JPH0522458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging current compensator that is grounded to a power transmission line with a large capacitance and is suitable for eliminating zero current in a system.

[Background of the invention]

For example, 1981 National Institute of Electrical Engineers of Japan Conference Paper No.875
As shown in "Prediction of Zero Miss Occurrence of Fault Current", if the amplitude of the DC generated during a power system fault is greater than the amplitude of the AC, a phenomenon may occur in which the zero point of the current does not occur over several cycles of the AC. It has been known.

Currently, a command to open the circuit breaker is given to the circuit breaker due to the detection of an accident despite the occurrence of this no-current phenomenon.

In this case, the circuit breaker mechanically opens the poles, but electrically DC continues to be applied, creating an arc-connected state that may cause circuit breaker damage such as contact melting. There is. Further, more than this, the problem is that the stability of the power system decreases due to the inability to eliminate faults for a long time.

Various studies have been conducted from the viewpoints of how to prevent this no-current phenomenon from occurring, how to quickly attenuate it after it occurs, and how to respond to it with circuit breakers or protective relays. There is. However, the reality is that there is no fixed answer.

This non-zero current phenomenon is said to easily occur in ultra-high voltage systems.

[Purpose of the invention]

In light of the above, an object of the present invention is to provide a charging current compensator that can quickly eliminate the problem of zero current in a power transmission line with a large capacitance.

[Summary of the invention]

In ultra-high voltage power transmission systems, it is essential to install a shunt reactor between the bus bar or transmission line and the ground in order to compensate for charging current and suppress abnormal voltage in the event of an unbalanced accident. In the present invention, by installing a capacitor in series with the shunt reactor, a low-order frequency oscillation is caused in the current flowing out from the shunt reactor in the event of a transmission line fault, and this current causes a zero point in the current passing through the circuit breaker. This is to enable quick shutoff operation.

[Embodiments of the invention]

An example of a conventional ultra-high pressure system to which the present invention is applied will be explained with reference to FIG. In the figure, electric station S ₁ is a transformer.
This shows an example in which power is sent to the electric station _S2 via T _r1 , T _r2 , and power transmission lines L ₁ to _{L 3} .
Circuit breakers CB ₁ to _{CB 6} are installed at both ends of L ₁ to L ₃ . Moreover, in order to compensate for the capacitance of the transmission line, a shunt reactor L _h1 is installed on the bus side of the circuit breaker CB.
~L _h6 is installed. In such a system, if a two-wire short circuit occurs at a point on the receiving side of power transmission lines L ₁ to _{L 3} , for example at point F in this figure, the current passing through the lagging phase of the transmission line, that is, circuit breaker CB ₂ , will No current zero occurs. The reason for this is that the DC component determined by the power flow before the accident, the DC component determined by the voltage at the time of the accident, and the DC component generated by the capacitance of the power transmission line act in the direction of adding to each other. When a shunt reactor is installed on the busbar side, as shown in Figure 4, the current that was flowing through the shunt reactor L at the time of the accident flows out through the fault point F (as shown in Figure 4). il), depending on the phase in which the fault occurs, this may lead to an increase in the transient DC current, making it more likely that the current will not reach zero. In the figure, E and Le indicate each equivalent power supply and the equivalent reactance on the power supply side. For this reason,
Even if a shutdown command is issued to the circuit breaker CB upon detection of an accident, the circuit breaker cannot be opened, and there is concern that the circuit breaker may be damaged. The present invention seeks to compensate for the aforementioned drawbacks. FIG. 1 shows an embodiment of the present invention, and a feature of the present invention is that capacitances C ₁ to C ₅ are provided in series with the shunt reactors L _h1 to _{L h6} .

FIG. 3 is for explaining the effect of the shunt reactor proposed by the present invention, and in the same figure, C is the capacitance.

In the case of FIG. 3, due to the voltage applied to the reactor L and capacitor C due to the fault at point F, a low-order harmonic current is generated in the current passing through the circuit breaker. The frequency at this time is The magnitude of this current is determined as follows.

Here, V is the shunt reactor terminal voltage.

This current i _o is determined by the power flow as a transient DC current i _p ,
When the current becomes larger than the sum of the transient direct current components i _c determined by the charging current, the composite current has a zero point and is no longer zero. From these relationships, the conditions for eliminating zero are: becomes.

Next, we will discuss the value of the capacitor installed in series with the shunt reactor.

If the compensation degree of the shunt reactor is γ, and the ratio of the capacitor's impedance at the system frequency to the reactance of the shunt reactance is η, then ω ₀ L=1/ω ₀ Clγ ……(4) ω ₀ Lη=1/ω ₀ C ……(5) Here, Cl: Pairwise capacitance of the transmission line, ω ₀ = 2πf
shall be.

When η is obtained from equations (3) to (5), η<1/(2πf ₀ Li _p /V+r) ² ...(6). If the condition shown in equation (6) is satisfied, the non-zero condition disappears rapidly.

〔Effect of the invention〕

According to the present invention, by simply installing a capacitor determined by power flow, terminal voltage, and shunt reactor compensation degree in series with the shunt reactor, it is possible to solve the problem of no current zero, and the economic effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is an ultra-high voltage power transmission system according to the present invention, FIG. 2 is a conventional system, FIG. 3 is a system diagram according to the present invention, and FIG. 4 is a conventional analysis diagram. S ₁ , S ₂ ... Electrical station, T _r1 , T _r2 ... Transformer, L ₁
~L ₃ ...Transmission line, CB ₁ ~CB ₆ ...Breaker, L _h1 ~
L _h6 ...Shunt reactor.

Claims (1)

[Claims] 1. A charging current compensator installed between the line and the ground to compensate for the charging current of the line. The capacitor has a maximum current of the line as ip, a terminal voltage of the reactor as V, and a compensation degree of the reactor as γ.
When , the charging current compensator is a capacitor with a ratio η to the reactor determined by the following equation. η<1/(2πfoLip/V+r) ²