JPH061909B2 - Power line carrier signal transmission device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power line carrier signal transmission device, and more particularly to a method for determining a signal sending impedance capable of coping with a wide range of system changes.

[Conventional technology]

Regarding the zero-phase carrier transmission system to which the present invention is applied,
"Hitachi Review" No. 737 (Vol. 65, No. 6), pages 1 to 6 explain the principle, but do not describe how to select a transmitting capacitor, but the difference between 1, 2, and 4 Until now, we have prepared related condenser groups and combined them to make an actual machine so as to have all integer multiples.

[Problems to be Solved by the Invention] Although various methods have been proposed for signal transmission using wiring lines, one of them has been proposed, in which the zero-phase voltage existing in a three-phase circuit is used, and in particular its change. The zero-phase transmission method that focuses on the minute has been put to practical use.

In this system, an ungrounded or high-resistance ground distribution system has three-phase ground capacitances with respect to the ground, and this value hardly changes at all times, but only one phase has an impedance (for example, a capacitor) in the ground phase. Inserting changes the previously generated zero-phase voltage. It is a zero-phase transmission method that attempts to use this change as a zero-phase signal for information transmission. In a non-grounded or high-resistance grounded system, three relative ground impedances, that is, about 1% of the zero-phase impedance, is electrostatic. Capacitance or equivalent impedance (resistance or reactance) is used for transmission.

However, the capacitance to ground changes depending on the operating state of the distribution system, and is large when the distribution line length of the same distribution system diagram is long and small when it is short. As shown in FIG. 6, when the electricity stepped down by the distribution transformer TR ₁ is supplied from the bus BUS to the distribution lines 1 and 2 via the distribution breakers CB ₁ and CB ₂ , the power supply range related to TR ₁ (That is, the length of the distribution line) is the division switch DM _{11 to} D existing in each distribution line.
It largely changes depending on the open / closed states of M _1n , DM _{21 to} DM _{2n and} the open / closed states of CB ₁ and CB ₂ .

That is, the transmission capacitor corresponding to the maximum capacitance to ground when the entire supply range of the transformer is connected (that is, the total capacity of the adjacent transformer TR 'system when the system is connected to the adjacent section 3 at the time of system switching). If is prepared, zero-phase transmission / reception can be performed during the switching operation between the system and the adjacent section.

Hereinafter, a case where a capacitor is used as a signal transmitting impedance will be described as an example of a zero-phase transmission method in a non-grounded system, but it is clearer in terms of resistance and reactance in principle. In Fig. 6, substation bus BUS
10 connected to the DM control devices 11 to 1 on the distribution line
n, 21 to 2n are master station transceiver devices for transmitting and receiving signals, and 11 to 1n and 21 to 2n are slave station transceiver devices for monitoring and controlling each DM.

It is necessary to always prepare a transmission capacitor capacity of about 1% of the ground capacitance (total value) of the systems to which they are connected, so that optimum transmission is possible according to changes in the system. It is necessary to select the level (capacitor value) by a separate circuit and send the zero-phase signal according to the command.

FIG. 2 shows an example of a transmission circuit, where A, B and C indicate each phase of the three-phase distribution line, and the transmission capacitor C is a static switch S.
It is opened and closed by W and is connected between the reference phase A and the land through the transmission transformer T ₁ . Here, the transmission capacitors C have respective SWs so that they can be selected according to the change of the system.

Conventionally, the capacitance to ground changes continuously and greatly, so the capacitors C _{1 to} C _n have values of 1, 2, 4, 8, ..., That is, 2
ⁿ (an integer of 0 or more) is selected and these are combined to select an arbitrary value from 1.

Therefore, when the fluctuation range of the ground capacitance changes from 1 to 2 ^n, n + 1 transmission capacitors C ₁ , C ₂ , ... C
_{n + 1} and n + 1 transmission SWs, SW ₁ , SW ₂ , ...,
Since SW _{n + 1} is required, the device becomes large and the control is very troublesome.

Assuming that the difference ratio of the transmission transformer T ₁ is N _T = 1 here, the maximum transmission capacitor capacity seen from the distribution system is Becomes

FIG. 3 shows the relationship between the ground capacitance of the system and the transmission capacitor level according to the conventional example. The horizontal axis shows the range of the ground C that changes according to the system operation status, and the vertical axis shows the transmission capacitor level. As shown in FIG. 2, the transmission capacitor is selected in a stepwise manner, so that it can only be changed stepwise for the continuously changing ground C.

Now, if a set of points showing a value of 1% of the ground C is shown by a straight line 30 on the upper right side in FIG. 3, ideally, the transmission capacitor level should coincide with this line, but a stepwise shape Since the switching is performed, the ratio to the ground C (that is, the zero-phase signal level) changes at the switching point, which is not preferable. If the zero-phase signal level is too low, the signal S / N
If the ratio deteriorates and becomes too large, the change in the zero-phase voltage will affect the sensitivity of the protective relay.

In FIG. 3, when the ground electrostatic capacitance C is reduced from N to N-1, the limit point for switching the transmission C level from n to N-1 is (a). The ratio of the transmission capacitor to the ground C Becomes

Similarly, the ratio at the limit (b) of switching the transmission C from n to n + 1 when increasing from N to N + 1 is Becomes This ratio is when N is large In both cases, the target n / N is approximately the same, and the intended purpose is achieved, but when N is small, especially when N = 1 or 2, the influence becomes large.

That is, at the limit point (C) where N = 2 is switched to N = 1 … The transmission C is doubled and too large. That is, it means that the change width of the zero-phase voltage used as a signal is doubled, which is not preferable.

Also, at the limit point (d) where N = 1 is switched to N = 2 ... This means that the transmission C is halved and is too small. That is, the change width of the zero-phase voltage used as a signal becomes half, which is not preferable.

Further, in FIG. 6, when CB ₁ and CB ₂ are all "OFF", the ground C is the ground C of BUS and TR ₁ , and the short sections are connected. For example, only CB ₁ needs to communicate with 11 when closed, and it is necessary to have a very small transmission capacitor as a unit.

Thus, the conventional method (1) requires a large number of condenser groups and open / close SW groups.

(2) When the ground C becomes small, the transmission level fluctuates up to twice or half the target value at the switching limit, which is not preferable. Further, since the conventional system has many condenser groups, it can be said that the variation of the transmission level at the switching point is small when the ground C is large.

(3) The minimum ground capacity changes for each installation location,
Cannot standardize.

From the above, the object of the present invention is to cover a wide range of transmission range (variation range of ground impedance) with a small number of transmission circuits by effectively using a transmitting capacitor (impedance) step.

[Means for solving problems]

In the present invention, a capacitor capacity determined by a geometric series is prepared, and the capacitors are appropriately switched so as to have a constant ratio.

[Action]

Since the capacity of the condenser can always be set to a fixed ratio, the transmission level does not change when the condenser is switched.

〔Example〕

 An embodiment of the present invention will be described below.

First, FIG. 4 illustrates the situation of the switching points corresponding to FIG. 3 for the case according to the invention. Now, assuming that the transmission level ratio is an upper limit and a lower limit centering on 30, respectively, 31 and 32, in FIG. 4, when the comparison C = X _N , the upper limit and the lower limit are switched. From equations (1) and (2) And

That is, a and b are ideal values (control target values) , The upper and lower limits are shown, and α shows the ratio thereof.

Thus, if each transmission level is selected so that the ratio of the transmission impedance (condenser) when switching from the level Y _N to Y _{N + 1} is α, it is always between a and b, that is,
The range surrounded by 31 and 32 can be switched in the equal ratio step as shown in FIG. The optimum value of α is determined below.

Now, when α is selected such that 1 + α = α ² , To get

Further, a ³ = (1 + α) · α = α + α ² = 1 + 2α a ⁴ = (1 + 2) · α ² = α ² + α ³ = (1 + 2) + α ³ = 2 + 3α α ⁵ = (1 + α) · α ³ α ⁶ = ( 1 + α) · α ⁴ = (1 + α) α ² + α ⁵ = (1 + α) + α ³ + α ⁵ : Further, since α ² −α = 1 in the above equation, both sides are α
When divided by, 1 / α = α-1 Therefore, if α is selected so that 1 / α = α-1, α will be the same. Becomes

That is, when the minimum unit is selected as "1", it is possible to select the ratio between the transmission impedance levels as α as shown in FIG. 1 and when the minimum unit is selected as 1 / α as shown in FIG. .

In other words, each transmission impedance group to be prepared is multiplied by α ^(2n-1) times the minimum unit (n = positive integer, Then, by combining these as shown in FIG. 1 or FIG. 7, the ratio between the levels to be switched can be made to be a constant value α, and always between a and b (%). It becomes possible to set a transmission level.

If you apply a specific number Therefore, α ² = (1.618) ² = 2.618 = 1 + α = 1 + 1.618 α ³ = (1.618) ³ = 4.236 = α + α ² = 1.618 + 2.618 α ⁴ = (1.618) ⁴ = 6.854 = α ² + α ³ = 2.618 +4.236 :::::::::::.

By substituting these numerical values, the relationship between the transmission level value and the transmission impedance is summarized as shown in FIG.

That is, in the transmitter circuit configuration as shown in FIG. 2, C ₁ = 1.0, C
₂ = 1.618, C ₃ = 4.236, C ₄ = 11.088, C ₅ = 29.030
If you prepare the 5 condensers, the upper and lower limit ratio of the transmission level will always be kept at 1.618 = α.

Now, when setting the transmission level to 1 (%), the upper limit is 1.2
(%) From α = a / b = 1.618 Therefore, it means that the transmission level can be set between 0.74 (%) and 1.2 (%).

Also, if the upper limit is 1.3 (%) That is, the transmission level can always be kept between 0.8 and 1.3 (%).

When actually manufacturing a product and controlling the switching of the capacitors, it is naturally implemented that the switching control has a hysteresis with a width slightly larger than ab (%) in consideration of hardware errors and the like. It should be, and I won't go into the details here.

Next, since the transmission level is from the minimum system in the distribution system to the maximum system, that is, it is necessary to communicate even when the ground capacitance including the interconnection with the adjacent system becomes large, A large transmission impedance switching range (that is, step) is required. As a countermeasure against this, No. 9
As shown, a tap is provided on the secondary side of the transmission transformer. That is, the same symbols as in FIG. 2 indicate the same items.

Now, when the number of turns on the primary side of the transformer is n ₁ and the winding ratio on the secondary side is n ₂ , n ₃ , the capacitance seen from the primary side is (1) the minimum unit in the secondary winding line n _2. when the capacitor C ₁ of is connected with _{(n 2 / n 1) 2} · C 1 (2) when all of the capacitors .SIGMA.C is connected to the secondary winding _{n 3 (n 3 / n 2} ) 2 · ΣC Become. Therefore, if n ₂ and n ₃ are determined so that (1) and (2) are equal to each other, it is possible to cope with a wide range of ground capacitance with a half capacitor group.

For example, suppose now that the condenser group is C ₁ (1), C
₂ (α), C ₃ (α ³ ), the maximum condenser capacity is 1 + α + α ³ = α ² + α ³ = α ² (1+
Since α) = α ⁴ , (n ₃ / n ₁ ) ² α ⁴ = (n ₂ / n ₁ ) ² 1 → (n ₂ / n ₃ ) ² = α ⁴ → n ₂ / n ₃ = α ² Therefore, if n ² = 100 Becomes

FIG. 10 shows a concrete example to which the present invention is applied in the case of having three capacitor groups and one intermediate tap.

That is, in tap n _3, the tap n ₂ 1 to alpha ^4, it is possible to realize the steps of the capacitor capacitance from alpha ⁴ to alpha ^3.

The reason why the switching from both directions is overlapped at α ⁴ is only for smooth switching, and in the case of tap n ₃ , taps n 1 to α ⁴ and tap n are performed.
May also be made from _2, alpha ⁵ to alpha ^9, or should be apparent that it may be suitably selected tap relation to duplicate.

In the above description, the case where the number of intermediate taps is one has been described, but it is clear that any tap may be similarly provided.

By doing so, the step of the condenser can be realized in a wide range with a small number of condensers, but the ratio is determined by the ratio of the minimum time and the maximum time of the system.

Generally, the maximum capacity of the system is determined from the point of preventing malfunction of the ground fault protection relay, but the minimum capacity is the ground C of the transformer and bus.
Therefore, it is not uniformly decided, and therefore it is not easy to decide how many steps of the capacitor to prepare.

Now, in the distribution line of 6.6 (kV) and 60 (Hz), the ground C in the system where the ground fault current of one line is 10 (A) is Now, the first switching method for capacitors in this system
Applying the α ³ step in Fig. 0, the minimum step is Becomes

In this way, the optimum ground capacitance of the system and the number of capacitor groups are determined, and when the number of taps of the transmission transformer is determined, the optimum controllable minimum ground capacitance by the zero-phase carrier method is determined.

However, since such a ground C is not necessarily guaranteed, a power supply bus having a ground C below this is divided into three equal capacitances to insert each phase between the grounds. You can do it.

That is, as shown in FIG. 11, the distribution transformer TR, the bus BUS,
The ground capacitance C ₀ is constantly inserted in the bus BUS composed of the transmitting capacitor C, the transformer T, and the breaker CB ₁ .

This value is equivalent to 1 in the system shown in Fig. 10 above. The degree is enough. Further, what is inserted into the bus bar and the ground phase for each phase is not a capacitor but a resistor or a reactance as long as it has an equivalent zero-phase impedance.

〔The invention's effect〕

According to the present invention, a zero-phase signal level within an optimum range can always be ensured even in a system that fluctuates over a wide range with a minimum transmission impedance group, so that stable power line carrier transmission can be realized at low cost. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of level switching according to the present invention, FIG. 2 is a system diagram to which the present invention is applied, FIG. 3 is a conventional system, and FIG.
5 to 5 are explanatory diagrams of transmission level switching showing the system according to the present invention, FIG. 6 is a distribution system diagram, and FIGS. 7 to 8 are diagrams showing examples of level switching according to the present invention, FIGS. 9 and 10. FIG. 11 is a diagram showing an example of transmission level switching and its circuit configuration, and FIG. 11 is a partial system diagram showing an embodiment of the present invention. 1, 2 ... Distribution line of applicable effect, C ₁ , C ₂ , ... C _n ... Capacitor for signal transmission which is the object of the present invention, C ₀ ... Capacitance to ground,
TR ... Transformer.

Claims (1)

[Claims] 1. A zero-phase signal detector for detecting a zero-phase signal of a three-phase distribution line including a circuit breaker which is open-controlled by the magnitude of the zero-phase signal, a primary winding and a secondary winding, and a primary winding. A transformer whose winding is connected between a specific phase of the three-phase distribution line and ground, a series circuit in which an impedance and a switching circuit are connected in series between the secondary winding terminals of the transformer, and the switching circuit as transmission information. In a power line carrier signal transmission device configured by installing a signal transmission device including a signal modulation circuit that opens and closes on the basis of a plurality of positions of a three-phase distribution line, a series circuit of at least one signal transmission device includes an impedance and a switching circuit. A plurality of series circuits are provided, one end of which is connected to one end of the secondary winding, and the other end of which is connected to the other end of the secondary winding through a selection circuit,
A power line carrier signal transmission apparatus, wherein step ratios of impedances used in combination of impedance groups selected by a selection circuit are in a geometrical relation.