CN114609517A - Post-arc current measuring system and control method thereof - Google Patents
Post-arc current measuring system and control method thereof Download PDFInfo
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- CN114609517A CN114609517A CN202210278172.XA CN202210278172A CN114609517A CN 114609517 A CN114609517 A CN 114609517A CN 202210278172 A CN202210278172 A CN 202210278172A CN 114609517 A CN114609517 A CN 114609517A
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- 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
- G01R31/3271—Testing of circuit interrupters, switches or circuit-breakers of high voltage or medium voltage devices
- G01R31/3272—Apparatus, systems or circuits therefor
- G01R31/3274—Details related to measuring, e.g. sensing, displaying or computing; Measuring of variables related to the contact pieces, e.g. wear, position or resistance
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
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Abstract
The invention discloses a post-arc current measuring system and a control method thereof, and relates to the technical field of current measurement. The system comprises a large-current circuit module, a current injection circuit module, a voltage forming network module and a zero-zone current measuring network module; the high-current circuit module comprises a first capacitor, a first auxiliary circuit breaker, a first inductor and a second auxiliary circuit breaker which are sequentially connected in series; the current injection circuit module comprises a second inductor, a third auxiliary circuit breaker and a second capacitor which are sequentially connected in series; the voltage forming network module comprises a circuit resistor and a third capacitor which are sequentially connected in series; the zero zone current measurement network module comprises a test circuit breaker and a zero zone current measurement device which are sequentially connected in series. In the invention, two ends of the shunt of the zero zone current measuring device are connected with a plurality of diodes in anti-parallel, when a large current flows through the measuring unit, the diodes automatically conduct the current, and the measuring precision can be adjusted according to the number and the type of the diodes connected in parallel.
Description
Technical Field
The invention relates to the technical field of current measurement, in particular to a post-arc current measurement system and a control method thereof.
Background
Mechanical gas circuit breakers are widely used in high voltage ac power grids and also as mechanical components of high voltage dc switchgear. Due to the key role of safe and reliable operation of the power grid, it is very important to investigate the on-off behavior of the power grid in detail. The critical moment of disconnection is the time around the current zero. When the breaker is used for cutting off large current, the current after the arc exists under the action of transient recovery voltage due to residual plasma in the arc gap after the current passes zero. The post-arc current is an important parameter of the circuit breaker, particularly the breaking process of the vacuum circuit breaker, and can be used for judging the breaking performance of the circuit breaker. Measurements of arc resistance and post-arc current at or shortly before zero current can be used to evaluate the breaking capability of the test circuit breaker. Thus, accurate measurement of the arc current near the zero crossing provides important information.
The difficulty of zero zone measurement of the high-voltage circuit breaker comprises the following steps: 1) the difference of the arc voltage and the current amplitude at different moments is large, and the measuring range of the sensor is difficult to be considered. In the near zone fault test, the peak value of the short-circuit current is up to hundreds of kA, and the post-arc current is as low as hundreds of mA. Meanwhile, the arc voltage is only several kV or even hundreds of V, and the transient recovery voltage is as high as hundreds of kV; 2) the arc current and voltage are converted very fast, and the requirement on the frequency response of measuring equipment is high; 3) the existence of the distributed inductance of the measuring loop and the break capacitance of the circuit breaker makes the arc voltage and the current difficult to be directly and independently measured.
The existing zero zone measurement methods include a conventional method and a current transfer method. The traditional method uses a current divider and a voltage divider to directly measure, is simple, but needs a special current divider to obtain ideal results, and needs to calculate the current and the voltage according to the parameters of a loop. The current transfer method uses a mechanical switch to help the shunt bear large current, can better protect the shunt, but has complex operation and needs to control the closing of the mechanical switch at a specific time before the arc.
Disclosure of Invention
The invention aims to provide a post-arc current measuring system and a control method thereof, so as to solve the problem of difficult post-arc current measurement.
In order to achieve the above object, an embodiment of the present invention provides a post-arc current measurement system, which includes a large current circuit module, a current injection circuit module, a voltage formation network module, and a zero zone current measurement network module, which are connected in parallel;
the high-current circuit module comprises a first capacitor, a first auxiliary circuit breaker, a first inductor and a second auxiliary circuit breaker which are sequentially connected in series;
the current injection circuit module comprises a second inductor, a third auxiliary circuit breaker and a second capacitor which are sequentially connected in series;
the voltage forming network module comprises a circuit resistor and a third capacitor which are sequentially connected in series;
the zero zone current measurement network module comprises a test circuit breaker and a zero zone current measurement device which are sequentially connected in series.
Preferably, after the first and second capacitors are charged, the first and third auxiliary breakers will initiate current flow in the high current circuit module and the current injection circuit module, respectively.
Preferably, the zero zone current measuring device comprises a shunt and a plurality of diodes connected in anti-parallel across the shunt.
Preferably, the first capacitor, the first inductor and the circuit resistor are used for determining the frequency of the main current, and the charging voltage of the first capacitor is used for determining the peak value of the main current.
Preferably, the second capacitor, the second inductor and the circuit resistor are used for determining the frequency of the injection current, and the charging voltage of the second capacitor is used for determining the peak value of the injection current.
The embodiment of the invention also provides a control method of the post-arc current measurement system, which comprises the following steps:
closing the first auxiliary breaker so that a sinusoidal main current through the test breaker starts to flow;
before the main current crosses zero, the second auxiliary breaker and the test breaker are disconnected;
before the main current crosses zero, closing a third auxiliary circuit breaker and injecting a second sinusoidal current;
at the current zero point of the main current, the second auxiliary circuit breaker is enabled to cut off the large current, and the injected current still flows through the test circuit breaker;
when the next current is zero, the injection current is cut off by using a test breaker, so that the transient recovery voltage is increased;
adjusting the transient recovery voltage waveform on the test object by selecting appropriate values of the circuit resistor, the third capacitor, the first inductor, the second inductor, the first capacitor and the second capacitor;
the post-arc current is measured by a zero zone current measurement network.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a post-arc current measuring system, which comprises a large-current circuit module, a current injection circuit module, a voltage forming network module and a zero-zone current measuring network module, wherein the large-current circuit module is connected with the current injection circuit module; the high-current circuit module comprises a first capacitor, a first auxiliary circuit breaker, a first inductor and a second auxiliary circuit breaker which are sequentially connected in series; the current injection circuit module comprises a second inductor, a third auxiliary circuit breaker and a second capacitor which are sequentially connected in series; the voltage forming network module comprises a circuit resistor and a third capacitor which are sequentially connected in series; the zero zone current measurement network module comprises a test circuit breaker and a zero zone current measurement device which are sequentially connected in series. In the invention, two ends of the shunt of the zero zone current measuring device are connected with a plurality of diodes in anti-parallel, when a large current flows through the measuring unit, the diodes automatically conduct the current, and the measuring precision can be adjusted according to the number and the type of the diodes connected in parallel.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a post-arc current measurement system according to an embodiment of the present invention;
FIG. 2 is a circuit diagram of a diode according to an embodiment of the present invention;
FIG. 3 is a circuit diagram of a diode according to an embodiment of the present invention;
FIG. 4 is a graph of measurements taken when a diode according to an embodiment of the present invention is not conducting;
FIG. 5 is a graph of the measurement results of the diode when conducting according to one embodiment of the present invention;
FIG. 6 is a graph of the measurement results of a diode provided by an embodiment of the present invention that remains on for a longer period of time;
fig. 7 is a diagram illustrating the test result of the shunt effect of the diode under a large current according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be understood that the step numbers used herein are only for convenience of description and are not used as limitations on the order in which the steps are performed.
It is to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a post-arc current measurement system according to an embodiment of the present invention. In this embodiment, the post-arc current measurement system includes a large current circuit module a, a current injection circuit module B, a voltage forming network module C, and a zero zone current measurement network module D; the high-current circuit module A comprises a first capacitor C1, a first auxiliary breaker S1, a first inductor L1 and a second auxiliary breaker S2 which are sequentially connected in series; the current injection circuit module B comprises a second inductor L2, a third auxiliary circuit breaker SG and a second capacitor C2 which are sequentially connected in series; the voltage forming network module C comprises a circuit resistor R and a third capacitor CN which are sequentially connected in series; the zero zone current measurement network module D comprises a test circuit breaker TO and a zero zone current measurement device D which are sequentially connected in series.
In particular, after said first capacitor C1 and said second capacitor C2 are charged, the first auxiliary breaker S1 and the third auxiliary breaker SG will initiate a current flow in the high current circuit module a and the current injection circuit module B, respectively.
In one embodiment, the zero zone current measuring device d includes a shunt and several diodes connected in anti-parallel across the shunt.
It can be understood that when a large current flows through the measuring unit, the diodes automatically conduct the current, the measuring accuracy can be adjusted according to the number and the types of the parallel diodes, and the inductance of the measuring unit influences the tested current change rate.
Specifically, the first capacitor C1, the first inductor L1 and the circuit resistor R are used for determining the frequency of the main current, and the charging voltage of the first capacitor C1 is used for determining the peak value of the main current.
Specifically, the second capacitor C2, the second inductor L2 and the circuit resistor R are used for determining the frequency of the injection current, and the charging voltage of the second capacitor C2 is used for determining the peak value of the injection current.
The embodiment of the present invention further provides a control method for a post-arc current measurement system, which is applied to the post-arc current measurement system described in any of the above embodiments, and the control method includes:
closing the first auxiliary breaker S1 so that a sinusoidal main current through the test breaker TO starts TO flow; before the main current crosses zero, the second auxiliary breaker S2 and the test breaker TO are opened; before the main current crosses zero, closing a third auxiliary circuit breaker SG and injecting a second sinusoidal current; at the current zero point of the main current, the second auxiliary breaker S2 is opened TO cut off a large current, and the injected current still flows through the test breaker TO; when the next current is zero, the injection current is cut off by using a test breaker TO, so that the transient recovery voltage is increased; adjusting the transient recovery voltage waveform on the test object by selecting appropriate values of the circuit resistor R, the third capacitor CN, the first inductor L1, the second inductor L2, the first capacitor C1 and the second capacitor C2; the post-arc current is measured by a zero zone current measurement network.
In order to accurately measure the current in the milliampere or one-digit ampere range before and after zero crossing, a measuring system for limiting an output signal at a high current stage is needed, so that the post-arc current measuring system is provided.
In an embodiment of the invention, the anti-parallel connected diodes do not conduct below a certain threshold voltage (forward voltage V)F) Of the current sensor. Thus, the voltage across the measurement system can be considered to be proportional to the total current within a defined range.
I0＝VF/Rs
ID(VF)≤x·I0
Wherein, I0For measuring the resulting current, VFIs a certain threshold voltage (forward voltage), RSFor selected shunt resistance, IDTo forward bias the diode current, x is the desired precision value.
Once the threshold voltage V is exceededFI.e. the current rises to a higher level, the forward biased diode will take over an increasingly larger share of the current. This results in a sharp drop in the rise of the voltage. Effectively limiting the output voltage of the measurement system. Due to this effect, the input range of the data acquisition system can be adjusted accordingly and the range around current zero can be recorded, thereby improving accuracy.
It will be appreciated that the post-arc current measurement system may select the shunt resistance and diode threshold voltage to match the desired measurement range. The quiescent voltage current characteristics define the width of the measurement range (VF) and the clipping capability (forward slope resistance rf, peak forward current). Furthermore, the whole system needs to be adapted to high frequencies in order to quickly commutate the current in and out of the shunt (stray inductance, reverse recovery, package inductance). Often, a trade-off must be made because high power diodes are not suitable for high frequencies and vice versa. Due to the high requirements on system bandwidth and low output voltage, it is important to consider the non-ideal behavior of the parasitic elements and diodes.
Schottky diodes and fast recovery diodes are preferred over high power diodes because the total current carrying capacity of the system can be increased by the parallel assembly of multiple cells. However, to avoid thermal runaway of the parallel diodes, a considerable safety margin is important. If the application needs to conduct very high currents, additional high power diodes may need to be connected in parallel.
Schottky diodes and fast recovery diodes are preferred over high power diodes because the total current carrying capacity of the system can be increased by the parallel assembly of multiple cells. However, to avoid thermal runaway of the parallel diodes, a considerable safety margin is important. If the application needs to conduct very high currents, it may be necessary to connect additional high power diodes in parallel.
The two ends of the shunt are reversely connected with the diodes in parallel, when a large current flows through the measuring unit, the diodes automatically conduct the current, the measuring precision can be adjusted according to the number and the type of the diodes connected in parallel, and the inductance of the measuring unit influences the current change rate of the test.
The selection of the shunt resistance and the threshold voltage of the diode can be matched to the desired measurement range.
The quiescent voltage-current characteristic defines the width (± V) of the measurement rangeF) And clipping capability (forward slope resistance rf, forward peak current). In addition, the whole system needs to be adapted to high frequencies to achieve fast commutation of current in and out of the shunt (stray inductance, reverse recovery, package inductance). Usually, a trade-off has to be made, since high power diodes are not suitable for high frequencies and vice versa. Due to the high requirements on system bandwidth and low output voltage, it is important to consider the non-ideal behavior of the parasitic elements and diodes.
Schottky diodes and fast recovery diodes are preferred over high power diodes because the total current carrying capacity of the system can be increased by the parallel assembly of multiple cells. However, to avoid thermal runaway of the parallel diodes, a considerable safety margin is important. If the application needs to conduct very high currents, additional high power diodes may need to be connected in parallel.
Embodiments of the present invention provide low power testing using a pre-charged low voltage LC circuit for the first evaluation of different types of diodes and system components. Tuned to a resonant frequency in the two-digit kilohertz range and provide a current at least five times greater than the selected linear range of the assembly. Using this test setup, the maximum rate of rise of current can be easily adjusted to determine the dynamic limit performance of different types of diodes and components. Due to the damping of the circuit, multiple current zero crossings are observed in each measurement, the rate of current rise is reduced, which can determine the performance of the system under different conditions. Once the appropriate component is determined, it can be amplified to the desired current level using parallel connection. The main drawback of this test setup is that it is not possible to generate a current similar to the expected current amplitude of the breaker test. Therefore, the diode cannot be tested with a low-ohmic shunt used in practical applications of the measurement system.
Embodiments of the present invention provide high power testing, and once a suitable diode configuration is determined, an amplified version with low ohmic shunt and multiple diodes in parallel must be verified. This can be done on the circuit breaker test stand if the voltage and current parameters can be adequately adjusted.
In a specific embodiment, the built loop model is divided into a circuit with or without a diode and a diode circuit as shown in fig. 2 and 3, and V1 is a 50Hz alternating current voltage source with a changeable effective value; s1 is a delay switch, can control the time of the switch, and is set as the switching time of 0.0S for conduction and 0.02S for off, which is just one period; r5 simulates a loop resistor during turn-off, the resistance value is 1000 ohms, R1 simulates the resistor of a shunt, and the resistance value is smaller than the loop resistor, is set to be 0.001 time of that of R5, and is 1 ohm; XSC1 is an oscilloscope, wherein a channel 1 monitors the overall voltage change, and a channel 2 monitors the voltage at two ends of R1; d1 and D2 are ideal diodes, and the conduction voltage is about U after detection0＝0.25V。
When the diode is not conducting:
setting V1At 170V, the diode should be in a non-conducting state, so that the loop is formed by connecting two resistors in series, and the two signal values measured by the oscilloscope should be different by about 1000 times, so that the ranges of the channel 1 and the channel 2 are adjusted to be different by 1000 times, as shown in fig. 4, the two curves are completely overlapped and are consistent with the simulation result without the diode, which indicates that the voltage at the two ends of the diode is low and the diode is not conducting.
When the diode is conducting:
setting V1 to 200V, the diode should be turned on at some time t1 that should be at the voltage rise, so when t1 is reached<t1 the loop is composed of two resistors connected in series, and the time is 5ms>t>At t1, the diode is turned on to share the current, and the voltage is lower than that without the diode. Continuing to scale channels 1 and 2 by a factor of 1000, as shown in fig. 5, the two curves in fig. 5(a) still completely coincide, while the diode is turned on at 3.59ms in fig. 5(b), when the voltage across the diode is 0.250V.
When the diode remains conducting for a longer time:
when V1 is set to 2000V, the simulation result is as shown in fig. 6, no diode still overlaps, but the diode in fig. 6(b) reaches the on-voltage of the diode early, so that the diode shunts R1, and although the current flowing through the diode cannot be accurately measured in the large current stage, the accurate current can be measured in the small current interval 0-307 us.
The embodiment of the invention provides a protection function, when V1 is set to 2000V, the voltage U between two ends of the diodeD389mV, i.e., the voltage across the shunt; when V1 is set to 20000V, the simulation result is shown in fig. 7, UDThis means that the diode can help the shunt and protect the shunt at the same time.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (6)
1. A post-arc current measuring system is characterized by comprising a large-current circuit module, a current injection circuit module, a voltage forming network module and a zero-zone current measuring network module which are connected in parallel;
in a series circuit of the high current circuit module and the zero zone current measurement network module;
the high-current circuit module comprises a first capacitor, a first auxiliary circuit breaker, a first inductor and a second auxiliary circuit breaker which are sequentially connected in series;
the current injection circuit module comprises a second inductor, a third auxiliary circuit breaker and a second capacitor which are sequentially connected in series;
the voltage forming network module comprises a circuit resistor and a third capacitor which are sequentially connected in series;
the zero zone current measurement network module comprises a test circuit breaker and a zero zone current measurement device which are sequentially connected in series.
2. The post-arc current measurement system of claim 1, wherein after the first and second capacitors are charged, first and third auxiliary circuit breakers will initiate current flow in the high current circuit module and the current injection circuit module, respectively.
3. The post-arc current measurement system of claim 1, wherein the zero zone current measurement device comprises a shunt, and a number of diodes connected in anti-parallel across the shunt.
4. The post-arc current measurement system according to claim 1, wherein the first capacitor, the first inductor and the circuit resistor are used for determining a frequency of the main current, and a charging voltage of the first capacitor is used for determining a peak value of the main current.
5. The post-arc current measurement system according to claim 1, wherein the second capacitor, the second inductor and the circuit resistor are used for determining a frequency of the injection current, and a charging voltage of the second capacitor is used for determining a peak value of the injection current.
6. A control method of a post-arc current measuring system applied to the post-arc current measuring system according to any one of claims 1 to 5, comprising:
closing the first auxiliary breaker so that a sinusoidal main current through the test breaker starts to flow;
before the main current crosses zero, the second auxiliary breaker and the test breaker are disconnected;
before the main current crosses zero, closing a third auxiliary circuit breaker and injecting a second sinusoidal current;
at the current zero point of the main current, the second auxiliary circuit breaker is enabled to cut off the large current, and the injected current still flows through the test circuit breaker;
when the next current is zero, the injection current is cut off by using a test circuit breaker, so that the transient recovery voltage is increased;
adjusting the transient recovery voltage waveform on the test object by selecting appropriate values of the circuit resistor, the third capacitor, the first inductor, the second inductor, the first capacitor and the second capacitor;
the post-arc current is measured by a zero zone current measurement network.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116908675A (en) * | 2023-09-08 | 2023-10-20 | 清华四川能源互联网研究院 | Circuit breaker post-arc current measurement system and method |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116908675A (en) * | 2023-09-08 | 2023-10-20 | 清华四川能源互联网研究院 | Circuit breaker post-arc current measurement system and method |
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