Electric snow melter sensor and monitoring system

Abstract

To easily detect an electric abnormality of an electric snow-melting device.SOLUTION: An electric snow-melting device sensor 1 comprises a voltage sensor 3, a current sensor 4, and a control unit 5. The voltage sensor 3 measures a supply voltage V supplied to a heater 21. An electric snow-melting device 2 is supplied with electric power by a single-phase three-wire system. The voltage sensor 3 measures the supply voltage V supplied to the heater 21. The current sensor 4 measures load current I of voltage lines 22a and 22b. The control unit 5 determines existence of an abnormality of the electric snow-melting device 2 on the basis of measurement values of the supply voltage V and the load current I of the voltage lines 22a and 22b. When the supply voltage V is higher than or equal to a prescribed voltage threshold value V7 for a low-current abnormality and the load current I is less than a prescribed low-current abnormality threshold value I1, the control unit 5 determines that a low-current abnormality has occurred. When the load current I becomes higher than or equal to a prescribed low-current abnormality recovery threshold value I2, the control unit 5 determines that the electric snow-melting device has recovered from the low-current abnormality. The low-current abnormality recovery threshold value I2 is set to a value higher than or equal to the low-current abnormality threshold value I1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric snow melting sensor for detecting an abnormality in an electric snow melting device, and a monitoring system having the same. [Background technology]

[0002] In railways, a turnout is provided at a branch point of the track (see Non-Patent Document 1). As shown in FIG. 9, the turnout 9 has fixed base rails 92, 93 and tongue rails 94, 95 to be switched at a point 91 (point section), and when a vehicle passes, the tongue rail comes into close contact with either the left or right base rail. If snow accumulates on the turnout 9, there is a risk that the point 91 will not come into close contact properly or will not switch. For this reason, in areas with heavy snowfall, a snow melter that melts fallen snow is provided at the turnout 9. As a snow melter, there is an electric snow melter having a heater (see, for example, Patent Document 1). The heater of the electric snow melter is attached to the rail body or the lower part of the floorboard of the turnout 9, and melts snow by generating Joule heat with an electric current. Therefore, in order for the electric snow melter to function normally, the heater needs to be energized appropriately.

[0003] Conventionally, an abnormality monitoring system that detects occurrence of an abnormality in the conduction of electricity in a snow melting device (electric snow melting device) has been known (see Patent Document 2). Power is supplied to the snow melting device via a single-phase three-wire system. The single-phase three-wire system has two voltage wires and one neutral wire (referred to as a "neutral voltage wire" in Patent Document 2). This abnormality monitoring system monitors the unbalanced current flowing through the neutral wire to detect occurrence of an abnormality such as a disconnection. However, since this abnormality monitoring system balances the current in the neutral wire under normal conditions, if the number of snow melting devices connected to each voltage wire is different, the wiring with the fewer number of snow melting devices requires that the wiring for one snow melting device be passed twice through the current transformer of the neutral wire, which makes the wiring complicated. In addition, since the current of the common neutral wire is monitored, it is not possible to know which of the two voltage wires has an abnormality in the conduction of electricity.

[0004] If an abnormality in an electric snow melter could be detected based on the measured values ​​of each voltage line, rather than the current in the neutral line, the wiring would not become complicated and it would be possible to determine which voltage line has an abnormality. However, this has not been possible in the past. This is because the power source that supplies power to each electric snow melter is received at the station and distributed to each load equipment such as the electric snow melter, air conditioning, lighting, station equipment, etc. As a result, the voltage supplied to the electric snow melter fluctuates depending on the operating status of these load equipment. In addition, there are various types of heaters for electric snow melters, and some have resistance values ​​that vary depending on the temperature (see, for example, Patent Document 3). This fluctuation in supply voltage and resistance values ​​makes it difficult to set a threshold value for detecting an abnormality in the measured values ​​of the voltage lines. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Utility Model Registration No. 3163730 [Patent Document 2] JP 2015-94660 A [Patent Document 3] Japanese Utility Model Application Publication No. 5-30203 [Non-patent literature]

[0006] [Non-Patent Document 1] JIS E 1303:2001 "Railway switches" Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is intended to solve the above problem, and has an object to easily detect electrical abnormalities in an electric snow melter. [Means for solving the problem]

[0008] The electric snow melter sensor of the present invention is for detecting abnormalities in an electric snow melter having multiple heaters, wherein the electric snow melter is supplied with power via a single-phase three-wire system using two voltage lines and one neutral line, and the heaters are provided at a branch. The electric snow melter sensor is equipped with a voltage sensor that measures the supply voltage supplied to the heaters, a current sensor that measures the load current of each voltage line, and a control unit that determines whether or not there is an abnormality in the electric snow melter based on the measured values ​​of the supply voltage and the load current of each voltage line. When the supply voltage is equal to or greater than a predetermined small current abnormality voltage threshold and the load current is less than a predetermined small current abnormality threshold, the control unit determines that a small current abnormality has occurred, and when the load current becomes equal to or greater than a predetermined small current abnormality recovery threshold, the control unit determines that recovery has occurred from the small current abnormality, and the small current abnormality recovery threshold is set to a value equal to or greater than the small current abnormality threshold.

[0009] In this electric snow melter sensor, the electric snow melter has a distribution board that distributes the received power to each branch and supplies power to the heater, and wiring that connects the distribution board to the heater, and it is preferable that the voltage sensor measures the supply voltage within the distribution board and the current sensor measures the load current for each branch within the distribution board.

[0010] In this electric snow melter sensor, when the load current exceeds a predetermined large current abnormality threshold, the control unit determines that a large current abnormality has occurred, and when the load current falls below a predetermined large current abnormality recovery threshold, it determines that the large current abnormality has been recovered from, and it is preferable that the large current abnormality recovery threshold is set to a value below the large current abnormality threshold.

[0011] In this electric snow melter sensor, when the supply voltage is less than a predetermined low voltage abnormality threshold, the control unit determines that a low voltage abnormality has occurred, and when the supply voltage becomes equal to or greater than a predetermined low voltage abnormality recovery threshold, it determines that the low voltage abnormality has been recovered from, and it is preferable that the low voltage abnormality recovery threshold is set to a value equal to or greater than the low voltage abnormality threshold.

[0012] In this electric snow melter sensor, when the supply voltage exceeds a predetermined high voltage abnormality threshold, the control unit determines that a high voltage abnormality has occurred, and when the supply voltage falls below a predetermined high voltage abnormality recovery threshold, it determines that the high voltage abnormality has been recovered from, and it is preferable that the high voltage abnormality recovery threshold is set to a value below the high voltage abnormality threshold.

[0013] In this electric snow melter sensor, when the supply voltage is less than a predetermined no-voltage determination threshold, the control unit determines that there is no supply voltage, and when the supply voltage becomes equal to or greater than a predetermined voltage-present determination threshold, it determines that there is a supply voltage, and it is preferable that the voltage-present determination threshold is set to a value equal to or greater than the no-voltage determination threshold.

[0014] In this electric snow melter sensor, it is preferable that the electric snow melter sensor further includes an earth sensor that measures the insulation resistance between the neutral wire and earth, and when the insulation resistance remains below a predetermined insulation resistance lower threshold for a predetermined period of time, the control unit determines that a ground fault has occurred.

[0015] The monitoring system of the present invention is a system having an electric snow melting sensor and a monitoring device, wherein the electric snow melting sensor has a communication unit that performs data communication with the monitoring device, the communication unit transmits the judgment result by the control unit to the monitoring device, and the monitoring device issues an alarm when the judgment result received from the electric snow melting sensor is a predetermined abnormal result. Effect of the Invention

[0016] According to the electric snow melter sensor of the present invention, the presence or absence of an abnormality in the electric snow melter is determined based on the supply voltage and load current of the voltage line, so it is possible to know which heater connected to which voltage line an abnormality has occurred. Since there is no need to use the current of the neutral line for the determination, there is no need to balance the current of the neutral line under normal conditions, and the electric snow melter can be installed without changing the wiring of the existing electric snow melter. Furthermore, when the supply voltage is equal to or greater than the voltage threshold for small current abnormality and the load current is less than the small current abnormality threshold, it is determined that a small current abnormality has occurred, so it is possible to prevent erroneous determination of a small current abnormality caused by a drop in supply voltage. Furthermore, when the load current becomes equal to or greater than the small current abnormality recovery threshold, it is determined that recovery from the small current abnormality has occurred, so it is possible to prevent erroneous determination of recovery from a small current abnormality caused by a drop in supply voltage. Since erroneous determinations caused by a drop in supply voltage are prevented, it is easy to set the threshold for determining the presence or absence of an abnormality. Since the small current abnormality recovery threshold is set to a value equal to or greater than the small current abnormality threshold, chattering in determining a small current abnormality can be prevented. Therefore, the electric snow melter sensor can easily detect electrical abnormalities in the electric snow melter. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram of an electric snow melter sensor and monitoring system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the arrangement of electric snow melting sensors and monitoring devices in the monitoring system. [Diagram 3] 4 is a diagram illustrating a supply voltage threshold and supply voltage fluctuation. [Figure 4] 4 is a diagram illustrating a load current threshold and a load current fluctuation. [Diagram 5] FIG. 11 is a state transition diagram for determining a small current anomaly. [Figure 6] FIG. 11 is an explanatory diagram for preventing erroneous determination of a small current anomaly. [Figure 7] 11 is an explanatory diagram for preventing erroneous determination of recovery from a small current anomaly. [Figure 8] FIG. 4 is an explanatory diagram of determination of the presence or absence of a supply voltage. [Figure 9] Plan view of the switch. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An electric snow melting device sensor and monitoring system according to an embodiment of the present invention will be described with reference to Figures 1 to 8. As shown in Figure 1, the electric snow melting device sensor 1 is a device for detecting an abnormality in an electric snow melting device 2. The electric snow melting device 2 has multiple heaters 21.

[0019] Electric snow melter 2 is supplied with power via a single-phase, three-wire system using two voltage wires 22a, 22b and one neutral wire 22c. The single-phase, three-wire system is one of the AC power supply methods, and is described in "32.1.1 Current-carrying conductors in AC circuits" of the Japanese Industrial Standard JIS C60364-1:2010 "Low-voltage electrical equipment - Part 1: Basic principles, evaluation of general characteristics and definitions of terms" (see Figure 2 in the standard).

[0020] As shown in Fig. 2, the heater 21 is provided at the turnout 9. In this embodiment, the heater 21 is provided at a point 91 (point portion) of the turnout 9. The location at which the heater 21 is provided is not limited to the point 91, and may be near the nose 96 of the turnout 9, or the like. The heater 21 is attached to the middle part of the rail of the turnout 9, the lower part of the floor plate, or the like.

[0021] In the electric snow melter 2, the heater 21 is connected as a load (see FIG. 1). A load is something that consumes electrical energy. The heater 21 is a load because it converts electrical energy into thermal energy (Joule heat). In this embodiment, the heater 21 is connected between the voltage line 22a and the neutral line 22c, and between the voltage line 22b and the neutral line 22c. In FIG. 1, the wiring from the terminal box 23 to the heater 21 is shown as a single line instead of three lines (single-line wiring diagram). Note that since the electric snow melter sensor 1 does not need to measure the current in the neutral line 22c, it is also electrically possible to connect the heater 21 between the pair of voltage line 22a and voltage line 22b.

[0022] The electric snow melter sensor 1 includes a voltage sensor 3, a current sensor 4, and a control unit 5. The voltage sensor 3 measures the supply voltage V supplied to the heater 21. The value of the measured supply voltage V is input to the control unit 5. The current sensor 4 measures the current of each voltage line 22a, 22b. In a single-phase three-wire system, a load is connected to each voltage line 22a, 22b, so the current of each voltage line 22a, 22b is a load current I. In other words, the current sensor 4 measures the load current I of each voltage line 22a, 22b. The value of the measured load current I is input to the control unit 5. The control unit 5 determines whether or not there is an abnormality in the electric snow melter 2 based on the measured values ​​of the supply voltage V and the load current I of each voltage line 22a, 22b.

[0023] In addition to the heater 21, the electric snow melter 2 has a distribution board 24 and wiring. The distribution board 24 distributes the received power to each branch 9 and supplies the power to the heaters 21 (see FIG. 2). A terminal box 23 is provided near each branch 9. The wiring of the electric snow melter 2 is connected from the distribution board 24 to the terminal box 23 near each branch 9, and is connected from the terminal box 23 to the heaters 21. The voltage sensor 3 measures the supply voltage V in the distribution board 24 (see FIG. 1). The current sensor 4 measures the load current I for each branch 9 in the distribution board 24. That is, the current sensor 4 measures the load current I of each voltage line 22a, 22b distributed to each branch 9 (see FIGS. 1 and 2). Since multiple heaters 21 are provided in each branch 9, the measured load current I is the sum of the currents flowing through the multiple heaters 21 provided in each branch 9 for each voltage line 22a, 22b.

[0024] The electric snow melting sensor 1 has a voltage sensor 3, a current sensor 4, and a control unit 5, as well as an earth sensor 6, a communication unit 7, and a power supply unit 11. The earth sensor 6 measures the insulation resistance between the neutral wire 22c of the electric snow melting device 2 and the earth. The communication unit 7 is a device that performs data communication with the monitoring device 8. The power supply unit 11 is a power source that supplies power to each part of the electric snow melting sensor 1. The electric snow melting sensor 1 is housed in a housing 12.

[0025] The configuration of the electric snow melting sensor 1 will be described in further detail. The electric snow melting device 2 is the target for abnormality detection by the electric snow melting device sensor 1. The power received by the electric snow melting device 2 is distributed to multiple breakers 27 via a main breaker 25 and a control switch 26 of a distribution board 24. The main breaker 25 is a breaker that automatically cuts off the electric circuit when an abnormal accident such as an overload or short circuit occurs. The control switch 26 is a switch that opens and closes the electric circuit during normal operation. Opening and closing the control switch 26 is used to control the use and stop of the electric snow melting device 2. The breaker 27 is a breaker that cuts off the power supply from the primary side when an overcurrent flows in the secondary side circuit (heater 21 and wiring). The main breaker 25 and the breakers 27 are coordinated for protection. Wiring from each breaker 27 is connected to each terminal box 23. Since a plurality of heaters 21 are provided in one branch unit 9, the plurality of heaters 21 are connected in parallel to each terminal box 23.

[0026] The voltage sensor 3 is an AC voltage transducer that is connected to the electric path between the control switch 26 and the breaker 27, and converts each AC voltage (supply voltage V) of the voltage lines 22a, 22b relative to the neutral line 22c into a DC signal and outputs it to the control unit 5.

[0027] The current sensor 4 is a clamp-type AC current sensor that is clamped to the voltage lines 22a, 22b between each breaker 27 and the terminal box 23, and measures each AC current (load current I) in a non-contact manner and outputs the measured value to the control unit 5.

[0028] The control unit 5 is a microcontroller and includes a CPU, a memory, and the like.

[0029] The housing of the distribution board 24 is grounded (earthed). The earth sensor 6 is a ground detector, which is connected to the neutral wire 22c between the control switch 26 and the breaker 27 and to the housing earth of the distribution board 24, and constantly monitors the insulation resistance between the neutral wire 22c and the housing earth. When the insulation resistance falls below a predetermined insulation resistance lower limit threshold, an alarm is output to the control unit 5.

[0030] The communication unit 7 is a device that performs data communication using a low-power (low power consumption) wide-area (long-distance) wireless communication method. The communication unit 7 is connected to the control unit 5.

[0031] The power supply unit 11 is a device that converts alternating current into direct current of a constant voltage. Alternating current is input between the main breaker 25 and the control switch 26, and direct current is supplied to each part of the electric snow melting device sensor 1.

[0032] To determine the presence or absence of an abnormality in the electric snow melting device 2, a plurality of threshold values are set for the supply voltage V and the load current I in the electric snow melting device sensor 1, respectively. In FIG. 3, the vertical axis represents the supply voltage V. As shown in the figure, the following threshold values are set for the supply voltage V in ascending order: no-voltage determination threshold value V1, voltage-present determination threshold value V2, low-voltage abnormality threshold value V3, low-voltage abnormality recovery threshold value V4, high-voltage abnormality recovery threshold value V5, and high-voltage abnormality threshold value V6. The low-voltage abnormality threshold value V3 is the lower limit of the normal range of the supply voltage V, and the high-voltage abnormality threshold value V6 is the upper limit of the normal range of the supply voltage V. In addition to these threshold values of the supply voltage V, a small-current abnormality voltage threshold value V7 is set. The small-current abnormality voltage threshold value V7 is within the normal range of the supply voltage V, that is, not less than the low-voltage abnormality threshold value V3 and not more than the high-voltage abnormality threshold value V6 (V3 ≤ V7 ≤ V6). In FIG. 4, the vertical axis represents the load current I. As shown in the figure, the following threshold values are set for the load current I in ascending order: small-current abnormality threshold value I1, small-current abnormality recovery threshold value I2, large-current abnormality recovery threshold value I3, and large-current abnormality threshold value I4. The small-current abnormality threshold value I1 is the lower limit of the normal range of the load current I, and the large-current abnormality threshold value I4 is the upper limit of the normal range. These threshold values are stored in the control unit 5 and used for determination by the control unit 5 (see FIG. 1).

[0033] The detection of a small-current abnormality by the electric snow melting device sensor 1 configured as described above will be described with reference to FIG. 4. In FIG. 4, the horizontal axis represents time t, and the load current I is fluctuating. Between times t0 ≤ t < t1, the load current I is not less than the small-current abnormality threshold value I1 (I ≥ I1). That is, the load current I is not less than the lower limit of the normal range.

[0034] At time t = t1, the load current I has dropped below the small current anomaly threshold I1. At this time, if the supply voltage V is equal to or higher than the small current anomaly voltage threshold V7, since the load current I is below the lower limit of the normal range, the control unit 5 determines that a small current anomaly has occurred in the electric snow melter 2. That is, when the supply voltage V is equal to or higher than the predetermined small current anomaly voltage threshold V7 and the load current I is less than the predetermined small current anomaly threshold I1, the control unit 5 determines that a small current anomaly has occurred. In this way, the small current anomaly of the electric snow melter 2 is detected by the electric snow melter sensor 1. The cause of the small current anomaly is, for example, an open circuit or an electrical contact failure of the heater 21.

[0035] Then, at time t = t3, the load current I has risen to equal to or higher than the small current anomaly recovery threshold I2. At this time, the control unit 5 determines that the electric snow melter 2 has recovered from the small current anomaly. That is, when the load current I becomes equal to or higher than the predetermined small current anomaly recovery threshold I2, the control unit 5 determines that it has recovered from the small current anomaly. The cause of the recovery from the small current anomaly is, for example, the repair of a failure. That is, by detecting the recovery from the small current anomaly, it can be known that the repair has been completed.

[0036] In this embodiment, the small current anomaly recovery threshold I2 is larger than the small current anomaly threshold I1 (I2 > I1). Therefore, during the time t2 ≦ t < t3, although the load current I has risen to equal to or higher than the small current anomaly threshold I1 (I ≧ I1), the control unit 5 does not determine that it has recovered from the small current anomaly. Such a threshold hysteresis is to prevent the control unit 5 from repeatedly switching between the normal determination and the small current anomaly state in a short time (chattering). If chattering is prevented by other methods, the small current anomaly recovery threshold I2 may be the same as the small current anomaly threshold I1 (I2 = I1). For chattering prevention, for example, there is integration by an analog circuit of the measured value of the load current I. Therefore, the small current anomaly recovery threshold I2 is set to a value equal to or higher than the small current anomaly threshold I1 (I2 ≧ I1).

[0037] FIG. 5 is a state transition diagram showing the determination of normal and small current abnormality by the control unit 5. As described above, for the determination of abnormality detection (event e01) from normal (state s0) to small current abnormality (state s1), there are conditions for the supply voltage V and the load current I (V ≧ V7 and I < I1). For the determination of recovery (event e10) from small current abnormality (state s1) to normal (state s0), there is a condition for the load current I (I ≧ I2), but there is no condition for the supply voltage V.

[0038] If the determination of abnormality detection (event e01) from normal (state s0) to small current abnormality (state s1) is made only based on the condition of the load current I (I < I1), when the voltage supplied to the electric snow melting device 2 decreases, since the load current I decreases due to the decrease in the supply voltage V, there is a possibility of an incorrect determination that a small current abnormality has occurred in the electric snow melting device 2 even if the heater 21 is not disconnected. Therefore, even if the load current I is less than the small current abnormality threshold I1, when the supply voltage V is less than the small current abnormal voltage threshold V7, it is not determined that a small current abnormality has occurred. That is, when the supply voltage V is equal to or higher than a predetermined small current abnormal voltage threshold V7 and the load current I is less than a predetermined small current abnormal threshold I1 (V ≧ V7 and I < I1), the control unit 5 determines that a small current abnormality has occurred.

[0039] The negation of the logical formula "V ≥ V7 and I < I1", that is, "not (V ≥ V7 and I < I1)" is "V < V7 or I ≥ I1" (De Morgan's law in Boolean algebra). Considering the threshold hysteresis described above, it becomes "V < V7 or I ≥ I2" (I2 ≥ I1). If the determination of recovery from a small current anomaly (state s1) to normal (state s0) (event e10) is made based on this condition (V < V7 or I ≥ I2), when the supply voltage V becomes less than the small current anomaly voltage threshold V7 (V < V7), even if the disconnection of the heater 21 has not been resolved, an incorrect determination that the electric snow melter 2 has recovered from the small current anomaly will occur. That is, even if the load current I has actually decreased due to the disconnection of the heater 21, it will be incorrectly determined that the load current I is small because the supply voltage V is low. Therefore, the supply voltage V is not included as a condition for the determination of recovery. That is, when the load current I becomes equal to or greater than a predetermined small current anomaly recovery threshold I2 (I ≥ I2), the control unit 5 determines that recovery has occurred from the small current anomaly. Note that a hysteresis may be provided for the small current anomaly voltage threshold V7 in the same manner as for the other voltage thresholds (V1 and V2, V3 and V4).

[0040] In this way, providing asymmetry in the handling of the supply voltage V in the conditions for determining the occurrence and recovery of a small current anomaly was found by the inventor of the present application through testing.

[0041] The prevention of incorrect determination of a small current anomaly and the threshold setting will be further described with reference to FIG. 6. The upper graph illustrates the time change of the supply voltage V, and the lower graph illustrates the time change of the load current I.

[0042] At time t = t4, the electric snow melter 2 starts to be used. Immediately thereafter, since the temperature of the heater 21 is low, the resistance value of the heater 21 is low and the load current I is large. Thereafter, as the temperature of the heater 21 rises, the load current I gradually decreases. Note that even if the electric snow melter 2 has a heater 21 with a constant resistance value regardless of the temperature, the following explanation is the same.

[0043] At time t = t5, the supply voltage V starts to fluctuate. In this example, the supply voltage V fluctuates periodically. The load current I fluctuates with the fluctuation of the supply voltage V. Note that the supply voltage V tends to be low during the time when there are many station users.

[0044] At time t = t6, the threshold values of the supply voltage V and the load current I are set. The low-current abnormal voltage threshold V7 is set to the supply voltage V at this time. The low-current abnormal voltage threshold V7 is within the normal range of the supply voltage V. The low-current abnormal threshold I1 is set to a value that is a certain value (for example, 1.1 [A]) smaller than the load current I at this time. This low-current abnormal threshold I1 is a value that can detect the decrease in the load current I when one of the heaters 21 is disconnected. The setting of the low-current abnormal recovery threshold I2 will be described later.

[0045] At time t = t7, the load current I becomes less than the low-current abnormal threshold I1. The cause is the decrease in the supply voltage V, and there is no abnormality in the electric snow melting device 2. During the time when t7 ≤ t < t8, since the supply voltage V is less than the low-current abnormal voltage threshold V7, the control unit 5 does not determine that a low-current abnormality has occurred in the electric snow melting device 2.

[0046] At time t = t8, the load current I becomes equal to or greater than the low-current abnormal threshold I1. At time t = t9, the load current I becomes less than the low-current abnormal threshold I1 again. The cause is the decrease in the supply voltage V, and there is no abnormality in the electric snow melting device 2. During the time when t9 ≤ t < t10, since the supply voltage V is less than the low-current abnormal voltage threshold V7, the control unit 5 does not determine that a low-current abnormality has occurred in the electric snow melting device 2.

[0047] In this way, in the electric snow melting device sensor 1, false determination of low-current abnormality due to the decrease in the supply voltage V is prevented.

[0048] Prevention of false determination of recovery from low-current abnormality and threshold setting will be further described with reference to FIG. 7. The upper graph illustrates the time change of the supply voltage V, and the lower graph illustrates the time change of the load current I.

[0049] At time t = t11, the electric snow melter 2 starts to be used. Immediately after that, since the temperature of the heater 21 is low, the resistance value of the heater 21 is low and the load current I is large. After that, as the temperature of the heater 21 rises, the load current I gradually decreases. Even if the electric snow melter 2 has a heater 21 with a constant resistance value regardless of the temperature, the following explanation is the same.

[0050] At time t = t12, the supply voltage V starts to fluctuate. In this example, the supply voltage V fluctuates periodically. The load current I fluctuates with the fluctuation of the supply voltage V.

[0051] At time t = t13, the threshold values of the supply voltage V and the load current I are set. The low-current abnormal voltage threshold V7 is set to the supply voltage V at this time. The low-current abnormal voltage threshold V7 is within the normal range of the supply voltage V. The low-current abnormal threshold I1 is set to a value that is a certain value (for example, 1.1 [A]) smaller than the load current I at this time. This low-current abnormal threshold I1 is a value that can detect a decrease in the load current I when one of the heaters 21 is disconnected. The low-current abnormal recovery threshold I2 is set to a value slightly larger than the low-current abnormal threshold I1.

[0052] At time t = t14, the load current I drops below the low-current abnormal threshold I1. At this time, some of the heaters 21 are disconnected. However, since the supply voltage V is less than the low-current abnormal voltage threshold V7 during the period t14 ≦ t < t15, the control unit 5 has not yet determined that a low-current abnormality has occurred in the electric snow melter 2.

[0053] At time t = t15, since the supply voltage V is equal to or higher than the low-current abnormal voltage threshold V7 and the load current I is less than the low-current abnormal threshold I1, the control unit 5 determines that a low-current abnormality has occurred in the electric snow melter 2.

[0054] After that (t ≧ t15), the disconnection of some of the heaters 21 continues. At time t = t16, the supply voltage V becomes less than the low-current abnormal voltage threshold V7, but the control unit 5 does not misjudge that the electric snow melter 2 has recovered from the low-current abnormality. That is, the determination that a low-current abnormality has occurred in the electric snow melter 2 continues.

[0055] In this way, in the electric snow melter sensor 1, the asymmetry of the conditions for determining occurrence and recovery prevents erroneous determination of recovery from a small current anomaly caused by a drop in the supply voltage V.

[0056] The electric snow melting device sensor 1 detects abnormalities other than the small current abnormality of the electric snow melting device 2.

[0057] When the load current I exceeds a predetermined large current abnormality threshold I4, the control unit 5 determines that a large current abnormality has occurred in the electric snow melter 2. Then, when the load current I becomes equal to or less than a predetermined large current abnormality recovery threshold I3, the control unit 5 determines that the electric snow melter 2 has recovered from the large current abnormality (see FIG. 4). The large current abnormality recovery threshold I3 is set to a value equal to or less than the large current abnormality threshold I4. A large current abnormality occurs, for example, due to a short circuit or incomplete short circuit in the heater 21 or wiring.

[0058] As a modified example, the control unit 5 may determine that the electric snow melter 2 has recovered from the large current abnormality when the supply voltage V is equal to or higher than a predetermined voltage threshold (e.g., low voltage abnormality threshold V3) and the load current I is equal to or lower than a predetermined large current abnormality recovery threshold I3. As a result, even if the load current I decreases due to a drop in the supply voltage V, the control unit 5 does not determine that the electric snow melter 2 has recovered from the large current abnormality.

[0059] When the supply voltage V is less than a predetermined low voltage abnormality threshold V3, the control unit 5 determines that a low voltage abnormality has occurred (time t=t17 in FIG. 3). Then, when the supply voltage V becomes equal to or greater than a predetermined low voltage abnormality recovery threshold V4, the control unit 5 determines that the low voltage abnormality has been recovered from (time t=t18 in FIG. 3). The low voltage abnormality recovery threshold V4 is set to a value equal to or greater than the low voltage abnormality threshold V3. A low voltage abnormality occurs, for example, due to a drop in the voltage received by the electric snow melter 2. For example, when the normal range of the supply voltage V is 105 [V] ±10 [V], the low voltage abnormality threshold V3 is set to 105 [V]-10 [V]. The low voltage abnormality threshold V3 is a threshold value that is set independently of the small current abnormality voltage threshold V7.

[0060] When the supply voltage V exceeds a predetermined high voltage abnormality threshold V6, the control unit 5 determines that a high voltage abnormality has occurred (time t=t19 in FIG. 3). Then, when the supply voltage V becomes equal to or lower than a predetermined high voltage abnormality recovery threshold V5, the control unit 5 determines that the high voltage abnormality has been recovered from (time t=t20 in FIG. 3). The high voltage abnormality recovery threshold V5 is set to a value equal to or lower than the high voltage abnormality threshold V6. A high voltage abnormality occurs when the voltage received by the electric snow melter 2 rises excessively. For example, if the normal range of the supply voltage V is 105 [V] ±10 [V], the high voltage abnormality threshold V6 is set to 105 [V] +10 [V].

[0061] As shown in FIG. 8, when the supply voltage V is less than a predetermined no-voltage determination threshold V1, the control unit 5 determines that there is no supply voltage (time t=t21 in FIG. 8). Then, when the supply voltage V becomes equal to or greater than a predetermined voltage-presence determination threshold V2, the control unit 5 determines that there is a supply voltage (time t=t22 in FIG. 3). The voltage-presence determination threshold V2 is set to a value equal to or greater than the no-voltage determination threshold V1. Also, when it is determined that there is no supply voltage for both of the two voltage lines 22a and 22b, the control unit 5 determines that the electric snow melter 2 is out of use. The determination that there is no supply voltage occurs, for example, when the control switch 26 is turned off, the main breaker 25 is shut off, or when the voltage received by the electric snow melter 2 drops excessively or there is a power outage (see FIG. 1). In order for the electric snow melter sensor 1 to stably detect the absence of a supply voltage for the electric snow melter 2, a capacitor may be provided in the power supply unit 11 of the electric snow melter sensor 1.

[0062] When the insulation resistance measured by earth sensor 6 remains below a predetermined insulation resistance lower limit threshold (earth detection) for a predetermined time T, control unit 5 determines that a ground fault has occurred in electric snow melter 2. Weather conditions can cause the insulation resistance of electric snow melter 2 to become unstable. Setting the predetermined time T (duration condition) (T>0) prevents erroneous detection due to weather conditions. Note that if fluctuations in insulation resistance due to changes in weather conditions are also monitored, the predetermined time T may be set to 0 (immediate warning).

[0063] The monitoring system 10 according to one embodiment of the present invention includes an electric snow melting sensor 1 and a monitoring device 8. As described above, the electric snow melting sensor 1 includes a communication unit 7 that performs data communication with the monitoring device 8. The communication unit 7 transmits the judgment result by the control unit 5 to the monitoring device 8. The monitoring device 8 issues an alarm when the judgment result received from the electric snow melting sensor 1 is a predetermined alarm target. The alarm is issued by a screen display or a sound. The predetermined alarm targets are, for example, a small current abnormality, a large current abnormality, a low voltage abnormality, a high voltage abnormality, a ground fault, and no supply voltage. Recovery from each of the small current abnormality, large current abnormality, low voltage abnormality, high voltage abnormality, and a ground fault, and a change to a supply voltage are also alarm targets. In this embodiment, the electric snow melting sensor 1 has a scheduled transmission function in addition to a function of immediately transmitting the judgment result by the control unit 5 to the monitoring device 8. As a scheduled transmission function, the electric snow melting sensor 1 transmits the measured values ​​of voltage, current, etc., the duration of earth detection, and the status of each sensor, etc. to the monitoring device 8 at regular intervals. The regular interval can be set in 10-second increments within a range from 10 seconds to 24 hours, for example. This scheduled transmission function makes it possible to monitor whether the electric snow melting sensor 1 itself is alive or not.

[0064] As described above, the electric snow melter sensor 1 according to this embodiment judges whether or not an abnormality has occurred in the electric snow melter 2 based on the supply voltage V and the load current I of the two voltage lines 22a and 22b, so it is possible to know which of the voltage lines 22a and 22b the heater 21 connected to has an abnormality. Since it is not necessary to use the current of the neutral line 22c for the judgment, it is not necessary to balance the current of the neutral line 22c during normal operation, and the electric snow melter can be installed without changing the wiring of the existing electric snow melter 2. In addition, when the supply voltage V is equal to or greater than the small current abnormality voltage threshold V7 and the load current I is less than the small current abnormality threshold I1, it is judged that a small current abnormality has occurred, so it is possible to prevent erroneous judgment of a small current abnormality caused by a drop in the supply voltage V. Furthermore, when the load current I becomes equal to or greater than the small current abnormality recovery threshold I2, it is judged that recovery has occurred from the small current abnormality, so it is possible to prevent erroneous judgment of recovery from a small current abnormality caused by a drop in the supply voltage V. Since erroneous judgments caused by a drop in the supply voltage V are prevented, it is easy to set the threshold for judging whether or not an abnormality has occurred. Since the small current anomaly recovery threshold I2 is set to a value equal to or greater than the small current anomaly threshold I1, chattering can be prevented in determining the small current anomaly. Therefore, the electric snow melter sensor 1 can easily detect an electrical anomaly in the electric snow melter 2.

[0065] Since the current sensor 4 measures the load current I for each branch 9, the load current I of each voltage line 22a, 22b distributed to each branch 9 is measured, and an abnormality in each voltage line 22a, 22b for each branch 9 can be detected. In addition, since the voltage sensor 3 measures the supply voltage V in the distribution board 24 and the current sensor 4 measures the load current I in the distribution board 24, the installation of the voltage sensor 3 and the current sensor 4 is easy.

[0066] Since the current sensor 4 measures the load current I of the voltage lines 22a and 22b, the occurrence of a large current anomaly can be detected by setting the large current anomaly threshold I4, and the recovery from the large current anomaly can be detected by setting the large current anomaly recovery threshold I3. The large current anomaly recovery threshold I3 is set to a value equal to or less than the large current anomaly threshold I4, so chattering in determining the large current anomaly can be prevented.

[0067] Since the voltage sensor 3 measures the supply voltage V of the voltage lines 22a and 22b, the occurrence of a low voltage abnormality can be detected by setting the low voltage abnormality threshold V3, and recovery from a low voltage abnormality can be detected by setting the low voltage abnormality recovery threshold V4. The low voltage abnormality recovery threshold V4 is set to a value equal to or greater than the low voltage abnormality threshold V3, which makes it possible to prevent chattering in determining a low voltage abnormality.

[0068] Since the voltage sensor 3 measures the supply voltage V of the voltage lines 22a and 22b, the occurrence of a high voltage abnormality can be detected by setting the high voltage abnormality threshold V6, and the recovery from the high voltage abnormality can be detected by setting the high voltage abnormality recovery threshold V5. The high voltage abnormality recovery threshold V5 is set to a value equal to or less than the high voltage abnormality threshold V6, so chattering in the determination of the high voltage abnormality can be prevented.

[0069] Since the voltage sensor 3 measures the supply voltage V of the voltage lines 22a and 22b, the absence of supply voltage can be detected by setting the no-voltage determination threshold V1, and the presence of supply voltage can be detected by setting the voltage-present determination threshold V2. The voltage-present determination threshold V2 is set to a value equal to or greater than the no-voltage determination threshold V1, which makes it possible to prevent chattering when determining whether or not there is no supply voltage.

[0070] The earth sensor 6 measures the insulation resistance between the neutral wire 22c and the earth, so that a ground fault in the electric snow melter 2 can be detected.

[0071] According to the monitoring system 10 of this embodiment, the monitoring device 8 issues an alarm when the judgment result received from the electric snow melter sensor 1 is a specified abnormal result, so that the user of the system can remotely know of the abnormality in the electric snow melter 2.

[0072] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible without departing from the spirit of the invention. For example, the monitoring system 10 may be configured so that the communication unit 7 communicates data with the monitoring device 8 by a wireless communication method other than low power wide area or by wired communication. [Explanation of symbols]

[0073] 1 Electric snow melting sensor 2. Electric snow melter 21 Heater 22a, 22b voltage lines 22c neutral wire 3 Voltage Sensor 4 Current Sensor 5. Control section 6 Earth Sensor 7. Communications Department 8 Monitoring device 10. Surveillance System I load current I1 Small current abnormality threshold I2 Small current abnormal recovery threshold I3 Large current abnormal recovery threshold I4 Large current abnormality threshold V supply voltage V1 No voltage judgment threshold V2 Voltage presence determination threshold V3 Low voltage abnormal threshold V4 Low voltage abnormal recovery threshold V5 High voltage abnormal recovery threshold V6 High voltage abnormal threshold V7 Small current abnormal voltage threshold

Claims

1. An electric snow melting device sensor for detecting an abnormality in an electric snow melting device having multiple heaters, Electric snow melters are powered by a single-phase, three-wire system using two voltage wires and one neutral wire. The heater is provided in the switch, The electric snow melter sensor includes a voltage sensor for measuring a supply voltage supplied to the heater; A current sensor for measuring a load current of each of the voltage lines; a control unit that determines whether or not there is an abnormality in the electric snow melter based on the measured values ​​of the supply voltage and the load current of each of the voltage lines, when the supply voltage is equal to or greater than a predetermined small current anomaly voltage threshold and the load current is less than a predetermined small current anomaly threshold, the control unit determines that a small current anomaly has occurred, and when the load current becomes equal to or greater than a predetermined small current anomaly recovery threshold, the control unit determines that a recovery has been made from the small current anomaly; An electric snow melting sensor characterized in that the small current abnormality recovery threshold is set to a value equal to or greater than the small current abnormality threshold.

2. The electric snow melter includes a distribution board that distributes received power to each of the branches and supplies power to the heater, and wiring that connects the distribution board and the heater, The voltage sensor measures a supply voltage in the distribution board, The electric snow melting sensor according to claim 1 , wherein the current sensor measures the load current for each of the branch switches within the distribution board.

3. When the load current exceeds a predetermined large current abnormality threshold, the control unit determines that a large current abnormality has occurred, and when the load current becomes equal to or less than a predetermined large current abnormality recovery threshold, determines that the large current abnormality has been recovered from, 3. The electric snow melter sensor according to claim 1, wherein the large current abnormality recovery threshold is set to a value equal to or lower than the large current abnormality threshold.

4. When the supply voltage is less than a predetermined low voltage abnormality threshold, the control unit determines that a low voltage abnormality has occurred, and when the supply voltage becomes equal to or greater than a predetermined low voltage abnormality recovery threshold, determines that the power supply has recovered from the low voltage abnormality; 4. The electric snow melter sensor according to claim 1, wherein the low voltage abnormality recovery threshold is set to a value equal to or greater than the low voltage abnormality threshold.

5. When the supply voltage exceeds a predetermined high voltage abnormality threshold, the control unit determines that a high voltage abnormality has occurred, and when the supply voltage becomes equal to or less than a predetermined high voltage abnormality recovery threshold, determines that the high voltage abnormality has been recovered from; 5. The electric snow melter sensor according to claim 1, wherein the high-voltage abnormality recovery threshold is set to a value equal to or lower than the high-voltage abnormality threshold.

6. When the supply voltage is less than a predetermined voltage absence determination threshold, the control unit determines that a supply voltage is absent, and when the supply voltage becomes equal to or greater than a predetermined voltage presence determination threshold, the control unit determines that a supply voltage is present; 6. The electric snow melter sensor according to claim 1, wherein the voltage presence determination threshold is set to a value equal to or greater than the voltage absence determination threshold.

7. The electric snow melting sensor further includes an earth sensor for measuring insulation resistance between the neutral conductor and earth, The electric snow melter sensor according to any one of claims 1 to 6, characterized in that when the insulation resistance remains below a predetermined insulation resistance lower threshold for a predetermined period of time, the control unit determines that a ground fault has occurred.

8. A monitoring system comprising the electric snow melting sensor according to any one of claims 1 to 7 and a monitoring device, The electric snow melting device sensor has a communication unit that performs data communication with the monitoring device, The communication unit transmits a determination result by the control unit to the monitoring device, A monitoring system characterized in that the monitoring device issues an alarm when the judgment result received from the electric snow melting sensor is a predetermined abnormal result.

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