JPH11135335A - Insulating transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce discharge current and to absorb energy, so that the energy accumulated in a capacitor formed between a low-tension side shield plate on a primary coil of an insulating transformer and a high-tension side shield plate under a secondary coil do not give damages to a load at load-grounding. SOLUTION: Where a transformer 2 is housed is provided, and the metal case 1 is filled with an insulating oil 6, and the metal case 1 is provided with a low-tension side power supply terminal 3, a high-tension side power tapping bushing 4, and a ground terminal 5. Here, a metal conduit 16 is provided at a central part of the high-tension side power tapping bushing 4. Then a plurality of iron cores 31 are split-allocated around the metal conduit 16 with an insulating plate 32 in between, so as to provide a gap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating transformer for use in an apparatus for accelerating electrons and ions at a high DC voltage of several hundred kV. The present invention relates to an insulating transformer used for the purpose of supplying power from a ground potential point. That is, the primary and secondary coils of the insulating transformer have a low voltage of 200 V AC and a predetermined capacity.
Number of terminals always between primary coil terminal and primary coil terminal, iron core
The present invention relates to an improvement of an insulation transformer used in a state where a high DC voltage of 00 kV is applied.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing the internal structure of a conventional insulating transformer. A metal case 1 containing a transformer 2 is filled with insulating oil 6, and the metal case is provided with a low voltage side power supply terminal 3, a high voltage side power extraction bushing 4, and a ground terminal 5. The high-voltage side power lead-out bushing 4 is composed of a porcelain tube 7 and flanges 8 and 9. The porcelain tube 7 is made of ceramic or resin having an insulating creepage distance sufficient to withstand the working voltage. The high-pressure side flange 8 and the low-pressure side flange 9 made of metal are fixed to each other with an adhesive, and the low-pressure side flange 9 is attached to a mounting flange 11 provided on a top plate of the metal case 1 by screws or the like. Airtightness is maintained between the mounting flange 11 and the packing 11 via a packing 10. A metal top plate 12 is attached to the high-pressure side flange 8 with screws or the like, and the space between the top plate 12 and the insulator tube 7 is kept airtight through a packing 13. Further, on the upper surface of the top plate 12, a high-potential-side extraction terminal 14 for extracting an insulated secondary voltage is provided.
And top cover 1 which also prevents the terminal from being damaged and alleviates the electric field
5, a metal conduit 16 serving as a central conductor is attached to the lower surface of the top plate 12 by welding, brazing, screws, or the like. Inside the metal conduit 16, a secondary lead wire 29 of the transformer 2 passes. , The metal conduit 16 itself is a secondary lead 29
Plays the shielding effect. The outer layer of the metal conduit 16 is provided with an insulating layer 17 formed by winding insulating paper or insulating film so as to withstand an insulating voltage between the mounting flanges 11 of the metal case.

[0003] The transformer 2 secures insulation between the primary coil 22 and the iron core 20, and places the primary coil 22 on a bobbin 21 serving as a core.
A secondary coil 22 and a secondary coil 26 are wound, and an insulating layer 24 having a thickness that can withstand a working voltage is provided between the two coils.
Further, in order to prevent an induction failure between the primary coil 22 and the secondary coil 26, the copper foils 23 and 25 are not short-circuited for one turn at a position where the primary coil 22 and the secondary coil 26 face each other.
(Hereinafter referred to as a shield plate), and the low-voltage shield plate 23 on the primary coil side is provided with a low-voltage shield wire 28 so as to be electrically grounded, and is connected to the ground terminal 5.
A high voltage shield wire 30 is also provided on the high voltage side shield plate 25 on the secondary coil side, and is electrically connected to the metal conduit 16 of the high voltage side power extraction bushing 4. Also, the primary coil 22
Are electrically connected to the low voltage side power supply terminal 3 at the ground potential, and the secondary leads 29 at both ends of the secondary coil 26 are metal conduits of the high voltage side power lead-out bushing 4. The secondary lead wire 29 is drawn out from the upper opening of the metal conduit through the inside of the metal conduit 16 and is connected to the high-potential side lead-out terminal 14 provided on the top plate 12.

FIG. 4 shows an insulating transformer having a single-phase internal iron-type one-leg winding structure. The structure per leg of a single-phase double-leg winding structure and a three-phase three-leg insulating transformer is similar. FIGS. 5A and 5B show examples of single-phase and three-phase equivalent circuits. The numbers in the figure are the same as those described in FIG.

[0005]

In such a transformer 2, the low voltage side shield plate 23 on the primary coil side and the high voltage side shield plate 25 on the secondary coil side serve as opposing electrodes to form a capacitor. Become. In general, the voltage drop that determines the quality of an insulating transformer is determined by the degree of coupling between the primary and secondary coils, and the value deteriorates in proportion to the gap between the coils or improves in proportion to the winding width. . Therefore, in the transformer 2, the thickness of the insulating layer 24 between the primary and secondary coils is made as thin as possible, and the winding width of the coil is made as wide as possible. As a result, the low voltage side shield plate 23 provided above the primary coil and the high voltage side shield plate 25 provided below the secondary coil 25
In between, a large capacitor will be formed.

[0006] For the above reasons, when an insulating transformer is used under a high DC voltage, a large amount of energy is stored in a capacitor, and when a ground fault discharge occurs on the load side to be used, a direct short circuit occurs and a large short circuit occurs. There is a problem that a current is emitted and a large damage is given to the load side.

[0007]

The insulating transformer of the present invention comprises:
The current at the time of such a load ground fault is suppressed, and further, the stored energy is to be absorbed in the insulating transformer.

That is, the insulating transformer according to the present invention comprises a transformer
2 was filled with an insulating oil 6 in the metal case 1 and the metal case containing and isolation transformer having a low pressure-side power supply terminal 3 and the high-voltage side power lead bushing 4 and the ground terminal 5 to the metal casing In the above, a metal conduit 16 is arranged at the center of the high-voltage side power extraction bushing, and a plurality of iron cores 31 are divided and arranged around the outer periphery of the metal conduit with an insulating plate 32 interposed therebetween.
It is characterized in that a gap 18 is provided.

Further, a metal foil 33 is interposed between the iron core 31 and the metal conduit 16 and between the insulating plates 32, and a resistor 34 is connected between the metal foils.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, by providing an iron core having a gap around the outer periphery of a metal conduit, a short circuit (ground fault) current on the load side can be suppressed. By providing a metal foil acting as a secondary coil and connecting a resistor, the discharge time constant can be shortened and the emitted energy can be absorbed by the resistor.

[0011]

FIG. 1 is an internal structural view of an insulating transformer according to the present invention. 1, except that a number of iron cores 31 are inserted between the metal conduit 16 and the insulating layer 17 of the high-voltage side power lead-out bushing 4 and the insulating layer 17 via the insulating plate 32. Is the same. 2 (a), (b),
(C) is an enlarged view of the iron core part of the present invention, and FIG.
Is a plan view in which a large number of iron cores 31 are inserted through the metal conduit 16 via an insulating plate 32, and FIG.
(C) is a partial perspective view of a section taken along line AA 'of (b). The core 31 shown in FIG. 2 is formed by winding a tape-shaped ultra-thin magnetic material having high magnetic permeability and high saturation magnetic flux density such as a silicon steel plate or an amorphous core and having excellent high-frequency characteristics into a disk shape, and then cutting. And the interval length of the gap 18 is x /
In FIG. 2, n = 2 (m / number of cut portions).

When an insulating transformer is used for DC high voltage insulation, a capacitor formed between a primary coil and a secondary coil includes

[0013]

(Equation 1)

When a ground fault discharge (short-circuit) occurs on the high voltage side (load side), a short-circuit discharge current determined by the inductance L and the resistance value R of the circuit floating in the discharge current path is stored. Flow, causing heavy damage to the load side. The equivalent short-circuit discharge circuit is Cd-L shown in FIG.
The short-circuit current waveform is shown in FIG.
It becomes the attenuated sine wave current shown in (b) and is approximately represented by the following equation.

[0015]

(Equation 2)

In order to reduce the short-circuit current I (t), the inductance L of the circuit is increased to suppress the peak current value Ip, and the circuit resistance value R is increased to decrease the decay time constant τ so that the decay time is reduced. It is conceivable that the circuit resistance R
Increasing the power loss increases the steady-state loss, which is the original mission of the insulating transformer, and is not preferable. The insulating transformer of the present invention increases the inductance L and suppresses the peak current value Ip, and increases the inductance of the high-side power lead-out bushing 4, which is a part of the insulating transformer, with respect to the short-circuit current path. It was designed so as not to affect the stationary (alternating current) current path, which is the original mission of the insulating transformer.

As described above, by arranging the iron core 31 having a high magnetic permeability around the outer periphery of the metal conduit 16 of the bushing 4 for drawing out the high-voltage power, the inductance of the metal conduit 16 forming the short-circuit current path is increased. The steady (alternating) current path flowing through the secondary lead 29 of the transformer 2 inserted into the metal conduit 16 is completely reciprocated in the metal conduit 16 and there is no flux leakage outside the metal conduit. , And the steady current is not affected by the iron core 31. When the load is short-circuited, the energy En stored in the capacitor of the insulating transformer alternates between the capacitor and the inductance L, and an attenuated sine wave current flows. Assuming that the inductance of the road is a lumped constant, the inductance needs to have a capacity capable of receiving the entire energy.

It is well known that the energy stored in an iron core is represented by the following equation as a function of the magnetic flux density Bm.

[0019]

(Equation 3)

Here, as an example, when a single-phase 200 V, 1 kVA insulating transformer for DC 400 kV isolation is considered, if the stray capacitance Cd of the capacitor is Cd = 500 pF, the energy En stored therein is (1 ), En = 40J. This energy is applied to an iron core having a relative magnetic permeability μ _S = 10,000 and Bm = 1.5 close to the saturation magnetic flux density.
When trying Takuwaeyo in T, core volume required ⁽³⁾ Vcore = 0.447m 3 becomes from the equation, it becomes about 3.5 tons weight basis, since several times the weight of a conventional isolation transformer,
No longer practical. As a countermeasure, the iron core 31 is cut in the diameter direction, and a gap 18 is provided at the cut portion. If the material of the gap 18 of the cut portion is a non-magnetic material, the relative magnetic permeability μ _S = 1, and the energy stored therein is represented by the following equation.

[0021]

(Equation 4)

As in the above example, the gap volume required to store 40 J of energy at a maximum magnetic flux density of 1.5 T is given by the following equation (4): Vgap = 0.47 · 10 ⁻⁴ m ³ (= 44.7 c)
c) is a value for practical use. Now, here, iron core 3
If the inner radius of 1 is 20 mm, the outer radius is 40 mm, and the sum of the axial lengths of a plurality of iron cores is 1 m, the necessary gap length x of the gap 18 is 2.24 mm, and the iron core is moved by 2 mm in the diameter direction.
In the case of division, the gap 18 can be provided at two places, and the gap 18 may be set to 1.12 mm per place, which is a value practically used. On the other hand, when the load is short-circuited, a vibration voltage equivalent to a voltage of 400 kV charged in the capacitor is applied in the axial direction in which the total axial length of the iron core is 1 m, and the iron core 31 is divided in the axial direction to withstand the applied voltage. An insulating layer of an insulating plate 32 is provided between the iron cores 31.

When the above-described iron core 31 is used, the inductance L of the metal conduit 16 of the bushing 4 for drawing out the high-voltage power is set.
Is about 11 .mu.H. At 400 kV, the short-circuit current at the time of load ground fault is expressed by the equation (2), and the peak current value Ip = 2697 A. On the other hand, in the conventional product using no iron core, the stray inductance L of the short circuit is estimated to be at most about 1 μH, and the short circuit peak current value Ip is 8944 A. As an effect of the present invention, the peak current at the time of short circuit is 1/3. 3 The energy stored in the capacitor is consumed by the circuit resistance as a sine wave damped oscillating current represented by the equation (2), and although the resistance component of the short-circuit discharge path cannot be specified, it is assumed that most is the arc resistance of the discharge part. Most of the stored energy is injected into the discharge portion, and even if the inductance L is increased, the effect of the present invention does not appear on the amount of energy injected into the discharge portion. However, in a discharge in a high vacuum such as an acceleration tube in which a load accelerates electrons or ions, the damage often depends on the peak value of the current, and the effect of the present invention is great.

[0024]

Embodiment 2 FIGS. 3 (a), 3 (b) and 3 (c) are enlarged views of an iron core according to another embodiment of the present invention, and FIG. 3 (a) is a drawing of electric power on the high voltage side in FIG. The core 31 having the gap 18 between the metal conduit 16 of the bushing 4 and the insulating layer 17 is attached to the insulating plate 3.
2, a metal foil 33 such as a copper foil having a thickness of several tens of μm is interposed between the iron core 31 and the metal conduit 16 and between the insulating plates 32 to form a U-shaped cross section. A plan view in which a resistor 34 is connected in parallel between the open ends of the metal foil while covering the iron core at least, (b) is a cross-sectional view thereof, and (c) is a sectional view taken along line AA 'of (b). It is a partial perspective view of a cross section. The present invention, for the iron core 31,
The metal conduit 16 serves as a primary coil having one turn, and the metal foil 33 such as a copper foil serves as a secondary coil having one turn, thereby forming a current transformer having a composition ratio of 1: 1 (hereinafter, referred to as a current transformer). Annular current transformer). A large number of resistors 34 are connected in parallel at equal intervals to the outer periphery of the annular current transformer, which corresponds to the open end of the metal foil 33. The resistor is connected to the outer periphery of the annular current transformer by two coated and insulated resistors. A non-induction winding resistance in which the wire has two layers of reverse winding may be used, and a wire having a required resistance value may be inserted.

FIG. 7 shows a short-circuit equivalent circuit of the insulating transformer according to the present invention in practical use. In FIG. 7, the secondary coil 33
Iron cores having a metal foil 33 acting as
D2, D3,..., Dn), a resistance having a resistance value r is connected to each secondary circuit, and when the electric charge stored in the capacitor is short-circuited on the load side G, the primary current I ₁ at the same time the short-circuit current flows is, the secondary current I ₂ flows by transformer coupling the metal foil 33 of the iron core. When the degree of coupling of the annular current transformer is 100%, the primary current I ₁ and the secondary current I ₂ are equal, and FIG.
FIG. 9 is an equivalent circuit diagram obtained by converting the following into the first order. Here, L is the sum of the exciting inductances of the respective annular current transformers, and corresponds to the inductance L of the annular core with a gap described in the first embodiment, and the resistance of the resistance value R is applied to the secondary coil 33 of each annular current transformer. It is the total sum of the connected resistance values r (R = n · r). In the equivalent circuit shown in FIG. 8, when the charge stored in the capacitor is short-circuited on the load side G, the discharge current Ic from the capacitor is divided into the exciting inductance L and the secondary resistance having the resistance value R, and the current I _L Flows as the current I _R. Each current at that time is calculated by the following equation.

[0026]

(Equation 5)

The current I _L flowing through the inductance L of the central metal conduit 16 of the high voltage side power lead bushing 4 (5)
The equation becomes a second-order differential equation, which becomes a vibration damping current or a non-vibration damping current depending on the value of the secondary resistance. When the value of the secondary resistance becomes larger than the critical resistance value Rc shown by the equation (9), the current _IL Becomes a vibration system. The current I _R flowing through the resistance of the secondary circuit of the ring-shaped current transformer is expressed by the inductance L
As the result multiplied by a coefficient differentiated waveform of the current I _L flowing through the current current Ic flowing through the capacitor corresponding to the short-circuit current of the load side flowing through inductance L I _L and the resistance value R
Equation (7) shows the sum of the currents I _R flowing through the resistors of FIG.

FIG. 9 shows the case where the secondary coil 26 is arranged on the iron core 31 shown in the first embodiment and a resistance having a resistance value R is added to the secondary coil. It is expressed whether it changes to. In FIG. 9, the resistance is set to 1, 2, 3, 5, 1 of the critical resistance Rc based on the equation (9).
The calculation results are shown with a resistance value of 0 and 100 times. The maximum current value becomes minimum when the critical resistance value Rc is 3 to 5 times. However, the peak current value increases. Also, if the resistance value is 10
The waveform of 0Rc corresponds to the case where the secondary coil and the resistor shown in the first embodiment are not inserted. The optimum condition must be selected according to the situation of the damage on the load side. However, as is clear from the circuit configuration, any energy stored in the capacitor is a resistance value R which is a resistance component.
Is absorbed (consumed) by the resistor, the energy injection into the discharge portion on the load side is suppressed, and the damage on the load side can be greatly reduced, and the effect is enormous.

[0029]

By arranging an iron core having a gap around the outer periphery of the metal conduit, a short-circuit (ground fault) current on the load side can be suppressed. Further, by providing a metal foil acting as a secondary coil on the iron core and connecting a resistor, the discharge time constant can be shortened and the released energy can be absorbed by the resistor.

[Brief description of the drawings]

FIG. 1 is an internal structural diagram of an insulating transformer according to the present invention.

2 (a), 2 (b), and 2 (c) are enlarged views of an iron core portion of the present invention, and FIG.
FIG. 2B is a plan view in which many are inserted through an insulating plate 32, FIG.
Is a cross-sectional view thereof, and (c) is a partial perspective view of a cross-sectional portion taken along line AA ′ of (b).

3 (a), 3 (b) and 3 (c) are enlarged views of an iron core portion according to another embodiment of the present invention, and FIG. 3 (a) shows the connection between an iron core 31 and a metal conduit 16; FIG. 4B is a plan view in which a metal foil is interposed between the insulating plates 32 and has a U-shaped cross section to cover the iron core and resistors are connected in parallel between open ends of the metal foil, and FIG. (C) is a partial perspective view of a section taken along line AA ′ of (b).

FIG. 4 is an internal structural view of a conventional insulating transformer.

FIG. 5 is a circuit diagram of an equivalent circuit of the isolation transformer.
(A) is for a single phase, and (b) is for a three phase.

FIG. 6A is an equivalent circuit diagram of a short-circuit discharge,
(B) is a discharge current waveform.

FIG. 7 is a short-circuit discharge circuit diagram of the insulating transformer of the present invention at the time of practical use.

FIG. 8 is an equivalent circuit in practical use of the insulating transformer of the present invention.

9A is an operation circuit diagram for explaining the circuit of FIG. 8, and FIG. 9B is a discharge current waveform accompanying a change in resistance value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal case 2 Transformer 3 Low-voltage side power supply terminal 4 High-voltage side power lead-out bushing 5 Grounding terminal 6 Insulating oil 7 Insulator tube 8 High-pressure side flange 9 Low-voltage side flange 10 Packing 11 Mounting flange 12 Top plate 13 Packing 14 High potential Side lead-out terminal 15 Top cover 16 Metal conduit 17 Insulating layer 18 Gap 20 Iron core 21 Bobbin 22 Primary coil 23 Low voltage side shield plate 24 Insulation layer 25 High voltage side shield plate 26 Secondary coil 27 Primary lead wire 28 Low voltage shield wire 29 2 Next lead wire 30 High voltage shield wire 31 Iron core 32 Insulation plate 33 Metal foil 34 Resistor

Claims (2)

[Claims] A metal case (1) accommodating a transformer ( 2 ), an insulating oil (6) filled in the metal case, and a low voltage side power supply terminal (3) and a high voltage side power supply in the metal case. In an insulating transformer provided with a lead-out bushing (4) and a ground terminal (5), a metal conduit (16) is arranged at the center of the high-voltage side power lead-out bushing, and an insulating plate is provided on the outer periphery of the metal conduit. An insulating transformer, wherein a plurality of iron cores (31) are divided and arranged via (32) and a gap (18) is provided. 2. A metal foil (33) is interposed between the iron core (31) and the metal conduit (16) and between the insulating plate (32), and a resistor (34) is connected between the metal foils. The insulation transformer according to claim 1, wherein: