JP2002218652A - Automatic voltage regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic voltage regulator to be installed at a distribution line wherein a regulating voltage is superimposed on a voltage of a power source and a predetermined voltage is fed to a load, and wherein if an external load is short-circuited, a short-circuit current flowing the superimposed portion can be reduced. SOLUTION: A tap voltage selected by a tap selector TS of a tap changeover apparatus LTC when load by superimposing on the voltage of the power source as a regulating voltage. A shunt reactor DR is connected in parallel to a secondary coil ST2 of a series transformer ST which is the superimposed portion of a voltage regulating transformer. For a larger current such as a short-circuit current generated when an external short-circuit is caused at the load, the current is shunted to the shunt reactor DR.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of superposing a tap voltage, which is provided in the middle of a distribution line and obtained by switching a tap of a voltage regulating transformer, on a power supply side voltage as a regulation voltage, and applying a predetermined voltage to a load side. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic voltage regulator having a function of shunting a short-circuit current flowing from a power supply side to a reactor connected in parallel with a superimposed portion of the tap voltage when an external short circuit occurs on a load side when power is supplied.

[0002]

2. Description of the Related Art When an automatic voltage regulator is provided in the middle of a distribution line and a predetermined voltage is always supplied to a load side, for example,
If the line current that flows as normal current is large, the voltage transformer is a voltage transformer that combines a series transformer and a regulating transformer, and the tap winding of the regulating transformer and the tap changer during load are distributed by the series transformer. And an indirect method in which line current does not flow through the tap changer under load is used. When the line current is small, an autotransformer having a tap winding is used as the voltage adjusting transformer, and a direct method in which the line current flows directly to the tap winding or the on-load tap changer is used.

[0003]

This is because, in the case of a conventional automatic voltage regulator, when an external short circuit occurs on the load side,
A current of 5 to 6000 A, nearly 30 times the rated value, flows directly from the line directly into the series transformer for voltage adjustment or the tap winding, and furthermore, an excessively large current flows through the winding of the voltage adjustment transformer. It will flow.

Therefore, these series transformers and tap windings for voltage superimposition are manufactured with a structure that is more thermally and mechanically resistant to a large current at the time of external short circuit than other windings of the voltage adjustment transformer. I have to do it. Especially in the direct method, the tap winding through which the line current flows occupies the majority of the windings of the autotransformer. There is a problem that the overall size and cost increase because the design is made with a structure that can cope with the problem.

An object of the present invention is to provide a voltage adjusting transformer for supplying a predetermined voltage to a load side in accordance with a power supply side voltage, in which a reactor is connected in parallel to a superimposing section for superimposing the tap voltage on the power supply side voltage. Connected, and when an external short circuit occurs on the load side,
It is an object of the present invention to provide an automatic voltage regulator capable of shunting a part of a short-circuit current, which is a large current flowing from a power supply, to the reactor.

[0006]

In order to achieve the above object, according to the present invention, there is provided a voltage regulating transformer having a plurality of taps, and a voltage adjusting transformer having a plurality of taps for setting a load side voltage to a predetermined voltage. An on-load tap changer having a tap selector for selecting one of the taps and switching control of the tap selector so as to control the supply of a predetermined voltage to the load side. A reactor connected in parallel is provided in a superimposing part of the voltage adjusting transformer, which superimposes a tap voltage at a tap selected by the tap selector on a power supply side voltage.

According to a second aspect of the present invention, in the automatic voltage regulator according to the first aspect, the reactor is a reactor having a core with a gap, and the reactance thereof is larger than the impedance of the superimposed portion at a superimposed voltage of about the rated value. When the voltage between the superposed portions becomes larger than the rated voltage due to the short-circuit current, the reactance is set to be smaller than the impedance of the superposed portion due to the saturation of the iron core of the reactor.

As a result, in a normal state in which a rated current flows, almost no current is shunted to the shunting reactor, whereas the output side of the automatic voltage regulator is
For example, with respect to a large current at the time of an external short circuit such as a load-side ground fault, a part of the current can be diverted to the shunting reactor side, then merged again and output to the load side.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. Here, the line is a single phase for the sake of simplicity.

FIG. 1 shows an embodiment of an automatic voltage regulator of the indirect system. In the present embodiment, an auto-transformer as a voltage adjustment transformer for superimposing an adjustment voltage at which a load side, which is an output side, on the power supply voltage in the distribution line becomes a predetermined voltage, a series transformer ST and an adjustment transformer RT It consists of.

The adjusting transformer RT includes a plurality of taps T1 'to
T9 ', which has a tap winding TC, outputs a tap voltage serving as an adjustment voltage from the tap, and connects the series transformer ST
Is to change the voltage and superimpose it as an adjustment voltage in the same direction or the opposite direction with respect to the line voltage on the power supply side, and output a predetermined voltage to the load side.

Therefore, one terminal of the winding ST2 on the secondary side of the series transformer ST is connected to one terminal B of the distribution line on the normal power supply side, and the other terminal of the winding ST2 and the adjusting transformer are connected. One terminal of the RT is normally connected to one terminal A of the distribution line on the load side. And the regulating transformer R
The other terminal of T is connected to terminal B 'of the power distribution line on the power supply side and terminal A' of the distribution line on the load side.

The terminal of the primary winding ST1 having the same polarity as the terminal A of the secondary winding ST2 of the series transformer ST is connected to the tap T1 'of the tap winding TC, that is, of the adjusting transformer RT. It is connected to the terminal having the same polarity as the terminal connected to terminal A. The other terminal of the winding ST1 is connected to the tap selector TS of the load tap changer LTC.

For this reason, in the case of this indirect system, a shunt reactor DR, which is a reactor with a core with a gap, is connected in parallel with the winding ST2 on the secondary side of the series transformer ST, so that the line current is normally reduced. Mostly winding ST2
, And a short-circuit current, which is a large current when the load is externally short-circuited, is diverted to the shunt reactor DR and the winding ST2 of the series transformer ST.

When the shunt reactor DR is set to have a large reactance when the excitation voltage is small and a small reactance when the excitation voltage is large, a normal load current (small excitation voltage) is obtained.
, The impedance of the shunt reactor DR becomes larger than the impedance of the voltage adjusting transformer side, and the shunt to the shunt reactor DR decreases.

For a short-circuit current (high excitation voltage), the impedance becomes smaller than the impedance of the voltage adjusting transformer due to the saturation of the iron core of the reactor. As a result, the current flowing to the voltage regulating transformer is reduced.

That is, by using a core with a gap for the shunt reactor DR, the reactor has both characteristics of an air core and a core and has a large and constant reactance for a rated current in a range where the core is not saturated. In addition, the rate at which the rated current is divided into the shunt reactor DR can be kept small. Then, for a short-circuit current that saturates the iron core of the shunt reactor DR, the reactance is significantly reduced compared to the normal state, so that a large amount of short-circuit current can be shunted to the reactor side.

In FIG. 1, when a power-supply-side voltage indicated by a voltage vector ^* E ₁ (hereinafter, the vector amount is represented by using [ ^* ]) is applied between terminals B and B ′, a series transformer ST And the regulating transformer RT. And
On the basis of the voltage shared by the regulating transformer RT, the tap-on-load switching device LT from the secondary side of the tap winding TC is used.
Tap voltage parts selected by C tap selector TS is superimposed on the power supply side voltage as an adjustment voltage via a series transformer ST, the voltage vector ^* E ₂ is a predetermined voltage to the load side and the current vector ^* I ₂ is output between terminals A and A '.

[0019] When the voltage indicated by the voltage vector ^* E ₂ is output to the load side, the winding ST2 of the secondary side of the series transformer ST, along with the voltage indicated by the voltage vector ^* Es induced since current flows as indicated by the current vector ^* I _1, the relationship is established as indicated by the following equation.

[0020]

(Equation 1)

At this time, the current flowing through the shunt reactor DR
The current vector^*I_R And the current flowing in the load side line
The current vector^*I_S Then the current vector^*I₁ ,
 ^*I _R, ^*I_2, ^*I_S Has a relationship expressed by the following equation:
Stand up.

[0022]

(Equation 2)

[0023] The series transformer ST and the adjustment transformer RT, because both at terminal A is connected so that the same poles terminal B, and the voltage indicated by the voltage vector ^* E ₁ between B 'is applied that when, in the winding ST2 in series transformer ST voltage to the voltage vector ^* E ₁ represented by the voltage vector ^* E ₃ is induced as an adjustment voltage.

Furthermore, the overall impedance of the voltage regulator transformer as seen from the line side of the series transformer ST ^* and Z _1, current flows as indicated by the current vector ^* I ₁ series transformer ST, this time shunt reactor Assuming that the voltage applied to DR is a voltage vector ^* E _AB , the relationship expressed by the following equation is established.

[0025]

(Equation 3)

When the equation (1) is expanded, the following equation is obtained.

[0027]

(Equation 4)

Then, the following expression is obtained by substituting the expression 4 into the expression 3 and rearranging the expression.

[0029]

(Equation 5)

By substituting Equations 4 and 5 into Equation 2, the following equation is obtained.

[0031]

(Equation 6)

Next, the following expression is obtained by substituting the expression 6 into the expression 3 and rearranging the expression.

[0033]

(Equation 7)

Here, since it is handled as a single phase, ^* Es
= 300 / √3 [V], ^* E ₂ = 6600 / √3
[V], ^* Z ₁ = j0.1 [Ω], ^* Es and ^* E ₂ and ^*
Is is assumed to be in phase, and the value obtained after the impedance Zs of the shunt reactor DR is saturated with the iron core is ^* Z _R = 0.1Ω.
And ^* Is = Is [A], the following equation is obtained from Equation (6) as the value after iron core saturation.

[0035]

(Equation 8)

When I ₁ [A] at the time of an external short circuit is obtained from Expression 8, the following expression is obtained.

[0037]

(Equation 9)

Further, the following assumption is obtained by applying the above assumption to the equation (7) and rearranging it.

[0039]

(Equation 10)

Further, when E _AB [V] is obtained from the equation (10), the following equation is obtained.

[0041]

[Equation 11]

Here, the shunt reactor DR and E _AB are 3
If magnetic saturation is set when 50 / √3 [V], Is = 3586 [A] from equation (11), whereas I ₁ = 2039 [A] from equation (9). When the external short-circuit current at the load side is Is = 3586 [A], the current borne by the voltage adjustment transformer can be reduced to 0.57 times (2039 [A] / 3586 [A]). it can.

That is, since the temperature rise of the winding and the electromagnetic mechanical force due to the current at the time of the short circuit are both proportional to the square of the current, the current is reduced to 0.32 times by the shunting. The line structure can be reduced and simplified.

Similarly, under the above assumption, the rated state (I
s = about 200 A), the reactance ^* Z _R of the shunt reactor DR, and ^* Z _R =
When j20 [Ω] is set, the following expression is obtained from Expression 6.

[0045]

(Equation 12)

From the equation (12), I in the rated state is obtained.
_{When 1} [A] is obtained, the following equation is obtained.

[0047]

(Equation 13)

From the above equation (13), when a rated current is supplied to the load side, the current flowing to the automatic voltage regulator side is | ^* I ₁ | = 200 [A]. At this time, the current shunted to the shunt reactor DR side is obtained by adding the equation [Equation 12] to the equation [5] and ^*
Substituting and Z _R = j20 [Ω], ^* I _R = -1.0
42 + j8.61 and | I _R | = 8.7 [A], which is very small. Even if a small-diameter conducting wire is used as the shunt reactor DR, it is possible to cope with a temperature rise at the time of rating and reduce the size of the shunt reactor DR. .

FIG. 2 shows another embodiment of the present invention in which a direct system is used.

The autotransformer used as the voltage adjusting transformer has a configuration in which the tap winding TC 'and the shunt winding DC are connected in series. On the other hand, nine taps including both ends are drawn as taps T ₁ ′ to T ₉ ′ from the winding in which the tap windings are equally divided into eight.

The tap T ₁ '~T _9' is connected to the fixed contact T ₁ through T ₉ of each load tap changer LTC, tap selector TS for contact with the fixed contact T ₁ through T ₉ are the normal power supply side Is connected to one of the line terminals B.

Here, the tap T ₅ ′ is a tap which becomes a reference tap (shows a through tap) at the time of progressive power transmission, and is normally connected to one terminal A on the load side.

Tap winding T with shunt winding DC of autotransformer
The terminal opposite to C 'is connected to the other terminal B' on the normal power supply side and the other terminal A 'on the normal load side.

In the case of this direct system, the shunt reactor DR is interposed between the tap selector TS and the tap T5 'which is the reference tap, so that the winding corresponding to the tap selected by the tap selector TS is selected. The shunt reactor DR is installed in parallel with the above.

As a result, most of the load current is normally
Tap selected by tap selector TS and reference tap T5 '
The current flows to the load side through the tap winding between the two, and when an external short circuit occurs on the load side, the short-circuit current can be divided into the shunt reactor DR and the tap winding portion.

[0056]

As described above, in any of the methods, the tap voltage of the voltage adjusting transformer is superimposed on the voltage on the power supply side as an adjustment voltage and output as a predetermined voltage on the load side. If a shunting reactor is installed in parallel with the part, the large current at the time of short circuit can be shunted to the reactor side in addition to the voltage adjustment transformer. The thermal and mechanical resistance to the short-circuit current of the automatic voltage regulator including the fixed contact can be designed to be small, and the size and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a basic configuration of an embodiment according to the present invention.

FIG. 2 is a connection diagram showing a basic configuration of another embodiment according to the present invention.

[Explanation of symbols]

A, A 'Terminal on the load side of the distribution line B, B' Terminal on the power side of the distribution line RT Adjustment transformer TC Tap winding T1 'to T9' Tap ST Series transformer ST1 Primary winding of series transformer ST ST2 series transformer secondary winding LTC-load tap changer TS tap selector T1~T9 fixed contact DR voltage vector shunt reactor DC shunt winding TC 'tap winding ^* E ₁ power supply side ^* E ₂ loads ST side of the voltage vector ^* E ₃ tap selector TS is selected taps of the voltage vector ^* Es voltage vector ^* regulated voltage vector ^* E _AB series transformer windings ST2 to the current vector of ST E ₃ ^*
When the current represented by I ₁ flows, voltage vector ^* I ₁ current vector flowing through the series transformer windings ST2 of ST ^* I ₂ adjusting transformer current vector ^* I ₃ indirectly flowing to RT applied to shunt reactor DR seen from the line side of the current vector ^* I _R shunt reactor current flowing through the DR vector ^* I _P current vector ^* Z ₁ series transformer ST output from the power source side to the current vector ^* I _S load input flowing through the circuit reactance of total impedance vector ^* Z _R shunt reactor DR of the voltage adjusting transformers

Claims (2)

[Claims] 1. A voltage regulating transformer having a plurality of taps, and a tap selector for selecting one tap from the plurality of taps to set a load side voltage to a predetermined voltage, wherein a predetermined voltage is provided on a load side. And an on-load tap changer for switching and controlling the tap selector so as to control the supply of the tap signal. The tap voltage at the tap selected by the tap selector is superimposed on the power supply side voltage. An automatic voltage regulator, comprising: a reactor connected in parallel to a superposition section of the voltage regulator transformer. 2. The automatic voltage regulator according to claim 1, wherein the reactor according to claim 1 is constituted by a reactor having a core with a gap.