Transient first half-wave method based on sampling data adjustment and fault positioning system

Abstract

The invention relates to a transient first half-wave method based on sampling data adjustment and a fault positioning system, and belongs to the technical field of power distribution networks of power systems. The transient first half-wave method comprises the following steps: 1) when transient first half-wave discrimination is carried out, carrying out zero-voltage clipping discrimination on zero-sequence voltage data sampled by a power distribution terminal; 2) after judging that zero-voltage topping occurs, taking a zero-sequence voltage value corresponding to a mid-value moment between a zero-sequence voltage sudden change starting point moment and a zero-sequence voltage first zero crossing point moment as a zero-voltage peak value; (3) finding a zero-current peak value in a time period from the transient zero-current starting time to the transient zero-current ending time by taking the period that the zero-voltage peak value moment forwards moves by one third of the transient capacitive current as the transient zero-current ending time and taking the period that the zero-voltage peak value moment forwards moves by one third of the transient capacitive current as the transient zero-current starting time; and 4) performing fault position judgment according to the zero-voltage peak value and the zero-current peak value.

Description

Technical Field

[0001] The invention relates to a transient first half-wave method and a fault location system based on sampling data adjustment, belonging to the technical field of power system distribution network. Background Art

[0002] The transient first half-wave method in the power system is a method used for power system fault diagnosis and location. Generally, the distribution terminal will calculate the zero-voltage sampling value and the zero-current sampling value in real time. After determining that the zero-voltage mutation has started, the transient first half-wave method can be used for fault analysis. The method for determining the transient first half-wave is as follows: first find the zero-voltage peak value within the first half-wave time and record its polarity, then use the zero-voltage peak moment as the transient zero-current end moment, push forward one cycle of the transient zero-current moment to find the zero-current peak value within the first half-wave and record its polarity, and use this as the basis for judgment to diagnose and locate the power system fault. If the polarities of the zero-voltage peak value and the zero-current peak value are opposite, it is determined that the transient polarity condition of the fault within the first half-wave is met.

[0003] The Chinese invention patent with the authorization announcement number CN 117347787B discloses a method and system for identifying and analyzing the type of single-phase grounding fault in a distribution network. In step S3.2 of the method, the fault direction is judged based on the first half-wave correlation of the zero-sequence voltage and zero-sequence current of the three-phase circuit (i.e., the transient first half-wave polarity method), and the judgment principle is: the zero-sequence voltage and the zero-sequence current first half-wave present a negative correlation for the fault line / area fault, and the zero-sequence voltage and the zero-sequence current first half-wave present a positive correlation for the non-fault line / area fault. At present, this judgment method has defects: for grounding faults under the arc suppression coil grounding system, the zero-sequence voltage value is large when the fault occurs, which may cause the saturation of the zero-voltage PT (Potential Transformer) of the distribution terminal, thereby clipping the zero-voltage data used for calculation, resulting in the inability to correctly find the zero-voltage peak moment in the first half-wave, and also affecting the search for the zero-current peak in the first half-wave. Incorrect search for the zero-voltage peak and zero-current peak will directly affect the polarity judgment of the zero-voltage peak and the zero-current peak, that is, affect the judgment of the correlation between the zero-sequence voltage and the zero-sequence current in the first half-wave, resulting in the inability to correctly judge the refusal to operate of grounding faults within the area and the inability to correctly judge the false operation of grounding faults outside the area. Summary of the invention

[0004] The purpose of the present invention is to provide a transient first half-wave method and a fault location system based on sampling data adjustment, so as to solve the problem of inaccurate polarity judgment in the transient first half-wave method caused by excessive zero-sequence voltage causing zero-voltage data clipping when a grounding fault occurs in an arc suppression coil grounding system.

[0005] To achieve the above object, the solution of the present invention includes:

[0006] A transient first half-wave method based on sampled data adjustment of the present invention comprises the following steps:

[0007] 1) When determining the transient first half-wave, the zero-sequence voltage data sampled at the distribution terminal is subjected to zero-voltage clipping determination;

[0008] 2) After the occurrence of zero voltage clipping is determined, the zero-sequence voltage value corresponding to the median time of the zero-sequence voltage mutation starting point and the zero-sequence voltage first zero-crossing point is taken as the zero-voltage peak value;

[0009] 3) The zero-voltage peak moment is shifted forward by one-third of the transient capacitor current cycle as the transient zero-current end moment, and the zero-voltage peak moment is shifted forward by one cycle of the transient capacitor current as the transient zero-current start moment. The zero-current peak value is found in the period from the transient zero-current start moment to the transient zero-current end moment;

[0010] 4) Determine the fault location based on the zero-voltage peak value and the zero-current peak value.

[0011] Furthermore, when determining zero voltage clipping in step 1), if the zero-sequence voltage sampled by the distribution terminal is greater than a preset zero voltage clipping threshold value, it is considered that zero voltage clipping has occurred.

[0012] Furthermore, the zero voltage clipping threshold value is slightly smaller than the voltage rating in the specification of the voltage transformer used in the power distribution terminal.

[0013] Furthermore, in step 4), when the fault location is determined, the polarities of the zero-voltage peak value and the zero-current peak value are compared. If the polarities are opposite, it is determined to be an in-zone fault; if the polarities are the same, it is determined to be an out-of-zone fault.

[0014] Furthermore, if the zero-sequence voltage is not greater than the zero-voltage clipping threshold value, it is considered that zero-voltage clipping does not occur.

[0015] Furthermore, after determining that no zero-voltage clipping occurs, the zero-voltage peak value within the first half-wave time is found, and the zero-voltage peak moment is used as the transient zero-current end moment, and a transient capacitor current cycle is pushed forward to find the zero-current peak value within the first half-wave.

[0016] A fault location system of the present invention includes a processor, and the processor is used to execute instructions to implement the following steps:

[0017] 1) When determining the transient first half-wave, the zero-sequence voltage data sampled at the distribution terminal is subjected to zero-voltage clipping determination;

[0018] 2) After the zero voltage clipping is identified, the zero-sequence voltage value corresponding to the median time of the zero-sequence voltage mutation starting point and the zero-sequence voltage first zero-crossing time is taken as the zero voltage peak value;

[0019] 3) The zero-voltage peak moment is shifted forward by one-third of the transient capacitor current cycle as the transient zero-current end moment, and the zero-voltage peak moment is shifted forward by one cycle of the transient capacitor current as the transient zero-current start moment. The zero-current peak value is found in the period from the transient zero-current start moment to the transient zero-current end moment;

[0020] 4) Determine the fault location based on the zero-voltage peak value and the zero-current peak value.

[0021] Furthermore, when performing the zero voltage clipping determination in step 1), if the zero-sequence voltage sampled by the distribution terminal is greater than a preset zero voltage clipping threshold value, it is considered that zero voltage clipping has occurred.

[0022] Furthermore, the zero voltage clipping threshold value is slightly smaller than the voltage rating in the specification of the voltage transformer used in the power distribution terminal.

[0023] Furthermore, in step 4), when the fault location is determined, the polarities of the zero-voltage peak value and the zero-current peak value are compared. If the polarities are opposite, it is determined to be an in-zone fault; if the polarities are the same, it is determined to be an out-of-zone fault.

[0024] The beneficial effects of the present invention are:

[0025] The present invention is a pioneering invention. When a fault occurs in the power system, in order to make the fault location more accurate when using the transient first half-wave method, the present invention judges whether the collected zero-voltage data actually undergoes zero-voltage clipping when the fault occurs. If zero-voltage clipping occurs, the search criteria for the zero-voltage peak value and the zero-current peak value are adjusted: the zero-voltage value at the median of the zero-voltage mutation start point and the first zero-voltage zero-crossing point is used as the zero-voltage peak value; the zero-voltage peak value is shifted forward by one third of the cycle of the transient capacitor current as the transient zero-current end time, the zero-voltage peak value is shifted forward by one cycle of the transient capacitor current as the transient zero-current start time, and the zero-current peak value is found in the period from the transient zero-current start time to the transient zero-current end time; the polarities of the zero-voltage peak value and the zero-current peak value are compared, and if the polarities are opposite, it is judged as an in-zone fault, and if the polarities are the same, it is judged as an out-of-zone fault. The present invention solves the problem of inaccurate polarity judgment in the transient first half-wave method caused by clipping of zero-voltage data due to excessive zero-sequence voltage when a grounding fault occurs in an arc suppression coil grounding system, thereby avoiding the situation where the grounding fault within the zone cannot be correctly judged as refusal to operate and the grounding fault outside the zone cannot be correctly judged as false operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall process of the transient first half-wave method based on sampled data adjustment;

[0027] Figure 2 It is a schematic diagram of the steps for implementing the transient first half-wave method based on sampled data adjustment;

[0028] Figure 3 It is a waveform diagram of the zero-sequence voltage data without and with clipping when a distribution network fails. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] The concept of the present invention is that Figure 1 As shown in the figure, when a distribution network fault occurs, if it is determined that zero-voltage clipping has occurred, the polarity of the zero-voltage peak value and the zero-current peak value of the first half-wave is compared after adjusting the criteria for finding the zero-voltage peak value and the zero-current peak value: the zero-voltage value at the median of the zero-voltage (zero-sequence voltage) mutation start time and the zero-voltage first zero-crossing time is taken as the zero-voltage peak value; the transient zero-current end time is the zero-voltage peak time, which is one-third of the transient capacitor current cycle shifted forward; the transient zero-current start time is the zero-voltage peak time, which is one cycle of the transient capacitor current shifted forward; the zero-current peak value is found from the transient zero-current start time to the transient zero-current end time; the polarity of the zero-voltage peak value and the zero-current peak value are compared. If the polarity is opposite, it is determined that the transient polarity condition of the fault in the first half-wave is met, and it is determined to be an in-zone grounding fault. If the polarity is the same, it is determined to be an out-of-zone grounding fault.

[0031] Method Example:

[0032] like Figure 2 A transient first half-wave method based on sampled data adjustment is shown, and the specific implementation steps are as follows:

[0033] S1, set the zero-voltage clipping threshold value U0MAXsill. When setting, mainly refer to the instruction manual of the voltage transformer and set the zero-voltage clipping threshold value U0MAXsill to a value slightly smaller than the rated value in the instruction manual.

[0034] S2, real-time sampling and calculation of zero-sequence voltage and zero-sequence current are performed through the channel that collects the corresponding data of the distribution terminal.

[0035] S3.1, after determining that the real-time sampling data has a zero-voltage mutation, the zero-voltage data value obtained in step S2 is subjected to zero-voltage clipping judgment. If the zero-sequence voltage is greater than the zero-voltage clipping threshold value U0MAXsill set in step S1, Figure 3 The waveform shown by the middle line ② indicates that zero-pressure top clipping has occurred, and step S4 is performed;

[0036] S3.2, if the zero-sequence voltage is not greater than the zero-voltage clipping threshold value U0MAXsill, such as Figure 3The waveform shown by the middle line ① means that there is no zero-voltage clipping. The zero-voltage peak value in the first half-wave time is found and its polarity is recorded. Then, the moment of the zero-voltage peak value is taken as the end moment of the transient zero current. The zero-current peak value in the first half-wave is found and its polarity is recorded one cycle of the transient capacitor current, and then step S8 is performed.

[0037] S4, after the zero-pressure clipping is identified, the criterion for finding the zero-pressure peak value of the first half wave needs to be adjusted, such as Figure 3 As shown, the median time between the zero-pressure mutation starting point and the zero-pressure first zero-crossing time is found, and the zero-pressure value corresponding to the median time is taken as the zero-pressure peak value.

[0038] Since the zero-voltage peak moment found according to step S4 generally has an error with the actual zero-voltage peak moment (lags behind the actual zero-voltage peak moment), and there is a difference between the transient zero-current end moment when zero-voltage clipping occurs and the transient zero-current end moment when no data clipping occurs, the zero-voltage peak moment found in step S4 cannot be directly used as the transient zero-current end moment and pushed forward one transient capacitor current cycle to find the zero-current peak. Therefore, the criterion for finding the zero-current peak needs to be adjusted according to the following steps S5 to S7.

[0039] S5, the moment of zero voltage peak is shifted forward by one third of the transient capacitor current cycle as the transient zero current end moment.

[0040] S6, the moment of zero voltage peak is pushed forward by one cycle of transient capacitor current as the moment of transient zero current start.

[0041] For example: when a metallic grounding fault occurs in the arc suppression coil grounding system and the oscillation frequency of the transient capacitor current is 300Hz, that is, the transient capacitor current period is 3ms, if zero-voltage data clipping does not occur, the zero-voltage peak value within the first half-wave time can be directly found, and then the zero-current peak value within the first half-wave can be found by pushing forward one period of the transient capacitor current, that is, 3ms; if zero-voltage data clipping occurs, the zero-voltage peak value of the first half-wave is adjusted to find the criterion, that is, first find the median time of the zero-voltage mutation starting point and the time when the zero voltage first crosses zero, and the zero-voltage value corresponding to the median time is used as the zero-voltage peak value, and then the zero-voltage peak time is moved forward by one-third of the period of the transient capacitor current, that is, 1ms, as the end time of the transient zero current, and the zero-voltage peak time is pushed forward by one period of the transient capacitor current, that is, 3ms, as the start time of the transient zero current.

[0042] When a small resistance grounding fault occurs in the arc suppression coil grounding system and the oscillation frequency of the transient capacitor current is 200Hz, that is, the transient capacitor current period is 5ms, if zero-voltage data clipping does not occur, the zero-voltage peak value within the first half-wave time can be directly found, and then the zero-current peak value within the first half-wave can be found by pushing forward one period of the transient capacitor current, that is, 5ms; if zero-voltage data clipping occurs, the zero-voltage peak value of the first half-wave is adjusted to find the criterion, that is, first find the median time of the zero-voltage mutation starting point and the first zero-crossing time, and the zero-voltage value corresponding to the median time is used as the zero-voltage peak value, and then the zero-voltage peak time is moved forward by one-third of the transient capacitor current period, that is, 1.7ms, as the end time of the transient zero current, and the zero-voltage peak time is pushed forward by one period of the transient capacitor current, that is, 5ms, as the start time of the transient zero current.

[0043] S7, finding the zero current peak value within the period from the moment when the transient zero current starts to the moment when the transient zero current ends.

[0044] S8, compare the polarities of the zero voltage peak and the zero current peak. If the polarities are opposite, it is determined that the transient polarity condition of the fault within the first half wave is met and it is determined to be an in-zone fault; if the polarities are the same, it is determined to be an out-of-zone fault.

[0045] System Example:

[0046] This embodiment provides a fault location system based on sampled data adjustment, including a processor for executing instructions for implementing a transient first half-wave method based on sampled data adjustment. The transient first half-wave method based on sampled data adjustment has been introduced clearly enough in the method embodiment and will not be repeated here.

Claims

1. A transient first half-wave method based on sampled data adjustment, characterized in that: The steps include: 1) When determining the transient first half-wave, the zero-sequence voltage data sampled at the distribution terminal is subjected to zero-voltage clipping determination; 2) After the occurrence of zero voltage clipping is determined, the zero-sequence voltage value corresponding to the median time of the zero-sequence voltage mutation starting point and the zero-sequence voltage first zero-crossing point is taken as the zero-voltage peak value; 3) The zero-voltage peak moment is shifted forward by one-third of the transient capacitor current cycle as the transient zero-current end moment, and the zero-voltage peak moment is shifted forward by one cycle of the transient capacitor current as the transient zero-current start moment. The zero-current peak value is found in the period from the transient zero-current start moment to the transient zero-current end moment; 4) Determine the fault location based on the zero-voltage peak value and the zero-current peak value.

2. The transient first half-wave method based on sampled data adjustment according to claim 1, characterized in that: When performing the zero voltage clipping determination in step 1), if the zero-sequence voltage sampled by the power distribution terminal is greater than a preset zero voltage clipping threshold value, it is considered that zero voltage clipping has occurred.

3. The transient first half-wave method based on sampled data adjustment according to claim 2, characterized in that: The zero-voltage clipping threshold value is slightly smaller than the voltage rating in the specification of the voltage transformer used in the power distribution terminal.

4. The transient first half-wave method based on sampled data adjustment according to claim 1, characterized in that: In the step 4), when the fault location is determined, the polarities of the zero-voltage peak value and the zero-current peak value are compared. If the polarities are opposite, it is determined to be an in-zone fault; if the polarities are the same, it is determined to be an out-of-zone fault.

5. The transient first half-wave method based on sampled data adjustment according to claim 2, characterized in that: If the zero-sequence voltage is not greater than the zero-voltage clipping threshold value, it is considered that zero-voltage clipping does not occur.

6. The transient first half-wave method based on sampled data adjustment according to claim 5, characterized in that: After determining that the zero-voltage clipping does not occur, the zero-voltage peak value within the first half-wave time is found, and the zero-voltage peak moment is used as the transient zero-current end moment, and a transient capacitor current cycle is pushed forward to find the zero-current peak value within the first half-wave.

7. A fault location system, comprising a processor, characterized in that: The processor is used to execute instructions to implement the following steps: 1) When determining the transient first half-wave, the zero-sequence voltage data sampled at the distribution terminal is subjected to zero-voltage clipping determination; 2) After the zero voltage clipping is identified, the zero-sequence voltage value corresponding to the median time of the zero-sequence voltage mutation starting point and the zero-sequence voltage first zero-crossing time is taken as the zero voltage peak value; 3) The zero-voltage peak moment is shifted forward by one-third of the transient capacitor current cycle as the transient zero-current end moment, and the zero-voltage peak moment is shifted forward by one cycle of the transient capacitor current as the transient zero-current start moment. The zero-current peak value is found in the period from the transient zero-current start moment to the transient zero-current end moment; 4) Determine the fault location based on the zero-voltage peak value and the zero-current peak value.

8. The fault location system according to claim 7, characterized in that: When performing the zero voltage clipping determination in step 1), if the zero-sequence voltage sampled by the power distribution terminal is greater than a preset zero voltage clipping threshold value, it is considered that zero voltage clipping has occurred.

9. The fault location system according to claim 8, characterized in that: The zero-voltage clipping threshold value is slightly smaller than the voltage rating in the specification of the voltage transformer used in the power distribution terminal.

10. The fault location system according to claim 7, characterized in that: In the step 4), when the fault location is determined, the polarities of the zero-voltage peak value and the zero-current peak value are compared. If the polarities are opposite, it is determined to be an in-zone fault; if the polarities are the same, it is determined to be an out-of-zone fault.

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