Design method of novel high-temperature superconducting current limiter applied to power supply and distribution system

Abstract

The invention discloses a design method of a novel high-temperature superconducting current limiter applied to a power supply and distribution system. The high-temperature superconducting current limiter is additionally arranged in a circuit of the power supply and distribution system, so that when a circuit connected with the current limiter is short-circuited, the current limiter is matched with a circuit breaker to cut off the circuit; comprising the following steps: based on parameters of a circuit connected with the current limiter, determining a wire material of a superconducting coil of the high-temperature superconducting current limiter, a wire diameter, a layer number of a coil winding and an optimal geometric dimension of the coil; designing a circuit connection structure and a refrigerating system of the high-temperature superconducting current limiter; and constructing an equivalent structure model comprising a power supply and distribution network circuit and the high-temperature superconducting current limiter based on the designed circuit structure, and verifying the current limiting effect of the current limiter by using the equivalent structure model. The transformation cost of a power grid is reduced, and the service life of electrical equipment is prolonged; the fault short-circuit current of the power transmission line can be limited quickly, stably and effectively, and a foundation is laid for solving the key technical problem of safe and stable operation of a power transmission network.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting current limiters, and in particular to a design method for a novel high-temperature superconducting current limiter applied to a power supply and distribution system. Background Art

[0002] As the capacity of the power system increases, it is a practical problem for the power system to fully and effectively limit the fault short-circuit current and reduce the breaking capacity of the circuit breaker. At present, when a fault occurs in the system, the short-circuit current is mainly cut off by a high-voltage circuit breaker. It is difficult to simply improve the breaking capacity of the circuit breaker both technically and economically. Moreover, it usually takes two or more cycles to complete the short-circuit current using a mechanical circuit breaker. If necessary, a current limiting device is required to cooperate with the circuit breaker, that is, the current limiting device is used to quickly control the short-circuit capacity within the breaking capacity W of the circuit breaker to ensure that the circuit breaker safely and reliably cuts off the fault line. In this way, the system equipment can be protected from the impact of large short-circuit current on the system and system equipment, and the service life of important equipment such as switchgear such as circuit breakers and transformers can be extended, bringing significant economic benefits to the power sector and users.

[0003] The superconducting current limiter can essentially be considered as an equivalent variable impedance, which is usually divided into two states: steady state and current limiting state. When the power grid is operating normally, the superconducting current limiter is in a steady state and the impedance is low because it will not affect the power grid; when a short circuit occurs in the power grid, the superconducting current limiter quickly changes from a steady state to a current limiting state, presenting a large reverse induced voltage and effectively limiting the current; when the fault is eliminated, the superconducting current limiter can be restored from the current limiting state to a steady state to ensure the normal operation of the power grid. By utilizing this characteristic of superconducting materials, it has no effect on the power system under normal conditions. When a short circuit occurs, the impedance can be rapidly increased, becoming an ideal fault current limiting device, namely a superconducting current limiter. The prior art publication number CN214204938U discloses a power plant substation based on an improved bridge-type high-temperature superconducting current limiter, wherein the improved bridge-type high-temperature superconducting current limiter is disclosed, and its power electronic module is composed of a rectifier bridge composed of power diodes, a current limiting resistor and its bypass switch device, a freewheeling circuit of a superconducting magnet, and a fault trigger unit. However, this prior art is applicable to power plant substations. How to apply the superconducting current limiter to the distribution network circuit, and how to set the superconducting current limiter that meets the corresponding working conditions according to the different conditions of the connected lines have become important factors in promoting the application of superconducting current limiters. Summary of the invention

[0004] 1. Technical problems to be solved:

[0005] In view of the above technical problems, the present invention provides a design method for a novel high-temperature superconducting current limiter applied to a power supply and distribution system.

[0006] 2. Technical solution:

[0007] A design method for a new type of high-temperature superconducting current limiter applied to a power supply and distribution system, characterized in that: the high-temperature superconducting current limiter is added to the circuit of the power supply and distribution system to realize that when a short circuit occurs in a line connected to the current limiter, the current limiter cooperates with a circuit breaker to cut off the circuit; specifically comprising the following steps:

[0008] Step 1: Obtain the circuit parameters connected to the current limiter; the circuit parameters include the rated voltage, bias current, and voltage cycle of the power supply and distribution network:

[0009] Step 2: Based on the circuit parameters, determine the wire material, wire diameter, number of layers of the coil winding, and optimal geometric dimensions of the superconducting coil of the high-temperature superconducting current limiter;

[0010] Step 3: Design the circuit connection structure and cooling system of the high temperature superconducting current limiter; the circuit connection structure includes: the connection between the power diode bridge, the superconducting coil, and the bias power supply;

[0011] Step 4: Based on the circuit structure of step 3, an equivalent structural model including a power supply and distribution network circuit and a high-temperature superconducting current limiter is constructed, and the current limiting effect of the current limiter obtained in step 3 is verified using the equivalent structural model.

[0012] Furthermore, step 2 specifically includes:

[0013] S21: Determine the minimum inductance value of the superconducting coil when the maximum energy storage value of the superconducting coil takes the minimum value according to the circuit parameters connected to the current limiter; the specific implementation process is:

[0014] The maximum energy storage Wm of a superconducting coil with inductance L is shown as follows:

[0015]

[0016] Where L represents the inductance of the coil; I Lm is the maximum current allowed to pass through the superconducting coil. It is the current in the superconducting coil when the circuit breaker is separated by n half cycles after the line fails. It is composed of the bias current I0 and the current increment nΔI, that is,

[0017] I Lm =I0+nΔI (2)

[0018] Where nΔI is the line voltage U=U after the fault occurs. m sin(kt) is caused by the sinusoidal rectified voltage applied to the superconducting coil in n half cycles; the increment of the coil current in half a cycle is:

[0019]

[0020] Where T is the period of the sinusoidal voltage of the line voltage, U a is the average value of the line voltage U within half a cycle:

[0021]

[0022] By solving equation (1) to equation (4), we can get:

[0023]

[0024] There is only one variable L on the right side of formula (5), so W m is a function of L, given by dW m / dL=0 can get the maximum energy storage value W of the superconducting coil m When it is the minimum, the inductance of the superconducting coil is the minimum, and the minimum value L is:

[0025]

[0026] According to the above formula (6), when the maximum energy storage value of the superconducting coil takes the minimum value, the corresponding inductance value L of the superconducting coil is as shown in the above formula;

[0027] S22: determining the size of the superconducting wire cross section of the superconducting spiral coil corresponding to the inductance value L of the superconducting coil when the maximum energy storage value of the superconducting coil is the smallest;

[0028] From equation (2), equation (3) and equation (6), we can get the following equation:

[0029] I Lm >2I0 (7)

[0030] According to the inductance L value selected by formula (6), when a line fault occurs, the current interrupted by the circuit breaker, that is, the maximum current in the superconducting coil, is always equal to 2I0; formula (7) shows that, considering the overload operation of the line, the bias current I0>I m , I m represents the maximum current of the circuit where the current limiter is located, so I Lm >2I m ;

[0031] The maximum current I of the circuit where the current limiter is located Lm The central field strength of the solenoid coil is B0 when the solenoid coil is at the same time. The ratio of the height to the inner diameter of the solenoid coil is represented by β. By estimating β, the maximum field strength B of the superconducting coil can be approximately estimated by the following formula: m :

[0032] Bm / B0=1+0.64 / 4 β (8)

[0033] After determining the percentage of the short-sample critical performance that the superconducting wire of the superconducting coil is intended to achieve, according to the short-sample characteristics J of the superconductor used sc -B curve, and obtain the current density J of the superconductor sc (B m ), and thus calculate the superconducting coil current I Lm The cross-sectional area of ​​the superconductor required, the appropriate copper-to-superconductor ratio of the superconducting wire is selected, the cross-sectional size of the superconducting wire is determined, and the working current density J is calculated;

[0034] S23: Based on the voltage of the line where the current limiter is located and its withstand voltage level, the electrical properties of the insulating material are selected to determine the insulation thickness between turns and layers of the superconducting coil, thereby estimating the conductor filling factor λ of the superconducting coil; and then calculating the full current density λJ of the superconducting coil;

[0035] Assuming the number of turns of the superconducting coil is N, the current I Lm The total current density of the superconducting coil can be expressed as:

[0036]

[0037] Wherein, 2a1 is the inner diameter of the superconducting coil, 2a2 is the outer diameter of the superconducting coil, and 2b is the height of the superconducting coil;

[0038] S24: Since the cross-sectional dimensions and insulation dimensions of the superconducting wire of the superconducting coil have been selected, the average layer thickness ω of the winding of the superconducting coil can be determined; the winding thickness of the superconducting coil wound with m layers should be as shown in the following formula:

[0039] a2-a1=mω(10);

[0040] When the current in the circuit where the current limiter is located is the maximum, the central magnetic field of the solenoid coil can be expressed as

[0041]

[0042] Where, α = 2a2 / (2a1), β = 2b / (2a1); 2b is the height of the superconducting coil; μ0 is the vacuum magnetic permeability, which is a constant; λ represents the conductor filling factor;

[0043] The relationship between the inductance of a solenoid coil and its geometric dimensions is:

[0044]

[0045] Where, the unit of coil size is m; the unit of inductance is H; μ0 = 4π × 10 -7 H / m;

[0046] In the four formulas (9) to (12), there are five unknowns: 2a1, 2a2, 2b, N and m. If a value of m is selected, the geometric dimensions of a group of superconducting coils can be determined. For different m, the corresponding geometric dimensions of the superconducting coils can be obtained. A group of superconducting coils with different geometric dimensions can be obtained.

[0047] S25: Check the working point, thermal stability, electromagnetic stability and allowable stress of a group of superconducting coils with different numbers of layers respectively; select different central field strength values, fit the relationship curve between the field strength value of the central magnetic field of the solenoid coil and the weight of the superconducting wire, select the geometric dimensions of the superconducting coil corresponding to the minimum superconducting wire weight, and then obtain the optimal solution for the coil.

[0048] Furthermore, the circuit connection structure of the high temperature superconducting current limiter in step three adopts a single-phase bridge type high temperature superconducting current limiter with a DC bias power supply.

[0049] Furthermore, the equivalent structural model constructed in step four includes: a system simulation circuit of a single-phase bridge-type high-temperature superconducting current limiter with a DC bias power supply is set. Under the premise that the superconducting coil does not lose superconductivity, the system power supply U1 in the simulation circuit is set to 50V, the DC bias power supply U2 is set to 3V, and the inductance L of the superconducting coil is taken as 10mH; R1, L1 and R2, L2 are the impedances on the system side and the transmission line side respectively, R3 is the system load resistance, and the voltage divider resistance R4=R5=0.1nΩ is set; through simulation, it is possible to analyze the changes in the system line current before and after the fault when the current limiter is not connected and the changes in the system line current before and after the fault after the current limiter is connected, thereby verifying the current limiting effect of the current limiter.

[0050] 3. Beneficial effects:

[0051] The method discloses a design method for a new type of high-temperature superconducting current limiter used in a power supply and distribution system. Starting from the requirements of the line circuit to which the current limiter is connected, the size of the wire cross-section of the superconducting coil, the cross-section of the superconducting wire in the coil, the size of the insulator in the coil, and the weight control of the coil are designed in sequence according to the importance of the components. The superconducting coil as the most important factor in the superconducting coil is determined; then the overall circuit structure and the refrigeration system are determined according to the requirements of the circuit. The design method has strong applicability and can be designed according to the corresponding working conditions. In addition, since the design process is carried out in steps, the best solution can be selected according to the existing conditions. For example, in step 2, a suitable superconducting material can be selected according to the actual situation.

[0052] The introduction of high-temperature superconducting current limiters in distribution networks can not only significantly reduce the capacity of circuit breakers, greatly reduce the cost of power grid transformation and extend the service life of electrical equipment; it will also achieve rapid, stable and effective limitation of short-circuit currents caused by transmission line faults, laying the foundation for solving key technical problems in the safe and stable operation of transmission networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The overall flow chart of this design method;

[0054] Figure 2 A schematic diagram of a circuit structure in which a high temperature superconducting current limiter is applied to a power distribution network in a specific embodiment;

[0055] Figure 3 A partial cross-sectional view of a superconducting coil of a high-temperature superconducting current limiter designed in a specific embodiment;

[0056] Figure 4 It is a simulation circuit diagram of a novel high-temperature superconducting current limiter system in a specific embodiment;

[0057] Figure 5 It is a schematic diagram of a refrigeration system in a specific embodiment. DETAILED DESCRIPTION

[0058] The present invention will be described in detail below with reference to the accompanying drawings.

[0059] As attached Figure 1 As shown, a design method for a new type of high-temperature superconducting current limiter applied to a power supply and distribution system is characterized in that: the high-temperature superconducting current limiter is added to the circuit of the power supply and distribution system to realize that when a short circuit occurs in the line connected to the current limiter, the current limiter cooperates with the circuit breaker to cut off the circuit; specifically, the following steps are included:

[0060] Step 1: Obtain the circuit parameters connected to the current limiter; the circuit parameters include the rated voltage, bias current, and voltage cycle of the power supply and distribution network:

[0061] Step 2: Based on the circuit parameters, determine the wire material, wire diameter, number of layers of the coil winding, and optimal geometric dimensions of the superconducting coil of the high-temperature superconducting current limiter;

[0062] Step 3: Design the circuit connection structure and cooling system of the high temperature superconducting current limiter; the circuit connection structure includes: the connection between the power diode bridge, the superconducting coil, and the bias power supply;

[0063] Step 4: Based on the circuit structure of step 3, an equivalent structural model including a power supply and distribution network circuit and a high-temperature superconducting current limiter is constructed, and the current limiting effect of the current limiter obtained in step 3 is verified using the equivalent structural model.

[0064] Furthermore, step 2 specifically includes:

[0065] S21: Determine the minimum inductance value of the superconducting coil when the maximum energy storage value of the superconducting coil takes the minimum value according to the circuit parameters connected to the current limiter; the specific implementation process is:

[0066] The maximum energy storage Wm of a superconducting coil with inductance L is shown as follows:

[0067]

[0068] Where L represents the inductance of the coil; I Lm is the maximum current allowed to pass through the superconducting coil. It is the current in the superconducting coil when the circuit breaker is separated by n half cycles after the line fails. It is composed of the bias current I0 and the current increment nΔI, that is,

[0069] I Lm =I0+nΔI(2)

[0070] Where nΔI is the line voltage U=U after the fault occurs. m sin(kt) is caused by the sinusoidal rectified voltage applied to the superconducting coil in n half cycles; the increment of the coil current in half a cycle is:

[0071]

[0072] Where T is the period of the sinusoidal voltage of the line voltage, U a is the average value of the line voltage U within half a cycle:

[0073]

[0074] By solving equation (1) to equation (4), we can get:

[0075]

[0076] There is only one variable L on the right side of formula (5), so W m is a function of L, given by dW m / dL=0 can get the maximum energy storage value W of the superconducting coil m When it is the minimum, the inductance of the superconducting coil is the minimum, and the minimum value L is:

[0077]

[0078] According to the above formula (6), when the maximum energy storage value of the superconducting coil takes the minimum value, the corresponding inductance value L of the superconducting coil is as shown in the above formula;

[0079] S22: determining the size of the superconducting wire cross section of the superconducting spiral coil corresponding to the inductance value L of the superconducting coil when the maximum energy storage value of the superconducting coil is the smallest;

[0080] From equation (2), equation (3) and equation (6), we can get the following equation:

[0081] I Lm >2I0 (7)

[0082] According to the inductance L value selected by formula (6), when a line fault occurs, the current interrupted by the circuit breaker, that is, the maximum current in the superconducting coil, is always equal to 2I0; formula (7) shows that, considering the overload operation of the line, the bias current I0>I m , I m represents the maximum current of the circuit where the current limiter is located, so I Lm >2I m ;

[0083] The maximum current I of the circuit where the current limiter is located Lm The central field strength of the solenoid coil is B0 when the solenoid coil is at the same time. The ratio of the height to the inner diameter of the solenoid coil is represented by β. By estimating β, the maximum field strength B of the superconducting coil can be approximately estimated by the following formula: m :

[0084] Bm / B0=1+0.64 / 4 β (8)

[0085] After determining the percentage of the short-sample critical performance that the superconducting wire of the superconducting coil is intended to achieve, according to the short-sample characteristics J of the superconductor used sc -B curve, and obtain the current density J of the superconductor sc (B m ), and thus calculate the superconducting coil current I Lm The cross-sectional area of ​​the superconductor required, the appropriate copper-to-superconductor ratio of the superconducting wire is selected, the cross-sectional size of the superconducting wire is determined, and the working current density J is calculated;

[0086] S23: Based on the voltage of the line where the current limiter is located and its withstand voltage level, the electrical properties of the insulating material are selected to determine the insulation thickness between turns and layers of the superconducting coil, thereby estimating the conductor filling factor λ of the superconducting coil; and then calculating the full current density λJ of the superconducting coil;

[0087] Assuming the number of turns of the superconducting coil is N, the current I Lm The total current density of the superconducting coil can be expressed as:

[0088]

[0089] Wherein, 2a1 is the inner diameter of the superconducting coil, 2a2 is the outer diameter of the superconducting coil, and 2b is the height of the superconducting coil;

[0090] S24: Since the cross-sectional dimensions and insulation dimensions of the superconducting wire of the superconducting coil have been selected, the average layer thickness ω of the winding of the superconducting coil can be determined; the winding thickness of the superconducting coil wound with m layers should be as shown in the following formula:

[0091] a2-a1=mω(10);

[0092] When the current in the circuit where the current limiter is located is the maximum, the central magnetic field of the solenoid coil can be expressed as

[0093]

[0094] Where, α = 2a2 / (2a1), β = 2b / (2a1); 2b is the height of the superconducting coil; μ0 is the vacuum magnetic permeability, which is a constant; λ represents the conductor filling factor;

[0095] The relationship between the inductance of a solenoid coil and its geometric dimensions is:

[0096]

[0097] Where, the unit of coil size is m; the unit of inductance is H; μ0 = 4π × 10 -7 H / m;

[0098] In the four formulas (9) to (12), there are five unknowns: 2a1, 2a2, 2b, N and m. If a value of m is selected, the geometric dimensions of a group of superconducting coils can be determined. For different m, the corresponding geometric dimensions of the superconducting coils can be obtained. A group of superconducting coils with different geometric dimensions can be obtained.

[0099] S25: Check the working point, thermal stability, electromagnetic stability and allowable stress of a group of superconducting coils with different numbers of layers respectively; select different central field strength values, fit the relationship curve between the field strength value of the central magnetic field of the solenoid coil and the weight of the superconducting wire, select the geometric dimensions of the superconducting coil corresponding to the minimum superconducting wire weight, and then obtain the optimal solution for the coil.

[0100] Furthermore, the circuit connection structure of the high temperature superconducting current limiter in step three adopts a single-phase bridge type high temperature superconducting current limiter with a DC bias power supply.

[0101] Furthermore, the equivalent structural model constructed in step four includes: a system simulation circuit of a single-phase bridge-type high-temperature superconducting current limiter with a DC bias power supply is set. Under the premise that the superconducting coil does not lose superconductivity, the system power supply U1 in the simulation circuit is set to 50V, the DC bias power supply U2 is set to 3V, and the inductance L of the superconducting coil is taken as 10mH; R1, L1 and R2, L2 are the impedances on the system side and the transmission line side respectively, R3 is the system load resistance, and the voltage divider resistance R4=R5=0.1nΩ is set; through simulation, it is possible to analyze the changes in the system line current before and after the fault when the current limiter is not connected and the changes in the system line current before and after the fault after the current limiter is connected, thereby verifying the current limiting effect of the current limiter. Specific embodiment:

[0103] As attached Figures 2 to 5 Figures related to the high-temperature superconducting current limiter constructed using this method.

[0104] As attached Figure 2 In the embodiment shown, a bridge-type high-temperature superconducting current limiter is installed on the transmission line. When a fault current occurs, the current flowing through the new high-temperature superconducting current limiter increases instantaneously, and its inductor coil instantly generates inductive reactance to prevent the instantaneously increased fault current, while cooperating with the circuit breaker to cut off the power supply and distribution system circuit.

[0105] The standard withstand voltage level of the superconducting coil of the current limiter is determined according to the rated voltage of the line where the current limiter is located, the insulation material between turns and layers of the superconducting coil is selected, and the insulation thickness between turns and layers of the superconducting coil is determined according to the electrical properties of the insulation material, so as to calculate the conductor filling factor λ of the superconducting coil, and then calculate the total current density λJ of the superconducting coil. Figure 1 As shown, the specific design method includes the following steps:

[0106] Step 1: Obtain the circuit parameters connected to the current limiter; the circuit parameters include the rated voltage, bias current, and voltage cycle of the power supply and distribution network:

[0107] Step 2: Based on the circuit parameters, determine the wire material, wire diameter, number of layers of the coil winding, and optimal geometric dimensions of the superconducting coil of the high-temperature superconducting current limiter;

[0108] Step 3: Design the circuit connection structure and cooling system of the high temperature superconducting current limiter; the circuit connection structure includes: the connection between the power diode bridge, the superconducting coil, and the bias power supply;

[0109] Step 4: Based on the circuit structure of step 3, an equivalent structural model including a power supply and distribution network circuit and a high-temperature superconducting current limiter is constructed, and the current limiting effect of the current limiter obtained in step 3 is verified using the equivalent structural model.

[0110] As attached Figure 3 As shown, it is a partial cross-sectional view of the superconducting coil of the high-temperature superconducting current limiter designed in this embodiment; in the figure, 2a1 is the inner diameter of the superconducting coil, 2a2 is the outer diameter of the superconducting coil, and 2b is the height of the superconducting coil.

[0111] As attached Figure 4 : is a simulation circuit diagram of the new high-temperature superconducting current limiter system in this embodiment; under the premise that the superconducting coil does not lose superconductivity, it is assumed that a three-phase short circuit occurs to the ground when the simulation circuit runs for 25ms, that is, Figure 4The middle switch K is closed; the system power supply U1 in the circuit is 50V, the DC bias power supply U2 is 3V, the superconducting coil inductance L is 10mH, R1, L1 and R2, L2 are the impedances on the system side and the transmission line side respectively, R3 is the system load resistance, according to the requirements of the digital simulation software, R4 and R5 need to be set, and in this embodiment, it is set to R4 = R5 = 0.1nΩ. Because the three-phase circuit is symmetrical, this embodiment only analyzes one phase. This simulation will study and analyze the changes in the system line current before and after the fault when the current limiter is not connected and the changes in the system line current before and after the fault after the current limiter is connected, so as to verify the current limiting effect of the current limiter.

[0112] As attached Figure 5 As shown, it is a schematic diagram of the refrigeration system in the embodiment, which consists of current leads, GM dry refrigerator, primary and secondary cooling heads, high-temperature superconducting current leads, radiation screen, copper plate, and twisted wire harness. Since it is a prior art, it will not be described one by one.

[0113] Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A design method for a new high-temperature superconducting current limiter used in a power supply and distribution system, characterized in that: Wherein the high temperature superconducting current limiter is added to the circuit of the power supply and distribution system so that when a short circuit occurs in the line connected to the current limiter, the current limiter cooperates with the circuit breaker to cut off the circuit; The specific steps include: Step 1: Obtain the circuit parameters connected to the current limiter; the circuit parameters include the rated voltage, bias current, and voltage cycle of the power supply and distribution network: Step 2: Based on the circuit parameters, determine the wire material, wire diameter, number of layers of the coil winding, and optimal geometric dimensions of the superconducting coil of the high-temperature superconducting current limiter; Step 3: Design the circuit connection structure and cooling system of the high temperature superconducting current limiter; the circuit connection structure includes: the connection between the power diode bridge, the superconducting coil, and the bias power supply; Step 4: Based on the circuit structure of step 3, an equivalent structural model including a power supply and distribution network circuit and a high-temperature superconducting current limiter is constructed, and the current limiting effect of the current limiter obtained in step 3 is verified using the equivalent structural model.

2. The design method of a new type of high temperature superconducting current limiter applied to a power supply and distribution system according to claim 1 is characterized in that: Step 2 specifically includes: S21: Determine the minimum inductance value of the superconducting coil when the maximum energy storage value of the superconducting coil takes the minimum value according to the circuit parameters connected to the current limiter; the specific implementation process is: The maximum energy storage Wm of a superconducting coil with inductance L is shown as follows: Where L represents the inductance of the coil; I Lm is the maximum current allowed to pass through the superconducting coil. It is the current in the superconducting coil when the circuit breaker is separated by n half cycles after the line fails. It is composed of the bias current I0 and the current increment nΔI, that is, I Lm =I0+nΔI (2) Where nΔI is the line voltage U=U after the fault occurs. m sin(kt) is caused by the sinusoidal rectified voltage applied to the superconducting coil in n half cycles; the increment of the coil current in half a cycle is: Where T is the period of the sinusoidal voltage of the line voltage, U a is the average value of the line voltage U within half a cycle: By solving equation (1) to equation (4), we can get: There is only one variable L on the right side of formula (5), so W m is a function of L, given by dW m / dL=0 can get the maximum energy storage value W of the superconducting coil m When it is the minimum, the inductance of the superconducting coil is the minimum, and the minimum value L is: According to the above formula (6), when the maximum energy storage value of the superconducting coil takes the minimum value, the corresponding inductance value L of the superconducting coil is as shown in the above formula; S22: determining the size of the superconducting wire cross section of the superconducting spiral coil corresponding to the inductance value L of the superconducting coil when the maximum energy storage value of the superconducting coil is the smallest; From equation (2), equation (3) and equation (6), we can get the following equation: I Lm >2I0 (7) According to the inductance L value selected by formula (6), when a line fault occurs, the current interrupted by the circuit breaker, that is, the maximum current in the superconducting coil, is always equal to 2I0; formula (7) shows that, considering the overload operation of the line, the bias current I0>I m , I m represents the maximum current of the circuit where the current limiter is located, so I Lm >2I m ; The maximum current I of the circuit where the current limiter is located Lm The central field strength of the solenoid coil is B0 when the solenoid coil is at the same time. The ratio of the height to the inner diameter of the solenoid coil is represented by β. By estimating β, the maximum field strength B of the superconducting coil can be approximately estimated by the following formula: m : Bm / B0=1+0.64 / 4 β (8) After determining the percentage of the short-sample critical performance that the superconducting wire of the superconducting coil is intended to achieve, according to the short-sample characteristics J of the superconductor used sc -B curve, and obtain the current density J of the superconductor sc (B m ), and thus calculate the superconducting coil current I Lm The cross-sectional area of ​​the superconductor required, the appropriate copper-to-superconductor ratio of the superconducting wire is selected, the cross-sectional size of the superconducting wire is determined, and the working current density J is calculated; S23: Based on the voltage of the line where the current limiter is located and its withstand voltage level, the electrical properties of the insulating material are selected to determine the insulation thickness between turns and layers of the superconducting coil, thereby estimating the conductor filling factor λ of the superconducting coil; and then calculating the full current density λJ of the superconducting coil; Assuming the number of turns of the superconducting coil is N, the current I Lm The total current density of the superconducting coil can be expressed as: Wherein, 2a1 is the inner diameter of the superconducting coil, 2a2 is the outer diameter of the superconducting coil, and 2b is the height of the superconducting coil; S24: Since the cross-sectional dimensions and insulation dimensions of the superconducting wire of the superconducting coil have been selected, the average layer thickness ω of the winding of the superconducting coil can be determined; the winding thickness of the superconducting coil wound with m layers should be as shown in the following formula: a2-a1=mω (10); When the current in the circuit where the current limiter is located is the maximum, the central magnetic field of the solenoid coil can be expressed as Where, α = 2a2 / (2a1), β = 2b / (2a1); 2b is the height of the superconducting coil; 0 is the vacuum permeability, which is a constant; λ represents the conductor filling factor; The relationship between the inductance of a solenoid coil and its geometric dimensions is: Where, the unit of coil size is m; the unit of inductance is H; μ0 = 4π × 10 -7 H / m; In the four formulas (9) to (12), there are five unknowns: 2a1, 2a2, 2b, N and m. If a value of m is selected, the geometric dimensions of a group of superconducting coils can be determined. For different m, the corresponding geometric dimensions of the superconducting coils can be obtained. A group of superconducting coils with different geometric dimensions can be obtained. S25: Check the working point, thermal stability, electromagnetic stability and allowable stress of a group of superconducting coils with different numbers of layers respectively; select different central field strength values, fit the relationship curve between the field strength value of the central magnetic field of the solenoid coil and the weight of the superconducting wire, select the geometric dimensions of the superconducting coil corresponding to the minimum superconducting wire weight, and then obtain the optimal solution for the coil.

3. The design method of a new high temperature superconducting current limiter applied to a power supply and distribution system according to claim 2 is characterized in that: The circuit connection structure of the high-temperature superconducting current limiter in step three adopts a single-phase bridge-type high-temperature superconducting current limiter with a DC bias power supply.

4. The design method of a new type of high temperature superconducting current limiter applied to a power supply and distribution system according to claim 3 is characterized in that: The equivalent structure model constructed in step 4 includes: a system simulation circuit of a single-phase bridge-type high-temperature superconducting current limiter with a DC bias power supply. Under the premise that the superconducting coil does not lose superconductivity, the system power supply U1 in the simulation circuit is set to 50V, the DC bias power supply U2 is set to 3V, and the inductance L of the superconducting coil is 10mH; R1, L1 and R2, L2 are the impedances on the system side and the transmission line side respectively, R3 is the system load resistance, and the voltage divider resistance R4=R5=0.1nΩ is set; through simulation, it is possible to analyze the changes in the system line current before and after the fault when the current limiter is not connected and the changes in the system line current before and after the fault after the current limiter is connected, thereby verifying the current limiting effect of the current limiter.

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