JPS6356504B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an electric meter for measuring phase difference or power factor in a power supply line.

[Technical background of the invention]

FIG. 1 is a block diagram of a conventional electric meter for measuring phase difference or power factor in a power supply line. This electric meter transforms the load voltage on a power supply line (not shown) using a meter transformer 1 and outputs it as a first voltage signal ev proportional to the load voltage. It is output as a second voltage signal ei proportional to the flowing current consumption. Here the first
And the second voltage signals ev, ei are expressed as ev=√2Vsinωt...(1) ei=√2lsin(ωt−)...(2), assuming their phase difference. These first and second voltage signals ev, ei are sent to the active power measuring section 3 and the apparent power measuring section 4. Here, the active power measuring section 3 calculates the active power W based on the following formula.

W=∫ ^T _O ev・eidt=VIcos…(3) On the other hand, the apparent power measurement unit 4 measures the apparent power P based on the following formula. P=∫ ^T _O |ev|dt ・∫ ^T _O |ei|dt =VI (4) T is one period of the first and second voltage signals ev, ei. The electric powers W and P measured by these measuring sections 3 and 4 are sent to a dividing section 5, and the dividing section 5 performs the calculation (W/P). That is, the first
From equation (3) and equation (4), (W/P) becomes W/P=vIcos/VI=cos (5).

Then, the power factor cos is determined, and then cos ^-1 is calculated using a microcomputer, etc. (not shown).
(cos) is performed to determine the phase difference.

[Problems with background technology]

However, in the electric meter shown in Figure 1, (3)
Because the power factor cos is determined by the measurement means and calculations shown in equations (4) and (5), errors occurring in the active power measurement section, apparent power measurement section, and division section are The superimposed error becomes the final error. Therefore, each of these parts required a measuring means with excellent linearity of characteristics.

In addition, since the active power measuring section in particular has a phase characteristic in which the measurement error increases as the phase difference increases, the accuracy of the entire device also increases.
There was a problem that the problem worsened as the phase difference increased. Furthermore, if the phase difference becomes large, there is a problem in that it greatly affects the power factor characteristics.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
It is an object of the present invention to provide a highly accurate electric meter that can accurately measure power factor and phase difference regardless of the magnitude of the phase difference.

[Summary of the invention]

The present invention provides a first
and the second voltage signal is delayed by a delay circuit, and based on the first and second voltage signals and the delayed signal, the correlation calculation unit calculates the active power and the apparent power, and then the division value of these powers. Based on this division value, the delay drive circuit makes the phase difference between the first and second voltage signals to the correlation calculation section zero, and the delay circuit outputs a drive signal with a frequency that maximizes the division value. The electric meter is an electric meter that drives the delay circuit by sending a signal to the drive signal, and calculates a phase difference and a power factor using an arithmetic circuit based on the drive signal.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Note that the same parts as in FIG. 1 are given the same reference numerals and detailed explanations will be omitted. As shown in FIG. 2, the electric meter of the present invention is newly provided with an analog delay circuit 10, an analog delay drive circuit 11, and an arithmetic circuit 12, and further includes an active power measuring section 3, an apparent power measuring section 4, and a dividing section 5. Correlation calculation unit 1
3.

The analog delay circuit 10 is provided between the instrument current transformer 2 and the apparent power measuring section 4, and delays the second voltage signal ei from the instrument current transformer 2. (Charge Coupled Device) or BBD (Bucket Brigade Device) is used, and the number of analog delay stages is N (N is an integer).
is determined by the required accuracy of the meter and is driven by an analog delay drive circuit 11.

The analog delay drive circuit 11 has a function of inputting the calculation result from the division unit 5 in time series and controlling the delay time of the analog delay circuit 10 at a driving frequency at which the calculation result, that is, the division value is maximum. The arithmetic circuit 12 is the analog delay drive circuit 1
This is a circuit for calculating phase difference or power factor from a single drive frequency.

Next, the operation of the electric meter configured as described above will be explained. An instrument transformer 1 and an instrument current transformer 2 provide first and second voltage signals ev, ei that are proportional to the load voltage and current consumption in a power supply line (not shown). Here, assuming the phase difference, the first and second voltage signals ev and ei are as follows: ev=√2Vsinωt (8) ei=√2lsin(ωt−)…(9). Here, the second voltage signal ei becomes a voltage signal delayed by the phase difference θ by the analog delay circuit 10 as follows: eiθ=√2Isin(ωt−−θ) (10).

This phase difference θ is as follows, where N is the number of shift stages of the analog delay circuit 10 and the frequency driven by the analog delay drive circuit 11 is θ=N//1/ ₀ ×2π [radians] (11). ( ₀ is the power supply frequency) and the first voltage signal ev and voltage signal eiθ are sent to the active power measurement unit 3 and apparent power measurement unit 4 of the correlation calculation unit 13, respectively.
sent to. The active power measuring section 3 calculates the active power Wθ based on the following formula.

Wθ=∫ ^T _O ev·eiθdt = VI cos (+θ) (12) Further, the apparent power measuring section 4 calculates the apparent power P based on the following formula.

P=∫ ^T _O |ev|dt×∫ ^T _O |eiθ|dt=VI (13) Then, the division value (Wθ/P) of each power value Wθ, P is calculated by the division unit 5 and obtained. .

Wθ／P＝∫ ^T ／ _O ev・eiθdt／∫ ^T ／ _O |ev｜dt×∫ ^T ／
_O | eiθ | dt = cos (+θ) ... (14) The analog delay drive circuit 11 uses this divided value cos
The analog delay circuit 10 is driven at a driving frequency that maximizes (+θ). That is, the phase difference θ is controlled so as to satisfy +θ=2nπ (n: integer). Therefore, the voltage signals ev and eiθ having no phase difference are input to the active power measuring section 3 and the apparent power measuring section 4.

The arithmetic circuit 12 inputs the driving frequency and calculates the following: =2nπ-θ = (n-N//1/ ₀ )×2π [radian]...(
15) Perform phase calculation using , and power factor calculation using cos.

In this way, in this electric meter, the two signals ev and eiθ input to the active wattmeter are controlled so that there is always no phase difference, so the phase characteristics of the active wattmeter do not matter. In addition, in the conventional technology, the power factor cos or phase difference is obtained by measuring the active power value W and the apparent power value P, and then calculating W/P based on these values. Since the final error is the superimposition of errors occurring in the measurement section, apparent power measurement section, and division section, each section required a measuring means with excellent realistic characteristics. With this electric meter, it is only necessary to correctly judge the magnitude comparison in equation (14), and if you know the drive frequency at which this is the maximum, you can find the phase difference using equation (15).
The active power measurement section, apparent power measurement section, and division section include
Highly accurate measurement is possible without requiring any linearity.

Next, another embodiment of the present invention will be described with reference to FIG. Note that the same parts as in FIG. 2 are given the same reference numerals and detailed explanations will be omitted. FIG. 3 is a configuration diagram showing another embodiment of the electric meter according to the present invention. The electric meter shown in FIG.
ev is delayed so that the phase difference with the second voltage signal ei from the instrument current transformer 2 is made zero.

It goes without saying that an electric meter configured as shown in FIG. 3 also has the same effects as the first embodiment.

〔Effect of the invention〕

According to the present invention, the delay means is driven at a driving frequency that maximizes the division value obtained by the correlation calculation section, and the phase difference between the first and second voltage signals to the correlation calculation section is set to zero, and the power factor and Since the phase difference is measured, it is possible to provide a highly accurate electric meter that can accurately measure the power factor and phase difference regardless of the magnitude of the phase difference between the first and second voltage signals.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional electric meter, Figure 2
The figure is a block diagram showing one embodiment of the electric meter according to the present invention, and FIG. 3 is a block diagram showing another embodiment of the electric meter. 1...Instrument transformer, 2...Instrument current transformer, 3
... Active power measurement section, 4 ... Apparent power measurement section, 5
...Division section, 10... Analog delay circuit, 11...
... Analog delay drive circuit, 12 ... Arithmetic circuit, 1
3...Correlation calculation section.

Claims (1)

[Claims] 1. A transformer that outputs a first voltage signal proportional to the load voltage of the power supply line, a current transformer that outputs a second voltage signal that is proportional to the consumed current flowing through the power supply line, and the transformer and the transformer. a delay circuit that delays either one of the first and second voltage signals from the current transforming means; and the first and second voltage signals from the voltage transforming means and the current transforming means and a delayed signal from the delay circuit. a correlation calculation unit that calculates the active power and apparent power in the feeder line and calculates a division value between the active power and the apparent power; a delay drive circuit that supplies a drive signal with a frequency that makes the phase difference of the second voltage signal zero to the delay circuit; and a delay drive circuit that calculates the power factor in the feed line based on the frequency of the drive signal from the delay drive circuit. An electric meter characterized by comprising an arithmetic circuit for determining a phase difference.