JPS5983526A - Grounding method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-speed grounding switch, and particularly to a grounding method suitable for UHV system lines.

Conventional earthing switches are used to reduce the voltage induced in a working line from an idle line. For this reason, it was mainly used to ground both ends of power transmission lines to protect people during maintenance of idle lines. For this reason, high speed is not particularly required, only reliability is required.

On the other hand, in the UHV system, if no measures are taken,
The re-closing time after the accident has been cleared will be approximately 6 seconds. on the other hand,
Considering system stability, cooperation with back-up protection relays, etc.
The reclosing time must be within 2 seconds. in this way,
In order to achieve high-speed reclosing, it is necessary to adopt a grounding method, and this grounding switching method must be able to open and close at high speed, and the conventional offline method cannot be used. I can't.

An object of the present invention is to provide a grounding system for a grounding switch that enables reliable grounding at high speed.

The main purpose of the earthing switch is to extinguish secondary arc currents. For this reason, it is desirable to close the earthing switch immediately after the fault phase is disconnected from the system. On the other hand, since the open phase voltage is only the electrostatic induction from the healthy phase, the phase changes significantly compared to when it is healthy. Therefore, by paying attention to the voltage phase change, it is possible to reliably detect that the fault phase has been disconnected from the system.

An embodiment of the present invention will be explained below with reference to FIG. 1st
In the figure, ``Electric station G+, Gt is bus line B,
Electric power is transferred and received via the B2 power transmission lines L+ and L2. Considering the case where an accident occurs at point F on the transmission line L2, the circuit breakers CB, , C at both ends of the transmission line L2
B. Breaker CB, CB, for re-closing the circuit after it is fully opened and the recovery voltage has decreased.

to be omitted. If no operation is performed after circuit breaker CB is opened, the recovery voltage of the transmission line will not drop rapidly due to electrostatic induction and electromagnetic induction from the healthy line. Therefore, as a means to shorten the re-closing time, the power transmission line Ltt is grounded using the grounding switch GS. By doing so, the recovery voltage decreases rapidly. In this case, grounding must be done after both ends of the power transmission line are electrically opened, and high reliability is required.

Therefore, in order to obtain bird reliability, we detect open circuits at both ends of the power transmission line based on the voltage phase of the power transmission line, as described later.
This is an attempt to perform grounding.

Figure 2 shows the changes in the voltage and current of the power transmission line over time. If no measures are taken after opening (B), the voltage at the fault point will drop slowly and approximately 6 seconds of voltage-free time will be required to wait for the secondary arc current to disappear and reclose the circuit. . After 6 seconds of no-voltage time ('e) has elapsed, by re-closing the circuit,
Voltage is relative to rating. On the other hand, after opening the circuit breakers at both ends of the transmission line, the voltage at the fault point decreases by closing the earthing switch, so after 2 seconds of no-voltage time (t.) has elapsed,
If the earthing switch is opened and the circuit can be reclosed, the rated voltage will be reached more quickly than if no measures were taken. On the other hand, as shown in the figure, a current equivalent to a tidal current was flowing before the accident. When the circuit is opened, a voltage induced from the healthy phase to the faulty phase via the capacitance becomes a current flowing through the capacitance of the faulty phase. Thereafter, after a period of no voltage, the circuit is reclosed, resulting in a current equivalent to a tidal current. Here, after the accident occurs, breaker Cf
Since the voltage when 3+ and CBt are opened is the voltage induced from the healthy phase via the capacitance, it has the following value. That is, as shown in FIG. 3, in the example of one line, the capacitance (C) between phases.

~Ca) are all equal and Co+ and the capacitance t(04~Ca) to ground is equal to C02, then C02
After a phase fault occurs, the voltage a@voltage V2 when the C-phase circuit breakers CB, CB2 are opened is isometrically equal to the voltage V2 when the circuits are healthy.

2co+ and CO2 in the vector sum of C phase voltage, Vb, V,
Figure 4 shows the phase difference between the internally divided value and #1, which shows a phase difference of approximately 180 degrees from the normal V.

Next, after the a-b phase two-wire fault occurred, the a and b phase breaker CB
+, C phase and b phase voltage VI when CBt is opened
, VI is determined by C6IsCO2 as mentioned above. V/4 is approximately 120 degrees ahead of V in normal condition, and VI is V in normal condition.
I, Yoshi #1 will be delayed by 120 degrees.

In a 3-phase fault, in a 1-line system, breaker CB.

Basically, no voltage is applied to the CBt opening amount phase discharge, and if the above determination is made with the magnitude of the voltage above a certain value, the opening of the circuit breakers CB, CB2 can be reliably detected at both speeds. In principle, the phase difference is 120 degrees, but considering capacitance imbalance and application to a two-line system, some deviation must be taken into consideration. On the other hand, under the condition that CJ-CB2 is a closed circuit, the phase difference is zero, so the setting value for phase difference detection may be selected between 10° and 110°.

Next, a specific example will be explained.

Figure 5 shows an example of this, where the voltage transformer PT
Then, input the voltage of power transmission line L2.

The judgment unit ay stores the input voltage for a certain period of time, calculates the effective value of the input voltage, and if it is below a certain value, it is determined that the circuit breakers CB, CB2 are already open, and the grounding switch is activated. A closing command is issued to the device ()S, and the circuit is opened after a certain period of time.

Also, if the input voltage is above a certain value, the phase difference of the voltage from a certain time ago is determined, and if the difference is more than 90 degrees, it is determined that the circuit breakers CBI and CBt are open. , performs the process described above.

Here, the calculation of the effective value (V) of the voltage and the calculation of the phase difference (θ) are performed at fixed time intervals (π/*
To explain using an example using data sampled by rad), it can be done as follows. That is, V"==V(t)"+V(t-π/z) Shout-・Shout...-(1) V-V, cos θ=v(t)" v(
t)+v(t-x/l ev+ (t-to/2) (
21 Here, ■(S: voltage at time t, V(i-π/2)
: t-π7'x 1 voltage v at 1 time, (i): Voltage V+ (t
-r:/*) 'Indicates the voltage at a certain time before time t-π/2. The above-mentioned fixed time may be the time from when the accident occurs until the accident is cleared.

According to the invention, the opening M of the circuit breakers CBl, CBt
can be reliably detected at high speed, and the efficiency of system operation can be improved, which is extremely effective.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the necessity of a grounding switch, Figure 2 is an explanatory diagram of the effect of an uninvented grounding type embodiment, Figure @3 is an explanatory diagram showing the relationship of Shizukame Yard, and Figure 4 Is it vector related? FIG. 5 is an explanatory diagram of a grounding type embodiment of the present invention. a, , G2...Electric station, B+, By...Bus bar, LltL2...Transmission line, CB+ -CB2...
Breaker, GS...Grounding switch, F...Fault point, T
'T: Voltage transformer, RY: Determining unit. Fig. 1) Fig. 2 (A) (β) Wa■ Shyness ￥9-■ 1 ? Den ゛: □ -potted plant- ,,,51 1 → regret: 1! 1 i Figure 3 α Figure 5

Claims (1)

[Claims] 1. In a system equipped with a grounding switch for each phase of the power transmission line, after detecting that the phase of the voltage one cycle or several cycles ago and the current voltage at the commercial frequency of that phase is out of phase by more than a certain value, A grounding method characterized in that the grounding switch of the own phase is closed and opened after a certain period of time.