JPH02240903A - Winding of zero-phase current transformer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of winding a zero-sequence current transformer for detecting zero-sequence current.

[Conventional technology]

A conventional zero-phase current transformer with an oval shape such as an ellipse or a track type has an iron core 2 placed inside a protective case 1 as shown in FIGS. 8 and 9, and a coil 3 wound around the outside of the core 2. An inner shield 4, a side shield 5, and an outer shield θ are made of magnetic material on the outside. If we consider an easy-to-understand elliptical magnetic flux distribution of this elliptical zero-phase current transformer, it will be as shown in FIGS. 11(a) and 11(b). The direction of magnetic flux is indicated by an arrow.

From now on, the relationship between the primary current that does not include the zero-sequence current and the secondary winding will be determined by using two current transformers with gaps and connecting the secondary windings in series as shown in Figure 12. It can be seen that is a combination of current transformers that each conduct the same current in opposite directions. This equivalent circuit is as shown in Figure 13.

In FIG. 13, Rt is a zero-sequence current burden resistance, and this voltage vL is a differential voltage between the induced voltages in the windings, which is a residual voltage. The value obtained by converting this voltage into a zero-sequence current is the residual current.

Here, XLI and XL2 are on the order of several Ω due to the actance of the current transformer with a gap, and the current It/n flowing from the equivalent circuit to the secondary side is almost an exciting current. Therefore, even if the load resistor Rt is disconnected, the magnetization state of the core hardly changes, resulting in a circuit as shown in FIG. When the iron core is demagnetized and used at the 0 point of the B-H curve shown in Figure 15, the output of each current transformer A and B side also has a small change in magnetic flux with respect to the primary current, as shown in Figure 18. In this range, it becomes a sine wave.

Figure 16 (1) is the waveform of the current and magnetic field strength, Figure 18 ■
is the magnetic flux density B1. Fig. 18 (2) shows the waveforms of the induced voltage vl and Va, and Fig. 16 (2) shows the residual voltage. That is, the residual current has a small value. However, if direct current is included in the zero-sequence current, an overcurrent occurs, or a short circuit occurs in the primary current, and the magnetic flux of the iron core suddenly becomes O in the saturation region, it becomes magnetized, and B1 in Fig. 15 It is magnetized to a point.

When the primary current flows at this time, the magnetic flux and voltage waveforms of each current transformer become as shown in FIGS. 17 and 18.

That is, the magnetic flux is no longer a sine wave and the maximum value of the differential value of the magnetic flux is far from the zero point of the magnetic field, so the induced voltage Vt+v2, which is the voltage obtained by multiplying the differential value by the number of turns, becomes as shown in FIG. This value becomes the basis of the residual current.

In such cases, in order to reduce the leakage magnetic flux that enters the iron core, the conventional method is to use a shield material with high magnetic permeability and increase the volume so that the shield absorbs the leakage magnetic flux and reduces the magnetic flux that enters the iron core. Methods of increasing the cross-sectional area of the iron core, reducing the magnetic flux density in the iron core due to leakage magnetic flux, and reducing the amount of harmonics contained are being used.

[Problem to be solved by the invention]

In the conventional oblong zero-phase current transformer described above, a zero-sequence burden resistance RL is connected as shown in Figure 10, and two or three primary conductors 8 are passed through the window θ of the zero-phase current transformer. It is used by

The residual current is generated here because the leakage magnetic flux from the primary conductor 8 enters the iron core, so the shield material is made of a material with high magnetic permeability and is made thicker so that more of the leakage magnetic flux is absorbed by the shield. The cross-sectional area of the iron core was increased to prevent the amount of magnetic flux that has partially entered the iron core from becoming saturated due to leakage magnetic flux, and to reduce the harmonic distribution of the voltage (residual voltage) generated by leakage magnetic flux.

In order to compensate for the residual voltage caused by leakage magnetic flux due to variations in magnetic permeability in the magnetic path of the iron core, the density of the windings was partially changed. That is, in order to reduce the leakage flux that enters the iron core, a method is taken in which a shield is applied and the induced voltage generated by the leakage flux that has entered the iron core is offset by the terminal voltage borne by the zero-sequence. Therefore,
When the primary current increases, the only options are to increase the number of shields, use higher permeability and higher saturation magnetic flux density, or increase the cross-sectional area of the iron core.

In addition, the iron core may cause ground fault current (zero-sequence current) to flow on the primary side.
When measuring the resistance of the secondary winding, it may be magnetized to a maximum residual magnetic flux density B by flowing a direct current. In this state, when a current is rapidly passed through the primary conductor, ■
In addition, DC current is also included, and the output as shown in Figure 19 (■) is applied to the zero-sequence load, the transient state is stabilized, and the 17th
The waveform will be like ■ in the figure. Therefore, even if a core made of high permeability material is used, it is necessary to suppress the residual current by operating at the Br point, so the oval zero-phase current transformer has to be large compared to the core size required for zero-phase characteristics. ing.

The present invention provides an oval zero-phase current transformer that uses the same shielding material, core, and winding as conventional transformers, and even when the primary rated current is several times higher, the residual current is reduced compared to conventional transformers. It is an object of the present invention to provide a method of winding a zero-phase current transformer that can reduce the number of windings.

[Means for solving problems]

In order to achieve the above object, the present invention has an oval iron core built into an oval zero-phase current transformer, in which the long diameter side is
Winding wires with the same number of turns and opposite winding directions are wound around one half-circumference part and the other half-circumference part when viewed from the dividing center line, and the beginning and end of each winding are connected. It is characterized by allowing

[Effect]

The operation of the present invention will be explained below.

FIG. 1(a) is a wiring diagram of an example of the method of the present invention, showing the current flowing through the primary conductor 8! 8. The leakage reactance due to the A side of one half circumference of the iron core from the primary conductor 8 is Xt, ^, and the leakage reactance due to the B side of the other half circumference of the iron core is Xi,
If the winding on the a-A-B side is nI, the zero-sequence load is R, and the DC resistance of the winding is r, then the equivalent circuit in Figure 1(a) is as shown in Figure 1(b).
)become that way. This can also be rewritten as shown in FIG. 1(C). ILA and Ichika LB have different values.

Residual current converted to primary side1. becomes the exciting current of the current transformer, and the smaller the DC resistance, the smaller the residual current. As can be seen from FIGS. 1(a), (b), and (c), the present invention
, the secondary windings of the U-shaped current transformers with gaps are short-circuited on the B side, so the current flowing to the secondary flows as a circulating current between the windings and has no effect on the secondary zero-phase output. Don't give,
It acts as a magnetomotive force to reduce the leakage flux that enters the iron core due to the primary current.

If three-phase currents flow within the zero-phase current window as shown in Figure 2(a), the 11 currents in the center will be 1 as shown in Figure 2(b).
．． , 1. 1/2 on the side! Current value added by 8! .

: I, + 1/2・I, -1, :1. ÷1/2・
! The current of 3 changes to I□ and IT and can be replaced with a circuit as shown in FIG. 1(a).

FIG. 3 shows a case where the primary current flows on one side, and the magnetic flux distribution due to leakage flux at each core location is as shown in FIG. 3(b). The secondary winding of the current transformer with a gap is 1-1 in the diagram.
Since the section between 011 and 20 acts as the secondary side of each current transformer, as shown in Figure 3 (C)! , a value of 11, which is slightly lower than , works equivalently as the primary current in FIG. 1(a).

During magnetization, in the conventional type, the primary current acts as the excitation current of the U-shaped geared current transformer, so the excitation current is only alternating current, so the magnetic flux contains harmonics, and moreover, it is difficult to operate. Since the magnetic field is a sine wave, the points do not move at 87 points, and a large residual current is generated for a long time. In the conventional case, when viewed from an equivalent circuit, the direct current resistance of the winding is in series with the zero-sequence load RL, so changes in rl have little effect on the residual current.

In the present invention, as shown in FIG. 1(0), as the value of r becomes smaller, 1t/n flows toward the r side, and the sine wave component of the induced voltage of the XLA increases. The magnetic flux change is also an integral value of the induced voltage, so it becomes close to a sine wave, and when the iron core is magnetized, a DC component flows in the exciting current, which acts as self-demagnetization, so the generation of the second harmonic component disappears immediately. do.

〔Example〕

The present invention will be described in detail below based on FIGS. 4 to 7. In FIG. 4(a), reference numeral 10 denotes an oval iron core, and a center line 1 that bisects the long diameter side of this iron core 10
On one half circumference part A side when viewed from 1, a winding 12 is wound by winding from near one end C3 close to the center line 11 to near the other end C2, and then winding back from near the other end C2 to near one end C3. , intermediate tap 1 from the end of winding 12
3, and on the other half circumference part B side as seen from the center line 11, from near one end C3 close to the center line 11 to near the other end C2, the number of turns is the same as that of the winding 12 on the A side, but the winding direction is opposite. Then, from near the other end C2 to near one end C3, a winding 14 having the same number of turns as the winding 12 on the A side but wound in the opposite direction is wound. The winding end is connected to the winding beginning of the winding 12 15 , and the zero-sequence burden resistor 1B is connected between the connection part 15 and the middle tap 13 . The outer periphery of the iron core 10 around which the windings 12 and 14 are wound in this manner is provided with a shield similar to the conventional shield.

In addition to the above-described winding method, the present invention also provides windings 17 and 18 with the same number of turns and opposite winding directions on the A side and B side of the iron core 10, as shown in FIG. 4(b). winding, connecting 19 the beginning of winding 17 and the beginning of winding 18;
The end of the winding 17 and the end of the winding 18 may be connected 20, and a zero-sequence burden resistor 21 may be connected between these connections 19 and 20, as shown in FIG. 4(C). Winding wire 17.1B, which is the same as the winding shown in FIG.
Connect the end of winding 22 to the end of winding 17 and winding 1.
In some cases, the winding start of 8 is connected 23, and a zero-sequence burden resistor 24 is connected between these connecting parts 22 and 23. As shown in FIG. A winding 25 is wound around the winding 25, and a zero-sequence burden resistance 2
6, wind the same windings 17 and 18 as the winding shown in Fig. 4(b) around the A side and B side of the iron core 10, and connect the winding start of the winding 17 and the winding start of the winding 18. 27,
The end of the winding 17 and the end of the winding 18 may be connected 28. This winding 17,18 may be wound on the outside of the winding 25 or on the inside.

The difference in residual current characteristics between the conventional method and the method of the present invention is shown in FIGS. 6 and 7. Fig. 5 (2) shows a conventional type in which windings are uniformly wound around an iron core, inner, outer, and side shields 29 are provided, and a zero-phase load RL is connected.

The winding was cut at the midpoint P of the winding, the wire connection was changed as shown in Fig. 5 (1), and the burden resistance □ was set to 172. Look at the differences in current characteristics.

FIG. 6 shows the values of residual current when the iron core is demagnetized and the primary current is increased for the conventional product and the present invention. The diagram in the graph shows the position of the primary conductor within the zero-phase current transformer window and whether it is 2-phase or 3-phase. From FIG. 6(1), ■I■, and (2), there is no significant difference in residual characteristics when demagnetized.

FIG. 7 shows a comparison when a direct current is applied to the iron core to magnetize it.

In principle, the residual current of conventional products includes many even-numbered harmonics, such as the second harmonic, and will remain forever unless demagnetized. In the method of the present invention, the secondary winding of the zero-phase current transformer acts as a secondary short circuit of the gapped current transformer, so leakage flux in the iron core is reduced and residual current is reduced. The method of the present invention has the same effect even if it is performed on the iron core or on the iron core with a conventional winding and a shield applied thereon.

〔Effect of the invention〕

By applying the winding method of the present invention to oval-shaped zero-phase current transformers such as oval and track types, it is possible to suppress the amount of leakage magnetic flux from the primary side into the iron core, and reduce residual current, especially Since residual current during magnetization can be suppressed, characteristics can be improved. By increasing the diameter of the winding, the direct current resistance decreases, and the residual current can also be reduced.

Even if the same 9-winding iron core and the same shielding material are used, the rated primary current can be increased several times by carrying out the method of the present invention.

[Brief explanation of drawings]

Drawings 1 to 7 show examples of the method of the present invention, and FIG. 1(a) is a wiring diagram of an example of the method of the present invention;
Figures (b) and (c) are equivalent circuit diagrams of Figure 1 and Figure 2 (a).
, (b) is a diagram illustrating the present invention in detail in the case of three phases,
3(a), (b), and (c) are diagrams illustrating the present invention in detail in the case where the primary conductor is offset, and FIG. 4(a),
(b), (c) % (d) is a diagram showing four examples of winding wires according to the method of the present invention, FIG. 5 is a diagram showing an example of wiring for a comparative experiment between the present invention and a conventional product, and FIG. 6 (1),■,■,(
2) is a diagram showing the characteristics when the iron core is demagnetized in Figure 5, Figure 7 is a diagram showing a comparison of the residual current characteristics of the present invention and the conventional product when the iron core is magnetized, and Figure 8 is a diagram showing the characteristics when the iron core is magnetized. A diagram showing the structure of a conventional oval zero-phase current transformer, FIG. 8 is a sectional view taken along the line A-A in FIG. 8, FIG. 10 is a diagram showing an example of use of the conventional product, and FIG.
Figures (a) and (b) are diagrams showing the distribution of leakage magnetic flux generated from the primary current when current flows only in the R phase and T phase in Figure 10, and Figure 12 is a diagram showing the distribution of leakage magnetic flux as seen from the leakage magnetic flux. A diagram showing the equivalent magnetic flux distribution, FIG. 13 is a diagram showing the equivalent circuit of FIG. 12, FIG. 14 is a diagram showing the equivalent circuit of FIG. 12, FIG. 15 is a diagram showing the B-H curve of the iron core material, Figure 18 (1), ■, ■,
(2) is a waveform diagram of each location, Figure 17 is a diagram of each waveform accompanying the primary current on one half circumference side of the iron core when the iron core is magnetized, and Figure 18 is a diagram of each waveform accompanying the primary current on one half circumference side of the iron core when the iron core is magnetized. Each waveform diagram accompanying the primary current on the other half circumference side of the iron core, 1st
FIG. 9 is (1) and ■ is a waveform diagram of the residual current at the time of primary current inrush of the present invention and the conventional product when the iron core is magnetized. 10... Oval iron core, 11... Center line, 12...
・Winding 13...Intermediate tap, 4...Winding, 6...Connection part 7...Winding, 8...Winding, 9...Connection part,...Connection part.

Claims (1)

[Claims] In the oval iron core built in the oval zero-phase current transformer, one half circumference part when viewed from the center line that bisects the long diameter side,
A zero-phase current transformer characterized in that windings having the same number of windings and opposite winding directions are wound around the other half circumferential portion, and the winding start and winding end of each winding are connected. winding method.