A method for adaptively suppressing sheath circulating current in high-voltage parallel cables in phase

Abstract

The present invention relates to a high-voltage co-phase parallel cable sheath circulating current adaptive suppression device, comprising a resistance-inductance suppressor, one end of the resistance-inductance suppressor is connected to the sheath end of each phase cable, the other end of the resistance-inductance suppressor is connected to one end of an adjustable grounding resistance suppressor, and the other end of the adjustable grounding resistance suppressor is grounded; the control device is composed of an electrical quantity acquisition unit for collecting the voltage across the adjustable grounding resistance suppressor, a signal generator, and a central controller CPU. The present invention also discloses a suppression method for a high-voltage co-phase parallel cable sheath circulating current adaptive suppression device. The present invention can appropriately reduce the voltage on the high-voltage cable sheath grounding resistance and the size of the sheath circulating current, give priority to the sheath circulating current not being greater than a set value, and appropriately reduce the value of the sheath voltage when the sheath circulating current is allowed, which can not only effectively reduce the insulation pressure of the equipment, but also effectively ensure the personal safety of the operator.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage cables in a transmission and distribution network, in particular to a method for adaptively suppressing sheath circulating currents of high-voltage in-phase parallel cables. Background Art

[0002] High-voltage cables have the advantages of high power supply reliability, little influence from external environmental factors, small footprint, and little impact on the urban environment, and have been widely used in urban transmission and distribution networks. Since the cable load current and other currents will induce a large induced voltage in the metal sheath, there is a safety hazard, so the metal sheath must be grounded, and a grounding current will be formed on the metal sheath, also known as sheath grounding loop current. When the line length is long, the induced voltage is very large, and the metal sheath cross-interconnection grounding method is often used to suppress the induced voltage of the metal outer sheath of the high-voltage cable, thereby achieving the purpose of reducing the circulating current.

[0003] At present, the loop current suppression methods such as series resistor suppressor, inductor suppressor and choke are generally used to further suppress the ground loop current. For long-distance cross-connection, the above methods are combined and multi-point grounding is optimized. Among them, the series resistor suppressor does not change the induced electromotive force. It is to insert a resistor in series at the sheath grounding point to increase the sheath-earth loop resistance to reduce the loop current. This method can be used not only in single-circuit cable lines but also in multi-circuit cables in parallel in phase. It has universal applicability. Compared with direct grounding, the series resistor increases the voltage drop at the grounding point while reducing the current, and there are still great safety hazards. The inductor suppressor is to insert a compensation inductor in series at the sheath grounding point, so that the alternating magnetic field generated by the cable core current intersects with it, and generates an induced electromotive force to offset the induced electromotive force of the metal sheath, and reduce the sheath loop current by reducing the synthetic induced electromotive force. Its advantage is that it can synchronously induce an electromotive force of appropriate size through the core current, but the voltage at the connection of the compensation inductor is large. The choke also has the problem of large voltage at the connection point while reducing the sheath loop current, and the fixed compensation method is not suitable for the case of multi-circuit cables in parallel.

[0004] For the same-phase parallel cables, the sheath circulation generated by the double-circuit cable is larger than that of the single-circuit cable. The more cable loops there are, the greater the impact on the sheath circulation. The different spatial positions of the parallel cables will cause the electromagnetic field between different cables to change, which will greatly affect the sheath circulation on the cable. In engineering, the number of cable laying loops in the same tunnel is increasing. With the increase of new cables, the sheath circulation is also increasing. In the actual cable installation and sheath grounding process, due to environmental restrictions, the position and connection of the cable are not exactly the same as the theory, and the sheath circulation will also have corresponding differences from the theoretical value. If a larger grounding resistance is used, the grounding resistance will be seriously too large, endangering the safety of equipment and personnel; if a normal grounding resistance is used, the grounding circulation will increase after expansion or when various faults occur during operation. The original grounding resistance will be difficult to effectively suppress the grounding current. The original fixed resistance value can no longer be fully applicable to the new expansion situation. Exceeding the standard grounding circulation not only affects the current carrying capacity and service life of the cable, but in severe cases, it may even burn the grounding wire or grounding box. Failure to eliminate the fault in time may also cause a vicious power grid accident. Summary of the invention

[0005] The primary purpose of the present invention is to provide a high-voltage cable sheath circulating current adaptive suppression device that can appropriately reduce the voltage on the grounding resistance of the sheath and the size of the sheath circulating current. When the sheath circulating current allows, the sheath voltage value can be appropriately reduced, which can not only effectively reduce the insulation pressure of the equipment, but also effectively ensure the personal safety of the operator.

[0006] To achieve the above object, the present invention adopts the following technical solution: a high-voltage in-phase parallel cable sheath circulating current adaptive suppression device, comprising:

[0007] Resistive inductor suppressor, used to suppress sheath circulating current;

[0008] Adjustable ground resistance suppressor to control sheath voltage while suppressing sheath circulating current;

[0009] The control device is used to collect electrical quantity information, send signals through logical judgment, and realize the switching of resistors;

[0010] One end of the resistance-inductance suppressor is connected to the end of the sheath of each phase cable, the other end of the resistance-inductance suppressor is connected to one end of an adjustable grounding resistance suppressor, and the other end of the adjustable grounding resistance suppressor is grounded; the control device is composed of an electrical quantity acquisition unit for collecting the voltage across the adjustable grounding resistance suppressor, a signal generator for controlling the closing / closing of the switch in the adjustable grounding resistance suppressor, and a central controller CPU.

[0011] The resistance-inductance suppressor is divided into three routes, the first route is composed of a resistor R11 and an inductor X11 connected in series, the second route is composed of a resistor R12 and an inductor X12 connected in series, and the third route is composed of a resistor R13 and an inductor X13 connected in series. The resistor R11 is connected to the sheath end of the C-phase cable, the resistor R12 is connected to the sheath end of the B-phase cable, and the resistor R13 is connected to the sheath end of the A-phase cable. One end of the inductor X11, the inductor X12 and the inductor X13 are connected in parallel.

[0012] The adjustable grounding resistance suppressor is composed of resistors R1, R2, R3, and switches S1, S2, S3. One end of the resistor R1 is connected to the resistance-inductance suppressor. The resistors R1, R2, R3 are connected in series in sequence. The other end of the resistor R3 is grounded. The switch S1 is connected in parallel to the resistor R1, the switch S2 is connected in parallel to the resistor R2, and the switch S3 is connected in parallel to the resistor R3.

[0013] The electrical quantity acquisition unit adopts a voltage transformer, and the voltage transformer is installed at both ends of the adjustable grounding resistance suppressor.

[0014] The signal generator adopts a relay.

[0015] The output end of the electrical quantity acquisition unit is connected to the signal input end of the central controller CPU, and the signal output end of the central controller CPU is connected to the signal input end of the signal generator.

[0016] Another object of the present invention is to provide a method for suppressing a high-voltage in-phase parallel cable sheath circulating current adaptive suppression device, the method comprising the following steps in sequence:

[0017] (1) According to the input voltage U and the grounding resistance R at both ends of the adjustable grounding resistance suppressor s-0 To calculate the current sheath circulation I s ;

[0018] (2) Determine the current sheath circulation I s Is it greater than I s1 , where I s1 is the maximum permissible value of the given circulation current. If it exceeds I s1 If the value of the sheath circulating current I is reached, the adjustable grounding resistance suppressor is automatically adjusted up by one gear. Each gear can adjust the resistance value of 0.5 times the rated grounding resistance, and its value is recorded as p. s ≤I s1 , record the number of times of increase as m and pre-output R s-1 ,I s , U s , where R s-1 =R s-0 +mp,R s-1 To increase the total grounding resistance value of the m-times pre-output;

[0019] (3) Determine R s-1 The voltage U s The size of U s It is the estimated voltage after the first resistance pre-adjustment calculation. At this time, the maximum voltage allowed by the system is set to U s1 , if U s s1 , then it ends directly, indicating that the current regulation does not meet the conditions for reducing the voltage, the grounding resistance R s =R s-1 , output R s , adjust the grounding resistance, and this adjustment is completed;

[0020] (4) If U s ≥U s1 , determine the current I s with I s2 The size of I s2 This is the maximum allowable sheath circulation value during the adjustment process at this stage, and the default value is I s2 ≤I s1 , automatically adjust the resistance down one gear when calculating, and judge the current size at this time. If I s ≥I s2 , then the calculation is completed, indicating that the current regulation does not meet the conditions for reducing the voltage, and the grounding resistance R s =R s-1 , output R s , adjust the grounding resistance, and this adjustment is completed;

[0021] (5) If U s ≥U s1 And I s <I s2 , adjust the resistance range to a lower level, that is, R s =R s-1 -p, return to step (3), continue to execute its judgment logic, and finally output R s =R s-1 -np, n is the number of times the resistance is lowered.

[0022] It can be seen from the above technical scheme that the beneficial effects of the present invention are: the present invention can appropriately reduce the voltage on the grounding resistance of the high-voltage cable sheath and the size of the sheath circulating current, give priority to the sheath circulating current not being greater than a set value, and when the sheath circulating current allows, appropriately reduce the value of the sheath voltage, which can not only effectively reduce the insulation pressure of the equipment, but also effectively ensure the personal safety of the operator. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of the device and the cable sheath;​

[0024] Figure 2 It is a structural schematic diagram of the device;

[0025] Figure 3 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0026] like Figure 1 , 2 As shown, a high-voltage same-phase parallel cable sheath circulating current adaptive suppression device comprises:

[0027] The resistance-inductance suppressor 2 is used to suppress the sheath circulation;

[0028] Adjustable ground resistance suppressor to control sheath voltage while suppressing sheath circulating current;

[0029] The control device 1 is used to collect electrical quantity information, send signals through logical judgment, and realize the switching of resistors;

[0030] One end of the resistance-inductance suppressor 2 is connected to the sheath end of each phase cable, and the other end of the resistance-inductance suppressor 2 is connected to one end of an adjustable grounding resistance suppressor, and the other end of the adjustable grounding resistance suppressor is grounded; the control device 1 is composed of an electrical quantity acquisition unit for collecting the voltage across the adjustable grounding resistance suppressor, a signal generator for controlling the closing / closing of the switch in the adjustable grounding resistance suppressor, and a central controller CPU.

[0031] The resistance-inductance suppressor 2 is divided into three routes, the first route is composed of a resistor R11 and an inductor X11 connected in series, the second route is composed of a resistor R12 and an inductor X12 connected in series, and the third route is composed of a resistor R13 and an inductor X13 connected in series. The resistor R11 is connected to the sheath end of the C-phase cable, the resistor R12 is connected to the sheath end of the B-phase cable, and the resistor R13 is connected to the sheath end of the A-phase cable. One end of the inductor X11, the inductor X12 and the inductor X13 are connected in parallel.

[0032] The adjustable grounding resistance suppressor is composed of resistors R1, R2, R3, and switches S1, S2, S3. One end of the resistor R1 is connected to the resistance-inductance suppressor 2. The resistors R1, R2, R3 are connected in series in sequence. The other end of the resistor R3 is grounded. The switch S1 is connected in parallel to the resistor R1, the switch S2 is connected in parallel to the resistor R2, and the switch S3 is connected in parallel to the resistor R3.

[0033] The electrical quantity acquisition unit adopts a voltage transformer, and the voltage transformer is installed at both ends of the adjustable grounding resistance suppressor.

[0034] The signal generator adopts a relay.

[0035] The output end of the electrical quantity acquisition unit is connected to the signal input end of the central controller CPU, and the signal output end of the central controller CPU is connected to the signal input end of the signal generator.

[0036] like Figure 3 As shown, the method comprises the following steps in order:

[0037] (1) According to the input voltage U and the grounding resistance R at both ends of the adjustable grounding resistance suppressor s-0 To calculate the current sheath circulation I s ;

[0038] (2) Determine the current sheath circulation I s Is it greater than I s1 , where I s1 is the maximum permissible value of the given circulation current. If it exceeds I s1 If the value of the sheath circulating current I is reached, the adjustable grounding resistance suppressor is automatically adjusted up by one gear. Each gear can adjust the resistance value of 0.5 times the rated grounding resistance, and its value is recorded as p. s ≤I s1 , record the number of times of increase as m and pre-output R s-1 ,I s , U s , where R s-1 =R s-0 +mp,R s-1 To increase the total grounding resistance value of the m-times pre-output;

[0039] (3) Determine R s-1 The voltage U s The size of U s It is the estimated voltage after the first resistance pre-adjustment calculation. At this time, the maximum voltage allowed by the system is set to U s1 , if U s s1 , then it ends directly, indicating that the current regulation does not meet the conditions for reducing the voltage, the grounding resistance R s =R s-1 , output R s , adjust the grounding resistance, and this adjustment is completed;

[0040] (4) If U s ≥U s1 , determine the current I s with I s2 The size of I s2 This is the maximum allowable sheath circulation value during the adjustment process at this stage, and the default value is I s2 ≤I s1 , automatically adjust the resistance down one gear when calculating, and judge the current size at this time. If I​s ≥I s2 , then the calculation is completed, indicating that the current regulation does not meet the conditions for reducing the voltage, and the grounding resistance R s =R s-1 , output R s , adjust the grounding resistance, and this adjustment is completed;

[0041] (5) If U s ≥U s1 And I s <I s2 , adjust the resistance range to a lower level, that is, R s =R s-1 -p, return to step (3), continue to execute its judgment logic, and finally output R s =R s-1 -np, n is the number of times the resistance is lowered.

[0042] The following combination Figures 1 to 3 The present invention is further described.

[0043] The electrical quantity acquisition unit mainly adopts PT to introduce the grounding resistance voltage into the control device 1, and calculates and gives the appropriate resistance value of the adjustable grounding resistance suppressor according to the set sheath circulating current and the grounding resistance sheath voltage. By adjusting the size of the resistance, the sheath circulating current and the voltage on the grounding resistance are controlled within a suitable range.

[0044] The rated resistance of the adjustable grounding resistor suppressor is the resistance distribution value at the maximum current carrying capacity. The series resistance is 0.5, 1.0 and 1.5 times the rated resistance respectively. A switch that can be maintained is connected in parallel to each resistor. Here, the switch adopts a relay, and its two ends are connected to the control device 1 through a cable. The control device 1 can realize variable control of the resistance by short-circuiting the resistor through a signal.

[0045] It is known from calculation that when the resistance inductance compensated in the resistance-inductance suppressor 2 is the same as the resistance value on the metal sheath, the suppression effect is the best, so the central resistance value of the adjustable resistor can be the resistance value on the metal sheath, and its compensation inductance is the same as the reactance value on the metal sheath. It can be calculated by the following formula:

[0046]

[0047] X=2πfL (3)

[0048] ω=2πf (4)

[0049] In the above formula,

[0050] R, X——resistance and inductance of metal sheath;

[0051] r1, r2 – outer radius and inner radius of the metal sheath (mm);

[0052] d1, d2 – outer and inner diameters of the metal sheath (mm);

[0053] μ0——Relative magnetic permeability of metal sheath;

[0054] ω——angular velocity, where f is the current transmission frequency;

[0055] ρ——Resistivity of metal sheath (uΩ·cm);

[0056] β——The resistance temperature coefficient of the metal sheath, that is, the resistance change for every 1°C change in sheath temperature;

[0057] T——working temperature of metal sheath;

[0058] ω——angular velocity, where f is the current transmission frequency;

[0059] Wherein, R is the adjustable compensation resistor in the resistance-inductance suppressor 2, X is the inductive reactance of the metal sheath, and the value of the grounding resistance is generally 0.4-0.7Ω.

[0060] like Figure 2 It is shown that the adjustable grounding resistor suppressor is mainly a series grounding resistor, and each adjustable resistor is divided into three, the first is 0.5 times the rated resistance, the second is 1.0 times the rated resistance, and the third is 1.5 times the rated resistance. In this way, the adjustable resistor has 6 gears of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 times the rated resistance, which can be freely combined according to needs. This can meet the problem of excessive sheath circulating current or excessive grounding voltage caused by the transformation and expansion of the same-phase parallel cable or some other reasons.

[0061] The first resistance adjustment is mainly applicable to the case where the sheath current is large, mainly to reduce the sheath circulation; the second resistance adjustment is mainly applicable to the case where the sheath circulation is not large but the grounding resistance is relatively large, mainly to reduce the grounding voltage of the grounding resistance. In fact, the sheath circulation of the cable will change greatly or frequently due to time, weather and later renovation and expansion, so in the actual process, it is necessary to adopt this whole set of adjustment process.

[0062] In summary, the present invention can appropriately reduce the voltage on the grounding resistance of the high-voltage cable sheath and the size of the sheath circulating current, give priority to the sheath circulating current not being greater than a set value, and appropriately reduce the value of the sheath voltage when the sheath circulating current allows, which can not only effectively reduce the insulation pressure of the equipment, but also effectively ensure the personal safety of the operator.

Claims

1. A method for adaptively suppressing sheath circulating current of high-voltage in-phase parallel cables, characterized in that: The method comprises the following steps in order: (1) According to the input voltage U and the grounding resistance at both ends of the adjustable grounding resistance suppressor To calculate the current sheath circulation ; (2) Determine the current sheath circulation Is it greater than ,in is the maximum permissible value of the given circulation current. If it exceeds If the value of the grounding resistance suppressor is reached, the adjustable grounding resistance suppressor is automatically adjusted up one gear. Each gear can adjust the resistance value of 0.5 times the rated grounding resistance, and its value is recorded as p, until the calculated sheath circulating current , record the number of times of increase as m and pre-output ,in , To increase the total grounding resistance value of the m-times pre-output; (3) Re-judgment Voltage The size of is the estimated voltage after the first resistor pre-adjustment calculation. At this time, the maximum voltage allowed by the system is set to ,if , then it ends directly, indicating that the current regulation does not meet the conditions for reducing the voltage, the grounding resistance , output , adjust the grounding resistance, and this adjustment is completed; (4) If , determine the current and The size of The maximum allowable sheath circulation value during this stage of adjustment is , automatically adjust the resistance down one gear when calculating, and judge the current size at this time. If , then the calculation ends, indicating that the current regulation does not meet the conditions for reducing the voltage, the grounding resistance , output , adjust the grounding resistance, and this adjustment is completed; (5) If and , adjust the resistance to a lower level. , return to step (3), continue to execute its judgment logic, and finally output , n is the number of times the resistance is lowered; It also includes a high-voltage same-phase parallel cable sheath circulating current adaptive suppression device, the device comprising: Resistive inductor suppressor, used to suppress sheath circulating current; Adjustable ground resistance suppressor to control sheath voltage while suppressing sheath circulating current; Control device, used to collect electrical quantity information, send signals through logical judgment, and realize the switching of resistors; One end of the resistance-inductance suppressor is connected to the sheath end of each phase cable, and the other end of the resistance-inductance suppressor is connected to one end of the adjustable grounding resistance suppressor, and the other end of the adjustable grounding resistance suppressor is grounded; the control device is composed of an electrical quantity acquisition unit for collecting voltages at both ends of the adjustable grounding resistance suppressor, a signal generator for controlling the closing / closing of a switch in the adjustable grounding resistance suppressor, and a central controller CPU; The resistance-inductance suppressor is divided into three routes, the first route is composed of a resistor R11 and an inductor X11 connected in series, the second route is composed of a resistor R12 and an inductor X12 connected in series, and the third route is composed of a resistor R13 and an inductor X13 connected in series. The resistor R11 is connected to the sheath end of the C-phase cable, the resistor R12 is connected to the sheath end of the B-phase cable, and the resistor R13 is connected to the sheath end of the A-phase cable. One end of the inductor X11, the inductor X12, and the inductor X13 are connected in parallel; The adjustable grounding resistance suppressor is composed of resistors R1, R2, R3, and switches S1, S2, S3. One end of the resistor R1 is connected to the resistance-inductance suppressor. The resistors R1, R2, R3 are connected in series in sequence. The other end of the resistor R3 is grounded. The switch S1 is connected in parallel to the resistor R1, the switch S2 is connected in parallel to the resistor R2, and the switch S3 is connected in parallel to the resistor R3.

2. The method for adaptively suppressing sheath circulating current of high-voltage in-phase parallel cables according to claim 1 is characterized in that: The electrical quantity acquisition unit adopts a voltage transformer, and the voltage transformer is installed at both ends of the adjustable grounding resistance suppressor.

3. The method for adaptively suppressing sheath circulating current of high-voltage in-phase parallel cables according to claim 1 is characterized in that: The signal generator adopts a relay.

4. The method for adaptively suppressing sheath circulating current of high-voltage in-phase parallel cables according to claim 1 is characterized in that: The output end of the electrical quantity acquisition unit is connected to the signal input end of the central controller CPU, and the signal output end of the central controller CPU is connected to the signal input end of the signal generator.

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