JP3015780B2 - Current limiting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current limiting device, and more particularly, to a current limiting device, which is applied to all power systems such as low-voltage, high-voltage, extra-high-voltage, and extra-high-voltage systems, to increase the capacity of the power system, and to expand grid interconnection. The present invention relates to a current limiting device for suppressing a short-circuit current that increases with the current limiting.

[0002]

2. Description of the Related Art For example, in all power systems such as low-voltage, high-voltage, extra-high-voltage, and extra-high-voltage systems, the short-circuit current flowing when a system short-circuit occurs tends to increase with the increase in capacity and system interconnection. As a measure to suppress this short-circuit current, it is necessary to install a current limiting device in the power system.

Conventionally, a current limiting reactor has been generally used as a current limiting device installed in an electric power system. That is, as shown in FIG. 8, in a basic grid interconnection system of two electric power systems, the current limiting device has a current limiting reactor 3 connected in series between a power source 1 and a power source 2. In this system interconnection system, when a short-circuit accident occurs, an excessive short-circuit current flowing in the power system is suppressed by the current-limiting action of the current-limiting reactor 3.

[0004]

By the way, in a current limiting device in which a current limiting reactor 3 is connected in series with a power system as in the prior art, the current limiting reactor 3 is always inserted in the power system. , The steady-state stability of the battery decreased, and the transmission capacity was limited. Further, when a short circuit accident occurs, it is not preferable to disconnect the interconnection of the two power supply systems before removing the point of the accident.

Accordingly, the present invention has been proposed in view of the above-mentioned problems, and aims at ensuring the stability of the system and maintaining the interconnection between the two power supply systems at the time of a short circuit accident. Another object of the present invention is to provide a current limiting device exhibiting a predetermined current limiting effect.

[0006]

As a technical means for achieving the above-mentioned object, the present invention relates to a method for connecting an AC terminal of a single-phase diode bridge circuit in series with a power system, A current limiting device in which a DC reactor is connected between DC terminals and an AC reactor is connected in parallel with a single-phase diode bridge circuit. Divided by the current limiting ratio divided by the short-circuit current without the current limiting device, and multiplied by the short-circuit impedance (inductance) of the power system, the inductance of the DC reactor within the range of 2 to 24 times Is selected.

[0007] The current limiting device of the present invention is a rectifier type current limiting device. Since current flows through a single-phase diode bridge circuit under normal conditions without a short circuit, the impedance seen from the AC side becomes zero. No voltage drop occurs at the time,
There is no limit on the transmission capacity, and the stability of the system does not decrease.

Further, since the AC reactor is bypass-connected to the single-phase diode bridge circuit, in the event of a short-circuit accident, the current is limited at a high speed by the DC reactor and then commutated to the AC reactor to connect the power system. The current limiting function for suppressing the short-circuit current can be continued without interrupting the system.

Further, in this current limiting device, the inductance of the DC reactor is selected within a range of 2 to 24 times the value obtained by dividing the current limiting time by the current limiting ratio and multiplying by the short-circuit impedance (inductance). based on the selection range of the inductance of the DC reactor, it can be adapted to the conditions in the various power system embodying the best current limiting device having a desired limiting ratio.

Here, if the inductance is smaller than twice the value obtained by dividing the current limiting time by the current limiting ratio and multiplying by the short-circuit impedance (inductance), it is difficult to exert a desired current limiting effect, and it is unsuitable. Yes, and an inductance larger than 24 times is not suitable in terms of cost in terms of lack of economy.

Further, the impedance of the AC reactor is set to an upper limit value determined from system conditions, five times the short-circuit impedance (when the above-mentioned current limiting ratio is less than 0.25), and twice (when the current limiting ratio is 0.25). (When the current limiting ratio is less than 0.4 to 0.55), and 0.2 times (when the current limiting ratio is 0.55 or more). by the choice between the lower limit value, the selection of the inductance of the DC reactor, it is possible to implement the economic current limiter in accordance with the specifications of the power system.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the current limiting device according to the present invention will be described in detail below.

The current limiting device of the embodiment shown in FIG.
A single-phase diode bridge circuit 11 is inserted and connected between a power supply 1 and a power supply 2. The single-phase diode bridge circuit 11 has a bridge configuration composed of _four diodes D _{1 to} D _4, with AC terminals 12 and 13 connected in series with the system, and a DC reactor 16 connected between DC terminals 14 and 15. Having. Further, the AC reactor 17 is bypass-connected in parallel with the single-phase diode bridge circuit 11.

In this current limiting device, the impedance viewed from the AC side becomes zero at the time of normal operation without a short circuit accident. As a result, no voltage drop occurs during normal operation without a short circuit accident,
There is no limit on the transmission capacity, and the stability of the system does not decrease.

On the other hand, when a short-circuit current flows due to the occurrence of a short-circuit accident, the DC reactor 16 is inserted in series between the AC terminals 12 and 13, and the DC reactor 16 is inserted.
By generating the terminal voltage, a current limiting function for suppressing a short-circuit current is exhibited. After current limiting at a high speed by the DC reactor 16, the circuit breaker 18 is opened while the current limiting function is being performed, and the single-phase diode bridge circuit 11 is disconnected. By commutating the short-circuit current to the AC reactor 17 by the disconnection by the circuit breaker 18, the current limiting function for suppressing the short-circuit current is continued without disconnecting the power system from the interconnection.

Here, the single-phase diode bridge circuit 11
By selecting the impedance of the inductance and AC reactor 17 DC reactor 16 at, it is possible to realize a current limiting device having a desired limiting ratio adapted to the various power system, detailing the method below I do.

First, a current limiting device of the type without the AC reactor 17 (FIG. 3A) will be considered. In the current limiting device, the short-circuit impedance of the power system is represented by X
_S (FIG. (A)), the short-circuit current without the current limiting device is represented by I
FIG. 4 (a) shows a simplified equivalent circuit of the _SCR [FIG. 4 (b)] and the target current limiting value at the time of a short-circuit _fault when there is a current limiting device _Itgt [FIG. 4 (c)]. FIG. 2B shows an equivalent circuit as viewed from the DC side.

The DC back voltage (average value) shown in FIG.

[0019]

(Equation 1)

Here, E indicates a line voltage.

On the other hand, if the DC current flowing through the DC reactor 16 is I _dc , the corresponding AC current (effective value)
I _ac

[0022]

(Equation 2)

## EQU1 ## This AC current _Iac is the current limit target value _Ittgt at the time of a short circuit accident. Therefore, the AC voltage _Vac at the input terminal of the single-phase diode bridge circuit 11 is

[0024]

(Equation 3)

## EQU1 ## However, ωL _S is a short-circuit impedance X _S. This AC voltage V
_When the relationship between _ac and the DC voltage V _dc is obtained, the DC voltage V
_dc is

[0026]

(Equation 4)

As shown in FIG. 4B, an equivalent circuit is obtained in which the inductance on the AC side is regarded as a resistance. When the DC current I _dc flowing through the DC reactor 16 is obtained from the equation (4), the general solution is as follows.

[0028]

(Equation 5)

The next, in a short circuit accident occurs when t = 0, the initial value of the DC current flowing through the inductance L _dc DC reactor _{16 I 0, t = ∞,} I SCR = V
₀ / _RS . Here, R _S is the equivalent resistance R in FIG.
_S = 2ωL _S / π. The constants A and B in the above equation (5) are obtained, and the DC reactor 16 is obtained from the equation (5).
DC current I _dc flowing through

[0030]

(Equation 6)

## EQU1 ## Thus, by giving the the current limiter to be limiting target value I _dc and duration maintained by t (time to open the circuit breaker 18 from the occurrence of short-circuit fault) in the equation (6), require inductance L _dc DC reactor 16 can be determined.

[0032]

(Equation 7)

Here, if the current before the short-circuit accident of the DC reactor 16 is omitted as I ₀ I _SCR , the above equation (7) becomes:

[0034]

(Equation 8)

## EQU1 ## Here, T ₀ is the period of the fundamental wave. This equation (8) (original equation) is represented by a curve shown by a solid line in FIG. FIG. 5 is for obtaining the inductance L _dc of the DC reactor 16 necessary for limiting the current in one cycle. The horizontal axis indicates the current limiting ratio ( _Itgt / I _SCR ), and the vertical axis indicates the inductance ratio (L _dc). / L _S / τ). Where τ = t
/ T ₀ , indicating the current limiting time (cycle number).

The denominator of the above equation (8) is I _dc / I _SCR <
Assuming I _dc / I _SCR = x, if the denominator of equation (8) is expanded in series,

[0037]

(Equation 9)

## EQU4 ## Therefore, as a first approximation of equation (8),

[0039]

(Equation 10)

Is obtained. As a result, the inductance L _dc of the DC reactor 16 becomes equal to the current limiting time τ (τ = t / T
₀ ) and the inductance behind the system L _S (short-circuit impedance X _S = ωL _S ) of the power system, and inversely proportional to the current-limiting ratio (target current-limiting value at short-circuit accident / short-circuit current without a current-limiting device). It turns out to be. Thus, if the current limiting time, the current limiting ratio, and the short-circuit impedance are determined as necessary in the power system, the inductance L _dc
Can be selected.

The selection range of the inductance _Ldc of the DC reactor 16 is as follows: when the inductance _Ldc selected by the first approximation of the equation (10) is near the current-limiting ratio ≒ 1, the equation of the equation (8) is used. The inductance L _dc selected by the first approximation is approximately twice as large as the selected inductance L _dc.
Is set to about 1/2 of the lower limit. Further, the upper limit is set to about twice the inductance _Ldc selected by the first approximation formula on the assumption that there is no extra margin in consideration of economy.

Therefore, the lower limit of the inductance L _dc of the DC reactor 16 is:

[0043]

[Equation 11]

Where the upper limit is

[0045]

(Equation 12)

Therefore, finally, the range of the inductance _Ldc of the DC reactor 16 is

[0047]

(Equation 13)

Is as follows. That is, the selection range of the inductance _Ldc is determined by setting the current limiting time τ (τ = t / T ₀ ) to the current limiting ratio (I _tgt).
/ I _SCR ) and multiplying by 2 to 8 times the value obtained by multiplying by the inductance L _S behind the system.

The inductance L smaller than twice the value obtained by dividing the current limiting time τ (τ = t / T ₀ ) by the current limiting ratio ( _Itgt / I _SCR ) and multiplying by the inductance L _S behind the system.
_{In the case of dc} , it is difficult to exhibit the desired current limiting effect, which is unsuitable.
_DC is not suitable because it lacks economy in terms of cost.

Next, an equivalent circuit of the current limiting device of the present invention having the AC reactor 17 as viewed from the DC side is shown in FIG.
(A) and (b). The equivalent circuit of FIG. 2B and FIG.
Comparing with the equivalent circuit of (b), it is the same equivalent circuit except that the inductance of the AC system is connected in parallel with the AC reactor 17 and that the DC power supply voltage is divided by the inductance. Therefore, similarly for the current limiting device having the AC reactor 17, the inductance L _dc of the DC reactor 16 can be obtained, and the inductance L _dc is:

[0051]

[Equation 14]

Is as follows. However,

[0053]

(Equation 15)

Here,

[0055]

(Equation 16)

Is the short-circuit current itself without the current limiting device. Therefore, normalizing the above equation (14) with the short-circuit current,

[0057]

[Equation 17]

Is obtained. Here, x = X _bps / X _S , and the current before the short-circuit accident of the DC reactor 16 is I ₀ ≪
Omitting as I _SCR ,

[0059]

(Equation 18)

From this equation (18), the current limiting ratio (I _tgt
/ I _SCR ) and the inductance ratio (L _dc / L _S / τ) for each value of x = X _bps / X _S in FIG.
Shown in The inductance L _dc of this DC reactor 16
When selecting the DC reactor 16, the impedance X _dc of the DC reactor 16 can be reduced as the impedance X _bps of the AC reactor 17 increases.
However, when the impedance X _bps of the AC reactor 17 is inserted into the system (when the circuit breaker 18 is opened), the stability of the system deteriorates and the amount of transmitted power decreases. The DC reactor 16
The impedance X _dc of the AC reactor 17
It is necessary to reduce the impedance X _bps.

However, during the current limiting operation of the DC reactor 16, the short-circuit current is also shunted to the AC reactor 17, so that the impedance X _{dc of the} DC reactor 16 is reduced.
Is larger than a certain value, the impedance X _bps of the AC reactor 17 becomes too small, and the current limiting effect of the AC reactor 17 decreases.

From these facts, an economically appropriate range is selected for the impedance of the DC reactor 16. Here, the current (corresponding to I _dc / √2) flowing through the single-phase diode bridge circuit 11 is inversely proportional to the impedance X _dc of the DC reactor 16 as a first approximation. That is,
The current I _dc flowing through the DC reactor 16 is I _dc / √2 = K / X _dc (where K is a proportional constant) Here, the current limit target value at the time of a short circuit accident is _Itgt , and the short circuit current of the AC reactor 17 is When I _bps, the _{I tgt = K / X dc +} I bps ∴ I bps = I tgt -K / X dc. The current limit target value _Itgt is a constant value determined by the power system. Impedance X of AC reactor 17
Impedance X of DC reactor 16 when _bps = ∞
_Assuming that _dc is X _{dc 短}絡, at this time, the short-circuit current I _bps of the AC reactor 17 becomes 0. Therefore, 0 = I _tgt −K / X _dc ∞ K = X _dc ∞ · I _tgt ＩI _bps = I _tgt (1−X _dc ∞ / X _dc ) Here, if n = X _dc / X _{dc お く} , I _bps = _Itgt (1-1 / n) _Ibps / _Itgt = (1-1 / n) And the ratio I _bps / I _tgt is represented by a curve (1-1 / n) as shown in FIG. 7, and the short-circuit current I _bps of the AC reactor 17 is changed when the short-circuit _fault occurs. Is the transmission current when the circuit breaker 18 cuts off. As is apparent from the figure, the rate of increase in the amount of transmitted power when the AC reactor 17 is inserted is large (the slope of the curve is steep) up to a magnification n of about 3; Is getting smaller.

Therefore, the selection range of the inductance _Ldc of the DC reactor 16 selected by the current limiting device having no AC reactor 17 is determined by the equation (13) from the current limiting time τ.
(Τ = t / T ₀ ) divided by the current limiting ratio (I _tgt / I _SCR ) and multiplied by the inductance L _S behind the system, from 2 to 8
Based on the fact that the double was preferred, the AC reactor 17
It is possible to set the selection range of the inductance L _dc DC reactor 16 in the current limiting device having a.

That is, the inductance of the DC reactor 16
L_dcAbout the lower limit of
Current limiting time τ (τ = t / T)₀)
Flow ratio (I_tgt/ I_SCR) And the inductance behind the system
Tance L_SIs doubled. This is described earlier.
The current limiting ratio (I_tgt/ I_SCR) And Inn
Ductance ratio (L_dc/ L_S/ Τ) (see Figure 6)
In, X_bps/ X _S= ∞.

On the other hand, as for the upper limit of the inductance _Ldc of the DC reactor 16, in the case of a current limiting device having no AC reactor 17, the current limiting time τ (τ = t / T ₀ ) is determined by the current limiting ratio (I _tgt / Since the upper limit is eight times the value obtained by multiplying by the inductance L _S behind the system after dividing by I _SCR ), the rate of increase in the amount of power transmitted by the AC reactor 17 alone is three times as described above. The current limiting time τ (τ = t / T ₀ ) is set to the current limiting ratio (I
_tgt / I _SCR ) and the inductance L behind the system
It is preferable that the value obtained by multiplying _S is 8 times × 3 = 24 times. This is because the current limiting ratio (I
_tgt / I _SCR) and the inductance ratio _{(L dc / L S / τ} )
(See FIG. 6), X _bps / X _S = 3 × ∞
Is represented by the following curve.

The inductance L smaller than twice the value obtained by dividing the current limiting time τ (τ = t / T ₀ ) by the current limiting ratio (I _tgt / I _SCR ) and multiplying by the inductance L _S behind the system.
_{In the case of dc} , it is difficult to exert a desired current limiting effect, which is unsuitable, and in the case of an inductance _Ldc larger than 24 times, it is unsuitable in terms of cost in terms of lack of economy.

Next, the impedance of AC reactor 17
X_bpsThe upper limit is determined from the system stability as described above.
It is determined. That is, the impedance of the AC reactor 17
X _bpsBecomes too large, the AC reactor 17
Stability of the system when inserted into the system (steady state stability and excess
Stability, etc.), and through a current limiting device.
Transmission power is limited. So try to apply
Impedance of AC reactor 17 based on the specifications of the power system
-Dance X_bpsIs defined.

On the other hand, the lower limit of the impedance X _bps of the AC reactor 17 is selected based on the following table since it is necessary to satisfy the current limiting ratio.

[0069]

[Table 1]

In the above table, the curve (in the case of X _bps / X _S = 3 × ∞) and the X _bps / X _S of FIG. 6 required for selecting the upper limit value of the inductance L _dc of the DC reactor 16 are shown. the lower limit of the impedance X _{bp s} of AC reactors 17 to the intersection of the different curves for each value as a boundary is case analysis.

That is, when the current limiting ratio is less than 0.25, X_bps
/ X_S= X crossing the 3x∞ curve _bps/ X_S= 5 songs
The line is the impedance X of the AC reactor 17_bpsLower limit of
To obtain the value, and the impedance X
_bpsIs 5 × X_SBecomes Current limiting ratio 0.25
If it is less than 0.4, X_bps/ X_SIntersects the curve of = 3 × ∞
X_bps/ X_S= 2 curve shows the AC reactor 17
Peacedance X_bpsTo find the lower limit of
Its impedance X_bpsIs 2 × X_SBecomes
When the current limiting ratio is less than 0.4 to 0.55, X_bps/ X_S= 3
X crossing the curve of × ∞_bps/ X_S= 1 is the curve
The impedance X of the actuator 17_bpsFind the lower limit of
And its impedance X_bpsLower limit of
Is 1 × X_SBecomes When the current limiting ratio is 0.55 or more, X_bps
/ X_S= X crossing the 3x∞ curve_{bp s}/ X_S= 0.2
Is the impedance X of the AC reactor 17_bpsof
It is used to find the lower limit, and its impedance
X_bpsIs 0.2 × X_SBecomes

By setting the impedance X _bps of the AC reactor 17 within the range defined by the lower limit value selected in this way and the upper limit value defined as described above, the specifications of the applicable power system are satisfied. And an economical current limiting device can be realized.

[0073]

According to the present invention, there is provided a rectifier type current limiting device in which an AC terminal of a single-phase diode bridge circuit is connected in series with a power system, and a DC reactor is connected between the DC terminals of the single-phase diode bridge circuit. Therefore, the reliability can be improved without impairing the stability of the system at the time of normal operation without a short circuit accident.

Further, since the AC reactor is bypass-connected to the single-phase diode bridge circuit, when a short circuit occurs, the current is limited at a high speed by the DC reactor and then commutated to the AC reactor, thereby connecting the power system. Since the current limiting function for suppressing the short-circuit current can be continued without disconnecting the system, it can be applied to a power system that cannot be disconnected, and the versatility is improved.

Furthermore, in this current limiting device, the inductance of the DC reactor is selected within a range of 2 to 24 times the value obtained by dividing the current limiting time by the current limiting ratio and multiplying the short-circuit impedance (inductance) by: based on the selection range of the inductance of the DC reactor, it can be adapted to the conditions in the various power system embodying the best current limiting device having a desired limiting ratio.

The inductance of the DC reactor is selected by selecting the impedance of the AC reactor between an upper limit determined from system conditions and a lower limit that is a predetermined multiple of the short-circuit impedance according to the current limiting ratio. together, it is possible to implement the economic current limiter in accordance with the specifications of the power system.

[Brief description of the drawings]

FIG. 1A is a circuit configuration diagram showing a current limiting device having an AC reactor according to an embodiment of the present invention. FIG. 1B is a circuit diagram showing a short-circuit current I _SCR when there is no current limiting device in FIG.
(C) is a circuit diagram showing a current limiting target value _Ittgt at the time of a short circuit accident in the presence of the current limiting device of (a).

2A is an equivalent circuit viewed from the DC side in FIG. 1A, and FIG. 2B is an equivalent circuit viewed from the DC side in FIG.

3A is a circuit configuration diagram showing a current limiting device having no AC reactor on the premise of the present invention. FIG. 3B is a circuit diagram showing a short-circuit current I _SCR without the current limiting device of FIG.
(C) is a circuit diagram showing a current limiting target value _Ittgt at the time of a short circuit accident in the presence of the current limiting device of (a).

4 (a) is an equivalent circuit obtained by simplifying the current limiting device of FIG. 3 (a). FIG. 4 (b) is an equivalent circuit viewed from the DC side of FIG. 3 (a).

FIG. 5 shows a current limiting device having no AC reactor.
Characteristic diagram for determining the inductance of the DC reactor required to limit the current for one cycle

FIG. 6 is a characteristic diagram showing a relationship between an inductance ratio and a current limiting ratio for a current limiting device having an AC reactor.

[7] The current limiting device having an AC reactor, characteristic diagram showing the relationship between the ratio (I _bps / I _{tg t)} for magnification

FIG. 8 is a circuit diagram showing a conventional example of a current limiting device.

[Explanation of symbols]

11 Single-phase diode bridge circuit 12, 13 AC terminal 14, 15 DC terminal 16 DC reactor 17 AC reactor τ Current limiting time I _tgt Current limiting target value I _SCR short circuit current X _S short circuit impedance L _dc inductance X _bps impedance

──────────────────────────────────────────────────続 き Continuing on the front page (72) Shoichi Honjo 4-1 Egasakicho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Electric Power Technology Research Institute, Tokyo Electric Power Company (72) Inventor Masakuni Asano Umezu Takaune, Ukyo-ku, Kyoto-shi, Kyoto 47, Nisshin Electric Co., Ltd. (72) Katsuo Matsubara, Inventor 47, Umezu Takanecho, Ukyo-ku, Kyoto City, Kyoto Prefecture Nisshin Electric Co., Ltd. (72) Noriaki Tokuda 47, Umezu Takanecho, Ukyo-ku, Kyoto, Kyoto Sun (56) References JP-A-9-130966 (JP, A) JP-A-49-45349 (JP, A) JP-A-48-97042 (JP, A) JP-A-49-50448 (JP JP, A) JP-A-56-81039 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02H 9/02

Claims (2)

(57) [Claims] An AC reactor is connected in series with a power system, a DC reactor is connected between DC terminals of the single-phase diode bridge circuit, and an AC reactor is connected in parallel with the single-phase diode bridge circuit. The current limiting time to which the current limiting effect should be maintained is divided by the current limiting ratio obtained by dividing the current limiting target value at the time of a short circuit accident by the short circuit current when there is no current limiting device, A current limiting device wherein the inductance of the DC reactor is selected within a range of 2 to 24 times a value obtained by multiplying the divided value by a short-circuit impedance (inductance) of a power system. 2. The impedance of the AC reactor is set to an upper limit value determined from system conditions and five times the short-circuit impedance (when the current limiting ratio is less than 0.25),
Times (when the current limiting ratio is less than 0.25 to 0.4), 1 times (when the current limiting ratio is less than 0.4 to 0.55), 0.2 times (when the current limiting ratio is 0.55 or more) 2. The current limiting device according to claim 1, wherein the current limit value is selected from a lower limit value selected from the above.