JPH0314145B2 - - Google Patents

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, with this method of measuring an effective value using integration, although it is possible to measure the average line-to-line impedance of a power line, it is not possible to 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, we find that 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 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.

SUMMARY OF THE INVENTION An object of the present invention is to provide a line-to-line impedance measurement method that can eliminate the drawbacks of the prior art and measure line-to-line impedance at any phase of a power line AC voltage.

To achieve this objective, the present invention injects a measurement wave of known frequency between the lines of a power line, such as a low-voltage distribution line, and during the injection of the measurement wave, said measurement at a predetermined phase of the power line alternating voltage. Measure the maximum value of the voltage waveform, the maximum value of the current waveform, and the phase difference between the voltage waveform and the current waveform, respectively, and calculate the line impedance in the power line from the measured values of the two maximum values and the phase difference. It is characterized by

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.

In Figure 1, 1 is the low-voltage distribution line whose 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. . Reference numeral 2 denotes a measurement wave power supply, from which a measurement wave of a known frequency is injected between the lines of the low-voltage distribution line 1 via an injection circuit 3. 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 wave, and 8 includes 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 line impedance based on each detected value from.

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

When a measurement is to be made, the injection circuit 3 sends a measurement wave of a known frequency from the measurement wave power source 2 to the low voltage distribution line 1.
Inject between the lines. Figure 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 the one-cycle interval of the injected measurement wave, t _a
is the phase difference time between the voltage waveform v and the current waveform i, V _P is the maximum value of the voltage waveform, and I _P is the maximum value of the current waveform. Therefore, the absolute value |Z| of the line impedance at this time can be calculated as |V _P /I _P |, and the phase difference ψ can be calculated as _ta /T×2π.

FIGS. 3A, 3B, 3C, and 3D are diagrams for explaining that the line impedance changes depending on the phase of the power line AC voltage in the low-voltage distribution line 1.
Figure A is a waveform diagram of the power line AC voltage, and Figure B is a diagram showing the voltage level of the injection measurement wave. In the figure, V _P indicates the maximum voltage value, and V indicates the effective voltage value. Figure 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 the difference in phase of the power line AC voltage. In the figure, I _1P is the maximum current value between t ₀ and _{t 1} , I _2P is the maximum current value between t ₁ and t ₂ , and I ₁ is t ₀
−t ₁ is the effective current value, I ₂ is the current effective value between t ₁ − t ₂ ,
I indicates the overall effective current value. In the same figure, the absolute value of impedance in each phase |
It is a calculation diagram showing that Z| is different.

By the way, the voltage v and current i of the measurement wave are expressed by the following _equations ( ₁ ) and (2). ωt−θ−ψ) …(2) If these equations are replaced by complex voltage V and complex current I, V=|V _P |ε ^j( 〓 ^t- 〓 ⁾ …(3) I=|I _P |ε ^j( 〓 ^t- 〓 ^- 〓 ⁾ …(4). Therefore, the impedance Z is Z=V/I=|V _P | | I _P |×ε ^j( 〓 ^t- 〓 ⁾ /ε ^j( 〓 ^t-
〓 ^- 〓 ⁾ = ｜V _P ｜ / ｜I _P ｜×ε ^j 〓…(5). As mentioned above, |Z|=|V _P |/|I _P | …(6) ψ=t _a /T×2π …(7), so by substituting these into equation (5), Z= ｜Z｜ε ^j (t _a /T)×2π=｜Z｜cos｜
(t _a /T)×2π}+j｜Z｜sin{(t _a /T)×2π}
…(8), and Z=R+jX …(9) (where R is equivalent resistance value and X is equivalent reactance), then from equations (8) and (9), R=｜Z｜cos｜t _a / T)×2π} …(10) X=|Z|sin{t _a /T)×2π} …(11) is derived.

By using the above equations (6), (7), (9), (10), and (11), the arithmetic unit 8 calculates the line impedance at any phase of the power line AC voltage. For example, when measuring the line-to-line impedance between phases t ₀ and _{t 1} , the power line AC wave phase detection circuit 7 detects the phase between t ₀ and _{t 1} , and the measurement wave measured by the voltmeter 5 during that period is The maximum value of the voltage waveform V _P and the maximum value of the current waveform I _1P measured by the ammeter 4
Using equation (6), find the absolute value |Z ₁ | of the impedance between phases t ₀ and t ₁ (see Figure 3 D), and then calculate the measured wave between this value and phases t ₀ to _{t 1} . Using the phase difference time t _a measured by the phase difference detection circuit 6, (9)
From equation (11), the line impedance between phases t ₀ and _{t 1}
Calculate Z ₁ .

In addition, when measuring the line impedance between phases t ₁ and _{t 2} , the power line AC wave phase detection circuit 7 similarly detects the phase between t ₁ and _{t 2} and detects the maximum voltage waveform of the measurement wave during that period. Maximum value of value V _P and current waveform
Using I _2P , find the absolute value of impedance |Z ₂ | (see Figure 3 D) between phases t ₁ and _{t 2} , and further calculate this value and the phase difference time _ta between phases t ₁ and _{t 2} . using phase
Calculate the line impedance _Z2 between _t1 and _t2 .

FIG. 4 shows the calculation of the impedance absolute value |Z| by conventional integration, which corresponds to FIG.
| is only calculated as a constant value at 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 the drawing]

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. 3A is a waveform diagram of the power line AC voltage, Figure B shows the voltage level of the injection measurement wave, Figure 3C shows the current level of the injection measurement wave, Figure 3D shows the calculation of the absolute value of impedance, and Figure 4 shows the impedance measured by the conventional measurement method. It is a calculation diagram of an absolute value. 1...Low voltage distribution line, 2...Measurement wave power supply, 3...
Injection circuit, 4... Ammeter, 5... Voltmeter, 6...
Measurement wave phase difference detection circuit, 7...Power line AC wave phase detection circuit, 8...Arithmetic unit, v...Voltage waveform of measurement wave, i...Current waveform of measurement wave, V _P ...Maximum value of voltage waveform , I _P ... maximum value of current waveform, t _a ... phase difference time, Z ... line impedance.

Claims (1)

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