JPH0545913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the power factor of a particularly small portable power factor meter equipped with a phase detection function.

[Conventional technology]

Small portable measuring instruments such as phase detectors that measure the positive and negative phases of three-phase circuits and power factor meters that measure the power factor have traditionally been constructed separately, but recently they have been equipped with a phase detection function. Integrated digital power factor meters are becoming available.

An example is shown in FIG.
For example, a switch 2, a three-phase/single-phase switching means 3,
A phase detection section 4 and a power factor measurement section 5 are provided, and when the electrical circuit to be measured has three phases, the switch 2 is set to the three-phase side, and when it is single-phase, the switch 2 is set to the single-phase side. There is. The three-phase/single-phase switching means 3 reads the information from this switch, and in the case of three phases, operates the phase detection section 4, for example, and operates the power factor measuring section 5 as a three-phase power factor meter, and inputs the voltage. The phase detection unit 4 measures the positive phase, negative phase, or open phase of the line voltage applied to the terminal, and the power factor measurement unit 5 measures the line current applied to the current input terminal and the above voltage. Measure power factor. In the case of a single phase, there is no need for phase detection, so for example, the power factor measuring section 5 is operated as a single phase power factor meter to measure the power factor of the electric circuit. These measurement data are displayed on the display 6, respectively.

[Problem to be solved by the invention]

The above-mentioned device has the advantage that it is convenient, especially when working outdoors, because it reduces the need for two measuring instruments to one.

However, whether the circuit to be measured is three-phase or single-phase is usually known in advance by the measurer, and in handheld measuring instruments that can be held in the palm of your hand, operating parts such as switches are It is desirable to reduce the amount.

This invention was made in view of the above circumstances,
The purpose is to provide a power factor measurement method suitable for a small portable power factor meter that detects the phase of an electric circuit and measures the power factor without switching between three-phase and single-phase using a switch or the like.

[Means to solve the problem]

An embodiment of a device to which this invention is applied is shown in FIG. Referring to the figure, in order to solve the above problem, the phase detector 10 and the power factor measuring section 20 are equipped with the following means.

B For example, the two line voltages V _RS and V _TS of a three-phase circuit
A rise detector 15 and a level detector 16 which shape the waveforms into square waves of levels 0 and 1 by waveform shapers 13 and 14, respectively, and detect the rise and level of the waves.

(b) For example, by receiving the outputs of the rise detector 15 and level detector 16, two voltages V _RS ' and
A level comparator 17 that compares which of V _TS ' is level 1 and which is level 0.

C. Receive the comparison output of the level comparator 17, and if the level relationship is, for example, V _RS ′:V _TS ′=0:1, it is determined that the phase is positive, and if V _RS ′:V _TS ′=1:0, it is determined that the phase is reversed. , V _RS ', V _TS ', if there is no level change from 0 to 1 or from 1 to 0 indicating rising or falling in one or both of them, the phase order discriminator 18 determines that a phase is missing.

D. For example, the current I _R flowing through the electric path R detected by the sensor 21 is converted into a voltage V _IR , and this voltage V _IR and the voltage V _RS are converted into rectangular shapes of levels 0 and 1 by the waveform shapers 23 and 24, respectively. A rise detector 25 and a level detector 26 detect the rise and level of the wave after shaping the wave.

E The above rise detector 25 and level detector 2
a phase difference φ detector 27 which receives the output of 6, detects the phase difference φ between the voltage V _IR ' representing the current component with respect to the voltage V _RS ', and sends out a phase difference signal proportional to the magnitude of the phase difference φ; A phase polarity detector 28 detects the lead/lag of the phase difference φ and sends out a corresponding - or + polarity signal, for example.

(f) Digital conversion data of the phase difference signal sent from the phase difference φ detector 27, a lead/lag polarity signal sent from the phase polarity detector 28, and a positive phase, negative phase, or For example, if a phase sequence signal indicating an open phase is received, the circuit R
a phase angle θ calculator 30 that calculates the phase angle θ of the current I _R with respect to the phase voltage V _R ; and a cos θ calculation path 31 that calculates the power factor cos θ of a three-phase or single-phase circuit based on this phase angle θ.

[Effect]

By providing the above means, in the case of a three-phase electrical circuit, it is possible to determine whether the two electrical circuits R-S and T-S are in positive phase or reverse phase, and the lead/lag power factor cosθ
are determined and displayed on the display 32, for example. Also, if there is an open phase in the electrical circuit, it will be displayed as open phase.

In the case of a single phase, there is one set of electrical circuits to be measured, so if this is, for example, R-S, the input terminal T becomes an empty terminal and is not used. In this case, an open phase is displayed, and the measured power factor value is displayed for the original single-phase circuit R-S.

〔Example〕

Referring again to FIG. 1, this device includes a phase detection section 1.
0, a power factor measuring section 20, a display 32, etc., and input terminals R, S, and T are connected to electrical circuits to be measured. Further, the current flowing through the electric path is taken into the power factor measuring section 20 via the sensor 21, for example.

Here, to explain the phase detection of a three-phase circuit while also referring to Fig. 2, the input terminals R, S, T
The two voltages V _RS and V _TS applied to the circuit are divided, for example, through attenuators 11 and 12 into electronic circuit level voltages as shown in FIG. 2A. In FIG. 1A, the voltage waveform V _TS shown by a solid line is ahead of V _RS in phase, and the voltage waveform V _TS shown by a dotted line is behind V RS in phase. In this embodiment, phase lead and lag are represented by, for example, - and + symbols.

The divided voltages V _RS and V _TS are converted into square wave voltages V _RS ′ and V _TS ′ by waveform shapers 13 and 14, for example, as shown in B, C, or D of FIG. 2. . These square wave voltages are applied to a rise detector 15 and a level detector 16, respectively, and the level of the other voltage at the time when one voltage rises is detected and sent to a level comparator 17.

The level comparator 17 compares the two input level detection signals and detects which voltage is level 1 and which voltage is level 0 based on the added rise detection signal. The phase order discriminator 18 determines that this detector signal is, for example, V _RS ′=0, V _TS ′
If =1, it is determined that the phase is positive, and if the level is the opposite, it is determined that the phase is reversed. If the voltage V _RS ′=V _TS ′, and V _RS ′,
When the rising edge (or falling edge) of one or both of V _TS ' is not detected by the rising edge detector 15, the phase order discriminator 18 determines that there is an open phase.

Next, power factor measurement will be explained with reference to FIG. For example, if the current flowing through the electrical circuit connected to the terminal R is I _R , this current is detected by the sensor 21, and is converted to an electronic circuit level voltage V _IR by the current/voltage converter 22 as shown in Figure 3A. converted. Here, the voltage V _IR shown by the solid line in Figure A is in a leading phase with respect to the line voltage V _RS , and the voltage shown by the dotted line
Let V _IR represent the delayed phase.

The voltage V _IR representing this current component and the voltage V _RS are applied to waveform shapers 23 and 24, for example, and
As shown in C or D, the waveforms are shaped into square wave voltages V _RS ′ and V _IS ′ at levels 0 and 1, and then sent to the rise detector 25 and level detector 26, respectively, where the rise and level are detected. It is becoming more and more common.

The phase difference φ detector 27 detects the phase difference φ between the voltages V _{RS ′} and V _{IR ′} as shown in FIG. , a phase difference signal whose magnitude is proportional to this φ is generated. Further, the phase polarity detector 28 detects, for example, the lead or lag of the phase difference φ, and correspondingly -
Alternatively, a + phase polarity signal is sent out.

The phase difference signal emitted from the phase difference φ detector 27 is digitally converted by, for example, an A/D converter 29 and is applied to a phase angle θ calculator 30.
The phase angle θ calculator 30 calculates the circuit current with respect to the phase voltage V _R as shown in FIG. I _R phase angle +θ (or -
Find θ). As a result, the power factor cosθ (or -cosθ) is calculated in the cosθ calculator 31, and the display 3
2 is now displayed. In this case, if there is an open phase in the electric circuit, it is displayed as an open phase, and the power factor with θ = φ without three-phase correction is also displayed, but this value has no meaning as power factor data for the three-phase electric circuit. Since there is no phase difference, ignore it and re-measure it after the circuit is in a state where there is no open phase.

In the case of a single phase, the power factor is naturally determined by setting the phase angle θ=φ as shown in FIG. 4A. Note that, as described above, one of the three input terminals becomes an empty terminal, so that the power factor of the original single-phase circuit is displayed, and an open phase is also displayed.
This indication of open phase has no meaning as a single-phase circuit, so it can be ignored.

FIG. 5 shows a flow diagram of an example in which the operations of some units in the phase detection section 10 and power factor measurement section 20 are replaced by, for example, a microcomputer. In the figure, for example, polarity measurement and phase measurement may be performed before determining the presence or absence of an open phase.

〔effect〕

As explained above in detail, the present invention operates the phase detection means for detecting the positive phase, reverse phase, open phase, etc. of the electrical circuit under test and its power factor measuring means in parallel without switching, and For example, when measuring a phase circuit, when an open phase is detected, priority is given to it and the power factor measurement value at that time is ignored, and when a positive phase or negative phase is detected, the power factor measurement value is used as the normal power factor. I'm trying to figure out the data.

Further, in the measurement of a single-phase electric circuit, even if the phase detection data indicates an open phase, it is ignored, and the power factor measurement value obtained at that time is used as the original power factor data of the single-phase electric circuit.

Therefore, according to the present invention, it is possible to perform power factor measurement that also serves as phase detection without the need for switching between 3-phase/single-phase including the operation of a switch, etc., resulting in a more compact and cost-effective device. It can be of great help. Furthermore, since there is no changeover switch, operational errors such as performing three-phase measurement in a single-phase state are also prevented.

[Brief explanation of drawings]

1 to 5 relate to embodiments of the present invention; FIG. 1 is a block diagram showing the configuration of a device to which this invention is applied; FIGS. 2 and 3 are waveform diagrams for explaining operation; FIG. 4 is a vector diagram showing an example of phase angle measurement, FIG. 5 is a flowchart showing an example of the measurement operation by a microcomputer, and FIG. 6 is a block diagram showing an example of the configuration of a conventional device. In the figure, 10 is a phase detector, 18 is a phase order discriminator, and 20
3 is a power factor measuring section, 31 is a cos θ calculator, 32 is a display, and T, S, and R are input terminals connected to the electrical circuit to be measured.

Claims (1)

[Claims] 1 Phase detection of the electrical circuit to be measured is performed using the phase detection means, and if an open phase is not detected, the power factor measuring means is made to perform a three-phase measurement operation, and when an open phase is detected, the above means is made to perform a single phase measurement operation. A power factor measuring method characterized by performing measurement operations and displaying a power factor measurement value for each operation.