JP2747043B2 - DC bias detection method for transformer core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for detecting the presence or absence of DC bias of a transformer core and the polarity of the DC bias.

(Prior art) Generally, in a frequency converter or a transformer for a DC power transmission system, a variation in the firing angle of the thyristor causes a problem.
Since the polarity of the current is unbalanced, a small amount of DC component current flows through the winding. Due to this DC current, the magnetic flux vibration A of the transformer core undergoes so-called DC bias, in which the magnetic flux vibration A is biased in either the positive or negative direction, as shown in FIG.

(Problems to be Solved by the Invention) However, if the transformer core is subjected to such DC bias, noise and loss will increase, and adverse effects such as overheating of the metal structure material around the core due to saturation of the core will occur. Occurs. For this reason, it is necessary to provide a means for preventing the above-mentioned adverse effects from being noticeable in the transformer, and there is a disadvantage that the cost is generally increased.

Therefore, in order to eliminate such drawbacks, the state of magnetization of the transformer core is detected, and a thyristor is controlled so as to generate a DC current in the direction of eliminating the magnetization, thereby demagnetizing the transformer core. Various methods for reducing the amount have been studied. However, at present, a method for measuring the state of magnetization of the iron core inexpensively and accurately has not been obtained.

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned drawbacks, and an object of the present invention is to provide a method for detecting DC bias of a transformer core which can easily detect the presence or absence of the DC bias of a transformer core and its polarity. Is to provide.

[Configuration of the invention]

(Means for Solving the Problems) The DC bias detection method for a transformer core according to the present invention uses an ampere-turn (number of turns × current) of each winding wound around the same iron leg of the transformer as a current transformer or the like. Of the transformer, determine the waveform of the sum of the ampere turns of each winding, and compare the positive and negative peak values of the sum of the ampere turns to determine the presence or absence of the DC bias of the transformer core and its polarity. It is characterized by detecting.

(Operation) According to the DC bias detection method of the transformer core of the present invention, the ampere-turn of each winding wound on the same core leg is detected by a measuring instrument such as a current transformer for an instrument, and the winding of each winding is detected. The waveform of the sum of the ampere turns is obtained, and the positive and negative peak values of the waveform of the sum of the ampere turns are compared to detect the presence or absence and the polarity of the DC bias of the transformer core.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of one embodiment of the present invention, in which the present invention is applied to a two-winding transformer. As shown in the figure, 1
A current transformer (hereinafter referred to as CT) 3 and CT4 are provided for detecting currents of the secondary winding 1 and the secondary winding 2. CT3, C
The output of T4 is taken into the arithmetic unit 5, where the CT
The ampere turn of each winding is calculated by multiplying the current of each winding obtained by 3 and CT4 by the number of turns of each winding, and the sum of each ampere turn is also calculated.

The sum of the ampere turns calculated by the arithmetic unit 5 is input to the waveform judging device 6 to judge the presence or absence of the DC bias.

The DC bias detection method of the present embodiment having such a configuration utilizes a phenomenon peculiar to DC bias described below. That is, generally, when a DC component current flows through the transformer winding, the iron core is demagnetized, and as shown in FIG. 2, the magnetic flux A and the exciting current B in the iron core become the excitation characteristic curve C (φ−I
(Characteristics) Vibrates in a biased manner. Therefore, the oscillation of the exciting current B becomes asymmetric because the DC component current D is included, and the iron core is magnetized until the DC component current D becomes equal to the DC component of the current flowing from the outside.

The excitation current waveform at the time of DC bias is shown in FIG.
Distortion occurs due to the excitation characteristic C of the iron core, and the peak value on the same polarity side as the DC bias becomes larger and the peak on the opposite polarity side as the bias becomes smaller.

On the other hand, the sum of the ampere turns of each winding calculated by the arithmetic unit 5 cancels out the load current and becomes zero, and eventually becomes an ampere turn corresponding to the exciting current.

Therefore, the waveform determination device 6 compares the ampere-turn sum of each winding, that is, the positive and negative peak values of the exciting current waveform, and if the magnitudes are equal, “no DC bias”;
If the magnitudes are different, it can be determined that "DC bias exists". Also, by determining which of the positive and negative peaks is larger, the polarity of the DC bias can also be determined.

As described above, according to the present embodiment, the presence / absence of the DC bias of the transformer core and the polarity thereof can be easily and accurately detected. Further, since the detection device is simple, it can be obtained at low cost. In addition, it is possible to obtain a system that detects the state of magnetic polarization of the transformer core and controls the thyristor based on the detection result, thereby reducing the amount of magnetic polarization of the core. And transformer costs can be reduced.

Although the above embodiment has been described with respect to the two-winding transformer, it is apparent that the present invention can be applied to other transformers to detect the presence or absence of the DC bias and the polarity thereof.

〔The invention's effect〕

As described above, according to the present invention, the ampere-turn of each winding wound on the same iron leg of the transformer is detected by a simple means such as a current transformer, and the waveform of the sum of the ampere-turns of each winding is detected. The presence or absence of the DC bias of the transformer core and the polarity thereof can be detected from the positive and negative peak values of.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment in which the DC bias detection method for a transformer core according to the present invention is applied to a transformer, and FIG. 2 is a diagram showing magnetic flux, exciting current, and core excitation characteristics at the time of DC bias. is there. DESCRIPTION OF SYMBOLS 1 ... Primary winding, 2 ... Secondary winding 3 ... CT for primary winding 4, ... CT for secondary winding 5 ... Computing device, 6 ... Waveform judging device A ... Core Internal magnetic flux, B: Excitation current C: Core excitation characteristics, D: DC component of excitation current E: Amount of core deflection

Claims (1)

(57) [Claims] 1. An ampere-turn of each winding wound around the same iron core leg of a transformer is detected by a measuring device such as a current transformer, and a waveform of the sum of the ampere-turns of each winding is obtained. A method for detecting DC polarization of a transformer core, comprising comparing the positive and negative peak values of the sum waveform to detect the presence or absence and the polarity of DC polarization of the transformer core.