JPH0237735B2 - SHINGODENSOHOHOOYOBISOCHI - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal transmission method and device that use power distribution lines as transmission lines, and in particular, to a signal transmission method and device that uses power distribution lines as transmission lines, and in particular, a signal transmission method and device that is suitable for return-to-ground transmission through ungrounded power distribution lines. The present invention relates to a transmission method and device.

[Conventional technology]

Generally, most distribution line systems are ungrounded, and are configured so that the voltage transformed by a transformer 1 is sent to feeders 3, 4, and 5 via a bus 2, as shown in FIG. There is. In such an ungrounded power distribution line system, a signal transmission device that uses current and voltage of a so-called zero-phase circuit as a signal is known from Japanese Patent Publication No. 49-38495. In this known example, a feeder 5 is provided with a zero-sequence current detector, and a master station 6 is provided that uses the zero-sequence current 12 detected from the zero-sequence current detector as a transmission signal. Further, a switch 8 is connected to one line of the feeder 5 near the master station 6 via an impedance 7, and when this switch 8 is closed by a signal from the master station 6, the other end of the switch 8 is grounded. be done. On the other hand, a slave station 9 is provided at an appropriate distance away from the master station 6 to detect the zero-sequence current on the feeder and catch the transmission signal from the master station 6. Similarly to the master station 6, this slave station 9 also has 1 of the feeder 5.
It is configured such that a one-wire ground fault is caused by a switch 11 via an impedance 10 in the wire. Since it is configured in this way, one line of the feeder 5 is now passed through the impedance 7 at the master station 6 and closed by the transmission code signal of "1, 0" by the switch 8. It is possible to cause a one-line ground fault and convert it into a minute zero-sequence voltage for signal transmission. The slave station 9 receives this transmission from the master station 6, and transmits an answer output to the master station 6 using the impedance 10 and switch 11 as necessary in the same manner as described above. The master station 6 receives a signal from the slave station 9 using a zero-phase current 12.

In this system of Special Publication No. 49-38495,
A low frequency power source is prepared as a power source for the transmission signal, and on the receiving side, only the low frequency signal is discriminated and used as a received signal.

[Problem that the invention seeks to solve]

This known system is particularly problematic in that it increases the size of the slave station, and is not suitable for installation on telephone poles or in individual homes.

In other words, in order to obtain a low-frequency power source, it is essential to step down the voltage on the distribution line while insulating it with a transformer, convert it to DC with a converter, and then create the low-frequency voltage again. Since this method requires a rectifying capacitor, a rectifying capacitor, an amplifier, etc., it is impossible to avoid increasing the size of the device.

In addition, the zero-sequence circuit of the distribution line used for signal transmission contains zero-sequence voltage and zero-sequence current (hereinafter referred to as residual zero-sequence components) that are fixedly determined depending on the configuration of the distribution system on the load side of the transformer 1. ) has occurred, and the distribution line's protective relay detects a change in the residual zero-sequence component to detect an accident on the distribution line. Therefore, even if a transmission signal is injected into the zero-phase circuit, it must not cause unnecessary operation of the protective relay, and it is essential to increase the injection signal to improve the S/N ratio. becomes.

From the above, the purpose of the present invention is to
It is an object of the present invention to provide a signal transmission method and device that can transmit signals with high accuracy using a small device.

[Means for solving problems]

In the present invention, on the transmitting side, an impedance and a switch are connected in series between one line of the power distribution line and the ground, and the switch is opened and closed as appropriate in accordance with the transmitted signal.
Also, on the receiving side, the zero-sequence current or zero-sequence voltage (hereinafter referred to as zero-sequence signal) and the phase voltage or line voltage (hereinafter referred to as reference signal) are detected, and from the signal component obtained by multiplying these two components. A good S/N ratio is obtained by removing the second harmonic component and obtaining a change in the remaining signal component as an information signal.

[Effect]

The received waveform of a zero-phase signal, zero-phase voltage, or zero-phase current, which is a received signal at the receiving end, is a signal vector 14, which is a zero-phase signal component, generated by the opening and closing of a switch at the transmitting end, as shown in FIG. The vector sum is 15 with a steady error vector 13 which is a residual zero-sequence component constantly occurring in the distribution line.
Therefore, by storing the waveform of the steady error vector 13 in an alternating current manner and subtracting it from the vector sum 15 in an analog manner, only the signal vector 14 can be detected as an information signal. However, since alternating current storage of waveforms is complicated in terms of circuitry, the present invention introduces a reference vector 16 having a constant phase relationship with the signal vector 14, and calculates the product of the reference vector 16 and the received waveform vector 15. By removing the second harmonic component included in the output and separating the variation in the remaining signal component as a component of the signal vector 14, a high S/N ratio can be easily ensured.

〔Example〕

An embodiment of the present invention will be described below.

In general, when the switch 11 is opened and closed on the slave station 9 side, the state shown in FIG. 3A is shown in a zero-phase circuit using symmetrical coordinates. In other words, when one wire of the three-phase distribution line (for example, the a phase) is grounded by the switch 11 through the impedance 10 at the grounding point of the slave station 9, the zero-sequence current determined by the phase voltage V _a of the a-phase and the zero-sequence impedances 10 and 17 A zero-phase circuit that can flow is constructed between the a-phase and the ground. The zero-phase impedance 17 of this zero-phase circuit is shown as a representative of the zero-phase impedance of all feeders other than the feeder 18 connected to the slave station 9. In an ungrounded distribution line system, the zero-sequence impedance 17 is a capacitive impedance determined by the ground capacity of all feeders. Now, if the impedance 10 is a capacitor that is sufficiently smaller than the capacitance of the zero-sequence impedance 17, the zero-sequence current flowing through the feeder 18 advances with respect to the zero-sequence power supply 16 as shown in FIG. is detected on the secondary side of

An embodiment of a signal demodulation device based on the zero-phase signal detected from this zero-phase CT 19 is shown in FIG. In this embodiment, as an example, the phase voltage V _a is used as the reference signal. Now switch 1 of slave station 9
The zero-sequence current that flows when 1 is closed is I ₀ , and the zero-sequence CT
19. However, for convenience of explanation, first consider an ideal state in which the zero-sequence current I ₀ does not include any residual error at any time. As mentioned above, the zero-sequence current I ₀ leads the phase voltage V _a by 90°.
In other words, the phase voltage vector V〓 _a and the zero-phase voltage vector I〓 ₀ are respectively V〓 _a =V _a sin(ωt) ……(1) I〓 ₀ =I ₀ sin(ωt+90゜) ……(2) This is the relationship.

Here, V _a and I ₀ are their respective maximum values, and ω is the angular velocity. And V _a is a known constant value.

In the figure, V = _a is advanced by 90° and passed through the phase shift circuit 20.
I〓 ₀ is applied to a multiplier circuit 22 with I〓 0, and I〓 ₀ is inputted to a multiplier circuit 23 with V〓 _a through a 90° delay phase shift circuit 21 . The outputs of the multiplier circuit 22 and the multiplier circuit 23 are added together by an adder circuit 24. That is, the addition circuit 24
From equations (1) and (2) above, the output of is V _a sin (ωt + 90°) × I ₀ sin (ωt + 90°) + V _a si
n (ωt) × I ₀ sin (ωt) V _a I ₀ (cos ² ωt + sin ² ωt) = V _a I ₀ ...(3). That is, this shows that the output of the adder circuit 24 can be demodulated as a signal component determined as the product of the magnitude of the reference signal V _a and the magnitude of the zero-sequence current I ₀ . Here, the reference signal V _a is a known value, and V _a I ₀ is determined by I ₀ , that is, the open/close signal of the switch at the transmitting end.

On the other hand, the output of the zero-phase CT 19 actually contains I〓ε shown by 13 in FIG. 2 as a zero-phase steady-state residual error. Therefore, I〓e＝Ie sin(ωt+)...(4) However: If the phase difference between _V〓a and I〓e, the output of zero-phase CT19 is the sum of equations (2) and (4). I need to think about it. At this time, the output from the adder circuit 24 is V _a sin (ωt + 90°) × {I ₀ sin ((ωt + 90°) + Ie sin
(ωt+)}+V _a sinωt × {I ₀ sin(ωt)+Ie sin(ωt+−90°)}=V _a
×I ₀ {cos ² ωt＋sin ² ωt} ＋V _a ×Ie {cosωt sin(ωt+)−sinωt cos(ωt
+)}=V _a ×I ₀ +V _a ×Ie sin……(5).

The first term V _a ×I ₀ in equation (5) is the signal component in equation (3) itself, and is a value that changes during signal transmission, whereas the second term V _a ×Ie sin is the residual zero-phase component. It is a constant DC component determined by the configuration of the power distribution system. From this, the DC value of the output (V _a ×Ie sin) of the adder circuit 24 is held in the analog hold circuit 25 immediately before the reception timing, and the output of the adder circuit 24 and the output of the hold circuit 25 during the reception period. is applied to the subtraction circuit 26, even if the error in equation (4) occurs constantly, the subtraction circuit 26 extracts only V _a ×I ₀ of the received signal components as the demodulated output. Can be done.

Therefore, according to the present invention, it is possible to construct a demodulation circuit that can extract only the transmission signal regardless of the residual zero-phase component.

Further, according to this embodiment, the AC signal is "1, 0"
Since the DC signal conversion does not use a time constant circuit like the DC conversion circuit after rectification, the demodulated signal can be obtained instantaneously and the speed can be increased. Furthermore, according to this embodiment, since there is a function to determine the phase difference with the reference signal, it is possible to distinguish between the installation signal current of the own feeder slave station and that of other feeder slave stations. Each slave station can transmit an answer output to the master station.

With reference to FIG. 4, we have described an embodiment in which the installation impedance is a capacitor and the reference vector is V _a when phase a is grounded.The basic idea of the present invention will now be explained. By multiplying the frequency vector, the DC component and the second
It takes advantage of the fact that harmonic components are generated. This will be explained with reference to FIG. In the figure, a represents the zero-sequence current of the distribution line, of which Ie
is a component that constantly flows as a residual error current, and is fixedly determined once the power distribution system is determined. On the other hand, I ₀ is a zero-phase component as a signal applied to a zero-phase circuit by transmission using a power distribution line according to the present invention. Therefore, a zero-sequence current of Ie+I ₀ flows during signal transmission, and Ie flows otherwise. Note that this signal transmission method is different from other signal transmission methods in that generally I ₀ >Ie and the signal transmission method has a poor S/N ratio. On the other hand, the reference signal (b in the same figure) to be multiplied by the zero-phase signal may use any current or voltage in the power distribution system, and in the illustrated example, V _a
The signal has an arbitrary phase. The signal obtained by multiplying these signals becomes zero when either signal to be multiplied is zero level, becomes a negative level when the polarities of the multiplied signals do not match, and becomes a positive level signal when the polarities match, as shown in FIG. As is clear from the figure, the signal after the product has an appropriate bass value and has twice the frequency of the signal before the product. V〓 _a
and I〓e are respectively expressed by the above equations (1) and (4), and I〓 ₀ is generally expressed by the following equation (6), then the signal after the product is expressed by the equation (7).

I〓 ₀ = I ₀ sin (ωt + θ) ... (6) θ: V〓 Phase difference between _a (I〓 ₀ + I〓e)・V〓 _a = {I ₀ sin (ωt + θ) + Ie sin (
ωt+)}・V _a sinωt =I ₀・V _a sin(ωt+θ)・sinωt+Ie・V _a sin(ωt+
)・sinωt =I ₀・V _a /2 {−cos(2ωt+θ)+cosθ}+Ie・V _a
/2{−cos(2ωt+)+cos}……(7) This equation (7) represents the signal received during signal transmission using the distribution line, and when no signal is being sent, the second term is Only components are received. And during this ceremony
cos(2ωt+θ) and cos(2ωt+) are the second
The harmonic components, cosθ, and cos are values as bias. Among these, the information to be extracted by demodulation is I ₀ ·V _a /2cosθ. For this reason, first the second harmonic component is removed. In the embodiment shown in FIG. 4 described above, this filter action is performed by performing a first multiplication by circuits 22 and 20 and a second multiplication by circuits 21 and 23, and the second harmonic component generated by one multiplication is This is achieved by adding in the adder 24 so that it is canceled by the second harmonic component generated by another multiplication. Therefore, it goes without saying that only the bias component can be extracted using a generally known second harmonic removal filter. After such filtering, the output of equation (8) is obtained.

I ₀・I _a /2cosθ+Ie・V _a /2cos ……(8) However, the true information is the first term, and the first term is sufficiently small compared to the second term, so the demodulation as it is is satisfactory. It won't happen. Therefore, in the present invention, the second
We focused on the fact that the term is constant, and decided to extract the change as a transmission signal.

As explained above, according to the present invention, good S/
The N ratio can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing an ungrounded distribution line system, Figure 2
The figure is a vector diagram of the received signal when the signal is received, Figure 3A is a zero-phase circuit diagram in symmetrical coordinates when the switch on the slave station side is opened and closed, and Figure 3B is the zero-phase current flowing through the feeder shown in Figure 3A. 4 is a circuit diagram showing an embodiment of the signal receiving and demodulating device according to the present invention,
FIG. 5 is an explanatory diagram of the operating principle of the present invention. 19...Zero phase CT, 20...90° advance phase shift circuit,
21...90° delay phase shift circuit, 22, 23...multiplication circuit, 24...addition circuit, 25...hold circuit, 26...subtraction circuit.

Claims (1)

[Scope of Claims] 1. A signal transmission method using a distribution line-based signal transmission system in which an impedance and a switch are connected in series between one line of a distribution line and the ground, and a zero-phase signal when the switch is opened/closed is used as a transmission signal, comprising: The zero-phase signal in the electric wire and the signal obtained by leading the phase of the reference vector obtained from this distribution line by 90 degrees are multiplied, and the signal obtained by delaying the phase of the zero-phase signal by 90 degrees and the signal obtained from this distribution line are calculated. Multiply the reference vector and add the two signals obtained by the product to obtain a DC signal component. Find the difference between the DC signal component stored for a predetermined time and the DC signal component obtained at the current time. A signal transmission method characterized in that the signal is an information signal. 2. In a signal transmission device using a distribution line signal transmission method, in which an impedance and a switch are connected in series between one line of a distribution line and the ground, and a zero-phase signal when the switch is opened/closed is used as a transmission signal, an artificial one wire on said distribution line A first means for detecting a zero-phase signal generated at the time of a ground fault, a second means for delaying the phase of the output signal of the first means by 90 degrees, and a second means for advancing the phase of the reference vector obtained from the distribution line by 90 degrees. a fourth means for multiplying the output signal of the first means and the output signal of the third means; a fifth means for multiplying the output signal of the second means and the reference vector; means, a sixth means for adding the output of the fourth means and the output of the fifth means to output a DC signal component, and storing and holding the value output from the sixth means immediately before transmission reception. and eighth means for subtracting the value held by the seventh means from the signal output from the sixth means during transmission and reception. Transmission device.