JPH0712938Y2 - Transmission line fault current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a fault current detection device for a power transmission line, and more particularly, it detects a fault current of a power transmission line that detects a current at the time of a fault of the power transmission line to locate a fault section Regarding the device.

[Prior Art] FIG. 5 shows a fault current detecting device for detecting a fault current of a power transmission line flowing in an overhead ground wire. The light emitting diode 13 is operated by the output of the current transformer 2 according to the electric current, and the light is transmitted to the measurement system via the optical fiber 15. FIG. 6 is a further improvement of the circuit of FIG. 5, in which a load resistance (reference resistance) 3 is connected to the secondary side of the current transformer 2 provided in the overhead ground wire 1, and a diode 7 is connected in parallel with the load resistance. , 8, 9 and 10 are assembled into a bridge circuit A, B, C and D, and a limiting resistor 14 and an LED (light emitting diode) 13 are connected in series on the diagonal lines C and D to provide an overhead ground wire. The LED 13 emits light in proportion to the magnitude of the overhead ground wire current flowing through the LED 1.
Two Zener diodes 4, 5 are connected in parallel to the load resistor 3.
Is inserted in the opposite direction. One Zener diode 4 having a sufficiently high Zener voltage and one Zener diode 5 having a sufficiently low Zener voltage are selected and used.

In the above configuration, when the overhead ground wire current flows in the overhead ground wire 1, when the overhead ground wire current is in the forward direction (when the output potential of the current transformer 2 is A> B), it is equal to or lower than the Zener voltage of the Zener diode 4. In the case of the above signal, an optical signal proportional to the overhead ground current is obtained at the LED 13, but in the opposite direction, an optical signal corresponding to the Zener voltage of the Zener diode 5 is obtained at the LED 13. The former is used for measurement and the latter is used for calibration. As shown in FIG. 7, since a calibration signal can be obtained for each half wave of the overhead ground wire current waveform, the current value of the fault current and its phase difference can be accurately detected.

[Problems to be Solved by the Invention] However, according to the fault current detection device for a transmission line described above, the value of the current flowing through the light emitting diode 13 is determined according to the resistance value of the load resistor 3. For example, in the case of the straight line a in FIG. 8, the detection accuracy is good in the region where the current value of the current transformer 2 is small, but in the region where the current value is large, the current value exceeds the rating and the LED 13 is destroyed. In the case of the straight line b, it is possible to measure a region where the current value of the current transformer 2 is large, but the detection accuracy of the region where the current value is small is lowered.

[Means for Solving the Problems] The present invention has been made in view of the above, and has a wide dynamic range and enables detection of a fault current flowing through an overhead ground wire with high detection accuracy in that range. Therefore, the detection signal according to the fault current is 2 as shown in Fig. 8C.
Provided is a fault current detection device including a detection signal conversion circuit that is stepwise.

That is, the transmission line fault current detecting apparatus of the present invention comprises the following means.

(1) Detection signal generation means A current transformer (current transformer) is attached to the overhead ground wire, a current signal corresponding to a fault current flowing in the overhead ground wire is detected, and the current signal is supplied to a load resistance (reference resistance). Signal voltage across the load resistance. The signal voltage is used as a detection signal.
The current transformer is preferably a through type through which an overhead ground wire passes, but is not particularly limited thereto. Further, the overhead ground wire preferably has an optical fiber for transmission inside.

(2) Level conversion circuit This is composed of first and second Zener diodes provided in parallel with the load resistance. The two diodes are connected in series in opposite directions, the Zener voltage of the first Zener diode is set to the predetermined value of the detection signal, and the Zener voltage of the second Zener diode is sufficiently smaller than the predetermined value. To do.

(3) Detection signal conversion circuit It is composed of, for example, a resistor inserted in series with the first Zener diode.

[Operation] When a fault current flows through the overhead ground wire, a current signal corresponding to the fault current is output to the output terminal of the current transformer. Since the load resistance is connected to this output terminal, a voltage detection signal corresponding to the fault current is obtained across the load resistance. When this detection signal is in the forward direction, it becomes a reverse voltage with respect to the first Zener diode having the first Zener voltage. Therefore, when the detection signal becomes larger than the first Zener voltage, the first Zener diode is fixed. It becomes a voltage circuit. Therefore, a current also flows through the resistor inserted in series with the first Zener diode, and regulates the current flowing through the light emitting diode. Therefore, by setting the resistance value of this resistor to a predetermined value,
A stepped signal current is obtained. On the other hand, when the detection signal is in the reverse direction, the reverse voltage is applied to the second Zener diode having the smaller Zener voltage. Therefore, when the detection signal is higher than the Zener voltage, the level is limited to the Zener voltage. . Therefore, when the detection signal is in the forward direction, a measurement optical signal corresponding to the fault current can be obtained. In addition, since the measuring optical signal can be divided into two stages by the predetermined resistance, the dynamic range becomes large and high detection accuracy can be obtained in all ranges. On the other hand, when the detection signal is in the reverse direction, a calibration optical signal corresponding to the Zener voltage of the second Zener diode is obtained. In this case, if the diode of the same direction is inserted in parallel with the first Zener diode, the detection signal conversion circuit inserted in series with the first Zener diode is not affected.

Hereinafter, a fault current detecting device for a power transmission line according to the present invention will be described in detail.

[Embodiment] FIG. 1 shows an embodiment of the present invention, and the same parts as those in FIG. Is provided with a first Zener diode 20, and a resistor 21 is inserted in series therewith. A diode 22 is connected in parallel to the series circuit of the first Zener diode 20 and the resistor 21 in the opposite direction to the second Zener diode 5. The Zener voltage of the first Zener diode 20 is set to the voltage of the LED section when the current transformer current Ip of FIG. 8 flows.

The operation of the present invention will be described with the above configuration.

(1) When a forward signal is applied to the circuit and the level of the fault current is below the current corresponding to the current transformer current Ip When the fault current flows through the overhead ground wire 1, the current transformer 2 detects it and the load A detection signal is obtained at both ends of the resistor 3. Since the level of the detection signal is equal to or lower than the first Zener voltage of the Zener diode 20, the forward detection signal is the bridge circuit A,
The A, B, C, and D terminals have the second detection signal in the opposite direction.
The second zener voltage of the zener diode is applied to the B terminal. Here, since the forward detection signal is lower than the first Zener voltage of the first Zener diode, the detection signal mainly proportional to the resistance value of the resistor 14 is obtained. As shown by the straight line c ₁ in FIG. 8, by setting the slope of this signal to a circuit constant having a relatively large value, it is possible to suppress a decrease in detection accuracy in a small current region.

(2) The forward current signal causes the level of the fault current to be the current transformer current Ip
When the current is equal to or higher than the current corresponding to the detection signal level of the first Zener diode 20
Since it becomes higher than the Zener voltage of, the first Zener diode 20 becomes a constant voltage circuit, and the detection signal is the resistance 3 and the resistance.
Regulated by 21 combined resistances. Therefore, it becomes like the straight line c ₂ in FIG. 8, and it becomes possible to detect even in a large current region without destroying the LED.

In the above example, when the detection signal is in the reverse direction, the diode
Since 22 becomes conductive, the effect of the resistor 21 on the circuit disappears.

FIG. 2 shows a second embodiment of the present invention, in which the same parts as in the first embodiment are designated by the same reference numerals. However,
Instead of the bridge circuit composed of the diodes 7, 8, 9 and 10, the anode of the light emitting diode 13 is connected to the connection point of the zener diodes 5 and 20, and the light emitting diode 13 is connected.
Is connected to the series circuit of the diode 9 and the resistor 24, and the series circuit of the diode 10 and the resistor 25, and the resistor 23 is connected in parallel with the load resistor 3 unlike the first embodiment. To do. In this embodiment, the number of diodes is reduced, and in addition, the resistor 23 is connected to the light emitting diode 13
Can be used as a current limiter.

FIG. 3 shows a third embodiment of the present invention. In the first embodiment, a pair of first Zener diodes 20 and a resistor are provided.
21 are arranged in parallel, each with a small capacity can be used.

FIG. 4 shows a fourth embodiment of the present invention. In the second embodiment, a pair of first Zener diodes 20 and a resistor are provided.
21 are arranged in parallel.

[Effects of the Invention] As described above, according to the fault current detection device for a power transmission line of the present invention, the detection signal corresponding to the fault current is reduced as the level of the fault current increases, so that the dynamic range is widened. In addition, it is possible to suppress a decrease in detection accuracy in that range.

[Brief description of drawings]

1 to 4 are circuit diagrams showing first to fourth embodiments of the present invention, FIGS. 5 and 6 are circuit diagrams showing a proposed fault current detecting device for a transmission line, and FIG. The figure is a waveform diagram showing the measurement signal and the calibration signal, and FIG. 8 is an explanatory diagram showing the relationship between the current transformer current and the operating current of the light emitting diode. [Explanation of symbols] 1 ... Overhead ground wire 2 ... Current transformer 3 ... Load resistance 4, 5, 20 ... Zener diode 7, 8, 9, 10 ... Rectifying diode 13 ... Light emitting diode 21, 23, 24, 25 ... resistance 22 ... diode

Claims (3)

[Scope of utility model registration request] 1. A detection signal according to forward and reverse fault currents flowing in an overhead ground wire is supplied to an optical signal generating means to generate a measurement optical signal based on the forward detection signal, and the reverse direction is generated. In a fault current detection device for a power transmission line that generates a calibration optical signal based on the detection signal of No. 1, a first Zener diode having a first Zener voltage corresponding to a predetermined level of the detection signal, and the first Zener diode. A level conversion circuit, in which a second Zener diode having a second Zener voltage smaller than the Zener voltage is connected in series in the reverse direction and arranged in parallel with the detection signal generating section, and the first Zener diode is provided. A fault current detection device for a transmission line, which is configured by inserting a resistor as a detection signal conversion circuit in series. 2. The transmission line according to claim 1, wherein the first Zener diode and the resistor are provided in parallel with a diode having the same direction as that of the first Zener diode. Fault current detector. 3. The fault current detecting device for a transmission line according to claim 1, wherein the first Zener diode and the resistor are arranged in parallel in two groups.