Measurement device, measurement method, and recording medium

Abstract

A measurement device according to the present invention measures the three-phase power or the phase voltages supplied to a three-phase load that is accommodated in a housing. The measurement device comprises a first voltage measurement unit that measures a first voltage between a first terminal of the three-phase load and the housing, a second voltage measurement unit that measures a second voltage between a second terminal of the three-phase load and the housing, and a third voltage measurement unit that measures a third voltage between a third terminal of the three-phase load and the housing. The measurement device also comprises a computation unit that computes a three-phase power or phase voltages that are based on the potential at a neutral point N of the three-phase load on the basis of the magnitude of the first voltage, the second voltage, and the third voltage.

Description

Measuring device, measuring method, and recording medium

[0001] The present invention relates to a measuring device, a measuring method, and a recording medium.

[0002] JP2018 - 185149A discloses a measuring device that measures three - phase power based on each phase voltage and each phase current with respect to the neutral point of a Y - connected three - phase load.

[0003] Since the above - mentioned three - phase load is housed in a housing, there may be parasitic capacitances or the like between the housing and the three - phase load. In such a case, a part of each phase current supplied to the three - phase load leaks to the housing through parasitic impedances such as parasitic capacitances, and due to this leakage current, there is a problem that the accuracy of measuring the operating state of the three - phase load decreases.

[0004] The present invention has been made paying attention to such problems, and an object thereof is to suppress a decrease in measurement accuracy caused by leakage current from a three - phase load to a housing.

[0005] In a first aspect of the present invention, a measuring device that measures three - phase power supplied to a three - phase load housed in a housing includes a current measurement unit that measures each line current input to the three - phase load. Further, the measuring device includes a first voltage measurement unit that measures a first voltage between a first terminal of the three - phase load and the housing, a second voltage measurement unit that measures a second voltage between a second terminal of the three - phase load and the housing, and a third voltage measurement unit that measures a third voltage between a third terminal of the three - phase load and the housing. And the measuring device includes an arithmetic unit that calculates the three - phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of the respective line currents.

[0006] In a second embodiment of the present invention, a measuring device for measuring the phase voltage supplied to a three-phase load housed in a housing comprises: a first voltage measuring unit for measuring a first voltage between the first terminal of the three-phase load and the housing; a second voltage measuring unit for measuring a second voltage between the first terminal of the three-phase load and the housing; and a third voltage measuring unit for measuring a third voltage between the second terminal of the three-phase load and the housing. Furthermore, the measuring device comprises a calculation unit for calculating the phase voltage based on the magnitudes of the first voltage, the second voltage, and the third voltage, with reference to the potential of the neutral point of the three-phase load.

[0007] In a third aspect of the present invention, a measurement method for measuring three-phase power supplied to a three-phase load housed in a housing comprises the steps of: measuring each line current of the three-phase load; measuring a first voltage between a first terminal of the three-phase load and the housing; measuring a second voltage between a second terminal of the three-phase load and the housing; measuring a third voltage between a third terminal of the three-phase load and the housing; and calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of each line current.

[0008] In a fourth aspect of the present invention, the recording medium is a computer-readable storage medium on which a program is recorded causing a computer that measures three-phase power supplied to a three-phase load housed in a casing to perform the following steps: measuring each line current of the three-phase load; measuring a first voltage between the first terminal of the three-phase load and the casing; measuring a second voltage between the second terminal of the three-phase load and the casing; measuring a third voltage between the third terminal of the three-phase load and the casing; and calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of each line current.

[0009] In a fifth aspect of the present invention, a measurement method for measuring the phase voltage supplied to a three-phase load housed in a housing comprises the steps of: measuring a first voltage between a first terminal of the three-phase load and the housing; measuring a second voltage between a second terminal of the three-phase load and the housing; measuring a third voltage between a third terminal of the three-phase load and the housing; and calculating the phase voltage with reference to the potential of the neutral point of the three-phase load based on the magnitudes of the first voltage, the second voltage, and the third voltage.

[0010] In a sixth aspect of the present invention, the recording medium is a computer-readable recording medium on which a program is recorded causing a computer that measures the phase voltage supplied to a three-phase load housed in a housing to perform the following steps: measuring a first voltage between a first terminal of the three-phase load and the housing; measuring a second voltage between a second terminal of the three-phase load and the housing; measuring a third voltage between a third terminal of the three-phase load and the housing; and calculating the phase voltage with respect to the potential of the neutral point of the three-phase load based on the magnitudes of the first voltage, the second voltage, and the third voltage.

[0011] According to these embodiments, the first voltage, second voltage, and third voltage are measured with reference to the potential generated in the enclosure through which leakage current flows from the three-phase load via parasitic impedance, and can therefore be considered as phase voltages that take into account the effect of leakage current.

[0012] Therefore, by using the above-mentioned first, second, and third voltages when measuring the state of a three-phase load, it is possible to suppress the decrease in measurement accuracy caused by leakage current flowing through the enclosure via parasitic impedance.

[0013] Figure 1 is a schematic diagram showing the configuration of a measurement system equipped with a measuring device according to the first embodiment. Figure 2 is a block diagram showing an example of the functional configuration of the measuring device. Figure 3 is a flowchart showing an example of the processing procedure of a measurement method using the measuring device. Figure 4 is a block diagram showing the functional configuration of a processing unit according to the second embodiment. Figure 5 is a flowchart showing an example of the processing procedure of a measurement method using the processing unit. Figure 6 is a schematic diagram showing a modified example of a three-phase load to be measured by the measuring device.

[0014] Embodiments of the present invention will be described below with reference to the attached drawings. Throughout this specification, the same or equivalent elements will be denoted by the same reference numerals.

[0015] (First Embodiment) Figure 1 is a schematic diagram showing the configuration of a measurement system equipped with a measuring device according to the first embodiment.

[0016] The measurement system 100 is a system for measuring the phase voltage, line voltage, or three-phase power of each phase supplied to a three-phase load housed in a casing. Examples of three-phase loads housed in a casing include a Y-connected three-phase winding and a Delta-connected three-phase winding.

[0017] Examples of devices composed of a three-phase load include a three-phase motor, a three-phase transformer, a three-phase reactor, and a three-phase capacitor, and in the first embodiment, a three-phase motor 2 is used as an example.

[0018] The measurement system 100 of the first embodiment includes a measuring device 1 for measuring the operating state of a three-phase motor 2, and current sensors 11 to 13 for detecting the phase currents Iu, Iv, and Iw of each phase supplied to the three-phase motor 2. In the first embodiment, the first phase, second phase, and third phase correspond to the U phase, V phase, and W phase, respectively.

[0019] In the first embodiment, the three-phase motor 2, which is the object of measurement for the measuring device 1, is composed of a Y-connected three-phase load with a neutral point N. Figure 1 shows the equivalent circuit of the three-phase motor 2, with the impedances Zu, Zv, and Zw of the U-phase, V-phase, and W-phase windings. One end of each winding is connected to the neutral point N. The other ends of each winding are connected to the input terminals 21 to 23 of the motor case 3, respectively.

[0020] Furthermore, the three-phase load constituting the three-phase motor 2 has parasitic capacitance between it and the motor case 3. An equivalent parasitic impedance Zr is shown where one end is connected to the neutral point N and the other end is connected to the motor case 3.

[0021] The motor case 3 is a conductive case that houses the three-phase motor 2 and is an enclosure that houses the connected three-phase load. The motor case 3 is connected to the external ground potential.

[0022] The measuring device 1 is a computer composed of a processor, ROM (Read Only Memory), RAM (Random Access Memory), input / output interfaces, and buses that connect these components to each other. Examples of processors include CPUs (Central Processing Units) and MPUs (Micro Processor Units).

[0023] The measuring device 1 measures the three-phase AC power supplied from the three-phase power supply 9 to the three-phase motor 2. The measuring device 1 acquires three-phase current detection signals from current sensors 11 to 13, each indicating the magnitude of the phase currents Iu, Iv, and Iw.

[0024] Furthermore, the measuring device 1 has four voltage detection cables. The terminals of three of the voltage detection cables are connected to the three-phase input terminals 21 to 23, respectively, and the terminal of the remaining voltage detection cable is connected to the detection terminal 24 of the motor case 3. The measuring device 1 then detects the input voltage of the three-phase load using the potential of the motor case 3 as a reference.

[0025] The input terminals 21 to 23 correspond to the first to third terminals of the three-phase load. Alternatively, the measuring device 1 may have three sets of voltage detection cables, with the H side of each of the three sets of voltage detection cables connected to the three-phase input terminals 21 to 23, and the L side of each of the three sets of voltage detection cables connected to the detection terminal 24 of the motor case 3.

[0026] Hereinafter, the potential of the motor case 3 will be referred to as the "enclosure potential." Furthermore, the first voltage between the input terminal 21 and the detection terminal 24, which correspond to the first terminal of the three-phase load, will be referred to as the "U-phase enclosure reference voltage Uue." In addition, the second voltage between the input terminal 22 and the detection terminal 24, which correspond to the second terminal of the three-phase load, will be referred to as the "V-phase enclosure reference voltage Uve," and the third voltage between the input terminal 23 and the detection terminal 24, which correspond to the third terminal of the three-phase load, will be referred to as the "W-phase enclosure reference voltage Uwe."

[0027] The measuring device 1 acquires voltage detection signals indicating the magnitudes of the three-phase housing reference voltages Uue, Uve, and Uwe. The measuring device 1 then calculates the three-phase power of the three-phase motor 2 based on the three-phase current detection signals and voltage detection signals.

[0028] The three-phase voltage detection signals described above are time-series signals that show detected amounts proportional to the instantaneous values ​​of the enclosure reference voltages Uue, Uve, and Uwe. Similarly, the three-phase current detection signals are time-series signals that show detected amounts proportional to the instantaneous values ​​of the phase currents Iu, Iv, and Iw.

[0029] The current sensors 11 to 13 can be non-contact or contact type current sensors, and the current sensors 11 to 13 in the first embodiment are clamp-type current sensors that detect the magnitude of the current in each phase without contact. Specifically, the current sensors 11 to 13 output a current detection signal obtained by detecting the magnetic flux created by the current flowing through each phase.

[0030] In the first embodiment, non-contact current sensors are used as current sensors 11 to 13, but contact current sensors (for example, shunt resistors) may also be used.

[0031] Next, the configuration of the measuring device 1 will be explained with reference to Figure 2.

[0032] Figure 2 is a block diagram showing the functional configuration of the measuring device 1 according to the first embodiment.

[0033] The measuring device 1 comprises a current measuring unit 10, a voltage measuring unit 20, a processing unit 30, a storage unit 40, and a display unit 50.

[0034] The current measuring unit 10 measures the line current of each phase of the three-phase load. In the first embodiment, the phase currents of each phase (Iu, Iv, Iw) are measured as the line currents of each phase of the three-phase load.

[0035] In the first embodiment, the current measurement unit 10 generates current measurement data that shows the measured amount of the phase current (Iu, Iv, Iw) for each phase in a time series, based on the current detection signals for each phase output from the current sensors 11 to 13. The current measurement unit 10 outputs the generated current measurement data to the processing unit 30.

[0036] The current measurement unit 10 is composed of, for example, an adjustment circuit for adjusting the level of the input voltage, a filter circuit for removing noise components from the input voltage, an A / D conversion circuit, and a calculation circuit that calculates the measured amounts of the three-phase phase currents Iu, Iv, and Iw based on the output data of the A / D conversion circuit. Note that circuits other than the calculation circuit may be located outside the current measurement unit 10.

[0037] The voltage measurement unit 20 generates voltage measurement data showing the measured amounts of the housing reference voltages Uue, Uve, and Uwe for each phase in time series, based on the acquired voltage detection signals for each phase, and outputs it to the processing unit 30.

[0038] The voltage measuring unit 20 of the first embodiment includes a first voltage measuring unit 20a, a second voltage measuring unit 20b, and a third voltage measuring unit 20c.

[0039] The first voltage measurement unit 20a converts a voltage detection signal, which shows the detected amount of the housing reference voltage Uue between the U-phase input terminal 21 and detection terminal 24 in a time series, into voltage measurement data that shows the measured amount of the housing reference voltage Uue in a time series. The first voltage measurement unit 20a outputs the converted U-phase voltage measurement data to the processing unit 30.

[0040] The first voltage measurement unit 20a is composed of, for example, an attenuator that reduces the input voltage, an adjustment circuit that adjusts the level of the input voltage after reduction, a filter circuit, an A / D conversion circuit, and a calculation circuit that calculates the amount of the chassis reference voltage Uue based on the output data of the A / D conversion circuit. Circuits other than the calculation circuit may be located outside the first voltage measurement unit 20a.

[0041] The second voltage measuring unit 20b and the third voltage measuring unit 20c have the same or equivalent configuration as the first voltage measuring unit 20a.

[0042] For example, the second voltage measurement unit 20b converts a voltage detection signal showing the detected amount of the housing reference voltage Uve between the V-phase input terminal 22 and detection terminal 24 in a time series into U-phase voltage measurement data and outputs it to the processing unit 30. The third voltage measurement unit 20c converts a voltage detection signal showing the detected amount of the housing reference voltage Uwe between the W-phase input terminal 23 and detection terminal 24 in a time series into W-phase voltage measurement data and outputs it to the processing unit 30.

[0043] The processing unit 30 functions as a calculation unit that calculates the three-phase power supplied to the three-phase load based on the magnitudes of the casing reference voltages (Uue, Uve, Uwe) of each phase to be measured and the magnitudes of the phase currents (Iu, Iv, Iw) of each phase. The processing unit 30 is configured by, for example, one or more processors.

[0044] For example, the processing unit 30 obtains the power of each phase by multiplying the magnitudes of the casing reference voltage (Uue, Uve, Uwe) and the phase current (Iu, Iv, Iw) of each corresponding phase, and obtains the three-phase power supplied to the three-phase motor 2 by adding or averaging the power of each phase.

[0045] The processing unit 30 of the first embodiment obtains the three-phase power Pe of the three-phase motor 2 using the instantaneous values of the waveforms shown in the output data of the current measurement unit 10 and the voltage measurement unit 20 as shown in the following formula (1).

[0046] [Equation 1] Pe = Iu · Uue + Iv · Uve + Iw · Uwe ··· (1)

[0047] Thus, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and the instantaneous voltage value shown in the U-phase current measurement data and voltage measurement data, and obtains the average value of the waveforms of one cycle or a plurality of cycles to calculate the power value (Iu · Uue). Then, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and the instantaneous voltage value shown in the V-phase current measurement data and voltage measurement data, and obtains the average value of the waveforms of one cycle or a plurality of cycles to calculate the power value (Iv · Uve).

[0048] Further, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and the instantaneous voltage value shown in the W-phase current measurement data and voltage measurement data, and obtains the average value of the waveforms of one cycle or a plurality of cycles to calculate the power value (Iw · Uwe). The processing unit 30 adds the calculated power value (Iu · Uue) of the U phase, the power value (Iv · Uve) of the V phase, and the power value (Iw · Uwe) of the W phase to obtain the three-phase power Pe. Note that the processing unit 30 may use the measurement quantity obtained by averaging the obtained three-phase power Pe as the three-phase power Pe.

[0049] Furthermore, the processing unit 30 records the voltage measurement data and current measurement data for each phase of the three-phase motor 2, as well as the three-phase power Pe of the three-phase motor 2, in the storage unit 40.

[0050] The storage unit 40 stores the output results of the current measurement unit 10, the voltage measurement unit 20, and the processing unit 30. For example, the storage unit 40 stores the current waveform shown in the current measurement data for each phase, the voltage waveform shown in the voltage measurement data for each phase, and the calculation results of the effective values ​​of the current and voltage for each phase obtained by the processing unit 30, as well as the three-phase power Pe.

[0051] Furthermore, the storage unit 40 stores a program for controlling the operation of the measuring device 1. In other words, the storage unit 40 constitutes a recording medium that can be read by a computer. The storage unit 40 in this embodiment is composed of, for example, ROM, RAM, and flash memory.

[0052] The display unit 50 displays the results calculated by the processing unit 30. The display unit 50 is composed of a display device such as a display.

[0053] In the first embodiment, the display unit 50 displays the output results of the current measurement unit 10, the voltage measurement unit 20, and the processing unit 30. Specifically, the display unit 50 displays the measured amount of three-phase power Pe stored in the storage unit 40, the current waveform shown in the current measurement data, the voltage waveform shown in the voltage measurement data, or the effective value of the waveform.

[0054] Next, the operation of the measuring device 1 will be explained with reference to Figure 3.

[0055] Figure 3 is a flowchart showing an example of the processing procedure for a measurement method using the measuring device 1.

[0056] In step S1, the measuring device 1 measures the phase currents (Iu, Iv, Iw) of each phase as the line currents flowing through the three-phase motor 2.

[0057] In the first embodiment, the measuring device 1 acquires current measurement data showing the measured amounts of the three-phase phase currents Iu, Iv, and Iw in a time series, based on the three-phase voltage detection signals acquired from the current sensors 11 to 13.

[0058] In step S2, the measuring device 1 measures the three-phase chassis reference voltages Uue, Uve, and Uwe as the first, second, and third voltages, respectively, with the chassis potential of the motor case 3 as the reference voltage. Specifically, the measuring device 1 measures the chassis reference voltage Uue as the first voltage between the input terminal 21 of the three-phase load and the detection terminal 24 of the motor case, and measures the chassis reference voltage Uve as the second voltage between the input terminal 22 of the three-phase load and the detection terminal 24. Then, the measuring device 1 measures the chassis reference voltage Uwe as the third voltage between the input terminal 23 of the three-phase load and the detection terminal 24.

[0059] In the first embodiment, the measuring device 1 acquires three-phase voltage detection signals between the input terminals 21 to 23 of each phase and the detection terminal 24 of the motor case 3. Based on the acquired three-phase voltage detection signals, the measuring device 1 acquires voltage measurement data showing the measured amounts of the three-phase housing reference voltages Uue, Uve, and Uwe in a time series.

[0060] Since the measured values ​​of the enclosure reference voltages Uue, Uve, and Uwe are obtained with reference to the enclosure potential of the motor case 3, the three-phase voltage measurement data is affected by the current leaking from the three-phase load constituting the three-phase motor 2 to the motor case 3 via the parasitic impedance Zr.

[0061] In step S3, the measuring device 1 calculates the three-phase power Pe consumed by the three-phase motor 2 based on the current measurement data and voltage measurement data for each phase.

[0062] In the first embodiment, the measuring device 1 calculates the power of each phase by multiplying the magnitudes of the housing reference voltages (Uue, Uve, Uwe) and phase currents (Iu, Iv, Iw) of each corresponding phase according to equation (1) above. The measuring device 1 then obtains the three-phase power Pe supplied to the three-phase motor 2 by adding up the powers of each phase.

[0063] In step S4, the measuring device 1 displays the calculation result. In the first embodiment, the measuring device 1 displays voltage measurement data for each phase, current measurement data for each phase, or three-phase power Pe.

[0064] When the process in step S4 is completed, the series of processing steps (S1 to S4) is completed, and the measurement method of the first embodiment is finished.

[0065] Next, the effects and benefits of the first embodiment will be described.

[0066] The measuring device 1 according to the first embodiment measures the three-phase power Pe supplied to a three-phase motor 2, which is composed of a three-phase load housed in a motor case 3 as a housing. The measuring device 1 includes a current measuring unit 10 that measures the phase currents (Iu, Iv, Iw) of each phase as the line currents of the three-phase load, and a first voltage measuring unit 20a that measures the housing reference voltage Uue as the first voltage between the input terminal 21, which is the first terminal of the three-phase load, and the detection terminal 24 of the motor case 3.

[0067] Furthermore, the measuring device 1 includes a second voltage measuring unit 20b that measures the housing reference voltage Uve as the second voltage between the input terminal 22, which is the second terminal of the three-phase load, and the detection terminal 24 of the motor case 3, and a third voltage measuring unit 20c that measures the housing reference voltage Uwe as the third voltage between the input terminal 23, which is the third terminal of the three-phase load, and the detection terminal 24 of the motor case.

[0068] The measuring device 1 includes a processing unit 30 that functions as a calculation unit that calculates the three-phase power Pe supplied to the three-phase motor 2 based on the magnitudes of the three-phase housing reference voltages Uue, Uve, and Uwe, and the magnitudes of the phase currents (Iu, Iv, Iw) of each phase.

[0069] Furthermore, the measurement method according to the first embodiment measures the three-phase power Pe supplied to a three-phase load housed in a motor case 3 as a housing. This measurement method comprises: step S1 of measuring the phase currents (Iu, Iv, Iw) of each line as the line currents of the three-phase load; step S2 of measuring the three-phase housing reference voltages Uue, Uve, and Uwe; and step S3 of calculating the three-phase power Pe based on the magnitudes of the three-phase housing reference voltages Uue, Uve, and Uwe, and the magnitudes of the phase currents (Iu, Iv, Iw) of each line.

[0070] Step S2 described above includes measuring the chassis reference voltage Uue as the first voltage between the first terminal of the three-phase load and the chassis, measuring the chassis reference voltage Uve as the second voltage between the second terminal of the three-phase load and the chassis, and measuring the chassis reference voltage Uwe as the third voltage between the third terminal of the three-phase load and the chassis.

[0071] Furthermore, the recording medium according to the first embodiment is a computer-readable recording medium on which a program for executing steps S1 to S3 is recorded for a computer that measures the three-phase power Pe supplied to a three-phase load housed in a motor case 3 as an enclosure.

[0072] In these configurations, a leakage current Ir flows from the three-phase load constituting the three-phase motor 2 into the motor case 3 via a parasitic impedance Zr consisting of parasitic capacitance and the like. Therefore, in a typical measurement method that calculates the three-phase power of the three-phase motor 2 using the phase voltages of each phase with respect to the neutral point N of the three-phase load, the effect of the leakage current Ir from the three-phase load to the motor case 3 is not taken into account in the calculation result of the three-phase power.

[0073] In contrast, with the above configuration, the chassis reference voltages for each phase (Uue, Uve, Uwe) are measured with reference to the chassis potential generated in the motor case 3 into which leakage current Ir flows from the three-phase load. Therefore, they can be considered as phase voltages that reflect the effect of leakage current Ir on the motor case 3. This makes it possible to perform power measurements that also take leakage current Ir into account.

[0074] Therefore, by using the three-phase enclosure reference voltages Uue, Uve, and Uwe when measuring the state of the three-phase load, it is possible to suppress the decrease in measurement accuracy caused by a portion of the three-phase phase currents Iu, Iv, and Iw leaking into the motor case 3 via the parasitic impedance Zr.

[0075] Furthermore, in the first embodiment, the processing unit 30 calculates the power of each phase (Iu・Uue, Iv・Uve, Iw・Uwe) by multiplying the magnitudes of the housing reference voltages (Uue, Uve, Uwe) and phase currents (Iu, Iv, Iw) of the corresponding phases. The processing unit 30 then obtains the three-phase power Pe of the three-phase motor 2 by adding the powers of each phase.

[0076] It is difficult to determine which phase of the three-phase load the leakage current Ir flowing into the motor case 3 originates from. Therefore, by adding up the power of each phase to obtain the three-phase power Pe, as in the above configuration, the influence of the leakage current Ir is reliably reflected in the calculated three-phase power Pe, thereby suppressing a decrease in measurement accuracy.

[0077] Furthermore, the measuring device 1 in the first embodiment further includes a display unit 50 that displays the results calculated by the processing unit 30.

[0078] With this configuration, the calculation result, which takes into account the leakage current Ir to the motor case 3, is displayed on the display unit 50 to the operator, so that the operator can accurately understand the operating state of the three-phase motor 2.

[0079] Furthermore, the measuring device 1 in the first embodiment may further include current sensors 11 to 13 arranged on the wires through which the phase currents (Iu, Iv, Iw) of each phase flow. The current sensors 11 to 13 detect the phase currents (Iu, Iv, Iw) of each phase, and the current measuring unit 10 calculates the measured amount of the phase currents (Iu, Iv, Iw) of each phase from the output signals of the current sensors 11 to 13.

[0080] With this configuration, the phase currents (Iu, Iv, Iw) of each phase can be measured using current sensors 11 to 13.

[0081] (Second Embodiment) In the first embodiment, the three-phase power Pe of the three-phase motor 2 was calculated, but it is also possible to calculate other parameters that indicate the operating state of the three-phase motor 2. The second embodiment describes below an embodiment in which parameters other than the three-phase power Pe are calculated.

[0082] Figure 4 is a block diagram showing the functional configuration of the processing unit 30A of the measuring device 1A according to the second embodiment.

[0083] The measuring device 1A is equipped with a corresponding processing unit 30A instead of the processing unit 30 shown in the first embodiment in Figure 2. Therefore, this section will mainly describe the processing unit 30A. Note that other components are the same as or equivalent to those of the measuring device 1 shown in Figure 2, so the same reference numerals are used and redundant explanations are omitted.

[0084] The processing unit 30A functions as a calculation unit that calculates parameters indicating the operating state of the three-phase motor 2. For example, the processing unit 30A calculates the phase voltages based on the potential of the neutral point N of the Y-connected three-phase load, based on the magnitude of the measured housing reference voltages (Uue, Uve, Uwe) of each phase.

[0085] The phase voltages of a three-phase load, with the potential of the neutral point N as the reference, are the phase voltage of the first phase between the input terminal 21 of the U phase and the neutral point N, the phase voltage of the second phase between the input terminal 22 of the V phase and the neutral point N, and the phase voltage of the third phase between the input terminal 23 of the W phase and the neutral point N. Hereinafter, the phase voltages of the U, V, and W phases with the potential of the neutral point N as the reference will be referred to as "phase voltages Uun, Uvn, and Uwn."

[0086] The processing unit 30A of the second embodiment includes a phase voltage conversion unit 31, a motor analysis unit 32, and a three-phase power calculation unit 33.

[0087] The phase voltage conversion unit 31 of the second embodiment converts the housing reference voltages Uue, Uve, and Uwe shown in the three-phase voltage measurement data into three-phase phase voltages Uun, Uvn, and Uwn. That is, the phase voltage conversion unit 31 calculates the three-phase phase voltages Uun, Uvn, and Uwn based on the magnitudes of the three-phase housing reference voltages Uue, Uve, and Uwe. The calculation of the phase voltages (Uun, Uvn, Uwn) is performed using instantaneous voltage values.

[0088] Here, we will briefly explain the method for deriving the three-phase phase voltages Uun, Uvn, and Uwn, with respect to the neutral point N, from the three-phase enclosure reference voltages Uue, Uve, and Uwe.

[0089] First, using the Y-Δ transformation in equation (2), the line voltages Uuv, Uvw, and Uwu are determined from the measured three-phase enclosure reference voltages Uue, Uve, and Uwe.

[0090] [Math 2] Uuv = Uue-Uve Uvw = Uve-Uwe ... (2) Uwu = Uwe-Uue

[0091] Next, the phase voltages Uun, Uvn, and Uwn of the three phases are derived from the obtained line voltages Uuv, Uvw, and Uwu by using the Δ-Y transformation shown in equations (3) to (5).

[0092] [Math. 3] Uun = (Uuv-Uwu) / 3 = {(Uue-Uve)-(Uwe-Uue)} / 3 = (2Uue-Uve-Uwe) / 3...(3) [Math. 4] Uvn = (Uvw-Uuv) / 3 = {(Uve-Uwe)-(Uue-Uve)} / 3 = (2Uve-Uwe-Uue) / 3 ... (4) [Math. 5] Uwn = (Uwu-Uvw) / 3 = {(Uwe-Uue)-(Uve-Uwe)} / 3 = (2Uwe-Uue-Uve) / 3...(5)

[0093] Thus, using equations (3) to (5) above, the three-phase enclosure reference voltages Uue, Uve, and Uwe can be converted to the three-phase phase voltages Uun, Uvn, and Uwn.

[0094] Therefore, the phase voltage conversion unit 31 of the second embodiment calculates the phase voltage of each phase by subtracting the sum of the housing reference voltages of the other two phases from a voltage value obtained by doubling the housing reference voltage of one phase, and then dividing the result by 3.

[0095] For example, the phase voltage conversion unit 31 obtains a subtraction result (2Uue - Uve - Uwe) by subtracting the sum of the housing reference voltages Uve and Uwe of the other V and W phases from a voltage value (2Uue) obtained by doubling the housing reference voltage Uue of the U phase. Then, the phase voltage conversion unit 31 calculates the phase voltage Uun of the U phase by dividing this subtraction result by 3.

[0096] Furthermore, the phase voltage conversion unit 31 obtains a subtraction result (2Uve - Uwe - Uue) by subtracting the sum of the housing reference voltages Uwe and Uue of the other W and U phases from a voltage value (2Uve) obtained by doubling the housing reference voltage Uve of the V phase. Then, the phase voltage conversion unit 31 calculates the phase voltage Uvn of the V phase by dividing this subtraction result by 3.

[0097] Furthermore, the phase voltage conversion unit 31 obtains a subtraction result (2Uwe - Uue - Uve) by subtracting the sum of the housing reference voltages Uue and Uve of the other U and V phases from a voltage value (2Uwe) obtained by doubling the housing reference voltage Uwe of the W phase. Then, the phase voltage conversion unit 31 calculates the phase voltage Uwn of the W phase by dividing this subtraction result by 3.

[0098] The phase voltage conversion unit 31 outputs the calculated three-phase phase voltages Uun, Uvn, and Uwn to the motor analysis unit 32.

[0099] The motor analysis unit 32 performs known motor analysis processing to calculate analysis parameters related to the three-phase voltages Uun, Uvn, and Uwn. For example, the motor analysis unit 32 calculates the amplitude or phase of the phase voltage (Uun, Uvn, Uwn) of each phase as analysis parameters. Examples of indicators representing amplitude include peak value, RMS value, or average value.

[0100] Furthermore, the motor analysis unit 32 calculates the amplitude or phase of the fundamental frequency with respect to the phase voltage (Uun, Uvn, Uwn) of each phase by performing frequency analysis used in motor analysis processing. In addition, the motor analysis unit 32 calculates the amplitude or phase of the harmonic frequencies with respect to the fundamental frequency of the phase voltage (Uun, Uvn, Uwn) of each phase by performing frequency analysis.

[0101] In addition, the motor analysis unit 32 obtains the three-phase phase currents Iu, Iv, and Iw from the current measurement unit 10, and uses the three-phase phase currents Iu, Iv, and Iw, along with the three-phase phase voltages Uun, Uvn, and Uwn, to calculate the amplitude or phase of the phase power of each phase.

[0102] In this way, the motor analysis unit 32 outputs the amplitude and phase of the phase voltages (Uun, Uvn, Uwn) of each phase, the amplitude and phase of the fundamental frequency and harmonic frequency, and the amplitude and phase of the phase power of each phase to the storage unit 40 or the display unit 50 as analysis parameters.

[0103] The three-phase power calculation unit 33 calculates an instantaneous power value by multiplying the instantaneous current value and instantaneous voltage value shown in the output data of the current measurement unit 10 and the voltage measurement unit 20, similar to the processing unit 30 in the first embodiment. The three-phase power calculation unit 33 then calculates the power value by finding the average value of the waveform of the calculated instantaneous power value over one or more cycles, and calculates the three-phase power value from the above equation (1) to calculate the three-phase power Pe of the three-phase motor 2. The three-phase power calculation unit 33 outputs the calculated three-phase power Pe to the storage unit 40 or the display unit 50.

[0104] In this way, the processing unit 30A can measure the three-phase power Pe of the three-phase motor 2 using the three-phase power calculation unit 33, and perform analysis processing of the three-phase motor 2 using the phase-voltage conversion unit 31 and the motor analysis unit 32 without changing the connection destination of the voltage detection cable terminals.

[0105] Next, the operation of the measuring device 1A will be explained with reference to Figure 5.

[0106] Figure 5 is a flowchart showing an example of the processing procedure for a measurement method using measuring device 1A.

[0107] The measurement method of the second embodiment includes steps S11 and S12 in addition to the processing of the measurement method of the first embodiment shown in Figure 3, and also includes a corresponding step S4a instead of step S4. Note that other processing steps are the same as or equivalent to the processing of the measurement method shown in Figure 3, and are therefore given the same reference numerals and their explanation is omitted here.

[0108] In step S11, the measuring device 1A converts the three-phase housing reference voltages Uue, Uve, and Uwe measured in step S2 into three-phase phase voltages Uun, Uvn, and Uwn.

[0109] In the second embodiment, the measuring device 1A calculates the phase voltages (Uun, Uvn, Uwn) of each phase based on the magnitudes of the three-phase housing reference voltages Uue, Uve, and Uwe, according to equations (3) to (5) above.

[0110] In step S12, the measuring device 1A performs motor analysis processing using the three-phase phase currents Iu, Iv, and Iw and the three-phase phase voltages Uun, Uvn, and Uwn. As a result, the measuring device 1A calculates analysis parameters related to the phase voltages (Uun, Uvn, Uwn) of each phase.

[0111] For example, the measuring device 1A calculates the amplitude and phase of the phase voltages (Uun, Uvn, Uwn) of each phase, the amplitude and phase of the fundamental and harmonic frequencies of the phase voltages (Uun, Uvn, Uwn), and the amplitude and phase of the power of each phase as analysis parameters.

[0112] In step S4a, the measuring device 1A displays the results analyzed in step S2 or the results calculated in step S3 on the display unit 50.

[0113] When the process in step S4a is completed, the series of processing steps (S1, S2, S11, S12, S3, S4a) is completed, and the measurement method of the second embodiment is finished.

[0114] Next, the effects and benefits of the second embodiment will be described.

[0115] In the second embodiment, the measuring device 1A measures the phase voltages Uun, Uvn, and Uwn supplied to a three-phase load housed in a motor case 3, which serves as the housing. The measuring device 1A includes a current measuring unit 10 that measures the phase currents (Iu, Iv, Iw) of each phase as the line currents of the three-phase load, and a first voltage measuring unit 20a that measures the housing reference voltage Uue as the first voltage between the input terminal 21, which serves as the first terminal of the three-phase load, and the detection terminal 24 of the motor case 3.

[0116] Furthermore, the measuring device 1A includes a second voltage measuring unit 20b that measures the housing reference voltage Uve as a second voltage between the input terminal 22, which is the second terminal of the three-phase load, and the detection terminal 24 of the motor case 3, and a third voltage measuring unit 20c that measures the housing reference voltage Uwe as a third voltage between the input terminal 23, which is the third terminal of the three-phase load, and the detection terminal 24 of the motor case.

[0117] The measuring device 1A includes a processing unit 30A that calculates the phase voltages Uun, Uvn, and Uwn based on the potential of the neutral point N of the three-phase load, based on the magnitudes of the housing reference voltages Uue, Uve, and Uwe.

[0118] Furthermore, the measurement method according to the second embodiment measures the phase voltages Uun, Uvn, and Uwn supplied to a three-phase load housed in a motor case 3 as a housing. This measurement method comprises: step S1 of measuring the phase currents (Iu, Iv, Iw) of each line as the line currents of the three-phase load; step S2 of measuring the three-phase housing reference voltages Uue, Uve, and Uwe; and step S11 of calculating the phase voltages Uun, Uvn, and Uwn based on the potential of the neutral point N of the three-phase load, using the magnitudes of the housing reference voltages Uue, Uve, and Uwe as a reference.

[0119] Step S2 described above includes measuring the chassis reference voltage Uue as the first voltage between the first terminal of the three-phase load and the chassis, measuring the chassis reference voltage Uve as the second voltage between the second terminal of the three-phase load and the chassis, and measuring the chassis reference voltage Uwe as the third voltage between the third terminal of the three-phase load and the chassis.

[0120] Furthermore, the recording medium according to the second embodiment is a computer-readable recording medium on which a program for executing steps S1, S2, and S11 is recorded for a computer that measures the phase voltages Uun, Uvn, and Uwn supplied to a three-phase load housed in a motor case 3 as an enclosure.

[0121] In these configurations, first, a leakage current Ir flows from the three-phase load constituting the three-phase motor 2 into the motor case 3 via a parasitic impedance Zr consisting of parasitic capacitance and the like. On the other hand, in many cases, the object to be measured, such as a three-phase motor, cannot be accessed from its neutral point N, or is structurally impossible to measure due to its delta connection. In such cases, the three-phase three-wire three-wattmeter method is used, and the effect of the leakage current Ir is not considered.

[0122] In contrast, with the above configuration, the chassis reference voltages for each phase (Uue, Uve, Uwe) are measured with reference to the chassis potential generated in the motor case 3 into which leakage current Ir flows from the three-phase load. Therefore, they can be considered as voltages that reflect the influence of leakage current Ir on the motor case 3. This allows for power measurement that also takes leakage current Ir into account. Furthermore, since the motor case 3, which is the chassis of the three-phase motor 2 and is grounded, often coincides with the reference potential (ground) of measuring instruments such as the measuring device 1, measurements can be performed under conditions where the influence of common-mode voltage is smaller.

[0123] Furthermore, in the second embodiment, the processing unit 30A calculates the phase voltage of each phase of the three-phase load by dividing the result obtained by subtracting the sum of the other two voltage values ​​of the three-phase housing reference voltages Uue, Uve, and Uwe from a voltage value obtained by doubling one of the three-phase housing reference voltages Uue, Uve, and Uwe by 3.

[0124] With this configuration, the three-phase phase voltages Uun, Uvn, and Uwn are obtained using the Y-Δ conversion and Δ-Y conversion calculation methods as shown in equations (3) to (5) above. Therefore, compared to the case where a measurer actually changes the connection point of the voltage detection cable terminal from the detection terminal 24 of the motor case 3 to the neutral point N to measure the three-phase phase voltages Uun, Uvn, and Uwn, the three-phase phase voltages Uun, Uvn, and Uwn can be obtained using a simpler method.

[0125] Furthermore, some three-phase motors 2 do not allow the terminals of the voltage detection cable to be connected to the neutral point N. Therefore, even with three-phase motors where the terminals of the voltage detection cable cannot be connected to the neutral point N, the three-phase voltages Uun, Uvn, and Uwn can be obtained.

[0126] In this way, by calculating the phase voltages (Uun, Uvn, Uwn) of each phase from the three-phase chassis reference voltages Uue, Uve, and Uwe, the phase voltages can be reliably obtained, and the three-phase phase voltages Uun, Uvn, and Uwn can be obtained accurately using a simple method.

[0127] Furthermore, the processing unit 30A calculates the amplitude or phase of the phase voltages (Uun, Uvn, Uwn) of each phase.

[0128] With this configuration, the amplitude or phase of the phase voltages (Uun, Uvn, Uwn) of each phase can be obtained as parameters indicating the operating state of the three-phase motor 2, allowing the operator to analyze the operating state of the three-phase motor 2.

[0129] Furthermore, the processing unit 30A performs frequency analysis to calculate the amplitude or phase of the fundamental frequency related to the phase voltage (Uun, Uvn, Uwn) of each phase, or the amplitude or phase of the harmonic frequency with respect to the said fundamental frequency.

[0130] With this configuration, the amplitude or phase of the fundamental frequency and harmonic frequencies can be obtained by frequency analysis of the acquired phase voltages (Uun, Uvn, Uwn) of each phase. Therefore, the operating state of the three-phase motor 2 can be analyzed in more detail compared to when frequency analysis is not performed.

[0131] <Modification> In the above embodiment, the object of measurement was a three-phase motor 2 having a Y-connected three-phase load. However, the measuring device 1 in the above embodiment can also measure a three-phase motor having a three-phase load that does not have a neutral point N. Below, an embodiment in which a three-phase motor without a neutral point N is measured will be briefly described.

[0132] Figure 6 is a conceptual diagram showing a modified example of a three-phase motor 2 measured by the measuring device 1.

[0133] The modified three-phase motor 2A has a three-phase load housed in a motor case 3 as its enclosure. The equivalent circuit of the three-phase motor 2A is shown as follows: the impedance Zuv of the first-phase winding between the U-phase and V-phase, the impedance Zvw of the second-phase winding between the V-phase and W-phase, and the impedance Zwu of the third-phase load between the W-phase and U-phase.

[0134] One end of impedance Zuv is connected to one end of impedance Zvw, the other end of impedance Zvw is connected to one end of impedance Zwu, and the other end of impedance Zwu is connected to the other end of impedance Zuv.

[0135] Thus, the three-phase motor 2A has a delta-connected three-phase load that does not have a neutral point N, and is housed in the motor case 3. Even in this case, it can be assumed that a virtual leakage current Ir' flows from the three-phase load through a virtual parasitic impedance Zr' from a virtual neutral point N' shown by the dotted line in Figure 6 to the motor case 3. At this time, the virtual impedances Zu', Zv', and Zw' can be obtained using delta-y transformation as shown in equation (6) below.

[0136] [Math 6] Zu' = Zuv・Zvw / (Zuv+Zvw+Zwu) Zv' = Zvw・Zwv / (Zuv+Zvw+Zwu) ...(6) Zw' = Zwv・Zuv / (Zuv+Zvw+Zwu)

[0137] Therefore, in Figure 6, the other end of a virtual parasitic impedance Zr', one end of which is connected to the motor case 3, is connected to a virtual neutral point N'. Then, as the equivalent circuit of the three-phase motor 2A, we can assume virtual impedances Zu', Zv', Zw', a virtual neutral point N', and a virtual parasitic impedance Zr'. Thus, the assumed virtual phase voltages Uun', Uvn', and Uwn' can be obtained from equations (3) to (5) above.

[0138] In other words, the measuring device 1 measures the housing reference voltages Uue, Uve, and Uwe of the three-phase load constituting the three-phase motor 2A, similar to the embodiment described above, and calculates the measured amount of the three-phase power Pe of the three-phase motor 2A based on the measured amounts of the three-phase housing reference voltages Uue, Uve, and Uwe as shown in equation (1) above.

[0139] Alternatively, the measuring device 1 calculates the measured values ​​of the phase voltages (Uun', Uvn', Uwn') for each phase based on the measured values ​​of the three-phase housing reference voltages Uue, Uve, and Uwe, as shown in equations (3) to (5) above. The measuring device 1 then performs motor analysis processing based on the measured values ​​of the phase voltages (Uun', Uvn', Uwn') for each phase to calculate the amplitude or phase of the fundamental frequency related to the phase voltage of each phase, or the amplitude or phase of the harmonic frequencies with respect to that fundamental frequency.

[0140] Thus, the measuring device 1 of the above embodiment, like the three-phase motor 2 shown in Figure 1, can measure the operating state of a three-phase motor 2A having a three-phase load that does not have a neutral point N, in particular the phase voltages of each phase (Uun, Uvn, Uwn).

[0141] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0142] This application claims priority under Japanese Patent Application No. 2024-197651, filed with the Japan Patent Office on November 12, 2024, and all contents of that application are incorporated herein by reference.

[0143] 100 Measurement System 1, 1A Measurement device 2 Three-phase motor (three-phase load) 3 Motor case (housing) 10 Current measurement unit 20a First voltage measurement unit 20b Second voltage measurement unit 20c Third voltage measurement unit 21-23 Input terminals (first to third terminals of the three-phase load) 30, 30A Processing unit (calculation unit) 31 Phase voltage conversion unit (calculation unit) 32 Motor analysis unit (calculation unit) Uue, Uve, Uwe Housing reference voltage (first voltage, second voltage, third voltage) Uun, Uvn, Uwn Phase voltage Uun', Uvn', Uwn' Virtual phase voltage

Claims

1. A measuring device for measuring three-phase power supplied to a three-phase load housed in a housing, comprising: a current measuring unit for measuring each line current of the three-phase load; a first voltage measuring unit for measuring a first voltage between the first terminal of the three-phase load and the housing; a second voltage measuring unit for measuring a second voltage between the second terminal of the three-phase load and the housing; a third voltage measuring unit for measuring a third voltage between the third terminal of the three-phase load and the housing; and a calculation unit for calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of each line current.

2. A measuring device according to claim 1, wherein the calculation unit calculates the power of each phase of the three-phase load by multiplying the first voltage, the second voltage, and the third voltage, and the magnitude of the line current, which correspond to each other, and obtains the three-phase power by adding the powers of each phase.

3. A measuring device for measuring the phase voltage supplied to a three-phase load housed in a housing, comprising: a first voltage measuring unit for measuring a first voltage between a first terminal of the three-phase load and the housing; a second voltage measuring unit for measuring a second voltage between a second terminal of the three-phase load and the housing; a third voltage measuring unit for measuring a third voltage between a third terminal of the three-phase load and the housing; and a calculation unit for calculating the phase voltage based on the magnitudes of the first voltage, the second voltage, and the third voltage, with reference to the potential of the neutral point of the three-phase load.

4. A measuring device according to claim 3, wherein the calculation unit calculates the phase voltage of each phase of the three-phase load by dividing by 3 the result obtained by subtracting the sum of the other two voltage values ​​among the first voltage, second voltage, and third voltage from a voltage value obtained by doubling one of the voltage values ​​among the first voltage, second voltage, and third voltage.

5. A measuring device according to claim 3 or claim 4, wherein the calculation unit calculates the amplitude or phase of the phase voltage of each of the phases.

6. A measuring device according to any one of claims 3 to 5, wherein the calculation unit calculates the amplitude or phase of the fundamental frequency relating to the phase voltage of each phase, or the amplitude or phase of the harmonic frequency with respect to the fundamental frequency, by performing frequency analysis.

7. A measuring device according to claim 1 or claim 2, further comprising a plurality of current sensors arranged on the electric wire through which each line current flows and for detecting each line current.

8. A measuring device according to any one of claims 1 to 7, further comprising a display unit for displaying the results calculated by the calculation unit.

9. A measurement method for measuring three-phase power supplied to a three-phase load housed in a housing, comprising: a step of measuring each line current of the three-phase load; a step of measuring a first voltage between a first terminal of the three-phase load and the housing; a step of measuring a second voltage between a second terminal of the three-phase load and the housing; a step of measuring a third voltage between a third terminal of the three-phase load and the housing; and a step of calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of each line current.

10. A computer-readable recording medium that records a program for causing a computer to measure three-phase power supplied to a three-phase load housed in a casing to perform the following steps: measuring each line current of the three-phase load; measuring a first voltage between the first terminal of the three-phase load and the casing; measuring a second voltage between the second terminal of the three-phase load and the casing; measuring a third voltage between the third terminal of the three-phase load and the casing; and calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, and the magnitudes of each line current.

11. A measurement method for measuring the phase voltage supplied to a three-phase load housed in a housing, comprising: a step of measuring a first voltage between a first terminal of the three-phase load and the housing; a step of measuring a second voltage between a second terminal of the three-phase load and the housing; a step of measuring a third voltage between a third terminal of the three-phase load and the housing; and a step of calculating the phase voltage with reference to the potential of the neutral point of the three-phase load based on the magnitudes of the first voltage, the second voltage, and the third voltage.

12. A computer-readable recording medium that records a program for causing a computer to measure the phase voltage supplied to a three-phase load housed in a casing to perform the following steps: measuring a first voltage between the first terminal of the three-phase load and the casing; measuring a second voltage between the second terminal of the three-phase load and the casing; measuring a third voltage between the third terminal of the three-phase load and the casing; and calculating the phase voltage with respect to the potential of the neutral point of the three-phase load based on the magnitudes of the first voltage, the second voltage, and the third voltage.

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