JP2009281979A - Electronic watt-hour meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic watt-hour meter for easily recognizing the degree of reverse current. <P>SOLUTION: This electronic watt-hour meter has a reverse current level monitoring section 6 for monitoring the magnitude of the total-phase watt-hour and controlling the display state of a total-phase reverse current state display section 21a according to the magnitude of the total-phase watt-hour when the direction of the total-phase electric power is reverse direction. The reverse current level monitoring section 6 includes a reverse direction watt-hour counter section 6a for performing count up proportionally to the total-phase watt-hour. The fact that the total-phase electric power is in the reverse direction is displayed by coming of the total-phase reverse current state display section 21a into a lighting state. Whenever the reverse direction watt-hour counter section 6a counts it by a predetermined value, the total-phase reverse current state display section 21a is temporarily extinguished to come into a blinking state, and the degree of the reverse current is displayed with the blinking speed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electronic watt-hour meter that measures and displays load power.

  The conventional electronic watt-hour meter is configured to generate a pulse having a frequency proportional to the load power, count the pulse, and display it as a power amount by a display. The load state of the electronic watt-hour meter , Equipped with state calculation means that calculates the operating state, no-load state, and reverse current state from the pulse, and displays the measurement value display section that displays the measured value of the electric energy on the display and the state calculated by the state calculation means In addition, the state display unit is integrally formed, and the load state and the reverse current state are displayed on the state display unit (for example, Patent Document 1).

No. 8-6298

Since the conventional electronic watt-hour meter is configured as described above, the direction of current flowing from the load side to the power source side of all phase power, which is the sum of the power of all the phases being measured (hereinafter referred to as reverse) The reverse current mark is lit on the status display section.
However, only lighting the reverse current mark only indicates that the all-phase power is in the reverse direction, and there is a problem that the degree of the reverse direction cannot be recognized. On the other hand, in the mechanical watt-hour meter, when the all-phase power is in the reverse direction, the disk rotates in reverse depending on the degree of the reverse direction, and the degree of reverse direction (the magnitude of the reverse current) is determined by looking at the reverse rotation speed. Since it can be recognized, more information can be obtained compared to an electronic watt-hour meter.

  Furthermore, the load state in which the all-phase power is in the reverse direction is rare, and the all-phase power in the reverse direction is mainly caused by a connection mistake when installing the electronic watt-hour meter. Here, when using a mechanical watt-hour meter, it is possible to obtain information such as fast and slow rotation speed by looking at the reverse rotation speed of the disk, so based on this information, there is an empirical connection mistake. It was possible to identify the location. However, since the conventional electronic watt-hour meter only displays that the direction is the reverse direction, there is insufficient information for identifying the location where the connection is missed compared to the mechanical watt-hour meter.

  The present invention has been made in order to solve the above-described problems. When all-phase power is in the reverse direction, it is possible to display so that the degree of the reverse direction can be recognized. An object of the present invention is to obtain an electronic watt-hour meter that can quickly identify the location of a connection mistake during installation.

  An electronic watt-hour meter according to the present invention calculates an all-phase power from a voltage value and a current value of an electric circuit, integrates the all-phase power, and calculates the all-phase power amount, An all-phase power direction discriminating unit that discriminates the direction of phase power, an all-phase reverse current state display unit that displays that the direction of the all-phase power is reverse, and a discrimination result of the all-phase power direction discriminating unit is reverse A reverse current level monitoring unit that monitors the magnitude of the all-phase power amount and controls the display state of the all-phase reverse current state display unit according to the magnitude of the all-phase power amount. It is.

  According to the electronic watt-hour meter of the present invention, there is an effect that the presence / absence and the degree of the reverse direction of the all-phase power can be confirmed by observing the display state of the all-phase reverse current state display unit.

Embodiment 1 FIG.
An electronic watt-hour meter according to Embodiment 1 of the present invention will be described with reference to FIGS.
FIG. 1 is an external perspective view of an electronic watt hour meter 100 according to Embodiment 1 of the present invention, and a display panel 20 is provided on the front side of the electronic watt hour meter 100.
FIG. 2 is an enlarged view of the display panel 20 of FIG. 1, and when the all-phase power of the electronic watt-hour meter 100 is a reverse current (reverse direction), the all-phase reverse current state displayed as “reverse current” The display unit (all-phase display unit (reverse current)) 21a is turned on. Further, when the all-phase power is no load or in the forward direction (operating state), the all-phase no-load state display section (all-phase display section (no load)) 21b displayed as “no load” or “operation” or The all-phase operation state display section (all-phase display section (operation)) 21c is turned on. The all-phase current state display unit 21 is configured by the all-phase display units 21a, 21b, and 21c.

  Further, in the display panel 20, when the 1-side power or the 3-side power, which is each phase current, is a reverse current (reverse direction), a 1-side reverse current state display portion displayed as "1" or "3" The 22a or 3 side reverse current state display part 22b is turned on. Each phase reverse current state display unit 22 includes the 1-side reverse current state display unit 22a and the 3-side reverse current state display unit 22b.

  FIG. 3 is a block diagram showing the configuration of the electronic watt-hour meter 100. As shown in FIG. 3, the electronic watt-hour meter 100 includes an electronic watt-hour meter block 50 connected to an electric circuit and a state display unit 60 connected to the electronic watt-hour meter block 50. The electronic watt-hour meter block 50 includes a voltage detection unit 1, a current detection unit 2, each phase power calculation unit 3, an all-phase power amount calculation unit 4, an all-phase power direction determination unit 5, and a reverse direction energy counter 6a. The built-in reverse current level monitoring unit 6, each phase power direction discriminating unit 8, and each phase reverse current display control unit 9 are included, and the status display unit 60 includes an all-phase current status display unit 21, each phase reverse current status. The display unit 22 is included.

Although Embodiment 1 describes the case where the phase wire system is a three-phase three-wire system, the same applies to a single-phase three-wire system.
The voltage detection unit 1 inputs the 1 side voltage and the 3 side voltage from the electric circuit, transforms the voltage to an appropriate voltage, and transmits a digital value obtained by A / D conversion to each phase power calculation unit 3.
Similarly, the current detection unit 2 inputs the 1 side current and the 3 side current from the electric circuit, converts the current to voltage, transforms it to an appropriate voltage, and then calculates the digital value obtained by A / D conversion for each phase power calculation. Send to part 3.

  Each phase power calculation unit 3 inputs the digital value of the 1 side voltage and 3 side voltage that are the output of the voltage detection unit 1 and the digital value of the 1 side current and 3 side current that is the output of the current detection unit 2. Multiply the side voltage and the 1-side current to calculate the 1-side power, and multiply the 3-side voltage and the 3-side current to calculate the 3-side power. Further, by removing a frequency twice the power supply frequency through a low-pass filter (not shown), the 1-side power and the 3-side power are stabilized. Here, the result of multiplying the voltage and the current is a positive value when each phase power is in the forward direction, and a negative value when the phase power is in the reverse direction.

The all-phase power amount calculation unit 4 inputs and adds the 1-side power and the 3-side power calculated by each phase power calculation unit 3, sets the total value as all-phase power, and adds the values to all-phase power. Calculate the amount. Actually, it has a counter unit that accumulates all phase power and counts once when a preset threshold value is exceeded, and calculates the total phase power amount by the increment of the count value. .
The all-phase power direction discriminating unit 5 discriminates whether the all-phase power calculated by the all-phase power amount calculating unit 4 is the forward direction, no load, or the reverse direction. The all-phase display part (reverse current) 21a in the current state display part 21 is turned on.

  The reverse current level monitoring unit 6 includes a reverse power amount counter unit 6a that counts in proportion to the total phase power amount when the determination result of the all phase power direction determination unit 5 is in the reverse direction. Every time the count value increases by a fixed value (predetermined value) determined in advance by 6a, the all-phase display portion (reverse current) 21a is temporarily turned off (predetermined time).

  FIG. 4 is an example of a time chart showing the on / off state of the all-phase current state display unit 21. FIG. 4 shows that the all-phase power direction determination unit 5 determines one of “forward direction (operation)”, “no load”, and “reverse direction (reverse current)”, and reverse power The quantity counter unit 6a and the all-phase reverse current state display unit (all-phase display unit (reverse current)) 21a indicate that they operate only when the determination result of the all-phase power direction determination unit 5 is “reverse direction”. .

  When the discrimination result of the all-phase power direction discriminating unit 5 is in the reverse direction, the reverse-direction power amount counter unit 6a in the reverse current level monitoring unit 6 counts in proportion to the all-phase power amount, and the magnitude of the all-phase power amount is large. When the count value reaches a fixed value (500 in the example of FIG. 4) determined in advance, a signal indicating that is transmitted to the reverse current level monitoring unit 6. At the same time, the count number is reset to 0 and counting is started again.

  The reverse current level monitoring unit 6 inputs a signal from the reverse power amount counter unit 6a indicating that the count number has reached a predetermined fixed value, and temporarily displays the all-phase display unit (reverse current) 21a. Turns off. After that, the reverse current level monitoring unit 6 keeps the all-phase display unit (reverse current) 21a off for a fixed time (250 ms in FIG. 4) determined in advance. Control to light up. By this process, when the all-phase power is in the reverse direction, the all-phase display part (reverse current) 21a can be blinked at a speed corresponding to the degree of the reverse direction, and the operator visually recognizes the degree of the reverse direction. be able to.

  Here, suppose that after turning off the all-phase display section (reverse current) 21a, the process is turned on again when the count value of the fixed value determined in advance by the reverse power amount counter section 6a increases again. When installed in a load state in which the all-phase power is slightly in the reverse direction, the number of counts in the reverse power amount counter unit 6a increases very slowly and the turn-off time becomes long. There are many timings at which it cannot be identified that the direction is reverse, which may lead to misrecognition. In order to avoid this, the extinguishing time is set to a fixed time determined in advance.

  When the determination result of the all-phase power direction determination unit 5 is in the reverse direction, the electronic watt-hour meter 100 of the present invention repeats the series of operations described above, and the determination result of the all-phase power direction determination unit 5 indicates the forward direction or no load. In this case, the display mode of the all-phase display unit (reverse current) 21a is turned off, and the reverse mode, such as the measurement in the reverse power counter 6a and the measurement of the fixed time determined in advance, etc. The processing necessary for displaying is terminated.

  In the above-described example, the fixed value determined in advance of the reverse power amount counter unit 6a is 500, and is cleared to 0 when the fixed value determined in advance is reached. However, the reverse power amount counter unit Since it is important that the count value of 6a has increased by a fixed value determined in advance, it is not necessary to clear 0, and the next fixed value may be counted as 1000 (an integral multiple of the fixed value).

  Further, the length of the fixed time for turning off the all-phase display portion (reverse current) 21a needs to be a length that can be recognized by the operator's eyes, so it is considered that about 100 ms or more is desirable. I can say that.

  Since the electronic watt-hour meter 100 of the present invention is a standard for payment of electricity charges, it takes a certification test. A measurement pulse is output from the watt-hour meter for the verification test, and the verification test is performed by measuring an error using the measurement pulse. The metering pulse is adjusted so that it is output at about 1000 Hz when the all-phase power is the rated power.

  The reverse current power amount counter unit 6a counts up when a measurement pulse is output, and increases at about 1000 Hz when all phase power is rated power, for example, counts a fixed value (500) in 0.5 seconds. Assuming that the light is turned off for a fixed time (250 ms) every time the fixed value (500) is counted, when the measurement pulse is 1000 Hz, the light is turned off repeatedly for 250 ms and 250 ms for lighting. Here, precisely, the metering pulse has a width between 822.7 and 1200 Hz.

If the reverse current power amount counter unit 6a does not count the fixed value (500) in 0.5 seconds, but instead counts the fixed value at an interval shorter than 250 ms, which is the fixed time for turning off, the light is turned off. Since time is continuous, it is conceivable that the display of the all-phase display part (reverse current) 21a cannot be blinked even if the all-phase current is in the reverse direction. However, in order to count the fixed value (500) at intervals shorter than 250 ms, the measurement pulse is considered to be 2000 Hz or more, and the actual measurement pulse is 1200 Hz at the maximum as described above. If set to (500), it is considered that the turn-off time will not continue.
In any case, a fixed value (predetermined value) that is counted so that the fastest flashing state is predicted to turn off the fixed time and turn on for a fixed time that can be visually confirmed. And the fixed time of turning off and turning off shall be set.

  In addition, if the speed is set to flash once per second at rated power, the number of flashes is small (flashing speed is slow) and it is difficult for the operator to observe the display state. It is desirable to set it so that it is displayed at the speed of flashing once. In this case, the time required for one flashing is set to 500 ms, the lighting and extinguishing times are set to 1: 1, and the extinguishing fixed time is set to 250 ms. As described above, since the actual measurement pulse value is 822.7 to 1200 Hz, the interval for counting the fixed value (500) is 416 ms to 608 ms, and when the extinguishing fixed time is 250 ms, the lighting time is necessary for visual observation. 100 ms or more can be secured, and the worker can easily check the blinking state of the display unit.

Next, the display of the direction of each phase power will be described.
Each phase power direction determination unit 8 determines whether the direction of each phase power calculated by each phase power calculation unit 3 is a forward direction or a reverse direction.
Each phase reverse current display control unit 9 inputs the determination result of each phase power direction determination unit 8 and controls each phase reverse current state display unit 22 that displays the state of each phase power.

  Each phase reverse current display control unit 9 follows the determination result of each phase power direction determination unit 8 when the determination result of the all phase power direction determination unit 5 is in the reverse direction, and 1 side when the one side power is in the reverse direction. The reverse current state display unit 22a is turned on, and when the 3-side power is in the reverse direction, the 3-side reverse current state display unit 22b is turned on.

  In addition, each phase reverse current display control unit 9 is configured such that when the determination result of the all-phase power direction determination unit 5 is the forward direction and no load, each phase power direction determination unit 8 is in the reverse direction. When the absolute value of the calculation result of the phase power calculation unit 3 is smaller than a predetermined value determined in advance, each phase reverse current state display unit 22 is controlled to be turned off. For example, if the determination result of each phase power direction determination unit 8 indicates that the direction of the 1 side power is the forward direction and the direction of the 3 side power is the reverse direction, but the 3 side power is smaller than the predetermined value determined in advance, The reverse current display control unit 9 does not light the 3-side reverse current state display unit 22b. In this way, by not displaying the minute each phase reverse current, the operator can confirm only the important display, so that the work efficiency is improved.

  FIG. 5 is a diagram showing a list of lighting and extinguishing states of each phase reverse current state display unit 22. Each phase reverse current display control unit 9 inputs the determination result of each phase power direction determination unit 8 and the all phase power direction determination unit 5, and turns on / off each phase reverse current state display unit 22 as shown in FIG. Control the state.

Next, taking the case of a three-phase three-wire system, a balanced load, and a power factor of 1 as an example, the display of the all-phase current state display unit 21 and each phase reverse current state display unit 22 A case where the connection side and load side are mistakenly connected will be described.
In this case, the calculation result of each phase power calculation unit 3 is in the reverse direction because the 1-side power is misconnected, and the 3-side power is in the forward direction because of normal connection. Here, since the balanced load and the power factor are 1, the 1 side power is in the reverse direction, so it is a negative value, and the 3 side power is in the forward direction, it is a positive value, and their absolute values are equal.

The all-phase power amount calculation unit 4 inputs and adds 1-side power and 3-side power, and integrates the values of all-phase power as 0. Therefore, the total phase power amount does not change.
The all-phase power direction discriminating unit 5 inputs the calculation result of the all-phase power amount calculating unit 4 and sets the discrimination result to no load.
In the all-phase current state display unit 21, since the determination result of the all-phase power direction determination unit 5 is no load, the all-phase display unit (reverse current) 21a is turned off and the all-phase display unit (no load) 21b is turned on. .

Each phase power direction discriminating unit 8 receives the calculation result of each phase power calculating unit 3 and discriminates that the 1 side power is the reverse direction and the 3 side power is the forward direction.
Each phase reverse current display control unit 9 inputs the discrimination result of each phase power direction discrimination unit 8, and when the absolute value of the one-side power is larger than a predetermined value, each phase reverse display that displays the state of each phase power The 1 side reverse current state display part 22a of the current state display part 22 is turned on, and the 3 side reverse current state display part 22b is turned off.
Conversely, when the absolute value of the 1-side power is smaller than the predetermined value, the 1-side reverse current state display unit 22a is turned off and the 3-side reverse current state display unit 22b is turned off.

Usually, the value determined in advance as the threshold value of each phase power is set to be considerably smaller than the rated power of each phase at the rated voltage and rated current of the electronic watt-hour meter 100.
For example, when the connection is normal and the determination result of the all-phase power direction determination unit 5 is no load, the actual phase power is a value close to 0 for both the 1-side power and the 3-side power. However, the data of each phase power may remain in the forward direction (positive value) and the reverse direction (negative value) because the data fluctuation remains after averaging. In such a case, as shown in FIG. 5, the on / off state of each phase reverse current state display unit 22 is controlled to eliminate the data fluctuation as described above. Control is performed so that the current state display unit 22 is not lit.

  Similarly, when the connection is normal and the discrimination result of the all-phase power direction discriminating unit 5 is the forward direction, the all-phase power obtained by adding the actual phase powers is the forward direction, so that each phase power can be ignored. In such a small reverse direction, control is performed so that each phase reverse current state display unit 22 is not lit. On the other hand, when each phase power is in a reverse direction that cannot be ignored, there is a possibility of a connection error, so that each phase reverse current state display unit 22 is controlled to be lit.

  FIG. 5 shows a case where the discrimination result of the all-phase power direction discriminating unit 5 is “reverse direction” in each phase power direction (1 side power: forward direction) and (3 side power: forward direction). However, if both 1 side and 3 side are forward, all phase power is always forward, and if the absolute value is large, it is judged as “forward”, and if close to 0, “no load” is judged. Is not an actual operation. Therefore, each display of each phase reverse current state display unit 22 is “off”. Even when each phase power direction is the reverse direction and the determination result of the all-phase power direction determination unit 5 is “forward direction”, the operation is not actually performed, and each display of each phase reverse current state display unit 22 “Lights off”.

  Note that the “no-load” state determined by the all-phase power direction determining unit 5 indicates a case where the all-phase power takes a value near 0 as well as when the all-phase power is 0. Therefore, there is a case where both the 1-side power and the 3-side power are minute reverse currents, and the all-phase power is “no load”, and each phase reverse current state display unit 22 sets each display to “off”.

  Further, each phase reverse current display control unit 9 operates by assuming that the 3-side power (or 1-side power), which is an unnecessary phase, is always in the forward direction when the phase wire system is a single-phase 2-wire system. As a result, the three-phase reverse current state display unit 22b (or the one-side reverse current state display unit 22a) of the unnecessary phase is not turned on, and the single-phase two-wire is not changed without changing the operations shown in the list of FIG. It can be used corresponding to the equation.

  As described above, according to the first embodiment of the present invention, the operator who installs the electronic watt-hour meter 100 can change the display state of the all-phase display unit (reverse current) 21a of the all-phase current state display unit 21. The presence / absence of the reverse direction of all-phase power and the degree thereof can be recognized, and each phase reverse current state display unit 22 can recognize the phase in the reverse direction. It is possible to obtain more than the electronic watt-hour meter, and there is an effect that the location of the connection mistake can be identified early.

  Further, in the above-described example, the blinking display of the all-phase display unit (reverse current) 21a is blinked so that it is extinguished for a fixed time (for example, 250 ms) every time the reverse power amount counter unit 6a counts a fixed value. However, the lighting time and the light-off time are 1: 1 at the rated power, and it is also possible to set the fixed time that can secure the visible lighting or light-off time. Even in this case, the operator can easily confirm the presence or absence and the degree of reverse current of all-phase power by the blinking speed displayed by the all-phase display unit (reverse current) 21a.

  Further, in the display example of the all-phase display portion (reverse current) 21a shown in FIG. 2, "reverse current" is written in one square display space, and the characters "reverse current" are indicated according to the degree of reverse current. In addition to that, the display blinks so as to repeatedly turn on and off, but in addition to this, the display space of the all-phase display part (reverse current) 21a is divided into several parts so that a bar can be displayed, and the degree of reverse current By controlling the display state so as to increase the display space to be lit as the power increases, the worker can easily check the presence and degree of the reverse current of the all-phase power. In addition, it is possible to adopt a configuration capable of multicolor display so that the presence / absence and degree of the all-phase display portion (reverse current) 21a can be identified by the color to be lit, such as bar display and multicolor display. It is also possible to use the above-mentioned blinking display in combination.

  In the above-described example, the degree of reverse current is displayed on the all-phase display unit (reverse current) 21a so that the degree is large when the blinking speed is fast and small when it is slow. However, the display state of the 1-side reverse current state display unit 22a or the 3-side reverse current state display unit 22b of each phase reverse current state display unit 22 is not only turned on when the reverse current is present, As in the case of the all-phase display section (reverse current) 21a, it is also possible to add a function indicating the degree of current by the blinking speed. Needless to say, the status of the electronic watt-hour meter 100 can be displayed.

It is an external appearance perspective view of the electronic watt-hour meter in Embodiment 1 of this invention. 3 is an enlarged view showing a display panel of the electronic watt-hour meter according to Embodiment 1. FIG. 1 is a block diagram illustrating a configuration of an electronic watt-hour meter according to Embodiment 1. FIG. FIG. 4 is a diagram illustrating a time chart representing the operation of the electronic watt-hour meter according to the first embodiment. FIG. 4 is a diagram showing a list representing operations of the electronic watt-hour meter in the first embodiment.

Explanation of symbols

1 voltage detector 2 display panel,
3 Each phase power calculation section 4 Each phase power calculation section,
5 All-phase power direction discriminator 6 Reverse current level monitor
6a Reverse current energy counter unit 8 Each phase power direction discriminating unit,
9 Each phase reverse current display controller 20 Display panel,
21 All-phase current status display section 22 Each phase reverse current status display section,
21a All-phase reverse current status display (all-phase display (reverse current)),
21b All-phase no-load status display (all-phase display (no load)),
21c All-phase operation status display section (all-phase display section (operation)),
22a 1 side reverse current state display part 22b 3 side reverse current state display part,
100 Electronic watt-hour meter.

Claims (8)

  All-phase power calculation unit that calculates all-phase power by calculating all-phase power from the voltage value and current value of the circuit, and summing up all-phase power, and all-phase power direction that determines the direction of all-phase power When the discrimination result of the discrimination unit, the all-phase reverse current state display unit that displays that the direction of the all-phase power is in the reverse direction, and the all-phase power direction discrimination unit is in the reverse direction, the magnitude of the all-phase power amount An electronic watt-hour meter comprising a reverse current level monitoring unit for monitoring the display and controlling the display state of the all-phase reverse current state display unit according to the magnitude of the all-phase electric energy.   The reverse current level monitoring unit includes a reverse power amount counter unit that counts up in proportion to the total phase power amount, and the all-phase reverse current when the determination result of the all-phase power direction determination unit is in the reverse direction. 2. The state display unit is turned on, and each time the reverse power amount counter unit counts a predetermined value, the all-phase reverse current state display unit is temporarily turned off to blink. The electronic watt-hour meter as described.   The predetermined value of the reverse power amount counter unit is adjusted so that the blinking off time of the all-phase reverse current state display unit is a predetermined time, and the lighting state is turned on after the predetermined time has elapsed. The electronic watt-hour meter according to claim 2.   Each phase power calculation unit for calculating each phase power based on the voltage value and current value of the electric circuit, each phase power direction determination unit for determining the direction of each phase power calculated by each phase power calculation unit, Each phase reverse current state display unit for displaying the phase power state, and each phase reverse current display control unit for inputting the determination result of each phase power direction determination unit and controlling the display state of each phase reverse current state display unit The electronic watt-hour meter as described in any one of Claims 1-3 characterized by the above-mentioned.   Each phase reverse current display control unit, when the determination result of the all-phase power direction determination unit is forward or no load, even if the determination result of each phase power direction determination unit is the reverse direction, 5. The electronic watt-hour meter according to claim 4, wherein when the absolute value of the calculation result of the power calculation unit is smaller than a predetermined value, control is performed so as not to display each phase reverse current state display unit.   2. Each phase reverse current state display part is comprised by the 1 side reverse current state display part showing the direction of 1 side electric power, and the 3 side reverse current state display part showing the direction of 3 side electric power, It is characterized by the above-mentioned. 4. Electronic watt-hour meter according to 4.   When each phase reverse current display control unit is a three-phase three-wire type or a single-phase three-wire type, the 1-side power or the 3-side power is in the reverse direction. The electronic watt-hour meter according to claim 6, wherein control is performed so that the side reverse current state display unit or the three side reverse current state display unit is lit.   Each phase reverse current display control unit uses the one-side reverse current state display unit or the three-side reverse current state display unit when the phase wire type of the circuit is a single-phase two-wire type. 7. The electronic watt-hour meter according to claim 6, wherein a direction is displayed, and the three-side reverse current state display unit or the one-side reverse current state display unit is controlled to be always turned off.

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