JPS595867B2 - AC amount detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an alternating current amount detection device.

For example, in the case of a protective relay that inputs voltage or current obtained from the system to be protected, the relay operates to open the system and prevent the spread of an accident.

Therefore, protective relays are required to operate with high precision and high speed. In this way, the voltage or current of the system is usually converted to an appropriate amount via a transformer (instrument transformer, instrument current transformer, etc.) and then output, which becomes the input of the protective relay. In the case of conventional protective relays, the above input is first converted to an appropriate amount through an AC input transformer, and then ripples are removed by a full-wave rectification circuit and a rectification and smoothing circuit, and then the input is sent to a DC level detection circuit. When the output level of this circuit reaches a predetermined value, the output relay circuit is driven.

By the way, even through the rectifying and smoothing circuit described above, a DC level containing some ripples will be detected, resulting in a decrease in accuracy.

On the other hand, if the ripple is to be reduced and accuracy is increased, the time constant of the smoothing circuit must be increased, resulting in a delay in the operating time and return time. In view of the above points, it is an object of the present invention to provide an alternating current amount detection device that can detect alternating current amount with high precision and high speed.

Embodiments of the present invention will be described below based on FIG. 1 and with reference to FIG. 2.

1 is a power system line, 2 is a transformer (instrument transformer, instrument current transformer, etc.) connected to the line 1. From this, the amount of alternating current on the line 1 is determined and applied to the input transformer 3.

Here, the secondary side of the input transformer 3 is composed of two windings, and one of the windings 4 is provided with a center tap, and a CR circuit 4 is formed with a resistor and a capacitor, with a phase shift of 900 with respect to the input AC amount V. Thus, the AC amount V1' is obtained. In this way, there is a phase difference of 900 between the other winding 6 and the winding 4, and alternating current quantities V1 and V1' having the same magnitude (absolute value) are obtained, and these are transferred to the full-wave rectifier circuit 7. , 8 and the output V2, V
Try to get 2'. Numerals 9 and 10 are nonlinear circuits composed of elements such as resistors and Zener diodes, and waveforms V3 and V3' as shown in FIG. 2 can be obtained as outputs thereof.

Reference numeral 11 denotes a level detection circuit which operates to close the contact 13 of the relay 12 when the sum of the outputs of the nonlinear circuits 9 and 10 reaches a predetermined level, and may be a known type such as a Schmitt circuit.

Note that various types of nonlinear circuits are possible for the above nonlinear circuit, but for example, the nonlinear circuit shown in FIG.
In terms of characteristics, V3 and V3' have linear characteristics as shown in FIG. 2, so their sum V3+V3' is a DC component without pulsation.

Furthermore, as shown in Fig. 3, if the output characteristic of the nonlinear circuit for waveform V2 is made point symmetrical with respect to B such as ΛBC, (B
It is clear that the sum of the outputs of the nonlinear circuit is a non-pulsating DC component, and the nonlinear characteristics for ABC are shown by the dotted line in FIG. As described above, according to the present invention, the nonlinear characteristics are set so that the sum of the outputs of the nonlinear circuit becomes a non-pulsating DC component at the level to be detected of the AC amount obtained from the system to be protected, and this level is detected. By doing so, highly accurate level detection is possible.

Also, considering the response speed of this device, the part that causes the time delay is the 90° phase shift circuit of the input transformer 3, and the time constant of this circuit is about CR=-ω-3ms at 50Hz. High-speed response can be obtained.

Therefore, it is highly effective when applied to a rectifying device for obtaining a pulsation-free DC component with respect to an AC amount, and a device for detecting the level of an AC amount at high speed and with high accuracy.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention. Figure 1 is an electrical connection diagram, Figure 2 is an electrical connection diagram,
, 3 and 4 are waveform diagrams for explaining the operation. 1...Power system line, 2...Transformer,
3... Input transformer, 7, 8... Full wave rectifier circuit, 9, 10... Nonlinear circuit, 11...
... Lebel detection circuit, 12, 13... Relay and contact.

Claims (1)

[Claims] 1. A circuit that converts the amount of alternating current obtained from the system to be protected into two alternating current waveforms with a phase difference of 90° and equal absolute values, a circuit that performs full-wave rectification of each of the above-mentioned alternating current waveforms, and this full-wave rectifying circuit. An alternating current amount detection device comprising a nonlinear circuit that receives an output as an input, and detects a direct current level corresponding to the alternating current amount by calculating the sum of the outputs of the nonlinear circuit.