JPS5850474A - Measuring method for line-to-line impedance - Google Patents

Abstract

PURPOSE:To measure a line impedance in an arbitrary phase by computing the line-to-line impedance from the maximum values of voltage and current and the phase difference of an injected wave to be measured in a prescribed phase of a power-line AC voltage. CONSTITUTION:The phase of a power-line AC voltage in a low-voltage distribution line 1 is detected by a power-line AC wave phase detecting circuit 7. When it becomes a phase to be measured, a wave to be measured of known frequency is injected into the line of the low-voltage distribution line 1 via an injection circuit 3. The graph shows the waveform of the voltage (curve v) of the injected wave to be measured and the waveform of the current (curve i) thereof, wherein T denotes the interval of one cycle of the injected wave to be measured, ta a time of the phase difference between the waveform of the voltage v and that of the current i, Vp the maximum value of the waveform of the voltage, and Ip the maximum value of the waveform of the current, respectively. Accordingly, the absolute value¦Z¦of a line-to-line impedance on the occasion can be calculated by¦Vp/Ip¦and the phase difference theta by ta/TX 2pi, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring line impedance, and particularly to a method for measuring line impedance in a low voltage distribution line.

Currently, power lines such as low-voltage distribution lines are used for remote measurement and remote control that transmit signals using a phase pulse method. In this case, in order to know the signal transmission characteristics of the power line, it is necessary to measure the line-to-line impedance of the power line at the signal frequency.

Conventionally, to measure this line-to-line impedance, a measurement wave of a known frequency is injected between the power lines, the voltage and current values at that time are measured, and the line-to-line impedance is calculated from the measured values. A method is being taken. However, although this integration-based effective value measurement method can measure the average line-to-line impedance of a power line, it cannot measure the line-to-line impedance at any phase of the power line AC voltage.

In other words, many of the loads connected to low-voltage distribution lines include various household electrical appliances and other electrical equipment that have built-in rectifiers and thyristors. When we actually look at the current flow state of a load that incorporates these rectifiers and thyristors, no current flows near the zero-crossing point of the voltage wave, and the conduction angle of the flowing current varies depending on the conduction angle control of the thyristor.

For this reason, line impedance varies depending on the phase of the power line AC voltage.

Conventional measurement methods cannot accurately determine the difference in line impedance due to phase.

The purpose of the present invention is to eliminate such drawbacks of the prior art,
An object of the present invention is to provide a line impedance measurement method capable of measuring line impedance at any phase of a power line AC voltage.

To achieve this objective, the present invention injects a measurement wave of a known frequency between the lines of a power line such as a low-voltage distribution line at a predetermined phase of the power line AC voltage, and the maximum value of the voltage waveform of the measurement wave is The method is characterized in that the maximum value of the current waveform and the phase difference between the voltage waveform and the current waveform are measured, respectively, and the line-to-line impedance in the power line is calculated from these measured values.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram for explaining the method for measuring line impedance of the present invention, and FIG. 2 is a diagram of voltage and current waveforms of measurement waves.

Figure 1 shows a low-voltage power distribution line whose line-to-line impedance is to be measured.Although not shown, it has countless drop-in wires, and each drop-in wire is connected to various household appliances and other electrical devices. . 2 is a measurement wave power supply, from which the measurement wave of a known frequency is outputted to the injection circuit 3.
It is injected between the lines of the low-voltage distribution line 1 via the. 4 is an ammeter, 5 is a voltmeter, 6 is a measurement wave phase difference detection circuit that detects the phase difference between the voltage waveform and current waveform of the measurement wave injected into the low-voltage distribution line 1, and 7 is the power line AC of the low-voltage distribution line 1. A power line AC wave phase detection circuit 8 detects the phase of a power line AC wave based on each detected value from the ammeter 4, voltmeter 5, measurement wave phase difference detection circuit 6, and power line AC wave phase detection circuit 7. This is an arithmetic device that calculates inter-impedance.

Next, a method for measuring line impedance will be explained.

The phase of the power line AC voltage on the low voltage distribution line 1 is detected by the power line AC wave phase detection circuit 7 as described above, so when the phase to be measured is reached, a measurement wave of a known frequency is sent via the injection circuit 3. Inject between 10 low-voltage distribution lines.

FIG. 2 is a diagram showing the voltage waveform (curve V) and current waveform (curve i) of the injected measurement wave, where T in the figure is one cycle interval of the injected measurement wave, 1. is the phase difference time between the voltage waveform V and the current waveform i, ■ is the maximum value of the voltage waveform, and IP is the maximum value of the current waveform. Therefore, the phase difference θ is t Samurai x 2x
can be calculated respectively.

Figure 3 (a), (b), (c), ni) shows the low voltage distribution line 1
FIG. 3 is a diagram for explaining that line impedance changes depending on the phase of a power line AC voltage in FIG. Same figure (
(a) is a waveform diagram of the power line AC voltage, and (b) is a diagram showing the voltage level of the injection measurement wave. L in the diagram is the maximum voltage value,
indicates the effective voltage value. FIG. 3(C) is a diagram showing the current level of the injection measurement wave, and shows a state in which the current value changes in two stages due to a difference in the phase of the power line AC voltage. Il+1 in the figure is t. - The maximum current value between t8, h, is 11
-1. Maximum value of current between, ■1 is 1o-1, effective value of current between, ■.

is 1. -1. The rms current value in between, and . ) is a calculation diagram showing that the absolute value IZI of impedance is different in each phase.

By the way, impedance Z is expressed by the following equation (1).

Z=R+ jx ・・・・・・・・・
(1) However, in the formula, 几 is an equivalent resistance value, and X is an equivalent reactance. And the equivalent resistance value R is as follows (2
), the equivalent reactance X is determined by the following equation (3), so the equation (1) can be transformed into equation (4).

t.

几＝IZI cos〒×2π ・・・・・・
・・・・・・・・・(2)°t1 ・
・・・・・・・・・・・・・・・(3)X=l Zl
s t n T
n 〒 The respective impedances can be calculated accurately. As shown in FIG. 1, the phase of the power line AC wave is determined by the power line AC wave phase detection circuit 7 based on the phase difference time t between the voltage waveform and the current waveform.

is the maximum voltage value ■ of the measurement wave phase difference detection circuit 6.

is measured by the voltmeter 5, and the maximum value of the current is measured by the ammeter 4, and these measured values are input to the calculation device 8,
The line impedance is calculated based on the above equations (4) and (5).

FIG. 4 is a calculation diagram of the impedance absolute value IZI by conventional integration corresponding to FIG. 3), in which IZ+ is only calculated as a constant value in any phase.

As explained above, according to the present invention, line impedance is calculated from the voltage maximum value, current maximum value, and phase difference of the injection measurement wave at a predetermined phase of the power line AC voltage. Line-to-line impedance can be calculated within two cycles, and line-to-line impedance at any phase can be measured.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the method for measuring line impedance of the present invention, Fig. 2 is a voltage and current waveform diagram of the injection measurement wave, Fig. 3 (a) is a waveform diagram of the power line AC voltage, Figure 3 (b) is a diagram showing the voltage level of the injection measurement wave, Figure 3 (c) is a diagram showing the current level of the injection measurement wave, Figure 3) is a diagram for calculating the absolute value of impedance, and Figure 4 is a calculation diagram of an absolute value of impedance using a conventional measurement method. DESCRIPTION OF SYMBOLS 1... Low voltage distribution line, 2... Measurement wave power source, 3... Injection circuit, 4... Ammeter, 5... Voltmeter, 6... Measurement wave phase difference detection circuit, 7... ...Power line AC wave phase detection circuit, 8... Arithmetic device, V... Voltage waveform of measurement wave, i
... Current waveform of measurement wave, ■, ... Maximum value of voltage waveform, ■, ... Maximum value of current waveform, 1. ...Phase difference time, Z...Line impedance patent applicant Osaki Electric Co., Ltd. agent Nakamura
Fertility 1 Kosai 2 days

Claims (1)

[Claims] 1. Inject a known frequency measurement wave at a predetermined phase of the power line AC voltage between the power lines, and calculate the maximum value of the voltage waveform and the maximum value of the current waveform of the measurement wave, and the phase difference between the voltage waveform and the current waveform. A method for measuring line-to-line impedance, characterized in that the line-to-line impedance is calculated from the measured values.