阅读说明：本技术 电力变压器直流偏磁的监测方法 (Monitoring method for direct current magnetic bias of power transformer ) 是由 汪鹏 陈龙 严亮 张繁 谷若雨 严平 池方仁 肖黎 于 2019-08-26 设计创作，主要内容包括：本申请提供了一种电力变压器直流偏磁的监测方法,包括：实时获取电力变压器的中性点电流。将中性点电流按照同一预设间隔时间分为多个连续的时间段,并对每个时间段内的中性点电流的数据进行傅里叶分析,得到直流电流信号Im。将直流电流信号Im与第一预设电流阈值进行比较,并确定电力变压器是否发生直流偏磁。若确定电力变压器发生直流偏磁,则判断第一时间点之后第一时间周期内的直流电流信号Im的最大值是否大于第二预设电流阈值,且在第一时间周期内的直流电流信号Im的最小值是否小于第三预设电流阈值；若满足条件,则确定电力变压器的直流偏磁是由杂散电流引起的。(The application provides a monitoring method of direct current magnetic biasing of a power transformer, which comprises the following steps: and acquiring the neutral point current of the power transformer in real time. Dividing the neutral point current into a plurality of continuous time periods according to the same preset interval time, and performing Fourier analysis on data of the neutral point current in each time period to obtain a direct current signal Im. And comparing the direct current signal Im with a first preset current threshold value, and determining whether the power transformer generates direct current magnetic biasing. If the power transformer is determined to generate direct current magnetic biasing, judging whether the maximum value of the direct current signal Im in a first time period after a first time point is larger than a second preset current threshold value and whether the minimum value of the direct current signal Im in the first time period is smaller than a third preset current threshold value; if the condition is satisfied, determining that the direct current magnetic bias of the power transformer is caused by the stray current.)

1. A monitoring method for DC magnetic bias of a power transformer is characterized by comprising the following steps:

acquiring neutral point current of the power transformer in real time;

dividing the neutral point current into a plurality of continuous time periods according to the same preset interval time, and performing Fourier analysis on data of the neutral point current in each time period to obtain a direct current signal Im, wherein m is a natural number;

comparing the direct current signal Im with a first preset current threshold, and determining whether the power transformer generates direct current magnetic biasing based on the comparison result;

if the fact that the direct current magnetic bias occurs to the power transformer at a first time point is determined, whether the maximum value of the direct current signal Im in a first time period after the first time point is larger than a second preset current threshold value and whether the minimum value of the direct current signal Im in the first time period is smaller than a third preset current threshold value are judged, and the second preset current threshold value is the same as the third preset current threshold value in absolute value;

if the maximum value of the direct current signal Im in the first time period is greater than the second preset current threshold value and the minimum value of the direct current signal Im in the first time period is less than the third preset current threshold value, determining that the direct current magnetic bias of the power transformer is caused by stray current.

2. The method for monitoring dc bias of a power transformer according to claim 1, wherein if the maximum value of the dc current signal Im during the first time period is greater than the second predetermined current threshold and the minimum value of the dc current signal Im during the first time period is less than the third predetermined current threshold, the method further comprises, before the step of determining that the dc bias of the power transformer is caused by stray current:

if the maximum value of the direct current signal Im in the first time period is less than or equal to the second preset current threshold value and/or the minimum value of the direct current signal Im in the first time period is greater than or equal to the third preset current threshold value, calculating the frequency of positive and negative occurrence of the direct current signal Im in the first time period to obtain the number of positive data and the number of negative data;

calculating the occurrence proportion of the positive data number and the negative data number in the first time period, and determining whether the proportion result is in a preset range so as to determine whether the direct current magnetic bias of the power transformer is caused by the stray current.

3. The method for monitoring the dc bias of a power transformer according to claim 2, wherein the step of calculating the ratio of the positive data number to the negative data number in the first time period and determining whether the ratio result is within a predetermined range to determine whether the dc bias of the power transformer is caused by the stray current comprises:

calculating the occurrence proportion of the positive data number and the negative data number in the first time period to obtain a proportion result;

judging whether the proportion result is in the preset range or not, and if the proportion result is in the preset range, determining that the direct current magnetic bias of the power transformer is caused by the stray current;

and if the proportion result is not in the preset range, determining that the direct current magnetic bias of the power transformer is not caused by the stray current.

4. A method for monitoring the dc bias of a power transformer as recited in claim 3, wherein said predetermined range is 0.4-2.5.

5. The method for monitoring dc magnetic bias of a power transformer according to claim 2, wherein said step of calculating the frequency of positive and negative occurrences of said dc current signal Im during said first time period to obtain a positive data number and a negative data number comprises:

calculating the number of the positive data of the direct current signal Im in the first time period, wherein the calculation formula is as follows:

wherein N is₁For the positive number of data, X_iAnd i is the ith data in the first time period, and i is a natural number.

6. The method for monitoring dc magnetic bias of a power transformer according to claim 5, wherein said step of calculating the frequency of positive and negative occurrences of said dc current signal Im during said first time period to obtain positive and negative data numbers further comprises:

calculating the number of the negative data of the direct current signal Im in the first time period, wherein the calculation formula is as follows:

wherein N is₂The number of the negative data is shown.

7. A method for monitoring dc magnetic bias of a power transformer according to claim 1, wherein the step of comparing the dc current signal Im with a first predetermined current threshold and determining whether dc magnetic bias occurs in the power transformer based on the comparison comprises:

acquiring the first preset current threshold, and performing difference comparison on the direct current signal Im and the first preset current threshold to obtain a difference comparison result;

if the difference comparison result is greater than zero at the first time point, determining that the direct current magnetic bias occurs to the power transformer at the first time point;

and if the difference comparison result is less than or equal to zero, determining that the direct current magnetic biasing does not occur to the power transformer.

8. The method for monitoring dc magnetic bias of a power transformer according to claim 1, wherein said step of obtaining the neutral point current of said power transformer in real time is preceded by the step of:

and acquiring the neutral point current of the power transformer in real time through a Hall current sensor, and outputting the neutral point current.

9. The method of claim 8, wherein the sampling frequency of the hall current sensor is greater than or equal to 2 KHz.

10. A method for monitoring the dc bias of a power transformer according to any of claims 1-9, wherein said first period of time is 5 min.

11. A method for monitoring the dc bias of a power transformer according to any of claims 1-9, wherein said first predetermined current threshold is 18A.

Technical Field

The application relates to the technical field of power transformers, in particular to a monitoring method for direct current magnetic biasing of a power transformer.

Background

The power transformer in the power system has a direct current magnetic bias phenomenon. Because urban rail transit mostly adopts the direct current drive vehicle, rail transit's direct current power supply carries out the backward flow through the rail, and the track is not totally insulated to ground moreover for there is stray current in the ground. The subway stray current enters the power transformer from the neutral point, so that the current of the neutral point of the transformer is increased, and direct current magnetic flux is generated in an iron core of the power transformer, and the direct current magnetic bias phenomenon is generated.

Along with the continuous promotion of the urbanization process of China and the continuous expansion of the urban construction scale, the application of the rail transit of each large city is gradually common. Particularly for large cities with dense track traffic lines, the influence of stray current generated by track traffic on urban power substations is increasing day by day.

At present, a direct-current magnetic biasing judgment method for a power transformer can only judge whether the power transformer generates direct-current magnetic biasing or not, and no judgment method can determine whether the direct-current magnetic biasing of the power transformer is caused by stray current or not.

Disclosure of Invention

Therefore, it is necessary to provide a method for monitoring dc magnetic bias of a power transformer, aiming at the problem that the existing method for determining dc magnetic bias of a power transformer cannot determine whether dc magnetic bias of the power transformer is caused by stray current.

A monitoring method for DC magnetic bias of a power transformer comprises the following steps:

acquiring neutral point current of the power transformer in real time;

dividing the neutral point current into a plurality of continuous time periods according to the same preset interval time, and performing Fourier analysis on data of the neutral point current in each time period to obtain a direct current signal Im, wherein m is a natural number;

comparing the direct current signal Im with a first preset current threshold, and determining whether the power transformer generates direct current magnetic biasing based on the comparison result;

if the fact that the direct current magnetic bias occurs to the power transformer at a first time point is determined, whether the maximum value of the direct current signal Im in a first time period after the first time point is larger than a second preset current threshold value and whether the minimum value of the direct current signal Im in the first time period is smaller than a third preset current threshold value are judged, and the second preset current threshold value is the same as the third preset current threshold value in absolute value;

if the maximum value of the direct current signal Im in the first time period is greater than the second preset current threshold value and the minimum value of the direct current signal Im in the first time period is less than the third preset current threshold value, determining that the direct current magnetic bias of the power transformer is caused by stray current.

In one embodiment, if the maximum value of the dc current signal Im in the first time period is greater than the second preset current threshold and the minimum value of the dc current signal Im in the first time period is less than the third preset current threshold, before the step of determining that the dc magnetic bias of the power transformer is caused by stray current, the method further includes:

if the maximum value of the direct current signal Im in the first time period is less than or equal to the second preset current threshold value and/or the minimum value of the direct current signal Im in the first time period is greater than or equal to the third preset current threshold value, calculating the frequency of positive and negative occurrence of the direct current signal Im in the first time period to obtain the number of positive data and the number of negative data;

calculating the occurrence proportion of the positive data number and the negative data number in the first time period, and determining whether the proportion result is in a preset range so as to determine whether the direct current magnetic bias of the power transformer is caused by the stray current.

In one embodiment, the step of calculating the occurrence ratio of the positive data number and the negative data number in the first time period and determining whether the ratio result is within a preset range to determine whether the dc bias of the power transformer is caused by the stray current comprises:

calculating the occurrence proportion of the positive data number and the negative data number in the first time period to obtain a proportion result;

judging whether the proportion result is in the preset range or not, and if the proportion result is in the preset range, determining that the direct current magnetic bias of the power transformer is caused by the stray current;

and if the proportion result is not in the preset range, determining that the direct current magnetic bias of the power transformer is not caused by the stray current.

In one embodiment, the predetermined range is 0.4-2.5.

In one embodiment, the step of calculating the frequency of positive and negative occurrences of the dc current signal Im in the first time period to obtain the number of positive data and the number of negative data includes:

calculating the number of the positive data of the direct current signal Im in the first time period, wherein the calculation formula is as follows:

wherein N is₁For the positive number of data, X_iAnd i is the ith data in the first time period, and i is a natural number.

In one embodiment, the step of calculating the frequency of positive and negative occurrences of the dc current signal Im in the first time period to obtain the number of positive data and the number of negative data further includes:

calculating the number of the negative data of the direct current signal Im in the first time period, wherein the calculation formula is as follows:

wherein N is₂The number of the negative data is shown.

In one embodiment, the step of comparing the dc current signal Im with a first preset current threshold and determining whether dc magnetic biasing of the power transformer occurs based on the comparison result comprises:

acquiring the first preset current threshold, and performing difference comparison on the direct current signal Im and the first preset current threshold to obtain a difference comparison result;

if the difference comparison result is greater than zero at the first time point, determining that the direct current magnetic bias occurs to the power transformer at the first time point;

and if the difference comparison result is less than or equal to zero, determining that the direct current magnetic biasing does not occur to the power transformer.

In one embodiment, before the step of obtaining the neutral point current of the power transformer in real time, the method further includes:

and acquiring the neutral point current of the power transformer in real time through a Hall current sensor, and outputting the neutral point current.

In one embodiment, the sampling frequency of the Hall current sensor is greater than or equal to 2 KHz.

In one embodiment, the first time period is 5 min.

In one embodiment, the first predetermined current threshold is 18A.

Compared with the prior art, the monitoring method for the direct current magnetic bias of the power transformer comprises the steps of firstly, acquiring the neutral point current of the power transformer in real time; dividing the neutral point current into a plurality of continuous time periods according to the same preset interval time, and performing Fourier analysis on data of the neutral point current in each time period to obtain a direct current signal Im; secondly, comparing the direct current signal Im with a first preset current threshold value, and determining whether the power transformer generates direct current magnetic biasing; if the direct current magnetic biasing occurs, further judging whether the direct current magnetic biasing of the power transformer is caused by stray current; finally, if the maximum value of the dc current signal Im in the first time period is greater than the second preset current threshold and the minimum value of the dc current signal Im in the first time period is less than the third preset current threshold, it may be determined that the dc magnetic bias of the power transformer is caused by a stray current.

According to the method and the device, when the power transformer generates the direct current magnetic biasing phenomenon, whether the direct current magnetic biasing is caused by stray current or not is further monitored and judged, so that a direct current magnetic biasing restraining method is favorably and pertinently adopted, the influence of the direct current magnetic biasing phenomenon on the operation of the transformer is reduced to the minimum, and the operation safety and reliability of the power transformer are further improved.

Drawings

Fig. 1 is a first flowchart of a method for monitoring dc magnetic bias of a power transformer according to an embodiment of the present disclosure;

fig. 2 is a second flowchart of a method for monitoring dc magnetic bias of a power transformer according to an embodiment of the present disclosure.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present application more comprehensible, embodiments accompanying the present application are described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of embodiments in many different forms than those described herein and those skilled in the art will be able to make similar modifications without departing from the spirit of the application and it is therefore not intended to be limited to the embodiments disclosed below.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1 and fig. 2, an embodiment of the present application provides a method for monitoring a dc magnetic bias of a power transformer, which can be applied to a power transformer in urban rail transit, and is used to monitor whether the dc magnetic bias of the power transformer occurs, and meanwhile, the method can determine whether the dc magnetic bias of the power transformer is caused by stray current of a subway. The method comprises the following steps:

s102: and acquiring the neutral point current of the power transformer in real time.

In one implementation, a hall current sensor may be clamped at the neutral point of the power transformer, thereby collecting the neutral point current of the power transformer in real time. And transmitting the collected neutral point current to a processor in real time. In one embodiment, the processor may be a single chip or a central processing unit. In one embodiment, the neutral point current of the power transformer may be obtained by the processor in real time, and the neutral point current may be subjected to data processing.

S104: dividing the neutral point current into a plurality of continuous time periods according to the same preset interval time, and performing Fourier analysis on data of the neutral point current in each time period to obtain a direct current signal Im, wherein m is a natural number.

In one embodiment, the specific value of the preset interval time can be selected according to actual requirements, and is only in the range of 0.02s-0.5 s. In one embodiment, the preset interval time may be 0.1 s. In one embodiment, the preset interval time may be 0.3 s.

In one embodiment, the processor may be programmed to retrieve the data from t₀Starting from the moment, the neutral point current can be divided into a plurality of continuous time sections by the processor according to the same preset interval time, and each time section (t) is divided into_m～t_m+1) And carrying out Fourier analysis on the data of the neutral point current to obtain a direct current signal Im, wherein m can be a natural number (0, 1, 2, …).

S106: and comparing the direct current signal Im with a first preset current threshold, and determining whether the power transformer generates direct current magnetic biasing or not based on the comparison result.

In one embodiment, the dc current signal Im may be compared with a first preset current threshold value by the processor, that is, the dc current signal in each time period is compared with the first preset current threshold value. In one embodiment, if during the time period t_k～t_k+1If the dc current signal is greater than the first predetermined current threshold, t can be determined_kAnd the power transformer generates the direct current magnetic bias at the moment. If the dc current signal is less than or equal to the first predetermined current threshold during the time period, t may be determined_kAt the moment, the power transformer does not generate the direct current magnetic bias, and the processor can compare the next time period t_k+1～t_k+2The magnitude of the dc current signal and the first predetermined current threshold. Wherein k is a natural number.

In one embodiment, if the dc current signal in each of the time periods is less than or equal to the first preset current threshold, it may be determined that the dc magnetic biasing of the power transformer does not occur. In one embodiment, the first preset current threshold may be set according to actual requirements, such as 18A.

S108: if the fact that the direct current magnetic bias occurs to the power transformer at a first time point is determined, whether the maximum value of the direct current signal Im in a first time period after the first time point is larger than a second preset current threshold value or not and whether the minimum value of the direct current signal Im in the first time period is smaller than a third preset current threshold value or not are judged, and the second preset current threshold value is the same as the third preset current threshold value in absolute value.

In one embodiment, if it is determined that the power transformer is at the first time point (e.g., at t)_kTime) of the dc magnetic biasing, data analysis may be performed on all the dc current signals within a time period T (i.e., the first time period) after the first time point. Specifically, it can be judged at the time period t_k～t_k+T(i.e. during the first time period) whether the maximum value of the dc current signal Im is greater than the second predetermined current threshold value, and during the time period t_k～t_k+TWhether the minimum value of the direct current signal Im is smaller than a third preset current threshold value.

In one embodiment, if the maximum value of the dc current signal Im in the time period is greater than the second preset current threshold value and the minimum value of the dc current signal Im in the first time period is less than the third preset current threshold value, it may be determined that the dc magnetic bias of the power transformer is caused by stray current. At the moment, a direct-current magnetic biasing restraining method can be adopted in a targeted mode, the influence of a direct-current magnetic biasing phenomenon on the operation of the transformer is reduced to the minimum, and therefore the safety and the reliability of the operation of the power transformer are improved.

In one embodiment, the second preset current threshold may be a positive number, and the third preset current threshold may be a negative number, as long as the absolute values of the second preset current threshold and the third preset current threshold are guaranteed to be the same. In one embodiment, the second preset current threshold may be 10A and the third preset current threshold may be-10A. In one embodiment, the specific time of the first time period may be set according to actual requirements, such as 5min or 6 min.

S110: if the maximum value of the direct current signal Im in the first time period is greater than the second preset current threshold value and the minimum value of the direct current signal Im in the first time period is less than the third preset current threshold value, determining that the direct current magnetic bias of the power transformer is caused by stray current.

In one embodiment, after the direct current magnetic bias of the power transformer is determined to be caused by stray current, a direct current magnetic bias suppression method can be adopted in a targeted mode, the influence of a direct current magnetic bias phenomenon on the operation of the transformer is reduced to the minimum, and therefore the operation safety and reliability of the power transformer are improved.

In this embodiment, by the monitoring method, whether the dc magnetic bias occurs to the power transformer can be monitored. After the power transformer is determined to generate the direct current magnetic bias, whether the direct current magnetic bias is caused by stray current can be further determined, so that a direct current magnetic bias suppression method can be pertinently adopted, the influence of a direct current magnetic bias phenomenon on the operation of the transformer is reduced to the minimum, and the operation safety and reliability of the power transformer are further improved.

Referring to fig. 2, in an embodiment, before step S110, the method further includes: if the maximum value of the direct current signal Im in the first time period is less than or equal to the second preset current threshold value, and/or the minimum value of the direct current signal Im in the first time period is greater than or equal to the third preset current threshold value, calculating the frequency of positive and negative occurrence of the direct current signal Im in the first time period, and obtaining the number of positive data and the number of negative data. Calculating the occurrence proportion of the positive data number and the negative data number in the first time period, and determining whether the proportion result is in a preset range so as to determine whether the direct current magnetic bias of the power transformer is caused by the stray current.

In one embodiment, the maximum value of the direct current signal Im when in the first time periodIs less than or equal to the second preset current threshold, and/or the minimum value of the dc current signal Im in the first time period is greater than or equal to the third preset current threshold when the minimum value is greater than or equal to the third preset current threshold, at which time the processor may be used to perform a time period t_k～t_k+TThe frequency of positive and negative occurrence of the data corresponding to the direct current signal (i.e. within the first time period) is calculated to obtain the number of the positive data and the number of the negative data.

In one embodiment, the number of positive data of the dc current signal Im in the first time period may be calculated by the following formula:

wherein N is₁For the positive number of data, X_iFor the ith data in the first time period, i is a natural number (i.e., i is 0, 1, 2, 3, … …, n).

In one embodiment, the number of negative data of the dc current signal Im in the first time period may be calculated by the following formula:

wherein N is₂The number of the negative data is shown.

In one embodiment, after obtaining the positive data number and the negative data number, the processor may divide the positive data number and the negative data number, that is, calculate an appearance ratio of the positive data number and the negative data number in the first time period, so as to obtain the ratio result (K). If the proportional result is within the preset range, it may be determined that the dc magnetic bias of the power transformer is caused by the stray current. If the proportional result is not within the preset range, it may be determined that the dc bias of the power transformer is not caused by the stray current.

In one embodiment, the preset range may be set to 0.4-2.5. That is, the ratio result is only in the range of 0.4-2.5, and it can be determined that the dc bias of the power transformer is caused by the stray current. It can now be determined that the alternation of positive and negative of the neutral point current is significant. Therefore, a direct-current magnetic biasing restraining method can be adopted pertinently, the influence of a direct-current magnetic biasing phenomenon on the operation of the transformer is reduced to the minimum, and the operation safety and reliability of the power transformer are further improved.

In one embodiment, the step of comparing the dc current signal Im with a first preset current threshold and determining whether dc magnetic biasing of the power transformer occurs based on the comparison comprises: and acquiring the first preset current threshold, and comparing the difference value of the direct current signal Im with the first preset current threshold to obtain a difference value comparison result. And if the difference comparison result is larger than zero at the first time point, determining that the direct current magnetic bias occurs to the power transformer at the first time point. And if the difference comparison result is less than or equal to zero, determining that the direct current magnetic biasing does not occur to the power transformer.

In one embodiment, the dc current signal Im may be compared with a first preset current threshold by the processor, and whether the dc magnetic biasing occurs to the power transformer is determined based on the comparison result. If the direct current magnetic biasing occurs, whether the direct current magnetic biasing is caused by the stray current can be further judged through the processor.

In one embodiment, before the step of obtaining the neutral point current of the power transformer in real time, the method further comprises: and acquiring the neutral point current of the power transformer in real time through a Hall current sensor, and outputting the neutral point current. In one embodiment, the hall current sensor may be clamped at a neutral point of the power transformer, so that the neutral point current of the power transformer may be collected in real time. In one embodiment, the sampling frequency of the hall current sensor may be greater than or equal to 2 KHz. In one embodiment, the measurement range of the Hall current sensor can be set to-100A.

In summary, the monitoring method is adopted in the present application, and whether the dc magnetic bias occurs to the power transformer can be monitored. After the power transformer is determined to generate the direct current magnetic bias, whether the direct current magnetic bias is caused by stray current can be further determined, so that a direct current magnetic bias suppression method can be pertinently adopted, the influence of a direct current magnetic bias phenomenon on the operation of the transformer is reduced to the minimum, and the operation safety and reliability of the power transformer are further improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.