JPH09285013A - Control method of distribution system and voltage fluctuation suppressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the capacity of a voltage fluctuation suppressor by a method wherein the voltage fluctuation suppressor is provided in the lower hierarchy system of a distribution system which consists of an upper hierarchy system from which a power is supplied through a reactor and the lower hierarchy system to which a lower hierarchy load is connected. SOLUTION: A voltage fluctuation suppressor 9 and a lower hierarchy load 7 are connected through a transformer 6 to an upper hierarchy system 5 to which a fluctuating load 3 is connected. In such a distribution system, as a voltage variation (voltage fluctuation suppression value) caused by a reactive power output Qc is (Xs+XT).Qc, wherein Xs denotes the reactance of a system reactor 2 and XT denotes the reactance of the transformer 6, a larger voltage fluctuation suppression effect can be obtained without increasing the capacity of the voltage fluctuation suppressor. In other words, the same voltage fluctuation suppression effect for the lower hierarchy load can be obtained by the suppressor whose capacity is smaller than that of a conventional one, so that the capacity of the volatge fluctuation suppressor 9 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an upper system to which power is supplied from an AC system power supply via a system reactor and at least a variable load is connected, and to the upper system to which power is supplied via a transformer or a reactor. It relates to a distribution system consisting of a lower-level system to which a general load is connected, and in particular,
The present invention relates to a system configuration for suppressing voltage fluctuations due to the fluctuation load and a control method for the voltage fluctuation suppressing device.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a conventional power distribution system, in which an alternating current power supply 1 is fed through a system reactor 2 to which a variable load 3 and an upper load 4 are connected,
In order to suppress voltage fluctuations due to the variable load 3, in a distribution system composed of a lower system 8 to which power is supplied from the upper system 5 through a transformer 6 or a reactor and a lower load 7 is connected, voltage fluctuation suppression is performed. Device 9 is upper system 5
It was connected with the variable load 3.

In this power distribution system, if the voltage fluctuation suppressing device 9 is not provided, the bus voltage of the host system 5 fluctuates due to the power fluctuation of the fluctuating load 3. It is known that the voltage fluctuation is mainly due to the reactive power fluctuation. The magnitude ΔVL is the reactive power fluctuation of the fluctuating load 3, ΔQL, and the system reactor 2
Let Xs be the reactance of still,
In the following calculation expressions, the PU method is used unless otherwise specified, and PU is used as the unit of voltage, reactance, and power.

[0004]

## EQU1 ## ΔVL = XsΔQL (1) This voltage fluctuation ΔVL adversely affects the upper load 5 and the lower load 7 connected to the same bus bar, and particularly the flicker of the lighting device of the lower load 7 and the electronic device. Cause the malfunction of.

The voltage fluctuation suppressing device 9 uses the reactive power fluctuation Δ
By compensating QL, the voltage fluctuation ΔVL is suppressed. The voltage fluctuation suppressing device 9 has various circuit systems, and as an example thereof, a voltage type PW described in Japanese Patent Application No. 1-317859 (Japanese Patent Laid-Open No. 183324).
There is a device using an M inverter. This is a reactive power fluctuation ΔQ using the bus voltage detected by the instrument transformer 10 and the current of the variable load 3 detected by the current transformer 11.
By detecting the L and controlling the output reactive power Qc of the voltage variation suppressing device 9 so as to cancel it, the variation ΔQs of the reactive power supplied from the AC system power supply 1 is reduced to reduce the voltage variation ΔVs. It suppresses. This is represented by the following equation.

[0006]

[Formula 2] Qc = -ΔQL (2) ΔQs = ΔQL + Qc = ΔQL -ΔQL = 0 (3) ΔVs = Xs · ΔQs = 0 (4)

[0007]

A conventional voltage fluctuation suppressing device 9 is a high-order system 5 to which a variable load 3 and a high-order load 4 are connected.
Is installed in the
A device with the same capacity as QL is required. When the variable load 3 has a large electric power fluctuation of several tens of MVA as in a steelmaking arc furnace, the capacity of the voltage fluctuation suppressing device 9 also increases to the same extent, and the device price increases.

By the way, the high-order load 4 is generally connected to a large-capacity power load, for example, an electric motor, and these electric motors are often speed-controlled or auxiliary electric motors. The automatically controlled electric motor is not affected so much because the voltage fluctuation due to the fluctuating load 3 is added as a disturbance, but is automatically controlled. Further, since the auxiliary electric motor is not required to have high accuracy, the voltage fluctuation due to the fluctuating load 3 does not matter so much.

However, since the lower load 7 is often an illuminating device, an electronic device, or the like, these items cause the flicker of the illuminating device and cause the malfunction of the electronic device as described above, so that the voltage fluctuation due to the fluctuating load 3 is suppressed. There must be.

Therefore, the object of the present invention is made in view of the above-mentioned point, and in particular, the capacity of the voltage fluctuation suppressing device is reduced by suppressing the voltage fluctuation of the lower load which is easily affected by the voltage fluctuation. An object of the present invention is to provide a power distribution system that can be performed and a control method of a voltage fluctuation suppressing device installed in this power distribution system.

[0011]

In order to achieve the above object, a distribution system according to the present invention is a high-order system in which power is supplied from an AC system power source through a system reactor and at least a variable load is connected. And a lower-level system that is fed from the higher-level system through a transformer or a reactor and is connected to a lower-level load,
A voltage fluctuation suppressing device is installed in the lower system.

According to a second aspect of the present invention, in the voltage fluctuation suppressing device, the reactive power fluctuation ΔQL of the fluctuating load is detected from the current flowing in the fluctuating load and the applied voltage of the fluctuating load,
When the reactance of the system reactor is Xs and the reactance of the transformer or reactor is XT,
It is characterized in that control is performed so as to compensate the reactive power of [Xs / (Xs + XT) .ΔQL].

Further, in the invention according to claim 3, the voltage fluctuation suppressing device detects the fluctuation of received power reactive power ΔQs of the upper system from the current supplied from the AC system power source and the applied voltage of the fluctuating load, When the reactance of the system reactor is Xs and the reactance of the transformer or reactor is XT, control is performed so as to compensate the reactive power [Xs / XT · ΔQs].

Furthermore, the invention according to claim 4 is characterized in that the voltage fluctuation suppressing device detects the bus voltage fluctuation ΔVL of the upper system to which the variable load is connected, and detects the reactance of the transformer or the reactor as XT. When I did, [1 / XT
.DELTA.VL] is controlled so as to compensate the reactive power.

[0015]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the invention described in claim 1 will be described below with reference to FIG. The same parts as those in FIG. 5 showing the configuration of the power distribution system including the voltage fluctuation suppressing device 9 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, the voltage fluctuation suppressing device 9 and the lower load 7 are connected to the upper system 5 to which the variable load 3 is connected via a transformer 6. The voltage fluctuation suppressing device 9 has the same structure as that of the conventional technique and is controlled by the same principle. Here, the reactance of the system reactor 2 of the power transmission line that supplies power from the AC system power supply 1 to the upper system 5 is Xs, and the leakage reactance of the transformer 8 is XT. A reactor may be used instead of the transformer.

The voltage fluctuation suppressor 9 suppresses the influence of the power fluctuation of the fluctuating load 3 on the lower load 7. The voltage change (voltage fluctuation suppression amount) of the lower system 8 to which the lower load 7 is connected due to the reactive power output Qc of the voltage fluctuation suppression device 9 is (Xs + X
T) · Qc, which acts to cancel the voltage fluctuation caused by the reactive power fluctuation QL of the variable load 3 represented by the equation (1).

According to such a power distribution system, the voltage fluctuation suppression amount of the conventional voltage fluctuation suppression device 9 is Xs.Qc, whereas the voltage fluctuation (voltage fluctuation suppression) due to the reactive power output Qc of the same magnitude. Since (amount) is (Xs + XT) .Qc, a device with the same capacity has a large voltage fluctuation suppressing effect. In other words, the same voltage suppression effect can be obtained for a lower load with a device having a smaller capacity than the conventional device, so that the capacity of the voltage fluctuation suppressing device 9 can be reduced and the cost can be reduced.

Next, the invention according to claim 2 will be described with reference to FIG. 2 in which the same parts as those in FIG. The invention described in claim 2 is a transformer for an instrument for detecting the voltage of the upper system 5 to which the variable load 3 is connected in order to control the voltage fluctuation suppressing device 9 installed in the power distribution system according to claim 1. The transformer 10 and the current transformer 11 for detecting the current of the fluctuating load 3 are provided, and the host system 5 detected by the instrument transformer 10
Of the variable load 3 calculated from the voltage of the variable current and the current of the variable load detected by the current transformer 11, and the reactive power fluctuation ΔQL of the variable load 3 is multiplied by the coefficient Kc1 shown in the following equation. The voltage fluctuation suppressing device 9 controls the electric power so as to be compensated.

[0020]

## EQU3 ## Kc1 = Xs / (Xs + XT) (5) where Xs is the reactance of the system reactor 2 XT is the reactance of the transformer 6 or the reactor, that is, the reactive power Qc output by the voltage fluctuation suppressing device 9 is ,

[0021]

[Equation 4] Qc = -Kc1.DELTA.QL = -Xs / (Xs + XT) .DELTA.QL (6) As a result, the voltage fluctuation of the subordinate system 8 to which the subordinate load 7 is connected is as shown in the equation (7). Suppressed to.

[0022]

[Formula 5] ΔV = Xs.ΔQL + (Xs + XT) .Qc = Xs.ΔQL- (Xs + XT) .Xs / (Xs + XT) .ΔQL = Xs.ΔQL-Xs.ΔQL = 0 (7) Thus, according to the second aspect of the invention, the output reactive power Qc of the voltage fluctuation suppressing device 9 becomes a value obtained by multiplying the reactive power fluctuation ΔQL of the variable load 3 by the coefficient Kc1 shown in the equation (5). Therefore, as compared with the conventional voltage fluctuation suppressing device 9, the device capacity of the voltage fluctuation suppressing device 9 can be reduced.

Assuming, for example, an upper system which receives power at a special high voltage of 50 MVA, the reactance Xs of the system reactor 2 is generally 1% or less on the basis of 10 MVA, the capacity of the transformer 6 is 50 MVA, and its leak reactance XT is generally about 10%. Target. Therefore, X on a 10 MVA basis
Since the ratio of s and XT is about 1: 2, the capacity of the voltage fluctuation suppressing device 9 can be reduced to 1/3 of the conventional one, and the price can be reduced.

Although the voltage fluctuation of the upper system 5 cannot be suppressed to zero, the upper load 4 is not easily affected by the voltage fluctuation. However, by installing the voltage fluctuation suppressing device in the lower system to a certain extent. Can be obtained, and, for example, in the above-described example, a reduction effect of about 1/3 can be obtained.

Next, the invention according to claim 3 will be described with reference to FIG. 3 in which the same parts as those in FIG. The invention according to claim 3 is an instrument for detecting the voltage of the upper system 5 to which the variable load 5 is connected in order to control the voltage fluctuation suppressing device 9 installed in the power distribution system according to claim 1. Host system 5 to which transformer 10 and variable load 5 are connected
Is provided with a current transformer 11 for detecting the current flowing into the power source, and the received reactive power fluctuation ΔQs of the upper system 5 is detected from the current supplied from the AC system power source 1 and the applied voltage of the fluctuating load 3.
The received power fluctuation ΔQs is multiplied by a coefficient Kc2 shown in the following formula to control the voltage fluctuation suppressing device 9 so as to compensate the reactive power.

[0026]

[Equation 6] Kc2 = Xs / XT (8) The voltage fluctuation suppressor 9 calculates using the voltage of the upper system 5 detected by the voltage transformer 10 and the current detected by the current transformer 11. Receiving reactive power fluctuation ΔQs
Is compensated by the coefficient Kc2 of the equation (8) to compensate the reactive power [see the equation (9)].

[0027]

## EQU7 ## Qc = -Kc2..DELTA.Qs = -Xs / XT..DELTA.Qs
= -Xs / XT. (. DELTA.QL + Qc) When this is solved for Qc, Qc = -Xs / (Xs + XT) .DELTA.QL (9), resulting in the voltage of the lower system 8 to which the lower load 7 is connected. The fluctuation is suppressed as in the following equation (7 above), and the same result as the invention according to claim 2 is obtained.

ΔV = Xs.ΔQL + (Xs + XT) .Qc = Xs.ΔQL- (Xs + XT) .Xs / (Xs + XT) .ΔQL = Xs.ΔQL-Xs.ΔQL = 0 Thus, claim 3 The invention described in (1) has the same effect as the invention described in (2). In addition, since the fluctuation of the reactive power received is compensated, the voltage fluctuation suppressing device 9 can function with respect to a plurality of fluctuation loads.

Next, the invention according to claim 4 will be described with reference to FIG. 4, in which the same parts as those in FIG. In order to control the voltage fluctuation suppressing device 9 installed in the power distribution system according to claim 1, the invention described in claim 4 detects the voltage fluctuation of the upper system to which the variable load 3 is connected, A transformer 11 for measuring instruments is provided, and the upper system voltage fluctuation ΔVL
Is detected, and the reactive power [see the expression (10)] obtained by multiplying the upper system voltage fluctuation ΔVL by the coefficient Kc3 of the expression (10) is compensated.

[0030]

## EQU8 ## Qc = -Kc3..DELTA.VL = -1 / XT.DELTA.VL = -1 / XT.Xs (.DELTA.QL + Qc) (10) When this is solved for Qc, it becomes equal to the equation (9).
As a result, the voltage fluctuation of the lower system 8 to which the lower load 7 is connected is suppressed as in the expression (7), and the same result as the invention according to claim 2 is obtained. Moreover, since the compensation is performed by using the fluctuation of the received voltage, the voltage fluctuation suppressing device can function for a plurality of fluctuation loads.

[0031]

As is apparent from the above description, claim 1
According to the invention as set forth in claim 4, a high-order system to which power is supplied from the AC system power supply via the system reactor and at least a variable load is connected, and power is supplied from the high-order system via a transformer or a reactor. In a distribution system consisting of a subordinate system to which a subordinate load that is easily affected by voltage fluctuations is connected, by installing a voltage fluctuation suppressing device in the subordinate system, the output of the voltage fluctuation suppressing device is affected by power fluctuations of the fluctuating load. Since it is a value obtained by multiplying the reactance of the transmission line and the reactance of the transformer by a coefficient smaller than 1, the device capacity can be made smaller than the conventional voltage fluctuation suppressing device, and the price can be reduced. .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the invention described in claim 1.

FIG. 2 is a configuration diagram showing an embodiment of the invention described in claim 2.

FIG. 3 is a configuration diagram showing an embodiment of the invention described in claim 3.

FIG. 4 is a configuration diagram showing an embodiment of the invention described in claim 4.

FIG. 5 is a configuration diagram of a conventional voltage fluctuation suppressing device.

[Explanation of symbols]

1 ... AC power supply 2 ...
… System reactor 3 …… Variable load 4…
… Upper load 5 …… Upper system 6…
… Transformer 7 …… Lower load 8…
... Lower system 9 ... Voltage fluctuation suppressor 10 ...
… Instrument transformer 11 …… Current transformer

Claims (4)

[Claims] 1. An upper system to which power is supplied from an AC system power supply via a system reactor and at least a variable load is connected, and a higher system to which power is supplied from the upper system via a transformer or reactor and a lower load is connected. A distribution system including a lower system, wherein a voltage fluctuation suppressing device is installed in the lower system. 2. The distribution system according to claim 1, wherein the reactive power fluctuation ΔQL of the fluctuating load is detected from the current flowing through the fluctuating load and the applied voltage of the fluctuating load, and the reactance of the system reactor is Xs and the transformer. A method of controlling a voltage fluctuation suppressing device, characterized in that the reactance of a reactor or a reactor is XT, and the voltage fluctuation suppressing device compensates the reactive power of [Xs / (Xs + XT) · ΔQL]. 3. The distribution system according to claim 1, wherein the reactive reactive power fluctuation ΔQs of the upper system is detected from the current supplied from the AC system power source and the applied voltage of the fluctuating load, and the reactance of the system reactor is determined. A control method for a voltage fluctuation suppressing device, wherein Xs is a reactance of the transformer or the reactor, and XT is a reacting power of [Xs / XT · ΔQs]. 4. The voltage fluctuation suppressing device according to claim 1, wherein a fluctuation of a bus voltage ΔVL of a higher-level system to which the variable load is connected is detected, and a reactance of the transformer or reactor is set to XT. Is [1
/ XT · ΔVL] for compensating the reactive power.