JPH02177731A - Receiver for distribution line carrier current signal - Google Patents

Abstract

PURPOSE:To eliminate the 3-phase noise component at a signal transmission band and to improve the S/N at signal transmission by detecting a signal including the noise component in 2 phases among 3 phases at a receiver side of the signal, retarding the signal by 1/3 period of the signal and subtracting it from signals of the other phases. CONSTITUTION:A receiver 20 detects a current signal including a noise component of two phases among three phases of a distribution line, current-voltage conversion circuits 21,22 convert the signal into a voltage, which is filtered by band pass reception filters 23, 24. A signal and noise component received from an advanced phase is retarded by a 1/3 period delay circuit 26. Moreover, a signal and noise component received from a retarded phase is inverted by a phase inverting circuit 26, after the two signal and noise components are added and synthesized by an adder circuit 27, the resulting signal is demodulated by a demodulation circuit 28. Thus, the 3 phase noise component distributed on the distribution line r is eliminated and the S/N of the received signal output is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention converts a single-phase current signal injected from the secondary side of a distribution transformer connected to a three-phase distribution line into a three-phase current signal of a substation. Regarding the improvement of a receiving device for distribution line carrier current signals detected by two phases of feeder current transformers, it is suitable for transmitting distribution line information such as voltage and current of distribution lines and data of various control systems. .

(Background of the Invention) When remote monitoring and control of a power distribution system, collection of power distribution line information or data from various control systems, etc., power distribution lines are generally used as transmission paths for these information signals.

In this case, the transmission method for command signals for various monitoring and control from the master station device at the power supply end of the power distribution system to the slave station devices at the load side is a comparatively A ripple control method is used that superimposes a voltage signal in a low frequency band, but on the other hand, a method in which a current signal in a relatively low frequency band is conveyed from the slave station device to the master station device using the distribution line as a transmission path is used. It is a signal transmission method.

In the latter method, the signal is injected as a current from the low-voltage distribution line on the load side of the distribution line, and the signal is conveyed to the distribution substation by the high-voltage distribution line (feeder) via the distribution transformer. This is a method of detecting and receiving current signals with
Because it is possible to inject current signals on the load side, and existing distribution lines, distribution transformers, and feeder current transformers can be used as is, it is possible to monitor and control load-side switchgear control systems, etc. It is widely used as a simple and effective method for transmitting data of the target system to a master station device using command light.

FIG. 5 is a configuration diagram of a general current signal transmission system for carrying power distribution lines.

Data signals from various control systems such as a line switch 3 are injected as single-phase current signals from the slave station device 1 on the load side to the low-voltage distribution line 2, and are transferred to the three-phase high-voltage distribution line via the distribution transformer 4. (feeder) 5, is transported to a distribution substation having a substation main transformer 6, is detected by an auxiliary current transformer 8 provided on the secondary side of the feeder current transformer 7, and is detected by the substation equipment. It is received by the receiving device 10 of 9.

The receiving device 10 of the substation device 9 transmits the received data via a communication line 11 to the solid device 1 installed at the office of the electric power company.
Send to 2. The substation device 9 and the solid device 12 are the master station device 13
Configure.

The current signal transmission method has good transmission characteristics because it uses a low frequency band as a carrier signal, and as mentioned above, it is a very effective method for transmitting data signals from various systems in the power distribution system. In order to use a distribution line for commercial power supply instead of using a dedicated signal line as a transmission path, the slave station device 1, which is the signal transmitting side, connects the two of the Sanwa or single-phase distribution transformers 4. A signal is injected between the lines of the distribution line on the next side, and the receiving device 10 of the substation equipment 9 detects and receives the signal from two of the three phases.
Reception is generally done by receiving the demodulated signal from the lesser of the two phases (because there is always a signal in both the negative phases and the slave station is free to enter the signal phase), the demodulated signal is sent directly to the OR. In the conventional method of obtaining output through a circuit, if there is a load device that generates an excessive level of noise in the signal transmission band, the S/N ratio deteriorates when receiving the signal.
Reliability of signal transmission may be reduced.

In particular, three-phase load equipment generated large three-phase noise, and the three-phase noise had a high proportion of affecting the deterioration of the S/N ratio.

In order to solve these problems, conventionally, the standard injection level of the signal was set to a high level with sufficient margin to obtain an S/N ratio above a certain level with respect to the noise level. Although this ensures a good S/N ratio during signal transmission under most applicable fields and load conditions, it may be affected by the impact on load equipment connected to the power distribution system, the shape of the signal transmission circuit, etc. It is desirable that the signal injection level be as low as possible, and this has been an issue in current signal transmission systems for power distribution lines.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, reduce three-phase noise, and reduce the transmission signal level necessary for stable reception by improving the S/N ratio. It is an object of the present invention to provide a receiving device for a distribution line carrier current signal that can make a transmitting device smaller and cheaper.

(Features of the Invention) In order to achieve the above object, the present invention converts the signal and noise component detected in the leading phase of a two-phase feeder current transformer that detects a current signal into a third part of the signal. a delay means for delaying by one period; a subtraction means for subtracting the signal and noise component detected in the delayed phase of the two phases from the signal and noise component delayed by the delay means; and an output of the subtraction means. The present invention is characterized in that it is provided with means for demodulating t[, and thereby cancels noise having a phase difference of 2π/3 among the noise in the signal pass band detected in the two phases.

The present invention also provides a first delay means for delaying the signal and noise component detected in the first phase of the two phases by one-third of the period of the signal; a second delay means for delaying the signal and noise component detected in the second phase by one-third of the period of the signal; and the signal and noise component delayed by the first delay means, A first subtraction means for subtracting a signal and a noise component detected in a second phase of the two phases, and a signal and a noise component delayed by the second delay means. a second subtraction means for subtracting the signal and noise component detected in the first phase; a first demodulation means for demodulating the output of the first subtraction means; and a demodulation for the output of the second subtraction means. A second demodulation means and a reception determination means for comparing and determining the normality of the signal output from the first and second demodulation means are provided, so that when the phase rotation direction of the three-phase noise component changes, In order to cope with this problem, the present invention is characterized in that the processing from delay to demodulation is performed in two systems.

(Embodiment of the invention) There are two types of loads connected to distribution lines: three-phase loads and single-phase loads. Regarding current noise generated from load equipment, there are two types: those with a three-phase phase relationship and those with a single-phase phase relationship. Things are mixed.

On the other hand, current signals such as data signals sent from the slave station device to the master station device are usually injected as single-phase signals from the secondary side of the distribution transformer, so the three-phase phase relationship described above is This means that there is a difference in phase relationship between the noise component and the noise component that has .

Noise current for each phase of three phases 1 mls 1w5s l++
t has a phase difference of 120 degrees, many of which are shown in Figure 2 (
As shown in a), the phase rotation direction is the same as the phase rotation direction of the load current. On the other hand, as shown in Fig. 2(b), the single-phase current signal 1s1% IS'A and the single-phase noise current 1mm, I-s (R phase and S phase of the three phases flowing) has a phase difference of 1110 degrees.

The present invention focuses on the phase relationship between such a signal and noise, and
On the signal receiving side, a signal containing a noise component is detected in two of the three phases, and 17 of the signal is detected from the leading phase.
By delaying by 3 cycles and subtracting other phases from this, three-phase noise components in the signal transmission band are removed, improving S/NJt during signal transmission without increasing the signal injection level. It is something that makes you

FIG. 1 is a block diagram showing a current signal receiving device in a distribution line carrier master station device, which is an embodiment of the present invention.

In the receiving device 20, a two-phase feeder current transformer 7R.

7S and the auxiliary current transformer 8R18S, the current signal containing the noise component is detected in two of the three phases of the distribution line.
(R phase and S phase in the figure) are converted into voltage by current-voltage conversion circuits 21 and 22 made of resistors, for example, and filtered by band-pass receiving filters 23 and 24, respectively.

For the signal and noise component received from the phase leading in phase (R phase), a delay corresponding to 173 cycles of the signal is given by the 173 cycle delay circuit 25.

On the other hand, the phase of the signal and noise component received from the phase with a lag (S phase) is inverted by the phase inversion circuit 2G, and the two signals and noise components received from these two phases are combined by the addition circuit 27. After addition and synthesis, a signal output is obtained by demodulating in the demodulation circuit 28.

By performing the above processing, the three-phase noise components distributed in the power distribution line 5 can be removed, and the S/N ratio of the received signal output is improved.

In the configuration of the receiving device 20 shown in FIG. 1, the phase of the S-phase signal and the noise component is inverted by the phase inverting circuit 26,
Although it is assumed that the addition circuit 27 adds the delayed R-phase signal and noise component, the phase of the S-phase signal and noise component is not inverted, but is subtracted as is from the delayed R-phase signal and noise component. You can also do this.

Next, the above-mentioned noise and signal processing will be explained using mathematical formulas.

In Fig. 1, R-phase and S-phase auxiliary current transformers 8R, 8S
Assuming that the outputs of the receiving filters 23 and 24 connected to T are pm(t) and Ps(t), respectively, the above processing is performed as follows.

h(t--)-F, (t)...(1) To: Represented as the period (1/f,) of the center frequency of the signal passband.

First, the reduction effect on three-phase noise components is as follows, where the frequency of the noise is f, and the R-phase noise is a unit amplitude, Nu(t) = 5in2πf++t ・ ・ ・
Expressed as (2), the S-phase noise becomes N, (t) = 5in (2πfNt-Tπ) (3), and when formula (1) is processed for formulas (2) and (3), Nm(t-!-!')-Ns(t) -5in(2πfd-'π) xcos(2πf, +t T (1+ r++to)) ro: Center frequency of signal passband From equation (4), frequency f, The gain of the reduction process for three-phase noise is 1, π f.

Gm(fs) = l 2s+n-(1--) l ・
・(5)3 ``.

becomes. Gain of three-phase noise due to noise reduction processing, Gm
The frequency characteristic of (f I) is as shown in FIG. 3(a), and by processing in this way, the three-phase noise becomes extremely small near the center frequency r0 of the signal passband.

Next, the influence of processing on single-phase signals and noise components will be explained.

First, the signal and noise components that exist only in one phase, either the R phase or the S phase, are not affected by the processing of equation (1), and only the signal and noise components that exist in the R phase are delayed. No distortion occurs.

If there are signal (noise) components in both R and S phases,
The processing of equation (1) has the following effects.

That is, if the signal frequency is fs, and the R-phase signal is expressed as unit amplitude, Sm(t) = 5in2πfst (6), the S-phase signal is single-phase, so it has an opposite phase, and 5s(t ) = 5in2πfst...(7)
Therefore, when processing equation (1) for equations (6) and (7), xsin(2πf s t a f 5TO) ".:
If Gs (fs) is the center frequency of the signal passband and the gain of noise reduction processing for a single-phase signal component from equation (8), then the frequency characteristic is shown in FIG. 3(b).

That is, even if such processing is performed, the gain for the single-phase signal component does not change in the vicinity of the center frequency r0 of the signal passband.

Furthermore, the processing gain for single-phase noise components does not change as well.

FIG. 3(c) shows the result of determining the phase characteristic (delay characteristic) for the signal by this processing from equation (8).

That is, no phase distortion occurs up to 3'./2.

Further, the center frequency f is such that the gain G5 changes by 3 dB based on 65=1. Calculating the bandwidth centered at f
o+〇, 086fo, fo-0, 109fo, and the attenuation rate of three-phase noise in these bandwidths is ``.+
〇, 086f, 0.180 (-15dB) fo
O,109fo becomes 0.218 (-13 dB). As a result, the S/N ratio was improved by about 5 times in experiments.

In the above explanation, regarding the signal and noise component received from the leading phase of the three phases, 17
The three-phase noise component was removed by giving a delay equivalent to three periods and subtracting the signal and noise component received from the phase whose phase is delayed, but the phase rotation direction of the three-phase noise component may vary depending on the signal transmission band or the noise source such as a three-phase AC motor, and may not necessarily be in the same direction as the phase rotation of the load current, as shown in FIG. 2(c). In this way, when the phase rotation direction of the three-phase noise changes due to a change in the noise source, the processing effect cannot be obtained only by the process of fixing the leading phase of the three-phase noise component as described above.

Therefore, in the present invention, as shown in FIG. 4, the receiving device 20 transmits the current signal containing the noise component to the distribution line via the two-phase feeder current transformer 7R17S and the auxiliary current transformers 8R, 8S. 173-cycle delay circuit 2 detects signals and noise components received from the phase leading in phase (R phase) (R phase and S phase in Figure 4).
5 gives a delay equivalent to 1/3 of the period of the signal, and on the other hand, the phase of the signal and noise component received from the delayed phase (S phase) is inverted by the phase inverting circuit 26,
After the two signals and noise components received from these two phases are added and synthesized in the adder circuit 27, they are demodulated in the demodulator circuit 28 to obtain not only a signal output but also a phase whose phase is delayed (S phase). The 1/3 period delay circuit 29 also applies a delay equivalent to 173 periods of the signal to the signal and noise component received from the phase leading phase (
Regarding the signal and noise component received from the R phase, the phase is inverted by the phase inversion circuit 30, and the two signals and noise components received from these two phases are added and combined by the addition circuit 31, and then the demodulation circuit 32 The received data is demodulated to obtain another signal output, and these two signal outputs are subjected to serial-to-parallel conversion in parallel in the reception determination circuit 33 to determine the normality of the received data. The received data is selected and transmitted to the solid device 12 (FIG. 5).

By performing the above processing, the feeder current transformer 7
and the receiving device 20, and even if the phase rotation direction of the three-phase noise component changes due to load fluctuation, a signal with the three-phase noise component reduced is always available from one of the signal outputs. Obtainable.

Note that even in such processing, the processing effect on single-phase signals and noise is the same as in the above case.

(Effects of the Invention) As explained above, according to the invention of claim 1, the signal and noise component detected in the leading phase of the two-phase feeder current transformer that detects the current signal are a delay means for delaying by one-third of the cycle; a subtraction means for subtracting the signal and noise component detected in the delayed phase of the two phases from the signal and noise component delayed by the delay means; Since the demodulation means for demodulating the output of the means is provided to cancel out the noise in the signal passband detected in the two phases that has a phase difference of 2π/3, the three-phase noise can be canceled out. By improving the S/N ratio, the transmission signal level required for stable reception can be reduced, making it possible to reduce the size and cost of the transmitter.

Further, according to the invention of claim 2, the first delay means delays the signal and noise component detected in the first phase of the two phases by one third of the period of the signal; a second delay means for delaying the signal and noise component detected in the second phase of the two phases by one-third of the period of the signal; and a signal delayed by the first delay means and A first subtraction means for subtracting the signal detected in the second phase of the three phases and the noise component from the noise component, and a signal delayed by the second delay means and the noise component. a second subtraction means for subtracting the signal and noise component detected in the first phase of the two phases; a first demodulation means for demodulating the output of the first subtraction means; and a second subtraction means for demodulating the output of the first subtraction means. A second demodulating means for demodulating the output of the first demodulating means and a reception determining means for comparing and determining the normality of the signal output from the first and second demodulating means are provided. In order to deal with the case where the direction changes, the processing from delay to demodulation is performed in two systems, so even if the direction of phase rotation of the three-phase noise component changes, the S/N ratio will always improve and it will remain stable. By reducing the level of the transmitted signal necessary for receiving the information, it is possible to make the transmitting device smaller and cheaper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a distribution line carrier current signal receiving device according to the first embodiment of the present invention, and FIG. 2 is a three-phase noise vector, a single-phase signal, and the phase of the noise vector related to the present invention. FIG. 3 is a graph of noise and signal frequency vs. gain characteristics and signal frequency vs. phase characteristics according to an embodiment of the present invention, and FIG. 4 is a distribution line carrier current signal according to a second embodiment of the present invention. FIG. 5 is a block diagram illustrating a receiving device for power distribution, and FIG. 5 is a configuration diagram of a general current signal transmission system for carrying power distribution lines. 111. Slave station device, 216. Low voltage distribution line, 4゜1. Distribution transformer, 51. , three-phase high-voltage distribution line, 7/7R/7S
,,,Feeder current transformer, 8/8R/8S,,,Auxiliary current transformer,20. ,,receiving device, 23/24. ,,reception filter,25. ,． 1/3 period delay circuit, 26. , , phase inversion circuit, 27° addition circuit, 28. ,, demodulation circuit, 29.
,. 1/3 period delay circuit, 30. ,, phase inversion circuit, 311
9. Addition circuit, 32. ,, demodulation circuit, 33°9. Reception judgment circuit. Figure 2 (a) (b) , /) l , 0 tnl IS4F) To I 1 To 9ra song □

Claims (2)

[Claims] (1) Distribution line where two phases of the three-phase feeder current transformers in the substation detect the single-phase current signal injected from the secondary side of the distribution transformer connected to the three-phase distribution line. In the carrier current signal receiving device, a delay means for delaying the signal and noise component detected in the leading phase of the two phases by one-third of the period of the signal, and a signal delayed by the delay means. and a subtraction means for subtracting the signal and noise component detected in the delayed phase of the two phases from the noise component, and a demodulation means for demodulating the output of the subtraction means. Receiving device for current signals. (2) Distribution line carrier current signal that detects the single-phase current signal injected from the secondary side of the distribution transformer on the three-phase distribution line by two phases of the three-phase feeder current transformers in the substation. a first delay means for delaying a signal and a noise component detected in a first phase of the two phases by one-third of the period of the signal; a second delay means for delaying the signal and noise component detected in the second phase by one-third of the period of the signal; and the signal and noise component delayed by the first delay means, A first subtraction means for subtracting a signal and a noise component detected in a second phase of the two phases, and a signal and a noise component delayed by the second delay means. a second subtraction means for subtracting the signal and noise component detected in the first phase; a first demodulation means for demodulating the output of the first subtraction means; and a demodulation for the output of the second subtraction means. A receiving device for a distribution line carrier current signal, comprising: a second demodulating means; and a reception determining means for comparing and determining the normality of signal outputs from the first and second demodulating means.