JP7042659B2 - Lightning resistant transformer - Google Patents

Description

The present invention relates to a lightning resistant transformer for protecting electrical equipment and the like from abnormally high voltage such as a lightning surge.

For example, Patent Document 1 describes a lightning surge protection method for an electric device used by being connected to both a low-voltage power line provided with a lightning-resistant transformer and a communication signal line, wherein the lightning arrester or a surge absorbing element and an electric vibration A lightning surge protection method is disclosed, wherein a suppression device is provided between the power line and the communication signal line and / or between the ground.

Japanese Unexamined Patent Publication No. 2004-254487

By the way, the surge transition rate of a conventional lightning-proof transformer alone is generally designed to be 0.1% or less. This surge transition rate of 0.1% corresponds to the case where the ground resistance of the shield layer is 0Ω, and the surge transition rate increases as the ground resistance increases. Therefore, the grounding resistance of the lightning-proof transformer is set to 10Ω or less (class A grounding) as a standard.

However, depending on the surrounding environmental conditions, there are places where it is difficult to construct Class A grounding (for example, along railway tracks), and there are cases where Class D grounding (100Ω or less) must be used for grounding the lightning-proof transformer.

In such a case, since the ground resistance is large, the surge transition rate becomes high, the surge suppression effect of the lightning-resistant transformer is not fully utilized, and there is a problem that the equipment cannot be satisfactorily protected from abnormal voltage such as lightning surge. Occur.

An object of the present invention is to suppress the dependence of the surge transition rate on the ground resistance in a lightning-proof transformer.

Reduce the capacitance value of the stray capacity generated between the primary winding and the shield layer. As a result, the surge current flowing into the ground resistance is suppressed, the potential increase due to the ground resistance is reduced, and the increase in the surge transition rate is suppressed.

According to one aspect of the invention, the primary winding comprises a primary circuit having a primary winding and a secondary circuit having a secondary winding arranged in close proximity to the primary winding. Of the primary winding, between the first capacitor between one end side of the secondary winding and the other end side of the secondary winding, and between the other end side of the primary winding and the other end side of the secondary winding. A lightning-proof transformer having a second capacitor and a third capacitor in order from the other end side, and a ground resistance provided between the second capacitor and the third capacitor and between the ground. Provided is a lightning-proof transformer characterized in that the capacitance value of the second capacitor is set so that the surge transition rate is 1% or less when the value of the ground resistance is 100 Ω or less.

It is preferable that the capacity of the second capacitor is 1/100 or less of the capacity of the third capacitor.

The present invention is a lightning-proof transformer that can be installed at a D-class grounding point.

According to the present invention, it is possible to suppress the dependence of the surge transition rate on the ground resistance in a lightning-proof transformer, and to provide a lightning-resistant transformer capable of keeping the surge transition rate low even in a place where the ground resistance is large. Can be done.

As a result, it is difficult to construct class A grounding (grounding resistance 10Ω or less), and even in places where class D grounding (100Ω or less) is installed, the surge suppression effect of the lightning-resistant transformer can be fully utilized, and the equipment can be used for lightning surges, etc. You will be able to satisfactorily protect from abnormal voltage.

It is a figure which shows an example of the lightning surge voltage suppression measures by a lightning-resistant transformer. It is a figure which shows the equivalent circuit of the lightning-proof transformer against a surge. It is a figure which shows the current flow when a surge voltage is applied by an equivalent circuit. It is an equivalent circuit diagram for a new surge which took the ground resistance into consideration. It is a figure which showed the flow of the current when the surge voltage is applied to the equivalent circuit of FIG. It is a figure which showed the value of the impedance of the capacitance in FIG. 5 by a rough ratio. It is a figure which shows the principle of improving the surge transition rate by this embodiment. It is an equivalent circuit diagram used for the calculation. It is a figure which shows the surge transition rate calculation result of the new lightning-proof transformer and the current lightning-resistant transformer by this embodiment. It is a figure which shows the comparative example of the surge transition rate of the new lightning-proof transformer and the current lightning-resistant transformer in the general ground resistance. It is a figure which showed the surge transition rate actual measurement result of the prototype by the design concept based on the conventional product and this embodiment.

The lightning-proof transformer according to the embodiment of the present invention will be described below with reference to the drawings.

First, the inventor's consideration for providing a lightning-proof transformer having a low dependence of the surge transition rate on the ground resistance will be described.

FIG. 1 is a diagram showing an example of measures for suppressing a lightning surge voltage by a lightning-resistant transformer. Applies to AC power lines, etc. where lightning surges are expected to invade. The primary side circuit 1 is composed of wiring 1a, wiring 1b, and coil 1c. When a lightning surge voltage of V1 = 20 kV is applied to the primary side circuit 1, for example, from the AC power supply side, the secondary side circuit 11 (11a, 11c) , 11b) The voltage progressing to 20V or less (generally 0.1% or less of V1, that is, as shown in the following equation (1), surge transition rate: 0.1% or less) should be suppressed. Can be done. Here, the shield layer 15 is formed between the coil 1c and the coil 11c.

Due to this suppression effect, the device 17 connected to the secondary circuit can be protected from an excessive lightning surge voltage.

FIG. 2 is a diagram showing an equivalent circuit of a lightning-proof transformer against a surge. The equivalent circuit consisting of the primary side circuit 1 and the secondary side circuit 11 shown on the left side of FIG. 2 has the capacitance (C1, C2, C3) inside the transformer when a high frequency voltage such as a surge is applied. The current flowing through it becomes dominant. Therefore, the equivalent circuit for surge can be represented only by the capacitance C as shown in the right figure of FIG.

FIG. 3 is a diagram showing an equivalent circuit showing the current flow when a surge voltage is applied. As shown in FIG. 3, the voltage v2 generated in the secondary circuit 11 is the primary circuit via the capacitance C1 regardless of the current i1 flowing from the primary circuit 1 to the ground GND via the capacitance C2. It is determined by the current i2 that flows from 1 to the secondary side circuit 11 and then flows to the ground GND via the capacitance C3. That is, the secondary voltage v2 is a value obtained by dividing the applied voltage v1 by the capacitance C1 and the capacitance C3 (see equation (2) below).

Further, in the above-mentioned lightning-proof transformer, C3 is set to 1000 or more when the capacitance C1 is 1. As a result, the surge transfer rate of the transformer alone can be reduced to 0.1% or less.

As is clear from the above discussion, the surge transition rate of the lightning-resistant transformer is the transition rate of the transformer alone, and corresponds to the case where the ground resistance is 0Ω. That is, conventionally, the design was performed when the ground resistance was 0Ω.

(Effect of ground resistance)
However, when actually installing a lightning-proof transformer, there is always a grounding resistance. The surge transition rate is affected by this ground resistance. The inventor designed and prototyped a lightning-proof transformer using a new design method, as described below.

FIG. 4 is an equivalent circuit diagram for a new surge that takes ground resistance into account. 5 and 6 are diagrams showing the current flow when a surge voltage is applied to the equivalent circuit of FIG. FIG. 5 is a diagram showing the values of the capacitances C1, C2, and C3 in a rough ratio. FIG. 6 is a diagram showing the impedance values of the capacitances C1, C2, and C3 as a rough ratio (all are shown by the numerical values in parentheses after the parameters). Further, in FIGS. 5 and 6, the values of the current i1 flowing through the ground GND via the capacitance C2 and the ground resistance R1 and the current i2 flowing through the ground GND via the capacitances C1 and C3 and the ground resistance R are also compared. It is shown by. The primary winding is indicated by reference numeral 51, and the secondary winding is indicated by reference numeral 52.

With reference to these figures, the current flowing through the ground resistance R is dominated by i1 (100 times that of i2), and accordingly, the secondary voltage v2 is also dominated by i1 × R, and the surge transition rate is dominated by the ground resistance R. It can be seen that it is greatly affected by.

(How to improve surge migration rate)
The improvement of the surge transition rate of the lightning-proof transformer in consideration of the ground resistance will be described below.
FIG. 7A is a diagram showing a principle of improving the surge transition rate according to the present embodiment. In the secondary voltage v2 of the lightning-proof transformer when the ground resistance R is taken into consideration, the voltage vR generated in the ground resistance R is dominant. In vR, the current i1 flowing through the ground resistance R via the primary winding to the shield layer is dominant. Therefore, it can be seen that if the current i1 is suppressed, the voltage vR in the ground resistance R is suppressed and the surge transition rate is reduced.

Therefore, as shown in FIG. 7B, the capacitance between the primary winding and the shield layer is set to 1/10 of the conventional (current state), and the impedance is set to 10 times. As shown in the equation (3), the improvement (vR modification) by reducing the current i1 flowing through the ground resistance R to 1/10 becomes 1/10 of (vR), and the surge transition rate can be greatly reduced. be.

In the above example, an example in which the capacitance between the primary winding and the shield layer is set to 1/10 has been described, but it has been confirmed that a certain effect can be exhibited, for example, if it is about 1/3 or less. (See (Confirmation result by prototype) below).

(Improvement effect)
Next, the improvement effect of the lightning-proof transformer newly designed based on the above policy will be described.
Confirmation of Improvement Principle by Equivalent Circuit Calculation Figure 8 (a) is an equivalent circuit diagram used in the calculation. The theoretical calculation was performed based on an AC circuit using an AC 250 kHz power supply as a simulation of the surge voltage.

As shown in FIG. 8A, the equivalent circuit considering the ground resistance has a primary winding 71 and a secondary winding 72. The capacitance between the primary winding 71 and the secondary winding 72 is C1, the capacitance between the primary winding 71 and the shield layer is C2, and the capacitance between the secondary winding 72 and the shield layer is C3. And. Further, R is a ground resistance.

FIG. 8B is a diagram showing a model circuit for calculating the surge transition rate based on FIG. 8A.

Here, the following equation holds.

(Constant used in calculation)
Table 1 shows the constants used in the calculation. Two types of calculation target models were used: the current lightning-proof transformer and the lightning-resistant transformer (new lightning-resistant transformer) according to the present embodiment.

In the new lightning-proof transformer, in order to suppress the surge current flowing through the ground resistance, the calculation was made for an example in which the capacitance C2 between the primary winding and the shield layer was set to 1/5, 1/10, and 1/20 of the current transformer.

Here, the calculation conditions are as follows.
* 1 Calculation target model: Current lightning-resistant transformer, new lightning-resistant transformer * 2 AC power frequency: 250 kHz (equivalent to a surge with a wave front length of 1.0 μs)
* 3 The measured value is only for C3 of the current lightning-proof transformer. * 4 C1 of the current lightning-resistant transformer is 1/1500 of C3.
* 5 The C2 of the new lightning-resistant transformer is 1/5, 1/10, and 1/20 of the current lightning-resistant transformer C2.

(Calculation result)
FIG. 9 is a diagram showing the calculation results of the surge transition rate of the new lightning-proof transformer and the current lightning-resistant transformer according to the present embodiment. FIG. 10 is a diagram showing a comparative example of surge transition rates between a new lightning-proof transformer and an existing lightning-resistant transformer in a general ground resistance.

Looking at these calculation results, it can be seen that the smaller the capacitance C2 between the primary winding and the shield, the lower the migration rate.

In FIG. 10, the current lightning-proof transformer and the new lightning-resistant transformer in which C2 is 1/10 (35.2 pF) of the current one are compared. With a ground resistance of 1Ω, both are 0.1% (1/1000) or less. However, it can be seen that the current product has a level of 1% (1/100) or less when the ground resistance is 10Ω, while the new lightning-resistant transformer maintains 0.1% or less.

Further, the surge transition rate (0.59%) of the new lightning-resistant transformer with a ground resistance of 100 Ω and the surge transition rate (0.50%) of the current lightning-resistant transformer with a ground resistance of 10 Ω were almost the same values.

From this, it can be seen that according to the new lightning-proof transformer according to the present embodiment, a surge transition rate equivalent to the conventional class A grounding (grounding resistance 10Ω) can be secured even at the location of class D grounding (grounding resistance 100Ω).

(Confirmation result by prototype)
In order to confirm the basic validity of the above surge migration rate reduction effect principle, in the conventional product equivalent to the current lightning-proof transformer, the separation between the primary winding and the shield layer is increased and the capacitance C2 is reduced. (See below for the value of C2) was prototyped.

Here, the values of the capacitance C2 of the "conventional product" and the "prototype" are as follows.
(Conventional product) C2 = 195pF
(Prototype) C2 = 70pF (about 1/3 of the conventional product)

FIG. 11 is a diagram showing the actual measurement results of the surge transition rate of the conventional product and the prototype based on the design concept based on the present embodiment. As shown in FIG. 11, it can be seen that the prototype shows a lower surge transition rate than the conventional product for any ground resistance value.

From the above results, it can be seen that if the capacitance value of C2 is set to about 1/3 or less of that of the conventional product, an increase in the surge transition rate can be suppressed.

As described above, according to the lightning-proof transformer according to the present embodiment, it becomes possible to suppress the dependence of the surge transition rate on the ground resistance in the lightning-resistant transformer, and the surge transition rate is kept low even in a place where the ground resistance is large. Can provide a lightning resistant transformer that can.

In addition, due to this, it is difficult to construct class A grounding (grounding resistance 10Ω or less), and even in places where class D grounding (100Ω or less) is installed, the surge suppression effect of the lightning-resistant transformer is fully utilized to make the equipment lightning surge. It becomes possible to satisfactorily protect from abnormal voltage such as.

In the above embodiment, the configuration and the like shown in the illustration are not limited to these, and can be appropriately changed within the range in which the effect of the present invention is exhibited. In addition, it can be appropriately modified and implemented as long as it does not deviate from the scope of the object of the present invention.

In addition, each component of the present invention can be arbitrarily selected, and an invention having the selected configuration is also included in the present invention.

The present invention can be used for lightning resistant transformers.

1 Primary circuit 11 Secondary circuit C1, C2, C3 Capacitance 71 Primary winding 72 Secondary winding

Claims (4)

It has a primary side circuit having a primary winding and a secondary side circuit having a secondary winding arranged close to the primary winding, one end side of the primary winding and the secondary winding. The second capacitor in order from the other end side of the primary winding between the other end side of the primary winding and the other end side of the secondary winding. A lightning-proof transformer having a capacitor and a third capacitor, and a ground resistance provided between the second capacitor and the third capacitor and between the ground.
A lightning-resistant transformer characterized in that the capacitance value of the second capacitor is set so that the surge transition rate is 1% or less when the value of the ground resistance is 30 Ω to 100 Ω . The lightning-proof transformer according to claim 1, wherein the capacity of the second capacitor is set to 1/100 or less of the capacity of the third capacitor. The lightning-proof transformer according to claim 1 or 2, which can be installed at a D-class grounding point. The lightning-proof transformer according to any one of claims 1 to 3, wherein the capacitance value of the second capacitor is set based on the voltage at the ground resistance.

Images