JPS6160649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a protective relay device that protects power transmission lines by focusing on the propagation of traveling waves in power transmission lines.

In power systems, digital protective relay devices have already been proposed that transmit digital data of voltages and currents sampled at the same time to each other via microwave lines, and perform current differential or phase comparison between two terminals. ing. Conventionally, in this type of device, the fundamental wave component of the system voltage and current is extracted and introduced through an analog filter, and after analog-to-digital conversion, the above-mentioned current differential calculation and phase comparison calculation are performed to make a protection determination.

Now, conventional digital protection methods have the following drawbacks. As mentioned above, the conventional method is based on the theory of fundamental wave components and the premise that power transmission lines are represented by lumped constant circuits, so transient phenomena occur during system faults or switch operation. During the transition from a transient state to a steady state, the protective device often malfunctions or malfunctions, and the time delay characteristic provided for this purpose has the disadvantage of prolonging the operating time. .

Recently, we have abandoned both of the above two assumptions of conventional equipment, focused on the propagation of traveling waves, and always introduced measured values of the original waveforms of grid voltage and current, and also considered power transmission lines using distributed constant circuits. As a result, protective relay devices have been proposed that overcome all of the conventional drawbacks in power transmission line protection.

FIG. 1 shows a two-terminal power transmission line for introducing the traveling wave propagation principle that is the basis of this invention.
In Figure 1, the power transmission line is shown as a distributed constant circuit with inductance and capacitance of l and c per unit length, e ₁ (t), i ₁ (t), ex (t), ix
(t), e ₂ (t), i ₂ (t) are the voltage and current at terminal 1 at time t, the voltage and current at a distance x from terminal 1, and the voltage and current at terminal 2, respectively,
d is the distance between the two ends. According to the theory of distribution systems, ex(t), ix(t) are −∂ex(t)/∂x=l∂ix(t)/∂t (1) −∂ix(t)/∂x= They are combined by c∂ex(t)/∂t (2). The solutions of equations (1) and (2) are already known, ex(t)=F(t-x/v)+f(t+x/v) (3) ix(t)=1/z{F (t-x/v)-f(t+x/v
)} (4) v=1/〓lc, surge propagation speed z=√, given by surge impedance. F(t-x/v) is a traveling wave traveling from terminal 1 to terminal 2, and is called a forward wave. on the other hand,
f(t+x/v) is a traveling wave traveling from terminal 2 to terminal 1, and is called a backward wave.

As is clear from equations (3) and (4), the forward wave F and backward wave f at each point are determined from the measured values of voltage and current at each point.

Here, if we calculate (3)+z×(4) and (3)−z×(4), e _x (t)+zi _x (t)=2F(t-x/v) (5) e _x (t )−zi _x (t)=2f(t+x/v) (6) is obtained.

The following equation can be obtained from equation (5).

e ₁ = (t - τ) + zi ₁ (t - τ) = 2F (t - τ) (7) e ₂ (t) - zi ₂ (t) = 2F (t - τ) (8) τ = d/ v For the surge propagation times i ₁ and i _{2 , the direction flowing from terminals 1 and 2} is positive. The following equation can be obtained from equation (6).

e ₁ (t)−zi ₁ (t)=2f(t) (9) e ₂ (t−τ)+zi ₂ (t−τ)=2f(t) (10) i ₁ and i ₂ are terminal 1, The direction flowing from 2 is positive.

Therefore, from equations (7), (8), (9), and (10), regarding the voltage and current of terminals 1 and 2, e ₁ (t-τ) + zi ₁ (t-τ) = e ₂ (t) - zi ₂ (t) (11) e ₁ (t)−zi ₁ (t)=e ₂ (t−τ) +zi ₂ (t−τ) (12) The following relational expression holds true. Equation (11) means that the forward wave F at terminal 1 reaches terminal 2 after the surge propagation time τ. Equation (12) means that the backward wave f at terminal 2 reaches terminal 1 after the surge propagation time τ.

The relational expressions (11) and (12) always hold true unless an abnormality such as an accident occurs inside the power transmission line, and only fail when an accident occurs inside the transmission line, so they are effective for determining internal accidents for the purpose of protection. It is something.

Furthermore, since the relational expressions (11) and (12) hold true even during transient phenomena, the system can be protected even during transient phenomena, and the problems of conventional protective relay devices can be overcome.

By the way, the protective relay device based on the above principle utilizes the fact that a traveling wave entering from one end of a power transmission line reaches the other end after a surge propagation time, so the voltage and current must be maintained at both ends of the power transmission line. The forward wave F or the backward wave f must be determined from the measured value of . Therefore, when a power transmission line network consisting of multiple power lines is to be protected, it is necessary to measure the voltage and current at all terminals of each power line.

If it were possible to eliminate the need to measure voltage and current at terminals inside the protected power transmission line network, it would be economical because the measurement device and information transmission device for that terminal could be omitted.

The present invention has been made based on the above-mentioned viewpoints, and among the terminals included in the power transmission line network, traveling waves flow into the power transmission line network from outside, and traveling waves flow out from the power transmission line network to the outside. By measuring the traveling waves only at the terminals (hereinafter referred to as external terminals) that are connected to the transmission line, the measurement of traveling waves at the terminals inside the power transmission line network (hereinafter referred to as internal terminals) is omitted, and the protective relay device is configured. The purpose is to simplify.

In this invention, the measured value and the estimated value are compared at the external terminal that measures the traveling wave, and if the difference between the two is greater than or equal to a predetermined value, it is determined that an accident has occurred within the power transmission network.

If the surge impedance of all the power transmission lines included in the power transmission line network is known, the transmission coefficient and reflection coefficient of traveling waves at the connection points (internal terminals) between the power transmission lines inside the power transmission line network can be determined in advance. The traveling wave that enters the power transmission network from the external terminal reaches all the external terminals of the power transmission network while repeating reflection and transmission at the internal terminals, and flows out from the power transmission network.

Therefore, the value of the traveling wave flowing out from a certain external terminal is calculated from the transmission coefficient and reflection coefficient at the internal terminal and the measured value of the traveling wave at each external terminal a predetermined time ago (this predetermined time is different for each external terminal). , can be estimated by calculation. If there is no fault in the power transmission network, the estimated value should match the actual value.

The above principle will be explained by showing a four-terminal power transmission line in FIG.

In Figure 2, L is a transmission line without a traveling wave measurement point, L ₁ , L ₂ , L ₃ , and L ₄ are transmission lines with a traveling wave measurement point, and 1, 2, 3, and 4 are the above transmission lines. L ₁ , L ₂ ,
L ₃ and L ₄ are external terminals as well as traveling wave measurement points, X and Y are internal terminals that are both terminals of power transmission line L,
τ ₁ , τ ₂ , τ ₃ , τ ₄ , τ are the surge propagation times of the above power transmission lines L ₁ , L ₂ , L ₃ , L ₄ , L, respectively, F ₁ ,
F ₂ , F ₃ , and F ₄ are forward waves flowing from terminals 1, 2, 3, and 4. Here, the entire power transmission line inside terminals 1, 2, 3, and 4 is considered to be protected, and the power transmission lines L ₁ , L ₂ ,
A method for detecting an internal failure occurring in any one of the power transmission line networks formed by L ₃ , L ₄ , and L will be described.

As shown in the figure, if the traveling waves flowing out from each end of the power transmission line L are backward waves fx, fy, and the traveling waves flowing in the direction are forward waves Fx, Fy, then fx, fy can be obtained from the following equations.

_{f _ _ _ _ _ _ _ _ _ α X f _ _ _ _ _ _ _} f in Y
is the reflection coefficient of _X , f _Y , and α _X is the reflection coefficient of transmission lines L ₁ , L ₂ ,
From the surge impedance of L, α _Y is the transmission line
It is determined from the surge impedance of L ₃ , L ₄ , and L. β ₁ , β ₂ , β ₃ , β ₄ are forward waves, respectively.
Transmission lines L ₁ , L ₂ , L ₃ , L ₄ for F ₁ , F ₂ , F ₃ , F ₄
It is the transmission coefficient from to the power transmission line L. Equation (13) is established when the power transmission lines L, L ₃ and L ₄ are healthy, and expression (14) is established when the power transmission lines L, L ₁ and L ₂ are healthy.

In equations (13) and (14 ₎ , F ₁ , F ₂ , F ₃ , _and F ₄ are measurable, so if the initial values _{of f} Desired.

Now, it is assumed that the power transmission lines L ₁ , L ₂ , L ₃ , L ₄ , and L are initially uncharged, and charging starts at time t=0. _{Calculating f X and f Y at time} t _{= τ , f ( τ ) = α X f _ _} (τ) and f _Y (τ) are also zero.

Next, when f _X and f _Y at time t=2τ are determined, the following equation is obtained.

_{f _ _ _ _ _ _ _ _ _ _ _ 1} F ₁ (τ−τ ₁ )+β ₂ F ₂ (τ−τ ₂ ) (18) The first term on the right side, f _X (τ) and f _Y (τ), are zero as described above. However, τ>τ ₁ , τ ₂ , τ ₃ ,
Assuming that τ ₄ , the second and third terms on the right side take non-zero values. Here, f _X (2τ) and f _Y (2τ) are set as initial values for convenience. F ₁ (τ
−τ ₁ ), F ₂ (τ−τ ₂ ), F ₃ (τ−τ ₃ ), F ₄
(τ−τ ₄ ) is measured at external terminals 1, 2, 3, and 4.

Next, when f _X and f _Y at time t=3τ are determined, the following equations are obtained.

_{f _ _ _ _ _ _ _ _ _ _ _ 1} F ₁ (2τ−τ ₁ )+β ₂ F ₂ (2τ−τ ₂ ) (20) The first term on the right side, f _X (2τ) and f _Y (2τ), are obtained from equations (17) and (18), On the other hand, the second and third
The term is measured at each external terminal 1, 2, 3, 4.

In the above manner, the backward waves f _X (nτ) and f _Y (nτ) of the internal terminals X and Y, which are not measurement points, are obtained. _{That is , f _ _ _ _ _} (21) _{f Y ( nτ ) = α X f} } (22) f _X (nτ) and f _Y (nτ) are calculated. Equation (21) holds true if the power transmission lines L, L ₃ , and L ₄ are healthy for a predetermined period of time. If a failure occurs in the power transmission line L between time (n-1)τ and nτ, or time (n
−1) A failure occurs in the transmission line L ₃ between τ−τ ₃ and (n−1)τ, or a failure occurs at time (n−1) τ
1) Power transmission line between τ-τ ₄ and (n-1)τ
If a failure occurs in L ₄ , equation (21) no longer holds true. The calculation of equation (21) can be performed if each term on the right side is found. The second and third terms on the right side are external terminals 3,
It can be determined directly from the measured value in 4, but
For the first term on the right side, the previous calculated value f _y {(n-1)τ} according to equation (22) must be used,
The calculation of f _y {(n-1)τ} requires actual measured values at external terminals 1 and 2.

Therefore, in order to calculate equation (21), all past measured values of external terminals 1, 2, 3, and 4 are required. The same applies to the calculation of equation (22).

In the above explanation, it was assumed that τ>τ ₁ , τ ₂ , τ ₃ , τ ₄ , but even when this relationship does not hold, Kτ>τ
₁ , τ ₂ , τ ₃ , τ ₄ must exist, so f _X {(K+1)τ}, f _Y {(K+
1) τ} may be considered as the initial value.

Since the backward waves f _X and f _Y of the internal terminals X and Y of the power transmission line L without measurement points are obtained as described above,
From this, backward waves flowing out from each external terminal 1, 2, 3, 4 are calculated.

For example, the estimated value f^ ₁ (t) of the backward wave f ₁ (t) flowing out from external terminal 1 at an arbitrary time t is f^ ₁ (t) = α _X1 F ₁ (t-2τ ₁ ) + β _X1 It is calculated from the relational expression f _X (t-τ ₁ )+β _X2 F ₂ (t-τ ₁ −τ ₂ ) (23). At time t=nτ
Looking at +τ ₁ , it is as follows.

f _{^ 1} (nτ+τ ₁ ) _{= α X1} F _{1 (} nτ − _{τ 1 )} + β _{X1 f} X is the reflection coefficient, β _X1
is the transmission coefficient of _the backward wave f _X from the internal terminal X to _the transmission line L ₁ , and _β
is the transmission coefficient to α _X1 , β _X1 , β _X2 are power transmission lines
This is a constant determined from the surge impedance of L ₁ , L ₂ , and L.

F ₁ (nτ−τ ₁ ) and F ₂ on the right side of equation (24)
(nτ−τ ₂ ) is obtained from the actual measured values of the voltage and current at external terminals 1 and 2, and f _X (nτ) is calculated using equation (21)
required from. As mentioned above, f _X (nτ) is the forward wave F ₁ , F ₂ ,
All past measured values of F ₃ , F ₄ and f _X , f _Y
It is obtained from equation (21) by repeatedly calculating equations (13) and (14) from the initial value of . The estimated value f^ ₁ (nτ+τ ₁ ) of the backward wave of external terminal 1 obtained by equation (24) is
As long as there is no internal fault in the transmission lines in external terminals 3 and 4, it will match the measured value, so by comparing f^ ₁ (nτ + τ ₁ ) with the measured value, Internal accidents can be detected.

In other words, the actual measured value of the backward wave at external terminal 1 is f ₁
(t), if we define the quantity ε(t)=f^ ₁ (t)−f ₁ (t) (25), when |ε(t)|>K holds, it is an internal accident, |ε When (t)|≦K holds true, it can be determined that the power transmission network is healthy. However, K is a set value.

In the above explanation, Kτ>τ ₁ , τ ₂ , τ ₃ , τ
Since there must be an integer K that is ₄ , _f
{(K+1)τ}, f _Y {(K+1)τ} was set as the initial value. It is most accurate to perform calculations based on the initial values obtained in this way, but even if the initial values are set to appropriate values, the initial values can be calculated by repeating the calculations many times. The effect of this will gradually become smaller and eventually become negligible. Let me explain this.

Find f _Y (t-τ) from equation (14) and use equation (13)
Substituting into , we get the following equation.

_{f X ( t ) =} ^α _{X α Y f _ _ _ _} (t−τ−τ ₃ )+β ₄ F ₄ (t−τ−τ ₄ ) (26) If t−2τ is substituted for t, the following equation is obtained.

_{f X ( t - 2τ ) = α X α Y f 3} (t-3τ-τ ₃ )+β ₄ F ₄ (t-3τ-τ ₄ ) (27) By substituting equation (27) into equation (26), the following equation is obtained.

_{f X ( t ) = ( α X} ^α _{Y )} ² _{f _} )+α _Y β ₂ F ₂ (t-2τ-τ ₂ ) +α _X α ² _Y β ₂ F ₂ (t-4τ-τ ₂ )+β ₃ F ₃ (t-τ-τ ₃ )+α _X α _Y β ₃ F ₃ ( _t −3τ − _{τ 3} ) ₊ β ₄ F ₄ (t ₋ τ − τ ₄ ) + _α If we repeat , we can see that the term related to f _X on the right side becomes (α _X α _Y ) ⁿ f _X (t−2nτ). Since α _X and α _Y are transmission coefficients, both are smaller than 1. If n is made large enough, (α _X α _Y ) ⁿ becomes almost zero and can be ignored. Therefore, even if the initial value of f _X is set appropriately, f _X (n
The value of τ) can be determined accurately without being influenced by the initial value. The same holds true for f _Y (nτ) in equation (22). f _X (n
τ) to calculate Equation (24) and determine whether the power transmission network is healthy or not based on Equation (25).

Expressing equation (26) as a determinant gives the following equation.

Equation (29) is a relationship derived for the power transmission line network shown in Figure 2, but for a general power transmission line network, it can be considered as follows.

The traveling wave vector, which is a list of the momentary values of the traveling waves on a transmission line with no measurement points, is [ _G (t)], and it is known that the following relationship holds true if the surge propagation time between both ends of a power transmission line without a measurement point is τ.

[G _X (t)] = [A] _[ G G _X (t-
τ)] and [U(t-τ)] on [G _x (t)]. The first term on the right side of equation (30) is a term that represents the influence of the initial value of [ _G The term becomes smaller as equation (30) is calculated over time. Even if the initial value of [G _x ] is set appropriately, if the calculation is repeated many times, the value of [G _x ] will be found accurately.

Equation (29) corresponds to equation (30) as follows.

FIG. 3 is a block diagram showing an embodiment of the protective relay device according to the present invention in a four-terminal power transmission line.

In Figure 3, B ₁ , B ₂ , B ₃ , and B ₄ are the busbars of external terminals 1, 2, 3, and 4, respectively, CT is the instrument current transformer that measures the grid current, and PT is the voltage transformer that measures the grid voltage. An instrument transformer, 11, 12, 13, and 14 are forward wave detection devices for detecting forward waves flowing in from external terminals 1, 2, 3, and 4, and 21 is a backward wave detecting device for detecting backward waves flowing out from external terminal 1. Detection device, 32,3
3 and 34 are transmitting devices, 31 is a receiving device, and 5 is an arithmetic device. Since the other parts are the same as those in FIG. 2, their explanation will be omitted.

Next, the operation of the protective relay device shown in FIG. 3 will be explained.

Forward wave detection devices 11, 12, 13, and 14 detect forward waves F ₁ , F ₂ , F ₃ , and F ₄ at each external terminal. Detection of this forward wave is performed by introducing the outputs of the voltage transformer CT and the voltage transformer PT. The backward wave detection device 21 detects the backward wave f ₁ at the external terminal 1 . For the forward wave detection devices 11, 12, 13, 14 and the backward wave detection device 21, devices having a sample-hold circuit and an analog-to-digital conversion circuit are used, and the detection values of the traveling waves converted into digital signals are output. You can also do this. At the external terminal 1, a forward wave detection device 11 and a backward wave detection device 2 are connected.
The output of 1 is input to the arithmetic unit 5. The forward wave detection values at the external terminals 2, 3, and 4 are transmitted to the transmitter 32,
33 and 34 to the receiving device 31 of the external terminal 1. The receiving device 31 outputs the received signal to the arithmetic device 5. The calculation device 5 calculates equations (21), (22), based on the measured values of the traveling waves at the own end and the other end.
Execute the calculation in (24) to obtain the estimated value f^ ₁ (t) of the backward wave at external terminal 1, then compare this estimated value with the actual measurement value and calculate ε(t) in equation (25). When the calculated value is greater than the set value K, external terminals 1, 2, 3,
It is determined that there is an internal fault in the power transmission line within the power transmission line 4, and a trip signal is sent to a power disconnector (not shown).

As mentioned above, the relational expression (25) was shown as an example of internal accident determination for the protective relay device according to the present invention, but the basic principle of each relational expression is that The method is to calculate the value of the traveling wave flowing out from one external terminal based on the measured value of the traveling wave of the external terminal, the transmission coefficient, and the reflection coefficient, and compare it with the actual measurement value. This makes it possible to omit a measuring device for detecting a traveling wave and a device for transmitting a measured value to the other end at the internal terminals X and Y.

Although an example of application of the protective relay device according to the present invention to a 4-terminal power transmission line network has been described above, it is clear that the present invention can exert similar effects on multi-terminal power transmission line networks other than 4-terminal power transmission line networks. It is.

As described above, the protective relay device according to the present invention focuses on the propagation of traveling waves in power transmission lines, and can omit voltage/current measuring devices and devices for transmitting measurement information at some terminals of the power transmission line network. By doing so, the configuration of the protective relay device that reliably protects the system even during transient phenomena can be greatly simplified.

[Brief explanation of the drawing]

Fig. 1 is a distributed constant circuit diagram showing the propagation of traveling waves in a power transmission line, Fig. 2 is a four-terminal power transmission line diagram showing the principle of this invention, and Fig. 3 is an embodiment of a protective relay device according to this invention. FIG. In the figure, 1, 2, 3, 4, X, Y are power transmission line terminals, 5 is an arithmetic unit, 11, 12, 13, 14
21 is a forward wave detection device, 21 is a backward wave detection device, and 31 is a forward wave detection device.
is a receiving device, 32, 33, 34 is a transmitting device, L,
L ₁ , L ₂ , L ₃ , L ₄ are power transmission lines, CT is instrument current transformer,
PT is a potential transformer, F ₁ , F ₂ , F ₃ , F ₄ , F _X , F
_Y , _fX , and _fY are traveling waves. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a system for protecting a power transmission line network consisting of a plurality of power transmission lines and having internal terminals that connect the transmission lines and external terminals that connect the transmission lines at each end to an external power system, A first detection device is provided on all of the external terminals and detects the measured value of the traveling wave flowing into the power transmission line from the terminal, and a first detection device is provided on any one of the external terminals and detects the measured value of the traveling wave flowing from the terminal into the external power system. a second detection device that detects the actual measurement value of the traveling wave; and a second detection device that detects the actual measurement value of the traveling wave; and a second detection device that detects the actual value of the traveling wave; An estimated value of the traveling wave flowing into or flowing out from the internal terminal is calculated, and based on this calculated value and the various data used to obtain the calculated value, the traveling wave flows out from the external terminal provided with the second detection device. Protection comprising a calculation device that calculates an estimated value of a traveling wave and determines that an accident has occurred inside the power transmission line when the difference between this calculation value and the output of the second detection device is equal to or greater than a set value. Relay device. 2 If we assume that the traveling wave flowing in the direction from the external terminal to the power transmission line is the forward wave, and the traveling wave flowing out from the external terminal to the external power system is the backward wave, then the coefficient that is the data of the calculation device is the reflection of the backward wave. 2. The protective relay device according to claim 1, wherein the estimated value for the internal terminal calculated by the arithmetic unit is the estimated value for the backward wave.