JPS6124901B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a power system protection system, and 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 harmonics that are extremely severe for protection relays. 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 assumes that a power transmission line consists 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 Figure 1, a power transmission line mainly consists of inductance and capacitance (resistance and conductance are small, so they are ignored.) Figure 1 shows a single phase, but the wave equation and the propagation principle of traveling waves A single-phase circuit is sufficient to explain the content of the differential current method based on . The wave equation of voltage and current will be explained using FIG. The positions of two points S and R that are sufficiently close on the track are x and x+Δ, respectively.
x, the voltage drop between S and R at time t is Δe(x, t)=e(x, t)−e(x+Δx,
t) =L・Δx∂i(x,t)/∂t...(1). When Δx→0 is approached, equation (1) is -∂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).

[Table] The solution to equation (4) is generally expressed as follows. e(x, t)= ₁ (t-γx)+ ₂ (t+γ
x) ...(5) i (x, t) = 1/Z{ ₁ (t-γx)- ₂ (t + γx)} (6) Rewriting equations (5) and (6), ₁ (t- γx),
₂ (t+γx) is expressed as follows. e(x, t)+z・i(x, t)=2 ₁ (t−γ
x) ...(7) e(x, t)-zi(x, t)=2 ₂ (t+γx)
...(8) Here, ₁ (t-γx) is a wave that moves in the positive direction of x, and ₂ (t+γx) is a wave that moves 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 Δx at a speed of 1/γ and the time required to travel is Δt, then Δt=γ・Δx, so finding t-γx at time (t+Δx) and location (x+Δx), ( 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 Δx 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+Δx, t+Δt)+z・i ^R (x+Δx, t+Δt) ...(10) (e ^S , i ^S are the voltages at the S terminal , the current value at the time of collapse, e
^R and i ^R are the voltage and current values at the R end. If there is no fault between any two points on the transmission line and the inductance and capacitance are uniformly distributed, then (10) holds, but if there is a fault inside, the uniform distribution will be disrupted. Equation (10) does not hold. In other words, an accident within the protected area can be detected depending on whether equation (10) holds or does not hold. 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+Δx, t +Δt)+1/Z{e ^S (x, t)−e ^R (x +Δx, t+Δt)} ...(11) External accident In theory or under normal conditions, ξ
(t)=0, and in the case of an internal accident |ξ(t)|≠
It is 0. However, there are errors in the measurement system, rounding errors due to the finite number of calculation bits, truncation errors, etc., so by setting a certain slice level, |ξ
If (t)|<δ, it is determined that there is no accident, and 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 traveling waves on a polyphase line containing mutual induction components, this is equivalently decomposed into n independent single-phase circuits containing no induction components (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 power 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 relationship between the ground potential of each phase e _a , e _b , e _c (abbreviated as a function of distance x and time t; the same applies hereinafter) and the current (i _a , i _b , i _c ) is as follows. It is given by a set of expressions.

[Table] 〓……(12)
−∂e _b ∂i _a ∂i _b ∂i _c

Claims (1)

[Claims] 1. A first circuit provided at the own end of a three-phase power transmission line that samples the total amount of three-phase current and voltage every period Δt.
a second input means provided at the other end of the three-phase power transmission line and configured to sample the total amount of three-phase current and voltage every period Δt and at a different time from that of the first input means; an input means, a signal transmission device that transmits the output of the first input means to the opposite end and the output of the second input means to the own end; two sets of input means installed at the own end and the opposite end respectively; The traveling wave theoretical formula that holds for forward waves (backward waves) is implemented for each terminal from the three-phase current and voltage values that are the output of and a calculation unit that determines that an internal fault has occurred in the protected area transmission line when this difference is not zero, and outputs an output to open the corresponding transmission line or disconnection, according to the traveling wave theory in the calculation unit. The formula calculates the three-phase current and voltage values at that terminal, zero mode, α mode, and β.
Convert it to a value in a modal region consisting of modes, select either α mode or β mode of the current and voltage values in the modal region as a representative mode, and send when using the value in this representative mode. It is prepared in the form of a traveling wave theoretical equation that holds true for each phase of the electric wire, and the current and voltage values at the time of the representative mode, which are necessary when deriving the current and voltage values of the representative mode in the modal region, are as follows. Implementing a traveling wave theory formula using values sampled and input by making the sampling time difference between the two sets of input means correspond to the time difference in the representative mode, and using the characteristic impedance in the representative mode as the characteristic impedance. A transport protection relay system featuring: