JPS593263A - Current detecting apparatus - Google Patents

Abstract

PURPOSE:To prevent a voltage detecting part from receiving an overvoltage obstacle, by a method wherein two thyristors with mutually opposite polarities are provided in parallel between both terminals of the secondary side of a current transformer and a gate circuit including a diode is mounted between anode gates to set a gate level. CONSTITUTION:When a current having a wave form shown by the drawing is flowed to the secondary side of a current transformer 1 with respect to a thyristor 9 in a regular direction, a diode 11 is electrically disconnected during a time when the voltage of the secondary side is low and the tyristor 9 is held under an OFF state. In this state, the input voltage of a voltage detecting part 4 is abruptly raised as shown by a wave form 15 and the voltage detecting part 4 instantaneously carries out detecting operation. In addition, when voltage between both electrodes of the diode 11 is raised as the rising in the secondary side voltage and reaches threshold voltage 6, the diode 11 is electrically connected. By this mechanism, because the thyristor 9 is electrically connected to shortcircuit the secondary side of the current transformer 1, the voltage detecting part 4 can be avoided from receiving an obstacle due to overvoltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current detection device that detects current using a current transformer.

The most common means for detecting the current flowing through a line is to use a current transformer as a detector and detect the secondary current as it is or by converting it into voltage. FIG. 1 shows a conventional current detection device, where 1 is a current transformer and 2 is a current detection section provided on the secondary side thereof. Fig. 2 shows another conventional device, where 1 is a current transformer, 6 is a load connected to the secondary side of the current transformer, and 4 is a voltage detector that detects the voltage converted from the current by the load B. Department.

In such a conventional device, when a current having a waveform as shown in 5 in FIG. 3 flows through the secondary side of the current transformer 10, the detection unit 2 or 4 detects the current because the current value is This is the point at which the device-specific operating level B is reached, and there is always a delay of time T1 until then. In order to reduce this detection delay, it is possible to reduce the transformation ratio of current transformer 1 and obtain a high output as shown in 7. In this case, the detection delay time T2 (T1) may also be shortened. However, since this output level is limited by the detection unit 2 or 40 input permissible limit 8, the effect of shortening the detection delay is small and there is a drawback that a fast response cannot be achieved.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and utilizes the fact that when a current transformer is used in an open state, a high voltage is generated on the secondary side even with a small current. By keeping the current transformer in an open state until the detector operates, and shorting the secondary side of the current transformer after detection, the detector operates quickly in the micro current region and prevents overvoltage. It is an object of the present invention to provide a current detection device that is free from interference caused by.

An embodiment of the present invention will be described below with reference to the drawings. Fourth
In the figure, 1 is a current transformer, and 4 is a voltage detection section. Two thyristors 9 and 10 are connected to the secondary side of the current transformer 10 with opposite polarities so as to short-circuit both ends thereof. A gate circuit consisting of a diode 11 and a resistor 16 is connected between the anode and gate of the first thyristor 9, and a gate circuit consisting of a diode 12 and a resistor 14 is connected between the anode and gate of the second thyristor 10. The circuit is connected.

Next, the operation will be explained. Now, assume that a current having a waveform shown by 5 in FIG. 5 flows in the forward direction with respect to the thyristor 9 on the secondary side of the current transformer 10 due to the current flowing through the line. While the voltage on the secondary side of the current transformer 10 is low, the diode 11
is non-conducting, so the thyristor 9 is in an off state. In this state, the secondary side of the current transformer 10 is in an open state, so the input voltage of the voltage detection unit 40 has a waveform 15 in FIG.
The voltage rises rapidly as shown by , and the voltage detection section 4 instantly performs a detection operation. Further, as the voltage on the secondary side of the current transformer 10 rises, the voltage between the anode and cand of the diode 11 also rises, and when the value reaches the threshold voltage of the diode 11, the diode 11 becomes conductive. This causes the thyristor 9 to conduct and short-circuits the secondary side of the current transformer 10, so that no overvoltage is applied to the voltage detection section 4. Further, when current flows in the opposite direction to the above-mentioned direction on the secondary side of the current transformer 10, the same operation is performed for the second thyristor 10.

That is, the voltage detection unit 4 detects that the current flows at time T6 when the voltage shown by the waveform 15 reaches the operating level 6,
This voltage becomes almost zero at time T4 immediately after reaching the gate level 16 of the thyristor 9 or 10, which is lower than the breakdown level 8 of the voltage detection section 4. It can be seen that the time up to the operation point T3 at this time is significantly shorter than the time up to the operation point T1 in the conventional device, and a fast response is achieved.

As described above, according to the present invention, even when the current flowing through the line is minute or the current rises slowly, a high output voltage can be obtained instantaneously on the secondary side of the current transformer. Very fast response occurs. Further, after the voltage necessary for operation is obtained, the stain pressure becomes almost zero due to the operation of the thyristor, so there is no risk that the voltage detection section will be damaged by overvoltage.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional current detection device, FIG. 3 is a graph showing the relationship between input and operating point in the conventional device, and FIG. 4 is a current detection device according to an embodiment of the present invention. FIG. 5 is a graph showing the relationship between input and operation in the circuit of FIG. 4. 1... Current transformer, 4... Voltage detection section, 9.10.
...Thyristor, 11.12...Diode, 1
3゜14...Resistance. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Shin Kuzuno - (1 other person) 2nd
Figure 3 Figure 4 Figure 5 = 355

Claims (1)

[Claims] A voltage detection unit that detects that the voltage generated on the secondary side of the current transformer has reached a predetermined detection voltage is connected in parallel between both ends of the secondary side of the current transformer with mutually opposite polarities. The gate circuit includes two thyristors and a diode connected between the anode φ gate of each thyristor, and the diode has a secondary voltage of the current transformer that is at a high operating level of the voltage detection section. A current detection device characterized in that it is configured to become conductive when a gate level reaches a gate level lower than a breakdown level.