CN113030582A - Online measuring system for contact resistance of circuit breaker contact - Google Patents
Online measuring system for contact resistance of circuit breaker contact Download PDFInfo
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- CN113030582A CN113030582A CN202110413343.0A CN202110413343A CN113030582A CN 113030582 A CN113030582 A CN 113030582A CN 202110413343 A CN202110413343 A CN 202110413343A CN 113030582 A CN113030582 A CN 113030582A
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- 238000004364 calculation method Methods 0.000 claims description 5
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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
- G01R27/08—Measuring resistance by measuring both voltage and current
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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
- G01R31/327—Testing of circuit interrupters, switches or circuit-breakers
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Abstract
The invention discloses an on-line measuring system for contact resistance of a breaker contact, which comprises: the circuit breaker comprises a contact voltage difference sampling unit, a current sampling unit, a voltage amplitude limiting protection unit, an isolation operational amplifier unit, an ADC unit and an ARM processor, wherein the contact voltage difference sampling unit is used for measuring the voltage difference generated at two ends of a contact of the circuit breaker; the isolation operational amplifier unit is used for electromagnetic isolation; the ADC unit is used for converting the current and the voltage difference at the same moment into discrete digital signals; the ARM processor is used for calculating contact resistance. The measuring system can monitor and measure the contact resistance of the contact of the circuit breaker in real time, and provide basic data for predicting the electrical service life of the circuit breaker.
Description
Technical Field
The invention relates to a system for measuring contact resistance, in particular to a system for measuring contact resistance of an online breaker contact.
Background
The circuit breaker plays the effect of conducting and breaking current in a power transmission and distribution system of electric power, is a node carrier of primary current, and the size of contact resistance between the contacts of the circuit breaker is closely related to the service life of the contacts of the circuit breaker, and the quality of the contact resistance becomes the key for influencing the electrical reliability of the circuit breaker.
Whether the contact of the contact point of the circuit breaker is reliable or not at present, except for detecting the contact resistance during maintenance, quantitative observation on the contact point of the circuit breaker is unavailable during the normal operation of the circuit breaker, so that the change condition of the working condition of the contact of the circuit breaker cannot be mastered in real time, once the contact resistance of the contact of the circuit breaker is increased, the temperature rise of a movable contact and a fixed contact is rapidly increased, if the change condition is not processed as soon as possible, the situation is left to be worsened continuously, the contact body deformation and even adhesion between the movable contact and the fixed contact of the circuit breaker are probably caused, and the performance of an electric connector is influenced.
Disclosure of Invention
The invention aims to overcome the defect that the contact resistance of a contact of a circuit breaker cannot be detected during the normal operation of the circuit breaker in the prior art, and provides an online measurement system for the contact resistance of the contact of the circuit breaker.
The invention solves the technical problems through the following technical scheme:
the utility model provides a circuit breaker contact resistance on-line measuring system which characterized in that, it includes: a contact voltage difference sampling unit, a current sampling unit, a voltage amplitude limiting protection unit connected with the contact voltage difference sampling unit, an isolation operational amplifier unit connected with the voltage amplitude limiting protection unit, an ADC (Analog-to-Digital Converter) unit connected with the isolation operational amplifier unit and the current sampling unit, and an ARM processor (RISC processor designed by ARM company in England) connected with the ADC unit, wherein,
the current sampling unit is used for acquiring current flowing through a contact of the circuit breaker;
the contact voltage difference sampling unit is used for measuring the voltage difference generated at two ends of a contact of the circuit breaker;
the voltage amplitude limiting protection unit is used for sending a signal of a voltage difference into the isolation operational amplifier unit when the circuit breaker is closed and disconnecting the electrical connection with the isolation operational amplifier unit when the circuit breaker is disconnected;
the isolation operational amplifier unit is used for electromagnetically isolating the contact voltage difference sampling unit and the voltage amplitude limiting protection unit at the upstream from the ADC unit and the ARM processor at the downstream;
the ADC unit is used for converting the current from the current sampling unit and the voltage difference from the contact voltage difference sampling unit into discrete digital signals at the same time;
and the ARM processor is used for calculating the contact resistance according to the current and the voltage difference at the same moment.
Because the contact resistance of the circuit breaker is only less than 100 mu omega under normal working conditions, the conventional measurement mode of the contact resistance of the circuit breaker is to use a direct current measurement method, and according to the requirements of power standards such as national GB763-1990 and DL405-91, the direct current method not less than 100A is adopted for measurement, and according to ohm's law, U-I-R exists, and if the voltage drop at two ends of the contact resistance is measured, the actual resistance value of the contact resistance of the circuit breaker can be reversely deduced according to the current magnitude of the current flowing through the circuit breaker. The invention is based on ohm's law, utilizes the isolation operational amplifier and the analog-digital conversion (AD conversion), adopts the alternating current effective value calculation algorithm, calculates the resistance value of the current breaker contact resistance in real time, can provide the quantized resistance value with direct reference significance, and can be used for analyzing and predicting the contact electrical service life of the breaker so as to ensure the reliability of load power supply.
Preferably, the voltage amplitude limiting protection unit comprises a signal acquisition relay, the signal acquisition relay is connected between the output of the contact voltage difference sampling unit and the input of the isolation operational amplifier unit, and the signal acquisition relay is synchronously closed or opened with the circuit breaker. When the circuit breaker is in a closed state at present, the voltage drop between the contacts due to contact resistance is very small and is completely in the working range of the rear-stage isolation operational amplifier; however, when the circuit breaker is in the open position, the voltage may rise to the phase voltage of the system, for example, 220VAC, and at this time, for the isolated operational amplifier at the later stage, since the input voltage is far beyond the voltage that the operational amplifier can bear, the operational amplifier may be burned out, and the whole sampling system may fail. And the arrangement of the voltage amplitude limiting protection unit effectively protects the downstream units.
Preferably, the isolation operational amplifier unit includes a first filter circuit connected to the output of the voltage limiting protection unit, and an isolation circuit connected to the first filter circuit. The isolated signal is completely isolated from the high-voltage side electrically, so that the personal safety of a sampling system and an operator is ensured.
Preferably, the current sampling unit includes a current transformer. Due to the electromagnetic isolation of the Current Transformer (CT), the current can be directly sent to a secondary loop for sampling.
Preferably, the ADC unit includes a current conversion channel connected to the current sampling unit and a voltage conversion channel connected to the isolation operational amplifier unit, respectively, and the current sampling channel includes a voltage forming loop and a second filter circuit connected to the voltage forming loop.
Preferably, the ADC unit includes an AD conversion chip with 6 AD input channels.
Preferably, the ADC unit is connected to the ARM processor by an SPI (serial peripheral) bus.
Preferably, the ARM processor comprises an FPU (floating Point Unit) coprocessor.
Preferably, the voltage and current read from the ADC unit by the ARM processor are discrete ac sampled values, and the ARM processor is configured to perform effective value calculation by using FFT (fast Fourier transform).
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The positive progress effects of the invention are as follows: the method can monitor and measure the contact resistance of the contact of the circuit breaker in real time, provide basic data for predicting the electrical service life of the circuit breaker and provide a technical basis for the reliability of load power supply.
Drawings
Fig. 1a and 1b are schematic diagrams of a circuit breaker a-phase primary circuit and equivalent schematic diagrams thereof respectively.
Fig. 2 is a schematic diagram of a sampling slice protection circuit.
Fig. 3 is a schematic diagram of an isolated operational amplifier circuit.
Fig. 4 is a schematic diagram of an AD sample input.
Fig. 5 is an overall block diagram of the measurement system.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
Referring to fig. 1a, 1 b-5, an on-line measuring system for contact resistance of a contact of a circuit breaker according to an embodiment of the present invention is described, which includes: the device comprises a contact voltage difference sampling unit 1, a current sampling unit 2, a voltage amplitude limiting protection unit 3 connected with the contact voltage difference sampling unit 1, an isolation operational amplifier unit 4 connected with the voltage amplitude limiting protection unit 3, an ADC unit 5 connected with the isolation operational amplifier unit 4 and the current sampling unit 2, and an ARM processor 6 connected with the ADC unit 5. The current sampling unit 2 is used for acquiring current flowing through a contact of the circuit breaker; the contact voltage difference sampling unit 1 is used for measuring the voltage difference generated at two ends of a contact of the circuit breaker; the voltage amplitude limiting protection unit 3 is used for sending a signal of a voltage difference into the isolation operational amplifier unit 4 when the circuit breaker is closed, and disconnecting the electrical connection with the isolation operational amplifier unit 4 when the circuit breaker is disconnected; the isolation operational amplifier unit 4 is used for electromagnetically isolating the contact voltage difference sampling unit 1 and the voltage amplitude limiting protection unit 3 at the upstream and the ADC unit 5 and the ARM processor 6 at the downstream; the ADC unit 5 is configured to convert the current from the current sampling unit 2 and the voltage difference from the contact voltage difference sampling unit 1 into discrete digital signals at the same time; and the ARM processor 6 is used for calculating the contact resistance according to the current and the voltage difference at the same moment.
Since the contact configurations of the circuit breaker are all the same, for simplicity of illustration, only phase a is listed for discussion. Specifically, in the phase a contact of the circuit breaker, when the contact is closed, the movable contact of the circuit breaker is in close contact with the surface of the fixed contact under the action of spring pressure, and at this time, the surface resistance of the contact is R1, and the contraction resistance of the contact is R2, which together constitute the contact resistance R of the circuit breaker contact. When a current flows through the primary circuit, due to the contact resistance R, a voltage difference Uab is generated across the contacts of the circuit breaker, which is normally in the mV (millivolts) range. In addition, in order to measure the current, a path of CT sampling a-phase current Ia needs to be arranged on the a-phase. Ia can be directly sent into a secondary loop for sampling due to the electromagnetic isolation of CT.
The voltage amplitude limiting protection unit is shown in fig. 2 and comprises a signal acquisition relay K, wherein the signal acquisition relay is connected between the output of the contact voltage difference sampling unit and the input of the isolation operational amplifier unit, and the signal acquisition relay and the circuit breaker are synchronously closed or opened. Specifically, this unit primarily functions as a sample voltage clipping function. According to the fig. 1a and 1b, when the circuit breaker is currently in a closing state, the voltage drop Uab formed by the contact resistance between the contacts at this time is very small and only has a level of tens of mV, and is completely within the working range of the subsequent isolation operational amplifier; however, when the circuit breaker is in the open position, the Uab voltage rises to the phase voltage 220VAC of the system, and at this time, for the isolation operational amplifier of the rear stage, the input voltage far exceeds the voltage that the operational amplifier can bear, which may cause the operational amplifier to burn out and further cause the whole sampling system to fail. The simplest method for solving the problem is to introduce a signal acquisition relay K, the state of the relay is completely consistent with the state of the circuit breaker, the K is closed when the circuit breaker is closed, and the K is also opened when the circuit breaker is opened, so that the Uab voltage can be sent to the rear-stage isolation operational amplifier when the circuit breaker is closed, and the Uab is raised when the circuit breaker is opened, but the Uab cannot be sent to the rear-stage operational amplifier because the contacts of the K are in an open state, so that the isolation operational amplifier is prevented from being burnt.
The isolation operational amplifier unit comprises a first filter circuit connected to the output of the voltage amplitude limiting protection unit and an isolation circuit connected with the first filter circuit. Specifically, fig. 3 shows an isolation operational amplifier circuit for differential signals Uab, which is used to convert Uab differential signals on a high-voltage side into Uab 'on a low-voltage side after electromagnetic isolation, and the Uab' signals after isolation are completely isolated from the high-voltage side electrically, so as to ensure the personal safety of a sampling system and operators. R3, R4 and C1 in the figure are RC filter circuits for input filtering, and the specific cut-off frequency can be designed according to 550Hz, so that the power frequency signal intensity can be ensured, and high-frequency harmonics after 11 times are filtered, and the stable operation of a measuring system is facilitated.
The ADC unit comprises a current conversion channel connected with the current sampling unit and a voltage conversion channel connected with the isolation operational amplifier unit, and the current sampling channel comprises a voltage forming loop and a second filter circuit connected with the voltage forming loop. Referring to fig. 4 specifically, the ADC unit is divided into two voltage and current channels, both of which are in a differential input form, in the figure, R5 is a voltage forming loop and is responsible for converting a current signal sent by the current transformer CT into a voltage signal, and R6, R7, and C2 are RC filtering loops, and are consistent with the RC parameters in fig. 3. The Uab' is a circuit breaker contact differential voltage signal subjected to isolation operational amplification, and the signal is sent to the ARM processor for sampling calculation after AD sampling. The interface between the AD and the ARM can use a parallel port bus or an SPI.
Fig. 5 is a block diagram showing the overall structure of the on-line measuring system for the contact resistance of the contact of the circuit breaker. The whole body also comprises a power supply module, DI and DO, RS485, LCD display and the like. The power supply module is responsible for carrying out AC/DC conversion on 380VAC accessed from the outside to obtain stable 5VDC and 3.3VDC for the electronic module of the measuring system to use.
The ADC module converts the voltage and current collected by the front end into discrete digital signals, and in order to ensure accuracy, a 16-bit ADC may be used for data conversion. It should be noted that, because the contact resistance of the contact is calculated, the voltage and the current need to be synchronously converted at the same time, so that the voltage and the current at the same time can be accurately obtained, and the calculation of the resistance value according to the ohm's law is facilitated. An AD conversion chip having 6 AD input channels may be used here.
The 485 interface module provides a communication interface for a measuring device to a client, and supports an isolated 485 bus interface with a baud rate of up to 115200 bps.
The DI and DO open-in and open-out modules have 10 paths of open-in and 10 paths of open-out to control the switch, and the open-in and the open-out adopt an isolation design, so that the influence of external wiring errors on the measuring device is prevented to the greatest extent.
The man-machine interaction comprises a display part and a key part, wherein the display part is an LCD display of a 128-by-32 dot matrix and is used for displaying various current measured values and parameters. The key part is used for carrying out relevant parameter entry.
The ARM processor part is responsible for reading a conversion value of the AD conversion chip through the SPI interface, the read voltage and current are discrete alternating current sampling values, the sampling frequency of 64 points/cycle can be adopted, and the alternating current effective value can be calculated through FFT. Because the FFT needs a large number of multiplication operations, an ARM chip with an FPU coprocessor can be adopted, and the calculation speed of the FFT can be greatly improved.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that these are by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (9)
1. The utility model provides a circuit breaker contact resistance on-line measuring system which characterized in that, it includes: a contact voltage difference sampling unit, a current sampling unit, a voltage amplitude limiting protection unit connected with the contact voltage difference sampling unit, an isolation operational amplifier unit connected with the voltage amplitude limiting protection unit, an ADC unit connected with the isolation operational amplifier unit and the current sampling unit, and an ARM processor connected with the ADC unit,
the current sampling unit is used for acquiring current flowing through a contact of the circuit breaker;
the contact voltage difference sampling unit is used for measuring the voltage difference generated at two ends of a contact of the circuit breaker;
the voltage amplitude limiting protection unit is used for sending a signal of a voltage difference into the isolation operational amplifier unit when the circuit breaker is closed and disconnecting the electrical connection with the isolation operational amplifier unit when the circuit breaker is disconnected;
the isolation operational amplifier unit is used for electromagnetically isolating the contact voltage difference sampling unit and the voltage amplitude limiting protection unit at the upstream from the ADC unit and the ARM processor at the downstream;
the ADC unit is used for converting the current from the current sampling unit and the voltage difference from the contact voltage difference sampling unit into discrete digital signals at the same time;
and the ARM processor is used for calculating the contact resistance according to the current and the voltage difference at the same moment.
2. The on-line measuring system for the contact resistance of the circuit breaker as claimed in claim 1, wherein the voltage amplitude limiting protection unit comprises a signal acquisition relay, the signal acquisition relay is connected between the output of the contact voltage difference sampling unit and the input of the isolation operational amplifier unit, and the signal acquisition relay is synchronously closed or opened with the circuit breaker.
3. The on-line measuring system for the contact resistance of the contact of the circuit breaker according to claim 1, wherein the isolating operational amplifier unit comprises a first filter circuit connected to the output of the voltage amplitude limiting protection unit and an isolating circuit connected to the first filter circuit.
4. The circuit breaker contact resistance on-line measurement system of claim 1, wherein the current sampling unit comprises a current transformer.
5. The on-line measuring system for the contact resistance of the contact of the circuit breaker according to claim 1, wherein the ADC unit comprises a current conversion channel connected with the current sampling unit and a voltage conversion channel connected with the isolation operational amplifier unit, respectively, and the current sampling channel comprises a voltage forming loop and a second filter circuit connected with the voltage forming loop.
6. The on-line measuring system for the contact resistance of the contact of the circuit breaker according to any one of claims 1 to 5, wherein the ADC unit comprises an AD conversion chip with 6 AD input channels.
7. The circuit breaker contact resistance on-line measurement system of any one of claims 1-5, wherein the ADC unit is connected to the ARM processor through an SPI bus.
8. The circuit breaker contact resistance on-line measurement system of any one of claims 1-5, wherein the ARM processor comprises a FPU co-processor.
9. The circuit breaker contact resistance on-line measurement system of any one of claims 1-5, wherein the voltage and current read by the ARM processor from the ADC unit are discrete AC sampled values, the ARM processor being configured to perform effective value calculations using FFT.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110413343.0A CN113030582A (en) | 2021-04-16 | 2021-04-16 | Online measuring system for contact resistance of circuit breaker contact |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110413343.0A CN113030582A (en) | 2021-04-16 | 2021-04-16 | Online measuring system for contact resistance of circuit breaker contact |
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| CN113030582A true CN113030582A (en) | 2021-06-25 |
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| CN202110413343.0A Withdrawn CN113030582A (en) | 2021-04-16 | 2021-04-16 | Online measuring system for contact resistance of circuit breaker contact |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113447719A (en) * | 2021-07-21 | 2021-09-28 | 国网河北省电力有限公司检修分公司 | Detection device for contact surface resistance |
| CN115097297A (en) * | 2022-06-22 | 2022-09-23 | 云南电网有限责任公司电力科学研究院 | Method, device and system for monitoring contact state of auxiliary switch |
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| US20150198667A1 (en) * | 2014-01-16 | 2015-07-16 | Vanguard Instruments Company, Inc. | Dual ground breaker testing system |
| CN104977531A (en) * | 2015-07-22 | 2015-10-14 | 上海电气输配电试验中心有限公司 | 126kV synthesis loop arc voltage online detection system |
| CN108072833A (en) * | 2016-11-14 | 2018-05-25 | 天津中电华利电器科技集团有限公司 | A kind of high-voltage circuitbreaker on-line monitoring system based on DSP |
| CN110954811A (en) * | 2019-11-25 | 2020-04-03 | 威胜电气有限公司 | Low-voltage circuit breaker contact detection device and method |
| CN111751622A (en) * | 2020-05-14 | 2020-10-09 | 广西电网有限责任公司电力科学研究院 | Method and system for measuring circuit breaker loop resistance |
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2021
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150198667A1 (en) * | 2014-01-16 | 2015-07-16 | Vanguard Instruments Company, Inc. | Dual ground breaker testing system |
| CN104977531A (en) * | 2015-07-22 | 2015-10-14 | 上海电气输配电试验中心有限公司 | 126kV synthesis loop arc voltage online detection system |
| CN108072833A (en) * | 2016-11-14 | 2018-05-25 | 天津中电华利电器科技集团有限公司 | A kind of high-voltage circuitbreaker on-line monitoring system based on DSP |
| CN110954811A (en) * | 2019-11-25 | 2020-04-03 | 威胜电气有限公司 | Low-voltage circuit breaker contact detection device and method |
| CN111751622A (en) * | 2020-05-14 | 2020-10-09 | 广西电网有限责任公司电力科学研究院 | Method and system for measuring circuit breaker loop resistance |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113447719A (en) * | 2021-07-21 | 2021-09-28 | 国网河北省电力有限公司检修分公司 | Detection device for contact surface resistance |
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