JPH0537459Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The effect of this invention is that the shunt circuit is connected in parallel to the power system to absorb the charging current to the ground or line-to-line capacitance of the power transmission line. Regarding reactors.

[Conventional technology]

A shunt reactor is connected in parallel to a transmission line in order to suppress the voltage rise on the receiving side due to the charging current to the ground capacitance of the transmission line and line capacitance, and its capacity varies depending on the system. is a relatively large-capacity inductor with tens of thousands of kVA.

Since the power transmission system is a three-phase circuit, the shunt reactor is usually configured into one shunt reactor for three phases, and an example of its internal configuration is shown in FIG.

Figure 2 is an elevational view of the internal configuration of the shunt reactor, with a core leg with a gap having several voids, 2UA a coil wound around a core leg 1UA with a gap, and 2VA a coil wound around a core leg 1VA with a gap. The coil, 2WA, is the coil wrapped around the gapped core leg 1WA, 11A.
12A is an upper yoke that magnetically connects the air-gap core legs 1UA, 1VA, and 1WA at the upper part, and 12A is a lower yoke that magnetically connects the lower parts.

If the voltage of the system to which this shunt reactor is connected is a three-phase balanced voltage in a steady state, the magnetic flux induced by the coils 2UA, 2VA, and 2WA of each phase in the respective air-gapped core legs 1UA, 1VA, and 1WA is also Since it is a three-phase balanced magnetic flux, the magnetic fluxes of these three phases gather in the upper yoke 11A and cancel each other out, so that no magnetic flux leaks from the upper yoke 11 to the outside. In the same way, lower yoke 12
There is no magnetic flux leaking from A to the outside. Therefore, the reactance of each phase is 1UA, 1UA,
The value is determined by the void length and cross-sectional area of 1WA.
On the other hand, when an accident such as a line-to-ground fault occurs and the potential at the neutral point of the system increases, the voltage of each phase becomes unbalanced and includes a zero-sequence voltage, and this zero-sequence voltage is applied to the shunt reactor. Coil 2UA, 2 for each phase of
Applied to VA, 2WA, gapped core leg 1UA,
The magnetic fluxes induced in 1VA and 1WA are in phase in each phase, and the sum of the magnetic fluxes of each phase gathered on the upper yoke 11A does not become zero, so this magnetic flux leaks into space and is distributed around the shunt reactor. The magnetic circuit passes through the space and gathers at the lower yoke 12A, forming a magnetic circuit that makes the surrounding space a part of it. As a result, the magnetic resistance of the magnetic circuit becomes larger than in the case of three-phase balanced magnetic flux, and the zero-sequence reactance as the reactance of this shunt reactor with respect to the zero-sequence voltage is equal to the reactance in the case of three-phase balanced magnetic flux. The value is smaller than the positive phase or negative phase reactance. In normal core dimensions and shapes, the zero-sequence reactance is approximately 50% of the positive-sequence reactance.

Figure 3 is an elevational view of another internal configuration of the shunt reactor. In this figure, 1UB, 1VB, and 1WB are core legs with multiple voids, and 2UB is a core leg with voids wrapped around core leg 1UB. The coil, 2VB, is a coil wound around the gapped core leg 1VB, 2WB is the coil wound around the gapped core leg 1WB, and 11B is the upper part that magnetically connects the gapped core legs 1UB, 1VB, and 1WB at the top. The yoke 12B is a lower yoke which also magnetically connects the lower part, and these have the same structure as the one shown in FIG. 2, except that the indexes A and B are different. 13B and 14B are return legs that magnetically connect the upper yoke 11B and the lower yoke 12B.

When the voltage applied to the shunt reactor does not include a zero-phase component, the core legs 1UB and 1 with gaps of each phase gather at the upper yoke 11B and the lower yoke 12B.
Since the magnetic fluxes VB and 1WB cancel each other out, no magnetic flux flows through the return legs 13B and 14B. on the other hand,
When the applied voltage includes a zero-sequence component, this zero-sequence voltage causes the gap core legs 1UB, 1VB,
The magnetic flux induced in 1WB is the return legs 13B and 14B.
and flows from the upper yoke 11B to the lower yoke 1.
2B, so the magnetic resistance during this period is small, so the zero-sequence reactance in the case of the shunt reactor of the return leg as shown in this figure has almost the same value as the positive-sequence reactance.

In this way, when a return leg is not provided, the zero-sequence reactance of the shunt reactor is approximately 50% of the positive-sequence reactance, and when a return leg is provided, it is 100%.

Note that the resistance caused by coil resistance and iron loss is usually one order of magnitude smaller than the positive-sequence reactance and zero-sequence reactance, so the impedance of the shunt reactor as the vector sum of the reactance and resistance is the reactance. is almost the same.

[The problem that the idea aims to solve]

In order to detect faults in the grid, a method is sometimes used in which the zero-sequence current is measured and the occurrence of the fault is determined based on that value.In this case, if the zero-sequence impedance of the grid is large, the Because the phase current is small, there is a problem of low fault detection sensitivity, and conversely, if the zero-sequence impedance is too small, the zero-sequence current at the time of a fault becomes excessive, causing another problem. There will be an optimal zero-sequence impedance of . For this reason, there are cases where a shunt reactor is required to have a zero-sequence impedance that is, for example, 70% of the positive-sequence impedance. Although it is easy to manufacture a shunt reactor with a zero-sequence impedance of such an intermediate value, it has been impossible to design and manufacture a shunt reactor with such an intermediate value of zero-sequence impedance.

The purpose of this invention is to provide a configuration of a shunt reactor that can set the zero-sequence impedance of the shunt reactor to an intermediate value between about 50% and 100% of the positive-sequence impedance depending on the presence or absence of a return leg.

[Means to solve the problem]

In order to solve the above-mentioned problems, according to this invention, three core legs with gaps around which coils are wound,
An upper yoke that magnetically connects these gapped core legs at the top, a lower yoke that magnetically connects each of the gapped core legs at the bottom, and a magnetically connected upper yoke and the lower yoke. A coil is wound around the return leg, and a circuit element having an impedance of a predetermined value is connected to terminals at both ends of the coil.

[Effect]

In the configuration of this device, when the voltage applied to the shunt reactor contains a zero-sequence component, the magnetic flux of each air-gapped core leg induced by this zero-sequence voltage is magnetically connected by the return leg. It flows through a magnetic circuit that passes through the upper yoke and the lower yoke. When a return leg coil is wound around this return leg and a circuit element having a predetermined impedance, such as a reactor, is connected to this return leg coil, a voltage is induced in the return leg coil by the magnetic flux flowing through the return leg, and the voltage is induced in the circuit element. Current flows, but the value of the impedance of this circuit element changes the voltage induced in the return leg coil, which in turn changes the value of the magnetic flux passing through the return leg. In other words, if the impedance of the circuit element is made small, the magnetic flux flowing through the return leg will be reduced, so the impedance as a shunt reactor will be close to the value shown in Figure 2 without the return leg.If the impedance of the circuit element is made sufficiently large, the return leg will be Magnetic flux flows freely through the legs, and the impedance as a shunt reactor is the same as in Figure 3 with the return leg, so by setting the impedance of the circuit elements to an appropriate value, the impedance when there is no return leg can be changed. An intermediate value between a small zero-sequence impedance value and a large zero-sequence impedance value with a return leg can be arbitrarily set.

Furthermore, if a capacitor is used as a circuit element, the equivalent circuit becomes an LC parallel resonant circuit.
It is also possible to set the zero-sequence impedance of the shunt reactor to a value of 100% or more of the positive-sequence impedance.

〔Example〕

This invention will be explained below based on examples. Figure 1 is an elevational view of the core and coil of a shunt reactor showing an embodiment of this invention, 1U, 1V, 1W are core legs with air gaps, 11 is an upper yoke, 12 is a lower yoke,
13 is the return leg; 2U, 2V, and 2W are coils wound around each gap core leg 1U, 1V, and 1W; 2 is a return leg coil wound around the return leg 13; 3 is both ends of the return leg coil 3. A reactor is a circuit element connected to a reactor.

When the voltage applied to this shunt reactor includes a zero-sequence component, the magnetic flux induced in each air-gapped core leg by this zero-sequence voltage becomes zero-sequence magnetic flux with the same phase and direction in each phase. This zero-phase magnetic flux gathers in the upper yoke 11 and then separates into two parts: a magnetic flux that returns to the lower yoke 12 through the return leg 13 and a magnetic flux that returns to the lower yoke 12 through the surrounding space. If the impedance of the reactor 3 is sufficiently large or if the reactor 3 is not connected and the return leg coil 2 is open, it will be the same as the case of the shunt reactor with a return leg in Figure 3, and the zero-sequence impedance will be the positive-sequence impedance. becomes a value equal to .

On the other hand, if the impedance value of the reactor 3 is sufficiently small or if both ends of the return leg coil 2 are short-circuited, no magnetic flux can flow through the return leg 13, and all the zero-sequence magnetic flux that has gathered in the upper yoke 11 is separated. It reaches the lower yoke 12 through the space around the line reactor, and since this is the same as the shunt reactor without a return leg in Figure 2, its zero-sequence impedance is approximately 50% of the positive-sequence impedance as described above. %become.

In this way, the zero-sequence impedance of the shunt reactor changes between approximately 50% and 100% of the positive-sequence impedance depending on the impedance value of reactor 3, so set the impedance value of reactor 3 to an appropriate value. By doing so, the zero-sequence impedance of the shunt reactor can be set to an arbitrary value between about 50% and 100% of the positive-sequence impedance.

Furthermore, if a capacitor is used as a circuit element, the equivalent circuit becomes an LC parallel resonant circuit, so it is possible to set the zero-sequence impedance of the shunt reactor to a value of 10% or more of the positive-sequence impedance.

The cross-sectional area of the return leg 13 must have a value that does not saturate with respect to the maximum amount of magnetic flux passing through this cross-sectional area, but if the required zero-sequence impedance is close to the value without the return leg. Since the magnetic flux passing through the return leg may be small, the cross-sectional area of the return leg may be small. Conversely, if the required zero-sequence impedance is close to that with a return leg, a return leg with a large cross section is required. However, the zero-sequence voltage that occurs in the event of an accident such as a line-to-ground fault in a system is a value that depends on the constants of many devices connected to the system, so an appropriate value must be set taking these into account. Ru.

The smaller the required zero-sequence impedance, the larger the number of turns and conductor cross-sectional area of the return leg coil 2 should be. Since the time is generally several seconds or less, coil 2
Usually, a much smaller coil is required compared to U, 2V, and 2W.

In Figure 1, the return leg is provided only on one side on the left side, but it is also possible to install two return legs on both sides.In this case, a return leg coil of the same structure is wound around both of the two return legs. However, these two return leg coils are connected in series or in parallel to form one electrical unit.

By making both the return leg and the return leg coil larger than the originally required size, when this shunt reactor is relocated to another system, the impedance of the reactor 3 described above can be adjusted to the location where it is relocated. This shunt reactor can be reused by replacing it with a shunt reactor with a value that has a zero-sequence impedance suitable for the system.

The reactor 3 is an inductor as shown in FIG. 1, but in this case, the zero-sequence impedance of the shunt reactor is mostly composed of reactance and the resistance component is small. A resistor can be used instead of the reactor 3 as a circuit element connected to the return leg coil 2, and in this case, the zero-phase impedance of the shunt reactor to be set will contain a large resistance component. Furthermore, by using a capacitor as a circuit element, the zero-sequence impedance of the shunt reactor can be made larger than the positive-sequence impedance. The reason why the zero-sequence impedance is larger than the positive-sequence impedance in this way is because the inductance of the iron core leg and the capacitance of this capacitor form a parallel circuit as an equivalent circuit, and the value of the capacitor is such that this parallel circuit resonates. Then, it is theoretically possible to make the zero-sequence impedance several times the value of the positive-sequence impedance.

By appropriately selecting the circuit elements connected to the return leg coil 2, it is possible to set the zero-sequence impedance of the shunt reactor in a wide range.

[Effect of idea]

As mentioned above, this idea reduces the zero-sequence impedance of the shunt reactor by winding a return leg coil around the return leg of a three-phase shunt reactor having a return leg and connecting circuit elements to both ends of the coil. The value can be set to any value greater than approximately 50% of the positive sequence impedance. As a result, the zero-sequence impedance of the shunt reactor is set to provide appropriate detection sensitivity when a fault such as a line-to-ground fault in the system to which this shunt reactor is connected is detected by detecting zero-sequence current. be able to. In addition, by replacing the reactor connected to the return leg coil wound on the return leg with one with a different reactance, when this shunt reactor is transferred to another system, the zero-sequence impedance is adjusted to suit the system to which it is transferred. It can also be made into a shunt reactor with

[Brief explanation of the drawing]

Figure 1 is an elevational view showing the configuration of the iron core and coil of a shunt reactor as an embodiment of this invention;
The figure is a conventional elevational view, and FIG. 3 is another conventional elevational view. 1U, 1V, 1W, 1UA, 1VA, 1WA,
1UB, 1VB, 1WB... Core leg with void, 11,
11A, 11B... Upper yoke, 12, 12A, 1
2B...Lower yoke, 13, 13B, 14B...Return leg, 2U, 2V, 2W, 2UA, 2VA, 2
WA, 2UB, 2VA, 2WA...Coil, 2...
Return leg coil, 3...Reactor (circuit element).

Claims (1)

[Scope of utility model registration request] three core legs with gaps around which coils are wound; an upper yoke that magnetically connects the core legs with gaps at the upper part; and a lower part that magnetically connects each of the core legs with gaps at the bottom. In a device consisting of a yoke and a return leg that magnetically connects the upper yoke and the lower yoke, a coil is wound around the return leg, and an impedance of a predetermined value is applied to terminals at both ends of the coil. A shunt reactor characterized in that circuit elements having the following are connected.