JPH06189445A - Overvoltage protective control method for series capacitor - Google Patents

Abstract

PURPOSE:To control an overvoltage developed across a series capacitor, by inserting resistors in parallel or series with the capacitor for a short time and limiting a rapid change in current flowing into the series capacitor largely affecting the overvoltage occurring across the series capacitor when the series capacitor is inserted into an AC power system. CONSTITUTION:After removing a system failure, a control circuit 9 of an overvoltage developed across a series capacitor 1 is turned off by a switch 10, and a switch 7a is turned off immediately before the switch 10 is turned off. At this time, switches 7b, 7c and 7d are turned off and a switch 7e is turned on. Thus, a current flowing into the series capacitor 1 flows through resistors 6a, 6b, 6c and 6d and is limited by these resistors. Next, the switches 7b, 7c and 7d are sequentially short-circuited and the resistors 6a, 6b and 6c are removed. When the switch 7a is short-circuited and the switch 7e is turned off, the current flowing into the series capacitor 1 is gradually increased and a steady-state operation is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called series capacitor compensation system control method for compensating a reactance component of a transmission line by inserting a capacitor in series in an AC power transmission system, and in particular, after eliminating a system fault. The present invention relates to a protection control method for suppressing an excessive voltage generated in a series capacitor when the series capacitor is reinserted or when the series capacitor is inserted during steady operation.

[0002]

2. Description of the Related Art In an AC power system, an overhead power transmission line is generally installed on a steel tower to transmit electric power. Originally, it is economically desirable to locate the power source close to the demand area. However, it is becoming more difficult to find a power source location point in the developed area year by year, and the power source location point tends to be remote. In this way, when the location of the power supply facility or the power generation point and the power consumption area are far apart, the transmission line has to be long distance.

Since the reactance of the power transmission line is almost proportional to the distance of the power transmission line, in the AC power system, the longer the power transmission distance of the power transmission line, the greater the reactance of the power transmission line. Due to this reactance, the reactive power consumption of the transmission line increases, the power factor of the transmitted power deteriorates, the transmission loss increases, and the amount of transmitted power is limited due to problems such as system stability. .

Therefore, in order to compensate the reactance of the power transmission line, a so-called series capacitor compensation system in which a capacitor is inserted in series with the power transmission line has been conventionally adopted. However, like the series capacitor compensation method,
It is well known that in a power system using series capacitors, abnormal voltage (transient overvoltage) is generated in the series capacitors when disturbance such as system failure occurs. It was

For this reason, when a transient overvoltage occurs in the series capacitor due to a system failure and reaches a predetermined voltage, the discharge circuit provided in parallel with the series capacitor is discharged, and the resistor incorporated in the discharge circuit is discharged. The method of suppressing the transient overvoltage generated in the series capacitor by making it resonate with the reactor with a built-in capacitor is adopted.

[0006]

SUMMARY OF THE INVENTION In the above prior art,
The transient overvoltage that occurs in the series capacitor at the time of system failure can be suppressed by the discharge circuit. However, there is a problem that it is difficult to suppress overvoltage due to a transient phenomenon that occurs in the series capacitor when the discharge circuit of the series capacitor is removed and the series capacitor is restored to the original system after the failure is removed.

For this reason, there is an example in which a series capacitor and a reactor are combined to suppress overvoltage when the series capacitor is restored to the system, but there are various problems such as control problems. On the other hand, not only a system failure but also an overvoltage may occur when a series capacitor is inserted in the system. For this reason, it is common for the series capacitor to be used by deciding the maximum voltage to be used so as to withstand a voltage that is several times (for example, 2.5 times) the voltage applied to the series capacitor during steady operation. Depending on the maximum operating voltage, an overvoltage may occur depending on the situation. Therefore, if the ratio between this maximum voltage value and the value of the voltage applied during steady operation is small, there are various advantages such as reduction in the size of series capacitors and improvement in system reliability, so the development of an overvoltage suppression method is desired. It was

The present invention has been made in view of the above problems, and an object thereof is to suppress an overvoltage generated in a series capacitor when the series capacitor is inserted in the system and to improve the reliability of the system. Moreover, it is an object of the present invention to provide a method for controlling overvoltage protection of a series capacitor, which makes it easier to manufacture the series capacitor.

[0009]

In order to achieve the above object, a series capacitor overvoltage protection control method according to the present invention is basically a series capacitor for inserting a capacitor in series in a transmission line of an AC power system. In the method, one or more resistors are serially inserted into the transmission line at least when the series capacitor is reinserted into the transmission system after the system fault is removed or when the series capacitor is inserted into the transmission line. None, and the resistor is controlled so as to be short-circuited or the value of the resistor is gradually reduced.

Further, in a series capacitor system in which a capacitor is inserted in series in a transmission line of an AC power system, at least either when the series capacitor is reinserted in the transmission system after the system failure is removed or when the series capacitor is inserted in the transmission line. In this case, at least one or more resistors may be inserted in parallel with the series capacitor, and the value of the resistor may be controlled to be gradually increased.

[0011]

[Function] In the conventional way of thinking, the maximum withstand voltage value of the series capacitor was determined in consideration of the voltage applied to the series capacitor, but this method requires that the maximum withstand voltage value be large, and the withstand voltage of the capacitor should be reduced I can't. On the other hand, in the series capacitor overvoltage protection control method of the present invention having the above-mentioned characteristics, when inserting a series capacitor in the system, a resistor is inserted in parallel or in series with the series capacitor for a short time, It is possible to limit a rapid change in the current flowing through the series capacitor, which greatly affects the generated overvoltage, and suppress the overvoltage generated in the series capacitor.

In order to make the concept of the present invention easy to understand, only the part of the transmission line in which the series capacitor is inserted is taken out, and the voltage difference es of the busbars at both ends of the transmission line is expressed as es (t) = Emsin (ωt + θ ) (Where Em is the maximum voltage). If the capacitance of the series capacitor is C (μF) and the impedance of the transmission line is R (Ω) and L (H), and the bus voltage difference described above is applied to this series circuit, the idea becomes simple. The current is calculated by solving the transient phenomenon as follows.

[0013]

However,

[0015]

In addition,

[0017]

However,

[0019]

Here, the voltage v generated in the series capacitor
Is

[0021]

It is represented by As can be understood from the above equation 12, the magnitude of the current flowing in the series capacitor influences the voltage generated in the series capacitor. Therefore, if the magnitude of the change is reduced, the voltage generated in the series capacitor is suppressed to a small value. To be In other words, when a disturbance such as a system failure occurs and the disturbance is removed and the series capacitor is inserted in the transmission line, the current flowing through the series capacitor is suppressed by inserting a resistor, and the current change is reduced, causing the series capacitor to occur. Overvoltage can be suppressed.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 shows an embodiment to which the present invention is applied.
In this embodiment, for the purpose of suppressing the overvoltage generated in SrC when a series capacitor (hereinafter abbreviated as SrC) is inserted when a failure occurs, SrC is inserted when SrC is inserted.
A resistor is inserted in series to the transmission line in which rC is inserted to suppress the current.

In FIG. 1, the bus 5 of the SrC compensation transmission line is shown.
The SrC1, the resistor 6, and the power transmission line 8 are provided in series between a and 5b. An overvoltage suppressing circuit 9 is provided in parallel with the SrC1 via a switch 10. The overvoltage suppressing circuit 9 suppresses an overvoltage generated in SrC when a failure occurs. The resistor 6 inserted in series in the power transmission line 8 is divided into four resistors 6a, 6b, 6c, 6d.
At the connection points 5c and 5d, respectively,
It is connected to rC1 and the power transmission line 8. These resistors 6
a, 6b, 6c, 6d are switches 7b, 7c,
Short-circuiting is possible by 7d and 7a. Also, the resistor 6
Is connected to the power transmission line 8 via the switch 7e.

Further, the transmission line 8 is provided with a resistance 2 and a reactance 3 of the transmission line in series. 4a and 4b are capacitances of the power transmission line. In this embodiment, the capacitance of SrC inserted in the power transmission line 8 is C. In addition, in the power transmission line 8, the resistance 2 (Ro (Ω)), the reactance 3 (Lo (H)), and the electrostatic capacitances 4a, 4b (Co (F)) In this embodiment, the current i flowing through SrC is calculated from the equations (1) and (2) described above.

[0026]

It is represented by However,

[0028]

[0029] As described above, the magnitude of the current affects the overvoltage generated in SrC. Therefore, when the resistance R1 is input to the power transmission line as a method of adjusting the magnitude of Z, the resistance R becomes R = Ro + R1. As a result, the magnitude of Z is increased and the value of the current i is suppressed. Ie

[0030]

At the time of reinserting SrC into the power transmission line,
A resistor R1 is inserted in series with the power transmission line to suppress the current flowing in SrC and suppress the overvoltage generated in SrC. Thereby, overvoltage can be suppressed. In the past, it is known from experiments and the like that it is easier to suppress the overvoltage and to obtain good results by dividing the resistance R1 to change the current stepwise. The reason is that the larger the resistance R1, the more Sr.
This is because if the current flowing through C is suppressed and the resistance is gradually reduced, the current change can be changed in small steps, and the magnitude of the current and the magnitude of the current change may cause overvoltage. It is as described above that it is greatly involved.

Next, the operation of this embodiment will be described.
First, after the failure is removed, the overvoltage suppressing circuit 9 generated in SrC1 is turned off by the switch 10, and the switch 7a is turned off immediately before the switch 10 is turned off. At this time, the switches 7b, 7c and 7d are turned off, and the switch 7e is turned on. As a result, the current flowing through SrC1 flows through the resistors 6a, 6b, 6c, 6d, and the current i flowing through SrC is limited by these resistors. Next, the switches 7b, 7c, and 7d are short-circuited in this order to form the resistor 6a,
6b and 6c are removed. Further, 7a is short-circuited and then 7e is cut off. As a result, the current flowing through SrC1 is gradually increased, and finally all the resistors are short-circuited to start the steady operation.

By this method, the change in the current flowing through the SrC can be reduced and the overvoltage generated in the SrC can be reduced as compared with the method of directly returning the SrC to the power transmission line. In addition,
As described above, the smaller the current change is, the smaller the overvoltage generated in SrC is. Therefore, it is needless to say that it is preferable to continuously reduce the resistance. [Embodiment 2] FIG. 2 shows another embodiment of the present invention.
The same components as those shown in FIG. 1 are designated by the same reference numerals, duplicate description will be omitted, and different points will be mainly described.

The present embodiment is different from the first embodiment in that the resistance is one stage rather than multistage. With this configuration, after the failure is removed, the SrC1
The voltage suppression circuit 9 generated at the switch 10 is turned off by the switch 10, and the switch 7a is turned off immediately before the switch 10 is turned off.
It is assumed that e has been turned on. As a result, SrC1
The current flowing through the resistor flows through the resistor 6, and the current i flowing through SrC1 is limited by these resistors. Next, the switch 7a is short-circuited and then 7e is turned off. This allows S
Although the current flowing through rC1 changes stepwise, if the current flowing through SrC1 is small, the overvoltage generated in SrC1 does not become so large. [Embodiment 3] FIG. 3 shows another embodiment of the present invention.

In this embodiment, a resistor is inserted in parallel with SrC. First, in the description of the first embodiment, etc., S
Although it has been described that the current flowing through the rC greatly affects the overvoltage generated by the SrC, in the present embodiment, a method is adopted in which a resistance is inserted in parallel with the SrC, and the resistance is gradually turned on, and finally the resistance is cut off. Is. Hereinafter, this embodiment will be described with reference to FIG.

The parallel resistor 11 to be inserted in the SrC1 is divided into four to form 11a, 11b, 11c and 11d. Further, switches 12a, 12b, 12b for short-circuiting these resistors 11a, 11b, 11c are provided, and
A switch 12d for cutting off all the current flowing through the resistor 11 is provided. With such a configuration, first, after the failure is removed, 9
Switch off. At this point the switches 12a, 1
2b, 12c, and 12d are included. By this operation, the current i flowing through the power transmission line 8 is SrC 1 and the resistance 11
It splits into d and flows.

Next, when the switches 12a, 12b, 12c are opened in this order, SrC1 of the current flowing through the transmission line 8
As the resistance 11 increases, the current shunting to the resistance 11 increases, and the current flowing to SrC 1 increases. By turning off the switch 12d when the value of the resistor 11 becomes sufficiently large, all the current flowing through the power transmission line 8 will flow through SrC1, but if the change in the current flowing through SrC1 due to the turning off of the switch 12d is small. , SrC1
The voltage generated at is significantly suppressed. Therefore, by appropriately selecting the values of the resistors 11a, 11b, 11c, and 11d, the magnitude of the current flowing through SrC1 and its change can be made sufficiently small, so that the voltage generated at SrC1 does not exceed the specified voltage. It becomes possible to control. In this case, needless to say, it is desirable to continuously change the resistance, as in the case of the first embodiment.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the present invention described in the claims. It is possible to For example, in place of the resistor 11d in the illustrated example of FIG.
The same effect can be obtained by providing in series with 1a to 11c and increasing or decreasing the flowing current. In that case, the device can be downsized.

[0039]

As can be understood from the above description, according to the present invention, it is possible to suppress the magnitude of the current flowing in the series capacitor, and thereby suppress the overvoltage generated in the series capacitor. The reliability of the series capacitor is improved, and the series capacitor can be easily insulated.

[Brief description of drawings]

FIG. 1 is a first embodiment according to the present invention.

FIG. 2 is a second embodiment according to the present invention.

FIG. 3 is a third embodiment according to the present invention.

[Explanation of symbols]

 1 ... SrC (series capacitor) 2 ... Transmission line resistance 3 ... Transmission line reactance 4a, 4b ... Transmission line capacitance 6 ... Resistances 6a, 6b, 6c, 6d ... ...... Dividing resistors 7a, 7b, 7c, 7d, 7e ......... Switch 8 ......... Transmission line 11a, 11b, 11c, 11d ......... Dividing resistors 12a, 12b, 12c, 12d ...

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Otomo Takami 2-4-1 Nishitsutsujigaoka, Chofu-shi, Tokyo Tokyo Electric Power Company Technical Research Institute

Claims (2)

[Claims] 1. In a series capacitor system in which a capacitor is inserted in series in a transmission line of an AC power system, at least either when the series capacitor is reinserted in the transmission system after the system fault is removed or when the series capacitor is inserted in the transmission line. In this case, one or more resistors are inserted in series in the transmission line, and the resistors are short-circuited or the value of the resistors is controlled so as to gradually decrease. Overvoltage protection control method. 2. In a series capacitor system in which a capacitor is inserted in series in a transmission line of an AC power system, at least either when the series capacitor is reinserted in the transmission system after the system fault is removed or when the series capacitor is inserted in the transmission line. In the above method, at least one resistance is inserted in parallel to the series capacitor, and the series capacitor overvoltage protection control method is controlled so that the value of the resistance gradually increases.