JPH0213806B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a harmonic low impedance transformer that has lower impedance to harmonics than conventional ones and can reduce distortion occurring in the output voltage waveform. It is related to.

[Prior Art and Problems to be Solved by the Invention] Recently, more and more loads have been controlled by switches using thyristors. Therefore, a large harmonic current flows through the transformer supplying power to the load, causing a large voltage drop, and the voltage drop due to this harmonic current greatly distorts the output voltage waveform of the transformer. If the output voltage waveform of the transformer is distorted, it not only adversely affects the phase advancing capacitors and control equipment connected to the load side, reducing the quality of the supplied power, but also harming the load (which is not the source of harmonics). The impact also spreads to electricity consumers (power consumers), creating an unfavorable situation in terms of power supply.

Figure 1 shows a simplified equivalent circuit of a conventional transformer. In this equivalent circuit, if resistance is R, inductance is L, and angular frequency is ω, the impedance Z〓 of the transformer is Z〓 =R+jωL.

The voltage drop E〓 _T when an alternating current I〓 flows through the above transformer is E〓 _T = I〓 (R + jωL), and this voltage drop E〓 _T increases as the frequency increases. Therefore, if the load current contains a harmonic component, the harmonic current causes a large voltage drop _ET , and this voltage drop causes distortion in the output voltage. This distortion increases as the order of harmonics included in the load current increases.

An object of the present invention is to provide a harmonic low impedance transformer that is capable of suppressing voltage drop due to harmonic current and suppressing distortion of the output voltage waveform by lowering the impedance of the transformer relative to harmonics than before. Our goal is to provide the following.

[Means for Solving the Problem] In order to achieve the above object, the present invention provides an impedance adjustment comprising an impedance adjustment iron core and an impedance adjustment closed circuit provided so as to surround the impedance adjustment iron core. The device was placed between the primary and secondary windings.

The closed circuit for impedance adjustment is constituted by a short-circuited conductor that is provided to surround the iron core for impedance adjustment and is electrically connected at both ends,
It can be constructed by a conductor provided so as to surround the impedance adjusting iron core and a capacitor connected between both ends of the conductor.

[Function] When an impedance adjustment device including an impedance adjustment iron core and an impedance adjustment closed circuit surrounding the iron core is disposed between the primary winding and the secondary winding as described above, impedance adjustment is performed. The presence of the iron core makes it easier for magnetic flux to pass through the gap between the primary and secondary windings, increasing the leakage magnetic flux flowing between the primary and secondary windings. This increases the impedance of the transformer.

Furthermore, when leakage magnetic flux flows through the impedance adjusting iron core, a voltage is induced in a closed circuit provided so as to surround the iron core, and a current flows through the closed circuit.
This current generates a repulsive magnetic field that acts to prevent leakage magnetic flux from entering the impedance adjusting iron core. In the low frequency range, the current flowing through the closed circuit is small and the repulsive magnetic field is small, so a lot of leakage magnetic flux passes through the impedance adjustment iron core, but as the frequency increases, the current flowing through the closed circuit increases. As the repulsion magnetic field gradually increases, the leakage magnetic flux flowing into the impedance adjusting iron core decreases. Therefore, the impedance of the transformer increases as the frequency increases, but the rate of increase gradually decreases as the frequency increases.

As described above, according to the present invention, it is possible to reduce the rate of increase in the impedance of the transformer as the frequency increases, so that the impedance of the transformer at the fundamental frequency (for example, commercial frequency) can be kept the same as that of the conventional one. When designed to do so, the transformer impedance to harmonic components can be suppressed lower than that of conventional transformers. Therefore, the voltage drop in the transformer due to harmonic components of the load current can be suppressed to a low level, and the distortion of the output voltage can be suppressed.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a plan view of one embodiment of the present invention, in which 1 indicates leg portions 1a, 1b and yoke portion 1.
2 is a secondary winding wound around the legs 1a and 1b of the core 1, respectively;
is a primary winding wound concentrically with the secondary winding 2 outside the secondary winding 2. Reference numeral 4 denotes a wave-shaped duct spacer disposed between the secondary winding 2 and the primary winding 3, and this duct spacer forms a cooling duct between both windings.

5 is an impedance adjustment device inserted between the secondary winding 2 and the primary winding 3. Two impedance adjusting devices are provided, and both impedance adjusting devices 5, 5 are arranged in a positional relationship such that they face each other in the length direction of the yoke portion 1c with the iron core 1 in between.

Length dimension of each impedance adjustment device 5 (second
(in the figure, the dimension perpendicular to the plane of the paper) is set approximately equal to the axial length dimension of the primary winding 3 or the secondary winding, and both ends of each impedance adjustment device 5 are the ends of the primary and secondary windings. The windings are fixed to at least one of the two windings with their parts substantially flush with each other.

Referring to FIGS. 3 and 4, an example of the impedance adjustment device 5 is shown, with FIG. 3 being a front view and FIG. 4 being a sectional view taken along the line AA in FIG. 3.

The impedance adjustment device 5 includes an impedance adjustment iron core made by laminating a plurality of rectangular silicon steel plates (usually 4 to 5 pieces) each having a length l approximately equal to the axial length of the winding and an appropriate width d. 5a, and a short-circuiting conductor 5b provided so as to surround the impedance-adjusting iron core 5a and having both ends electrically connected, and the short-circuiting conductor 5b constitutes an impedance-adjusting closed circuit surrounding the iron core 5a.

The shorting conductor 5b is the impedance adjusting iron core 5.
It is formed by molding a copper plate having a width l' slightly shorter than the length l of a so as to surround the impedance adjusting iron core 5a and joining both ends thereof, so that the iron core 5a and the shorting conductor 5b are not separated from each other. They are integrated by gluing or welding, etc.

In the harmonic low impedance transformer of the present invention configured as described above, since the impedance adjusting iron core 5a is disposed between the primary winding 3 and the secondary winding 2, leakage flowing between the two windings can be prevented. The magnetic flux increases compared to before, and this increase in leakage magnetic flux acts to increase the transformer impedance. On the other hand, when leakage magnetic flux flows through the iron core 5a, an induced voltage is generated in the short-circuit conductor 5b (closed circuit for adjusting impedance), and a short-circuit current flows through the short-circuit conductor 5b due to the induced voltage. This short-circuit current generates a repulsive magnetic field that prevents leakage magnetic flux from entering the iron core 5a. In this case, the short circuit conductor 5
The voltage e induced in b is e=k(dφ/dt) (where k is a constant, φ is leakage magnetic flux, and t is time),
This induced voltage e increases as the frequency increases, that is, as the harmonic order increases. Therefore, the repulsive magnetic field becomes stronger as the frequency becomes higher.

While the frequency is low, the repulsion magnetic field is weak, so much leakage magnetic flux flows through the impedance adjustment iron core 5a, but as the frequency increases and the repulsion magnetic field becomes stronger, the leakage magnetic flux flowing through the impedance adjustment iron core decreases.

The impedance of the transformer increases as the frequency increases, but as the repulsive magnetic field becomes stronger and the leakage magnetic flux flowing into the iron core 5a decreases, the rate of increase in the transformer impedance increases. gradually becomes smaller.

Therefore, in the transformer of the present invention, the rate of increase in transformer impedance can be made smaller as the frequency becomes higher, that is, the order of the harmonics becomes higher.

The equivalent circuit of the above transformer can be expressed as shown in FIG. Here, R ₁ is the winding resistance of the transformer, L _{1 is the inductance due to the leakage magnetic flux passing through other than the iron core 5a of the impedance adjustment device (hereinafter, this leakage magnetic flux is referred to as main leakage flux), and L 1} is the inductance due to the leakage flux passing through the iron core 5a of the impedance adjustment device. Let the resistance and inductance components of impedance due to magnetic flux be R ₂ and L ₂ , respectively. In this case, the impedance Z〓 ₁ due to the main leakage magnetic flux is Z〓 ₁ = R ₁ + jωL ₁ , and the impedance Z〓 ₂ due to the leakage magnetic flux passing through the iron core 5a of the impedance adjustment device is Z〓 ₂ = jωL ₂ ×R ₂ / (R ₂₊
jωL ₂ ). The value of this impedance Z〓 ₂ increases monotonically as the harmonic order increases (frequency increases), but the rate of increase decreases as the frequency increases.

When the impedance adjustment device 5 is provided between the primary winding and the secondary winding as described above, the impedance naturally increases compared to the case where the adjustment device is not provided. Therefore, in order to keep the transformer impedance at the fundamental frequency (for example, commercial frequency) the same as before, it is natural that the transformer must be designed to lower the impedance Z〓 ₁ due to the main leakage flux.

Assuming that the transformer impedance at the fundamental frequency is the same, the transformer according to the present invention has a lower impedance in the high frequency region than a conventional transformer because the rate of increase in transformer impedance in the high frequency region is smaller. Therefore, the voltage drop due to harmonic components of the load current becomes smaller.

FIG. 6 shows that the transformer of the above embodiment and a conventional transformer are designed to have the same transformer impedance Z ₀ at the fundamental frequency, with the fundamental frequency being 60 Hz, and that the transformer impedance Z ₀ is equal to the frequency F [Hz ] shows the results of actual measurements of how it changes. In FIG. 6, curve a represents a conventional transformer, and curve b represents a harmonic low impedance transformer according to the present invention.
As can be seen from this measurement result, in the conventional transformer, the impedance Z ₀ increases rapidly as the frequency increases, but in the harmonic low impedance transformer of the present invention, the impedance Z 0 increases as the frequency increases.
Z ₀ tends to increase gradually. and fundamental frequency 60Hz
Comparing the impedance at the ninth harmonic of 540 Hz, it can be seen that the impedance Z ₀ of the transformer of the present invention is reduced to approximately 1/2 of that of the conventional transformer. As the frequency increases, the ratio of the impedance of the conventional transformer to the impedance of the transformer of the present invention becomes even larger.

FIG. 7 shows another configuration example of the impedance adjustment device used in the present invention. In this impedance adjustment device, rectangular core members 7a, 7b, . . . are formed by laminating a plurality of silicon steel plates. ,7
f for a given period with each long side facing horizontally 〓
The impedance adjusting iron core 5a is constructed by arranging the impedance adjustment iron cores 5a in tandem with each other. A short-circuiting conductor 5b is formed by winding a copper plate for one turn so as to surround this impedance-adjusting core 5a, and the impedance-adjusting core 5a and the short-circuiting conductor portion 5b are integrated by adhesive or the like to form an impedance adjusting device 5. is configured. In this example as well, the short-circuit conductor 5b constitutes a closed circuit for adjusting impedance.

According to this impedance adjustment device, since the gap 6 is formed in the middle of the leakage magnetic flux path of the impedance adjustment iron core 5a, magnetic saturation of the impedance adjustment iron core 5a can be prevented. Therefore, when an excessive current flows through the transformer, magnetic saturation does not occur even near the peak value of the current waveform, and the impedance of the transformer can be prevented from changing.

In the above embodiment, the impedance adjustment device 5
Although it is assumed that the impedance adjustment device is fixed inside the winding, the impedance of the transformer can also be made variable by having a structure in which the impedance adjustment device can be slid along the axial direction of the winding. With this configuration, by detecting an increase in resonant current caused by connection or disconnection of a capacitor connected to the load side and sliding the impedance adjustment device, the transformer can be protected from harmonics of the power supply. Since the resonant frequency of the power supply line can be removed, the resonance phenomenon of the power supply line can be effectively suppressed and the function of the harmonic low impedance transformer can be further demonstrated, allowing the supply of high quality power. .

In each of the above embodiments, the impedance adjustment device 5 is disposed in a part of the circumferential direction between the primary and secondary windings, but it may also be disposed between both windings over substantially the entire circumference. good.

In the above embodiment, the short-circuit conductor 5b is provided so as to surround the iron core 5a of the impedance adjustment device 5, and the short-circuit conductor constitutes a closed circuit for impedance adjustment. A similar effect can be obtained by providing a conductor that is not short-circuited (not short-circuited) and connecting an appropriate capacitor between both ends of the conductor. With this configuration, the reactance of the capacitor is large at the fundamental frequency, so the current flowing through the closed circuit for impedance adjustment is small, and almost no repulsion magnetic field is generated.However, as the frequency increases, the reactance of the capacitor becomes smaller, so the impedance adjustment becomes more difficult. The current flowing through the closed circuit increases, creating a repelling magnetic field and reducing the rate of increase in transformer impedance.

With this configuration, it is possible to reduce the current flowing through the impedance adjustment closed circuit when the frequency is low, so that heat generation in the closed circuit can be suppressed.

[Effects of the Invention] As described above, according to the present invention, an impedance adjustment device including an impedance adjustment iron core and an impedance adjustment closed circuit surrounding the iron core is provided between a primary winding and a secondary winding. This reduces the rate of increase in the transformer impedance as the frequency increases, making it possible to reduce the voltage drop that occurs within the transformer due to harmonic components included in the load current, thereby improving the output voltage waveform of the transformer. This has the advantage that high-quality power can be supplied to the load with less distortion.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of a conventional transformer, FIG. 2 is a plan view of an embodiment of the present invention, FIG. 3 is a front view showing an example of an impedance adjustment device used in the embodiment of FIG. Figure 4 is a sectional view taken along the line A-A in Figure 3, Figure 5 is an equivalent circuit diagram of the harmonic low impedance transformer of the present invention, and Figure 6 is the impedance frequency of the conventional transformer and the transformer of the present invention. FIG. 7 is a front view showing another configuration example of the impedance adjustment device used in the present invention. 1... Iron core, 2... Secondary winding, 3... Primary winding, 5...
Impedance adjustment device, 5a... Iron core for impedance adjustment, 5b... Short circuit conductor, 6... Between, 7a~
7f...Iron core member.

Claims (1)

[Scope of Claims] 1. A transformer including a primary winding wound around an iron core and a secondary winding wound concentrically with the primary winding, comprising: an impedance adjusting iron core; and a secondary winding wound concentrically with the primary winding. A harmonic low impedance transformer, characterized in that an impedance adjustment device including a closed circuit for impedance adjustment provided so as to surround the iron core is disposed between the primary winding and the secondary winding. . 2. The harmonic low impedance transformer according to claim 1, wherein the impedance adjustment closed circuit is formed of a short-circuited conductor that is provided to surround the impedance adjustment core and is electrically connected at both ends. vessel. 3. The harmonic low impedance according to claim 1, wherein the impedance adjustment closed circuit is comprised of a conductor provided to surround the iron core and a capacitor connected between both ends of the conductor. transformer.