Flexible grounding system high-resistance grounding fault line selection method based on zero sequence voltage amplitude ratio

Abstract

The invention discloses a flexible grounding system high-resistance grounding fault line selection method based on a zero-sequence voltage amplitude ratio, and the method comprises the steps: 1), sensing a fault in a resonant grounding state, and recording the zero-sequence voltage amplitude of a neutral point and the zero-sequence current amplitude of each outgoing line after the fault occurs; 2) after short time delay, inputting a parallel small resistor, and recording a neutral point zero-sequence voltage amplitude and a zero-sequence current amplitude of each outgoing line; 3) calculating the ratio of the neutral point zero-sequence voltage to the neutral point zero-sequence voltage in the arc suppression coil compensation stage after the parallel small resistor is input, and calculating the ratio of the zero-sequence current of each line in the small resistor input stage to the zero-sequence current of each line in the arc suppression coil compensation stage; 4) if the zero-sequence current amplitude ratio of a certain line is greater than 4.5 times of the neutral point zero-sequence voltage amplitude ratio, judging that the line is a fault line, and if the zero-sequence current amplitude ratio of all outgoing lines is less than 4.5 times of the neutral point zero-sequence voltage amplitude ratio, judging that the line is a bus fault; the invention provides a flexible grounding system high-resistance grounding fault line selection method based on a zero-sequence voltage amplitude ratio in order to solve the problem that when an existing flexible grounding system faces a high-resistance grounding fault, a fault line cannot be distinguished. The method has the advantages that the method is not influenced by the reverse connection of the mutual inductor and the compensation state of the arc suppression coil, the bus fault can be distinguished, and the high-resistance and low-resistance grounding faults can be distinguished.

Description

Technical Field

[0001] The invention relates to the field of power system fault protection, and in particular to a high-resistance grounding fault line selection method for a flexible grounding system based on a zero-sequence voltage amplitude ratio. Background Art

[0003] Flexible grounding methods often use zero-sequence overcurrent protection under low-resistance grounding methods to form single-phase grounding protection, but the protection action threshold is relatively high, and the ability to withstand transition resistance does not exceed 300Ω. In reality, there are grounding faults in conductors through sand, cement, etc., and the transition resistance can reach thousands of ohms. The current of the fault line is far lower than the protection start threshold, resulting in protection refusal to operate. Although the probability of a single-phase high-resistance grounding fault is small, it is difficult to detect it in a timely and accurate manner due to its unclear fault characteristics, which can easily lead to more serious phase-to-phase faults, causing inestimable losses to equipment and personnel safety. Therefore, how to accurately and quickly identify faulty lines under flexible grounding methods is an urgent problem that needs to be solved. Summary of the invention

[0004] The technical problem to be solved by the present invention is the long-standing difficulty in line selection in a flexible grounding system. To this end, the present invention provides a method for selecting a high-resistance grounding fault line in a flexible grounding system based on a zero-sequence voltage amplitude ratio, comprising: Step 1: Sense the fault in the resonant grounding state, and record the neutral point zero-sequence voltage amplitude and each outgoing line zero-sequence current amplitude after the fault occurs; Step 2: After a short delay, connect a small parallel resistor and record the amplitude of the neutral point zero-sequence voltage and the amplitude of the zero-sequence current of each outgoing line; Step 3: Calculate the ratio of the neutral point zero-sequence voltage after the small parallel resistor is put into operation to the neutral point zero-sequence voltage in the arc extinguishing coil compensation stage, and calculate the ratio of the zero-sequence current of each line in the small resistor input stage and the arc extinguishing coil compensation stage; Step 4: If the ratio of the zero-sequence current amplitude of a line is greater than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a faulty line; if the ratio of the zero-sequence current amplitude of all outgoing lines is less than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a busbar fault.

[0005] Furthermore, the method for recording the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line after the fault occurs in the resonant grounding state in step 1 is: In the arc suppression coil compensation stage, the sampled data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0.

[0006] Furthermore, in step 2, a small parallel resistor is put into operation after a short delay, and the method for recording the amplitude of the neutral point zero-sequence voltage and the amplitude of the zero-sequence current of each outgoing line is as follows: In the stage of small resistance input, the sampling data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0; Taking into account the accuracy of the zero-sequence voltage transformer, the neutral point zero-sequence voltage is indirectly obtained by using the current flowing through the small resistor during the small resistor input stage.

[0007] Furthermore, in step 3, the ratio of the neutral point zero-sequence voltage after the parallel small resistor is put into operation to the neutral point zero-sequence voltage in the arc extinguishing coil compensation stage is calculated, and the method for calculating the zero-sequence current ratio of each line in the small resistor input stage and the arc extinguishing coil compensation stage is: If a line satisfies If the fault occurs, it is judged as a faulty line, otherwise it is judged as a busbar fault; in , After the small resistor is put into any circuit j Steady-state zero-sequence current amplitude, arc suppression coil compensation stage line j Steady-state zero-sequence current amplitude, , They are respectively the steady-state zero-sequence voltage amplitude of the neutral point after the small resistor is put into operation and the steady-state zero-sequence voltage amplitude during the arc suppression coil compensation stage.

[0008] Further, in step 4, the method for determining that a line whose zero-sequence current amplitude ratio is greater than 4.5 times the neutral point zero-sequence voltage amplitude ratio is a fault line is: If the zero-sequence current amplitude of a line is recorded as 0A before and after the small resistor is put into operation, its zero-sequence current amplitude ratio is recorded as 0, and the ratio of the neutral point zero-sequence voltage amplitude is less than 4.5 times, and it is determined that the line is not faulty; If the denominator of the expression of the zero-sequence current amplitude ratio of a line is 0 and the numerator is not 0, the result is recorded as infinity. If the ratio of the neutral point zero-sequence voltage amplitude is greater than 4.5 times, it is determined to be a faulty line.

[0009] The invention discloses a method for selecting a high-resistance grounding fault line in a flexible grounding system based on a zero-sequence voltage amplitude ratio. After a fault occurs, the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line are recorded in the arc suppression coil compensation stage, the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line are recorded in the small resistor input stage, the neutral point zero-sequence voltage ratio and the neutral point zero-sequence voltage ratio in the arc suppression coil compensation stage are calculated after the parallel small resistor is put into use, and the zero-sequence current ratio and the zero-sequence voltage ratio of each outgoing line before and after the small resistor is put into use are compared. If the zero-sequence current amplitude ratio of a certain line is greater than 4.5 times the neutral point zero-sequence voltage amplitude ratio, it is determined to be a fault line, and if the zero-sequence current amplitude ratio of all outgoing lines is less than 4.5 times the neutral point zero-sequence voltage amplitude ratio, it is determined to be a busbar fault. The invention has the advantages of not being affected by the reverse connection of the mutual inductor, not being affected by the arc suppression coil compensation state, being able to distinguish busbar faults, and being able to distinguish high-resistance and low-resistance grounding faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Operation flow chart of the method for selecting high-resistance grounding fault line in flexible grounding system based on zero-sequence voltage amplitude ratio Figure 2 Simulation topology diagram Figure 3 The zero-sequence current of feeder L1, feeder L2, and feeder L5 when the transition resistance is 5000Ω, and the enlarged diagram of the zero-sequence current of each line 2.5s after the small resistance is put into use is also given Figure 4 It is the neutral point zero-sequence voltage waveform when the transition resistance is 5000Ω, the neutral point zero-sequence voltage amplified waveform at 2.5s, and the current waveform flowing through the small resistance at 2.5s. DETAILED DESCRIPTION

[0011] In order to better understand the present invention, the contents of the present invention are further described below in conjunction with the accompanying drawings and simulation cases.

[0012] Step 1: Sense the fault in the resonant grounding state, and record the neutral point zero-sequence voltage amplitude and each outgoing line zero-sequence current amplitude after the fault occurs; Step 2: After a short delay, connect a small parallel resistor and record the amplitude of the neutral point zero-sequence voltage and the amplitude of the zero-sequence current of each outgoing line; Step 3: Calculate the ratio of the neutral point zero-sequence voltage after the small parallel resistor is put into operation to the neutral point zero-sequence voltage in the arc extinguishing coil compensation stage, and calculate the ratio of the zero-sequence current of each line in the small resistor input stage and the arc extinguishing coil compensation stage; Step 4: If the ratio of the zero-sequence current amplitude of a line is greater than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a faulty line; if the ratio of the zero-sequence current amplitude of all outgoing lines is less than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a busbar fault.

[0013] Furthermore, the method for recording the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line after the fault occurs in the resonant grounding state in step 1 is: In the arc suppression coil compensation stage, the sampled data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0.

[0014] Furthermore, in step 2, a small parallel resistor is put into operation after a short delay, and the method for recording the amplitude of the neutral point zero-sequence voltage and the amplitude of the zero-sequence current of each outgoing line is as follows: In the stage of small resistance input, the sampling data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0; Taking into account the accuracy of the zero-sequence voltage transformer, the neutral point zero-sequence voltage is indirectly obtained by using the current flowing through the small resistor during the small resistor input stage.

[0015] Furthermore, in step 3, the ratio of the neutral point zero-sequence voltage after the parallel small resistor is put into operation to the neutral point zero-sequence voltage in the arc extinguishing coil compensation stage is calculated, and the method for calculating the zero-sequence current ratio of each line in the small resistor input stage and the arc extinguishing coil compensation stage is: If a line satisfies It is judged as a faulty line, otherwise it is judged as a busbar fault; in , After the small resistor is put into any circuit j Steady-state zero-sequence current amplitude, arc suppression coil compensation stage line j Steady-state zero-sequence current amplitude, , They are respectively the steady-state zero-sequence voltage amplitude of the neutral point after the small resistor is put into operation and the steady-state zero-sequence voltage amplitude during the arc suppression coil compensation stage.

[0016] Further, in step 4, the method for determining that a line whose zero-sequence current amplitude ratio is greater than 4.5 times the neutral point zero-sequence voltage amplitude ratio is a fault line is: If the zero-sequence current amplitude of a line is recorded as 0A before and after the small resistor is put into operation, its zero-sequence current amplitude ratio is recorded as 0, and the ratio of the neutral point zero-sequence voltage amplitude is less than 4.5 times, and it is determined that the line is not faulty; If the denominator of the expression of the zero-sequence current amplitude ratio of a line is 0 and the numerator is not 0, the result is recorded as infinity. If the ratio of the neutral point zero-sequence voltage amplitude is greater than 4.5 times, it is determined to be a faulty line.

[0017] Simulation Verification PSCAD / EMTDC was used to build a simulation model to verify the effectiveness of this method. Figure 2 As shown, feeder 1, feeder 2, and feeder 5 are cable lines with lengths of 6km, 5km, and 9km respectively, feeder 3 is an overhead line and cable hybrid line with lengths of 9km and 8km respectively, and feeder 4 is an overhead line and cable hybrid line with lengths of 6km and 7km respectively, and the arc suppression coil detuning degree is -8%.

[0018] <![CDATA[ R f / Oh]]> <![CDATA[|u'0 / u0|]]> <![CDATA[|i' 01 / i 01 |]]> <![CDATA[|i' 02 / i 02 |]]> <![CDATA[|i' 03 / i 03 |]]> <![CDATA[|i' 04 / i 04 |]]> <![CDATA[|i' 05 / i 05 |]]> Line selection results 0 0.83 0.87 29.59 0.87 0.87 0.87 L2 100 0.10 0.10 4.90 0.10 0.10 0.10 L2 1000 0.01 0.01 0.59 0.009 0.01 0.01 L2 3000 0.006 0 0.29 0 0 0 L2 5000 0.005 0 0.25 0 0 0 L2 10000 0.004 0 0.21 0 0 0 L2 13000 0.004 0 0.20 0 0 0 L2 From the data in Table 1, it can be found that the zero-sequence current amplitude ratio of the fault line is much larger than the zero-sequence voltage amplitude ratio of 4.5 times, which is obviously different from the non-fault line.

[0019] <![CDATA[ R f / Oh]]> <![CDATA[|u'0 / u0|]]> <![CDATA[|i' 01 / i 01 |]]> <![CDATA[|i' 02 / i 02 |]]> <![CDATA[|i' 03 / i 03 |]]> <![CDATA[|i' 04 / i 04 |]]> <![CDATA[|i' 05 / i 05 |]]> Is the busbar faulty? 0 0.93 0.93 0.92 0.93 0.93 0.93 yes 100 0.10 0.10 0.10 0.10 0.10 0.10 yes 1000 0.01 0.01 0.01 0.01 0.01 0.01 yes 3000 0.006 0 0 0 0 0 yes 7000 0.004 0 0 0 0 0 yes 13000 0.004 0 0 0 0 0 yes It can be seen from the data in Table 2 that when a busbar fault occurs, the ratio of the zero-sequence current amplitudes of the outgoing lines is much smaller than the ratio of the zero-sequence voltage amplitudes which is 4.5 times. Therefore, the present invention can distinguish busbar faults well.

[0020] Figure 3 The zero-sequence current of feeder L1, feeder L2, and feeder L5 when the transition resistance is 5000Ω is shown. At the same time, the zero-sequence current enlargement diagram of each line 2.5s after the small resistance is put into use is given. Figure 4 It is the neutral point zero-sequence voltage waveform when the transition resistance is 5000Ω, the neutral point zero-sequence voltage amplified waveform at 2.5s, and the current waveform flowing through the small resistance at 2.5s.

[0021] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. The present invention discloses a high-resistance grounding fault line selection method for a flexible grounding system based on zero-sequence voltage amplitude ratio, comprising: 1) Sense faults in the resonant grounding state, and record the neutral point zero-sequence voltage amplitude and each outgoing line zero-sequence current amplitude after the fault occurs; 2) After a short delay, a small parallel resistor is put into operation, and the amplitude of the neutral point zero-sequence voltage and the amplitude of the zero-sequence current of each outgoing line are recorded; 3) The ratio of the neutral point zero-sequence voltage after the small parallel resistor is put into operation to the neutral point zero-sequence voltage in the arc extinguishing coil compensation stage is calculated, and the ratio of the zero-sequence current of each line in the small resistor input stage and the arc extinguishing coil compensation stage is calculated; 4) If the ratio of the zero-sequence current amplitude of a line is greater than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a faulty line; if the ratio of the zero-sequence current amplitudes of all outgoing lines is less than 4.5 times the ratio of the neutral point zero-sequence voltage amplitude, it is determined to be a busbar fault.

2. The method according to claim 1, characterized in that Faults are detected in the resonant grounding state. After a fault occurs, the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line are recorded, including: In the arc suppression coil compensation stage, the sampled data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0.

3. The method according to claim 1, characterized in that After a short delay, a small parallel resistor is connected to record the neutral point zero-sequence voltage amplitude and the zero-sequence current amplitude of each outgoing line, including: In the stage of small resistance input, the sampling data is fast Fourier transformed to obtain the steady-state power frequency component; Taking into account the accuracy of the zero-sequence current transformer, if the amplitude of the power frequency component of the zero-sequence current of a line is less than 0.1414, it is recorded as 0; Taking into account the accuracy of the zero-sequence voltage transformer, the neutral point zero-sequence voltage is indirectly obtained by using the current flowing through the small resistor during the small resistor input stage.

4. The method according to claim 1, characterized in that Calculate the ratio of the neutral point zero-sequence voltage after the parallel small resistor is put into operation to the neutral point zero-sequence voltage in the arc suppression coil compensation stage, and calculate the ratio of the zero-sequence current of each line in the small resistor input stage and the arc suppression coil compensation stage, including: If a line satisfies If the fault occurs, it is judged as a faulty line, otherwise it is judged as a busbar fault; in , After the small resistor is put into any circuit j Steady-state zero-sequence current amplitude, arc suppression coil compensation stage line j Steady-state zero-sequence current amplitude, , They are respectively the steady-state zero-sequence voltage amplitude of the neutral point after the small resistor is put into operation and the steady-state zero-sequence voltage amplitude during the arc suppression coil compensation stage.

5. The method according to claim 1, characterized in that If the zero-sequence current amplitude ratio of a line is greater than 4.5 times the neutral point zero-sequence voltage amplitude ratio, it is determined to be a faulty line; if the zero-sequence current amplitude ratio of all outgoing lines is less than 4.5 times the neutral point zero-sequence voltage amplitude ratio, it is determined to be a busbar fault, including: If the zero-sequence current amplitude of a line is recorded as 0A before and after the small resistor is put into operation, its zero-sequence current amplitude ratio is recorded as 0, and the ratio of the neutral point zero-sequence voltage amplitude is less than 4.5 times, and it is determined that the line is not faulty; If the denominator of the expression of the zero-sequence current amplitude ratio of a line is 0 and the numerator is not 0, the result is recorded as infinity. If the ratio of the neutral point zero-sequence voltage amplitude is greater than 4.5 times, it is determined to be a faulty line.

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