High-resistance grounding identification method

Abstract

The invention discloses a high-resistance grounding identification method, which comprises the following steps of: connecting a resistor Rz capable of being switched in series between a neutral point of a system and the ground, switching the resistor Rz into the system when the system normally operates, and recording a zero-sequence voltage U0 when the system stably operates; and when the zero-sequence voltage U0 is greatly changed, calculating to obtain a ground capacitive reactance Xc1 and a grounding resistance value Rd in a system grounding state through the switching resistor Rz, and when the calculated grounding resistance value is smaller than or equal to a set threshold value, determining that a grounding fault occurs. A high-resistance recognition algorithm is adopted, the grounding resistance value and the system ground capacitive reactance can be calculated, the grounding state is recognized according to the calculated resistance value, the method is applied to a power distribution network system of a non-resonant grounding system, the problem that a zero-sequence voltage low protection device cannot recognize a grounding fault during a single-phase grounding fault is solved, and the reliability of the system is improved. The safe operation of a power system is effectively guaranteed, and the power supply reliability is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power distribution network protection, in particular to a method for identifying high-resistance grounding. Background Art

[0002] At present, the system grounded by the arc suppression pre-adjusted arc suppression coil in the distribution network usually identifies the single-phase grounding fault by the zero-sequence voltage exceeding the limit value. This method can easily identify the resistance grounding below 10kΩ. However, for non-resonant grounding systems or adjustable arc suppression grounding systems, such as low-resistance grounding systems, neutral point ungrounded systems, and adjustable phase control, the grounding can only be identified by zero-sequence voltage. Resistance grounding of several hundred ohms. Therefore, when a single-phase high-resistance grounding occurs in the system, the zero-sequence voltage value cannot reach the grounding start value, and the protection or compensation device will not be able to identify the fault. The grounding fault cannot be handled in time and it is easy to cause the fault to expand, endangering the safe operation of the system. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a high-resistance grounding identification method to improve the grounding identification capability of the protection device and ensure the safe and stable operation of the power system.

[0004] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0005] A method for identifying high-resistance grounding is to connect a retractable resistor R in series between the system neutral point and the ground. z , when the system is operating normally, the resistance R z Put the system into operation and record the zero-sequence voltage U0 when the system is running stably; when the zero-sequence voltage U0 changes significantly, the resistor R z Calculate the ground capacitive reactance X when the system is grounded c1 And the ground resistance value R d When the calculated grounding resistance value is less than or equal to the set threshold, it is determined that a grounding fault occurs.

[0006] The above-mentioned high-resistance grounding identification method, the specific calculation method of the capacitive current and the grounding resistance value when a single-phase grounding fault occurs in the system is as follows:

[0007] S1. When the zero-sequence voltage U0 changes significantly, disconnect the circuit breaker to make the resistor R z Exit the system, and the zero-sequence voltage will change as After data collection is completed, close the circuit breaker again to make the resistor R z When the system is put into operation, the zero-sequence voltage will change again, which is recorded as

[0008] S2. Assume that the voltage of the grounded phase is U x , the grounding resistance is Rd , the system capacitive reactance to ground is X c1 According to the loop equation, U 01 with U x relationship, get

[0009]

[0010] S3. Assuming impedance Z s ,make

[0011]

[0012] S4. According to formula 1, formula 2 and formula 3, we can get the vector

[0013]

[0014] S5. Order:

[0015]

[0016] Substitute equation 5 and equation 6 into equation 4, and equation 4 is simplified to:

[0017]

[0018] In formula 7, R1 and X1 are in series relationship. Converting the series relationship to parallel, the real part of the parallel impedance is:

[0019]

[0020] The imaginary part of the parallel impedance is:

[0021]

[0022] S6. Substitute equation 5 and equation 6 into equation 8 to obtain the grounding resistance value: R 并 =R d ,

[0023] Substituting equations 5 and 6 into equation 9, we get the grounding capacitance value: X 并 =X c1 .

[0024] In the above-mentioned method for identifying high-resistance grounding, the resistor R d The value of is the resistance value of ground identification capability.

[0025] In the above-mentioned high-resistance grounding identification method, when the system is operating normally, the bus voltage and zero-sequence voltage are collected in real time, and the capacitive reactance X to ground when the system is operating stably is calculated. c0 and the damping resistance R d0 ; When grounded, the capacitive reactance to ground is X c1The capacitive reactance X of the ground capacitance when the system is running stably c0 When the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R when the system is running stably d0 A ground fault must have occurred; when the grounding capacitive reactance X c1 The capacitive reactance X of the ground capacitance when the system is running stably c0 When the phase difference is large, the capacitive reactance to ground when grounding is X c1 Converted to the corresponding damping resistance value R when not grounded d1 , R d1＝ X c1* R d0 / X c0 , if the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R d1 A ground fault must have occurred.

[0026] In the above-mentioned high-resistance grounding identification method, when the system is operating normally, a fast fault identification algorithm is used to monitor the change of the zero-sequence voltage U0 to identify the occurrence of a grounding fault.

[0027] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0028] The present invention adds a retractable resistor Rz between the neutral point of the system and the ground. After the system is grounded with high resistance, a high resistance identification algorithm is used to calculate the grounding resistance value and the system capacitive reactance to the ground. The grounding state is identified according to the calculated resistance value. The present invention is applied to a distribution network system of a non-resonant grounding system, solves the problem that a zero-sequence voltage low protection device cannot identify a grounding fault during a single-phase grounding fault, effectively ensures the safe operation of the power system, and improves the power supply reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the electrical schematic diagram of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] A method for identifying high-resistance grounding is to connect a retractable resistor R in series between the system neutral point and the ground. z , when the system is operating normally, the resistance R z Put the system into operation and record the zero-sequence voltage U0 when the system is running stably; the electrical schematic diagram is as follows Figure 1 As shown. Resistor R d The value of grounding identification capability is the resistance value, the resistance R zIt forms a series branch with the circuit breaker KM1, and the resistance R is realized by turning on and off the circuit breaker KM1. z The investment withdrawal.

[0032] When the zero-sequence voltage U0 changes significantly, the resistor R z Calculate the ground capacitive reactance X when the system is grounded c1 And the ground resistance value R d , by comparing the calculated value with the system's ground capacitance reactance X during normal operation c0 and the damping resistance R d0 Compare and determine whether a ground fault has occurred.

[0033] The specific identification method of the present invention is as follows.

[0034] When the system is operating normally, the bus voltage and zero-sequence voltage U0 are collected in real time, and the capacitive reactance X to ground when the system is operating stably is calculated. c0 and the damping resistance R d0 The system uses a fast fault identification algorithm to monitor the change of zero-sequence voltage U0 and identify the occurrence of ground faults.

[0035] When a single-phase grounding fault occurs in the system, if it is low-resistance grounding, the zero-sequence voltage reaches the preset grounding start value at this time, and the single-phase grounding fault can be easily identified through the zero-sequence voltage and the bus voltage; but if it is high-resistance grounding, the zero-sequence voltage after grounding is lower than the grounding start value, and the grounding cannot be started through the zero-sequence voltage, but the zero-sequence voltage vector collected at this time will inevitably change.

[0036] At this time, disconnect the circuit breaker KM1, so that the resistor R z Exit the system, and the zero-sequence voltage will change as After data collection is completed, close the circuit breaker KM1 to make the resistor R z When the system is put into operation, the zero-sequence voltage will change again, which is recorded as

[0037] Assume that the voltage of the grounded phase is U x , the grounding resistance is R d , the system capacitive reactance to ground is X c1 According to the loop equation, U 01 with U x relationship, get

[0038]

[0039] Assuming the impedance Z s ,make

[0040]

[0041] According to formula 1, formula 2 and formula 3, we can get the vector

[0042]

[0043] make:

[0044]

[0045] Substitute equation 5 and equation 6 into equation 4, and equation 4 is simplified to:

[0046]

[0047] In formula 7, R1 and X1 are in series relationship, and the values ​​of the two quantities can be calculated according to the above formulas 5 and 6. The series relationship is converted to parallel, and the real part of the parallel impedance is:

[0048]

[0049] The imaginary part of the parallel impedance is:

[0050]

[0051] Substituting equations 5 and 6 into equation 8, we get the grounding resistance value: R 并 =R d ,

[0052] Substituting equations 5 and 6 into equation 9, we get the grounding capacitance value: X 并 =X c1 .

[0053] When grounded, the capacitive reactance to ground is X c1 The capacitive reactance X of the ground capacitance when the system is running stably c0 When the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R when the system is running stably d0 A ground fault must have occurred.

[0054] When grounded, the capacitive reactance to ground is X c1 The capacitive reactance X of the ground capacitance when the system is running stably c0 When the phase difference is large, the capacitive reactance to ground when grounding is X c1 Converted to the corresponding damping resistance value R when not grounded d1 , R d1＝ X c1* R d0 / X c0 , if the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R d1 A ground fault must have occurred.

[0055] The present invention realizes the resistor R by switching on and off the circuit breaker KM1 when the zero-sequence voltage changes. z The grounding resistance and capacitance values ​​at the time of the fault are obtained by combining the vector calculation, and then compared with the damping resistance value of normal operation and the set threshold value, so as to accurately identify the grounding fault, solve the problem that the single-phase grounding fault cannot be identified due to the high-resistance grounding zero-sequence voltage failing to reach the grounding starting value, and ensure the stable operation of the system.

Claims

1. A method for identifying high-resistance grounding, characterized in that: Connect a retractable resistor R in series between the system neutral point and ground. z , when the system is operating normally, the resistance R z Put the system into operation and record the zero-sequence voltage U0 when the system is running stably; when the zero-sequence voltage U0 changes significantly, the resistor R z Calculate the ground capacitive reactance X when the system is grounded c1 And the ground resistance value R d When the calculated grounding resistance value is less than or equal to the set threshold, it is determined that a grounding fault occurs.

2. A method for identifying high-resistance grounding according to claim 1, characterized in that: The specific calculation method of the capacitive current and grounding resistance value when a single-phase grounding fault occurs in the system is as follows: S1. When the zero-sequence voltage U0 changes significantly, disconnect the circuit breaker (KM1) to make the resistor R z Exit the system, and the zero-sequence voltage will change as After data collection is completed, close the circuit breaker (KM1) to make the resistor R z When the system is put into operation, the zero-sequence voltage will change again, which is recorded as S2. Assume that the voltage of the grounded phase is U x , the grounding resistance is R d , the system capacitive reactance to ground is X c1 According to the loop equation, U 01 with U x relationship, get S3. Assuming impedance Z s ,make S4. According to formula 1, formula 2 and formula 3, we can get the vector S5. Order: Substitute equation 5 and equation 6 into equation 4, and equation 4 is simplified to: In formula 7, R1 and X1 are in series relationship. Converting the series relationship to parallel, the real part of the parallel impedance is: The imaginary part of the parallel impedance is: S6. Substitute equation 5 and equation 6 into equation 8 to obtain the grounding resistance value: R 并 =R d , Substituting equations 5 and 6 into equation 9, we get the grounding capacitance value: X 并 =X c1 .

3. A method for identifying high-resistance grounding according to claim 1, characterized in that: The resistor R d The value of is the resistance value of ground identification capability.

4. A method for identifying high-resistance grounding according to claim 1, characterized in that: When the system is operating normally, the bus voltage and zero-sequence voltage are collected in real time, and the capacitive reactance X to ground when the system is operating stably is calculated. c0 and the damping resistance R d0 ; When grounded, the capacitive reactance to ground is X c1 The capacitive reactance X of the ground capacitance when the system is running stably c0 When the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R when the system is running stably d0 A ground fault must have occurred; when the grounding capacitive reactance X c1 The capacitive reactance X of the ground capacitance when the system is running stably c0 When the phase difference is large, the capacitive reactance to ground when grounding is X c1 Converted to the corresponding damping resistance value R when not grounded d1 , R d1＝ X c1* R d0 / X c0 , if the grounding resistance value R d Lower than the set threshold and much smaller than the damping resistance value R d1 A ground fault must have occurred.

5. A method for identifying high-resistance grounding according to claim 2, characterized in that: When the system is operating normally, a fast fault identification algorithm is used to monitor the change of zero-sequence voltage U0 and identify the occurrence of grounding faults.

Images