Mine low-voltage power distribution network single-phase earth fault line selection switch

Abstract

The utility model discloses a single-phase earth fault line selection switch of a mine low-voltage power distribution network, which is characterized in that an artificial neutral point is led out by a three-phase reactor SK behind a circuit breaker DW, the artificial neutral point is grounded through an adjustable zero sequence reactor LK, three zero sequence current transformers TA1, TA2 and TA0 measure effective values of three zero sequence currents before and after the artificial neutral point is led out and flowing through the zero sequence reactor LK, and the effective values of the three zero sequence currents pass through the zero sequence reactor LK. Secondary sides of the zero-sequence current transformers TA1 and TA0 are connected with the electromagnets YA1 and YA0 through the measuring switches K1 and K0 respectively, when a single-phase earth fault occurs in a line, the measuring switches are controlled by taking zero-sequence voltage U0 as an electric leakage starting criterion, the line fault is judged according to the magnitude relation of electromagnetic force generated by zero-sequence current, an armature is attracted, a normally-open contact is connected, the electromagnet YA4 is powered on to disconnect the circuit breaker DW, and the normally-open contact is switched off. The line selection method is simple and reliable, has high accuracy, and is suitable for the low-voltage distribution network of the underground neutral ungrounded system.

Description

Technical Field

[0001] The utility model relates to the field of power system distribution network protection, in particular to a single-phase grounding fault line selection switch for a mine low-voltage distribution network. Background Art

[0002] The neutral point ungrounded low-voltage distribution network, especially the coal mine power supply network, needs to quickly and accurately select the fault line and cut it off to ensure the continuous power supply of the non-fault line, while ensuring that the grounding point fault current is within the specified range to ensure the safety of people in case of electric shock. Considering the influence of the working environment, the line selection method needs to be simple and reliable. Based on this, the utility model proposes a single-phase grounding fault line selection switch for the mine low-voltage distribution network. Summary of the invention

[0003] In view of the above background, the utility model proposes a single-phase grounding fault line selection switch for a mine low-voltage distribution network, which is suitable for a distribution network of a neutral point ungrounded system.

[0004] Specifically, the utility model adopts the following technical solutions.

[0005] The utility model proposes a single-phase grounding fault line selection switch for a low-voltage power distribution network in a mine. An artificial neutral point is drawn out by a three-phase reactor SK after a circuit breaker DW, and the neutral point is grounded through an adjustable zero-sequence reactor LK. Three zero-sequence current transformers TA1, TA2 and TA0 measure three zero-sequence current effective values ​​before and after the artificial neutral point is drawn out and three zero-sequence current effective values ​​flowing through the zero-sequence reactor LK. The secondary sides of the zero-sequence current transformers TA1 and TA0 are connected to electromagnets YA1 and YA0 through measuring switches K1 and K0 respectively. When a single-phase grounding fault occurs in the line, the zero-sequence voltage U0 is used as a leakage start judgment criterion to close the measuring switches K1 and K0. According to the relationship between the magnitudes of the electromagnetic forces generated by the electromagnets YA1 and YA0, the line fault is judged and the armature is attracted, so that the electromagnet YA4 is energized to disconnect the circuit breaker DW.

[0006] Furthermore, an artificial neutral point is drawn from the three-phase reactor SK after the circuit breaker DW, and grounded through the adjustable zero-sequence reactor LK. The reactance value of the zero-sequence reactor LK is adjusted so that when a single-phase grounding fault occurs in the distribution network, the inductive current flows through the zero-sequence reactor LK to overcompensate the capacitive current of the line. The overcompensation degree is 1.35, that is, the effective value relationship is |I LK ∣=1.35∣I C ∣.

[0007] Furthermore, the inductive current flowing through the zero-sequence reactor LK to overcompensate the capacitive current of the line means that, when the load connected to the line is a device, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the device; when the load connected to the line is a power supply bus, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the bus, but does not include the capacitive current of the feeder line connected to the bus.

[0008] Furthermore, the three zero-sequence current transformers TA1, TA2, and TA0 measure the effective value of the zero-sequence current before and after the neutral point and flowing through the zero-sequence reactor LK. When a single-phase grounding fault occurs in the system, for the non-fault line, the relationship between the three zero-sequence current effective values ​​is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2; for the fault line, the relationship between the three zero-sequence current effective values ​​is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0.

[0009] Furthermore, the zero-sequence voltage U0 is used as the starting criterion for the leakage fault. It is set to 0.15 times the rated phase voltage according to the zero-sequence voltage value generated by the three-phase imbalance during normal operation of the system. The adjustable resistor R2 and the resistor R3 are used to divide the voltage to U0R3 / (R2+R3) to turn on the thyristor VT, and the electromagnet YA3 is energized to attract the measuring switches K1 and K0, so that the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0010] Furthermore, the electromagnetic force generated by a single-phase AC electromagnet is F=(iN) 2 / (2μ0A), adjust the turns ratio of the transformer TA1 and TA0 coils to 0.35:1.35, the turns of the electromagnet YA1 and YA0 coils are the same, when a single-phase grounding fault occurs in the system, for the non-fault line, the effective value of the current flowing through the electromagnet YA1 and YA0 coils is equal, and the electromagnetic forces generated are equal; for the fault line, the effective value of the current flowing through the electromagnet YA1 coil is greater than the effective value of the current flowing through the YA0 coil, the electromagnetic force generated by the electromagnet YA1 is greater than the electromagnetic force generated by the YA0, and the switch K4 is turned on to energize the electromagnet YA4 circuit and disconnect the circuit breaker DW.

[0011] Furthermore, the electromagnet YA4 circuit is connected in series with the time delay relay KT to adjust the tripping delay time of the circuit breaker DW.

[0012] Furthermore, a switch tripping test circuit is set up, and the test switch SB is closed to test whether the circuit breaker DW can trip reliably when a single-phase grounding fault occurs in this line. The sensitivity of the line selection switch is tested by adjusting the resistance value of R1.

[0013] Furthermore, a voltage stabilizing diode Z is provided to protect the thyristor VT from being damaged by a neutral point overvoltage.

[0014] The principle of the fault line selection switch is to judge the line fault by comparing the signal difference relationship at the artificial neutral point of the feeder outlet. Compared with the existing distribution network fault line selection technology which requires cumbersome algorithms or computer programs, this method is simple, reliable and has high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of a single-phase ground fault line selection switch for a mine low-voltage distribution network according to the utility model;

[0016] Figure 2 This is the principle diagram of fault line selection for the centralized radiation type distribution network of the utility model;

[0017] Figure 3 This is the principle diagram of fault line selection in the layered radial distribution network of the utility model. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings. The present invention includes but is not limited to the following embodiments.

[0019] The utility model proposes a single-phase grounding fault line selection switch for a low-voltage power distribution network in a mine. An artificial neutral point is drawn out by a three-phase reactor SK after a circuit breaker DW, and the neutral point is grounded through an adjustable zero-sequence reactor LK. Three zero-sequence current transformers TA1, TA2 and TA0 measure three zero-sequence current effective values ​​before and after the artificial neutral point is drawn out and three zero-sequence current effective values ​​flowing through the zero-sequence reactor LK. The secondary sides of the zero-sequence current transformers TA1 and TA0 are connected to electromagnets YA1 and YA0 through measuring switches K1 and K0 respectively. When a single-phase grounding fault occurs in the line, the zero-sequence voltage U0 is used as a leakage start judgment criterion to close the measuring switches K1 and K0. According to the relationship between the magnitudes of the electromagnetic forces generated by the electromagnets YA1 and YA0, the line fault is judged and the armature is attracted, so that the electromagnet YA4 is energized to disconnect the circuit breaker DW.

[0020] Furthermore, an artificial neutral point is drawn from the three-phase reactor SK after the circuit breaker DW, and grounded through the adjustable zero-sequence reactor LK. The reactance value of the zero-sequence reactor LK is adjusted so that when a single-phase grounding fault occurs in the distribution network, the inductive current flows through the zero-sequence reactor LK to overcompensate the capacitive current of the line. The overcompensation degree is 1.35, that is, the effective value relationship is |I LK ∣=1.35∣I C ∣.

[0021] Furthermore, the inductive current flowing through the zero-sequence reactor LK to overcompensate the capacitive current of the line means that, when the load connected to the line is a device, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the device; when the load connected to the line is a power supply bus, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the bus, but does not include the capacitive current of the feeder line connected to the bus.

[0022] Furthermore, the three zero-sequence current transformers TA1, TA2, and TA0 measure the effective value of the zero-sequence current before and after the neutral point and flowing through the zero-sequence reactor LK. When a single-phase grounding fault occurs in the system, for the non-fault line, the relationship between the three zero-sequence current effective values ​​is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2; for the fault line, the relationship between the three zero-sequence current effective values ​​is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0.

[0023] Furthermore, the zero-sequence voltage U0 is used as the starting criterion for the leakage fault. It is set to 0.15 times the rated phase voltage according to the zero-sequence voltage value generated by the three-phase imbalance during normal operation of the system. The adjustable resistor R2 and the resistor R3 are used to divide the voltage to U0R3 / (R2+R3) to turn on the thyristor VT, and the electromagnet YA3 is energized to attract the measuring switches K1 and K0, so that the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0024] Furthermore, the electromagnetic force generated by a single-phase AC electromagnet is F=(iN) 2 / (2μ0A), adjust the turns ratio of the transformer TA1 and TA0 coils to 0.35:1.35, the turns of the electromagnet YA1 and YA0 coils are the same, when a single-phase grounding fault occurs in the system, for the non-fault line, the effective value of the current flowing through the electromagnet YA1 and YA0 coils is equal, and the electromagnetic forces generated are equal; for the fault line, the effective value of the current flowing through the electromagnet YA1 coil is greater than the effective value of the current flowing through the YA0 coil, the electromagnetic force generated by the electromagnet YA1 is greater than the electromagnetic force generated by the YA0, and the switch K4 is turned on to energize the electromagnet YA4 circuit and disconnect the circuit breaker DW.

[0025] Furthermore, the electromagnet YA4 circuit is connected in series with the time delay relay KT to adjust the tripping delay time of the circuit breaker DW.

[0026] Furthermore, a switch tripping test circuit is set up, and the test switch SB is closed to test whether the circuit breaker DW can trip reliably when a single-phase grounding fault occurs in this line. The sensitivity of the line selection switch is tested by adjusting the resistance value of R1.

[0027] Furthermore, a voltage stabilizing diode Z is provided to protect the thyristor VT from being damaged by a neutral point overvoltage. Example

[0028] To explain the implementation method of the present utility model in detail, Figure 3 As an example, the hierarchical radial distribution network shown in the figure Figure 1The single-phase grounding fault line selection switch (hereinafter referred to as the line selection switch) of a mine low-voltage distribution network is shown. It is installed at the head end of each feeder of the distribution network. For the line that directly supplies power to the equipment, the line selection switch is set to instantaneous tripping, and the line selection switches of each layer of lines upward are tripped with increasing delay ∆t in sequence, that is, the line selection switches of lines 1, 10, 11, 12, and 13 are set to instantaneous tripping, the line selection switches of lines 3, 8, and 9 are set to trip after delay ∆t, and the line selection switch of line 2 is set to trip after delay 2∆t.

[0029] when Figure 3 A metallic single-phase grounding fault occurs at point d3 on the layered radial distribution network line 10 shown in the figure. The zero-sequence voltage U0 is the rated phase voltage, which is greater than the set threshold value of 0.15 times the rated phase voltage. The thyristor VT is turned on, so that the electromagnet YA3 is energized to attract the measuring switches K1 and K0, and the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0030] Furthermore, the direction of zero-sequence current flow in the distribution network fault (with the inductive current direction as the positive direction) is as follows: Figure 3 As indicated in the figure, the effective value relationship of the fault zero-sequence current measured by the zero-sequence current transformers of the line selection switches of lines 2, 8, and 10 is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0. K4 in the line selection switches of lines 2, 8, and 10 is energized; the effective value relationship of the three zero-sequence currents of the remaining other lines is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2, and K4 is not energized.

[0031] Furthermore, the line 10 selection switch trips instantaneously, and the line 2 and 8 selection switches are set with delays of 2∆t and ∆t respectively. After the line 10 selection switch trips, the fault tripping signals of the line 2 and 8 selection switches are restored, and therefore they do not trip.

[0032] Furthermore, when Figure 3 A metallic single-phase grounding fault occurs at point d2 on the layered radial distribution network line 8 shown in the figure. The zero-sequence voltage U0 is the rated phase voltage, which is greater than the set threshold value of 0.15 times the rated phase voltage. The thyristor VT is turned on, so that the electromagnet YA3 is energized to attract the measuring switches K1 and K0, and the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0033] Furthermore, the direction of zero-sequence current flow in the distribution network fault (with the inductive current direction as the positive direction) is as follows: Figure 3It is indicated in the figure that the effective value relationship of the fault zero-sequence current measured by the zero-sequence current transformer of the line selection switch of lines 2 and 8 is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0. K4 in the line selection switches of lines 2 and 8 is energized; the effective value relationship of the three zero-sequence currents of the remaining other lines is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2, and K4 is not energized.

[0034] Furthermore, the line 2 and 8 selection switches are set with delays of 2∆t and ∆t respectively. After the line 8 selection switch trips after ∆t, the fault signal of line 2 is restored after a delay of 2∆t, and line 2 does not trip.

[0035] Furthermore, when Figure 3 A metallic single-phase grounding fault occurs at point d1 on line 2 of the layered radial distribution network shown in the figure. The zero-sequence voltage U0 is the rated phase voltage, which is greater than the set threshold value of 0.15 times the rated phase voltage. The thyristor VT is turned on, causing the electromagnet YA3 to energize and close the measuring switches K1 and K0. The zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0036] Furthermore, the direction of zero-sequence current flow in the distribution network fault (with the inductive current direction as the positive direction) is as follows: Figure 3 It is indicated in the figure that the effective value relationship of the fault zero-sequence current measured by the zero-sequence current transformer of the line 2 selection switch is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0, and K4 in the line 2 selection switch is energized; the effective value relationship of the remaining three zero-sequence currents of the other lines is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2, and K4 is not energized.

[0037] Furthermore, the line selection switch of line 2 is set with a delay of 2∆t, so line 2 is tripped after a delay of 2∆t.

[0038] For Figure 2 In the centralized radial distribution network shown in the figure, each feeder selection switch is set to instantaneous tripping mode. Figure 2 A metallic single-phase grounding fault occurs at point d, and the zero-sequence voltage U0 is the rated phase voltage, which is greater than the set threshold of 0.15 times the rated phase voltage. The thyristor VT is turned on, so that the electromagnet YA3 is energized to attract the measuring switches K1 and K0, and the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

[0039] Furthermore, the direction of zero-sequence current flow in the distribution network fault (with the inductive current direction as the positive direction) is as follows: Figure 2As indicated in the figure, the effective value relationship of the fault zero-sequence current measured by the zero-sequence current transformer of the line 3 selection switch is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents of all non-fault lines after compensation, which is greater than (0.35 / 1.35)TA0, and K4 in the line 3 selection switch is energized; the effective value relationship of the three zero-sequence currents of the remaining other lines is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2, and K4 is not energized.

[0040] Further, Figure 2 The line selection switches of each line in the centralized radial distribution network shown are set to instantaneous tripping, so the line selection switch of line 3 trips instantly to eliminate the fault. Example

[0041] The utility model proposes a line selection switch for a single-phase grounding fault in a mine low-voltage distribution network. To ensure that the faulty line can be instantly cut off when a single-phase grounding fault occurs in the distribution network, the line selection switch is set as follows: three zero-sequence current transformers TA1, TA2, and TA0 measure the effective value of the zero-sequence current before and after the neutral point and flowing through the zero-sequence reactor LK, and input them into the microcomputer system at the same time. When a single-phase grounding fault occurs in the distribution network, if the relationship between the three effective values ​​of zero-sequence currents of a certain line is TA1+TA2=TA0, it is judged to be a non-fault state; if the relationship between the three effective values ​​of zero-sequence currents of a certain line is TA0+TA1=TA2, it is judged to be a fault state. The faulty line is selected and cut off based on the status of all lines in the distribution network (fault or non-fault). Figure 3 Taking the hierarchical radial distribution network shown in the figure as an example, the fault line selection criteria for each line are summarized in Table 1.

[0042] Table 1 Fault line selection criteria for each line

[0043] line Fault line selection criteria 1 Line 1 fault status 2 Line 2 is in fault state while lines 8, 9, 10, 11, 12, 13 are in non-fault state 3 Line 3 is in fault state and the lines connected to it are all judged to be in non-fault state. 8 Lines 2 and 8 are in fault state while lines 10 and 11 are in non-fault state 9 Lines 2 and 9 are in fault state while lines 12 and 13 are in non-fault state 10 Line 2, 8, 10 are in fault state at the same time 11 Line 2, 8, 11 are in fault state at the same time 12 Line 2, 9, 12 are in fault state at the same time 13 Lines 2, 9, and 13 are simultaneously faulty

[0044] When the distribution line meets the fault line selection criteria listed in Table 1, the microcomputer protection device instantly outputs a trip signal to trip the faulty line.

[0045] The utility model and its implementation methods are described above. This description is not restrictive. What is shown in the accompanying drawings is only one of the implementation methods of the utility model. The actual structure is not limited to this. Anyone can derive other forms of distribution network ground fault line selection methods under the inspiration of the utility model. All equal changes and modifications made within the scope of the utility model should fall within the scope of the utility model.

Claims

1. A single-phase ground fault line selection switch for a mine low-voltage distribution network, characterized in that: An artificial neutral point is drawn out from behind the circuit breaker DW by the three-phase reactor SK and grounded through the adjustable zero-sequence reactor LK. Three zero-sequence current transformers TA1, TA2 and TA0 measure the effective values ​​of the three zero-sequence currents before and after the artificial neutral point and flowing through the zero-sequence reactor LK. The secondary sides of the zero-sequence current transformers TA1 and TA0 are connected to the electromagnets YA1 and YA0 through the measuring switches K1 and K0 respectively. When a single-phase grounding fault occurs in the line, the zero-sequence voltage U0 is used as the leakage starting criterion to close the measuring switches K1 and K0. The line fault is judged according to the relationship between the electromagnetic forces generated by the electromagnets YA1 and YA0, and the armature is attracted to energize the electromagnet YA4 to disconnect the circuit breaker DW.

2. According to claim 1, a single-phase ground fault line selection switch for a mine low-voltage distribution network, characterized in that: After the circuit breaker DW, an artificial neutral point is drawn from the three-phase reactor SK and grounded through the adjustable zero-sequence reactor LK. The reactance value of the zero-sequence reactor LK is adjusted so that when a single-phase grounding fault occurs in the distribution network, the inductive current flows through the zero-sequence reactor LK to overcompensate the capacitive current of the line. The overcompensation degree is 1.35, that is, the effective value relationship is |I LK ∣=1.35∣I C ∣.

3. According to claim 2, a single-phase ground fault line selection switch for a mine low-voltage distribution network, characterized in that: The inductive current flowing through the zero-sequence reactor LK overcompensates the capacitive current of the line, which means that when the load connected to the line is a device, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the device; when the load connected to the line is a power supply bus, the capacitive current that needs to be overcompensated includes the capacitive current of the line and the bus, but does not include the capacitive current of the feeder line connected to the bus.

4. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 1, characterized in that: The three zero-sequence current transformers TA1, TA2, and TA0 measure the effective value of the zero-sequence current before and after the neutral point and flowing through the zero-sequence reactor LK. When a single-phase grounding fault occurs in the system, for the non-fault line, the relationship between the three zero-sequence current effective values ​​is TA1+TA2=TA0, that is, TA1=(0.35 / 1.35)TA0=0.35TA2; for the fault line, the relationship between the three zero-sequence current effective values ​​is TA0+TA1=TA2, and TA1 measures the sum of the residual inductive currents after compensation of the non-fault lines, which is greater than (0.35 / 1.35)TA0.

5. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 1, characterized in that: The zero-sequence voltage U0 is used as the starting criterion for leakage fault. It is set to 0.15 times the rated phase voltage according to the zero-sequence voltage value caused by three-phase imbalance during normal operation of the system. The adjustable resistor R2 and the resistor R3 are used to divide the voltage to U0R3 / (R2+R3) to turn on the thyristor VT, so that the electromagnet YA3 is energized to attract the measuring switches K1 and K0, so that the zero-sequence current measured by the current transformers TA1 and TA0 flows through the electromagnets YA1 and YA0.

6. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 5, characterized in that: The electromagnetic force generated by a single-phase AC electromagnet is F=(iN) 2 / (2μ0A), adjust the turns ratio of the transformer TA1 and TA0 coils to 0.35:1.35, the turns of the electromagnet YA1 and YA0 coils are the same, when a single-phase grounding fault occurs in the system, for the non-fault line, the effective value of the current flowing through the electromagnet YA1 and YA0 coils is equal, and the electromagnetic forces generated are equal; for the fault line, the effective value of the current flowing through the electromagnet YA1 coil is greater than the effective value of the current flowing through the YA0 coil, the electromagnetic force generated by the electromagnet YA1 is greater than the electromagnetic force generated by the YA0, and the switch K4 is turned on to energize the electromagnet YA4 circuit and disconnect the circuit breaker DW.

7. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 1, characterized in that: The electromagnet YA4 circuit is connected in series with the time delay relay KT to adjust the tripping delay time of the circuit breaker DW.

8. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 1, characterized in that: Set up a switch tripping test circuit, close the test switch SB, and test whether the circuit breaker DW can trip reliably when a single-phase grounding fault occurs in this line. By adjusting the resistance value of R1, test the sensitivity of the line selection switch.

9. A single-phase ground fault line selection switch for a mine low-voltage distribution network according to claim 1, characterized in that: The voltage stabilizing diode Z is provided to protect the thyristor VT from being damaged by the neutral point overvoltage.

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