Overload protection device

Abstract

To provide an overload protection device which improves accuracy of load protection.SOLUTION: A ground fault interrupter includes: a thermal relay connected between a power supply and a load; a current measurement part for measuring current flowing in the thermal relay; and a calculation processing unit for calculating an estimated value of the amount of heat accumulated inside the thermal relay based on a current value which the current measurement part measures.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an overload protection device. [Background technology]

[0002] There is known an overload protection device that includes a thermal relay connected between a power source and a load, and cuts off the power supply to the load when a current exceeding a settling current flows continuously through the load. Patent Document 1 discloses an overload protection device as a motor control device in which a relay (thermal relay) detects an abnormal current from the current value flowing through the motor coil and stops the motor to prevent damage to the motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-7992 Summary of the Invention [Problem to be solved by the invention]

[0004] Even if a current exceeding the settling current does not flow continuously through the load, the load may reach an overload state. Therefore, there is a demand for an overload protection device that can improve the reliability of load protection.

[0005] The present disclosure provides an overload protection device that provides increased reliability in protecting a load. [Means for solving the problem]

[0006] In a first aspect, the device includes a thermal relay connected between a power source and a load, a current measuring unit that measures a current flowing through the thermal relay, and a calculation processing unit that calculates an estimate of the amount of accumulated heat accumulated inside the thermal relay based on the current value measured by the current measuring unit. Effect of the Invention

[0007] According to the technique of the present disclosure, the reliability of load protection can be improved. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an example of an overall configuration of an overload protection device according to an embodiment; [Diagram 2] 2 is a block diagram showing an example of the configuration of a current measurement unit of the overload protection device according to the embodiment; FIG. [Diagram 3] 2 is a block diagram showing a configuration example of an edge controller of the overload protection device according to the embodiment; FIG. [Figure 4] 6 is a graph showing a transition of an estimated value of the accumulated heat amount calculated in a calculation processing unit of an edge controller of the overload protection device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an overload protection device according to an embodiment will be described with reference to the drawings. For ease of understanding, the scale of each part in the drawings may differ from the actual scale. In directions such as parallel, right angle, orthogonal, horizontal, vertical, up / down, left / right, deviations are permitted to a degree that does not impair the effects of the embodiment. The shape of the corners is not limited to right angles. For example, the shape of the corners may be rounded. Parallel, right angle, orthogonal, horizontal, and vertical may include approximately parallel, approximately right angle, approximately orthogonal, approximately horizontal, and approximately vertical.

[0010] In this specification, "connection" is not limited to physical connection, but may also include electrical connection. For example, connecting an object A to an object B is not limited to conductive connection of the object A to the object B, but may include conductive connection of the object A to the object B via the object C.

[0011] The overload protection device 1 according to this embodiment cuts off the power supply to the load 3 when a current exceeding the settling current flows continuously from the power source 2 to the load 3. Here, the settling current may be determined, for example, based on the rated current of the load 3. The settling current may also be determined by other methods.

[0012] An example of the power source 2 is a power system that transmits commercial AC power. The power source 2 may transmit three-phase AC power having U, V, and W phases, or may transmit single-phase AC power. Furthermore, the power source 2 may be a solar cell, a fuel cell, or the like that transmits DC power. The power source 2 of this embodiment is a power system that transmits three-phase AC power.

[0013] The load 3 in this embodiment is an electric motor such as a motor. An example of the electric motor is an electric motor for driving production equipment such as a conveyor that transports objects such as processed products. However, the type of the load 3 is not limited to this.

[0014] <Overall configuration of overload protection device 1> An example of the overall configuration of an overload protection device 1 according to an embodiment will be described in detail with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the overall configuration of an overload protection device 1 according to an embodiment.

[0015] 1, the overload protection device 1 includes a thermal relay 10, a current measuring unit 20, an edge controller 30, and an alarm unit 40. The overload protection device 1 of this embodiment further includes an electromagnetic contactor 50 that cuts off the power supply from the power source 2 to the load 3. The thermal relay 10 is connected to the electromagnetic contactor 50. The thermal relay 10 and the electromagnetic contactor 50 constitute an electromagnetic switch 60.

[0016] <Thermal relay> The following describes the configuration of the thermal relay 10. The thermal relay 10 is an electronic thermal relay that detects whether an overload state of the load 3 continues for a predetermined period of time.

[0017] Here, the overload state of the load 3 refers to a state in which a load current larger than the settling current flows through the load 3 because the conveyor is transporting an object whose weight exceeds the maximum allowable weight, for example. An example of the overload state is a state in which a load current equal to or greater than the threshold value Th10 flows through the load 3. Examples of the threshold value Th10 include values ​​such as 110%, 115%, and 120% of the settling current. However, the threshold value Th10 can be set appropriately. Furthermore, the threshold value Th10 may be adjusted, for example, by operating an operating current adjustment unit provided in the thermal relay 10.

[0018] 1, the thermal relay 10 is connected between a power source 2 and a load 3. The thermal relay 10 is disposed on the load 3 side of the electromagnetic contactor 50. The thermal relay 10 includes power feeders 11a, 11b, and 11c, power source side terminals 12a, 12b, and 12c, load side terminals 13a, 13b, and 13c, current transformers 14a, 14b, and 14c, a measurement circuit 15, a control circuit 16, and a contact circuit 17.

[0019] The measurement circuit 15, the control circuit 16, and the contact circuit 17 are each mounted on, for example, a circuit board disposed within the thermal relay 10. The measurement circuit 15, the control circuit 16, and the contact circuit 17 are each connected to each other via wiring provided within the circuit board. The thermal relay 10 may also include other circuit components, such as an A / D conversion circuit, provided between the measurement circuit 15 and the control circuit 16.

[0020] Each of the power supply lines 11a, 11b, and 11c corresponds to an electric path in the thermal relay 10 through which a current transmitted from the power source 2 flows to the load 3.

[0021] The power supply side terminal 12a is connected to a wiring 20a extending to the power supply 2 through a current measuring unit 20. The load side terminal 13a is connected to a wiring 3a extending to the load 3. A U-phase current transmitted from the power supply 2 flows to the load 3 through the wiring 20a, the power feeder 11a, and the wiring 3a.

[0022] The power supply side terminal 12b is connected to a wiring 20b extending to the power supply 2 through a current measuring unit 20. The load side terminal 13b is connected to a wiring 3b extending to the load 3. A V-phase current transmitted from the power supply 2 flows to the load 3 through the wiring 20b, the power feeder 11b, and the wiring 3b.

[0023] The power supply side terminal 12c is connected to a wiring 20c extending to the power supply 2 through a current measuring unit 20. The load side terminal 13c is connected to a wiring 3c extending to the load 3. A W-phase current transmitted from the power supply 2 flows to the load 3 through the wiring 20c, the power feeder 11c, and the wiring 3c.

[0024] Hereinafter, the U-phase current flowing from the power source 2 to the load 3 through the wiring 20a, the power feeder 11a, and the wiring 3a will be referred to as the "U-phase load current". The V-phase current flowing from the power source 2 to the load 3 through the wiring 20b, the power feeder 11b, and the wiring 3b will be referred to as the "V-phase load current". The W-phase current flowing from the power source 2 to the load 3 through the wiring 20c, the power feeder 11c, and the wiring 3c will be referred to as the "W-phase load current". The U-phase load current, the V-phase load current, and the W-phase load current will be collectively referred to as the "load current". The wiring 20a, the power feeder 11a, and the wiring 3a may be a series of electric paths. The wiring 20b, the power feeder 11b, and the wiring 3b may be a series of electric paths. The wiring 20c, the power feeder 11c, and the wiring 3c may be a series of electric paths.

[0025] The current transformer 14a detects a U-phase load current flowing through the power feeder 11a. The current transformer 14b detects a V-phase load current flowing through the power feeder 11b. The current transformer 14c detects a W-phase load current flowing through the power feeder 11c.

[0026] The measurement circuit 15 measures the current values ​​of the U-phase, V-phase, and W-phase load currents flowing from the power source 2 to the load 3 based on the detection signals detected by the current transformers 14a, 14b, and 14c, respectively. The measurement circuit 15 includes, for example, an integration circuit that integrates the detection signals detected by the current transformers 14a, 14b, and 14c, and an amplifier circuit that amplifies the signals integrated by the integration circuits. However, the configuration of the measurement circuit 15 is not limited to this.

[0027] The measurement circuit 15 of the present embodiment measures the effective current value of each of the load currents of the U phase, V phase, and W phase. However, the current value of each of the load currents of the U phase, V phase, and W phase measured by the measurement circuit 15 may be a maximum current value or an average current value of the AC current corresponding to each load current.

[0028] The control circuit 16 controls the operation of the thermal relay 10. The control circuit 16 in this embodiment is a processor such as a CPU (Central Processing Unit). The control circuit 16 executes various processes for controlling the operation of the thermal relay 10 according to a program stored in a storage medium such as a ROM (Read Only Memory) provided in the thermal relay 10. However, the control circuit 16 may be composed of other electronic circuits capable of realizing the same functions as a processor.

[0029] The control circuit 16 of this embodiment refers to the current value of the load current measured by the measurement circuit 15 and controls the contact circuit 17. Specifically, the control circuit 16 detects that the load 3 is in an overload state for a period of the threshold value Th20, and outputs a control signal to turn on the contact of the contact circuit 17. As will be described separately, when the control signal is input to the contact circuit 17, the contact of the contact circuit 17 is turned on. Accordingly, the electromagnetic contactor 50 cuts off the power supply from the power source 2 to the load 3.

[0030] The threshold value Th20 varies according to a characteristic curve of the inverse time limit with respect to the current value of the load current flowing through the load 3 after the overload state is reached. That is, the threshold value Th20 is set so that the time for turning on the switch of the contact circuit 17 becomes shorter as the current value of the load current flowing through the load 3 after the overload state is reached increases.

[0031] The contact circuit 17 includes, for example, an electromagnet and a contact that is turned on in response to power being supplied to the electromagnet. Power is supplied to the electromagnet in response to a control signal output from the control circuit 16. As a result, a movable part of the contact is attracted to the electromagnet. As a result, the contact is turned on.

[0032] The contact circuit 17 is connected to the electromagnetic contactor 50. When the contacts of the contact circuit 17 are turned ON, a circuit including the contacts and the electromagnetic contactor 50 is opened. Accordingly, power supply to the electromagnet on the electromagnetic contactor 50 side is stopped, and the contacts on the electromagnetic contactor 50 side are turned OFF. As a result, each circuit including the power feeders 11a, 11b, and 11c is opened, and the power supply from the power source 2 to the load 3 is cut off. This cut-off operation corresponds to the cut-off operation of the overload protection device 1.

[0033] <Current measuring unit 20> Next, the configuration of the current measuring section 20 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing an example of the configuration of the current measuring section 20.

[0034] 2, the current measurement unit 20 measures the current values ​​of U-phase, V-phase, and W-phase load currents flowing through the wirings 20a, 20b, and 20c, respectively. The current measurement unit 20 is configured to be detachable from the thermal relay 10. The current measurement unit 20 of this embodiment is integrated with the thermal relay 10 during use. However, the current measurement unit 20 may be structurally separated from the thermal relay 10 during use.

[0035] 1, the current measurement unit 20 is connected between the power source 2 and the thermal relay 10. However, the location of the current measurement unit 20 is not limited to between the power source 2 and the thermal relay 10. For example, the current measurement unit 20 may be connected between the thermal relay 10 and the load 3.

[0036] 2, the current measurement unit 20 includes current transformers 21a, 21b, and 21c, a measurement circuit 22, and a communication circuit 23. The current measurement unit 20 may further include other circuit components, such as an A / D conversion circuit that converts a signal output from the measurement circuit 22 into a digital signal. The current measurement unit 20 may include other current sensors instead of the current transformers 21a, 21b, and 21c. Examples of other current sensors include shunt resistors (chip resistors) and Rogowski sensors.

[0037] The current transformer 21a is connected to the wiring 20a. The current transformer 21a detects a U-phase load current flowing through the wiring 20a. The current transformer 21a outputs a detection signal of the U-phase load current to the measurement circuit 22. The current transformer 21b is connected to the wiring 20b. The current transformer 21b measures a V-phase load current flowing through the wiring 20b. The current transformer 21b outputs a detection signal of the V-phase load current to the measurement circuit 22. The current transformer 21c is connected to the wiring 20c. The current transformer 21c measures a W-phase load current flowing through the wiring 20c. The current transformer 21c outputs a detection signal of the W-phase load current to the measurement circuit 22.

[0038] The measurement circuit 22 includes, for example, an integration circuit that integrates the detection signals output from the current transformers 21a, 21b, and 21c, and an amplifier circuit that amplifies the detection signals integrated by the integration circuit. However, the configuration of the measurement circuit 22 is not limited to this.

[0039] Specifically, the measurement circuit 22 measures the current value of the U-phase load current flowing through the wiring 20a based on the detection signal output from the current transformer 21a. The measurement circuit 22 also measures the current value of the V-phase load current flowing through the wiring 20b based on the detection signal output from the current transformer 21b. The measurement circuit 22 also measures the current value of the W-phase load current flowing through the wiring 20c based on the detection signal output from the current transformer 21c. The measurement circuit 22 outputs a signal including the current value of the load current to the communication circuit 23.

[0040] The communication circuit 23 is communicatively connected to the edge controller 30. The communication circuit 23 outputs to the edge controller 30 a signal including the current value of the load current.

[0041] The current values ​​measured by the measurement circuit 22 in this embodiment are effective current values ​​of the load currents of the U phase, V phase, and W phase, respectively. However, the measurement circuit 22 may also measure maximum current values ​​and average current values ​​of the load currents corresponding to the AC currents.

[0042] <Edge Controller 30> Next, the configuration of the edge controller 30 will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a block diagram showing an example of the configuration of the edge controller 30. Fig. 4 is a graph showing the transition of the estimated value of the accumulated heat amount calculated in the calculation processing unit 31 of the edge controller 30.

[0043] 3, the edge controller 30 is connected to the current measuring unit 20. The edge controller 30 acquires a signal indicating the current value of the load current output from the current measuring unit 20. The edge controller 30 is also connected to the notification unit 40. The edge controller 30 outputs various information such as alarm information issued before the overload protection device 1 performs a cutoff operation to the notification unit 40. The edge controller 30 may be connected to an information processing device such as a cloud server via a communication network.

[0044] 3, the edge controller 30 includes a calculation processing unit 31, a storage unit 32, and a communication unit 33. The calculation processing unit 31, the storage unit 32, and the communication unit 33 are connected to each other via a bus 35. Note that, although the calculation processing unit 31 and the storage unit 32 in this embodiment are integrated as components of the edge controller 30, they may be structurally separated from each other.

[0045] The arithmetic processing unit 31 executes various arithmetic processing operations and controls the edge controller 30. The arithmetic processing unit 31 is a processor such as a CPU (Central Processing Unit). However, the arithmetic processing unit 31 may be another electronic circuit having the same arithmetic processing function as a processor.

[0046] Incidentally, when the weight of the object being transported by the conveyor temporarily increases, the load 3 may also temporarily reach an overload state. However, if the overload protection device 1 does not perform a cut-off operation because the overload state of the load 3 does not continue for the period of the threshold value Th20, the power supply from the power source 2 to the load 3 is not cut off. As a result, the load 3 continues to operate in the overload state. The calculation processing unit 31 executes a process for protecting the load 3 separately from the cut-off operation of the overload protection device 1.

[0047] Specifically, as shown in Fig. 4, the calculation processing unit 31 calculates an estimate of the amount of accumulated heat accumulated inside the thermal relay 10 based on the current value of the load current measured by the current measuring unit 20. The calculation processing unit 31 calculates an estimate Q11 of the amount of accumulated heat (hereinafter simply referred to as "accumulated amount of heat Q11") based on the U-phase load current flowing through the wiring 20a. The calculation processing unit 31 also calculates an estimate Q12 of the amount of accumulated heat (hereinafter simply referred to as "accumulated amount of heat Q12") based on the V-phase load current flowing through the wiring 20b. The calculation processing unit 31 also calculates an estimate Q13 of the amount of accumulated heat (hereinafter simply referred to as "accumulated amount of heat Q13") based on the W-phase load current flowing through the wiring 20c.

[0048] The calculation processing unit 31 may regard the maximum of the accumulated heat amounts Q11, Q12, and Q13 as the accumulated heat amount inside the thermal relay 10. In the following, a case will be described in which the calculation processing unit 31 regards the accumulated heat amount Q11 as the accumulated heat amount inside the thermal relay 10. However, when the accumulated heat amount Q12 is maximum, the calculation processing unit 31 regards the accumulated heat amount Q12 as the accumulated heat amount inside the thermal relay 10. Furthermore, when the accumulated heat amount Q13 is maximum, the calculation processing unit 31 regards the accumulated heat amount Q13 as the accumulated heat amount inside the thermal relay 10.

[0049] An example of the calculation of the accumulated heat quantity Q11 will be described with reference to Fig. 4. Here, the horizontal axis of the graph shown in Fig. 4 indicates the elapsed time from the point in time when the calculation processing unit 31 starts the calculation. The vertical axis on the left side of the graph shown in Fig. 4 indicates the current value I of the load current measured by the current measuring unit 20. The vertical axis on the right side of the graph shown in Fig. 4 indicates the accumulated heat quantity Q11. Line L1 indicates the change in the current value I of the load current. Line L2 indicates the change in the accumulated heat quantity Q11.

[0050] The calculation processing unit 31 calculates multiple heat quantity estimate values ​​Q (hereinafter simply referred to as "heat quantity Q") corresponding to the current values ​​I of multiple load currents (hereinafter simply referred to as "load current I") measured sequentially by the current measuring unit 20, and calculates an estimate of the accumulated heat quantity Q11 from the sum of the multiple heat quantities Q.

[0051] Specifically, the calculation processing unit 31 determines whether the magnitude of the load current I referred to at the latest calculation point corresponds to any one of the following conditions (1) to (3), and calculates the accumulated heat quantity Q11 using a calculation method determined for each of the corresponding conditions. When the load current I is relatively small, as in condition (1) described separately, the temperature inside the thermal relay 10 is considered to decrease. That is, the heat quantity Q converted from the load current I is considered to be a negative value. On the other hand, when the load current I is relatively large compared to condition (1), as in conditions (2) and (3) described separately, the temperature inside the thermal relay 10 is considered to increase. That is, the heat quantity Q converted from the load current I is considered to be a positive value. From these facts, the "sum of multiple heat quantities Q" means that the calculation processing unit 31 subtracts each of the heat quantities Q that are negative values ​​and adds each of the heat quantities Q that are positive values.

[0052] [Condition (1)] When the load current I is less than 80% of the settling current, the calculation processing unit 31 calculates the accumulated heat quantity Q11 by the formula (1). The load current I from time t0 to time t1 shown in FIG. 4 corresponds to the load current I of the condition (1). Note that "80% of the settling current" is an example of the "second relative value." Time t0 is the time when the calculation processing unit 31 starts calculating the accumulated heat quantity Q11.

[0053] Q11(n)=Q11(n-1)-γ (1) However, if "Q11(n)<0", the calculation processing unit 31 calculates "Q11(n)=0".

[0054] In the case of FIG. 4, in the period from time t0 to time t1, the amount of accumulated heat Q11(n) does not increase from "0."

[0055] Here, "Q11(n)" is an example of a "new accumulated heat quantity." "Q11(n-1)" is the accumulated heat quantity calculated once before the new accumulated heat quantity Q11(n). Also, "γ" corresponds to the heat quantity Q calculated by the calculation processing unit 31 based on the load current I referred to at the time of the latest calculation. In formula (1), since "γ" is multiplied by (-1), it is considered that the internal temperature of the thermal relay 10 decreases in the case of condition (1). "γ" is calculated by formula (2).

[0056] γ = I C1 (2) Here, C1 is a real number. C1 may be a constant determined in consideration of the magnitude of the load current I. Note that "γ" is an example of a "third heat quantity."

[0057] [Condition (2)] When the load current I is equal to or greater than 80% and less than 115% of the settling current, the calculation processing unit 31 calculates the accumulated heat amount Q11 by the formula (3). The load current I from time t1 to time t2 shown in FIG. 4 corresponds to the load current I of the condition (2).

[0058] Q11(n)=Q11(n-1)+β (3)

[0059] At this time, the calculation processing unit 31 compares Q11(n) with a threshold value Th1 (first threshold value). When the result of the comparison shows that Q11(n) is less than the threshold value Th1 (first threshold value), the calculation processing unit 31 calculates the accumulated heat quantity Q11(n) based on the formula (3). On the other hand, when Q11(n) is equal to or greater than the threshold value Th1 (first threshold value), the calculation processing unit 31 calculates Q11(n) as the same value as the threshold value Th1, unlike the formula (3). In this case, Q11(n) does not exceed the threshold value Th1. The threshold value Th1 is a value that can be appropriately set. An example of the threshold value Th1 is a value within a range of 50% to 60% of a threshold value Th3 (threshold value Th3 will be described separately) corresponding to the start of the interruption operation of the overload protection device 1. For example, when the threshold value Th1 is set to 55% of the threshold value Th3, the calculation processing unit 31 calculates Q11(n) as a value of 55% of the threshold value Th3.

[0060] 4, in the period from time t1 to time t2, when the calculation processing unit 31 calculates the accumulated heat quantity Q11(n) based on the formula (3), it is assumed that the temperature inside the thermal relay 10 is rising. That is, the accumulated heat quantity Q11(n) increases by "β" from the accumulated heat quantity Q11(n-1) calculated once previously. "β" corresponds to the heat quantity Q calculated by the calculation processing unit 31 based on the load current I referred to at the time of the latest calculation. Note that "β" is an example of the "second heat quantity."

[0061] β is calculated by equation (4).

[0062] β=I C2 (4) Here, C2 is a real number. C2 may be a constant determined in consideration of the magnitude of the load current I.

[0063] [Condition (3)] When the load current I is 115% or more of the settling current, the calculation processing unit 31 calculates the accumulated heat amount Q11 by the formula (5). The load current I from time t2 to time t3 shown in FIG. 4 corresponds to the load current I of the condition (3).

[0064] Q11(n)=Q11(n-1)+α (5)

[0065] The case where the accumulated heat quantity Q11 is calculated by the formula (5) corresponds to the case where the state of the load 3 has reached an overload state. Note that "115% of the settling current" is an example of the "first relative value".

[0066] As shown in Fig. 4, in the period from time t2 to time t3, it is assumed that the temperature inside the thermal relay 10 further increases, and the accumulated heat quantity Q11(n) increases by "α" from the accumulated heat quantity Q11(n-1) calculated once previously. "α" is a value larger than "β". "α" corresponds to the heat quantity Q calculated by the calculation processing unit 31 based on the load current I referred to at the most recent calculation point. "α" is an example of the "first heat quantity".

[0067] "α" is calculated using equation (6).

[0068] α=I C3 ... (6) Here, C3 is a real number larger than C2. C3 may be a constant determined in consideration of the magnitude of the load current I.

[0069] According to the above-mentioned calculation method for the accumulated heat quantity Q11, the calculation processing unit 31 changes the heat quantity Q to be added or subtracted according to the relative value of the load current I to the settling current (the percentage of the load current I corresponding to the settling current). This makes it possible to calculate the accumulated heat quantity Q11 that appropriately reflects the state of the load 3. As a result, it is possible to increase the accuracy of protection of the load 3.

[0070] In the above example, there are three conditions for determining the calculation method of the accumulated heat quantity Q11. However, the conditions for determining the calculation method of the accumulated heat quantity Q11 are not limited to three. In addition, the first relative value and the second relative value of the load current I with respect to the settling current, which define each of the conditions (1) to (3), can be changed as appropriate. In addition, another condition may be added to the conditions (1) to (3). When calculating each of the accumulated heat quantities Q12 and Q13, the calculation processing unit 31 executes the same process as the accumulated heat quantity Q11.

[0071] It is preferable that the calculation processing unit 31 refers to the accumulated heat quantity Q11 (Q12, Q13) and outputs pre-alarm information to the notification unit 40 before the overload protection device 1 performs a cut-off operation. The calculation processing unit 31 outputs pre-alarm information to the notification unit 40 before the overload protection device 1 performs a cut-off operation, thereby making it possible to notify the outside that the timing of cutting off the power supply from the power source 2 to the load 3 is approaching. This allows measures to be taken early to remove the load 3 from the overload state, and the load 3 can be protected separately from the cut-off operation of the overload protection device 1. As a result, the accuracy of protection of the load 3 can be improved. In addition, it is possible to prevent a situation in which production equipment such as a conveyor is stopped due to the stop of the load 3. This makes it possible to prevent economic losses caused by the stop of production equipment.

[0072] When determining whether to output pre-alarm information to the notification unit 40, the calculation processing unit 31 may compare the accumulated heat amount Q11 with a threshold value Th2 (second threshold value), and output the pre-alarm information at the timing when the accumulated heat amount Q11 becomes equal to or greater than the threshold value Th2 as a result of the comparison. In the case of Fig. 4, the calculation processing unit 31 outputs the pre-alarm information at time point t4. Note that the pre-alarm information is an example of a "first warning signal".

[0073] It is preferable that the calculation processing unit 31 refers to the accumulated heat quantity Q11 and outputs this alarm information to the notification unit 40 in accordance with the timing when the overload protection device 1 performs the cutoff operation. This makes it possible to notify the outside that the power supply from the power source 2 to the load 3 has been cut off.

[0074] When determining whether to output the main alarm information to the notification unit 40, the calculation processing unit 31 may compare the accumulated heat amount Q11 with a threshold value Th3 (third threshold value), and output the main alarm information at the timing when the accumulated heat amount Q11 becomes equal to or greater than the threshold value Th3 as a result of the comparison. In the case of Fig. 4, the calculation processing unit 31 outputs the main alarm information at time t3. Note that the threshold value Th3 may be a reference value when setting the threshold value Th1.

[0075] Threshold Th3 is a threshold value that is greater than threshold Th2. The relative value of threshold Th2 with respect to threshold Th3 can be set appropriately. As an example, threshold Th2 may be set to a value that is 70% to 90% of threshold Th3, more preferably 75% to 85% of threshold Th3. This alarm information is an example of a "second alarm signal."

[0076] The storage unit 32 is a non-volatile storage medium that stores programs and the like executed by the arithmetic processing unit 31. Moreover, the storage unit 32 preferably stores the time-series transition of the accumulated heat amounts Q11, Q12, and Q13 calculated by the arithmetic processing unit 31. An example of the storage unit 32 is an EEPROM (Electrically Erasable and Programmable Read Only Memory) such as a flash memory.

[0077] The storage unit 32 stores the time-series transitions of the accumulated heat amounts Q11, Q12, and Q13, so that the operation status of the load 3 and the operation status of the production equipment driven by the load 3 can be appropriately monitored. That is, the transitions of the heat amounts for each of the accumulated heat amounts Q11, Q12, and Q13 can be visualized. As a result, the operation of the production equipment driven by the load 3 can be optimized.

[0078] The communication unit 33 is a communication interface for communicating with other components such as the current measurement unit 20 and the notification unit 40. Specifically, the communication unit 33 acquires information on the current value of the load current measured by the current measurement unit 20. The communication unit 33 also outputs the information on the current value of the load current to the calculation processing unit 31. The communication unit 33 outputs information on the pre-alarm and main alarm output from the calculation processing unit 31 to the notification unit 40.

[0079] The above describes the configuration of the edge controller 30. Note that each of the arithmetic processing unit 31, the storage unit 32, and the communication unit 33 may be provided in an information processing device other than the edge controller 30. Examples of the other information processing device include a personal computer and a mobile terminal carried by an operator or manager of the production equipment.

[0080] <Notification section 40> Next, the configuration of the alarm unit 40 will be described. The alarm unit 40 is a member that is connected to the edge controller 30 and performs an alarm operation based on various information output from the edge controller 30. Examples of the alarm unit 40 include a buzzer that emits an alarm sound and a lamp that turns on an alarm lamp. The alarm unit 40 of this embodiment performs an alarm operation based on pre-alarm information and main alarm information output from the calculation processing unit 31. The alarm unit 40 may be integrated with the thermal relay 10.

[0081] <Action and effect> According to this embodiment, the calculation processing unit 31 calculates each of the accumulated heat amounts Q11, Q12, and Q13 based on the current value of the load current measured by the current measuring unit 20 separately from the thermal relay 10. This makes it possible to properly detect the overload state of the load 3 before the overload protection device 1 performs an interruption operation. As a result, it is possible to increase the accuracy of protection of the load 3.

[0082] According to the present embodiment, the calculation processing unit 31 changes the amount of heat Q to be added to the accumulated heat Q11 (Q12, Q13) in accordance with the relative value of the load current to the settling current of the thermal relay 10. Specifically, when the relative value of the load current to the settling current is equal to or greater than the first relative value and the load 3 is in an overload state, the calculation processing unit 31 adds a relatively large first amount of heat to the accumulated heat Q11 (Q12, Q13) and calculates a new accumulated heat Q11 (Q12, Q13). This makes it possible to quickly detect the overload state of the load 3. On the other hand, when the relative value of the load current to the settling current is less than the first relative value and the load 3 is approaching an overload state, the calculation processing unit 31 adds a second amount of heat smaller than the first amount of heat to the accumulated heat Q11 (Q12, Q13) and calculates a new accumulated heat Q11 (Q12, Q13). This makes it possible to suppress erroneous detection before the load 3 reaches an overload state, and quickly detect the overload state when the load 3 reaches an overload state. Furthermore, when the relative value of the load current to the settling current is less than the first relative value and the new accumulated heat amount Q11 (Q12, Q13) is equal to or greater than the first threshold value (threshold value Th1), the calculation processing unit 31 calculates that the new accumulated heat amount Q11 (Q12, Q13) is the same value as the first threshold value. This makes it possible to suppress erroneous detection before the load 3 reaches an overload state with higher accuracy.

[0083] According to this embodiment, the calculation processor 31 subtracts the third heat quantity when the relative value of the load current to the settling current is less than the second relative value that is smaller than the first relative value. This makes it possible to suppress erroneous detection before the load 3 reaches an overload state.

[0084] Moreover, according to this embodiment, the calculation processing unit 31 outputs a first alarm signal (pre-alarm information) before the overload protection device 1 performs a cutoff operation. Moreover, the notification unit 40 operates in response to the first alarm signal output from the calculation processing unit 31. This makes it possible to notify the outside that the timing of cutting off the power supply from the power source 2 to the load 3 is approaching. As a result, measures can be taken early to get the load 3 out of an overload state, such as reducing the weight of the transported object on the conveyor. That is, the load 3 can be protected from an overload state separately from the cutoff operation of the overload protection device 1. Therefore, the accuracy of protection of the load 3 can be improved. Also, a situation in which the production facility is stopped due to the stop of the load 3 is prevented. This makes it possible to prevent economic losses caused by the stop of the production facility.

[0085] Furthermore, according to this embodiment, the calculation processing unit 31 outputs a second alarm signal when the accumulated heat amount Q11 (Q12, Q13) is equal to or greater than a third threshold (threshold Th3) that is greater than the second threshold (threshold Th2). This makes it possible to notify the outside each time the timing for cutting off the power supply from the power source 2 to the load 3 is approaching. Furthermore, when the output timing of the second alarm signal from the calculation processing unit 31 is synchronized with the timing for cutting off the power supply from the power source 2 to the load 3, it is possible to notify the outside that the power supply from the power source 2 to the load 3 will be cut off.

[0086] Furthermore, according to the present embodiment, the storage unit 32 stores the time-series transitions of the accumulated heat quantities Q11, Q12, and Q13, and thus the transitions of the accumulated heat quantities Q11, Q12, and Q13 can be visualized. As a result, the operation of the production equipment driven by the load 3 can be optimized.

[0087] According to the present embodiment, the edge controller 30 communicatively connected to the current measuring unit 20 includes a calculation processing unit 31 and a storage unit 32. Therefore, the edge controller 30 calculates the accumulated heat amounts Q11, Q12, and Q13 separately from the control circuit 16 of the thermal relay 10. As a result, the load of calculation processing on the control circuit 16 can be reduced compared to the case where the accumulated heat amounts Q11, Q12, and Q13 are calculated by the control circuit 16 of the thermal relay 10. In other words, the edge controller 30 can increase the speed of calculation of the accumulated heat amounts Q11, Q12, and Q13, and as a result, an overload state of the load 3 can be quickly detected.

[0088] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0089] 1 Overload protection device 2 power supply 3. Load 10. Thermal relay 20 Current measurement section 30 Edge Controller 31 Processing unit 32 Storage section 40 Notification Department 50 Magnetic contactor 60 Electromagnetic switch

Claims

1. a thermal relay connected between the power supply and the load; a current measuring unit that measures a current flowing through the thermal relay; a calculation processing unit that calculates an estimated value of an amount of accumulated heat inside the thermal relay based on the current value measured by the current measuring unit; An overload protection device comprising:

2. The arithmetic processing unit is When the current value measured by the current measuring unit is equal to or greater than a first relative value with respect to a settling current of the thermal relay, a first heat quantity is added to the estimated value of the accumulated heat quantity to calculate a new estimated value of the accumulated heat quantity, when the current value measured by the current measuring unit is less than a first relative value with respect to a settling current of the thermal relay, a second heat quantity smaller than the first heat quantity is added to the estimated value of the accumulated heat quantity to calculate a new estimated value of the accumulated heat quantity.

2. The overload protection device of claim 1.

3. the calculation processing unit calculates a new estimated value of the accumulated heat amount to be the first threshold value when the current value measured by the current measuring unit is less than a first relative value with respect to a settling current of the thermal relay and a value obtained by adding the second heat amount to the estimated value of the accumulated heat amount is equal to or greater than a first threshold value.

3. The overload protection device of claim 2.

4. the calculation processing unit, when the current value measured by the current measuring unit is less than a second relative value that is smaller than a first relative value with respect to the settling current of the thermal relay, subtracts a third heat amount from the estimated value of the accumulated heat amount to calculate a new estimated value of the accumulated heat amount.

4. An overload protection device according to claim 2 or 3.

5. The calculation processing unit outputs a first warning signal when the estimated value of the accumulated heat amount is equal to or greater than a second threshold before the overload protection device performs an interruption operation.

2. The overload protection device of claim 1.

6. Further, a notification unit that operates in response to the first alarm signal output from the calculation processing unit is provided.

6. The overload protection device of claim 5.

7. The calculation processing unit outputs a second warning signal when the estimated value of the accumulated heat amount is equal to or greater than a third threshold value that is greater than the second threshold value.

7. An overload protection device according to claim 5 or 6.

8. The device further includes a storage unit that stores a transition of the estimated value of the accumulated heat amount calculated by the calculation processing unit.

4. An overload protection device according to claim 2 or 3.

9. An edge controller communicatively connected to the current measuring unit, The arithmetic processing unit and the storage unit are each disposed within the edge controller.

9. The overload protection device of claim 8.

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