JPS6126295B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a power system protection system, and more particularly to a carrier protection relay system suitable for use in power transmission line protection. Power transmission systems are becoming more diverse, with the emergence of long-distance transmission lines due to the construction of large-capacity power plants in remote areas, the construction of three-terminal systems due to land acquisition difficulties, and the installation of ultra-high voltage cable systems in urban areas. be. A common problem with this diversification is that the ground charging capacity increases, and in the event of an accident, resonance between the inductance of the power transmission line and the ground charging capacity generates extremely severe harmonics for the protection relay. However, conventional protection methods have drawbacks such as reduced detection sensitivity and slow operation time. The reason for this drawback is that the operating principle of conventional protection relays has been to make fault judgments based only on the fundamental wave component. The disadvantage of this conventional method is that it considers a power transmission line to consist of distributed constants of inductance and capacitance, and applies wave equations to voltage and current.
It has recently become clear that this problem can be solved by treating this behavior as a wave. An overview of this idea is given below. As shown in FIG. 1, a power transmission line mainly consists of inductance and capacitance. (Resistance and conductance are small so ignore them.) 1st
Although the diagram shows a single-phase circuit, a single-phase circuit is sufficient to explain the content of the differential current method based on the wave equation and the propagation principle of traveling waves. The wave equation of voltage and current values will be explained using FIG. The positions of two SR points that are sufficiently close on the track are x and x + △, respectively.
Assuming that /∂t...(1). When approaching △x→0, equation (1) becomes −∂e(x,t)/∂x=L∂i(x,t)/∂t
…(2) becomes. Similarly, the decrease in current is −∂i(x,t)/∂x=C∂e(x,t)/∂t
…(3) becomes. Equation (4), known as the wave equation, can be derived from equations (2) and (3). (Here, γ=√.) The solution to equation (4) is generally expressed as follows. e(x,t) = ₁ (t-γx)+ ₂ (t+γx) …(5) i(x,t) =1/Z{ ₁ (t-γx)- ₂ (t+γx)} …(6) Here and Z is wave impedance,

[Formula]. Rewriting equations (5) and (6), ₁ (t-γx) and ₂ (t+γx) can be expressed as follows. e(x,t)+Z・i(x,t) =2 ₁ (t-γx)...(7) e(x,t)-Zi(x,t) =2 ₂ (t+γx)...(8) Here ₁ (t-γx) is a wave traveling in the positive direction of x, and ₂ (t+γx) is a wave traveling in the negative direction of x. From equations (7) and (8), traveling waves can be divided into forward waves and backward waves depending on the combination of voltage and current of the transmission line. Here, if we focus on the forward wave in equation (7), t-γx remains constant. In other words, if you travel a distance of △x at a speed of 1/γ and the time required to travel is △t, then △t=γ・△x, so at time (t+△x) and location (x+△x) t
-γx is obtained as follows: (t+Δt)-γ(x+Δx) =t-γx+Δt-γΔx =t-γx, and t-γx is always constant. In other words, if the distribution system consisting of inductance and capacitance is uniform, a forward wave (or backward wave) will propagate between two points separated by △x without being attenuated or distorted at all. be. This can be expressed as an equation as follows. In other words, e ^S (x, t) + Z・i ^S (x, t) = e ^R (x+△x, t+△t) +Zi・^R (x+△x, t+△t) …(10) (e ^S , i ^S is the voltage at the S terminal, the current, the value at the time of cooling, and e
^R , i ^R is the voltage at the R end, the value at the time of energization). Equation (10) holds true if there is no fault between any two points on the transmission line and the inductance and capacitance are uniformly distributed, but if there is a fault inside, the uniform distribution will be disrupted. Equation (10) does not hold. That is (10)
Accidents within the protected area can be detected depending on whether the formula holds or not. In reality, the following equation, which is a modified version of equation (10), is calculated. In other words, ξ(t) = i ^S (x, t) − i ^R (x+△x, t+△t) +1/Z{e ^S (x, t) −e ^R (x+△x, t+△t)}... (11) In the event of an external accident or under normal conditions, theoretically ξ(t)
= 0, and |ξ(t)|≠0 at the time of an internal accident. However, since there are errors in the measurement system, rounding errors due to the finite number of calculation bits, truncation errors, etc., a certain slice level is set and |ξ(t)|
If <δ, there is no accident; if |ξ(t)|>δ, it is determined that there is an accident. The above judgment is based on a single-phase circuit, but the actual line consists of a multi-phase line, and mutual induction must also be taken into account. For a traveling wave on a polyphase line that contains mutual induction, it is equivalently decomposed into n independent single-phase circuits that do not contain induction (mode conversion), and for each independent circuit (11 ), and by inversely converting the result to obtain the difference current of each phase (A phase, B phase, C phase, etc.) of the actual transmission line, the presence or absence of an accident and fault phase can be determined. is possible. The details will be described in detail below. To simplify the explanation, a balanced three-phase single line will be described as an example. FIG. 2 shows the self-inductance, self-capacitance, mutual inductance, and mutual capacitance of a balanced three-phase single line. l is self inductance, m is mutual inductance, c is self capacitance, and c' is mutual capacitance. The following two sets of functions of the ground potentials e _a , e _b , e _c (abbreviated as functions of distance x and time t; the same shall apply hereinafter) and currents (i _a , i _b , i _c ) of each phase are as follows. It is given by the formula. In equations (12) and (13), each phase is mixed in one equation due to the induction component, and it is very complicated to solve the partial differential equation as it is. Therefore, by performing appropriate transformations, it is possible to equivalently decompose the circuit into three independent circuits that do not contain any inductive components. This is the same idea as conventionally, when determining voltage and current in an accident, etc., circuits were analyzed by breaking them down into three independent circuits: positive phase, negative phase, and zero phase. The voltage and current of each phase in equations (12) and (13) are converted into a region (referred to as a modal region) different from the phase region (a phase, b phase, c phase) using the following conversion matrix. By doing this, it is possible to decompose the circuit into three independent circuits (referred to as zero mode, α mode, and β mode for convenience) in the modal region. Applying the wave equation to each of the three independent circuits decomposed as above, the forward wave (or backward wave) of each mode circuit obtained from those solutions is Since the waveform propagates at both ends of the protected area without being attenuated or distorted, the same equation as equation (11) holds true. That is, the zero mode _difference current _calculation formula is ξ _O (t)=i _O ^S (t-τ _O )−i _O ^R (t) + ₁ ^{/ Z} _O t)}…(16
) The difference current in α mode is ξ〓(t) =i ^S〓 (t-τ〓)-i〓 ^R (t) +1/Z〓{e〓 ^S (t-τ〓)-e〓 ^R (t) }= 0 …(17) The difference current in β mode is ξ〓(t) =i〓 ^S (t−τ〓)−i〓 ^R (t) +1/Z〓{e ^S 〓(t−τ〓)− e ^R 〓(t)}= 0 …(18) However, τ _O =√(+2)(−2′). d τ〓=τ〓=√(+)(-′)・d…(19) If there are no accidents within the protected area, holds, and if a short circuit or ground fault occurs in a phase (a phase, b phase, or c phase) within the protection zone, the difference current in the modal region ξ _O (t), ξ〓(t), ξ〓 (t)
If it remains as is, it is possible to distinguish between a short circuit and a ground fault, but it is impossible to distinguish the fault phase. To determine the accident phase, it is necessary to convert ξ _O , ξ〓, and ξ〓 from the modal domain to the phase domain as shown below. Through this conversion, ground faults and short circuits for each phase can be detected in the attached table 1.
Discrimination is possible using the pattern shown in . Here, 〇 means that the discriminant holds true, and × means that it does not hold. Now, if we examine the a-phase discriminant in detail, we get the following equation. ξ _a =ξ _O +ξ〓+ξ〓 =i _O ^S (t−τ _O )−i _O ^R (t) +1/Z _O {e _O ^S (t−τ _O )−e _O ^R (t)} +i〓 ^S (t−τ〓)i〓 ^R (t) =1/Z〓{e〓 ^S (t−τ〓)−e〓 ^R (t)} +i〓 ^S (t−τ〓)−e〓 ^R ( t) +1/Z〓{e〓 ^S (t−τ〓)−e〓 ^R (t)} …(23) Here, the voltage and current in zero, α, and β modes are (14),
It can be expressed in terms of phase voltage and current using equation (15). Therefore, equation (23) becomes equation (24). ξ _a (t) = 1/3 {i _a ^S (t-τ _O )+i _a ^S (t-τ〓) +i _a ^S (t-τ〓)+i _b ^S (t-τ _O ) +i _b ^S ( t−τ〓)+i _c ^S (t−τ _O ) +i _c ^S (t−τ〓)}−i _a ^R (t) +1/3Z _O {e _a ^S (t−τ _O )+e _b ^S (t −τ _O )} +1/3Z〓{e _a ^S (t−τ〓)+e _b ^S (t−τ〓)
} +1/3Z〓{e _a ^S (t-τ〓)+e _c ^S (t-τ〓)
} −(1/Z _O +1/Z〓+1/Z〓) e _a ^R (t)/
3 −(1/Z _O +1/Z〓)e _b ^R (t)/3 −(1/Z _O −1/Z〓)e _c ^R (t)/3 …(24) Discriminant of phase b ξ _b (t) and c-phase discriminant ξ _c
(t) can also be obtained in exactly the same way. If the differential current protection system based on the traveling wave theory described above is to be put into practical use, the following method can be considered for the differential current calculation formula handled at both terminals of a two-terminal power transmission line. Before explaining the calculation formula, first let's talk about the S end, R
The forward and backward waves at the ends are defined as follows. For the forward wave at the S end, the direction from S to R is positive. For the backward wave at the S end, the direction from R to S is positive. For the forward wave at the R end, the direction from R to S is positive. For the backward wave at the S end, the direction from S to R is positive. The difference current calculation formula includes a method based on forward waves or backward waves at the S end and the R end. Namely, (1) A method of creating a differential current using a forward wave at the S end and a forward wave at the R end. (1st method) (2) A method of creating a differential current using a backward wave at the S end and a backward wave at the R end. (Second method) If we consider the formulas for these two methods, we get the following. Each method will be explained using the a-phase differential current as an example. First, in the first method, the calculation formula at the S end is ξ _a ^1S (t) = ξ _O ^1S (t) + ξ〓 ^1S (t) + ξ〓 ^1S (t) = i _O ^S (t−τ _O )−i _O ^R (t) +1/Z _O {e _O ^S (t-τ _O )−e _O ^R (t)} +i〓 ^S (t−τ〓)−i〓 ^R (t) +1/Z〓{e〓 ^S (t−τ _O )−e〓 ^R (t)} +i〓 ^S (t−τ〓)−i〓 ^R (t) +1/Z〓{e〓 ^S (t−τ〓)−e〓 ^R (t )} …(25) becomes. Here, ξ is the saphitx, IS
1 means method 1, and S means S end. Also, a means a phase. The arithmetic expression at the R end of the first method can be obtained by exchanging S and R in equation (25). That is, ξ _a ^1R (t) = ξ _O ^1R (t) + ξ〓 ^1R (t) + ξ〓 ^1R (t) = i _O ^R (t−τ _O )−i _O ^S (t) +1/Z _O {e _O ^R (t−τ _O )−e _O ^S (t)} +i〓 ^R (t−τ〓)−i〓 ^S (t) +1/Z〓{e〓 ^R (t−τ〓)−e〓 ^S ( t)} +i〓 ^R (t−τ〓)−i〓 ^S (t) +1/Z〓{e〓 ^R (t−τ〓)−e〓 ^S (t)} …(26) In the second equation, S The calculation formula at the end is as follows. ξ _a ^2S = −i _O ^S (t) + i _O ^R (t−τ _O ) −1/Z _O {e _O ^S (t)−e _O ^R (t−τ _O )} −i〓 ^S (t) +i〓 ^R (t−τ〓) −1/Z〓{e〓 ^S (t)−e〓 ^R (t−τ〓)} −i〓 ^S (t)+i〓 ^R (t−τ〓) −1 /Z〓{e〓 ^S (t)−e〓 ^R (t−τ〓)}…(2 7) ξ _a ^2R =−i _O ^R (t)+i _O ^S (t−τ _O ) −1/Z _O {e _O ^R (t)−e _O ^S (t−τ _O )} −i〓 ^R (t)+i〓 ^S (t−τ〓) −1/Z〓{e〓 ^R (t)−e〓 ^S (t−τ〓)} −i〓 ^R (t)+i〓 ^S (t−τ〓) −1/Z〓{e〓 ^R (t)−e〓 ^S (t−τ〓)}…(2 8) From the above, the data sampled at the S end and the R end is voltage and current information at time t, t-τ _O , t-τ _a , and when considered on a per-line basis, the amount reaches 18 at one terminal. . The above is illustrated in terms of timing at the S and R ends as shown in FIG. The sampling circuit associated with this is shown in Figure 4, and 18 sample holders are required per line at one end. Also, three types of timing circuits are required, and 18 multiplexers are required.
A channel multiplexer is required. Here, 41-a to 41-f are reduction filters, 42
-a to 42-r, sample and hold 43 is a multiplexer, 44 is an AD converter, 45 is a buffer register, 46 is a timing generation circuit, 47 is a timing generation circuit at time t, and 48 is at time t-τ〓 A timing generation circuit 49 is a timing generation circuit for time t-τ _O. An object of the present invention is to reduce the amount of sampling data at each terminal, thereby reducing the amount of hardware involved, and to provide an economical transport protection relay device. In the present invention, the differential current calculation formulas at both ends of the power transmission line to be protected are made the same. The equation for the differential current is the same for both terminals. That is, in the equation using forward waves, taking the a phase as an example, ξ _a ^1S (t) = ξ _a ^1R (t) = i _O ^S (t-τ _O ) − i _O ^R (t) +1/Z _O {e _O ^S (t-τ _O )−e _O ^R (t)} +i〓 ^S (t−τ〓)−i〓 ^R (t) +1/Z〓{e〓 ^S (t−τ〓)−e 〓 ^R (t)} +i〓 ^S (t-τ〓)-i〓 ^R (t) +1/Z〓{e〓 ^S (t-τ〓)-e〓 ^R (t)} ...(29) That is, S The end samples the data at time t-τ _O , t-τ〓, uses it in its own calculation formula, transmits it to the other end, and uses it in the calculation formula at the other end, and the R end samples the data at time t. sample,
This is used at the R end, transmitted to the S end, and also used in the arithmetic expression at the S end. By doing this, the sampling timing at the S end and R end becomes as shown in Figure 5,
It is sufficient to have two sampling timings at the S end and one sampling timing at the R end. Along with this, the sampling data for each line is 12 amounts in total, 6 voltages and 6 currents at the S end, and 6 amounts in total, 3 voltages and 3 currents at the R end. Data sampling based on the timing shown in Figure 4. This decreases significantly compared to the amount. Accordingly, the sampling circuit at the S end is now shown in FIG. 6, which is simpler than that in FIG. 4. Furthermore, the sampling circuit at the R end becomes as shown in FIG. 7, which further simplifies the circuit. Here 61-a to 61-f and 71-a to 71
-f is a low-pass filter, 62-a to 62-l and 72
-a to 72-f are sample hold, 63, 73
is a multiplexer, 64 and 74 are AD converters, 6
5, 75 are buffer registers, 66, 76 are timing generation circuits, 67 are t-τ _O generation circuits, 68
is a t-τ generation circuit. Regarding the formula based on the backward wave, the amount of sampling data can be greatly reduced by making the calculation formulas for the S and R ends exactly the same. In the above explanation, an arithmetic expression based on the basic principle was used as an example, but in practice, the following expression in which the propagation time τ and the wave impedance Z are unified into one type may be used. ξ _a ^S (t) =ξ _a ^R (t) =i _a ^S (t-τ)−i _a ^R (t) +1/Z{e _a ^S (t-τ)−e _a ^R (t)}… (30) In this equation, data at time t-τ is sampled at the S end, used at the S end, and transmitted to the R end, and the difference current is calculated at the R end based on (30). At the R end, data at time t is sampled,
It is used at the R end and transmitted to the S end. By doing this, there is no need to sample data at time t at the S end, and t-τ at the R end.
There is no need to sample point-in-time data. The present invention can also be realized, for example, in the following embodiments. (i) The effect is the same even if the arithmetic expression is converted into a voltage dimension and made into a voltage differential form. (ii) Even in the case of τ〓≠τ〓≠ and Z〓≠Z〓 in an unbalanced power transmission line, the effect of the invention is the same except that the sampling timing is increased by one (t-τ〓). As described above, according to the present invention, the amount of sampling data can be significantly reduced, so that the amount of hardware involved in sampling can be reduced.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the wave equation. Second
The figure is a diagram for explaining the wave equation in a balanced three-phase single line. FIG. 3 is a diagram showing the sampling timing in the basic method of the differential current method based on traveling waves. FIG. 4 is a diagram showing a sampling hardware configuration based on FIG. 3. FIG. 5 is a diagram showing the sampling timing according to the present invention. Figures 6 and 7
The figure shows a sampling hardware configuration according to the present invention. 61-a~61-f...low-pass filter, 62-a~
62-l...sample holder, 63...multiplexer, 64...AD conversion, 65...puffer register, 66...timing generation circuit, 67...t-τ
_O generation circuit, 68...t-τ〓 generation circuit, 7-a~
71-f...Low-pass filter, 72-a to 72-f...Sample holder, 73...Multiplexer, 74
...AD converter, 75...Buffer register, 76...
Timing generation circuit.

【table】

Claims (1)

[Scope of Claims] 1. A transport protection relay system in which a transport protection relay device is installed at a first terminal and a second terminal of a three-phase power transmission line, respectively, to control the opening of a break in the transmission line, The first terminal carrier protection relay device includes first and second input means configured to sample the total amount of three-phase current and voltage every cycle Δt, and outputs of the first and second input means. a first signal transmission device that transmits the signal to the second terminal side and receives the output of the third input means provided at the second terminal of the three-phase power transmission line; the first and second input means of the first terminal; and the output of the second
a three-phase current that is the output of the third input means of the terminal;
A traveling wave theoretical formula that holds true for forward waves (backward waves) is implemented using voltage values and predetermined characteristic impedances, and internal faults in protected area transmission lines are determined according to the solution value of the traveling wave theoretical formula. a first calculation unit that provides an output to open the corresponding power transmission line or disconnector on the first terminal side; and a third input means configured to sample at the same period Δt as the second input means; and a third input means configured to receive the outputs of the first and second input means from the first terminal and detect them at the second terminal. a second signal transmission device for transmitting the output of the third input means of the first terminal, the output of the first and second input means of the first terminal;
a three-phase current that is the output of the third input means of the terminal;
The same traveling wave theoretical formula as in the first calculation unit is implemented for forward waves (backward waves) using a voltage value and a predetermined characteristic impedance, and protection is performed according to the value of the solution to the traveling wave theoretical formula. a second calculation unit that determines an internal fault in the transmission line and provides an output to open the corresponding transmission line or disconnector on the second terminal side, and the first and second calculation units have the same The traveling wave theoretical formula uses the values obtained by converting the three-phase current and voltage values of the transmission line into values in the modal region consisting of zero mode, α mode, and β mode, and uses the values in this modal region. It is prepared in the form of a difference equation of the traveling wave theory equation that holds for each terminal and each phase of the transmission line when In order to obtain the current and voltage values at the time of each mode, the sampling time between the three sets of input means is determined in accordance with the time difference between each mode, and the values sampled and input at the same period but at different times are determined. A carrier protection relay system characterized by implementing the traveling wave theory formula using the following.