CN106199152B - A voltage sag identification system and method - Google Patents

Abstract

The present invention provides a voltage sag identification system, which includes a voltage sag trigger conduction module connected to a voltage transformer and a current transformer respectively, a data recording module connected to the voltage sag trigger conduction module, and A data processing module connected with the data recording module, and a display module connected with the data processing module. The invention also provides an identification method corresponding to the voltage sag identification system. The voltage sag identification system and identification method provided by the present invention carry out collaborative analysis and judgment on the characteristics of voltage effective value amplitude and current effective value amplitude, and analyze the amplitude deviation and sag duration in the process of voltage sag according to actual specific conditions. The threshold value of the voltage sag can be revised so as to reduce the judgment error caused by only analyzing the amplitude of the effective value of the voltage. At the same time, the present invention also introduces the slope, which can better characterize the global process of the voltage sag, thereby effectively reducing the analysis and judgment. The error rate is high, and the reliability of the analysis and judgment results is improved.

Description

A voltage sag identification system and method

technical field

The invention relates to the technical field of power quality transient analysis, and more specifically, to a voltage sag identification system and method.

Background technique

With the technological update of electrical equipment, especially since the 1980s, sensitive electrical equipment such as digital automatic control equipment such as frequency conversion speed regulation equipment, programmable logic controllers, various automatic production lines, and computer systems have been used in industrial production. In large-scale applications in China, the voltage quality requirements of the power supply system are getting higher and higher, and voltage sag is a common power quality problem. Voltage sags are generally caused by failures of power grids and substation facilities or sudden large changes in loads. Voltage sags will lead to a decline in enterprise productivity and product quality, increase manufacturing costs, and hinder the normal production plan of enterprises. At the same time, for each power sector, customer complaints and economic disputes caused by voltage sags will also increase, which will affect their competitiveness in the power market environment.

The identification of voltage sag refers to identifying the cause of the voltage sag according to the characteristics of the detected voltage sag data, which is one of the important evaluation indicators of voltage sag. Accurate identification of voltage sags not only helps to evaluate the regional power distribution system and select reasonable control measures, but also serves as an important basis for coordination disputes among power supply departments, users, and equipment suppliers in the electricity market environment. Therefore, it is more important to study a series of problems such as monitoring, analysis and solution of voltage sag disturbance.

At present, in the research on the identification method of voltage sag, a method of identifying voltage sag only by the effective value of voltage is proposed. Change, analyze and compare the voltage change trend during the voltage sag process, whether the three-phase voltage is balanced, and whether the voltage swell occurs, etc., extract the corresponding feature quantity, and realize the detection of line faults, transformer switching and large-capacity sensing Identification of voltage dips caused by motor starting. However, this method has the following deficiencies. For example, it only analyzes and judges the amplitude characteristics of the effective value of the voltage, and does not carry out collaborative analysis and judgment on the amplitude characteristics of the effective value of the current when the voltage sag occurs. The misjudgment rate of the analysis and judgment in the method increases; the global process of the voltage sag cannot be represented when the voltage jump is used as the characteristic quantity to identify the voltage sag, so the method has limitations in the identification process of the voltage sag, and The misjudgment rate of analysis and judgment is increased; the method's threshold setting for three-phase amplitude deviation and voltage sag duration does not match the actual engineering experience.

Contents of the invention

The object of the present invention is to provide a voltage sag identification system and method to solve the problem of high misjudgment rate in the existing voltage sag identification method described in the background art.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A voltage sag identification system, the system comprising:

a voltage sag trigger conduction module connected to the voltage transformer and the current transformer respectively,

a data recording module connected to the voltage sag trigger conduction module,

a data processing module connected to the data recording module,

a display module connected to the data processing module;

Wherein, the data recording module includes a data converter and a data recorder, the data converter is connected to the voltage sag trigger conduction module, and the data recorder is connected to the data converter and the data recorder respectively. The processing modules are connected;

The data processing module includes a data processing device connected to the data recorder, and the data processing device is respectively connected to a slope processing module, a duration processing module, a voltage RMS amplitude deviation processing module, and a current RMS amplitude deviation processing module. A processing module, the slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module are respectively connected to the result accumulation module;

The result accumulation module is connected with the display module.

Preferably, the data converter is an A/D converter, and the data processing device is a single-chip microcomputer.

Preferably, the slope processing module includes a Δk comparator and an A/D converter A connected to the microcontroller, and the Δk comparator is connected to the A/D converter A and a Δk threshold memory respectively.

Preferably, the duration processing module includes a Δt comparator and an A/D converter B connected to the microcontroller, and the Δt comparator is connected to the A/D converter B and a Δt threshold memory respectively.

Preferably, the voltage RMS amplitude deviation processing module includes a ΔU comparator and an A/D converter C connected to the single-chip microcomputer, and the ΔU comparator is connected to the A/D converter C and the ΔU threshold value respectively. Memory and trigger conduction are connected.

Preferably, the current RMS amplitude deviation processing module includes a ΔI comparator and an A/D converter D connected to the microcontroller, and the A/D converter D and the ΔI comparator are connected through a controllable switch The controllable switch is connected with the ΔU comparator, and the ΔI comparator is also connected with the ΔI threshold memory and the NOT gate.

A voltage sag identification method, the identification method comprising:

The thresholds of voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI are respectively set in advance;

Measure voltage RMS and current RMS;

Determine whether the effective value of the voltage is lower than the normal value;

If the effective value of the voltage is not lower than the normal value, continue to measure the effective value of the voltage and the effective value of the current;

If the effective value of the voltage is lower than the normal value, the voltage sag triggers the conduction module to conduct;

Sending the effective value of the voltage and the effective value of the current to a data converter for conversion into digital quantities;

Send the digital quantity to a data recorder, and the data recorder records U and I at the corresponding moment, and forms (U _i , I _i , t _i ) data group;

Send the (U _i , I _i , t _i ) data group to the data processing device, and calculate the corresponding voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU, and current RMS amplitude deviation characteristic ΔI;

The data processing device sends the voltage slope difference Δk, the duration Δt, the voltage RMS amplitude deviation characteristic ΔU, and the current RMS amplitude deviation characteristic ΔI to the slope processing module, the duration processing module, and the duration processing module respectively. module, voltage RMS amplitude deviation processing module and current RMS amplitude deviation processing module;

The slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module respectively compare the calculated value and the size of the threshold, and respectively obtain comparison results;

The slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module respectively send the comparison results to the result accumulation module;

The result accumulation module accumulates the comparison results to obtain an accumulation result;

judging whether the accumulation result is greater than 2;

If the cumulative result is greater than 2, the voltage sag is the start of the induction motor or the switching of the transformer;

If the accumulation result is less than or equal to 2, the voltage sag is a short circuit.

Preferably, the preset thresholds of voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI include:

Set the threshold of voltage slope difference Δk to 0.05; the threshold of duration Δt to 0.1; the threshold of voltage RMS amplitude deviation characteristic ΔU to 0.8; the threshold of current RMS amplitude deviation characteristic ΔI to 4.

Preferably, the formula for calculating the corresponding voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI is:

△t＝t_s-t₀；

其中，k₁、k₂分别为电压暂将开始、暂降结束时的电压斜率；t₀、t_s分别为电压暂将开始、暂降结束时的时间；U₀、U_s电压暂将开始、暂降结束时的电压值；I₀、I_m分别为电压暂将开始时的电流值及最大电流值。

Δt=t _s -t ₀ ;

Among them, k ₁ and k ₂ are the voltage slopes when the voltage is about to start and the sag is over; t ₀ and t _s are the time when the voltage is about to start and the sag is over; U ₀ and U _{s are} the time when the voltage is about to start , the voltage value at the end of the sag; I ₀ , I _m are the current value and the maximum current value when the voltage is about to start temporarily.

Preferably, said respectively comparing the calculated value and the size of the threshold, and respectively obtaining the comparison results includes:

Comparing the calculated value of the voltage slope difference Δk and the threshold value, if the calculated value of Δk is greater than the threshold value, the output of the comparison result is 1, otherwise, the output of the comparison result is 0;

Comparing the calculated value of the duration Δt with the size of the threshold, if the calculated value of Δt is greater than the size of the threshold, the output of the comparison result is 1, otherwise, the output of the comparison result is 0;

Comparing the voltage RMS amplitude deviation characteristic ΔU and the threshold value, if the calculated value of ΔU is smaller than the threshold value, the comparison result output is 0, otherwise, no result is output;

Comparing the current RMS amplitude deviation characteristic ΔI and the threshold value, if the calculated value of ΔI is greater than the threshold value, the output of the comparison result is 0, otherwise, the output of the comparison result is 1.

A voltage sag identification system, the system comprising: a voltage sag trigger conduction module connected to a voltage transformer and a current transformer respectively, a data recording module connected to the voltage sag trigger conduction module, A data processing module connected to the data recording module, a display module connected to the data processing module; wherein, the data recording module includes a data converter and a data recorder, and the data converter is connected to the voltage The sag trigger conduction module is connected, and the data recorder is connected with the data converter and the data processing module respectively; the data processing module includes a data processing device connected with the data recorder, so The data processing device is respectively connected to a slope processing module, a duration processing module, a voltage effective value amplitude deviation processing module, and a current effective value amplitude deviation processing module, and the slope processing module, the duration processing module, and the effective voltage The value amplitude deviation processing module and the current effective value amplitude deviation processing module are respectively connected to the result accumulation module; the result accumulation module is connected to the display module. The invention also provides a voltage sag identification method corresponding to the voltage sag identification system. The voltage sag identification system and identification method provided by the present invention carry out collaborative analysis and judgment on the characteristics of voltage effective value amplitude and current effective value amplitude, and analyze the amplitude deviation and sag duration during the voltage sag process according to the actual specific conditions. The threshold value of the time is revised so as to reduce the judgment error caused by only analyzing the amplitude of the effective value of the voltage. At the same time, the present invention also introduces the slope, which can better characterize the global process of the voltage sag, thus effectively reducing the analysis Judgment error rate, improve the reliability of analysis and judgment results.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings that need to be used in the description of the embodiments. Obviously, for those of ordinary skill in the art, without paying creative work Under the premise, other drawings can also be obtained based on these drawings.

Fig. 1 is a schematic structural diagram of a voltage sag identification system provided by an embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a specific device of a voltage sag identification system provided by an embodiment of the present invention;

Fig. 3 is a schematic flowchart of a voltage sag identification method provided by an embodiment of the present invention.

Detailed ways

The voltage sag identification system and method provided by the embodiments of the present invention solve the problem of high misjudgment rate in existing voltage sag identification methods.

In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are described below in conjunction with the accompanying drawings The program is described in further detail.

Please refer to accompanying drawing 1, which shows a schematic structural diagram of a voltage sag identification system provided by an embodiment of the present invention.

It can be seen from FIG. 1 that the voltage sag identification system provided by the embodiment of the present invention includes: a voltage sag trigger conduction module connected with the voltage transformer and a current transformer respectively, and the voltage sag trigger conduction module connected with the voltage sag A data recording module connected to the modules, a data processing module connected to the data recording module, and a display module connected to the data processing module. Wherein, the data recording module includes a data converter and a data recorder, the data converter is connected to the voltage sag trigger conduction module, and the data recorder is connected to the data converter and the data recorder respectively. The processing modules are connected; the data processing module includes a data processing device connected to the data recorder, and the data processing device is respectively connected to a slope processing module, a duration processing module, a voltage effective value amplitude deviation processing module and a current The RMS amplitude deviation processing module, the slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module are respectively connected to the result accumulation module; The result accumulation module is connected with the display module.

Specifically, the voltage transformer and the current transformer measure the voltage effective value U and the current effective value I respectively.

When the effective value U of the voltage is lower than the normal value, a voltage sag occurs, and the normal value of the voltage is generally 220V. When the voltage sag occurs, the voltage sag triggers the conduction module to be turned on, and when the voltage sag does not occur or recovers, the voltage sag triggers the conduction module to be turned off.

The data recording module includes a data converter and a data recorder, wherein the data converter is used to convert the measured voltage effective value U and current effective value I into digital quantities, and the data recorder records the voltage effective value U and current at regular intervals RMS value I, voltage RMS value U, current RMS value I and time form (U _i , I _i , t _i ) data group.

The data processing module includes a data processing device, a slope processing module, a duration processing module, a voltage RMS amplitude deviation processing module and a current RMS amplitude deviation processing module; wherein, the data processing device is used for recording ( U _i , I _i , t _i ) The data group calculates voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI; slope processing module, duration processing module, effective voltage The value amplitude deviation processing module and the current effective value amplitude deviation processing module respectively compare the calculated value and the threshold value, and then obtain the comparison results respectively.

The result accumulating module is used to receive the comparison result sent by the data processing module, and accumulate the comparison result to obtain the accumulative result. If the accumulative result is greater than 2, the cause of the voltage sag is the start of the induction motor or the switching of the transformer; if the accumulative If the result is less than or equal to 2, the cause of the voltage sag is a short circuit.

The display module is used to display the cause and result of the voltage sag.

The voltage sag identification system provided by the present invention can reduce judgment errors caused by only analyzing the voltage effective value amplitude through collaborative analysis and judgment of the characteristics of the voltage effective value amplitude and current effective value amplitude. At the same time, the present invention also The introduction of slope can better characterize the global process of voltage sag, thereby effectively reducing the error rate of analysis and judgment and improving the reliability of analysis and judgment results.

The embodiment of the present invention also provides a schematic structural diagram of a specific device of the voltage sag identification system, please refer to the accompanying drawing 2 for details. In the specific device of the voltage sag identification system provided in the embodiment of the present invention, the data converter is preferably an A/D converter, and the data processing device is preferably a single-chip microcomputer; the slope processing module includes a Δk comparator and an A k comparator connected to the single-chip microcomputer. /D converter A, the Δk comparator is respectively connected with the A/D converter A and the Δk threshold memory; the duration processing module includes a Δt comparator and an A/D converter B connected with the single-chip microcomputer , the Δt comparator is connected to the A/D converter B and the Δt threshold memory respectively; the voltage RMS amplitude deviation processing module includes a ΔU comparator and an A/D converter C connected to the microcontroller, The ΔU comparator is respectively connected with the A/D converter C, the ΔU threshold memory and the trigger conduction; the current RMS amplitude deviation processing module includes a ΔI comparator and an A/D converter connected with the single chip microcomputer D, the A/D converter D and the ΔI comparator are connected through a controllable switch, the controllable switch is connected to the ΔU comparator, and the ΔI comparator is also connected to the ΔI threshold memory, non- The door is connected.

Among them, the function of A/D converter A, A/D converter B, A/D converter C and A/D converter D is the same as that of the A/D converter as a data converter, only the converted data Different; Δk threshold memory, Δt threshold memory, ΔU threshold memory and ΔI threshold memory store the preset threshold respectively; Δk comparator, Δt comparator, ΔU comparator and ΔI comparator respectively store the input calculation value and Compare and output the result of the comparison. When the ΔU comparator is comparing the voltage RMS amplitude deviation, when the calculated value of ΔU is less than the threshold, the conduction part is triggered to conduct, and at the same time the controllable switch is turned off, and the output comparison result is 0; when the calculated value of ΔU When greater than or equal to the threshold value, the trigger conduction component is cut off, and at the same time the controllable switch is turned on, and the comparison result is not output. When the ΔI comparator is comparing the current RMS amplitude deviation, under the action of the NOT gate, when ΔI is greater than the threshold, the output comparison result is 0, and when ΔI is less than or equal to the threshold, the output comparison result is 1.

The specific working process of the specific device of the voltage sag identification system provided by the embodiment of the present invention is: the voltage transformer and the current transformer respectively measure the voltage effective value and the current effective value, and judge whether the voltage effective value is lower than the normal value, when the voltage effective value When not lower than the normal value, the voltage transformer and current transformer continue to measure the voltage effective value and current effective value until the voltage effective value is lower than the normal value; when the voltage effective value is lower than the normal value, the voltage sag triggers the conduction module Conduction, so that the voltage transformer and current transformer send the voltage effective value and current effective value to the A/D converter for conversion into digital quantities, and the converted digital quantities are sent to the data recorder, and the data recorder records the U at the corresponding time , I, and form (U _i , I _i , t _i ) data group; send the (U _i , I _i , t _i ) data group to the MCU, and the MCU calculates the corresponding voltage slope difference Δk, duration Δt, effective voltage Value amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI; the microcontroller sends the voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI to the slope processing module , duration processing module, voltage RMS amplitude deviation processing module and current RMS amplitude deviation processing module; slope processing module, duration processing module, voltage RMS amplitude deviation processing module and current RMS amplitude deviation processing module Comparing the calculated value and the threshold value respectively, and obtaining the comparison results respectively; the slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module respectively send the comparison results to the result accumulation module , and then the result accumulation module accumulates the comparison results to obtain the accumulation result; when the accumulation result is greater than 2, the cause of the voltage sag is the induction motor startup or transformer switching; when the accumulation result is less than or equal to 2, the voltage sag is caused The cause is short circuit, and the display module displays the final identification result.

Please refer to the accompanying drawing 3, which shows a schematic flowchart of a voltage sag identification method provided by an embodiment of the present invention.

It can be seen from Figure 3 that the voltage sag identification method provided by the embodiment of the present invention includes:

S01: Set the thresholds of the voltage slope difference Δk, the duration Δt, the voltage RMS amplitude deviation characteristic ΔU, and the current RMS amplitude deviation characteristic ΔI in advance;

S02: Measure voltage effective value and current effective value;

S03: Determine whether the effective value of the voltage is lower than the normal value;

S04: If the effective value of the voltage is not lower than the normal value, continue to measure the effective value of the voltage and the effective value of the current;

S05: If the effective value of the voltage is lower than the normal value, the voltage sag triggers the conduction module to conduct;

S06: Send the effective value of the voltage and the effective value of the current to a data converter for conversion into digital quantities;

S07: Send the digital quantity to the data recorder, and the data recorder records U and I at the corresponding time, and forms a (U _i , I _i , t _i ) data group;

S08: Send the (U _i , I _i , t _i ) data group to the data processing device, and calculate the corresponding voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU, and current RMS amplitude Deviation characteristic ΔI;

S09: The data processing device sends the voltage slope difference Δk, the duration Δt, the voltage RMS amplitude deviation characteristic ΔU, and the current RMS amplitude deviation characteristic ΔI to the slope processing module, continuously Time processing module, voltage RMS amplitude deviation processing module and current RMS amplitude deviation processing module;

S10: The slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module, and the current RMS amplitude deviation processing module respectively compare the calculated value and the threshold value, and obtain comparison results respectively ;

S11: The slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module, and the current RMS amplitude deviation processing module respectively send the comparison results to a result accumulation module;

S12: The result accumulation module accumulates the comparison results to obtain an accumulation result;

S13: judging whether the accumulation result is greater than 2;

S14: If the accumulated result is greater than 2, the voltage sag is the start of the induction motor or the switching of the transformer;

S15: If the accumulation result is less than or equal to 2, the voltage sag is a short circuit.

Specifically described as:

S01: Set the thresholds of voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU, and current RMS amplitude deviation characteristic ΔI in advance, and store the set thresholds in the Δk threshold memory and Δt threshold memory respectively , ΔU threshold value memory and ΔI threshold value memory, in order to call in subsequent steps, wherein, the threshold value of the voltage slope difference Δk is set to 0.05; the threshold value of the duration Δt is 0.1; the threshold value of the voltage RMS amplitude deviation characteristic ΔU is 0.8; The threshold of current RMS amplitude deviation characteristic ΔI is 4;

S02: The voltage transformer and the current transformer measure the effective value of the voltage and the effective value of the current respectively;

S03: Determine whether the effective value of the voltage is lower than the normal value, which is generally 220v;

S04: If the voltage effective value is not lower than the normal value, the voltage transformer and current transformer continue to measure the voltage effective value and current effective value until the voltage effective value is lower than the normal value;

S05: If the effective value of the voltage is lower than the normal value, the voltage sag triggers the conduction module to conduct;

S06: After the voltage sag triggers the conduction module to be turned on, the effective value of the voltage and the effective value of the current are sent to the data converter, and the effective value of the voltage and the current are converted into digital quantities;

S07: The data converter sends the digital quantity to the data recorder, and the data recorder records U and I at the corresponding time, and forms a (U _i , I _i , t _i ) data group;

S08: Send the (U _i , I _i , t _i ) data group to the data processing device, and calculate the corresponding voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU, and current RMS amplitude deviation characteristic ΔI;

△t＝t_s-t₀；

其中，k₁、k₂分别为电压暂将开始、暂降结束时的电压斜率；t₀、t_s分别为电压暂将开始、暂降结束时的时间；U₀、U_s电压暂将开始、暂降结束时的电压值；I₀、I_m分别为电压暂将开始时的电流值及最大电流值；k₁、k₂的计算式为

Specifically, the data set at the beginning of the voltage sag is (U ₀ , I ₀ , T ₀ ), the minimum voltage value U _n =min(U _j ), and the corresponding data set at this time is (U _n , I _n , T _n ), the maximum value of current effective value I _m =max(I _j ), the corresponding data set at this time is (U _m ,I _m ,T _m ), and the data set at the end of the voltage sag is (U _s ,I _s ,T _s ), the calculation formulas of voltage slope difference Δk, duration Δt, voltage RMS amplitude deviation characteristic ΔU and current RMS amplitude deviation characteristic ΔI are

Δt=t _s -t ₀ ;

Among them, k ₁ and k ₂ are the voltage slopes when the voltage is about to start and the sag is over; t ₀ and t _s are the time when the voltage is about to start and the sag is over; U ₀ and U _{s are} the time when the voltage is about to start , the voltage value at the end of the sag; I ₀ , I _m are the current value and the maximum current value when the voltage is about to start, respectively; the calculation formulas of k ₁ and k ₂ are

S09: The data processing device sends the voltage slope difference Δk, the duration Δt, the voltage RMS amplitude deviation characteristic ΔU, and the current RMS amplitude deviation characteristic ΔI to the slope processing module, the duration processing module, and the voltage RMS amplitude deviation respectively A processing module and a current RMS amplitude deviation processing module;

S10: the slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module respectively compare the calculated value and the threshold value, and respectively obtain the comparison results;

Specifically: compare the calculated value of the voltage slope difference Δk and the threshold value, if the calculated value of Δk is greater than the threshold value, the output of the comparison result is 1, otherwise, the output of the comparison result is 0;

Comparing the calculated value of the duration Δt with the size of the threshold, if the calculated value of Δt is greater than the size of the threshold, the output of the comparison result is 1, otherwise, the output of the comparison result is 0;

Comparing the voltage RMS amplitude deviation characteristic ΔU and the threshold value, if the calculated value of ΔU is smaller than the threshold value, the comparison result output is 0, otherwise, no result is output;

Comparing the current RMS amplitude deviation characteristic ΔI and the threshold value, if the calculated value of ΔI is greater than the threshold value, the output of the comparison result is 0, otherwise, the output of the comparison result is 1.

S11: the slope processing module, the duration processing module, the voltage RMS amplitude deviation processing module and the current RMS amplitude deviation processing module respectively send the above comparison results to the result accumulation module;

S12: The result accumulation module accumulates the received comparison results to obtain an accumulation result;

S13: judging whether the accumulation result is greater than 2;

S14: If the accumulative result is greater than 2, the cause of the voltage sag is the induction motor start or the transformer switching off;

S15: If the cumulative result is less than or equal to 2, the cause of the voltage sag is a short circuit.

The voltage sag identification method provided by the present invention conducts collaborative analysis and judgment on the characteristics of voltage effective value amplitude and current effective value amplitude, and determines the threshold value of amplitude deviation and sag duration in the process of voltage sag according to actual conditions Amendments can be made to reduce the judgment errors caused by only analyzing the amplitude of the effective value of the voltage. At the same time, the present invention also introduces the slope, which can better characterize the overall process of the voltage sag, thereby effectively reducing the errors of analysis and judgment. rate and improve the reliability of the analysis and judgment results.

The embodiments of the present invention described above are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (4)

1. The voltage sag identification method is characterized by being applied to a voltage sag identification system, and the voltage sag identification system comprises the following steps:

a voltage sag triggering and conducting module respectively communicated with the voltage transformer and the current transformer,

a data recording module connected with the voltage sag trigger conduction module,

a data processing module connected with the data recording module,

the display module is connected with the data processing module;

the data recording module comprises a data converter and a data recorder, wherein the data converter is connected with the voltage sag trigger conduction module, and the data recorder is respectively connected with the data converter and the data processing module;

the data processing module comprises a data processing device, a slope processing module, a duration processing module, a voltage effective value amplitude deviation processing module and a current effective value amplitude deviation processing module which are connected with the data recorder, wherein the data processing device is respectively connected with the slope processing module, the duration processing module, the voltage effective value amplitude deviation processing module and the current effective value amplitude deviation processing module, and the slope processing module, the duration processing module, the voltage effective value amplitude deviation processing module and the current effective value amplitude deviation processing module are respectively connected with the result accumulation module;

wherein the data processing means are arranged for recording (U _i ，I _i ，t _i ) The data set calculates a voltage slope difference delta k, a duration delta t, a voltage effective value amplitude deviation characteristic delta U and a current effective value amplitude deviation characteristic delta I; the slope processing module, the duration processing module, the voltage effective value amplitude deviation processing module and the current effective value amplitude deviation processing module respectively compare the calculated value and the threshold value, and further respectively obtain comparison results;

the result accumulation module is connected with the display module;

the voltage sag identification method comprises the following steps:

the voltage slope difference delta k, the duration delta t, the voltage effective value amplitude deviation characteristic delta U and the current effective value amplitude deviation characteristic delta I are preset respectively;

measuring a voltage effective value and a current effective value;

judging whether the effective voltage value is lower than a normal value;

if the effective voltage value is not lower than the normal value, continuing to measure the effective voltage value and the effective current value;

if the effective voltage value is lower than the normal value, the voltage sag triggers the conduction module to conduct;

transmitting the voltage effective value and the current effective value to a data converter to be converted into digital quantity;

the digital quantity is sent to a data logger, which records U, I the corresponding time and forms (U _i ，I _i ，t _i ) A data set;

the (U) _i ，I _i ，t _i ) The data set is sent to a data processing device, and corresponding voltage slope difference delta k, duration delta t, voltage effective value amplitude deviation characteristic delta U and current effective value amplitude deviation characteristic delta I are calculated;

the data processing device respectively sends the voltage slope difference delta k, the duration delta t, the voltage effective value amplitude deviation characteristic delta U and the current effective value amplitude deviation characteristic delta I to a slope processing module, a duration processing module, a voltage effective value amplitude deviation processing module and a current effective value amplitude deviation processing module;

the slope processing module, the duration processing module, the voltage effective value amplitude deviation processing module and the current effective value amplitude deviation processing module respectively compare the calculated value and the threshold value and respectively obtain comparison results;

the slope processing module, the duration processing module, the voltage effective value amplitude deviation processing module and the current effective value amplitude deviation processing module respectively send the comparison result to a result accumulation module;

the result accumulation module accumulates the comparison results to obtain accumulated results;

judging whether the accumulated result is more than 2;

if the accumulated result is greater than 2, the voltage sag is the start of the induction motor or the switching of the transformer;

and if the accumulated result is less than or equal to 2, the voltage sag is short circuit.

2. The voltage sag identification method according to claim 1, wherein the pre-setting of the thresholds of the voltage slope difference Δk, the duration Δt, the voltage effective value amplitude deviation characteristic Δu, and the current effective value amplitude deviation characteristic Δi, respectively, includes:

setting the threshold value of the voltage slope difference delta k to be 0.05; the threshold value of the duration Δt is 0.1; the threshold value of the voltage effective value amplitude deviation characteristic delta U is 0.8; the threshold value of the current effective value amplitude deviation characteristic Δi is 4.

3. The voltage sag identification method according to claim 1, wherein the calculation formulas for calculating the corresponding voltage slope difference Δk, duration Δt, voltage effective value amplitude deviation characteristic Δu, and current effective value amplitude deviation characteristic Δi are as follows:

Δt＝t _s -t ₀ ；/>

wherein k is ₁ 、k ₂ The voltage slopes at the beginning and end of the voltage sag are respectively; t is t ₀ 、t _s The time when the voltage sag will start and the time when the voltage sag ends are respectively; u (U) ₀ 、U _s Voltage values at which voltage sag will start and sag ends; i ₀ 、I _m The current value and the maximum current value at the beginning of the voltage sag are respectively.

4. The voltage sag identification method according to claim 1, wherein comparing the calculated values and the threshold values, respectively, and obtaining comparison results, respectively, includes:

comparing the calculated value of the voltage slope difference delta k with the magnitude of the threshold value, outputting a comparison result as 1 if the calculated value of delta k is larger than the magnitude of the threshold value, otherwise outputting a comparison result as 0;

comparing the calculated value of the duration delta t with the magnitude of the threshold, outputting a comparison result as 1 if the calculated value of delta t is larger than the magnitude of the threshold, otherwise outputting a comparison result as 0;

comparing the amplitude deviation characteristic delta U of the effective value of the voltage with the magnitude of the threshold, outputting a comparison result as 0 if the calculated value of delta U is smaller than the magnitude of the threshold, otherwise, not outputting the result;

comparing the amplitude deviation characteristic delta I of the effective value of the current with the magnitude of the threshold, outputting a comparison result as 0 if the calculated value of delta I is larger than the magnitude of the threshold, otherwise outputting a comparison result as 1.

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