JPS5913313A - Correction of d.c. field distortion in transformer - Google Patents

Abstract

PURPOSE:To positively correct D.C. field distortion produced in a transformer, by a method wherein current of second harmonic component to the power source frequency contained in exciting current flowing in a primary winding is detected by a current transformer and a band-pass filter, and output in a variable D.C. source is adjusted to make the current zero. CONSTITUTION:If exciting currents iU, iV, iW are detected at current transformers 3U, 3V, 3W and passed through band-pass filters 4U, 4V, 4W, output signals corresponding to D.C. field distortion amount are obtained in output side of the band-pass filters 4U, 4V, 4W. Variable D.C. power sources 5U, 5V, 5W receive the output signals of the band-pass filters and adjust respective outputs for these signals to become zero and supply D.C. currents to auxiliary windings 6U, 6V, 6W. D.C. field distortion existing in a transformer winding 1 is corrected to zero by D.C. currents supplied to the auxiliary windings 6U, 6V, 6W.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting DC bias in magnetic flux within an iron core generated in a transformer excited by a thyristor inverter or a transformer whose load is a thyristor converter.

In a transformer excited by a thyristor inverter or a transformer whose load is a thyristor converter, the excitation voltage waveform may vary between + and - due to irregularities in the thyristor firing phase angle and irregularities in the forward voltage drop of the thyristor diode.
This may cause an unbalance in the load current, or an imbalance in the + and – load currents. For this reason, a DC current flows through the transformer windings, and this DC current generates DC magnetic flux in the transformer core, and the DC magnetic flux is superimposed on the AC magnetic flux corresponding to the transformer winding terminal voltage. be done. This state is called DC biased magnetism. When DC bias magnetization occurs, adverse effects such as increased core loss, increased excitation current, increased magnetostriction, and, as a result, increased transformer noise occur. The magnitudes of iron loss, exciting current, and magnetostriction in the transformer core vary depending on the magnetic flux density corresponding to the applied AC voltage. For example, the magnetic flux density 'i7.7 (T)
From 1. When t, y (T:l is lowered by 10%, the iron loss decreases by about 25% and the excitation current decreases by about 70% in grain-oriented silicon steel sheets commonly used as power transformer cores.

For these reasons, conventional methods have been used to offset the deterioration of characteristics such as iron loss and excitation current due to DC bias magnetization by lowering the magnetic flux density corresponding to the applied AC voltage. Lowering the magnetic flux density results in an increase in the size of the transformer, which is undesirable from the viewpoint of resource conservation. Additionally, installing a transformer may pose transportation problems depending on the transportation conditions to the location.

In view of the above points, the present invention provides a method for actively correcting the DC bias magnetization that occurs.

δ Co■, CoW are the/next windings wound around the transformer core, JU.

3■, 3W are primary windings @2TJ, , 2V, JWK current transformers for detecting the flowing current, IU, dav, pw are current transformers JU.

3V, bandpass filter for extracting the co-harmonic of the current detected by JW 1. ltU, , ltV, &
W is an additional winding AU which takes as a signal input the =th harmonic current taken out by the bandpass filter 41U, DAV, and 4IW, generates a DC output according to the signal input, and is wound around the ℃ transformer iron core.

AV, 4WK each pass 4 DC currents, bandpass filter U14
The variable DC power supply 7U, 7V, 7W, which adjusts the output including the polarity so that the output of 1V, 41W becomes zero, uses a °C variable DC reactor by the AC voltage induced in the additional windings AU, AM, and AN. show.

tx secondary winding is omitted in the diagram, transformer iron core l
When no DC bias is generated in the excitation current iU, iV
, IW includes only odd harmonics of the power supply frequency,
When a DC bias occurs, even-order harmonics are included because the peak value on the positive side and the peak value on the one side of the exciting current are different in magnitude. For this purpose, the excitation currents iU, iV.

If 1W is detected by current transformer 3U%JV, 3W and passed through bandpass filter 4IU, da v1 da WK, bandpass filters U, da■
, DAW output signals corresponding to the amount of DC biased magnetism are obtained. The variable DC power supplies &U, jV, and jW receive this output signal, adjust their output so that the signal becomes zero voltage, and flow a current η directly to the additional windings 6U, 6V, and 4W. The direct current bias generated in the transformer core l is regulated to zero by the direct current flowing through the additional winding 6U%≦V%xWlca.

In this manner, the present invention achieves all of the stated objectives 1-
I can do that.

[Brief explanation of the drawing]

FIG. 1 is a partial circuit diagram of a three-phase transformer that implements this 8A power generation. lo...Transformer core, U, 2V, JW..., 7th winding, JU. JV, JW...Current transformer, GU%DAV, DAW...Band filter, jU, tV, SW...Variable DC power supply, 4U, AV, aw/7 additional winding, 7υ, 7V , 7W・
...Reactor. Agent Shin Kuzuno −

Claims (1)

[Claims] When a primary winding and an additional winding that does not conduct load current are wound around the transformer core, and a current transformer is provided on the primary winding, a bandpass filter is connected to the current transformer, and the additional winding is connected to a current transformer trap filter. A variable DC power source for flowing a DC vL current through the line is connected, and a current having a frequency component of one power supply frequency included in the excitation current flowing through the primary winding VC is detected by the current transformer and the bandpass filter. A method for correcting DC bias magnetism in a transformer, characterized in that the output kt4 of the variable DC power source is adjusted so that the current becomes zero, and the DC current is caused to flow through the additional winding.