JPH07104736B2 - DC bias magnetism detection method for transformer - Google Patents

Description

The present invention relates to a method for detecting DC bias magnetism in a transformer.

[Prior Art] For example, in an inverter using a transistor, a DC component is included in an output AC voltage due to variations in voltage drop of each arm of an inverter circuit, variations in conduction period of a transistor, and the like. Due to this DC component, the transformer of the load connected to the output of the main circuit of the inverter causes DC bias magnetization, which causes deterioration of characteristics such as increase in iron loss, exciting current, and noise. There must be.

Conventionally, as a method for detecting the DC bias magnetism of this type of transformer, for example, as in Japanese Patent Application No. 62-28353, a saturable reactor is connected in parallel to the main circuit of an inverter, and a current is supplied by the saturable reactor. There is a method of using the current detecting means for detecting and the polarity determining means for determining the current polarity of the reactor detected by the current detecting means by a photo coupler.

[Problems to be Solved by the Invention] However, in the conventional DC bias magnetic field detection method for a transformer as described above, since another device called a saturable reactor is required, an extra installation space is required, and There are problems that the saturable reactor itself causes loss and noise, or that the saturable reactor is difficult to maintain during operation.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for detecting a DC bias magnetic field in a transformer that does not require extra space and does not cause loss or noise. To aim.

[Means for Solving the Problems]

The direct current bias magnetic detection method for a transformer according to the present invention focuses on the fact that the magnetizing force of the iron core becomes positive and negative asymmetric when the direct current bias of the iron core of the transformer is generated, and the proximity of the magnetic circuit composed of the iron core is considered. A search coil is provided on the outer surface of the high resistance non-magnetic portion of the tank to detect the DC bias of the transformer by directly monitoring the magnetizing force of the iron core from outside the tank.

[Action]

In the present invention, the change in the magnetizing force of the iron core is detected by comparing the magnitudes of the positive and negative peak values of the waveform obtained by integrating the output voltage of the search coil, and the presence or absence of DC bias magnetization is determined.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
FIG. 1 is a horizontal sectional view showing a transformer for explaining an embodiment of the present invention, and here, an outer iron type transformer is taken as an example. 2 (a) and 2 (b) are configuration diagrams of the transformer of FIG. 1 when viewed from the front and side surfaces, and FIG. 1 shows a cross section taken along the line AA ′ of FIG. FIG. 3 is a block diagram showing a DC bias magnetic detection circuit used in an embodiment of the present invention. 4 (a) (b) and 5 (a) (b) are the third
FIG. 4 is a characteristic diagram showing a magnetic field H obtained by the DC bias magnetic detection circuit in the figure together with a magnetic flux φ. FIG. 4 shows a case where DC bias is not occurring, and FIG. 5 is a case where DC bias is occurring. There is.

In FIG. 1, 1-1 and 1-2 are iron cores of a transformer around which a high voltage coil 2 and a low voltage coil 3 are wound, and 4 is a high resistance non-contact of a tank 5 close to the transformer iron cores 1-1 and 1-2. A search coil provided on the outer surface of the magnetic part 15 (for example, made of stainless steel), which is housed in the search coil mounting box 8 and the cover 9, and is the transformer iron 1-1 in the tank 5.
A part of the magnetic flux leaking from 1-2 passes through the high resistance non-magnetic portion 15 of the tank and is mounted on the outer surface of the tank 5 in the search coil 4
Link to. An output terminal 7 is provided on the search coil 4 and is drawn out from the search coil mounting box 8. The symbols i _L , φ, and H shown in Fig. 1 respectively indicate the exciting current, magnetic flux, and magnetic field (magnetizing force of the iron core) when this transformer is in the unloaded excitation state from the low voltage side. (Corresponding to).

In FIG. 2, a tank 5 accommodates irons 1-1 and 1-2, a high-voltage coil 2 and a low-voltage coil 3, and constitutes a transformer. The high voltage coil 2 has pushers 6-1 and 6-2.
Are connected to secure insulation from the tank 5.

In FIG. 3, reference numeral 10 denotes the transformer shown in FIGS. 1 and 2, and an inverter 11 is connected to the high voltage coil 2 of the transformer 10.

The output voltage E obtained from the output terminal of the search coil 4 is integrated by the integrator 12, and the integrated output voltage E _H is input to the positive side peak value detector 13-1 and the negative side peak value detector 13-2. It

The positive side peak value H _{+ P} and the negative side peak value H- _P detected by the respective peak value detectors 13-1 and 13-2 are input to the comparator 14, and from this comparator 14, ΔH = H _{+ The} peak difference ΔH given by _P− H− _P is output.

Next, referring to the characteristic waveform diagrams of FIGS. 4 and 5,
An embodiment of the present invention for detecting a DC bias by comparing the positive peak value H _{+ P} and the negative peak value H _-P with each other will be described. The output voltage E of the search coil 4 is given by the time derivative of the magnetic field of the space where the search coil 4 is installed, that is, the equation (1).

E = N ・ S ・ μdH / dt (1) where E: Search coil output [V] N: Search coil winding [Turn] S: Search coil cross-sectional area [m ² ] μ: Search coil magnetic core Permeability [H / m] H: magnetic field [A] The output E _H of the integrator 12 is the time integration of the search coil output E and corresponds to the original magnetic field H.

That is, there is a relationship of the formula (2).

E _H = A∫Edt = AH / N · S · μ (2) where A: integration constant of integrator The positive peak value detector 13-1 and the negative side peak value detector 13 in FIG. -2 detects the positive side peak value H _{+ P} and the negative side peak value H _-P of the magnetic field shown in FIGS. 4 and 5, respectively.

At this time, if the DC bias is not generated, the magnetizing force of the iron core 1 is positive and negative symmetrical, so the positive peak value H _{+ P} and the negative peak value H _-P of the magnetic field H are symmetrical as shown in FIG. And the peak difference ΔH becomes zero.

On the other hand, when DC bias is generated, the magnetizing force of the iron core 1 becomes positive and negative asymmetrical. Therefore, for the magnetic flux φ similar to that in FIG. 4, the peak values H _{+ P} and H _-P are as shown in FIG. It becomes asymmetric, and for example, the negative peak value H _−P becomes smaller. Therefore, the comparator 14
It can be seen that the DC bias magnetism occurs due to the peak difference ΔH output from.

It is also possible to detect the DC bias magnetism by performing the Fourier series expansion of the output voltage waveform of the search coil 4 or the Fourier series expansion after integration. When DC bias is generated, the waveforms of E and E _H include even harmonics because the positive and negative sides are asymmetrical. Therefore, it is possible to determine that the DC bias is generated depending on whether or not there is an even number breakdown by performing Fourier series expansion.

By the way, as a method for detecting a DC bias magnetic field using a search coil, a method for detecting a DC bias magnetic field in the vicinity of an iron core in a tank of a transformer,
Although it may be possible to arrange it at approximately the center of -2, it is difficult to replace it when the search coil fails.

On the other hand, in the configuration as shown in FIG. 1 and FIG. 2, for example, when the search coil 4 fails, the cover 9 is removed and the search coil 4 is inspected to repair or replace the failed part entirely. Take appropriate action depending on the situation. After that, the cover 9 is attached and the work is completed. In this way, since the DC bias magnetism can be detected from the outside of the transformer, it is easy to replace it even if the search coil fails.

[Effects of the Invention] As described above, according to the present invention, a portion of the tank outer wall made of a magnetic material, which is close to the transformer iron core, is configured by a high resistance non-magnetic portion, and the outer surface of the high resistance non-magnetic portion is Since we installed a search coil to detect the biased state of the transformer core,
The DC bias magnetism of the transformer can be easily detected by the search coil provided outside the tank, and the search coil can be easily replaced and maintained even during operation of the transformer.

[Brief description of drawings]

FIG. 1 is a horizontal cross-sectional view of an outer iron type transformer for explaining an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are configuration diagrams of the transformer of FIG. 1 viewed from the front and side. FIG. 3 is a block diagram showing a DC bias magnetic detection circuit used in an embodiment of the present invention, and FIGS. 4 (a) (b) and 5 (a) (b) are embodiments of the present invention. FIG. 7 is various waveform diagrams showing characteristics of a magnetic field and a magnetic flux for explaining the above. 1-1, 1-2 ... iron core, 4 ... search coil 5 ... tank, 12 ... integrator 13-1 ... positive side peak value detector 13-1 ... negative side peak value detector 14 ... Comparator, 15 ... High resistance non-magnetic part of tank Incidentally, in the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A search coil is provided in the vicinity of a transformer core that constitutes a magnetic circuit, the output voltage of the search coil is integrated, and the magnitudes of the positive side peak value and the negative side peak value of the waveform after integration are compared. In the method of detecting a DC bias magnetic field of a transformer for detecting a DC bias magnetic field, a part of the outer wall of the tank made of a magnetic material that houses the transformer core is composed of a high resistance non-magnetic part, A method for detecting a DC bias in a transformer, characterized in that the search coil is provided on an outer surface of a resistance non-magnetic portion.