JP5039985B2 - Transformer type superconducting fault current limiter - Google Patents

Description

  The present invention relates to a transformer-type superconducting fault current limiter that suppresses fault currents in a power system, and in particular, the transition from a superconducting state to a normal conducting state of a superconductor for performing a current limiting operation can be freely performed by a control current. The present invention relates to a transformer type superconducting fault current limiter that can be used.

  The liberalization of electric power and the introduction of distributed power sources are global trends, and consumers are welcomed by introducing the principle of competition and lowering the price of electricity. In addition, the increase in capacity of IPP (Independent Power Producer) due to the liberalization of electric power, and in the self-supporting regional power network that is expected to become popular in the future, wind power, solar power, fuel cells, etc. Various distributed power sources are expected to be used.

  On the other hand, however, various dangers have been pointed out when such a self-supporting regional power network is connected to a power company's power grid. In other words, the current power transmission facilities are controlled so that the stability of the system is maintained even if a failure occurs somewhere, but the connection of regional networks composed of such new power facilities and distributed power sources is not possible. If it increases, the control area may be exceeded in some cases, the risk of the entire power system increases, and in the unlikely event of an accident, the entire system may become unstable, leading to a large-scale power outage.

  For example, as shown in FIG. 10, when the power system connected to the power plants 20Ga and 21Gb of the electric power company is connected to such an IPP power supply 24G0 and 25G1 and a self-supporting local power network having the IPP power supply 26G2 inside. When an accident occurs in 25G1 or 26G2, power consumption areas A and B connected to the power system are also affected.

  When an accident occurs in the power system, the voltage at the accident point is close to zero, and a short-circuit current or ground current that is one digit larger than usual flows from the power generation side to that point. In order to prevent damage to the system equipment due to this current, the fault point is usually separated from the system by a circuit breaker. However, the circuit breaker takes about 0.1 second to complete the circuit shut-off after receiving a command from the central command station. This means that a fault current flows through the system for a short period of time, and the circuit breaker has a rated current and cannot be used when a current exceeding the rating flows. Therefore, when using a circuit breaker, the equipment must be arranged so that the accident current does not exceed its capacity.

In order to avoid these problems, it is necessary to make the circuit breaker technology more reliable and faster than before, but the existence of a current limiter that suppresses the fault current for a short time that the circuit breaker cannot handle is extremely important. It has become. That is, also in the system shown in FIG. 10, an autonomous distributed system having a circuit breaker and current limiters (FCL) 10 ₃ , 10 ₄ connected to a system connecting power plants 20Ga, 21Gb, or having IPP power supplies 25G1 and 26G2 27 is connected to the power system via the current limiters 10 ₁ , 10 ₂ , the influence of the failure does not reach the entire area.

  However, the current limiter has little merit for the electric power company itself. In addition, because it is a series device, a voltage drop occurs, and a power semiconductor element is required to control a large current, which makes the device expensive, and conversely, an inexpensive non-semiconductor element type current limiter has a current limiting operation. There are problems such as inability to control freely. Also, when power semiconductor elements are used for current limiters, the elements are expensive, so there are few examples of using current limiters only, and they are usually used with circuits that control all parameters such as phase, frequency, voltage, and current. Is common. If only the current limiter circuit is composed of power semiconductor elements such as SCR, IGBT, GTO, etc., it is a method to suppress the fault current so that it flows through the bypass resistance during current limiting operation using a bypass resistor. If an expensive power semiconductor element is used only for countermeasures against accidents, economic efficiency cannot be established.

  Therefore, current limiters that do not use power semiconductor elements are attracting attention. For example, as the current limiters that do not use the simplest semiconductor elements, there are reactors having a value of about several mH connected in series. This reactor is also called a current-limiting reactor, and it is usual to provide a gap in the yoke so that magnetic saturation does not occur. However, since the current-limiting reactor always causes a voltage drop, it is necessary to increase the voltage of the power source accordingly.

  Current limiting devices that do not cause a voltage drop during normal operation include arc-driven current limiting devices and superconducting current limiting devices. An arc-driven current limiter is basically a circuit breaker with a bypass resistance. The fault current is interrupted by the circuit breaker, and the arc generated at that time is erased while the current is passed to the bypass circuit to suppress the fault current. It is a method to do. In the case of this arc drive type current limiting device, it is easy to reduce the size and weight, and since it operates at room temperature, a small-scale one is already in practical use. However, it is often used in systems that do not lead to major accidents even if the shutoff operation is unsatisfactory due to the mechanical shutoff operation.

  One superconducting fault current limiter uses the critical current characteristics of superconductors, and is zero resistance if the current is below the critical current value, but if an excessive current above the critical current value flows, the superconductor is transferred to normal conduction. The generated resistance suppresses the fault current. The superconducting fault current limiter has a self-safe function that always operates in a current limiting state regardless of the malfunction of the equipment, including the cooling system, and is highly reliable. A current limiting device has been proposed. Among them, typical ones are a resistance dislocation type current limiter that operates by directly passing a current through the superconductor, and a transformer type superconducting current limiter that causes the superconductor on the secondary side of the transformer to perform normal conduction transition. .

  Although the resistance dislocation type superconducting fault current limiter is simple in structure and principle, high voltage is applied to the superconductor, so the problem of low-temperature electrical insulation is always the most important issue. Therefore, liquid nitrogen cooling with a uniform density is used as the coolant. However, during current limiting operation, the superconductor is always in a gas-liquid mixed state due to the heat generated by the superconductor, so it is necessary to ensure electrical insulation with a solid insulator such as ceramics or FRP, making it difficult to design a cryostat. In the transformer type superconducting fault current limiter, a high voltage is not applied to the superconductor, so that the problem of low temperature electrical insulation can be avoided.

  The superconducting fault current limiter has a self-safe function and is highly reliable. However, since the current limiting operation is determined only by the critical current value of the superconductor, the current limiting operation setting conditions cannot be freely adjusted and controlled with the conventional methods. There is inconvenience. In the case of an air core transformer, there may be a method of adjusting the current coupling operating condition by adjusting the magnetic coupling of the primary coil and the secondary coil, but with such an adjustment method, the influence of the mutual impedance cannot be completely cancelled. Even during normal operation, a voltage drop always occurs and the superconducting fault current limiter is lost.

  For such a transformer type superconducting fault current limiter, for example, in Patent Document 1, a primary coil is fixedly installed in a heat insulation tank, and a secondary coil can be moved up and down by a secondary coil suspension flange and a secondary coil suspension rod. The current limiter is configured to adjust the operating current as a current limiter by moving the secondary coil in the axial direction with respect to the primary coil while being cooled with a refrigerant.

  Further, in the transformer type current limiting method and current limiter disclosed in Patent Document 2, the primary side is set to a high voltage and the secondary side is set to a low voltage using a normally conducting transformer, and the transformer On the secondary side, a high-current superconducting oxide thin-film current-limiting element having a high critical current density and a high resistivity during normal conduction made on a large-area insulator substrate is connected, and high-voltage electrical insulation is performed at room temperature. The transformer primary side coil is assigned the control action of the secondary side low voltage and large current to the superconducting current limiting element. The secondary current increases due to an increase in the primary current due to the accident, and a large impedance is generated on the primary side when the secondary superconductor changes from superconducting to normal conducting. Current limiting operation, reducing the thermal load on the superconducting element and reducing the amount of current limiting element using an expensive large-area superconducting thin film as much as possible, realizing a low-cost current limiter that can handle high voltages I can do it.

  Further, although the present applicant does not have the structure of the current limiter itself, in Patent Document 3, for example, in order to increase the critical current of the oxide high-temperature superconductor, the liquid component and the solid content are mixed for cooling the superconducting current limiter. It is proposed to use a slush refrigerant.

  Furthermore, Patent Document 4 shows an inductive current limiter that utilizes impedance changes due to phase transition of a superconducting material, and a relatively high resistance when a voltage equal to or lower than a predetermined voltage is applied. Proposed a fault current limiter that has a characteristic that the resistance value decreases rapidly, for example, a series circuit of a non-linear resistance element such as a varistor and a resistor, and an inductive current limiter and a series circuit connected in parallel Has been.

Japanese Patent Laid-Open No. 11-089085 JP 2002-262450 A JP 2006-052921 A JP 2006-295994 A

  However, the current limiter disclosed in Patent Document 1 requires a mechanism that moves the secondary coil in the axial direction with respect to the primary coil while being cooled with the refrigerant, and adjusts the operating current as the current limiter. It is possible to do this, but the configuration becomes complicated, and the voltage drop during normal operation cannot be reduced to zero. The current limiter disclosed in Patent Document 2 is also difficult to freely set and adjust the current limiting operating point, and the secondary current flowing in the superconducting thin film is limited to a small value immediately after the normal conducting transition. However, it takes some time to return from normal conduction to superconductivity.

  Furthermore, the apparatus disclosed in Patent Document 3 relates to a cooling method for a superconducting current limiter for increasing the critical current of an oxide high-temperature superconductor, and does not relate to the structure of the current limiter. The current limiting device is a combination of an inductive current limiting device and a non-linear resistance element, and there is no disclosure regarding the structure of the current limiting device itself.

  Therefore, in the present invention, the problem of low-temperature electrical insulation can be avoided with a simple and inexpensive configuration, and the current limiting operation setting conditions can be freely adjusted and controlled, and the current limiting operation is shifted from the superconducting state to the normal conducting state. It is an object to provide a transformer type superconducting current limiter that can return the superconductor from the normal conducting state to the superconducting state in a short time after the above.

In order to solve the above problems, the transformer type superconducting fault current limiter according to the present invention is
A primary side of a transformer wound with a power conductor connected to the power system, and a secondary side of a transformer placed in a superconducting environment around which a superconductor wire is wound. In a transformer type superconducting fault current limiter that performs current limiting operation with the primary side impedance generated by the transition from the superconducting state to the normal conducting state of the secondary superconductor wire due to abnormal current,
The superconductor wire on the secondary side of the transformer is a one-turn annular wire, and is alternately wound around a meander structure, and the next one-turn annular wire from the connection point with another one-turn annular wire adjacent to the one-turn annular wire. The distance between the right and left to the connection point with respect to is substantially the same distance.

  Thus, by using the one-turn annular wire as the superconductor wire on the secondary side of the transformer, each one-turn annular wire operates in parallel with respect to the annular current of the transformer secondary circuit. The current limiting operation can be performed without affecting.

  The transformer-type superconducting fault current limiter includes a control current circuit that detects an abnormality in the power system and changes the secondary superconductor to a normal conducting state in series with the plurality of one-turn annular wires having the meander structure. When a control current is supplied to the secondary superconductor, the control current flows through each one-turn annular wire from the input point to the connection point to the other one-turn annular wire. Therefore, the secondary superconductor can be transferred to the normal conducting state without affecting the annular current of the transformer secondary circuit, that is, without affecting the transformer operation, The transformer type superconducting current limiter can freely control the current limiting operating point.

  The control current circuit is turned ON by an abnormal current detector that detects an abnormality of the power system, a pulse current supply source, and an abnormal current detection result of the power system by the abnormal current detector, and the pulse current supply source A switch circuit that sends a pulse current from the superconductor one-turn annular wire, the control current circuit detects an abnormality in the power system, an abnormal current detector, a high-frequency current source, and the abnormal current detector The secondary superconductor is normally conducted with a very simple circuit by switching on the abnormal current detection result of the power system by the switch circuit and sending the high-frequency current from the high-frequency current source to the superconductor one-turn annular wire. It can be transferred to a state.

  Furthermore, the secondary superconductor wire is made in a superconducting state by a slush refrigerant in which a liquid component and a solid component are mixed so that, for example, slush nitrogen, slush / argon, slash / neon coexisting with solid / liquid / gas When slush, hydrogen, etc. are used, for example, slush nitrogen has a temperature of about 63 k, which is lower than that of liquid nitrogen of 77 k, and the critical current of the superconductor increases by about 50% compared to liquid nitrogen. When an alternating current is passed through the superconductor, hysteresis loss occurs in the superconductor as if a finite resistance exists. However, if the flowing current is the same, the AC loss can be reduced by about 40% in the slush nitrogen cooling operation.

In the preferred embodiment of the present invention, the superconductor is an oxide high temperature superconductor, and the superconductor is YBa ₂ Cu ₃ O _x or Bi ₂ Sr ₂ Cu ₃ O _x .

  As described above, the transformer-type superconducting fault current limiter according to the present invention uses a one-turn annular wire as the superconductor wire on the secondary side of the transformer. The annular wires operate in parallel, and the current limiting operation can be performed without affecting the transformer operation. In addition, since a plurality of one-turn annular wires have a meander structure and a control current circuit is connected, the current-limiting operating point for transitioning the superconductor wire on the secondary side of the transformer to the normal conducting state can be freely controlled by the control current. The secondary superconductor can be arbitrarily transferred to the normal conducting state without affecting the transformer operation, and the current limiting operation setting conditions can be freely adjusted and controlled.

  In addition, by using a slush refrigerant mixed with liquid and solid components to cool the superconductor wire on the secondary side of the transformer, it returns from the normal conducting state to the superconducting state after the current-limiting operation is performed. It is possible to provide a transformer type superconducting fault current limiter that can be performed in a short time, and that avoids the problem of low-temperature electrical insulation with a simple and inexpensive configuration.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a diagram showing a basic configuration of a transformer type superconducting fault current limiter 10 according to the present invention. FIG. 2 is a one-turn annular wire (hereinafter referred to as one turn) wound around a magnetic yoke 19 in the transformer type superconducting fault current limiter 10. (A) is a diagram for explaining the concept of (13), (A) is a view of each one-turn coil 13 as viewed from the top, for convenience of explanation of the current flow in each one-turn coil 13, (B) is FIG. 3 is an oblique view of the one-turn coil for explaining the current flow. FIG. 3 is a block diagram of an example of the control current circuit 16 in the transformer type superconducting fault current limiter 10 for transferring the superconductor one-turn coil 13 to the normal state. FIG. 4A shows a case where a high frequency current circuit is used, and FIG. 5B shows a case where a capacitor discharge method is used.

  In the figure, 10 is a transformer type superconducting fault current limiter according to the present invention, 11 is a secondary side one-turn coil 13 wound around a magnetic yoke 19, and is placed in a superconducting state, for example, slush nitrogen, slash argon, slash A cryostat that cools using a slush refrigerant 12 in which a liquid component such as neon, slush and hydrogen and a solid component are mixed, 14 is an electric power system connected to the primary side of the transformer, and 16 is a transformer type superconductivity according to the present invention. Control current circuits 17 and 18 for forcibly transferring the secondary one-turn coil 13 in the current limiter 10 to the normal conducting state are wirings for the control current.

In the transformer type superconducting fault current limiter according to the present invention, the power system 14 is connected to the primary winding coil 15 in the magnetic yoke 19 constituting the transformer, and the secondary side (low voltage side) is shown in FIG. As shown, high-temperature superconductivity such as YBa ₂ Cu ₃ O ₇ superconductor tape wire (Y-based superconducting tape wire) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x tape wire (Bi-based superconducting tape wire). A plurality of _one- turn coils 13 ₁ , 13 ₂ , 13 ₃ ,... 13 _n made of a body or a thin film high-temperature superconductor are wound, and a control current circuit 16 is connected in series.

A plurality of one-turn coils 13 ₁ , 13 ₂ , 13 ₃ ,... 13 _n on the secondary side (low-voltage side) of the transformer are shown in FIG. 13 as can be seen from Figure 2 viewed from oblique (B), for example one-turn coil 13 ₁ of the control current lines 13a to the one-turn coil 13 ₂ adjacent to the connection point 17 to the circuit 16, the wiring 13a and the next Wantan wire 13b of the coil 13 _3, ... are shifted alternately approximately 180 degrees each position, i.e. the distance between the left and right from the connection point 17 to the connection point 13a, the distance between the left and right wiring 13a to the wire 13b, ..., respectively It is connected to the meander structure so as to be substantially equidistant.

Therefore, the current fed from the control current circuit 16 to the one-turn coil 13 ₁ wiring 17 toward the wiring 13a from the one-turn coil 13 of the _input terminal 17 is divided into right and left sides, and flows through a path indicated by arrow 30 ₁ following one turn even coil 13 _2, like ... a path indicated by arrow 30 ₂ toward the wiring 13b is divided into left and right sides, so on, each one-turn coil _{13 1,} 13 2, ₁₃ 3, ... 13 _n flows through the left and right halves, and returns from the wiring 18 to the control current circuit 16.

Therefore, the _one- turn coils 13 ₁ , 13 ₂ , 13 ₃ ,... 13 _n are annular currents induced by the primary current indicated by 31 in FIG. On the other hand, since each one-turn coil 13 ₁ , 13 ₂ , 13 ₃ ,... 13 _n operates in parallel, the transformer operation is not affected, and the superconductor constituting the one-turn coil 13 is connected to the control current circuit 16. It is possible to transition from the superconducting state to the normal conducting state with a small control current sent from the.

Now, the transformer composed of the magnetic yoke 19 in the transformer type superconducting fault current limiter 10 is an ideal transformer, and the primary self-inductance of the primary winding coil 15 is L ₁ , and the conductor resistance is r ₁ , 2 The secondary side self-inductance of the secondary one-turn coil 13 is L ₂ , the resistance of the _one- turn coil 13 during normal conduction is Rx, the mutual inductance of L ₁ and L ₂ is M, the magnetic coupling coefficient is k, the primary and secondary sides Where I ₁ and I _{2 are} the primary power supply voltage, E ₀ is the primary power supply voltage, and ω is the power supply frequency.

仮に１次と２次の磁気結合が１００％（ｋ＝１）であれば、この（２）式はさらに簡単に下記（３）式となる。

If the above equation (1) is solved by substituting dI / dt = jωI, the primary-side impedance Z ₁ can be obtained by the following equation (2).

If the primary and secondary magnetic couplings are 100% (k = 1), this equation (2) can be further simply expressed by the following equation (3).

Here, if the secondary side is in a superconducting state, since Rx = 0, Z ₁ = r ₁ . In general, r ₁ is sufficiently small so that if ignored, Z ₁ ≈0 and no voltage drop occurs on the primary side. However, when the secondary side superconducting one-turn coil transitions from the superconducting state to the normal conducting state and Rx ≠ 0, the impedance of equation (3) appears, and a voltage drop of ΔV = Z ₁ · I ₁ occurs on the primary side. Suppress the fault current.

Further, the transformer type superconducting fault current limiter 10 according to the present invention is a slush refrigerant 12 in which a liquid component and a solid component are mixed to cool the cryostat 11 for bringing the secondary one-turn coil 13 into a superconducting state. Use nitrogen, slash / argon, slash / neon, slash / hydrogen, etc. Of these, normal liquid nitrogen is 77k, but slush nitrogen in which liquid and solid are mixed in this way is a 63k liquid in a triple point state. For example, the horizontal axis represents entropy and the vertical axis represents temperature (unit: As shown in FIG. 4 showing k), the heat of fusion from the point a in the solid region to the point b in the liquid region, and the supercooling enthalpy of (h _c −h _b ) between the evaporation point h _c and the liquefaction point h _b Since it can use all of the amount of latent heat of vaporization, and further TΔS, it has a large cooling capacity.

In the transformer type superconducting fault current limiter 10, an alternating current always flows through the secondary superconductor. However, when alternating current flows through the superconductor, the superconductor has a hysteresis loss as if a finite resistance exists. appear. The hysteresis loss is also known as AC loss, the superconductor having a thickness of [delta], the maximum current value I _m, Pac AC loss, the critical current value Jc, when the frequency is f, Pac AC loss below (4) It can be expressed by a formula.

From equation (4), AC loss Pac is proportional to the third power of the frequency f and the maximum current I _m, but understood to be inversely proportional to the critical current value Jc, slush nitrogen as described above 63k and liquid nitrogen 77k The critical current density (unit: A / cm ² ) is taken on the horizontal axis and the temperature (unit: k) is taken on the vertical axis, and the critical current of, for example, YBa ₂ Cu ₃ O ₇ thin film high-temperature superconductor is shown. As shown in FIG. 5, the critical current density increases by about 50%, which means that if the current _Im is the same, the AC loss can be reduced by about 40% by the slush nitrogen cooling operation.

  On the contrary, if the critical current value for transferring the superconductor state to the normal state using the slush refrigerant 12 becomes large, a large fault current is required to start the current limiting operation. Therefore, in the transformer type superconducting fault current limiter 10 of the present invention, the fault current is detected, the superconducting one-turn coil 13 is shifted to the normal conducting state from this detection signal, and the control current circuit 16 is used to start the current limiting operation. The operation setting conditions of the fluency can be adjusted freely.

An example of the circuit is shown in FIG. 3, where (A) shows a case where the control current circuit 16 is constituted by a high-frequency current circuit, and (B) shows a case where it is constituted by a capacitor discharge system. First, in FIG. 3A, 13 is the secondary one-turn coil shown in FIGS. 1 and 2, 14 is a current from the power system, 40 is a high frequency power supply, 41 is a switching device such as a thyristor, and 42 is a power system. Overcurrent detector, 43 is a high frequency transformer, 44 is a capacitor, L _H1 and L _H2 are impedances on the primary side and secondary side of the high frequency transformer 43, and the secondary superconducting one-turn coil 13 has its resistance R Then, the secondary side impedances L _H2 and C in the high frequency transformer 43 are set to resonate with the frequency of the high frequency power supply 40.

  Now, when the current 14 from the power system becomes an abnormal current and is detected by the overcurrent detector 42 of the power system, the switching device 41 is turned on, and the high frequency from the high frequency power supply 40 is passed through the high frequency transformer 43 to the capacitor 44, It is applied to the secondary one-turn coil 13 connected in series to the meander structure in the transformer type superconducting fault current limiter 10 of the invention.

Then, as shown in the equation (4), is proportional to the cube of the high frequency of f and the maximum current I _m from the high frequency power source 40, AC loss Pac is generated in inverse proportion to the critical current value Jc, by the heat The one-turn coil 13 instantaneously shifts to a normal conduction state, and the impedance Z ₁ according to the equation (3) appears on the primary side, a voltage drop of ΔV = Z ₁ · I ₁ occurs, and the fault current is suppressed.

On the other hand, in the capacitor discharge method of FIG. 3B, 45 is a DC power source, 46 is a charging resistor, 47 is a capacitor, 48 is a switching device such as a thyristor, 49 is an overcurrent detector of the power system 14, and 50 is a current. A limiting resistor, where the voltage of the DC power source 45 is E ₀ , the capacitance of the capacitor 47 is C, the stored charge is Q, and the resistance value of the current limiting resistor 50 is R ₀ , the current i (t that flows through the one-turn coil 13 ) will Q = C × _{E 0,} so the following equation (5).
i (t) = (E ₀ / R ₀ ) exp (−t / CR ₀ ) (5)
Therefore, when the current limiting resistance 50R ₀ is set so that (E ₀ / R ₀ )> 2I _c when the critical current flowing in the superconducting one-turn coil 13 is I _c , the superconducting one-turn coil 13 becomes normal conducting from the superconducting state. It becomes a state.

Now, when the current 14 from the power system becomes an abnormal current and is detected by the overcurrent detector 49 of the power system, the switching device 48 is turned on and passes through the current limiting resistor 50 from the capacitor 47 and is transformed. Applied to the secondary one-turn coil 13 connected in series to the meander structure in the superconducting current limiting device 10. At this time, the current limiting resistor 50R ₀ is set as described above, a superconducting one-turn coil 13 becomes normal state from the superconducting state, the impedance Z ₁ by the equation (3) to the primary side appeared ΔV = Z ₁ · I ₁ voltage drop occurs, and the fault current is suppressed.

Next, a specific example configuration image when the transformer type superconducting current limiting device 10 according to the present invention is applied to a 66 kV, 100 A current limiting device will be described with reference to FIGS. 6 to 8. FIG. 6 is a schematic diagram of an example configuration when the transformer type superconducting fault current limiter 10 of the present invention is applied to a 66 kV, 100 A current limiter, and FIG. 7 is a transformer according to the present invention shown in FIG. FIG. 8 is a diagram showing a waveform of an operation simulation result of the transformer type superconducting fault current limiter 10 according to the present invention. FIG. 8A is a solid line with a current limiter. , The broken line is without a current limiter, (B) is a current limiting operation simulation using the control current circuit 16, the solid line is with a current limiter, the broken line is with no current limiter, 9 is a graph showing the AC loss of the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x tape wire.

First, in FIG. 6, 60 is a magnetic yoke, 61 is a primary high voltage coil, 62 is a gap, 63 is a cryostat for cooling the secondary one-turn coil shown by 13 in FIG. 1, and 64 is a step-down bushing. and 0.8m as shown small diameter of the magnetic yoke 60, for example, as 60 _1, the height 4.8 m, the center distance of the primary and secondary sides and 3.6 m.

As described above, assuming that the voltage class is 66 kV of the basic system, the current is 100 A, and the magnetic yoke 60 is used for the transformer for the current limiter 10, the iron loss and the exciting current are sufficiently small, and an ideal transformer can be realized. In order to operate as the current limiting device 10, a coil of N ₁ = 400 turns is wound around the primary side of the transformer with a high-voltage line conductor, and a commercially available 4 mm wide YBa ₂ Cu ₃ O is formed as a secondary superconducting _one -turn coil 13. ₇ tape wire (hereinafter abbreviated as Y tape wire) is used.

When the magnetic permeability 60 of the magnetic yoke 60 that is a magnetic material is 1000 and the maximum saturation magnetic flux value is 1.5 T, the primary inductance L ₁ is 1.97 (H), and the secondary inductance L ₂ is 12.2. 3 (μH), 100% magnetic coupling is unrealistic, so if it is 95%, the mutual inductance M is 46.8 (mH). The number of turns N ₂ on the secondary side of the transformer is 1 because it is one turn, and the primary side current is I ₁ (100 A × 2 ^1/2 (A) in the above case), and the secondary side superconducting one-turn coil 13. If slush nitrogen, which is one of the slush refrigerants, is used for cooling of the transformer, the current I ₂ on the secondary side of the transformer is expressed by the following equation (6) from the basic characteristic N ₁ I ₁ = N ₂ I ₂ of the transformer. Is done.
I ₂ ≈6 × 10 ⁴ (A) (6)

Assuming that the critical current I _c flowing through the one-turn coil 13 is 80 (A), from this I _c value and the equation (6), in order to function as the transformer type superconducting current limiter 10,
^{6 × 10 4/80 = 750} ( the)
Y-type tape wire is required, and the total width of the secondary winding is 750 × 0.004 = 3.0 (m) because the tape wire width is 4 mm. The height of the cryostat that accommodates such a Y-based tape wire is 3.2 m as specifically shown in FIG. 6, and the small diameter of the yoke 60 is 0.8 m as described above. Considering the thickness of the heat insulating material, the diameter of the one-turn coil is 0.85 m, the circumference is 2.67 m and 750, so a Y-type tape wire with a total length of about 2000 m is required.

  FIG. 7 shows an example of a current limiter test circuit using the transformer type superconducting current limiter 10 shown in FIG. 6, in which 70 is an overcurrent detector of the power system, and 71 is a load resistance (700Ω as an example). , 72 is a switching device for causing the current limiter 10 to perform a current limiting operation, 73 is a load resistance (100Ω as an example), and 74 is an ammeter (CT).

  In the test circuit shown in FIG. 7, since the switching device indicated by 72 is normally open, the input voltage of 66 kV is the load resistance indicated by the current limiter 10 and the ammeters (CT) 74 to 71, 73. 700 + 100Ω). In this state, at time t = 0.5 sec, the switching device 72 is closed so that the current does not pass through the load resistance 71 (700Ω), and the simulation result when the load resistance is changed to only 100Ω of 73 is shown. Is FIG. 8 (A).

  In FIG. 8A, the horizontal axis is time (unit: sec), the vertical axis is current (unit: A), the solid line is when the current limiter 10 is present, the broken line is when there is no current limiter, and the time t = A peak current of about 116 A until 0.5 sec. When there is no current limiter (broken line), a fault current exceeding 0.5 A flows from 0.5 sec to 1000 A. When the current limiter 10 is present (solid line), the current is 400 A. It is suppressed to the extent. The example shown in FIG. 8A is a case where a large accident is assumed, and in such a large current accident, it operates as a transformer type superconducting current limiter regardless of the operation of the control system.

  FIG. 8B shows the simulation result when the load resistance is changed from 800Ω to 600Ω at the same time t = 0.5 sec. In this case, the secondary current exceeds the critical current value of the superconductor. Therefore, it does not operate as a transformer type current limiter, and at time t = 0.6 sec, the overcurrent detector 70 of the power system sends a control current to the secondary superconductor to forcibly shift to the normal conducting state. In this case, the current limiting operation is performed.

  In FIG. 8B as well as in FIG. 8A, the horizontal axis is time (unit: sec), the vertical axis is current (unit: A), the solid line is the current limiter 10, and the broken line is the current limiter. In the case where there is no fault current, a peak current of about 116 A until time t = 0.5 sec. When a fault current without a current limiter (broken line) flows from 0.5 sec to over 150 A, the overcurrent detector 70 The control current is sent to the secondary superconductor to forcibly shift to the normal conducting state and the current limiting operation is performed to suppress the current to about 120A. In the actual current limiter, a time delay of 0.1 seconds does not occur, but in FIG. 8B, a time delay is set for easy understanding.

  Thus, in the transformer type superconducting fault current limiter according to the present invention, the current limiting operating point can be freely set and adjusted, and the setting adjustment problem of the conventional superconducting current limiter can be completely solved. become.

  As described above, the current limiter is originally a power device that suppresses a failure current of several cycles until the circuit breaker operates. However, since it generates heat during operation, a cooling time is required for restarting. In particular, in a resistance dislocation type fault current limiter that applies a high voltage to the superconductor, the temperature of the superconductor rises to room temperature with a few cycles of current limiting operation, and in the worst case when the breaker does not operate, the superconductor burns out. . In order to suppress the temperature rise, a method of releasing heat to a metal block having a large heat capacity can be considered, but it is difficult due to a problem in electrical insulation.

On the other hand, the transformer type superconducting fault current limiter as in the present invention is parallel to 750 assuming that the resistance of a 4 mm-wide tape wire is 0.75Ω, for example, in the case of the configuration shown in FIG. 6, the total resistance is Rn = 1 mΩ. It becomes. As the cooling system, a slush nitrogen cooling system that circulates as described above is assumed, and β = 1.0 (W / cm ² · k) is conservatively predicted from the nucleate boiling phenomenon of liquid nitrogen. Accordingly, the total surface area of the superconducting tape wire is S = 2.67 × 3. Since = 8 (m ² ), the heat transfer coefficient is α = S × β = 80000 (W / k).

The calorific value at the normal conduction transition is Q = Rn × I ₂ ² = Rn × (N ₁ I ₁ ) ^2, so in the case of FIG. 8A, Q = 0.001 × (400 × 100) ² = 1. 6 × 10 ⁶ (W) [Because the peak value of the current is used, the actual heat generation is smaller than this]. Since the temperature rise from T → ∞ is ΔT = Q / α, in the case of FIG. 8B, ΔT = 20 (k). Since the slush nitrogen temperature is 63 k, the tape wire stays within a temperature rise of about 83 k even if the current limiting operation is performed, and is below the critical temperature. That is, the current limiter 10 can be restarted instantly when the cause of the excessive current is removed.

In the case of a serious failure as shown in FIG. 8A, since I ₁ = 360 A, ΔT = 260 (k) from T → ∞, and the temperature rises to room temperature, but does not burn out. In other words, even in the worst case where the circuit breaker does not operate, the current limiting device can be restarted by recooling. Generally, a transformer type current limiter has a smaller temperature rise during operation than a resistance shift type current limiter. The reason for this is that the transformer type current limiter This is because a large amount of the superconducting tape wire is required. As a result, the cooling surface area is increased and the temperature rise is reduced.

  Finally, the power of the refrigerator necessary for actually producing the high voltage 66 kV, 100 A class transformer type superconducting fault current limiter shown in FIG. 6 will be discussed. In the case of the transformer type superconducting fault current limiter shown in FIG. 6, the heat load is heat penetration from the outside (at room temperature), AC loss of the superconductor, dielectric loss from the electrically insulating material, and the like. In the case of the transformer type superconducting fault current limiter shown in FIG. 6, the dielectric loss can be ignored because the superconductor operates at a low voltage.

Regarding the AC loss of the superconductor, when using a Y-based wire with a large critical current density, it is considered to be smaller than the Bi wire. From the graph of FIG. 9 showing the AC loss characteristics of the Bi tape wire having a width of 1 cm, the current is about ^{−3 −3} (W / m) when the current is 80 A. Further, since the total length of the tape wire is slightly over 2000 m, the AC loss of the proposed transformer type superconducting fault current limiter shown in FIG.

On the other hand, regarding the heat intrusion from the outside, the transformer type superconducting fault current limiter shown in FIG. 6 has no power lead such as a cable or a magnet, so only the heat intrusion from the cryostat is shown in FIG. Assuming that the cryostat has a vacuum heat insulation structure, and the surface is shielded by a Mylar sheet, assuming that the thermal emissivity of the Mylar sheet is 0.01, the total surface area is about 20 m ^2, so it is about 50 W. Most of the heat load is heat penetration due to radiation. Further, for example, assuming that the COP of the slush nitrogen refrigerator is 0.05, the power is 1 kW, and since the actual power system is a three-phase AC, three current limiters are required, so the total required power of the refrigerator Is about 3kW.

  According to the present invention, it is possible to provide a transformer type superconducting current limiter that can freely adjust and control the current limiting operation setting conditions with a simple and inexpensive configuration, and can be used as a current limiting device such as a self-supporting local power network. In the unlikely event of an accident, the entire system becomes unstable, leading to a large-scale power outage.

It is a figure which shows the basic composition of the transformer type superconducting fault current limiter 10 which becomes this invention. FIG. 2 is a diagram for explaining the concept of a one-turn coil 13 wound around a magnetic yoke 19 in the transformer type superconducting fault current limiter 10 according to the present invention. FIG. FIG. 5B is a view of the one-turn coils 13 as viewed from the upper side, and FIG. 5B is a view of the one-turn coils as viewed obliquely in order to explain the current flow. In the transformer type superconducting fault current limiter 10 according to the present invention, it is a block diagram of an example of a control current circuit 16 for transferring the superconductor one-turn coil 13 to the normal conduction state, (A) is configured by a high-frequency current circuit, (B) shows the case of the capacitor discharge method. It is the graph which showed the cooling capacity of slush nitrogen which is a solid-liquid mixed fluid. YBa is a graph showing the temperature dependence of the critical current of ₂ Cu ₃ O ₇ thin superconductor. It is an example configuration image figure at the time of applying the transformer type superconducting fault current limiter of the present invention to a 66 kV, 100A current limiter. It is an example of a test circuit using the transformer type superconducting fault current limiter according to the present invention shown in FIG. The operation simulation result of the transformer type superconducting fault current limiter 10 according to the present invention is a diagram showing the system. (A) is when the solid line is with the current limiter, and when the broken line is without the current limiter, (B) is In the current limiting operation simulation by the control current circuit 16, the solid line indicates the case with a current limiter, and the broken line indicates the case without a current limiter. It is a graph showing the AC loss of the tape wire of _{Bi 2 Sr 2 Ca 2 Cu 3} O x. It is a figure which shows the image which shows the position which uses the transformer type superconducting fault current limiter of this invention in an electric power system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transformer type superconducting fault current limiter 11 Cryostat 12 Slash nitrogen 13 Secondary side one turn coil 14 To power system 15 Transformer primary side winding coil 16 Control current circuit 17, 18 Control current wiring 19 Magnetic yoke

Claims (7)

A primary side of a transformer wound with a power conductor connected to the power system, and a secondary side of a transformer placed in a superconducting environment around which a superconductor wire is wound. In a transformer type superconducting fault current limiter that performs current limiting operation with the primary side impedance generated by the transition from the superconducting state to the normal conducting state of the secondary superconductor wire due to abnormal current,
The superconductor wire on the secondary side of the transformer is a one-turn annular wire, and is alternately wound around a meander structure, and the next one-turn annular wire from the connection point with another one-turn annular wire adjacent to the one-turn annular wire. A transformer-type superconducting fault current limiter, characterized in that the left and right distances to the connection point are substantially the same distance.   In the transformer-type superconducting fault current limiter, a control current circuit that detects an abnormality in the power system and changes the secondary superconductor to a normal conducting state is connected in series to the plurality of one-turn annular wires having the meander structure. The transformer-type superconducting fault current limiter according to claim 1, wherein   The control current circuit is turned ON according to an abnormal current detection result of the power system by the abnormal current detector, an abnormal current detector that detects an abnormality of the power system, a pulse current supply source, and the pulse current supply source. The transformer-type superconducting fault current limiter according to claim 2, comprising a switch circuit for sending a pulse current to the superconductor one-turn annular wire.   The control current circuit is turned on by an abnormal current detector for detecting an abnormality in the power system, a high-frequency current source, and an abnormal current detection result of the power system by the abnormal current detector, and a high-frequency current from the high-frequency current source The transformer-type superconducting fault current limiter according to claim 2, comprising: a switch circuit that sends a current to the superconductor one-turn annular wire.   The transformer-type superconducting fault current limiter according to any one of claims 1 to 4, wherein the secondary superconductor wire is put in a superconducting state by a slush refrigerant in which a liquid component and a solid component are mixed.   6. The transformer type superconducting fault current limiter according to claim 1, wherein the superconductor is an oxide high temperature superconductor. The _{superconductor,} YBa 2 _Cu 3 _{O x} or _Bi 2 _Sr 2 _Cu 3 _{O x} transformer superconducting fault current limiter of claim 6, characterized in that the.

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