JP2014124062A - Overload detection device and overload detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overload detection device capable of detecting an overload by automatically selecting a threshold value for overload detection according to an AC voltage to be applied to a motor.SOLUTION: An overload detection device comprises a current detection unit 13b which detects current flowing in a three-phase motor 3; a threshold value definition unit 13a which defines a plurality of threshold values for detecting an overload of the three-phase motor 3; and a comparison unit 13f which compares the current detected by the current detection unit 13b with one threshold value defined by the threshold value definition unit 13a. This device further comprises: a voltage discrimination unit 13d which discriminates a level of the voltage to be applied to the three-phase motor 3; and a threshold value selection unit 13e which selects one threshold value defined by the threshold value definition unit 13a according to the discrimination results of the voltage discrimination unit 13d.

Description

  The present invention relates to an overload detection device and an overload detection method for detecting an overload of a motor.

  Dual voltage motors have been put into practical use. A dual voltage motor is a motor that can be driven using either of two different voltages. For example, the motor can be driven regardless of whether the voltage of the AC power supply is 230V or 400V. When a dual voltage motor is driven at 230V, a three-phase AC motor is delta-connected, and when driven at 400V, a three-phase AC motor is star-connected, and the line voltage applied to each phase coil Can be about 230V. When an AC voltage of 400V is applied to a delta-connected three-phase AC motor, the line voltage is 400 / √3 = about 230V.

On the other hand, as a motor overload protection method, a method of detecting an overcurrent flowing through the motor is used.
Patent Document 1 discloses a gear motor that includes a monitoring unit that detects that the current flowing through the motor exceeds a predetermined threshold, and issues an alarm when the current exceeds the threshold.
Patent Document 2 discloses a motor multi-relay that detects a voltage and a current flowing in a motor, calculates electric power, and protects the motor using the calculated electric power.
Patent Document 3 discloses an electric motor drive device that can be driven by switching between star connection and delta connection by an external signal, and that is configured to change a threshold value for overcurrent detection according to the connection mode. Yes.

JP 2011-1115025 A JP 2007-198844 A JP 2008-228513 A

  However, since the overload current flowing through the dual voltage motor varies depending on the magnitude of the applied voltage, the gear motor according to Patent Document 1 cannot detect the overload despite the occurrence of an overload, Problems such as erroneous detection of overload occur in a situation where no overload occurs.

  Also, a method of performing overload protection by calculating the power of a dual voltage motor, such as the motor multi-relay according to Patent Document 2, is conceivable. However, an arithmetic unit that always performs power processing is required, and the device However, there has been a problem that the size and size of the apparatus becomes high and complicated.

  Furthermore, in the electric motor drive device according to Patent Document 3, it is necessary to input a switching signal from the outside, and there is a problem that the threshold for detecting overcurrent cannot be automatically changed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to automatically select a threshold value for detecting an overload in accordance with an AC voltage applied to the motor and perform overload detection. It is an object to provide an overload detection device and an overload detection method.

  An overload detection device according to the present invention is detected by a current detection unit that detects a current flowing through a motor, a threshold value definition unit that defines a plurality of threshold values for detecting an overload of the motor, and the current detection unit. In an overload detection device comprising a comparison unit that compares a current and one threshold value defined by the threshold value definition unit, a determination unit that determines the level of a voltage applied to the motor, and a determination result of the determination unit And a threshold selection unit that selects one threshold defined by the threshold defining unit.

  In the present invention, one threshold value for detecting an overload of the motor is selected by the threshold selection unit in accordance with the level of the voltage applied to the motor. The overload detection device performs overload detection by comparing one threshold selected by the threshold selection unit with the current detected by the current detection unit.

  In the overload detection device according to the present invention, the determination unit includes a voltage detection unit that detects a voltage applied to the motor, a predetermined voltage for determining the level of the voltage applied to the motor, and the voltage detection. And a voltage comparison unit for comparing voltages detected by the unit.

  In the present invention, the voltage applied to the motor is detected, and the level of the voltage applied to the motor is determined by comparing the detected voltage with a predetermined voltage.

  In the overload detection device according to the present invention, the voltage detection unit includes a transformer that steps down an alternating voltage applied to the motor, a rectifier circuit that rectifies the voltage stepped down by the transformer, and the rectifier circuit. And a voltage dividing resistor for dividing the rectified voltage.

  In the present invention, the voltage applied to the motor is stepped down by a transformer, rectified by a rectifier circuit, and divided by a voltage dividing resistor. The voltage divided by the voltage dividing resistor corresponds to the voltage value applied to the motor.

  The overload detection device according to the present invention includes a regulator that generates a constant voltage from the voltage rectified by the rectifier circuit, and the voltage comparison unit is driven by the constant voltage generated by the regulator. It is characterized by.

  In the present invention, the voltage stepped down and rectified to drive the voltage comparator is detected by the voltage dividing resistor. Therefore, the voltage can be detected and the threshold value can be changed with few additional components.

  In the overload detection device according to the present invention, the voltage detection unit includes a rectifier circuit that rectifies an AC voltage applied to the motor, and a voltage dividing resistor that divides the voltage rectified by the rectifier circuit. Features.

  In the present invention, the voltage applied to the motor is rectified by the rectifier circuit and divided by the voltage dividing resistor. The voltage divided by the voltage dividing resistor corresponds to the voltage value applied to the motor.

  The overload detection device according to the present invention is characterized in that the determination unit includes a switch circuit that turns on and off according to the level of the voltage applied to the motor.

  In the present invention, the determination unit determines whether the voltage applied to the motor is high or low using a switch circuit that is turned on / off according to the voltage applied to the motor. Therefore, it is not necessary to perform a comparison process between the voltage detected by the voltage detection unit and the predetermined voltage by a microcomputer or the like.

  In the overload detection device according to the present invention, the switch circuit is connected in series with two Zener diodes connected in series with opposite polarity to a terminal of an AC power supply that supplies power to the motor, and the Zener diode, And a photocoupler that is turned on and off depending on whether or not the Zener diode is energized.

  In the present invention, when the voltage applied to the terminal of the AC power supply for supplying power to the motor is equal to or higher than the predetermined breakdown voltage, a current flows through the Zener diode and the photocoupler is turned on. When the voltage applied to the terminal of the AC power supply for supplying power to the motor is less than the predetermined breakdown voltage, no current flows through the Zener diode, and the photocoupler is turned off. Since the configuration is such that the energization state of the Zener diode is detected by a photocoupler, it is possible to determine the level of the voltage applied to the motor in the insulated state.

  In the overload detection device according to the present invention, the switch circuit is connected in series to a terminal of an AC power supply that supplies power to the motor with a reverse polarity in series with the rectifier diode and the Zener diode, and the rectifier diode and the Zener diode. And a switching element that is turned on and off in accordance with a voltage divided by the voltage dividing resistor.

  In the present invention, when the voltage applied to the terminal of the AC power supply for supplying power to the motor is equal to or higher than the predetermined breakdown voltage, a current flows through the Zener diode and a current also flows through the voltage dividing resistor. When a current flows through the voltage dividing resistor, the switch element is turned on by the divided voltage. When the voltage applied to the terminal of the AC power supply that supplies power to the motor is less than a predetermined breakdown voltage, no current flows through the Zener diode, and no current flows through the voltage dividing resistor. When no current flows through the voltage dividing resistor, the switch element is turned off.

  In the overload detection device according to the present invention, the determination unit includes a connection mode detection unit that detects a connection mode of a motor having a three-phase coil capable of changing a connection method to a delta connection or a star connection, It is characterized in that the level of the voltage applied to the motor is discriminated based on the connection mode of the motor.

  In the present invention, the connection mode of the motor is detected, and the level of the voltage applied to the motor is determined based on the connection mode.

  In the overload detection device according to the present invention, the connection state detection unit is connected (or disconnected) when the terminals are delta-connected among the ends of the three coils constituting the motor. The photocoupler includes a photocoupler that is connected between two terminals that are in a non-connected state (or a connected state) when star-connected, and that is turned on / off according to a voltage between the terminals.

  In the present invention, the voltage between the two terminals varies depending on the connection state of the motor. That is, the photocoupler is turned on and off by the voltage between the two terminals.

  An overload detection method according to the present invention detects an electric current flowing through a motor, and compares the detected current with one threshold selected from a plurality of thresholds for detecting an overload of the motor. The detection method includes a step of determining the level of the voltage applied to the motor, and a step of selecting one threshold value from the plurality of threshold values according to the determination result.

  In the present invention, one threshold value for detecting an overload of the motor is selected according to the level of the voltage applied to the motor. Then, overload detection is performed by comparing one threshold value with the current detected by the current detection unit.

  According to the present invention, it is possible to automatically select a threshold value for detecting an overload in accordance with an AC voltage applied to the motor, and perform an overload detection.

It is a circuit block diagram which shows one structural example of the overload detection apparatus which concerns on this Embodiment 1. It is the circuit diagram which showed the detailed structure of the voltage discrimination | determination part. It is a circuit diagram which shows the three-phase motor by which the delta connection was carried out. It is a circuit diagram which shows the three-phase motor by which star connection was carried out. It is a flowchart which shows the process sequence which concerns on an overload detection method. 6 is a circuit diagram illustrating a detailed configuration of a voltage determination unit according to a first modification of the first embodiment. FIG. 6 is a circuit diagram illustrating a detailed configuration of a voltage determination unit according to a second modification of the first embodiment. FIG. It is the circuit diagram of the overload detection apparatus which showed the detailed structure of the voltage discrimination | determination part concerning this Embodiment 2. FIG. It is a flowchart which shows the process sequence which concerns on an overload detection method. FIG. 10 is a circuit diagram illustrating a detailed configuration of a voltage determination unit according to a first modification of the second embodiment. FIG. 10 is a circuit diagram illustrating a detailed configuration of a voltage determination unit according to a second modification of the second embodiment. 6 is a circuit diagram of an overload detection device illustrating a detailed configuration of a voltage determination unit according to Embodiment 3. FIG. FIG. 10 is a circuit diagram illustrating a detailed configuration of a voltage determination unit according to a modification of the third embodiment.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit block diagram showing a configuration example of the overload detection apparatus according to the first embodiment. The overload detection device 1 according to Embodiment 1 includes a power supply connection unit 11, a motor connection unit 12, an overload detection unit 13, a transformer 14, a rectifier circuit 15, and a regulator 16. The overload detection device 1 is accommodated in a terminal box of a gear motor, for example.

The power supply connection unit 11 includes three terminals for connection to an AC power supply 2 that outputs a three-phase AC voltage.
The motor connection unit 12 includes three terminals for connection to the three-phase motor 3. The three terminals constituting the motor connection unit 12 and the three terminals constituting the power supply connection unit 11 are connected to each other by a feeder line 17.

  The three-phase motor 3 connected to the motor connection unit 12 has a U-phase coil 31, a V-phase coil 32, and a W that can change the connection method to delta connection (see FIG. 3) or star connection (see FIG. 4). A phase coil 33 is provided. The U-phase coil 31, the V-phase coil 32, and the W-phase coil 33 are wound around, for example, a stator, and a rotating magnetic field is applied when an AC voltage is applied to the U-phase coil 31, the V-phase coil 32, and the W-phase coil 33. Will occur. The rotor is rotated by a rotating magnetic field and outputs torque.

  A transformer 14 that steps down the AC voltage applied to the three-phase motor 3 is connected to the power supply connection portion 11. The transformer 14 includes a primary coil and a secondary coil that are magnetically coupled. The terminal pair of the primary coil is connected to the two terminals constituting the power supply connecting portion 11, respectively. When the alternating current output from the alternating current power supply 2 is applied to the primary coil, an alternating magnetic flux is generated in the primary coil, and an alternating current stepped down to the secondary coil is induced by the alternating magnetic flux.

  A rectifier circuit 15 that rectifies the AC voltage stepped down by the transformer 14 is connected to the secondary coil of the transformer 14. The rectifier circuit 15 is, for example, a diode bridge that performs full-wave rectification, and the terminal pair of the secondary coil is connected to the input terminal pair of the rectifier circuit 15. The negative output terminal of the rectifier circuit 15 is grounded, and the positive output terminal is connected to the input terminal of the regulator 16.

  The regulator 16 is a circuit that generates a constant voltage obtained by stabilizing the DC voltage rectified by the rectifier circuit 15. The ground terminal of the regulator 16 is grounded, and the output terminal is connected to the overload detection unit 13. The constant voltage generated by the regulator 16 is supplied to the overload detection unit 13, and the overload detection unit 13 is supplied from the regulator 16 and operates with electric power.

  The overload detection unit 13 includes a threshold value definition unit 13a, a current detection unit 13b, a current transformer 13c, a voltage determination unit 13d, a threshold selection unit 13e, and a comparison unit 13f. Each function part which comprises the overload detection part 13 is comprised with the microcomputer except for a part of voltage detection element and a current detection element, for example. In the following, it is assumed that the threshold value defining unit 13a, the threshold value selecting unit 13e, and the comparing unit 13f are configured by a microcomputer. In the first embodiment, an example in which a part of the voltage determination unit 13d is configured by circuit elements other than the microcomputer will be described.

  The current detection unit 13b includes, for example, a current transformer 13c that converts an alternating current flowing through the feeder line 17 into a voltage. The current detection unit 13b includes, for example, an electrical resistor, and both ends of a coil constituting the current transformer 13c are connected to both ends of the electrical resistor. A rectifier diode is connected to the electrical resistor. The rectifier diode rectifies the voltage generated by the electric resistor and supplies the rectified voltage to the amplifier. The amplifier amplifies the rectified voltage and supplies the amplified voltage to the A / D converter. The A / D converter AD converts the input voltage into a digital current value, and supplies the AD converted current value to the comparison unit 13f.

The threshold value defining unit 13a is, for example, a storage unit. The storage unit is a non-volatile memory such as an EEPROM (Electrically Erasable Programmable ROM) and stores two threshold values for detecting an overload of the three-phase motor 3, thereby defining the threshold values. That is, the first threshold value for overload detection when the three-phase motor 3 is driven at a high voltage of 400V and the second threshold value for overload detection when the three-phase motor 3 is driven at a low voltage of 230V are stored. doing.
Note that the storage unit is an example of the threshold value defining unit 13a, and the threshold value may be defined by the voltage value divided by the voltage dividing resistor. Further, the threshold value may be defined by the voltage value divided by the variable resistor. When a variable resistor is used, the threshold value itself to be selected can be made variable.

  The voltage determination unit 13d is a circuit that determines the level of the voltage applied to the three-phase motor 3, and is a circuit that provides a determination result to the threshold selection unit 13e. Details of the voltage determination unit 13d will be described later.

  The threshold selection unit 13e selects the first threshold or the second threshold defined by the threshold defining unit 13a according to the determination result given from the voltage determination unit 13d, and compares the selected first threshold or second threshold This is a circuit given to the section 13f. Specifically, when the voltage applied to the three-phase motor 3 is a high voltage, the first threshold value is selected and given to the comparison unit 13f. When the voltage is low, the second threshold value is selected and given to the comparison unit 13f. Hereinafter, one of the first threshold and the second threshold selected by the threshold selection unit 13e is referred to as an overcurrent threshold.

The comparison unit 13f detects an overload by comparing the current value detected by the current detection unit 13b with the overcurrent threshold selected by the threshold selection unit 13e.
When an overload is detected, the overload detection device 1 notifies that an overload has been detected by a not-shown notification means. Further, the power supply to the three-phase motor 3 may be stopped by a relay (not shown) provided in the middle of the power supply line 17.

  FIG. 2 is a circuit diagram showing a detailed configuration of the voltage determination unit 13d. The voltage determination unit 13d includes voltage dividing resistors R1 and R2 that divide the voltage of the positive output terminal of the rectifier circuit 15, for example. Specifically, one end of the voltage dividing resistor R1 is connected to the positive output terminal of the rectifier circuit 15, and the other end is connected to one end of the voltage dividing resistor R2. The other end of the voltage dividing resistor R2 is grounded. One end of the voltage dividing resistor R2, that is, the connection point of the voltage dividing resistors R1 and R2, is connected to the overload detection unit 13, and the voltage divided by the voltage dividing resistors R1 and R2 is input to the overload detection unit 13. It is comprised so that. The voltage determination unit 13d performs AD conversion of the input voltage into a digital voltage value, and compares the AD converted voltage value with a predetermined voltage value for determining the level of the voltage applied to the motor. It is determined whether the AC voltage applied to the phase motor 3 is a high voltage or a low voltage.

The three-phase motor 3 connected to the overload detection device 1 configured as described above changes the connection method of the U-phase coil 31, the V-phase coil 32, and the W-phase coil 33 constituting the three-phase motor 3. Thus, it can be driven using any of two different voltages.
FIG. 3 is a circuit diagram showing the three-phase motor 3 connected in a delta connection, and FIG. 4 is a circuit diagram showing the three-phase motor 3 connected in a star connection. When driving at 230 V, a three-phase AC motor is used with delta connection as shown in FIG. When driving at 400 V, a three-phase AC motor is used in a star connection as shown in FIG. By performing star connection, the line voltage applied to the U-phase coil 31, the V-phase coil 32, and the W-phase coil 33 can be set to about 230V.
However, the overload current value differs depending on whether the three-phase motor 3 is delta-connected or star-connected. The overload detection unit 13 according to the first embodiment automatically detects the voltage applied to the three-phase motor 3 to automatically select the first threshold value or the second threshold value for detecting the overload. Load detection is performed.

  FIG. 5 is a flowchart showing a processing procedure according to the overload detection method. A voltage determination part detects the alternating voltage applied to a motor (step S11), and determines whether the detected voltage value is larger than a predetermined voltage value (step S12). When the detected voltage value is larger than the predetermined voltage value (step S12: YES), the threshold selection unit 13e sets the first threshold value as an overcurrent threshold value, and provides the comparison unit 13f (step S13). When the detected voltage is equal to or lower than the predetermined voltage value (step S12: NO), the threshold selection unit 13e sets the second threshold as the overcurrent threshold and provides the comparison unit 13f (step S14).

Next, the current detector 13b detects the current flowing through the three-phase motor 3 (step S15). The comparison unit 13f compares the current value detected by the current detection unit 13b with the overcurrent threshold (step S16). When it is determined that the current value is larger than the overcurrent threshold (step S16: YES), the overload detection unit 13 performs predetermined overload processing such as notification that an overload has occurred and power supply stop (step S17). The process is terminated. When it determines with an electric current value being below an overcurrent threshold value (step S16: NO), the overload detection part 13 finishes a process.
The overload detection unit 13 monitors the overload of the three-phase motor 3 by periodically executing the above processing.

According to the overload detection device 1 and the overload detection method configured as described above, the threshold for detecting the overload is automatically selected according to the AC voltage applied to the three-phase motor 3, Overload detection can be performed.
Therefore, it is possible to realize overload protection of the three-phase motor 3 which is a so-called dual voltage motor with certainty, small size and low cost. The switching of the overcurrent threshold is a circuit configuration that is performed by determining only whether the voltage applied to the three-phase motor 3 is 230V or 400V, so that the circuit can be simplified. In particular, in the first embodiment, the voltage applied to the three-phase motor 3 using the transformer 14 and the rectifier circuit 15 provided for creating a constant voltage necessary for driving the overload detection unit 13. Therefore, the overcurrent threshold switching control can be performed only by adding the voltage dividing resistors R1 and R2, and the circuit can be further simplified.

(Modification 1)
FIG. 6 is a circuit diagram illustrating a detailed configuration of a voltage determination unit 13d according to a first modification of the first embodiment. The overload detection device 101a according to the first modification includes a diode D1 that performs half-wave rectification instead of the rectifier circuit 15 that performs full-wave rectification. More specifically, the anode of the diode D1 is connected to one end of the secondary coil constituting the transformer 14, and the cathode of the diode D1 is connected to the input terminal of the regulator 16. The voltage dividing resistors R1 and R2 are configured to divide the voltage of the cathode of the diode D1.

According to the first modification, the number of parts can be further reduced.
Since other configurations, operations, and effects of the overload detection device 101a according to the first modification are the same as those of the first embodiment, the corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.

(Modification 2)
FIG. 7 is a circuit diagram illustrating a detailed configuration of a voltage determination unit 13d according to a second modification of the first embodiment. The overload detection device 101b according to the modification 2 is configured to detect the voltage applied to the motor by directly dividing the AC voltage output from the AC power supply 2, in the embodiment. Different from 1.

The anodes of the diodes D2 and D3 are connected to the two terminals of the power supply connecting portion 11, respectively. The cathodes of the diodes D2 and D3 are connected to one end of the voltage dividing resistor R3, and the other end of the voltage dividing resistor R3 is connected to one end of the voltage dividing resistor R4. The other end of the voltage dividing resistor R4 is grounded. One end of the voltage dividing resistor R4, that is, the connection point of the voltage dividing resistors R3 and R4 is connected to the overload detecting unit 13, and the voltage divided by the voltage dividing resistors R3 and R4 is input to the overload detecting unit 13. It is comprised so that.
Further, the overload detection device 101b includes a non-insulated power supply unit or a non-step-down voltage unit as the transformer 114.

Other configurations, operations, and effects of the overload detection device 101b according to the modification 2 are the same as those in the first embodiment, and accordingly, corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.
In the modified example 2, the AC voltage output from the AC power source is full-wave rectified and directly divided, but it goes without saying that the AC voltage may be half-wave rectified and divided. good.

(Embodiment 2)
FIG. 8 is a circuit diagram of the overload detection device 201 showing a detailed configuration of the voltage determination unit 13d according to the second embodiment. Since the overload detection apparatus 201 according to the second embodiment is different from the first embodiment only in the configuration of the voltage determination unit 13d, the following mainly describes the differences. In the second embodiment, the voltage determination unit 13d is configured by a switch circuit that is turned on / off according to the level of the voltage applied to the motor. The configuration of the switch circuit will be specifically described below.

  Two Zener diodes Z1 and Z2 are connected in series with opposite polarity to one terminal of the power supply connecting portion 11. That is, the cathode of one Zener diode Z1 is connected to the one terminal, and the anode of the Zener diode Z1 is connected to the anode of the Zener diode Z2. The cathode of the Zener diode Z2 is connected to one end of the light emitting element constituting the AC input type photocoupler P1. The AC input type photocoupler P1 includes a light emitting element connected in parallel with opposite polarity, and a light receiving element disposed opposite to the light emitting element. The other end of the light emitting element that constitutes the photocoupler P1 is connected to one end of the resistor R5, and the other end of the resistor R5 is connected to the other terminal of the power supply connecting portion 11. The Zener diodes Z1 and Z2 have a breakdown voltage that is energized when the voltage applied between the terminals of the power supply connection portion 11 is a high voltage of 400V and does not conduct when the voltage is a low voltage of 230V. The breakdown voltage is, for example, 300V. A signal indicating the on / off state of the photocoupler P1 is input to the threshold selection unit 13e.

  FIG. 9 is a flowchart showing a processing procedure according to the overload detection method. The threshold selection unit 13e of the overload detection unit 13 determines whether or not an on signal of the photocoupler P1 is input (step S31). When it is determined that the ON signal is input (step S31: YES), the threshold selection unit 13e sets the first threshold as the overcurrent threshold and provides the comparison unit 13f (step S32). When it is determined that the ON signal is not input (step S31: NO), the threshold selection unit 13e sets the second threshold as the overcurrent threshold and gives the comparison unit 13f (step S33).

  Hereinafter, in the same manner as in the first embodiment, the current detector 13b detects the current flowing through the three-phase motor 3 (step S34). The comparison unit 13f compares the current value detected by the current detection unit 13b with the overcurrent threshold (step S35). When it is determined that the current value is larger than the overcurrent threshold (step S35: YES), the overload detection unit 13 performs predetermined overload processing such as notification that an overload has occurred and power supply stop (step S36). The process is terminated. When it determines with an electric current value being below an overcurrent threshold value (step S35: NO), the overload detection part 13 complete | finishes a process.

  The other configurations, operations, and effects of the overload detection device 201 according to the second embodiment are the same as those of the first embodiment, and accordingly, corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.

(Modification 1)
FIG. 10 is a circuit diagram illustrating a detailed configuration of the voltage determination unit 13d according to the first modification of the second embodiment. Since the overload detection device 201a according to the modification 1 is different from the second embodiment only in the configuration of the voltage determination unit 13d, the difference will be mainly described below.

  The cathode of the Zener diode Z3 is connected to one terminal of the power supply connecting portion 11, and the anode of the Zener diode Z3 is connected to the anode of the light emitting element constituting the photocoupler P2. The cathode of the light emitting element constituting the photocoupler P2 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the other terminal of the power supply connecting portion 11. Further, the anode of the diode D4 is connected to the cathode of the light emitting element constituting the photocoupler P2, and the cathode of the diode D4 is connected to the anode of the light emitting element. The zener diode Z3 has a breakdown voltage that is energized when the voltage applied between the terminals of the power supply connection portion 11 is a high voltage of 400V and is not conductive when the voltage is a low voltage of 230V. The signal indicating the on / off state of the photocoupler P2 is input to the threshold selection unit 13e.

  Other configurations, operations, and effects of the overload detection device 201a according to the first modification are the same as those in the first embodiment, and thus corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.

(Modification 2)
FIG. 11 is a circuit diagram illustrating a detailed configuration of a voltage determination unit 13d according to a second modification of the second embodiment. Since the overload detection device 201b according to the modification 2 is different from the second embodiment only in the configuration of the voltage determination unit 13d, mainly the differences will be described below.

The cathode of the diode D5 is connected to one terminal of the power supply connection portion 11, and the anode of the Zener diode Z5 is connected to the anode of the diode D5. The anode of the Zener diode Z5 is connected to one end of the voltage dividing resistor R7, and the other end of the voltage dividing resistor R7 is connected to one end of the voltage dividing resistor R8. The other end of the voltage dividing resistor R8 is grounded. In addition, the anode of the diode D6 is connected to the other terminal of the power supply connecting portion 11, and the cathode of the diode D6 is connected to the cathode of the Zener diode Z6. The anode of the Zener diode Z6 is connected to the one end of the resistor R7. The one end of the voltage dividing resistor R8 is connected via a resistor R9 to a switch element SW1 that turns on and off according to the voltage divided by the voltage dividing resistors R7 and R8.
The zener diodes Z5 and Z6 are energized when the voltage applied between the terminals of the power supply connection portion 11 is a high voltage of 400V, the switch element SW1 is turned on, and when the voltage is a low voltage of 230V, the zener diodes Z5 and Z6 are not conductive. The element SW1 is configured to be turned off.
Further, the overload detection device 201b includes a non-insulated power supply unit or a non-step-down voltage unit as the transformer 214.

  Since the other configuration, operation, and effect of the overload detection device 201b according to Modification 2 are the same as those in Embodiment 1, the corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.

(Embodiment 3)
FIG. 12 is a circuit diagram of the overload detection device 301 showing a detailed configuration of the voltage determination unit 13d according to the third embodiment. Since the overload detection device 301 according to the third embodiment is different from the first embodiment only in the configuration of the voltage determination unit 13d, the difference will be mainly described below. In the third embodiment, the voltage determination unit 13 d is configured by a connection mode detection unit that detects the connection mode of the three-phase motor 3. The configuration of the connection mode detection unit will be specifically described below.

  Of the end portions of the U-phase coil 31, V-phase coil 32, and W-phase coil 33 constituting the three-phase motor 3, when the terminals are delta-connected, they are connected (or disconnected) and star-connected. A photocoupler P3 and a resistor R10 are provided between two terminals that are in a non-connected state (or a connected state) in the event that the For example, a photocoupler P3 and a resistor R10 are provided between the X terminal of the U-phase coil 31 and the Z terminal of the W-phase coil 33. Specifically, one end of a resistor R10 is connected to the Z terminal, and the other end of the resistor R10 is connected to one end of a light emitting element that constitutes an AC input type photocoupler P3. The other end of the light emitting element constituting the photocoupler P3 is connected to the terminal Z.

  When the three-phase motor 3 is delta-connected as shown in FIG. 3, since a constant voltage is generated at the X terminal and the Z terminal, the photocoupler P3 is turned on. When the three-phase motor 3 is star-connected as shown in FIG. 4, since the X terminal and the Z terminal are connected, the photocoupler P3 is turned off.

  The threshold selection unit 13e selects the first threshold when the photocoupler P3 is in the off state, and selects the second threshold when the photocoupler P3 is in the on state.

  Other configurations, operations, and effects of the overload detection device 301 according to the third embodiment are the same as those of the first embodiment, and accordingly, corresponding portions are denoted by the same reference numerals and detailed description thereof is omitted.

(Modification)
FIG. 13 is a circuit diagram illustrating a detailed configuration of a voltage determination unit 13d according to a modification of the third embodiment. Since the overload detection device 301a according to the modified example is different from the third embodiment only in the configuration of the voltage determination unit 13d, the difference will be mainly described below. One end of the resistor R11 is connected to the Z terminal, and the other end of the resistor R11 is connected to the anode of the light emitting element constituting the photocoupler P4. The cathode of the light emitting element constituting the photocoupler P4 is connected to the terminal Z. The cathode of the diode D7 is connected to the anode of the light emitting element constituting the photocoupler P4, and the anode of the diode D7 is connected to the cathode of the light emitting element.
Since other configurations, operations, and effects of the overload detection device 301a according to the modification are the same as those of the first embodiment, the corresponding portions are denoted by the same reference numerals, and detailed description thereof is omitted.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Overload detection apparatus 2 AC power supply 3 Three-phase motor 31 U phase coil 32 V phase coil 33 W phase coil 11 Power supply connection part 12 Motor connection part 13 Overload detection part 13a Threshold regulation part 13b Current detection part 13c Current transformer 13d Voltage Discrimination unit 13e Threshold selection unit 13f Comparison unit 14 Transformer 15 Rectifier circuit 16 Regulator 17 Feed line

Claims (11)

A current detection unit that detects a current flowing through the motor, a threshold value definition unit that defines a plurality of threshold values for detecting an overload of the motor, a current detected by the current detection unit, and a threshold value definition unit In an overload detection device comprising a comparison unit for comparing the thresholds of
A discriminator for discriminating the level of voltage applied to the motor;
An overload detection device comprising: a threshold selection unit that selects one threshold defined by the threshold definition unit according to a determination result of the determination unit. The discrimination unit
A voltage detector for detecting a voltage applied to the motor;
The overload detection device according to claim 1, further comprising: a voltage comparison unit that compares a predetermined voltage for determining a level of a voltage applied to the motor and a voltage detected by the voltage detection unit. . The voltage detector is
A transformer for stepping down an AC voltage applied to the motor;
A rectifier circuit for rectifying the voltage stepped down by the transformer;
The overload detection device according to claim 2, further comprising: a voltage dividing resistor that divides the voltage rectified by the rectifier circuit. A regulator that generates a constant voltage from the voltage rectified by the rectifier circuit;
The overload detection device according to claim 3, wherein the voltage comparison unit is driven by a constant voltage generated by the regulator. The voltage detector is
A rectifier circuit for rectifying an AC voltage applied to the motor;
The overload detection device according to claim 2, further comprising: a voltage dividing resistor that divides the voltage rectified by the rectifier circuit. The discrimination unit
The overload detection device according to claim 1, further comprising a switch circuit that turns on and off according to a level of a voltage applied to the motor. The switch circuit is
Two Zener diodes connected in series with opposite polarity to a terminal of an AC power supply for supplying power to the motor;
The overload detection device according to claim 6, further comprising: a photocoupler that is connected in series to the Zener diode, and that is turned on and off depending on whether the Zener diode is energized. The switch circuit is
A rectifier diode and a zener diode connected in series with opposite polarity to a terminal of an AC power supply that supplies power to the motor,
A voltage dividing resistor connected in series to the rectifier diode and the Zener diode;
The overload detection device according to claim 6, further comprising: a switching element that turns on and off according to a voltage divided by the voltage dividing resistor. The discrimination unit
A connection mode detector for detecting a connection mode of a motor having a three-phase coil capable of changing the connection method to delta connection or star connection,
The overload detection device according to claim 1, wherein the voltage applied to the motor is determined based on a connection mode of the motor. The connection state detection unit
Of the end portions of the three coils constituting the motor, the terminals are connected (or disconnected) when they are delta-connected, and are disconnected (or connected) when star-connected. The overload detection device according to claim 9, further comprising a photocoupler connected between two terminals and turned on and off according to a voltage between the terminals. In an overload detection method for detecting a current flowing through a motor and comparing the detected current with one threshold selected from a plurality of thresholds for detecting an overload of the motor,
Determining the level of voltage applied to the motor;
And selecting one threshold value from the plurality of threshold values according to the determination result.

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