JPH0426068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection device for high frequency current components, particularly high frequency current components caused by corona discharge due to insulation deterioration in power systems, high frequency current signals for system control, etc.

In order to effectively detect partial discharge currents or control high-frequency current signals that contain high-frequency current components caused by insulation deterioration or other causes in power systems where commercial-frequency load currents are flowing, it is necessary to It is widely used to connect a reactor in series and detect the voltage generated between its ends.This voltage is proportional to the frequency, and up to a certain frequency, the higher the frequency, the more efficiently the signal can be detected. This is well known.

However, a very large load current flows through this reactor, and for example, with an air-core coil, a large coil must be used to obtain a constant inductance. This has the disadvantage that it is affected by electromagnetic induction and that the high frequency detection voltage is lowered thereby. To solve this problem, a magnetic circuit with a ferromagnetic material as the core has been used instead of an air-core coil, but there are problems such as magnetic saturation and heat generation due to the large magnetomotive force caused by the load current.
In any case, it is difficult to create a small-sized detection device for such a signal.

An object of the present invention is to provide a small and extremely efficient detection device for high frequency current components in a power system.

According to the present invention, the above object is achieved by canceling only the magnetic flux generated by the commercial frequency current component and generating only the magnetic flux due to the high frequency current component.

The present invention will be described based on one embodiment shown in the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention, in which a first core 1 is made of a ferromagnetic material, and a second core 1 is made of a ferromagnetic material having a different magnetic viscosity.
A magnetic closed circuit is constructed using the iron core 2, coils 3 and 4 are respectively provided on these iron cores, and both coils are connected by a series depolarization connection. Therefore, in principle, no commercial frequency voltage is generated at the terminals 5 of the series coils until the current reaches saturation of each core due to leakage magnetic flux.

Figure 2 shows the frequency dependence of the magnetic permeability of the iron core.

The magnetic permeability characteristic of iron core 1 is shown as 6, and the magnetic permeability characteristic of iron core 2 is shown as 7. In this example, iron core 1 is 10K.
Magnetic permeability decreases with currents at frequencies higher than Hz. Therefore, the coil 3 begins to exhibit the properties of a reactor when the current has a frequency higher than that. In other words, this magnetic circuit has a frequency of 10K
Above Hz, air core coil 3 and iron core coil 4
acts as a series reactor. Since there is no need to consider magnetic flux due to commercial frequency current, the magnetic circuit itself can be sufficiently miniaturized.

By the way, the magnetic flux φ in the iron core is obtained by the following equation.

φ=BS=μNS=μNIS Here, B is the magnetic flux density, S is the cross-sectional area of the iron core, μ is magnetic permeability, N is the number of turns of the coil I is the current in the coil.

Therefore, the frequency of the current flowing through coil 3 now is
Assume that the permeability of iron core 1 is 18000 when the frequency of the current flowing through coil 4 is 1KHz, the permeability of iron core 2 is 1800 when the frequency of the current flowing through coil 4 is 1KHz, the number of turns of coil 3 is 10, and the number of turns of coil 4 is 100. , Further, assuming that the cross-sectional areas S of the iron cores 1 and 2 are equal and the currents I flowing through the coils 3 and 4 are also the same, the magnetic flux φ ₁ in the iron core 1 and the magnetic flux φ ₂ in the iron core 2 are respectively calculated by the following equations.

φ ₁ = μ ₆ N ₃ IS φ ₂ = μ ₇ N ₄ IS Where, μ ₆ is the magnetic permeability of core 1, N ₃ is the number of turns of coil 3, μ ₇ is the magnetic permeability of core 2, and N ₄ is the coil The number of turns is 4.

Then, in Fig. 1, coils 3 and 4 are
Since it is a depolarization connection, the magnetic flux φ in the closed magnetic path of iron cores 1 and 2 is as follows: φ=φ ₁ −φ ₂ =18000×10×I×S−1800×100×I×S =0. In other words, the closed magnetic circuit magnetic fluxes cancel each other out and become zero.

Furthermore, the inductance of the entire coils 3 and 4 in Fig. 1 is proportional to the equivalent magnetic permeability of the iron cores 1 and 2 (see Fig. 2), and the reactance of the entire coils 3 and 4 is the sum of their inductance and the current flowing there. Proportional to frequency. On the other hand, coils 3 and 4
When a commercial frequency load current flows through both ends 5 of the first
According to the configuration shown in the figure, the inductance is high in the high frequency band and acts as an inductance with high magnetic permeability in the high frequency band, and as a result, high frequency current components can be detected.

As described above, according to the present invention, the magnetic flux due to the commercial frequency current is canceled by the depolarized connection of the coil, and no voltage output is generated at the terminal 5. On the other hand, the high frequency current component is detected at the terminal 5 as an unbalanced component since the magnetic viscosity of the iron core of each coil is different.

Note that if the magnetic permeability and saturation magnetic flux density of each core are different for the commercial frequency current, the dimensions of one core and coil may be different from those of the other. A magnetic material having other characteristics is further inserted into the cores 1 and 2.
It is also possible to reduce the amount used and make the device even smaller.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the frequency dependence of the magnetic permeability of the iron core in the magnetic circuit of FIG. 1, 2... Iron core, 3, 4... Coil, 5... Terminal.

Claims (1)

[Claims] 1 One magnetic circuit is constructed by two types of magnetic materials with different magnetorheological viscosity, a coil is provided in each magnetic material part, and these coils are connected in series with depolarization, thereby constructing the above-mentioned one magnetic circuit. Two types of magnetic materials both have a constant magnetic permeability for commercial frequency current components, but one has a constant magnetic permeability for high frequency current components, but the other has a constant magnetic permeability for high frequency current components. 1. A high-frequency current component detection device, characterized in that a voltage is generated between terminals only for high-frequency current components by reducing the voltage.