CN103018525B - Transformer station's internal short-circuit distribution of current is carried out to the apparatus and method of synchro measure - Google Patents

Abstract

The invention discloses a device and method for synchronously measuring short-circuit current distribution in a substation. The device includes a plurality of oscilloscopes, wherein the external trigger signal of one oscilloscope is used as the trigger source of other oscilloscopes, and the other oscilloscopes are connected through coaxial cables. Connect with this one oscilloscope respectively in parallel mode, realize the synchronous triggering of all multiple oscilloscopes, the described one oscilloscope is connected with the current transformer, measure the total fault current when the short-circuit grounding fault occurs through the current transformer, the described The other oscilloscopes are connected with corresponding current transformers, and the ground wire current and transformer neutral point current are measured through the corresponding current transformers when a short-circuit ground fault occurs. The device is used for synchronous measurement of the short-circuit current distribution when a short-circuit ground fault occurs in a substation. The invention simultaneously discloses a method for synchronously measuring the short-circuit current distribution in the substation.

Description

Device and method for synchronous measurement of short-circuit current distribution in substations

technical field

The invention relates to the field of high-voltage substation measurement, in particular to a device and method for synchronously measuring short-circuit current distribution in a substation.

Background technique

When a short-circuit ground fault occurs in a substation, the total fault current can be divided into the ground current part, the ground wire shunt part and the transformer neutral point return part. The total fault current, ground current, ground wire shunt and transformer neutral point return, the magnitude of these four currents is called the distribution of short-circuit current, referred to as short-circuit current distribution, and as long as the magnitude of three of them is obtained, it is easy to The size of the fourth quantity can be obtained by Kirchhoff's law.

The size of the ground current directly affects the equipment and personal safety in the station. This part of the current will generate ground potential rise, step potential difference and contact potential difference in the substation, causing some safety problems. However, the ground current does not enter the ground through a single path, but flows into the ground through the ground grid. This leads to the fact that this part of the current cannot be directly measured, but needs to be calculated indirectly by measuring the total fault current, the shunt current of the ground wire, and the return current of the transformer neutral point.

Therefore, obtaining the distribution of the fault current in the station is the prerequisite for obtaining the ground current and the basis for investigating the safety characteristics of the station.

At present, the methods for obtaining fault current distribution in substation mainly include:

Based on field artificial grounding test

To obtain the fault current distribution in the substation, an artificial short-circuit grounding test can be carried out to measure the total short-circuit fault current, ground wire current and transformer neutral point current on site, and then calculate the grounding current. The basic idea of this method is: use the artificial grounding device to generate a short-circuit grounding fault in the station.

Use an ammeter or current transformer to measure the short-circuit fault current, transformer neutral point current, and ground wire current, and record them with an oscilloscope.

According to the current measurement results, the short-circuit fault current is used to subtract the transformer neutral point current and the ground wire current to obtain the ground current.

The advantage of the above method is that all the data are obtained from on-site measurement, which is direct and true. However, there are the following disadvantages: there is no uniform time standard among the measured quantities, the triggering time of the oscilloscope is not uniform, and the initial recording time of each waveform is inconsistent. The measurement results obtained in this way can generally only be compared with the amplitude or effective value, and cannot be used in Compare the waveforms on the same time axis; when using the current measured in this way to calculate the value of the ground current, you can only use the effective value or amplitude of each current to add or subtract, resulting in a large error.

Based on the measurement of the shunt impedance of the ground wire and the ground resistance of the substation and the equivalent circuit, in order to obtain the distribution of the fault current in the substation, a shunt circuit model of the short-circuit current can be established, and the shunt impedance of each part can be measured and substituted into the shunt circuit model to obtain The short-circuit current distribution is obtained.

Use the potential drop method recommended in the national standard GB/T 17949.1-2000 "Guidelines for the Measurement of Soil Resistivity, Ground Impedance and Ground Potential of Grounding Systems Part 1: Conventional Measurements" to measure the substation grounding impedance Zg.

Disconnect the ground wire from the ground grid of the substation, and use the current-voltage method to measure the shunt impedance Zw of the ground wire.

Assuming that the short-circuit fault current is I0, the neutral point current of the transformer is IN, the ground current is Iw, and the ground current is Ig, then the equivalent circuit diagram of the current distribution is as follows. If the known short-circuit fault current is I0 and the neutral point of the transformer is If the point current is IN, the ground wire current and the ground current can be calculated from the equivalent circuit diagram.

The advantage of the above method is that it reduces the number of currents that need to be measured on site and reduces the complexity of the test. Moreover, for the same substation, the equivalent circuit is common. If the total short-circuit current value and the neutral point return value are given, the current distribution can be obtained only by using the equivalent circuit, and even the trouble of on-site testing is avoided. However, the above method has the following disadvantages: each grounding point is not connected to the ground grid at the same point, but distributed throughout the ground grid, so for the current distribution, the ground grid is not just a concentrated impedance, the model of this method is equivalent to There is an error; the magnetic field generated by the phase current of the line will generate an induced voltage on the ground wire, which will affect the shunt capacity of the ground wire. The method of equating the ground wire to a concentrated shunt impedance ignores the influence of the phase wire and will generate errors; these models Equivalence will introduce a lot of errors, which will affect the accuracy of the results. Compared with on-site measurement, its disadvantages are obvious.

It can be seen from the above that among the existing methods for obtaining fault current distribution in substations, the field measurement method is slightly better than the method using the equivalent model in terms of result accuracy. However, the existing on-site measurement methods basically ignore the importance of synchronous measurement, and synchronous measurement of current distribution is an important guarantee for the accuracy of measurement results. Especially when it is necessary to further obtain the waveform of the current into the ground, the synchronization of each current waveform is particularly important, because only the results of adding and subtracting the waveforms using the same time starting point are meaningful. In order to measure the accuracy of the results and meet the requirements of further calculation of the current into the ground, a new current distribution measurement method that can ensure the synchronization of the measurement is needed.

Therefore, a technical problem that needs to be urgently solved at present is: how to propose an effective measure to solve the problems existing in the prior art.

Contents of the invention

One of the purposes of the present invention is to provide a device for synchronously measuring the short-circuit current distribution in a substation, which is used for synchronously measuring the short-circuit current distribution when a short-circuit grounding fault occurs in a substation, and has a simple structure, easy operation, and results reliable.

The above object of the present invention is achieved through the following technical solutions: a device for synchronously measuring the short-circuit current distribution in a substation, characterized in that: the device includes a plurality of oscilloscopes, and the external trigger signal of one of the oscilloscopes is used as the trigger signal of other oscilloscopes trigger source, other oscilloscopes are connected to this oscilloscope in parallel through coaxial cables to realize synchronous triggering of all multiple oscilloscopes. For the total fault current when a short-circuit ground fault occurs, the other oscilloscopes described above are connected with current transformers correspondingly, and the ground wire current and transformer neutral point current when a short-circuit ground fault occurs are measured through the corresponding current transformers.

In the present invention, said other oscilloscopes include at least one oscilloscope for measuring the ground wire current when a short-circuit ground fault occurs and at least one oscilloscope for measuring the transformer neutral point current when a short-circuit ground fault occurs.

The second object of the present invention is to provide a method for synchronously measuring short-circuit current distribution in a substation. The method is used for synchronously measuring short-circuit current distribution when a short-circuit grounding fault occurs in a substation, and is easy to operate and reliable in result.

Above-mentioned purpose of the present invention is realized by following technical scheme: the method for synchronously measuring short-circuit current distribution in substation, this method comprises the following steps:

Step S101: Use the external trigger signal of one oscilloscope as the trigger source of other oscilloscopes to realize the synchronous triggering of all multiple oscilloscopes. The one oscilloscope measures the total fault current when a short-circuit ground fault occurs through a current transformer , said other oscilloscopes measure the ground wire current and the neutral point current of the transformer when a short-circuit ground fault occurs through corresponding current transformers, thereby synchronously measuring the short-circuit current distribution in the substation.

In the present invention, the method further includes step S102: using the synchronously measured current waveform to perform waveform addition and subtraction based on Kirchhoff's law to obtain the grounding current when a short-circuit grounding fault occurs.

Compared with the prior art, the device and method for synchronously measuring the short-circuit current distribution in the substation according to the present invention can use the external trigger signal of the oscilloscope to trigger the oscilloscopes measuring different currents at the same time and start recording waveforms, Thereby obtaining synchronous measurement results of fault current distribution accurately, conveniently and reliably.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the connection schematic diagram of the device that the present invention carries out synchronous measurement to short-circuit current distribution in substation;

Fig. 2 is a flow chart of the method for synchronously measuring short-circuit current distribution in a substation according to the present invention.

Explanation of reference signs

1. 1# oscilloscope; 2. 2# oscilloscope; 3. 3# oscilloscope; N, N# oscilloscope;

Detailed ways

As shown in Figure 1, a device for synchronously measuring short-circuit current distribution in a substation, the device includes multiple oscilloscopes 1# oscilloscope 1, 2# oscilloscope 2, 3# oscilloscope 3, ..., N# oscilloscope N, where The external trigger signal of one oscilloscope 1# oscilloscope 1 is used as the trigger source of other oscilloscopes, and the other oscilloscopes 2# oscilloscope 2, 3# oscilloscope 3,..., N# oscilloscope N are respectively connected in parallel with the The one oscilloscope is connected to realize synchronous triggering of all multiple oscilloscopes. The one oscilloscope 1# oscilloscope 1 is connected to a current transformer (not shown in the figure), and the current transformer is used to measure the short-circuit grounding fault. The total fault current, the other oscilloscopes 2# oscilloscope 2, 3# oscilloscope 3, ..., N# oscilloscope N are all connected with current transformers (not shown in the figure), through the corresponding current transformers Measures earth conductor current and transformer neutral point current in the event of a short-circuit earth fault.

Described other oscilloscopes 2# oscilloscope 2, 3# oscilloscope 3, ..., N# oscilloscope N include at least one oscilloscope for measuring the ground wire current when a short-circuit ground fault occurs and for measuring the short-circuit ground fault. The number of oscilloscopes used to measure the ground wire current when a short-circuit ground fault occurs depends on the actual measurement needs, and is used to measure the transformer neutral point current when a short-circuit ground fault occurs The number of oscilloscopes is also determined according to actual measurement needs.

An oscilloscope 1# oscilloscope 1 in the present invention is used for measuring the total fault current when the short-circuit grounding fault occurs, and uses a channel as the short-circuit current measurement channel, and other oscilloscopes then all leave a channel vacant, and start to connect from the second channel Measure the signal. 2# oscilloscope 2, 3# oscilloscope 3, ..., N# oscilloscope N are used to measure the ground wire current and transformer neutral point current when a short-circuit ground fault occurs, among which, it is used to measure the ground wire when a short-circuit ground fault occurs There can be one or more oscilloscopes for the current, and one or more oscilloscopes for measuring the neutral point current of the transformer when a short-circuit ground fault occurs.

Set the trigger mode of 1# oscilloscope 1 to edge trigger, the trigger source is one channel, single trigger. Use coaxial cables to connect the external trigger signal of 1# oscilloscope 1 to other 2# oscilloscope 2, 3# oscilloscope 3, ..., a channel of N# oscilloscope N, other 2# oscilloscope 2, 3# oscilloscope 3, ... 、N# The trigger mode of oscilloscope N is set to edge trigger, the trigger source is one channel, single trigger.

After a short-circuit fault occurs, 1# oscilloscope 1 is triggered and starts to record waveforms, and at the same time sends an external trigger signal to a channel of other oscilloscopes 2# oscilloscope 2, 3# oscilloscope 3, ..., N# oscilloscope N to trigger other oscilloscopes, and start recording the waveform.

Considering that the propagation speed of the electrical signal is close to the speed of light, and the main frequency of the short-circuit fault current is the power frequency, the propagation time of the external trigger signal on the connecting cable is negligible relative to each current waveform. In this way, the oscilloscopes can be considered to be triggered at the same time, and the obtained current waveforms have the same phase, which can be compared and analyzed on the same time axis, and the waveform of the ground current can be obtained through waveform addition and subtraction.

As shown in Figure 2, a method for synchronously measuring short-circuit current distribution in a substation, the method includes the following steps:

Step S101: Use the external trigger signal of one oscilloscope as the trigger source of other oscilloscopes to realize the synchronous triggering of all multiple oscilloscopes. The one oscilloscope measures the total fault current when a short-circuit ground fault occurs through a current transformer , said other oscilloscopes measure the ground wire current and transformer neutral point current when a short-circuit ground fault occurs through corresponding current transformers, thereby synchronously measuring the short-circuit current distribution in the substation;

Step S102: Using the synchronously measured current waveforms, the waveforms are added and subtracted based on Kirchhoff's law to obtain the grounding current when a short-circuit ground fault occurs.

The method utilizes an external trigger port of an oscilloscope to realize the synchronous triggering of other oscilloscopes measuring various currents, so that the obtained current waveforms have the same phase relationship.

The device and method described in the present invention are suitable for measuring the short-circuit current distribution after a short-circuit grounding fault occurs in substations of various voltage levels, and can realize synchronous measurement of each current amount, which is beyond the reach of general measuring devices and methods of. Moreover, the initial recording points of the current waveforms obtained through synchronous measurement are consistent, and can be compared on the same time axis, and the waveform of the current entering the ground can also be obtained through waveform addition and subtraction, which is also impossible for other measurement methods of. At the same time, the on-site measurement ensures the accuracy of the results, and the test wiring is simple. The measurement method is accurate, convenient and reliable.

The above-mentioned embodiments of the present invention do not limit the protection scope of the present invention. Under the premise of the above-mentioned basic technical ideas, other modifications, replacements or changes made to the above-mentioned structure of the present invention in various forms shall fall within the protection scope of the present invention.

Claims (2)

1. The device for synchronously measuring the short-circuit current distribution in a substation is characterized in that the device includes multiple oscilloscopes, and the external trigger signal of one oscilloscope is used as the trigger source of other oscilloscopes, and the other oscilloscopes are connected through coaxial cables. Connect with this one oscilloscope respectively in parallel mode, realize the synchronous triggering of all multiple oscilloscopes, the described one oscilloscope is connected with the current transformer, measure the total fault current when the short-circuit grounding fault occurs through the current transformer, the described The other oscilloscopes are correspondingly connected with current transformers, and the ground wire current and the neutral point current of the transformer are measured through the corresponding current transformers when a short-circuit ground fault occurs; At least one oscilloscope for earth current at earth fault and at least one oscilloscope for measuring transformer neutral current at short circuit earth fault. 2. A method for synchronously measuring short-circuit current distribution in a substation, the method comprising the steps of: Step S101: Use the external trigger signal of one oscilloscope as the trigger source of other oscilloscopes to realize the synchronous triggering of all multiple oscilloscopes. The one oscilloscope measures the total fault current when a short-circuit ground fault occurs through a current transformer , said other oscilloscopes measure the ground wire current and transformer neutral point current when a short-circuit ground fault occurs through corresponding current transformers, thereby synchronously measuring the short-circuit current distribution in the substation; Step S102: Using the synchronously measured current waveforms, the waveforms are added and subtracted based on Kirchhoff's law to obtain the grounding current when a short-circuit ground fault occurs.