Measuring device, measuring method, and program

Abstract

This suppresses the decrease in measurement accuracy caused by leakage current from the three-phase load to the enclosure. [Solution] The measuring device measures the three-phase power or phase voltage supplied to a three-phase load housed in a casing. The measuring device comprises a first voltage measuring unit 20a that measures the first voltage between the first terminal of the three-phase load and the casing, a second voltage measuring unit 20b that measures the second voltage between the second terminal of the three-phase load and the casing, and a third voltage measuring unit 20c that measures the third voltage between the third terminal of the three-phase load and the casing. Furthermore, the measuring device comprises a calculation unit that calculates the three-phase power or the phase voltage based on the potential of the neutral point N of the three-phase load, based on the magnitudes of the first, second, and third voltages.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 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.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the above-described three-phase load is housed in a housing, a capacitance or the like may parasitically exist 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 a parasitic impedance such as a parasitic capacitance, and due to this leakage current, there is a problem that the accuracy of measuring the operating state of the three-phase load decreases.

[0005] 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.

Means for Solving the Problems

[0006] In a first embodiment of the present invention, a measuring device for measuring three-phase power supplied to a three-phase load housed in a housing includes a current measuring unit for measuring each line current input to the three-phase load. The measuring device further includes 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, and a third voltage measuring unit for measuring a third voltage between the third terminal of the three-phase load and the housing. The measuring device also includes a calculation unit for calculating the three-phase power based on the magnitudes of the first voltage, the second voltage, and the third voltage, as well as the magnitudes of each line current.

[0007] 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.

[0008] 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.

[0009] In a fourth aspect of the present invention, the program is a program that causes a computer for measuring three-phase power supplied to a three-phase load housed in a casing to perform the steps of: 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. [Effects of the Invention]

[0010] 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.

[0011] 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. [Brief explanation of the drawing]

[0012] [Figure 1] 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] Figure 2 is a block diagram showing an example of the functional configuration of a measuring device. [Figure 3] Figure 3 is a flowchart showing an example of the processing procedure for a measurement method using a measuring device. [Figure 4] Figure 4 is a block diagram showing the functional configuration of the processing unit according to the second embodiment. [Figure 5] Figure 5 is a flowchart showing an example of the processing procedure for a measurement method using a processing unit. [Figure 6] Figure 6 is a schematic diagram showing a modified example of a three-phase load measured by the measuring device.

Embodiments of the Invention

[0013] Hereinafter, each embodiment of the present invention will be described with reference to the accompanying drawings. Throughout this specification, the same or equivalent elements are denoted by the same reference numerals.

[0014] (First Embodiment) FIG. 1 is a schematic diagram showing the configuration of a measurement system including a measurement device according to the first embodiment.

[0015] The measurement system 100 is a system that measures the phase voltage, line voltage, or three-phase power of each phase supplied to a three-phase load housed in a housing. Examples of the three-phase load housed in the housing include a three-phase winding connected in Y and a three-phase winding connected in Δ.

[0016] Examples of devices composed of three-phase loads include a three-phase motor, a three-phase transformer, a three-phase reactor, and a three-phase capacitor. In the first embodiment, a three-phase motor 2 is adopted as an example.

[0017] The measurement system 100 of the first embodiment includes a measurement device 1 that measures the operating state of the three-phase motor 2, and current sensors 11 to 13 that detect the phase currents Iu, Iv, and Iw of each phase supplied to the three-phase motor 2. In the first embodiment, the first phase, the second phase, and the third phase correspond to the U phase, the V phase, and the W phase, respectively.

[0018] The three-phase motor 2 that is the measurement object of the measurement device 1 is composed of a three-phase load connected in Y having a neutral point N in the first embodiment. In FIG. 1, the impedances Zu, Zv, and Zw of the windings of the U phase, V phase, and W phase are shown as an equivalent circuit of the three-phase motor 2, and one ends of the windings of the U phase, V phase, and W phase are connected to the neutral point N, respectively. On the other hand, the other ends of the windings of the U phase, V phase, and W phase are connected to the input terminals 21 to 23 of the motor case 3, respectively.

[0019] In addition, capacitance and the like parasitically exist between the three-phase load constituting the three-phase motor 2 and the motor case 3. As such parasitic impedance Zr, an impedance with one end connected to the neutral point N and the other end connected to the motor case 3 is equivalently shown.

[0020] The motor case 3 is a conductive case that houses the three-phase motor 2 and is a housing that houses the connected three-phase load. The motor case 3 is connected to an external ground potential.

[0021] The measuring device 1 is a computer constituted by a processor, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, and a bus that interconnects these components. Examples of the processor include a CPU (Central Processing Unit) or a MPU (Micro Processor Unit).

[0022] The measuring device 1 measures the AC three-phase 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 indicating the magnitudes of the phase currents Iu, Iv, and Iw from the current sensors 11 to 13, respectively.

[0023] In addition, the measuring device 1 has four voltage detection cables. The terminals of three voltage cables are respectively connected to the three-phase input terminals 21 to 23, and the terminal of the remaining one voltage detection cable is connected to the detection terminal 24 of the motor case 3. Then, the measuring device 1 detects the input voltage of the three-phase load with reference to the potential of the motor case 3.

[0024] Note that the input terminals 21 to 23 correspond to the first to third terminals of the three-phase load. Further, the measuring device 1 may have three sets of a pair of voltage detection cables, connect each H side of the three sets of voltage cables to the three-phase input terminals 21 to 23 respectively, and connect each L side of the three sets of voltage detection cables to the detection terminal 24 of the motor case 3.

[0025] 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," 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."

[0026] 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.

[0027] 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.

[0028] The current sensors 11 to 13 can be non-contact or contact type current sensors, and the current sensors 11 to 13 of 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.

[0029] 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.

[0030] Next, the configuration of the measuring device 1 will be explained with reference to Figure 2.

[0031] Figure 2 is a block diagram showing the functional configuration of the measuring device 1 according to the first embodiment.

[0032] 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.

[0033] 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.

[0034] 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 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.

[0035] 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.

[0036] The voltage measurement unit 20 generates voltage measurement data showing the measured values ​​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.

[0037] 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.

[0038] The first voltage measurement unit 20a converts a voltage signal showing the detected amount of the chassis reference voltage Uue between the U-phase input terminal 21 and detection terminal 24 in a time series into voltage measurement data showing the measured amount of the chassis 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.

[0039] 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.

[0040] 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.

[0041] For example, the second voltage measurement unit 20b converts a voltage 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 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.

[0042] The processing unit 30 functions as a calculation unit that calculates the three-phase power supplied to a three-phase load based on the magnitudes of the chassis reference voltages (Uue, Uve, Uwe) and the phase currents (Iu, Iv, Iw) of each phase that are measured. The processing unit 30 is composed of, for example, one or more processors.

[0043] For example, the processing unit 30 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, and obtains the three-phase power supplied to the three-phase motor 2 by adding or averaging the powers of each phase.

[0044] In the first embodiment, the processing unit 30 acquires 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 equation (1) below.

[0045] [Mathematics 1] Pe = Iu·Uue+Iv·Uve+Iw·Uwe ···(1)

[0046] Thus, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and instantaneous voltage value shown in the U-phase current measurement data and voltage measurement data, and calculates the power value (Iu·Uue) by taking the average value of the waveform over one or more periods. Then, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and instantaneous voltage value shown in the V-phase current measurement data and voltage measurement data, and calculates the power value (Iv·Uve) by taking the average value of the waveform over one or more periods.

[0047] Furthermore, the processing unit 30 calculates the instantaneous power value by multiplying the instantaneous current value and instantaneous voltage value shown in the W-phase current measurement data and voltage measurement data, and calculates the power value (Iw·Uwe) by taking the average value of the waveform for one or more periods. The processing unit 30 obtains the three-phase power Pe by adding the calculated U-phase power value (Iu·Uue), the V-phase power value (Iv·Uve), and the W-phase power value (Iw·Uwe). The processing unit 30 may also use the measured quantity obtained by averaging the acquired three-phase power Pe as the three-phase power Pe.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Next, the operation of the measuring device 1 will be explained with reference to Figure 3.

[0054] Figure 3 is a flowchart showing an example of the processing procedure for a measurement method using measuring device 1.

[0055] 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.

[0056] 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 obtained from the current sensors 11 to 14.

[0057] 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, 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, and 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.

[0058] 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.

[0059] Since the measured values ​​of the chassis reference voltages Uue, Uve, and Uwe are obtained with reference to the chassis 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Once the process in step S4 is completed, the series of processing steps (S1 to S4) is finished, and the measurement method of the first embodiment is completed.

[0064] Next, the effects and benefits of the first embodiment will be described.

[0065] 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.

[0066] Furthermore, the measuring device 1 includes a second voltage measuring unit 20b that measures the chassis 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 chassis 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.

[0067] 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.

[0068] Furthermore, the measurement method according to the first embodiment measures the three-phase power Pe supplied to a three-phase load housed in the motor case 3. 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.

[0069] 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.

[0070] Furthermore, the program according to the first embodiment is a program 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, to execute the above steps S1 to S3.

[0071] 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 parasitic impedance Zr, which consists of parasitic capacitance and other components. 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.

[0072] In contrast, with the above configuration, the chassis reference voltages (Uue, Uve, Uwe) for each phase 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.

[0073] Therefore, by using the three-phase enclosure reference voltages Uue, Uve, and Uwe when measuring the state of a 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.

[0074] 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 each corresponding phase. The processing unit 30 then obtains the three-phase power Pe of the three-phase motor 2 by adding the powers of each phase.

[0075] 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.

[0076] 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.

[0077] 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, allowing the operator to accurately understand the operating state of the three-phase motor 2.

[0078] 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.

[0079] With this configuration, the phase currents (Iu, Iv, Iw) of each phase can be measured using current sensors 11 to 13.

[0080] (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. A second embodiment describes a configuration in which parameters other than the three-phase power Pe are calculated.

[0081] 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.

[0082] 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.

[0083] 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) for each phase.

[0084] 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. Hereafter, 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."

[0085] 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.

[0086] 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.

[0087] Here, we will briefly explain the method for deriving the three-phase phase voltages Uun, Uvn, and Uwn, relative to the neutral point N, from the three-phase chassis reference voltages Uue, Uve, and Uwe.

[0088] 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.

[0089] [Math 2] Uuv = Uue-Uve Uvw = Uve - Uwe ···(2) Uwu = Uwe-Uue

[0090] Next, the phase voltages Uun, Uvn, and Uwn of the three-phase system are derived from the obtained line voltages Uuv, Uvw, and Uwu by using the Δ-Y transformation shown in equations (3) to (5).

[0091] [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) [Number 5] Uwn = (Uwu-Uvw) / 3 = {(Uwe-Uue)-(Uve-Uwe)} / 3 = (2Uwe-Uue-Uve) / 3 ···(5)

[0092] 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.

[0093] 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.

[0094] For example, the phase voltage conversion unit 31 obtains a subtraction result (2Uue-Uve-Uwe) by subtracting the sum of the chassis reference voltages Uve and Uwe of the other V and W phases from a voltage value (2Uue) obtained by doubling the chassis 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.

[0095] Furthermore, the phase voltage conversion unit 31 obtains a subtraction result (2Uve-Uwe-Uue) by subtracting the sum of the chassis reference voltages Uwe and Uue of the other W and U phases from a voltage value (2Uve) obtained by doubling the chassis 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.

[0096] Furthermore, the phase voltage conversion unit 31 subtracts the sum of the chassis reference voltages Uue and Uve of the other U and V phases from a voltage value (2Uwe) obtained by doubling the chassis reference voltage Uwe of the W phase to obtain a subtraction result (2Uwe-Uue-Uve). Then, the phase voltage conversion unit 31 divides this subtraction result by 3 to calculate the phase voltage Uwn of the W phase.

[0097] The phase voltage conversion unit 31 outputs the calculated three-phase phase voltages Uun, Uvn, and Uwn to the motor analysis unit 32.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 periods, 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.

[0103] 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.

[0104] Next, the operation of the measuring device 1A will be explained with reference to Figure 5.

[0105] Figure 5 is a flowchart showing an example of the processing procedure for a measurement method using measuring device 1A.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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 voltage (Uun, Uvn, Uwn) of each phase.

[0110] For example, 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.

[0111] 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.

[0112] Once the processing 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.

[0113] Next, the effects and benefits of the second embodiment will be described.

[0114] 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.

[0115] Furthermore, the measuring device 1A 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.

[0116] 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.

[0117] Furthermore, the measurement method and program according to the second embodiment are, respectively, the measurement method and program executed by the measurement device 1A described above.

[0118] 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 parasitic impedance Zr, which consists of parasitic capacitance and the like. On the other hand, in many cases, the measurement target, such as a three-phase motor, cannot be accessed from the 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.

[0119] 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, these voltages can be considered to reflect the influence of the 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.

[0120] 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 chassis reference voltages Uue, Uve, and Uwe from a voltage value obtained by doubling one of the three-phase chassis reference voltages Uue, Uve, and Uwe by 3.

[0121] With this configuration, the three-phase phase voltages Uun, Uvn, and Uwn are obtained using the Y-Δ and Δ-Y conversion 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.

[0122] 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 still be obtained.

[0123] 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.

[0124] Furthermore, the processing unit 30A calculates the amplitude or phase of the phase voltages (Uun, Uvn, Uwn) of each phase.

[0125] 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.

[0126] Furthermore, the processing unit 30A calculates the amplitude or phase of the fundamental frequency with respect 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, by performing frequency analysis.

[0127] 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.

[0128] <Variation> 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.

[0129] Figure 6 is a conceptual diagram showing a modified example of a three-phase motor 2 measured by the measuring device 1.

[0130] 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.

[0131] One end of impedance Zuv is connected to one end of impedance vw, 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.

[0132] 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.

[0133] [Number 6] Zu' = Zuv·Zvw / (Zuv+Zvw+Zwu) Zv' = Zvw·Zwv / (Zuv+Zvw+Zwu) ···(6) Zw' = Zwv·Zuv / (Zuv+Zvw+Zwu)

[0134] 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.

[0135] In other words, the measuring device 1 measures the chassis reference voltages Uue, Uve, and Uwe of the three-phase load constituting the three-phase motor 2A, as in 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 chassis reference voltages Uue, Uve, and Uwe as shown in equation (1) above.

[0136] 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.

[0137] 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 without a neutral point N, and in particular the phase voltages of each phase (Uun, Uvn, Uwn).

[0138] 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. [Explanation of Symbols]

[0139] 100 Measurement Systems 1. 1A measuring device 2. Three-phase motor (three-phase load) 3. Motor case (housing) 10 Current measurement section 20a First voltage measurement section 20b Second voltage measurement section 20c Third voltage measurement section 21-23 Input terminals (first to third terminals of a 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 Enclosure reference voltage (first voltage, second voltage, third voltage) Uun, Uvn, Uwn Phase Voltage Uun', Uvn', Uwn': Virtual phase voltages

Claims

1. A measuring device for measuring the three-phase power supplied to a three-phase load housed in an enclosure, A current measuring unit for measuring the line current of each of the three-phase loads, A first voltage measuring unit for measuring the first voltage between the first terminal of the three-phase load and the housing, A second voltage measuring unit for measuring the second voltage between the second terminal of the three-phase load and the housing, A third voltage measuring unit for measuring the third voltage between the third terminal of the three-phase load and the housing, A calculation 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 each line current, A measuring device equipped with the following features.

2. A measuring device according to claim 1, The calculation unit calculates the power of each phase of the three-phase load by multiplying the corresponding first voltage, second voltage, and third voltage, as well as the magnitude of the line current, and obtains the three-phase power by adding the powers of each phase. Measuring device.

3. A measuring device for measuring the phase voltage supplied to a three-phase load housed in a casing, A first voltage measuring unit for measuring the first voltage between the first terminal of the three-phase load and the housing, A second voltage measuring unit for measuring the second voltage between the second terminal of the three-phase load and the housing, A third voltage measuring unit for measuring the third voltage between the third terminal of the three-phase load and the housing, A calculation unit that calculates the phase voltages 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, A measuring device equipped with the following features.

4. The measuring device according to claim 3, The calculation unit 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 ​​from the voltage obtained by doubling one of the voltage values ​​of the first voltage, second voltage, and third voltage by 3. Measuring device.

5. The measuring device according to claim 3, The calculation unit calculates the amplitude or phase of the phase voltage of each phase. Measuring device.

6. The measuring device according to claim 3, The calculation unit performs frequency analysis to calculate the amplitude or phase of the fundamental frequency with respect to the phase voltage of each phase, or the amplitude or phase of the harmonic frequency with respect to the fundamental frequency. Measuring device.

7. A measuring device according to claim 1 or claim 3, A measuring device further comprising a display unit that displays the results calculated by the aforementioned calculation unit.

8. A measuring device according to claim 1, A measuring device further comprising a plurality of current sensors arranged on the electric wires through which the aforementioned line currents flow, for detecting the aforementioned line currents.

9. A measurement method for measuring the three-phase power supplied to a three-phase load housed in an enclosure, The steps include measuring the line current of each of the three-phase loads, The steps include measuring the first voltage between the first terminal of the three-phase load and the housing, The steps include measuring the second voltage between the second terminal of the three-phase load and the housing, The steps include measuring the third voltage between the third terminal of the three-phase load and the housing, 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, A measurement method comprising the following features.

10. A computer that measures the three-phase power supplied to a three-phase load housed in an enclosure, The steps include measuring the line current of each of the three-phase loads, The steps include measuring the first voltage between the first terminal of the three-phase load and the housing, The steps include measuring the second voltage between the second terminal of the three-phase load and the housing, The steps include measuring the third voltage between the third terminal of the three-phase load and the housing, A program for performing the steps 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.

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