KR950004299B1 - Apparatus to shield thermoelectronic for hyperconductive ac generator - Google Patents

Abstract

The narrow opening is made in the shielding screen of super conduction AC generator to improve thermior shielding characteristics. The super conduction AC generator includes a stator (110) and a rotor (200). To prevent inrush thermion from external, the stator is shielded by an external shielding unit (120) and the rotor (200) is shielded by an thermion shielding screen (230) which has X and Y directional narrow opening of 0.25 mm from the center.

Description

Thermo-electronic shielding device of superconducting alternator

1 is a view showing the structure of a general rotation field type superconducting alternator

2 is a view showing the typical rotor structure shown in FIG.

3 is a diagram showing the eddy current distribution when the rotor is in an asynchronous state in a conventional two-pole superconducting generator.

4 is a view showing a case in which a gap is formed in the hot electron shielding film according to the present invention.

(A)-(c) is a magnetic flux distribution map shown by the thermoelectromagnetic shielding film of the prior art and this invention.

6 to 11 are diagrams showing the autism characteristics of the superconducting alternator according to the present invention.

The present invention relates to a thermoelectromagnetic shield of a superconducting alternator, and more particularly, to a thermoelectromagnetic shield with improved electromagnetic shielding characteristics. As power demand increases, the demand for large capacity generators increases.

However, there is a limit to the unit capacity increase due to problems such as cooling technology and material strength.

In order to solve this problem fundamentally, a superconducting alternator using superconducting wires in the field winding has been proposed.

The superconducting generator currently being researched and developed is a rotating field type superconducting field winding unit 220 as shown in FIG. 1, a thermoelectric shielding membrane 230 as a rotor shield unit, an armature winding unit 110, and an outer shield unit 120. Are largely divided into

In FIG. 1, reference numeral 210 denotes a torque shield.

The dual superconducting field winding 220 and the rotor shield belong to the rotor 200 rotor, and the armature winding 110 and the outer shield 120 belong to the stator 100.

The superconducting alternator is considered to be the same as a conventional generator in view of the field winding of the rotor and the armature winding of the stator. However, the concrete structure is very different from the conventional generator because superconducting wire is used for the field winding.

Therefore, research on each part is continued and briefly explained as follows.

The superconducting wires currently commercially available in the superconducting field winding are NbTi and Nb ₃ Sn. Nb ₃ Sn is advantageous in terms of high criticality, but it is widely used because NbTi-based superconductors are easy to handle.

In addition, since there is no iron core in the field winding part, the magnetic field of the armature winding part is determined by the coil arrangement of the superconducting field winding. Therefore, there is a need for a coil arrangement that reduces harmonic components.

In general, a method of dividing a pole coil into several element coil rolls is widely used. A spiral wound field winding method (Vrestlnghouse method) and a race track type general electric method are used. have.

The field winding method plays an important role in the stability of superconducting wires in relation to the supporting structure of the field wires.

In order to keep the field winding of the superconducting generator at cryogenic temperature, it must be shielded thermally and magnetically.

For this heat shielding, a supporting steel pipe is installed between the superconducting field winding 22O and the stator 100, and the inside is kept in vacuum, but since there is heat loss due to radiation, the material having good thermal conductivity in the middle of the vacuum part is used. Let the lines fall on both ends.

On the other hand, electrically asynchronous magnetic flux such as inverse box due to unbalanced current in the armature, harmonic acceleration due to spatial harmonics in the armature winding 110, transient magnetic flux due to load variation, etc. is applied to the superconducting wire. Losses occur, which leads to a rise in the silver conduction rate of the superconductor wire, which leads to loss of superconductivity. The thermoelectron shielding film 230 serves to perform the above two functions.

In addition, a damper shell (damper shel1), which is a braking tube, is installed on the outer surface of the rotor to reduce vibration of the rotor when a sudden load change occurs in the generator.

On the other hand, the superconducting alternator does not need to use a magnetic material in the magnetic circuit in order to obtain an acceleration density of about 1 to 1.55 [T] necessary in the three armature winding 110 because the magnetoelectric force in the field is very large.

Therefore, the structure of the armature is very different from the current generator.

Between the armature windings there is no tooth of the silicon steel sheet to reduce the magnetic resistance of the magnetic circuit like in current generators.

Therefore, the armature winding 100 is manufactured separately and inserted into the yoke.

The outer shield 120 is made of an eddy current screen of copper or aluminum, or a laminated iron screen, which reduces the resistance of the magnetic circuit. It also serves to prevent.

The superconducting alternator, which is currently being researched and developed worldwide, shows the possibility of improving the efficiency, miniaturization, and capacity exceeding the capacity limit of the phase conductor generator, which is expected to be the next generation generator.

In addition, superconducting alternators can reduce the synchronous reactance, resulting in a system expansion effect.

However, due to the time constant of the thermoelectron shielding membrane of the superconducting alternator, the transient stability is almost equal to or lower than that of the current generator, so a countermeasure is required.

One of them is the adoption of the fast-acting method that enables the rapid change of the field voltage to improve the transient stability of the generator.

In order to respond to this fast-conducting superconducting generator, a superconducting wire that can withstand the excitation change must be used in the field winding, and at the same time, the magnetic flux generated by the field current change must pass through the shielding film easily.

Most superconducting generators studied so far employ a double structured shield as shown in FIG.

That is, the phase for the purpose of mechanical braking to the superconducting field winding 220 is a reverse electromagnetic shielding film for the purpose of coding the superconducting field winding 220 from the alternating magnetic field due to the imbalance or spatial harmonics of the damper shell 240 230).

This hot electron shielding film 230 has a relatively long time constant to shield the alternating magnetic field.

Therefore, like the shielding of the external magnetic field, the magnetic flux due to the change in the field current is also shielded by the thermo-electromagnetic shielding film 230, so that no rapid excitation is possible.

In recent years, generators that only shield heat and do not provide electromagnetic shielding have been studied.

In this case, since the alternating magnetic field generated in the armature winding 110 is directly transmitted to the superconducting field winding 220, there is a problem that an expensive superconducting wire having a low AC loss must be used.

In other words, the superconducting AC field field employing the fast response excitation method has a thermoelectron shielding membrane 230, which is a method of providing a quick change in the field voltage to control the field current to improve the transient stability. Even if it is changed to a degree, the change of the magnetic flux in the armature winding 110 is late, so it is difficult to improve the transient stability.

Therefore, in the superconducting generator with this method, it is necessary to change the field current at a higher speed than in the existing generator. This causes the field voltage to be very high, which causes the problem of winding insulation and increases the loss in the superconducting winding. Is also caused.

In addition, there is a method of employing a mechanical damper shell, but the superconducting alternator employing such a damper shell is connected to a turbine (not shown) by using the superconducting field wire 220 and the thermoelectron shielding membrane 230 as one rotor. In addition, a damper (i.e., an external rotor) is provided outside the internal rotor, and the structure can rotate freely.

In the generator of such a structure, when the accident occurs outside the field electricity generator, the external rotor rotates around the internal rotor and mechanically brakes, thereby improving the transient stability of the generator. However, since this structure has two rotors, there are some decisions that are not mechanically robust.

In addition, there is a method of improving the transient stability by providing a two-phase braking winding (that is, a third winding) in place of the damper in the generator employing the mechanical damper shell and controlling the voltage supplied to the winding.

Such a device has a good effect of improving transient stability, but has a complicated structure.

In the superconducting alternator adopting a heat shielding wire as in the fast excitation method, since the thermo-electromagnetic shielding film shields only heat and does not shield magnetic flux, the transient magnetic field caused by the armature winding 110 current is superconducting. Since the magnetic winding 220 directly affects, a large number of magnetic field changes occur in the superconducting field winding 220.

Therefore, the generator of this structure should use a low loss superconducting wire, the problem is that the price of the superconducting wire is expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting alternator thermoelectron shielding device which improves the electronic shielding characteristics while maintaining the inherent advantages of the superconducting alternator in order to solve such problems.

In order to achieve the above object, the superconducting alternator according to one aspect of the present invention is characterized by applying a soft electron shielding film having a gap.

Hereinafter, embodiments of the present invention will be described in detail.

2 is a view showing the heat flow of the rotor in the superconducting alternator shown in FIG.

1 and 2, the rotor 200 of the superconducting alternator basically has a superconducting field winding 220, which is mechanically coupled to the shaft via a torque shield 210.

The superconducting field winding 220 is cooled to cryogenic temperature using liquid helium. In order to reduce the consumption of the liquid helium, heat intrusion from the outside and loss in the superconducting field winding 220 should be reduced.

In FIG. 2, the cooling tube 211 is welded to the torque shield 210, in which the cryogenic gas helium passes, absorbing heat conducted axially through the torque shield, and thereby superconducting field winding 220 Saves the heat invading into). Using the vacuum shield between the torque shield 210 and the damper shell 240 to reduce the heat invaded by conduction or convection from the radial direction to the superconducting winding.

Even if the vacuum layer is provided as described above, the loss of heat in the superconducting field winding due to the asynchronous magnetic flux generated by the radiant heat penetrating through the vacuum layer and the armature current cannot be suppressed.

In order to solve such a problem, a hot electron shielding film 230 is usually installed in the middle of the vacuum layer.

The thermoelectron shielding film 230 is made of a material having high thermal conductivity and high electrical conductivity, and both ends thereof are welded at a temperature of about 70 [K] in the torque shield 210.

Accordingly, the radiant heat radiated from the damper shell 240 reaches the hot electron shielding film 230 and is conducted to both edges of the hot electron shielding film.

In addition, the asynchronous magnetic flux coming from the armature is shielded by the hot electron shielding film 230, thereby reducing the AC loss in the superconducting winding.

Improving the magnetic shielding characteristics of the thermo-electromagnetic shielding film 230 may prevent the asynchronous magnetic flux generated in the armature winding 110 from invading into the superconducting field winding 220, but the transient field magnetic flux generated by the superconducting field winding 220 may be controlled by the armature winding ( There is a large time delay to reach 110).

In other words. This will hamper the linear transient characteristics of the generator. As described above, by controlling the mutually opposite effects, the conventional superconducting generator sets the electrical time constant of the thermo-electromagnetic shielding film to about 1 to 2 seconds.

And the transient stability of the superconducting generator having a time constant of this degree is similar to the conventional phase-conducting field winding generator. Accordingly, the present invention provides a thermal transfer shielding film which can be selectively shielded while the side shielding maintains the same degree as that of the conventional thermal electron shielding film.

That is, when the external magnetic field reaches the hot electron shielding film, the electron shield generates an eddy current in the shielding film to prevent the external magnetic field from penetrating into the inside. Therefore, the eddy current path may be adjusted appropriately.

3 is an eddy current distribution when a rotor is asynchronous in a conventional two-pole superconducting generator.

Where the solid line is the eddy current path and the arrow indicates the direction of heat transfer.

The eddy current constitutes a closed circuit with a period of π. At this time, heat generated by external intrusion or eddy current is conducted to both ends in the axial direction.

4 shows a thermoelectron shielding film 230A of the present invention having a gap in a conventional thermal residue shielding film.

First, the gap is formed in the longitudinal direction at the center, and laterally in the transverse direction to reduce the flow of eddy current.

In this case, the eddy current is greatly reduced while the heat flow remains the same as before. Therefore, electronic shielding will show a big difference.

In the present invention, in order to analyze such a difference, the position and number of gaps are variously modified to improve the electromagnetic shielding characteristics.

(Example)

The stator 100 is made of silicon steel plate, and has three slots and two-pole windings with 36 slots. In the stator, a thermo-electron shielding film 230A made of a copper tube having a thickness of 1.8 [mm] was installed.

The conductivity of this copper tube was 2.6 x 10 ⁸ [11 / mm] at a liquid nitrogen temperature (77 [K]).

The magnetic flux distributions for the three cases when the frequency of the power supply is 60 [Hz] are shown in Figs. 5 (a) to (c).

That is, when there are no gaps (figure 5 (a)), there are four clearances (figure 5 (b)) and six (figure 5 (c)), the width of the gap is 0.25 [mm ]to be.

In this figure, as the number of gaps increases, the flux mill inside the thermo-electron shielding film increases.

In order to quantitatively examine the shielding property of the magnetic flux, the magnetic flux density on the circumference with a radius of 19 [mm] is shown in FIG.

In FIG. 6, (a) shows no shielding at all, (b) shows six gaps, (c) shows four gaps, and (d) shows a case where a hot electron shielding film without gaps is applied. .

In Fig. 6 (b) and (c), the symbol "I" is where there is a gap. If there is no gap, it can be seen that there is a lot of shielding in all positions.

However, in the case of a gap, the shielding is less where the gap is, and the shielding is much more in the middle of the gap and the gap.

The magnetic flux densities were measured for the case without a thermoelectromagnetic shield (case 1), for a thermoelectromagnetic shield without a gap (case 2), and for a thermoelectromagnetic shield with four gaps (case 3). Same as 1.

In Table 1, θ = 45 ° is the intermediate position between the gap and the gap, and θ = 90 ° means where the gap is located.

In Table 1, in case 1 and case 3, the measured value and the calculated value agree very well, but in case 2, the measured value is about 10-15% more than the calculated value. It is showing what it does. Table 2 shows the mean values of the radial magnetic flux densities that vary with the power source frequency variation.

In Table 2, as in Fig. 6, the larger the number of gaps, the more the passage of the magnetic flux, and the higher the magnetic flux density. Also, the lower the frequency, the higher the magnetic flux density, which is a predictable result. At low frequencies, the magnetic flux densities were similar in all three cases.

However, it can be seen that the higher the frequency, the larger the number of gaps and the less the shielding of acceleration.

On the other hand, since the shielding effect of the electronic shielding film does not have any gap, the shielding effect increases as the frequency increases, so that the fluctuation flux due to the change of the field current must be transmitted to the armature. Show the availability of electron shields.

In this embodiment, a new thermoelectron shielding membrane model was proposed for application to a fast-conducting superconducting generator, and the magnetic shielding effect of the present invention with a gap between the thermoelectric shielding membrane without a gap and the gap was compared.

The thermo-electron shielding film 230A having a gap provided by the present invention is simple in structure, can sufficiently conduct electric conduction, and can reduce electron shielding rate, and thus is suitable as a shielding film of a vaccinated superconducting generator.

In addition, since the shielding rate varies depending on the position, the position of the gap is well controlled to provide a shielding film having a large shielding effect against the magnetic flux caused by the armature and allowing the magnetic flux generated by the superconducting winding to pass through well.

[Table 1] Magnetic flux density [Gauss] for radial direction

[Table 2] Mean value of magnetic flux density according to frequency change [Gauss] (In parentheses,% transmittance)

Next, the magnetic shielding property of the transient magnetic field of the superconducting alternator according to the present invention is compared with the conventional one.

Three models were presented: a conventional electrothermal shield (CES), a slitted thermothermal shield (SES), and a no electrothermal shield (NES). Review the three cases and consider the effect of the slit on the generator in the event of a short circuit.

That is, a case where a three phase fault and a line to line fault occur is illustrated.

The generator was operated under no load condition before the short circuit accident, and the rotation speed of the generator before and after the short circuit accident did not change.

The short circuit accident occurs when the a-phase voltage is maximized, and the condition of the short-circuit between lines is that the a-phase is open, the b-phase and the c-phase are short-circuited, and I _b = -I _c , I _a = 0.

The terminal of a generator inducing balanced three-phase voltage is instantaneous (if a short circuit occurs, a transient current of several to several tens of the rated current flows but gradually decreases to become a permanent short circuit current after a few seconds).

This large current flows at the beginning of the short circuit because the armature reaction does not appear instantaneously, and the initial current of the short circuit is limited by direct axis transient reactance.

The armature reaction is then limited by synchronous reactance, which is the sum of the armature leakage reactance and the armature reaction reactance of the armature reaction, causing a permanent short circuit current to flow through the armature.

7 shows a two-dimensional cross-sectional view of the analysis target model in the case where there is a slit (SED).

In the figure, F is the superconducting field winding, SI is the electrothermal shield, S2 is the damper, A is the three phase armature winding and M is the environmental shield. )to be.

In the figure, the NES model does not have a hot electron shield (SI), and the CES model has a cylindrical conductive tube without a slit portion. In the case of a three-phase short circuit, the change in the field current is the same as in the eighth degree.

As shown in FIG. 8, the proposed model (SES) has a drastic change in the field current compared to the conventional model (CES) and has similar characteristics to the model without shield (NES).

In addition, when the time change of the synchronous reactance is obtained, the ninth degree is obtained. Between 0 and 0.1 seconds, the three models have the same synchronous reactance because the same room temperature dampers are used. After 0.1 seconds, the new models have different values because of the different characteristics of the thermoelectromagnetic shield. .

Therefore, the NES is the fastest synchronous reactance, the CES is the latest increase, SES is very close to the NES. Therefore, the linear axis transients of a generator with SES are similar to those of the NES. In the case of a three-phase short circuit, the magnetic flux density change outside the center of the field winding (see Fig. 7) is the same as in Fig. 10 (a). In the case of SES, the magnetic field change is larger than in the case of CES, but the rate of change of magnetic flux is lower than that of NES.

FIG. 10 (b) shows the case of the line short circuit, but the effect of the slit is similar to that of the three phase short circuit.

Here, the rate of change of the magnetic flux is the cause of the loss of the superconducting winding, so it is desirable to reduce the rate of change of the magnetic flux.

11 (a) and 11 (b) show the current densities at the center of the hot electron shielding film (point b in FIG. 7) after 0.2 sec. In three phase short circuit and line short circuit, respectively.

It can be seen that the SES case is about 40 [%] of the CES case.

As shown in FIG. 10 (a), the change in the magnetic field of the superconducting winding in the three-phase short circuit was about 4 [pu / s] for the NES and about 2 [pu / s] for the SES.

8, it can be estimated that the linear magnetic flux change with respect to the field current change is about 30 [%] below the NES.

From these results, the effects of SES on the low speed excitation generator (field flux rate of 1.5 [pu / s]) and the high speed excitation generator (field flux change rate of 2.0pu, / s or more) are as follows. In order to obtain a continuous change of 1.5 [pu / s] in the case of NES in a low speed generator, a current of 1.5 [pu / s] may be given. The change in the magnetic field of the superconducting winding at this time is 1.5 [pu / s].

However, since the change in the magnetic field of the superconducting winding in the three-phase short circuit is 4 [pu / s], the superconducting winding at this time should be designed based on the change in the magnetic field of 4 [pu / s].

However, with SES, the field current of about 2 [pu / s] must be changed to obtain a change of the magnetic field of 1.5 [pu / s], and the change in the magnetic field of the superconducting winding is 2 [pu / s].

However, since the change in the magnetic field of the superconducting winding during the three-phase short circuit is about 2 [pu / s], in this case, the superconducting winding may be designed based on the change in the magnetic field of 2 [pu / s].

Therefore, the low speed exciter can use superconducting winding which is less expensive than NES in case of SES. In the case of NES, the magnetic flux change rate during the three-phase short circuit is 4 [pu / s], which is much higher than the magnetic flux change 2 [pu / s] during the fast excitation. Therefore, the loss of superconductors should be designed based on the magnetic field change of 4 [pu / s], so the price of superconductors increases. However, in the case of SES, the rate of change of magnetic flux in a three-phase short circuit is about 2 [pu / s], so the price of the superconductor based on this is lower than that of the former. As described above, according to the present invention, the following results can be obtained.

(1) The electron shielding characteristics of the thermoelectromagnetic shielding membranes with a narrow gap between sine and magnetic field showed that the average shielding ratio was low when the gap number was large and the average shielding ratio was high when the gap number was small. In addition, it was found that the area near the gap is not shielded well, and the area near the gap is well shielded.

(2) From the results obtained above, it can be concluded that the clearance of magnetic flux by the field winding can be improved to improve the linear transient characteristics of the generator.

(3) As a result of analyzing the field current change for the three-phase short circuit and line short-circuit accident by making a gap only in the linear axis of the generator, it was found that it is similar to the case without the thermo-electromagnetic shielding film, which means that the linear transient characteristic is improved.

(4) On the other hand, the results of analyzing the change of the magnetic field showed similar characteristics to the case of complete shielding, and it was confirmed that the superconducting wire was better protected than the shielding.

As a result of the above, the superconducting generator having a thermoelectron shielding film with a gap according to the present invention has better linearity and characteristics than the superconducting generator having a full shielding film, and the superconducting winding is better protected than the generator without the thermoelectromagnetic shielding. Therefore, the niche hot electron shield is suitable as a hot electron shield of the fast-conducting super-superfine generator.

Claims (5)

In the superconducting alternator including a rotor 200 including a damper shell 240 and a thermoelectromagnetic shielding film 230, and a stator 100 including an external shield 120 and an armature winding 110, the rotor Thermoelectric shielding device of the superconducting alternator, characterized in that the gap between the hot electron shielding film 230 in the (200) at a predetermined interval. The apparatus of claim 1, wherein the hot electron shielding film has a gap in the longitudinal direction at a central portion thereof and a gap in the transverse direction on a straight axis. [3] The thermoelectromagnetic shield of the superconducting alternator according to claim 1 or 2, wherein the thermoelectromagnetic shielding film 230 is located between the superconducting field winding 220 and the damper shell 240. 3. The thermo-electro-shielding apparatus of the superconducting alternator according to claim 1 or 2, wherein the thermo-electron shielding film (230) is a copper tube having a conductivity of 2.6 × 10 ⁸ [1 / mm] in liquid nitrogen. The thermo-electro-shielding apparatus of a superconducting alternator according to claim 1 or 2, wherein the gap formed in the thermo-electro-shielding film 230 has a width of 0.25 [mm].