JPH0619409B2 - DC power transmission system fault location device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power transmission system fault point locating device that detects the position of a short circuit accident (ground fault) on a DC power transmission line on the power transmission end side.

<Background of the Invention> As a fault point locating device, it is well known that a bridge type circuit including a line is constructed and a distance to a fault point is obtained from its equilibrium condition, such as the Murray loop method or the Burley loop method. ing. This type of device requires a measuring operation to balance the bridge type measuring circuit, and it has been impossible to instantly and directly locate the failure point from the change in the current value in the DC power transmission system.

<Object of the Invention> An object of the present invention is to immediately detect the occurrence of a short-circuit accident in a DC power transmission line from a rapid change in its current value, and based on the change in the current value, detect the transmission line up to the accident occurrence point. Another object of the present invention is to provide a failure point locating device for a DC power transmission system, which enables quick calculation of distance.

<Structure of the Invention> In order to achieve the above object, the fault point locating device of the present invention is a means for continuously sampling a current value at a power transmission end side of a DC power transmission line in a predetermined cycle, and the above-mentioned sampling means. Means for constantly monitoring the change in current value to detect the occurrence of a short circuit accident in the above transmission line, and when the occurrence of an accident is detected,
In a transient state in which the current value is rapidly increasing due to the accident, the current values at three or more points to be sampled, the known sampling period, the voltage value on the transmission end side, and the impedance per unit length of the transmission line are measured. On the basis of,
And a means for calculating the length of the power transmission line up to the accident point by a differential analysis operation that is linearly approximated.

<Description of Embodiments> First, the principle of fault point localization according to the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, 1 is a DC power supply and 2 is a power transmission line. The resistance and the inductance per unit length of the power transmission line 2 are r and l, respectively. When the transmission line 2 is grounded at a distance x from the power transmission end as shown in the figure, the resistance R and the inductance L seen from the power transmission end are given by the following equations, where Rf is the resistance at the failure point.

R = rx + Rf (1) L = 1x (2) In this RL circuit, if the voltage at the power transmission end is v and the flowing current is i, the following differential equation holds.

FIG. 2 shows an example of changes in the voltage v and the current i due to the occurrence of the above ground fault. The accident occurs at the time point T, and then a current flows through the RL circuit described above, and the current i exponentially and rapidly increases. Further, as will be described later, the power supply 1 has a constant voltage, and the voltage v hardly changes.

In the device of the present invention, the current i is sampled at a predetermined period Δt. The sampling time points are t ₁ , t ₂ , t
₃ , and the corresponding sample values are i ₁ , i ₂ ,
i ₃ , ... In addition, the difference i ₂ −i ₁ , i ₃ −i ₁ , ... Of the current sample values at two points which are before and after each other is represented by the current change Δ.
i ₂ , Δi ₃ , ... Then, this current change Δi
constantly monitors the _n, exceeds the reference value K △ i _n is set in advance, determines that caused a ground fault in the transmission line 2. Then, the ground fault point is located by the principle described below.

The voltage v at each of the sample times t ₁ , t ₂ , t ₃ , ... Is represented as v ₁ , v ₂ , v ₃ ,.
The following first-order linear approximation holds for the differential equation of the equation.

From (4) + (5) Similarly, for t ₂ and t ₃ , Substituting equation (2) into equation (8) and rearranging, In equation (9), sampling period Δt and transmission line 2
Since the unit length inductance 1 of is known, calculate the distance x from the sample values i ₁ , i ₂ , i ₃ and v ₁ , v ₂ , v _{3 of} the current i and the voltage v to the fault point. You can

In the present invention, the above orientation calculation is further simplified as follows. In the current DC power transmission system, the power supply 1 is composed of a constant voltage rectifier such as a thyristor, and as shown in FIG. 2, the voltage v hardly changes even if a ground fault occurs. If the stabilized output voltage is represented by V and v ₁ , v ₂ , and v ₃ in the equation (9) are respectively represented by V, the following equation can be obtained.

That is, the current sample values i ₁ , i ₂ , i of three consecutive points
_The distance x can be calculated from ₃ . In equation (10), When expressed as, it can be organized as the following equation.

x = J × Q (i ₁ , i ₂ , i ₃ ) ... (13) That is, a simple operation of multiplying the variable Q obtained by the current sample values i ₁ , i ₂ , i ₃ at 3 points by a constant J so,
The distance x to the failure point can be calculated.

Next, a specific embodiment of the fault point control device according to the present invention will be described.

In FIG. 3, the AC power supply 11 is converted into DC by the constant voltage rectifier 12, and the voltage-stabilized DC power is supplied to the power transmission line 2. A circuit breaker 3 and a current detector 4 are provided on the power transmission end side of the power transmission line 2. The current detector 4 uses a hall element or the like and detects the magnitude of the direct current on the power transmission line 2. The detection output of this is converted into a digital signal by the A / D converter 5 and transmitted to the computer. Signal transmission during this period is preferably performed by an optical signal using an optical fiber.

The computer is a CPU 8, a memory 9, an input / output device 1
In addition to the general configuration of 0, a DMA interface 6 for taking in the current value i from the A / D converter 5,
A constant setter 7 is provided. The constant setter 7 stores the constant K for discriminating the occurrence of a failure and the constant J of the equation (11) (sampling period Δt, output voltage V of the rectifier 12, unit length inductance 1 of the transmission line 2). Set in advance.

FIG. 4 shows the processing contents by the CPU 8.

The operation of the present apparatus will be sequentially described below according to this flow chart.

In the first step 100, waits for the sampling timing of the set period △ t, at a predetermined timing proceeds to the next step 101, takes in the current values i _n at that time t _n via the DMA interferons chair 8, memory 9
Is temporarily stored in a predetermined area. At the next step 102,
Calculating a difference △ i _n the sample value i _n-1 of the current sample value i _n and the previous. In the next step 103, △ i _n and performs comparison between the constant K, to monitor the fault occurred.
When Δi _n <K, it is determined to be normal, and the above step 10 is performed.
Repeat 0 → 101 → 102 → 103.

When Δi _n ≧ K in step 103, it is determined that a failure has occurred, and the process proceeds to step 104. Step 1
In 04, based on the latest sample value i _n , the previous sample value i _n-1, and the sample value i _{n-2 two} times before,
The variable Q shown in equation (12) is calculated. Next step 105
Then, the distance to the failure point is calculated from the variable Q and the set constant J according to the equation (13), and is output from the input / output device 10 in an appropriate signal form. After that, the process returns to the first step 100 and the above processing is repeated.

<Effects of the Invention> As described in detail above, according to the fault location device of the DC power transmission system according to the present invention, the DC value is simple with a current value sampling means and a computing means such as a micro computer. When a short-circuit accident of a power transmission line occurs, the position of the failure point can be automatically and accurately detected immediately after that.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a DC power transmission system for explaining the principle of the device of the present invention, FIG. 2 is a diagram showing changes in current and voltage due to a short-circuit fault, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a flow chart showing the processing contents of the CUP 8 in FIG. 1 ... DC power supply, 11 ... AC power supply, 12 ... Constant voltage rectifier, 2 ... Transmission line, 3 ... Breaker, 4 ... Current detector, 5 ... A / D converter, 6 ... DMA interface, 7 ... constant setting device, 8 ... CPU, 9 ... memory,
10 ... I / O device.

Claims (1)

[Claims] 1. A means for continuously sampling a current value of a direct current transmission line at a power transmission end side in a predetermined cycle, and constantly monitoring a change in the sampled current value to prevent occurrence of a short circuit accident in the power transmission line. Means for detecting and, when an accident is detected, in the transient state in which the current value is rapidly increasing due to the accident, the current value of three or more points to be sampled and the known sampling period, the voltage at the transmission end side Means for calculating the length of the power transmission line up to the fault point by a first-order linear approximation differential analysis operation based on the value and the impedance per unit length of the electric wire, The means for calculating the length of the power transmission line includes a constant determined by the current sampling period, the voltage at the power transmission end of the power transmission line, and the inductance per unit length of the power transmission line, Characterized in that it is constituted by an arithmetic means for multiplying the variable defined by the ring is the 3-point or more current values, DC power transmission system of the fault point locating system.