signal of the feeder terminal in a wide range. The invention can collect current signals in a wide range of 1 mA-20A, thereby realizing the protection of traditional large current faults such as overcurrent and zero sequence current, and realizing the protection of small signal faults such as single-phase earth fault, and further realizing the self-adaptive distribution network protection.
Description
Technical Field
The invention relates to the technical field of relay protection, in particular to a device and a method for measuring a current signal of a feeder terminal in a wide range.
Background
The principle of the traditional relay protection device is that fault current signals with larger signal collection ratio, such as three-section current protection and three-section zero-sequence current protection, are often adopted, the difference between the fault signals and normal signals is larger, and the fault state or the normal state can be distinguished more easily. In a 10KV distribution network, however, single-phase earth faults are the most common faults and can account for 70-80% of the total distribution network faults. Because the 10KV power distribution network usually adopts an ungrounded system operation mode, when a fault occurs, a fault current signal is weak, particularly after arc suppression coils are widely put into a power distribution network at present, the fault signal characteristic is more unobvious, the current signals of a fault line and a non-fault line are not greatly different, and the traditional method for detecting the fault through zero sequence current is often invalid.
In order to realize single-phase earth fault detection, the method can be realized by a detection incremental current method, and the principle is that when a single-phase earth fault occurs, the vector increment of three-phase current of a non-fault line is equal, and the increment of two-phase current of a fault line is equal and is different from the increment of the other phase. In order to realize incremental protection, a mA level needs to be collected for the device, but the traditional relay protection device can only guarantee the current of dozens of mA to 20A levels generally, and the lower limit of the traditional relay protection device cannot meet the requirement of incremental protection.
Disclosure of Invention
The invention aims to provide a feeder terminal wide-range current signal measuring device capable of realizing wide-range current signal detection from 1mA to 20A.
In order to achieve the purpose, the invention adopts the following technical scheme: a feeder terminal wide-range current signal measuring device comprises a three-phase current input circuit and a three-phase voltage input circuit, wherein the three-phase current input circuit and the three-phase voltage input circuit are used for collecting external current signals, signal output ends of the three-phase current input circuit and the three-phase voltage input circuit are connected with a signal input end of an AD conversion circuit, an output end of the AD conversion circuit is connected with a first input end of a main control circuit, second and third input ends of the main control circuit are respectively connected with a switch signal input circuit used for receiving switch position signals of a circuit breaker and output ends of a reset circuit in a one-to-one correspondence mode, the main control circuit is communicated with a main station; the three-phase current input circuit comprises a first current transformer and a second current transformer, wherein the first current transformer adopts a 1:1 current transformer, and the second current transformer adopts a 1:10 current transformer.
The main control circuit is in two-way communication with the storage circuit.
The main control circuit is connected with an external device through an RS232 interface.
The power supply circuit is used for supplying power to the three-phase current input circuit, the three-phase voltage input circuit, the AD conversion circuit, the switch signal input circuit, the reset circuit, the storage circuit and the main control circuit.
The AD conversion circuit comprises a first AD chip and a second AD chip, wherein the output end of the first current transformer is connected with the input end of the first AD chip, and the output end of the second current transformer is connected with the input end of the second AD chip; the master control circuit comprises a first data buffer, a second data buffer and a master control CPU, wherein the output end of the first AD chip is connected with the input end of the first data buffer, the output end of the second AD chip is connected with the input end of the second data buffer, and the output ends of the first data buffer and the second data buffer are connected with the input end of the master control CPU.
Another objective of the present invention is to provide a measuring method for a feeder terminal wide-range current signal measuring device, wherein after obtaining the values of 2 sets of current transformers through an AD conversion circuit, a main control circuit obtains the values of different current transformers, and when the main control circuit judges that the current signal is above 1A, the value of a first current transformer is used as a current collecting value; and when the main control circuit judges that the current signal is below 1A, the numerical value of the second current transformer is used as a current acquisition value.
According to the technical scheme, the beneficial effects of the invention are as follows: the invention can collect current signals in a wide range of 1 mA-20A, thereby realizing the protection of traditional large current faults such as overcurrent and zero sequence current, and realizing the protection of small signal faults such as single-phase earth fault, and further realizing the self-adaptive distribution network protection.
Drawings
FIG. 1 is a block circuit diagram of the present invention;
fig. 2 is a circuit diagram of the three-phase current input circuit, the AD conversion circuit, and the main control circuit in fig. 1.
Detailed Description
As shown in fig. 1 and 2, a feeder terminal wide-range current signal measuring device includes a three-phase current input circuit and a three-phase voltage input circuit for collecting external current signals, signal output terminals of the two are connected to signal input terminals of an AD conversion circuit, an output terminal of the AD conversion circuit is connected to a first input terminal of a main control circuit, second and third input terminals of the main control circuit are respectively connected to output terminals of a switch signal input circuit and a reset circuit for receiving switch position signals of a circuit breaker in a one-to-one correspondence manner, the main control circuit communicates with a master station through a communication module, and the output terminal of the main control circuit is connected to the circuit breaker through a relay; the three-phase current input circuit comprises a first current transformer and a second current transformer, wherein the first current transformer adopts a 1:1 current transformer, and the second current transformer adopts a 1:10 current transformer.
As shown in fig. 1, the master control circuit is in bidirectional communication with the memory circuit. The main control circuit is connected with an external device through an RS232 interface. The power supply circuit is used for supplying power to the three-phase current input circuit, the three-phase voltage input circuit, the AD conversion circuit, the switch signal input circuit, the reset circuit, the storage circuit and the main control circuit.
As shown in fig. 1 and 2, the AD conversion circuit includes a first AD chip and a second AD chip, an output terminal of the first current transformer is connected to an input terminal of the first AD chip, and an output terminal of the second current transformer is connected to an input terminal of the second AD chip; the master control circuit comprises a first data buffer, a second data buffer and a master control CPU, wherein the output end of the first AD chip is connected with the input end of the first data buffer, the output end of the second AD chip is connected with the input end of the second data buffer, and the output ends of the first data buffer and the second data buffer are connected with the input end of the master control CPU.
When the current acquisition circuit works, after the AD conversion circuit obtains the numerical values of 2 groups of current transformers, the main control circuit obtains the numerical values of different current transformers, and when the main control circuit judges that a current signal is more than 1A, the numerical value of a first current transformer is used as a current acquisition value; and when the main control circuit judges that the current signal is below 1A, the numerical value of the second current transformer is used as a current acquisition value.
The invention is further described below with reference to fig. 1 to 2.
External current signals pass through current transformers with different proportions, a first current transformer adopts a 1:1 current transformer, a second current transformer adopts a 1:10 current transformer, and the original signals can be amplified by 10 times through the second current transformer so as to output current signals with different proportions. The current signal is converted into a digital signal through two AD chips, data caching is carried out through a data buffer, a main control CPU acquires signals through a data bus, and final signal data are obtained through analysis and processing.
For a measurement and control device, the realization of accurate measurement of a wide range of current depends mainly on two components: one is the accuracy of the current transformer and one is the accuracy of the AD chip.
For the current transformer, a high-precision micro current transformer on the market is selected, the specification is 1:1mA, the precision in the range of 1% to 20A is 0.05%, and therefore the linear range of the current transformer is 10 mA-20A.
Therefore, a single current transformer cannot meet the measurement requirement of 1 mA-20A. In order to realize wide-range measurement, the current transformer is divided into 2 groups, the first group of primary coils has 1 turn, the second group of primary coils has 10 turns, which is equivalent to amplifying the input signal by 10 times, so that the signal input range of the second group is reduced by 10 times, namely 1mA to 2A. The sampling resistance was 330 Ω.
For the AD chip, the more the number of bits, the wider the measurable range, but the higher the cost, this time using a 16 bit AD7606 chip, which represents a number range from 1 to 32767. The current signal corresponding to the lower digital limit 1 is 0.925mA, and the current signal corresponding to the upper digital limit is 30A, so that the measurement requirement of a wide range can be met by adopting a 16-bit AD chip.
When the input signal is the first current transformer, the linear range of 10mA to 20A corresponds to the digital range of 9 to 25205, and the value is in the conversion range of the AD chip, so that accurate measurement can be realized. For current signals in the range of 1mA to 2A, the values are 1 to 2520, thus it can be seen that for small current signals, the values are too small to be measured accurately.
When the input signal is the second current transformer, the digital range corresponding to the linear range of 1mA to 2A is 9 to 25205, which is within the conversion range of the AD chip. The current signals for 2A to 20A actually correspond to the input current signals of 20A to 200A, and the current transformer is saturated and cannot be accurately measured.
Therefore, the purpose of measuring the current in the range of 1mA to 20A is achieved by adopting two groups of mutual inductors and respectively measuring the current in different ranges through different windings.
After the values of 2 groups of current transformers are obtained through AD chip conversion, a data buffer is added, the main control CPU can obtain the values of different current transformers, analysis processing needs to be carried out on the main control CPU at the moment, when a judgment signal is above 1A, the value of a first current transformer is used as a current collection value, when the judgment signal is below 1A, the value of a second current transformer is used as a current collection value, and therefore the purpose of data smooth transition is achieved.
In summary, the invention can obtain the current signal in the range of 1mA to 20A by a method of measuring the current signal in a wide range, and provides a solution for realizing a device satisfying the single-phase ground fault detection and the traditional relay protection function. The invention has the relay protection function, and can trip the outlet breaker and automatically reclose once when detecting a line fault, thereby preventing instantaneous faults.
Claims (6)
1. A feeder terminal wide-range current signal measuring device is characterized in that: the three-phase current and voltage acquisition circuit comprises a three-phase current input circuit and a three-phase voltage input circuit which are used for acquiring external current signals, wherein the signal output ends of the three-phase current input circuit and the three-phase voltage input circuit are connected with the signal input end of an AD conversion circuit, the output end of the AD conversion circuit is connected with the first input end of a main control circuit, the second input end and the third input end of the main control circuit are respectively connected with the switch signal input circuit used for receiving switch position signals of a circuit breaker and the output end of a reset circuit in a one-to-one correspondence manner, the main control circuit is communicated with a; the three-phase current input circuit comprises a first current transformer and a second current transformer, wherein the first current transformer adopts a 1:1 current transformer, and the second current transformer adopts a 1:10 current transformer.
2. A feeder termination wide range current signal measuring apparatus as claimed in claim 1, characterised in that: the main control circuit is in two-way communication with the storage circuit.
3. A feeder termination wide range current signal measuring apparatus as claimed in claim 1, characterised in that: the main control circuit is connected with an external device through an RS232 interface.
4. A feeder termination wide range current signal measuring apparatus as claimed in claim 1, characterised in that: the power supply circuit is used for supplying power to the three-phase current input circuit, the three-phase voltage input circuit, the AD conversion circuit, the switch signal input circuit, the reset circuit, the storage circuit and the main control circuit.
5. A feeder termination wide range current signal measuring apparatus as claimed in claim 1, characterised in that: the AD conversion circuit comprises a first AD chip and a second AD chip, wherein the output end of the first current transformer is connected with the input end of the first AD chip, and the output end of the second current transformer is connected with the input end of the second AD chip; the master control circuit comprises a first data buffer, a second data buffer and a master control CPU, wherein the output end of the first AD chip is connected with the input end of the first data buffer, the output end of the second AD chip is connected with the input end of the second data buffer, and the output ends of the first data buffer and the second data buffer are connected with the input end of the master control CPU.
6. A method of measuring a feeder terminal wide range current signal apparatus as claimed in any one of claims 1 to 5, characterised in that: after the AD conversion circuit obtains the numerical values of 2 groups of current transformers, the main control circuit obtains the numerical values of different current transformers, and when the main control circuit judges that the current signal is more than 1A, the numerical value of the first current transformer is used as a current acquisition value; and when the main control circuit judges that the current signal is below 1A, the numerical value of the second current transformer is used as a current acquisition value.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011518626.3A CN112578177A (en) | 2020-12-21 | 2020-12-21 | Device and method for measuring current signal of feeder terminal in wide range |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011518626.3A CN112578177A (en) | 2020-12-21 | 2020-12-21 | Device and method for measuring current signal of feeder terminal in wide range |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN112578177A true CN112578177A (en) | 2021-03-30 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202011518626.3A Pending CN112578177A (en) | 2020-12-21 | 2020-12-21 | Device and method for measuring current signal of feeder terminal in wide range |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN112578177A (en) |
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2020
- 2020-12-21 CN CN202011518626.3A patent/CN112578177A/en active Pending
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