JPS63171374A - Monitor apparatus for multiphase ac power source - Google Patents

Abstract

PURPOSE:To detect the unbalance state between phases at a high speed with high accuracy, by detecting the hum component contained in the output of a rectifying circuit. CONSTITUTION:A three-phase AC power source having fundamental frequency (f) is subjected to full-wave rectification in a three-phase full-wave rectifying circuit 1. This full-wave rectifying output is applied to a 2Xf component extraction circuit 2 to extract and detect a higher harmonic hum component two times the fundamental frequency (f). The 2Xf hum component thus detected is applied to a level detection circuit 3 to detect the level thereof and, when said level exceeds a predetermined threshold value level, an alarm signal is generated to the outside. By this method, the detection of minute unbalance can be accurately performed without time delay.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multiphase AC power supply monitoring device, and more particularly to a multiphase AC power supply monitoring device for monitoring an unbalanced state of voltage of each phase.

Ryomai Ei I Load equipment may be adversely affected due to voltage imbalance between each phase of a multiphase AC power supply, so it is necessary to detect and monitor the voltage imbalance between each phase to prevent such adverse effects. becomes. Conventional monitoring devices of this type include open-phase detection devices, and thermal relays for electric motors.

The open phase detection device is only capable of detecting a large unbalance such as a lack of a certain phase, that is, an open phase, and is unable to detect a minute unbalance. Furthermore, when a thermal relay or the like is used, there is a drawback that there is a delay in the abnormality detection time.

OBJECTS OF THE INVENTION An object of the present invention is to provide a multiphase AC power supply monitoring device that can accurately detect minute imbalances without time delay.

R1 and 1 The multiphase AC power supply monitoring device according to the present invention includes a rectifier circuit that rectifies a multiphase AC power supply, and a hum component detection circuit that detects a hum component contained in the rectified output. The system is characterized in that the unbalanced state of the multiphase AC power supply is monitored according to the level of the AC power supply.

! 11 Hereinafter, the present invention will be explained in detail using the drawings.

The figure is a block diagram of an embodiment of the present invention, and is an example of a two-phase AC power supply. In the figure, a two-phase AC power source having a fundamental frequency f is full-wave rectified in a three-phase full-wave rectifier circuit 1. From this full-wave rectified output, a harmonic hum component twice the fundamental frequency f is extracted and detected in a 2×f component extraction circuit 2. The level of the 2Xf hum component thus detected is detected by a level detection circuit 3, and an alarm signal is generated to the outside when the hum component exceeds a predetermined threshold level.

Here, in a three-phase AC power supply, the full-wave rectified output from the three-phase full-wave rectifier circuit 1 has an original hum component of 6×f
However, if an unbalance occurs between the three phases, the hum component of 2×f will also increase depending on the degree of the unbalance. Therefore, the unbalance of the three-phase AC power supply can be monitored by selectively extracting and detecting the component at 2X using the 2×f component extraction circuit 2, and monitoring the detection level using the level detection circuit 3. be.

If the 2×f component extraction circuit 2 is configured to include a smoothing circuit consisting of an LG (choke coil and capacitor), for example, if it is configured in one stage with 10 circuits, the original hum component (6
xf), the attenuation of the hum component of 2Xf by the one-stage LC circuit is only 1/9,
It turns out that it is extremely easy to extract the 2×f component from the output of the circuit.

In this way, by detecting the 2Xf hum component,
Although it is possible to accurately detect the unbalanced state of a three-phase AC power supply, if it is not necessary to detect minute unbalanced states, the original hum component ( 6xf) may be extracted and detected.

The original 6xf component included in the output of the three-phase full-wave rectifier circuit 1 is a minute amount of 4%, but this original 6xf hum component also increases, albeit slightly, depending on the imbalance of the three-phase AC power supply. Therefore, a circuit for extracting the 6xt' hum component from the three-phase full-wave rectified output may be used.

Although the above description has been made for the case of a three-phase AC power supply, it is also applicable to the case of a polyphase AC power supply with four or more phases. All you have to do is detect it.

As described above, according to the present invention, by detecting the hum component included in the output of the rectifier circuit, an unbalanced state between each phase can be detected accurately and at high speed.

[Brief explanation of the drawing]

The figure is a block diagram of an embodiment of the invention. Explanation of symbols of main parts 1...3-phase full-wave rectifier circuit 2...2×f component extraction circuit 3...Level detection circuit

Claims (1)

[Claims] It has a rectifier circuit that rectifies a multiphase AC power supply, and a hum component detection circuit that detects a hum component included in the rectified output,
A polyphase AC power supply monitoring device characterized in that the unbalanced state of the polyphase AC power supply is monitored according to the level of the hum component.