JPH0568327A - Open-phase detection circuit for three-phase power source - Google Patents

Abstract

PURPOSE:To quickly detect an open phase if it occurs in the power source and protect equipment, in the equipment wherein three-phase power source is used, and constitute the equipment out of cheap parts. CONSTITUTION:The output signals from photocouplers 7, 8, and 9, which constitute a detection means 40 for detecting the current between each phase of a three-phase power source 30, are taken out, being put together into one, and further the waves, which have passed the integration circuit composed of a resistor 11 and an electrolytic capacitor 13, are input into the plus terminal of a comparator 17, and also the voltage, which becomes the reference to judge normality and open phase is input, being divided by resistors 15 and 16. And by the judgment results of the comparator 17, a control means 19 applies protection to a three-phase motor 21, and also a display element 20 notifies the user that the protection has worked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open phase detection circuit for equipment using a three-phase power source as a power source.

[0002]

2. Description of the Related Art Conventionally, in a device using a three-phase power source such as an air conditioner as a power source, the purpose is to protect the device when a phase loss occurs due to a wire breakage or connection loss. It is common to have means for detecting a phase loss. Conventionally, as such a detecting means, it has been general to use an open phase detection relay using bimetal. The configuration will be described below with reference to FIG.

As shown in the figure, a three-phase power source 109 is connected to a contact of a main relay 102 via an open phase detection relay 101. Further, the contacts of the main relay 102 are connected to the three-phase motor 103 which is a load. When the three-phase motor 103 is operated, an ON signal is output from the control means 104, the transistor 106 is turned on, the coil 102a of the main relay 102 is energized, and the main relay 102 is turned on.
By closing the contact of, the three-phase motor 103 is energized to start the operation.

In the above configuration, the R of the three-phase power source 109
When any one of the open phase, the S phase, and the T phase occurs, the bimetal of the open phase detection relay 101 operates to open the contact 101a of the open phase detection relay 101. As a result, the main connected in series with the contact 101a. Coil 102 of relay 102
The power supply to a is cut off and the contact of the main relay 102 opens,
The operation of the three-phase motor 103 is stopped. At the same time, the contact 101a of the open phase detection relay 101 opens and the main relay 1
The control means 104 detects that the voltage of the coil No. 02 has dropped.
The control is carried out by displaying the result on the display means 105 and notifying the user that the phase failure has occurred.

[0005]

In such a circuit for detecting an open phase which depends on the conventional open phase detection relay 101, the open phase detection relay 101 is expensive and has a large volume. Although it will be installed inside the unit, it may be an obstacle at the product development stage due to the large volume. Further, since the detection of the open phase depends on the characteristics of the bimetal, the open phase detection relay 101 can be used after the actual open phase occurs.
There is a problem that the time until the contact of the contact is closed varies, and as a result, the breakdown due to the variation must be considered for the purpose of protecting against the load.

An object of the present invention is to solve the above-mentioned problems, and an object thereof is to provide a control circuit which is inexpensive and has a small volume and which has a high detection accuracy.

[0007]

In order to achieve the above object, the present invention detects a phase difference based on a signal output from the detection means and a detection means for detecting a current between each phase of a three-phase power supply. Judgment means for judging, control means capable of protecting against a load based on the judgment result from the judgment means, and display means connected to the control means for informing the user that the protection has been applied. The configuration is provided with.

[0008]

According to the present invention, with the above-mentioned structure, the judging means determines whether the three-phase power supply is normal or open-phase on the basis of the output signal from the detection means for detecting the current between the respective phases provided between the respective phases of the three-phase power supply. If there is a phase loss, it immediately sends a signal to the control means,
The control means can protect the load and inform the user of the protection by the display means connected to the control means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the R phase of the three-phase power source 30,
The S phase and the T phase are connected to resistors 1, 2, and 3, respectively, and the opposite side of the resistors 1, 2, and 3 are connected to a photocoupler 7,
It is connected to 8 and 9 and acts as a current limiting resistor. The photocouplers 7, 8 and 9 become detection means 40 when a current flows between the respective phases of the three-phase power source 30, turn on the secondary side transistors of the photocouplers 7, 8 and 9, and commonly connect to the collector side of each transistor. By passing a current through the connected resistor 10 to the ground, the voltage at the positive terminal of the comparator 17 drops. Further, the resistor 10 is connected to the resistor 11, and an electrolytic capacitor 13 is connected between the opposite side of the resistor 11 and the ground, and works together with the resistor 11 as an integrating circuit. Further, the resistor 11 and the electrolytic capacitor 13 are connected to the diode 12 and the resistor 14, the diode 12 acts as an overvoltage protection, and the resistor 14 is connected to the plus terminal of the comparator 17 and acts as a limiting resistor. To do. Resistors 15 and 16 are connected to the negative terminal of the comparator 17, and a voltage divided by the two resistors is applied and acts as a reference voltage.
The reference voltage applied to the minus terminal and the voltage from the detection means 40 applied to the plus terminal are compared to serve as the determination means 45, and the determination result is output from the output terminal. The output terminal of the comparator 17 is connected to a resistor 18 acting as a pull-up resistor and a control means 19. The control means 19 is connected to a three-phase motor 21, which is a load, and a display means 20 for notifying the user of a missing phase.

With the above configuration, when the three-phase power source 30 is normal, the output waveforms on the secondary side of the photocouplers 7, 8 and 9 are as shown in FIG.
The waveform looks like. Further, the waveform of the positive terminal of the comparator 17 is the waveform a of FIG. 3, and the waveform of the negative terminal of FIG.
Since the waveform becomes like the waveform b, and the voltage is higher at the negative terminal, a low-level signal is output from the output terminal of the comparator 17 as the determination result. The control means receiving this signal controls the three-phase motor 21 as an operation in a normal state, and does not display on the display means 20.

Next, when a phase loss occurs in the three-phase power source 30 due to a wire breakage, a connection part detachment, or the like, the output waveforms on the secondary side of the photocouplers 7, 8 and 9 are as shown in FIG. It becomes a waveform. Further, the waveform of the plus terminal of the comparator 17 becomes like the a ′ waveform of FIG. 5, and the minus terminal becomes like the waveform of b ′ of FIG. 5. Since the voltage at the plus terminal is higher, the judgment result from the output terminal of the comparator 17 becomes high. The level signal is output. In the control means 19 which receives this signal,
As an operation in the open phase state, the three-phase motor 21 is stopped and protection is performed, and a display on the display unit 20 is performed to notify the user that protection has been performed.

Thus, the three-phase power source 30 of the embodiment of the present invention
According to the open-phase detection circuit of No. 3, the outputs of the photocouplers 7, 8 and 9 provided between the respective phases of the three-phase power supply 30 and the voltage output by combining the integration circuit are different when the three-phase power supply 30 is normal. Since a voltage difference occurs when the phase loss occurs, by using the comparator 17 in which the reference voltage is set near the intermediate voltage of this voltage difference, the phase loss is promptly detected and the three-phase motor 21 is protected. It is possible to notify the user that the protection has been applied by the display means 20 while applying the warning.

[0014]

As is apparent from the embodiments described above, according to the present invention, the open phase is detected based on the detection means for detecting the current between the phases of the three-phase power supply and the signal output from the detection means. If the three-phase power supply is out of phase, it can be surely detected in a short time by configuring the judging means for judging the above and the controlling means for protecting the equipment based on the judgment result output from the judging means. In designing the product because it can be composed of possible and low-priced parts, it improves the protection of the device against phase loss,
It is possible to provide a phase loss detection circuit for a three-phase power supply, which has effects such as cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an open phase detection means and a control means of a open phase detection circuit for a three-phase power supply according to an embodiment of the present invention.

[Fig. 2] Output waveform diagram of the photocoupler when the three-phase power supply of the open-phase detection circuit of the same three-phase power supply is normal

FIG. 3 is a waveform diagram of a comparator input terminal when the three-phase power supply of the open-phase detection circuit of the same three-phase power supply is normal.

FIG. 4 is an output waveform diagram of the photocoupler when a phase loss occurs in the three-phase power supply of the same three-phase power supply open-phase detection circuit.

FIG. 5 is a waveform diagram of a comparator input terminal when a phase loss occurs in the three-phase power source of the same three-phase power source open-phase detection circuit.

FIG. 6 is a block diagram showing a conventional open-phase detecting means.

[Explanation of symbols]

 19 control means 20 display means 21 three-phase motor 30 three-phase power supply 40 detection means 45 determination means

Claims (1)

[Claims] 1. A detection means for detecting a current between phases of a three-phase power supply, a determination means for determining a phase loss based on a signal output from the detection means, and a determination result from the determination means. An open-phase detection circuit for a three-phase power source, which comprises a control means capable of protecting the load against the load, and a display means connected to the control means and notifying the user that the protection has been applied.