JPH09200944A - Differential relay system - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To obtain a differential relay system in which there is no risk of erroneous determination even in a long-distance transmission line. SOLUTION: In a differential relay system in which a net differential current obtained by compensating a charging current with respect to a differential current of each phase of a transmission line is an operation amount,
The zero-phase component of the net difference current is added as a suppression amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential relay system for detecting an internal / external failure by detecting a difference current between an inflow and an outflow of an object to be protected.

[0002]

2. Description of the Related Art FIG. 5 is a single-line diagram of a three-phase transmission line to be protected by a differential relay. In the figure, reference numeral 1 denotes a transmission line to be protected, which connects between a bus A and a bus B. The outlet of the bus A is called a terminal A, and the outlet of the bus B is called a terminal B. The current and voltage at the terminal A are I _A and V _A , respectively, and the current and voltage at the terminal B are I _B and V _B , respectively.

According to the convention, the direction of the terminal current is the transmission line 1
Take the direction toward the inside of. F is the accident point, and the accident current I
_F flows. When there is no accident in the transmission line 1, it is treated as I _F = 0. X is the distance between the terminals A and B, M is the center point between the terminals A and B, and x is the distance between the center point M and the accident point F. The accident point F is described as being on the side of the terminal B with respect to the center point M, but as a result, it is the same on either side as described later.

The symbols commonly used in the description of the present invention are as follows. ω: angular frequency, K: electrostatic coefficient per unit length, C _s : self-capacitance of each phase per unit length, C _m : interphase electrostatic capacitance per unit length, ||: amplitude of alternating current amount.

Subscript A: terminal A, B: terminal B, d: differential amount, p: general phase,
r: r phase, s: s phase, t: t phase, r ': line 2 r phase,
s ': same s phase, t': same t phase, w: symmetrical part general, 0: zero phase part, 1: positive phase part, 2: opposite phase part. Superscript t: transposed matrix, i: inverse matrix.

FIG. 6 is a block diagram showing an example of the configuration of the conventional system. The device of the terminal A will be described as a representative. In FIG, 2 is a data generator, type current I _A and the voltage V _A, to generate a charging current compensated current data J _A (1) below.

[0007]

[Equation 1]

Hereinafter, the charging current compensated current data will be simply referred to as data. A data transmitter 3 transmits the data J _A of the equation (2) to the terminal B. 4 is a data receiving section, terminal B
To receive similar data J _B of equation (3). Reference numeral 5 denotes a determination unit, which uses the data J _A of the terminal _A and the data J _{B of the} terminal B,
Calculate the net difference current J _d in equation (3).

[0009]

[Equation 2]

The judgment unit 5 judges whether or not there is an accident inside the power transmission line 1 by the judgment of the equation (4). The left side of the equation (4) is commonly called the motion amount, the right side is the suppression amount, k (| J _Ap | + | J _Bp |) is the ratio suppression amount, and I _k is the constant suppression amount. When the equation (4) is satisfied, the output OP is generated, and the circuit breaker (not shown) of the power transmission line 1 is tripped as is well known.

[0011]

[ _Equation 3] | J _dp |> k (| J _Ap | + | J _Bp |) + I _k (4) p = r, s, t. k and I _k are constants. Hereinafter, unless there is a possibility of causing confusion, an accident inside the self-phase of the power transmission line 1 will be referred to as an internal accident or simply an inside, and the others will be simply expressed as an external or external accident.

As is well known, differential relay compensation is a method suitable for discriminating between the inside and outside of an accident. That is, the net difference current is approximately equal to the accident current in the internal accident, and becomes 0 in the external case. However, as the transmission line becomes longer, there is an error in the amount of net difference current, and the value becomes 0 outside
It gradually becomes a factor of misjudgment with distance. It will be explained again using FIG. 5 below.

The net difference current J _d is expressed by equation (5).

(Equation 4)

When the transformation matrix T is used for the equation (5) and the phase component is transformed into a symmetrical component, the equation (6) is obtained.

(Equation 5)

Substituting equation (6) into equation (5) yields equation (7), and T ⁱ KT in equation (7) is a diagonal matrix and becomes equation (8).

(Equation 6)

Using equation (8), equation (6) becomes equation (9).

[Equation 7] J _d = T (D _w −jωXK _w V _w ) = T [I _d0 −jωXC ₀ V ₀ I _d1 −jωXC ₁ V ₁ I _d2 −jωXC ₁ V ₂ ] ^t ………… ( 9)

On the other hand, when the symmetry component w = 0, 1, 2, the w component of each symmetry component can be represented by an independent single-phase circuit. For each of these single-phase circuits, the capacitance per unit length, The resistance and the inductance are C _w , R _w and L _w , respectively,
Given the condition of the expression (10), the w component I _Mw of the current at the central point M in FIG. 5 is expressed by the expression (11) using the current and voltage of the terminal A.

[0018]

(Equation 8)

Further, it is expressed as follows using the current and voltage at the fault point and the current and voltage at the terminal B.

I _Mw = (I _Fw + I _FBw ) cosh (ψ _w ) + Y _w V _Fw sin h (ψ _w ) = I _Fw cos h (ψ _w ) + {− I _Bw cos h (ψ _w −ψ _w ) + Y _w V _Bw sin h (Ψ _w −ψ _w )} cos h (ψ _w ) + Y _w {V _Bw cos h (Ψ _w −ψ _w ) −Z _w I _Bw sin h (Ψ _w −ψ _w )} sim h (ψ _w ) = I _Fw cos h (ψ _w ) −I _Bw cos h (ψ _w ) + Y _w V _Bw sin h (ψ _w )) …………………… (12)

The following equation is obtained by equating equations (11) and (12).

(I _Aw + I _Bw ) cos h (Ψ _w ) = I _Fw cosh (ψ _w ) + Y _w ( _{VA w} + V _Bw ) sinh (Ψ _w ) I _ww cos h (Ψ _w ) = I _Fw cos h (Ψ _w ) + 2Y _w V _w sin h (Ψ _w ) I _dw cos h = I _Fw cos h (ψ _w ) / cos h (Ψ _w ) +2 Y _w V _w tan h (Ψ _w ) I _dw = I _Fw cos h (ψ _w ) / cos h (Ψ _w ) + 2Y _w Ψ _w V _w tan h (Ψ _w ) / Ψ _w = I _Fw cos h (ψ _w ) / cos h (Ψ _w ) + 2Y _w Ψ _w V _w tan h (Ψ _w ) / Ψ _w = I _Fw cos h (ψ _w ) / cos h (Ψ _w ) + jωXC _w V _w tan h (Ψ _w ) / Ψ _w ………………… (13) I _dw − jωXC _w V _w = ξ _w I _Fw + jω XC _w V _w δ _w ξ _w = cos h (ψ _w ) / cos h (Ψ _w ) δ _w = {tan h (Ψ _w ) / Ψ _w −1} ……… …………(14)

Since the equation (14) is symmetrical with respect to the currents I _A and I _B , the same holds true even if the fault point F is located closer to the terminal A than the center point M. Further, since the propagation constants of the positive phase component and the negative phase component are the same, equation (15) is obtained, and equation (9) is rearranged using equations (14) and (15) to obtain equation (16).

[Formula 11] Ψ ₁ = Ψ ₂ , ψ ₁ = ψ ₂ ∴ξ ₁ = ξ ₂ , δ ₁ = δ ₂ …………………… (15)

[0022]

(Equation 12)

From equations (6) and (8), equation (17) is obtained.
Therefore, the net difference current is given by equation (18).

TK _w [V ₀ V ₁ V ₂ ] ^t = TK _w T ⁱ TV _w = KV ... (17) j _d = ξ ₁ [I _Fr I _Fs I _Ft ] ^t + (ξ ₀ −ξ ₁ ) I _F0 [111] ^t + jωXδ ₁ KV + jωXC ₀ (δ ₀ −δ ₁ ) V ₀ [111] ^t …………… (18)

Equation (18) means the following. That is, ξ ₁
Is close to 1, and therefore ξ ₁ [I _Fr I _Fs I _Ft ] ^t is approximately a fault current in a phase where there is a fault inside the transmission line 1 and 0 in a phase where there is no fault inside. Therefore, this term complies with the well-known principle of the differential system. Other terms are errors.

(Ξ ₀ −ξ ₁ ) I _F0 is due to the difference in the propagation constants of the zero-phase component and the positive-phase component and the zero-phase component of the fault current. jωXδ ₁ KV
Is the charging current multiplied by the coefficient δ ₁ , and is an error due to the difference between the lumped constant circuit and the distributed constant circuit. Last j
ωXC ₀ (δ ₀ −δ ₁ ) V ₀ is due to the difference in propagation constant between the zero-phase component and the positive-phase component.

[0026]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is caused by the difference in the propagation constants of the zero phase of the fault current or the approximation of the distributed constant circuit by the lumped constant circuit. It is an object of the present invention to provide a differential relay system that prevents erroneous determination of a sound phase due to an error in a difference current that occurs.

[0027]

A differential relay system according to claim 1 of the present invention is a differential relay that uses a net difference current obtained by compensating a charging current for a difference current of each phase of a transmission line as an operation amount. In the method, the zero-phase component of the net difference current is added as a suppression amount.

Further, in claim 2, the suppression amount by the zero-phase first component of the net difference current is added, and in claim 3, the suppression amount by the sum of the absolute values of the zero-phase current is added. Alternatively, in claim 4, the charging current is compensated by using the electrostatic coefficient corrected by the coefficient by the distributed constant circuit.

In the present invention, the erroneous determination of the sound phase is prevented by adding the amount of suppression of the net difference current by the zero-phase component or the zero-phase first component or the amount of suppression by the zero-phase component of each terminal data. Alternatively, by using the value obtained by multiplying the capacitance per unit length by the distance and the coefficient of the distributed constant circuit, the error for approximating with the lumped constant is prevented.

[0030]

FIG. 1 is a functional block diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. In the present embodiment, the characteristic portion is the content of calculation in the determination unit 6. That is, the determination unit calculates the net difference current similar to that of the equation (3), and further calculates the amount J _do of the zero difference of the net difference current by the equation (19).
Is calculated.

The value of J _do may be divided by 3 to calculate the zero-phase component, but any method is the same as long as it is included in the coefficient g. The determination unit 6 determines the presence / absence of an accident inside the power transmission line 1 by the determination formula shown in Formula (20). (20)
The right side of the equation is the ratio suppression amount k (| J _Ap | + of the determination equation of Equation (4).
| J _Bp |) and the constant suppression amount I _k , the suppression amount g | J _do | due to the zero phase component of the net difference current is added.

[0032]

[Equation 14] J _do = J _dr ＋ J _ds ＋ J _dt ………………………… (19) ｜ J _dp ｜> k ( _{│J Ap} │ + _{│J Bp} │) + I _k + _{g│J do} │ (20) p = r, s, t, k, I _k and g are constants.

The output OP pulls out the circuit breaker (not shown) of the power transmission line 1 as in the case of FIG. According to this method, even if an error occurs in a sound phase due to a zero-phase current due to an internal accident of another phase, the erroneous determination can be prevented by the suppression amount g | J _do |.

FIG. 2 is a functional block diagram showing another embodiment of the differential relay system. 2, the same parts as those in FIG. 6 are designated by the same reference numerals and the description thereof will be omitted. In this example, when the power transmission line 1 has two parallel lines, the two lines are collectively protected.

[I _A ] and [V _A ] collectively represent the current and voltage of the terminal A, respectively. The same applies to the terminal B or the differential current. Similarly, [K] represents the electrostatic coefficient of two lines at a time. 2-1 is a data generation unit that generates data [J _A ] according to equation (21), which is based on equation (1).

Equation 15] _{[J A] = [I A} ] - 1 / 2jωX [K] [V A] ...... (21)

Reference numeral 5-2 is a determination unit for calculating the net difference current [J _d ] according to the equation (22) according to the equation (3). Next, the amount J _dg corresponding to 6 times the zero-phase first component in the net difference current is calculated by the equation (23).

Equation 16] _{[J d] = [J A} ] + [J B] ........................... (22) J dg = J dr + J ds + J dt + J dr '+ J ds' + J dt' ...... (twenty three)

However, the subscripts r, s, and t represent the phase of Line 1 and r ', s', and t'are the phases of Line 2. The judgment formula is the following formula, and instead of the suppression amount g | J _do | of FIG. 1, g | J
_dg | is used.

[ _Equation 17] | J _dp |> k (| J _Ap | + | J _Bp |) + I _k + g | J _dg | (24) p = r, s, t, r ′, s ′, t ′, k, I _k , and g are constants. The output OP is the same as in FIG.

As is well known, in the case of two parallel lines, there are a zero-phase first component and a zero-phase first component, but the latter has a propagation constant substantially equal to a positive phase or a negative phase, so only the zero-phase first component is present. Has the same effect as the zero-phase component in the case of one line. Therefore, erroneous determination can be prevented by adding the suppression amount by the zero-phase first component as in this embodiment.

FIG. 3 is a functional block diagram showing still another embodiment of the differential relay system. In FIG. 3, the same parts as those in FIG. This example is characterized by the content of the calculation of the determination unit 5-3.

That is, the net difference current J _d similar to that in FIG. 1 is calculated, and then from the data J _A and the data J _B, J _Ao and J corresponding to three times of the respective zero phase are calculated by the equation (25). Calculate _Bo . Also, the judgment formula is formula (26), and g |
Use h (| J _Ao | + | J _Bo |) instead of J _do |.

[0041]

[ _Equation 18] J _Ao = J _Ar ＋ J _As ＋ J _At , J _Bo ＝ J _Br ＋ J _Bs ＋ J _Bt ……… (25) ｜ J _dp ｜ ＞ k (｜ J _Ap ｜ + ｜ J _Bp ｜) ＋ I _k + h ( | J _Ao | + | J _Bo |) (26) p = r, s, t, k, I _k , h are constants.

This example can be used instead of the embodiment of FIG. That is, in the example of FIG. 2, the relays for two lines are collectively used, but there is an idea that the relays for the respective lines should be separated as soon as possible. In that case, the zero-phase first component of the net difference current cannot be calculated. In this method, by using the suppression amount by the zero-phase component of the own line data as a substitute for the suppression amount by the zero-phase first component of the net difference current,
This idea can be satisfied.

The zero-phase component of the net difference current and the zero-phase first component of the net difference current are different amounts, but the zero-phase first component of the net difference current is the zero-phase component of the net difference current. It is common to two lines, and can be substituted by giving a margin to the constant h.

In this example, the zero-phase portion of the self-end and the partner-end data is used, but the presence or absence of the charging current compensation does not affect the suppression amount itself, so that the self-end data for which the charging current has been compensated is self-end. Not limited to the zero-phase component, the suppression effect is the same even when the zero-phase component of the self-end current is directly used. In short, the amount should be approximately equivalent to the zero-phase current of each terminal.

FIG. 4 is a functional block diagram showing still another embodiment of the differential relay system. In FIG. 4, the same parts as those in FIG. The characteristic part of this example is the data generator 2-2.

In the data generation unit 2-2, (2
Data J _A is generated by the equation (7).

[Formula 19]

By using such data,
The error with respect to the charging current described in equation (16) or equation (18) can be eliminated. That is, C _w tan h (Ψ _w ) /
Substituting Ψ _w = C _w ′ into equation (13) yields equation (28),
Equation (29) is obtained instead of equation or equation (18).

[0048]

I _dw = I _Fw cos h (ψ _w ) / cos h (Ψ _w ) + jωXC _w ′ V _w ∵ I _dw −jωXC _w ′ V _w = ξ _w I _Fw …………………… ( 28) J _d = ξ ₁ T [I _F0 I _F1 I _F2 ] ^t + (ξ ₀ −ξ ₁ ) I _F0 [111] ^t = ξ ₁ [I _Fr I _Fs I _Ft ] ^t + (ξ ₀ −ξ ₁ ) I _F0 [111] ^t …………………… (29)

In this example, as compared with the conventional method in which the electrostatic coefficient per unit length is simply multiplied by the distance to compensate the charging current, the error relating to the charging current is corrected by correcting the distribution constant effect due to the long distance transmission line. It is possible to eliminate all and eliminate the cause of erroneous determination. Data generator 2-2 shown in this example
Needless to say, can also be applied to all other examples.

The above examples relate to the differential relay system in which the net difference current of each phase is used as the operation amount and the internal / external discrimination for each phase is performed. Of course, this example can also be applied to such a relay system, but not necessarily for each phase,
It can also be applied to the case of a differential relay system for each line.

That is, the error related to the charging current explained by the equation (16) or the equation (18) occurs even when there is no fault in the system, or even when the zero phase component of the voltage occurs due to an external fault, It is also an error factor in the differential relay system, which makes judgments on a line at a time. By applying the present example to this, the error factor can be removed.

[0052]

As described above, according to the present invention, it is possible to provide a differential relay system in which there is no risk of erroneous determination even in a long distance transmission line.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of a differential relay system according to the present invention.

FIG. 2 is a functional block diagram showing another embodiment of the differential relay system according to the present invention.

FIG. 3 is a functional block diagram showing still another embodiment of the differential relay system according to the present invention.

FIG. 4 is a functional block diagram showing still another embodiment of the differential relay system according to the present invention.

FIG. 5 is a power transmission system diagram for explaining the present invention and a conventional system.

FIG. 6 is a functional block diagram of a conventional method.

[Explanation of symbols]

 1 Transmission line 2,2-1 Data generation unit 3 Data transmission unit 4 Data reception unit 5,5-1,5-2 Judgment unit

Claims (4)

[Claims] 1. A differential relay system in which a net differential current obtained by compensating a charging current for a differential current of each phase of a transmission line is used as an operation amount,
A differential relay system, wherein a zero-phase component of the net difference current is added as a suppression amount. 2. A differential relay system using a net difference current obtained by compensating a charging current for a difference current of each phase of a transmission line as an operation amount,
A differential relay system, wherein the zero-phase first component of the net difference current is added as a suppression amount. 3. A differential relay system in which a net differential current obtained by compensating a charging current with respect to a differential current of each phase of a transmission line is an operation amount,
A differential relay system characterized in that a zero-phase current or a zero-phase component of a current compensated for a charging current is added as a suppression amount. 4. A differential relay system in which a net differential current obtained by compensating a differential current in a transmission line for a charging current is used as an operation amount, and a distributed constant correction is added to the charging current compensation amount. .