TW201500741A - Three-phase four-wire power meter - Google Patents

Abstract

The present invention provides a three-phase four-wire power meter, comprising: a current detection unit, which measures an R-phase current Ir, an S-phase current Is, a T-phase current It, and an N-phase current In respectively flowing in a R-phase distribution wire, an S-phase distribution wire, a T-phase distribution wire, and an neutral wire; and a bypass tampering detection means, which determines occurrence of the bypass tampering when the absolute value of the difference between the absolute value obtained by vector synthesizing the R-phase current, S-phase current and T-phase current, and the N-phase current absolute value exceeds a predetermined threshold value, while the phase difference between each of the R-S phase, S-T phase, T-R phase is regarded as 120 DEG.

Description

Three-phase four-wire fuel gauge

The present invention relates to a three-phase four-wire fuel gauge for measuring electric power and the like, and more particularly to a tampering detection function.

In the fuel gauge, a smart meter belonging to a fuel gauge having a communication function and a load opening and closing function is taken as an example. A smart meter is installed in a power demand location (home, factory, etc.) by a power supplier such as a power company to measure and measure the amount of electricity or current used. Since abnormal wiring is applied to the smart meter after the setting, there is a power-cutting (tampering) behavior that masks the amount of electricity used and reduces the amount of electricity requested. In the bypass tampering of one of the tampering methods, the conventional smart meter measures the current connected to the upstream side and the downstream side of the distribution line of the smart meter, and detects tampering by the difference of one dimension (see, for example, Patent Document 1).

(previous technical literature) (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-203926

In the case of a single-phase circuit, although by the upstream side and the lower side of the distribution line In the case of a three-phase four-wire circuit, since there is a phase difference between the phases, the calculation of the first-order one of the prior art cannot be performed, and phase detection is required. However, when phase detection is performed, there is a problem that the processing of the arithmetic software is complicated.

The present invention has been made in view of the above problems, and an object thereof is to provide a three-phase four-wire fuel gauge which has a detection function of bypass tampering without performing phase detection.

The present invention is a three-phase four-wire fuel gauge for measuring the amount of electricity used, and includes: a current detecting unit that measures R-phase currents Ir, S flowing through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutral line, respectively. Phase current Is, T phase current It, N phase current In; and bypass tamper detecting means, the phase difference between the RS phase, the ST phase, and the TR phase is regarded as 120°, respectively, and the R phase detected by the current detecting unit When the absolute value of the difference between the absolute value of the vector synthesis of the current, the S phase current, and the T phase current and the absolute value of the N phase current exceeds a predetermined threshold, it is determined that the bypass falsification is generated.

Furthermore, the present invention is directed to a three-phase four-wire fuel gauge for measuring the amount of electricity used, and includes: a current detecting unit that measures R-phase currents flowing through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutral line, respectively. Ir, S-phase current Is, T-phase current It, N-phase current In; the memory unit memorizes the R-phase current Ir, the S-phase current Is, the T-phase current It before the bypass tampering measurement measured by the current detecting unit, The N-phase current In; and the bypass tamper detecting means are one of the R-phase distribution line, the S-phase distribution line, and the T-phase distribution line before and after the time point of determining the bypass tampering of the phase current measured by the current detecting unit. When the phase current has a larger change than the first predetermined threshold, When the N-phase current change of the neutral line is smaller than the second predetermined threshold value, it is determined that the bypass tampering has occurred.

Furthermore, the present invention is directed to a three-phase four-wire fuel gauge for measuring the amount of electricity used, and includes: a current detecting unit that measures R-phase currents flowing through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutral line, respectively. Ir, S-phase current Is, T-phase current It, N-phase current In; the memory unit memorizes the R-phase current Ir, the S-phase current Is, the T-phase current It before the bypass tampering measurement measured by the current detecting unit, The N-phase current In; and the bypass tamper detecting means, the phase difference between the RS phase, the ST phase, and the TR phase is regarded as 120°, respectively, when the R phase current, the S phase current, and the T phase current detected by the current detecting unit are When the absolute value of the difference between the absolute value obtained by vector synthesis and the absolute value of the N-phase current exceeds a predetermined threshold value, and before and after the time point of determining the bypass tampering of the phase current measured by the current detecting portion, When any of the phase currents of the R-phase distribution line, the S-phase distribution line, and the T-phase distribution line is larger than the second predetermined threshold, and the change in the N-phase current of the neutral line is smaller than the third predetermined threshold Next, it is determined that a bypass tampering has occurred.

According to the three-phase four-wire fuel gauge of the present invention, a three-phase four-wire fuel gauge having a bypass tampering detection function without phase detection can be provided.

Other objects, features, aspects and advantages of the present invention will become apparent from the Detailed Description of the invention.

1‧‧‧ Current Detection Department

2‧‧‧Opening and closing department

3‧‧‧Voltage detection department

4‧‧‧Communication Department

5‧‧‧ Calculation Control Department

6‧‧‧Display Department

7‧‧‧Memory Department

10‧‧‧Three-phase four-wire smart meter

1(a) and (b) are views showing a three-phase four-wire smart electric power according to Embodiment 1 of the present invention. A diagram of the detection principle of the bypass modification of the table.

Fig. 2 is a block diagram showing the internal circuit configuration of a three-phase four-wire smart meter according to the first embodiment of the present invention.

Fig. 3 is a flow chart showing the bypass tampering detection sequence of the three-phase four-wire smart meter according to the first embodiment of the present invention.

Fig. 4 is a flow chart showing the bypass tampering detection procedure of the three-phase four-wire smart meter according to the second embodiment of the present invention.

Fig. 5 is a flow chart showing the bypass tampering detection sequence of the three-phase four-wire smart meter according to the third embodiment of the present invention.

Embodiment 1

In the three-phase four-wire fuel gauge, a three-phase four-wire smart meter belonging to a fuel gauge having a communication function and a load opening and closing function is taken as an example. Fig. 1 is a view showing the principle of detection of bypass tampering of the three-phase four-wire smart meter according to the first embodiment of the present invention, and Fig. 1(a) shows the normal state without bypass tampering, Fig. 1(b) The system displays the bypass tampering. Fig. 2 is a block diagram showing the internal circuit configuration of the three-phase four-wire smart meter of the first embodiment. In the first diagram, the currents Ir, Is, It, and In are the R-phase distribution lines, the S-phase distribution lines, the T-phase distribution lines, and the neutral line (neutral distribution lines) that respectively flow through the connection power source (Y wiring) and the smart meter. The R phase current, the S phase current, the T phase current, and the N phase current of the vector. The 1S, 2S, 3S, and 0S of the smart meter are connected to the power supply side distribution line and the neutral line terminal, and the 1L, 2L, 3L, and 0L are connected to the load side distribution line and the neutral line terminal. In Ir, Is, It, and In, Δt is a time zone in which a current changes. In addition, in the following, the tampering system is set to appear as a bypass tamper.

Regarding the detection principle during tampering, one side is referred to the first figure. Description. In the three-phase four-wire circuit, when the direction of the arrow shown in Fig. 1 is set to the positive direction of the current, the vector sum of the phase currents of the normal (a) is as follows.

Ir+Is+It=In-----I

On the other hand, an example in which tampering occurs in the R phase will be described. When tampering occurs, the current Ir flowing through the R phase flows through the bypass portion to the inside of the three-phase four-wire smart meter, and is shunted into the current Ira (vector) to be measured and distributed to the outside of the smart meter (bypass). The current Irb (vector) is therefore as shown below.

Ir=Ira+Irb-----II

According to the type II, the current Ira flowing to the inside of the three-phase four-wire smart meter will reduce the Irb share compared with the normal time, so the amount of electricity measured by the three-phase four-wire smart meter will also become smaller, and the place is needed ( The electricity bill paid by the family or factory, etc., will be abnormally reduced.

The first embodiment will be described with reference to the second and third drawings. The three-phase four-wire smart meter of the first embodiment is not only a function of a smart meter, but also a measurement, measurement, and opening and closing of a power supply or a consumed power of a required place (home or factory). In addition to the communication function, and the tamper detection function, the detected tamper information is transmitted to the data concentrator by the communication function, and can be further transmitted from the data concentrator to the upper device.

Fig. 2 is a block diagram showing the internal circuit configuration of the three-phase four-wire smart meter of the first embodiment. 10 is a three-phase four-wire smart meter. The current detecting unit 1 is configured by a current transformer, a shunt resistor, or the like, and detects an R-phase current Ir, an S-phase current Is, a T-phase current It, and an N-phase current In, and converts them into a low-level electric motor proportional to the current thereof. The signal is output to the arithmetic control unit 5 inside the electric meter. In electricity The stream detecting unit 1 detects a vector (instantaneous value) of each phase and outputs it to the arithmetic control unit 5. The voltage detecting unit 3 is configured by a voltage transformer, a voltage dividing resistor, or the like, and detects an R-phase voltage Vr-n, an S-phase voltage Vs-n, and a T-phase voltage Vt-n based on the N-phase (that is, The inter-RN voltage, the inter-SN voltage, and the TN voltage are converted into an electric signal having a low level proportional to the voltage, and output to the arithmetic control unit 5 inside the electric meter. The voltage detecting unit 3 detects a vector (instantaneous value) of each phase, and outputs it to the calculation control unit 5.

In the calculation control unit 5, the calculation of the accumulated electric power consumption of the required location or the accumulation of the electric power consumption in the time zone of each time zone, the detection of tampering (detection by the bypass tampering detection means), and the like are performed. The cumulative electricity usage of the required location is obtained by Σ[[[Vr-n]×[Ir]+[Vs-n]×[Is]+[Vt-n]×[It]]×t]. Among them, [Vr-n], [Vs-n], [Vt-n], [Ir], [Is], [It] are the instantaneous values of the electrical quantity, and t is the time.

The smart meter 10 has an opening and closing unit 2 that opens and closes a circuit for a load by a signal from the arithmetic control unit 5. By the opening and closing unit 2, when the inhabitant stays in and out, the lock is opened to the circuit of the load. Also, when power requires all abnormal behavior of the field, the circuit for the load is opened. The smart meter 10 further includes a memory unit 7, a display unit 6, and a communication unit 4. The memory unit 7 has a first in first out table (FIFO table), and the R phase current Ir, the S phase current Is, the T phase current It, and the N phase current are obtained by the signal from the calculation control unit 5. In memory is about 4 times of 100m Sec. The memory unit 7 also stores measurement information such as various events such as tampering information or accumulated power usage of the place. The display unit 6 displays a measurement value such as a cumulative use amount of the required location, tampering information, and the like on the display. The communication unit 4 is connected to the R-phase distribution line, the S-phase distribution line, and the T phase, for example, by performing power line transmission communication. The distribution line and the N-phase distribution line are connected, exchange information with the calculation control unit 5, connect the accumulated power usage or tampering information with the host device, and receive a signal (instruction) from the host device.

As shown in Fig. 1, if the current flowing through the inside of the smart meter, for example, the R phase bypass is set to Ira, the normal (a) and the tampering (b) flow to the inside of the smart meter. The relationship between the phase currents is expressed by the following equation.

Normal ‧‧‧Ir+Is+It-In=0‧‧I’

‧‧‧Ira+Is+It-In≠0‧III

According to the difference between I' and III, the detection system can detect tampering by detecting the phase of each phase current and performing vector synthesis. However, when phase detection is performed, the processing of the calculus software will be rectified. The problem. Therefore, in the smart meter of the first embodiment, the tampering detection is performed without performing phase detection.

Fig. 3 is a flow chart showing the bypass tampering detection sequence of the three-phase four-wire smart meter according to the first embodiment of the present invention. The phase difference between the phases of the three-phase four-wire circuit (between RS, ST, and TR) is usually 120°, so phase detection is not performed, and the phase difference between the above phases is regarded as 120°, and it is determined that R is Whether the absolute value of the difference between the absolute value of the phase current, the S phase current, and the T phase current and the absolute value of the N phase current is larger than the predetermined threshold D1 (step S11). Further, the predetermined threshold D1 is set, for example, to about several % of the phase current for normal use.

That is to determine whether it is | | Ir+Is+It |-| In | |>D1-----IV. When the IV formula is not established, the starting point is returned, and step S11 is repeatedly executed and the determination is made. The reverse period is, for example, about 100 msec. When the IV formula is established, it is determined that tampering has occurred (step S12).

Further, when it is determined that tampering has occurred, the tampering display LED or LCD (Liquid Crystal Display) of the display unit 6 is turned on. Then, the communication unit 4 associates with the host device to generate an event (tampering) (step S13).

Further, according to the equations I and II, as shown in the following equation, for example, the tampering current Irb at the time of the R-phase bypass can be calculated.

| Irb |=| | Ira+Is+It |-| In | |-----V

Where Ira is the measured current of the R-phase distribution line detected by the current detecting unit 1 during the bypass tampering, | Ira+Is+It| is the absolute value obtained by vector-combining Ira, Is, and It, | In | The absolute value of the N-phase current.

At this time, phase detection is not performed, and the phase difference between the phases (between RS, ST, and TR) is regarded as 120°, and the absolute phase is obtained by vector-combining the R phase current, the S phase current, and the T phase current. The absolute value of the difference between the value and the absolute value of the N-phase current is obtained. Since the tampering current Irb can be calculated by the V formula, the tampering cumulative electric quantity can be calculated by Σ[[Vr-n]×[Irb]×t] (step S14), and can be used as a need for the power supplier. The reference value of the shortage request of the place, etc. Where [Vr-n] is the instantaneous value of the voltage Vr-n of the R-phase distribution line with the N-phase as a reference, [Irb] is the instantaneous value of Irb, and t is the occurrence time of tampering.

As described above, the detection of tampering can also be performed without phase detection, and the detected information can be notified to the upper position by the communication function of the smart meter. Furthermore, it is possible to grasp the location and phase of the tamper-evident smart meter in the upper position, and to reduce the local working time. Furthermore, the load can be interrupted by the opening and closing function of the smart meter according to the command from the upper position or the setting of the smart meter.

Embodiment 2

Figure 4 is a view showing the side of the three-phase four-wire smart meter according to the second embodiment of the present invention. The flow chart of the detection sequence is changed. The change of each phase current at the time of occurrence of tampering will be described with reference to Fig. 1 . According to the I formula, since the current In flowing to the N phase depends on the current flowing to the R phase, the S phase, and the T phase, In the normal state (a), for example, if the current Ir flowing to the R phase changes, In also changes. . However, the shunt caused by (b) during tampering occurs only at the tampering site, and the current flowing to the distribution line does not change, so In does not change.

Therefore, in the second embodiment, the current detecting unit 1 performs measurement, and the R-phase current Ir, the S-phase current Is, the T-phase current It, and the N-phase current In before the tampering determination are respectively stored in the memory unit 7. As shown in FIG. 4, before determining the time point of the bypass tampering of the phase current measured by the current detecting unit 1, the phase current of any of the R phase distribution line, the S phase distribution line, and the T phase distribution line has a predetermined ratio. The limit value E2 is greatly changed (step S21), and at this time, the change in the N-phase current flowing to the neutral line is smaller than the predetermined threshold F2 (step S22), and it is determined that the bypass tampering has occurred. The predetermined thresholds E2 and F2 are set, for example, to about several percent of the phase current used in normal use.

If it is explained in detail, in Fig. 4, | Ir |-| Ira |>E2,| Is |-| Isa |>E2,or | It |-| Ita |>E2-----VI

When the above formula is not satisfied in any of the R phase, the S phase, and the T phase, the process returns to the starting point, and step S21 is repeatedly performed. The reverse period is, for example, about 100 msec. Further, the phase currents Ir, Is, It, and In belonging to the vector in which the R phase, the S phase, the T phase, and the N phase before the tampering determination are transmitted are measured by the current detecting unit 1 and are controlled by the calculation control unit 5 at 100 m Sec. The period of about four times is stored in the memory unit 7. The phase current belonging to the vector in which the R phase, the S phase, the T phase, and the N phase are circulated after the tampering determination (at the time of determination) The phase currents Ira, Isa, Ita, and In to the inside of the electricity meter are measured by the current detecting unit 1, and are input to the calculation control unit 5.

If the above equation is established in any of the R phase, the S phase, and the T phase (step S21), it is determined in step S22 whether it is | | Ina |-| In | |<F2-----VII, If it is established, it is determined that tampering has occurred (step S23).

When it is determined that tampering has occurred, the tampering display LED or LCD (liquid crystal display) of the display unit 6 is turned on. Then, the communication unit 4 associates with the host device to generate an event (tampering) (step 24).

Further, in step S22, if | | Ina | - | In | | < F2 is not established, the starting point is returned, and step S21 is repeated.

Embodiment 3

Fig. 5 is a flow chart showing the bypass tampering detection procedure of the three-phase four-wire smart meter according to the second embodiment of the present invention. In the first embodiment and the second embodiment, the following advantages and disadvantages are obtained as described below.

Embodiment 1:

Advantages: Since the phase currents of the R phase, the S phase, and the T phase are vector-combined, it is also possible to correspond to a change in current due to load fluctuations generated by the respective phases.

Disadvantage: Since the phase difference between the phases is set to 120°, the vector composite value and the actual load current in step S11 of FIG. 3 are caused when the phase difference is different due to the load connected to each phase. Vector composite values can make a difference, even in the case of a normal connection, there is a possibility of erroneous detection.

Embodiment 2:

Advantages: Since the currents of the phases are monitored, they do not depend on the phase between the phases. Poor, can be monitored for tampering.

Disadvantages: Since the N-phase current changes when the currents of the phases of the R phase, the S phase, and the T phase change, the R phase, the S phase, and the T phase are each in an environment in which a current change due to a load fluctuation occurs. The change in phase current and the change in current of the N phase occur at the same time, and even in the case of normal connection, there is a possibility of erroneous detection of tampering.

Therefore, by using the combination of the first embodiment and the second embodiment as in the detection sequence of Fig. 5, the disadvantages of the first embodiment and the second embodiment can be compensated for, and the detection accuracy of the tampering can be improved.

In Fig. 5, phase detection is not performed, and the phase difference between the phases is regarded as 120°, and the absolute value of the vector of the R phase current, the S phase current, and the T phase current is determined to be the absolute value of the N phase current. Whether the absolute value of the difference is larger than the predetermined threshold D3 (step S31). The predetermined threshold D3 is set to, for example, about several percent of the phase current to be used normally. That is, it is determined whether or not | | Ir+Is+It |-| In | |>D3-----IV If the IV formula is not satisfied, the starting point is returned, and step S31 is repeatedly performed and determined. The reverse period is, for example, about 100 msec.

If the formula IV holds, in step S32, | Ir |-| Ira |>E3,| Is |-| Isa |>E3,or | It |-| Ita |>E3-----VI

When the above equation is not satisfied in any of the R phase, the S phase, and the T phase, the starting point is returned, and the process proceeds from step S31. The reverse period is, for example, about 100 msec. In addition, the R phase, the S phase, the T phase, and the N phase before the tampering are categorized by the vector. The phase currents Ir, Is, It, and In are measured by the current detecting unit 1 and are stored in the memory unit 7 via the calculation control unit 5 for about four times 100 m Sec. The phase current belonging to the vector in which the R phase, the S phase, the T phase, and the N phase are circulated after the tampering determination (at the time of determination), and the phase currents Ira, Isa, Ita, and In flowing through the inside of the electric meter are detected by the current detecting unit 1 The measurement is performed and input to the calculation control unit 5.

If the above formula holds in any of the R phase, the S phase, and the T phase (step S32), it is determined in step S33 whether it is | | Ina |-| In | |<F3-----VII, If it is established, it is determined that tampering has occurred (step S34).

When it is determined that tampering has occurred, the tampering display LED or LCD (liquid crystal display) of the display unit 6 is turned on. Then, the communication unit 4 associates with the host device to generate an event (tampering) (step 35).

Further, according to the V equation, for example, as described below, the tampering current Irb at the time of the R-phase bypass can be calculated.

Irb |=| | Ira+Is+It |-| In | |-----V At this time, phase detection is not performed, and the phase difference between the phases (between RS, ST, and TR) is observed. It is 120°, and is obtained by the difference between the absolute value of the N-phase current and the absolute value obtained by vector-combining the R-phase current, the S-phase current, and the T-phase current. Since the tampering current Irb can be calculated by the V equation, the tampering cumulative electric quantity can be calculated by Σ[[Vr-n]×[Irb]×t] (step S36), and can be used as a place for the electric power supplier. The reference value of the insufficient amount request. Where [Vr-n] is the instantaneous value of the voltage Vr-n of the R-phase distribution line with the N-phase as a reference, [Irb] is the instantaneous value of Irb, and t is the occurrence time of tampering.

Further, in step s22, when | | Ina |-| In | |<F3 When it is not established, it returns to the starting point and repeats step S31.

Further, the present invention can be freely combined with the respective embodiments within the scope of the present invention, or the respective embodiments can be modified or omitted as appropriate.

(industrial availability)

As described above, the present invention is applicable to a power supply system, and particularly to a smart meter used in a power supply system in an environment where there are many tampering cases.

1‧‧‧ Current Detection Department

2‧‧‧Opening and closing department

3‧‧‧Voltage detection department

4‧‧‧Communication Department

5‧‧‧ Calculation Control Department

6‧‧‧Display Department

7‧‧‧Memory Department

10‧‧‧Three-phase four-wire smart meter

Claims (5)

A three-phase four-wire fuel gauge is used for measuring the amount of electricity used. The three-phase four-wire fuel gauge has a current detecting unit that measures flow through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutrality. The R-phase current Ir, the S-phase current Is, the T-phase current It, and the N-phase current In of the line; and the bypass tamper detecting means, the phase difference between the RS phase, the ST phase, and the TR phase is regarded as 120°, respectively. When the absolute value of the difference between the absolute value of the R-phase current, the S-phase current, and the T-phase current detected by the current detecting unit and the absolute value of the N-phase current exceeds a predetermined threshold value, it is determined that the bypass tampering is generated. . The three-phase four-wire fuel gauge according to claim 1, further comprising: a voltage detecting unit that measures each phase voltage based on the N phase; and a means for calculating the cumulative amount of the tampering by the bypass, When the R-phase distribution line is used as a phase distribution line for bypass tampering, the following equation is used to determine the bypass tampering current Irb, | Irb |=| | Ira+Is+It |-| In | | where Ira is the bypass tampering The measured current of the R-phase distribution line measured by the current detecting unit, | Ira+Is+It | is Ira, Is It is the absolute value obtained by vector synthesis, | In | is the absolute value of the N-phase current, and the cumulative power of the bypass tampering is calculated by [Irb] × [Vr-n] × t, where [Irb] is Irb The instantaneous value, [Vr-n] is the instantaneous value of the R-phase voltage Vr-n with the N-phase as a reference, and t is the occurrence time of the bypass tampering. A three-phase four-wire fuel gauge is used to measure the amount of electricity used. The three-phase four-wire fuel gauge system has: The current detecting unit measures the R-phase current Ir, the S-phase current Is, the T-phase current It, and the N-phase current In flowing through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutral line, respectively; the memory unit is separately memorized by The R-phase current Ir, the S-phase current Is, the T-phase current It, and the N-phase current In before the bypass tampering measurement by the current detecting unit; and the bypass tamper detecting means determine the measurement by the current detecting unit When the phase current of the phase current bypass is tampering, when any one of the phase currents of the R phase distribution line, the S phase distribution line, and the T phase distribution line has a larger change than the first predetermined threshold, and is at the neutral line N When the phase current change is smaller than the second predetermined threshold, it is determined that the bypass tampering has occurred. A three-phase four-wire fuel gauge is used for measuring the amount of electricity used. The three-phase four-wire fuel gauge has a current detecting unit that measures flow through the R-phase distribution line, the S-phase distribution line, the T-phase distribution line, and the neutrality. The R-phase current Ir, the S-phase current Is, the T-phase current It, and the N-phase current In of the line; the memory portion memorizes the R-phase current Ir and the S-phase current Is before the bypass tampering determination by the current detecting unit, respectively , the T-phase current It, the N-phase current In, and the bypass tamper detecting means, the phase difference between the RS phase, the ST phase, and the TR phase is regarded as 120°, respectively, and the R phase current detected by the current detecting unit, S When the absolute value of the difference between the absolute value of the phase current and the T phase current and the absolute value of the N phase current exceeds a predetermined threshold value, and the bypass current tampering of the phase current measured by the current detecting portion is determined Before and after the time point, when the phase current of any one of the R phase distribution line, the S phase distribution line, and the T phase distribution line has a larger change than the second predetermined threshold, and the N phase current change ratio of the neutral line is the third When the predetermined threshold value is small, it is determined that the bypass tampering has occurred. The three-phase four-wire fuel gauge according to any one of claims 1 to 4, wherein the fuel gauge is a smart meter having a communication function and a load opening and closing function.