JPH0540677Y2 - - Google Patents

Description

[Detailed description of the invention] A. Industrial application field The present invention relates to a ground-fault directional relay used for ground-fault protection in power systems, and particularly relates to a residual-protection type ground-fault directional relay installed in a power distribution system. It is something.

B. Summary of the invention The present invention detects zero-sequence voltage and zero-sequence current in a residual protection type ground fault relay, and uses a trigger signal as a closing condition signal for a circuit breaker as a means for outputting these detection signals. By outputting the logical product signal, erroneous judgment of an accident is prevented.

C. Conventional technology In recent years, digital systems have been adopted as protective relays instead of analog systems. One of the advantages of adopting this digital system is that it provides residual protection, which is difficult to achieve with analog systems. This means that it has become possible to realize a ground-fault directional relay of the formula. This relay is less likely to malfunction or malfunction even if the residual zero-sequence voltage or residual zero-sequence current is large.

One type of relay that has been put into practical use is a change detection method as shown in FIG. In the figure, the zero-sequence current I _p and voltage V _p generated in the power distribution system are respectively converted into digital signals and then introduced into change detection means 1 and 2, where the changes before and after sampling are detected. Each detected change is output to the level detecting sections 3 and 4 and the phase determining section 5, using, for example, a rise in the zero-phase voltage from a predetermined value as a trigger. The AND section 6 generates a protection output based on the phase relationship between both signals and on the condition that each signal reaches a predetermined level or higher.

D. Problems that the invention aims to solve However, with this kind of conventional system, if a feeder's shield or disconnector is disconnected for some reason, a phenomenon occurs in which it is mistakenly determined that an accident has occurred at that feeder. . The cause of this will be explained in detail below.

Now, the judgment conditions for the ground fault direction relay are assumed as follows.

ΔI _p ≧0.1A ΔV _p ≧100V Phase condition: Phase of ΔI _p with respect to V _p is +150°~
Within -30° Trigger condition: When V _p >100V (where ΔI _p is the change in zero-sequence current, V _p is the change in zero-sequence voltage) Also, residual zero-sequence voltage V _p , residual zero-sequence current For the purpose of generating I _p , the conditions of the power distribution system shown in Figure 3 are as follows.

R phase voltage E _R = 6600/√3 [V] S phase voltage E _S = (6600/√ 3 ) × (-1/2-j√3/2) [V
] T-phase voltage E _T = (6600/√3)×(-1/2-j√3/2) [V
] Medium ground admittance Y _o = 1/20000 [S] Ground admittance of R phase, S phase, and T phase of feeder 1 (F ₁ ), respectively Y _R1 = Y _T1 = j2×π×50×0.4×10 ^-6 [S] Y _S1 = j2×π×50×0.6×10 ^-6 [S] Each phase admittance of feeder 2 (F ₂ ) is calculated as follows: Y _R2 = Y _T2 = j2×π×50×0.3×10 ^-6 [S] S] Y _S2 = j2×π×50×0.2×10 ^-6 [S] Each phase admittance of feeder 3 (F ₃ ) is determined as follows: Y _R3 = Y _S3 = Y _T3 = j2×π×50×0.9×10 ^{- 6} [S] Let each phase admittance be Y _R = Y _R1 + Y _R2 + Y _R3 Y _S = Y _S1 + Y _S2 + Y _S3 Y _T = Y _T1 + Y _T2 + Y _T3 , and the zero-sequence current of each feeder be I ₀₁ + I ₀₂ + I ₀₃ .
Assuming that the respective changes are ΔI ₀₁ , ΔI ₀₂ , ΔI ₀₃ , V _p =Y _R・E _R +Y _S・E _S +Y _T・E _T /Y _R +Y _S +Y _T +Y _N I ₀₁ =Y _R1 (E _R −V _p )+Y _S1 (E _S −V _p )+Y _T1 (E _T −
V _p ) I ₀₂ =Y _R2 (E _R −V _p )+Y _S2 (E _S −V _p )+Y _T2 (E _T −
V _p ) I ₀₃ =Y _R3 (E _R −V _p )+Y _S3 (E _S −V _p )+Y _T3 (E _T −
V _p ).

Substituting the specific numerical values mentioned above into the above formula, V _p = 77.7 [V] 〓118° (expressed with E _R as the reference phase) I ₀₁ = 0.205 [A] ∠88° (V _p 〃
) I ₀₂ =0.139〓〓92°（〃
) I ₀₃ =0.066〓〓90°（〃
), and the trigger is not activated because V _p <100 [V].
The earth fault direction relay is inactive. In this normal state, the R phase of feeder 2 is now 10kΩ.
If there is a ground fault, Y _R = (1/10000) = j2×π×50×1.6×10 ^-6
[S] Y _R2 = (1/10000) = j2×π×50×0.2×10 ^-6
[S], and substituting it into the previous equation with the other constants as they are, V _p = 315.7 [V] 91° (expressed with E _R as the reference phase) I ₀₁ = 0.135 [A] ∠ 32° ( V _p 〃
) I ₀₂ =0.220〔A〕∠25°(〃
) I ₀₃ =0.268〓〓90°（〃
), and V _p > 100 [V], so ΔV _p = 248.7 [V] 〓83° (expressed with E _R as the reference phase) ∆I ₀₁ = 0.109 [A] 〓 90° (∆V _p as 〃
) ΔI ₀₂ = 0.321 [A] ∠88° ( 〃
) ΔI ₀₃ = 0.211 [A] 〓90° ( 〃
), the ground fault direction relay treats F ₂ as the fault feeder and F ₁ and F ₃ as the normal feeders and determines normality.
In other words, the relays in each of the above columns correspond normally.

Next, if we consider a case where, for example, the feeder _F2 's cutter or disconnector is opened artificially or due to overcurrent under normal conditions, Y _R = Y _T = j2 x π x 50 x 1.3 x 10 ^-6 [S] Y _S = j2 × π × 50 × 1.5 × 10 ^-6 [S] Y _R2 = Y _S2 = Y _T2 = j∞, and the other constants remain as before, so Substituting into the formula, V _p = 185.7 [V] 〓 118° (E _R is expressed as the reference phase) I ₀₁ = 0.158 [A] ∠ 84° (V _p 〃
) I ₀₂ =0 [A] I ₀₃ =0.158A〓90°( 〃
), and V _p > 100 [V], so ΔV _p = 108.0 [V] 〓118° (expressed with E _R as the reference phase) ΔI ₀₁ = 0.048 [A] 〓 90° (∆V _p as 〃
) ΔI ₀₂ = 0.139 [A] ∠88° ( 〃
) ΔI ₀₃ = 0.092 [A] 〓90° ( 〃
), it is determined that an accident has occurred at feeder _F2 , where the circuit breaker has opened, and the relay will malfunction.

The present invention has been made with the aim of eliminating these drawbacks.

E Means for Solving Problems The present invention provides a ground fault direction relay in which each change detection means for zero-sequence voltage and zero-sequence current generates an output when a trigger occurs and performs a predetermined protection calculation. The AND signal with the closing condition signal of the breaker is used as the output command of each change detection means.

F Effect Each change detection means for detecting the residual zero-sequence voltage and current outputs an output only when a trigger occurs and the circuit breaker is in a closed circuit state, and phase determination and level detection are performed.

G. Embodiment FIG. 1 shows an embodiment of the present invention, and the same reference numerals as in FIG. 2 indicate the same parts. That is, the present invention is provided with a logical product section 7. A trigger that is generated when the zero-sequence voltage becomes larger than a predetermined value is applied to one gate of the AND section 7, and a closing condition signal for a line breaker placed in the feeder is applied to the other inhibit gate. , for example, a pallet condition signal of a breaker or a voltage signal of a feeder.

The operation of the present invention configured as above will be explained.

The change detection means 1 and 2 momentarily introduce the zero-sequence current I _p and voltage V _p generated or remaining in the power distribution system to detect the change, but no output command is applied from the logical product section 7. Therefore, no detection signal is output.

Now, when a trigger occurs and is input to the gate of the AND section 7, this AND section 7 judges whether or not the circuit breaker is in the open circuit state. In this case, the change detection means 1 and 2 are locked so that they are not triggered. Further, if the breaker is in the closed state, a trigger signal is output to the change detection means. Therefore, each detecting means 1, 2 includes a change level detecting section 3, 4 and a phase determining section 5, respectively.
sends an output signal to perform predetermined calculations and judgments,
The AND section 6 generates a protection output.

H. Effects of the invention According to the invention, the output trigger of the zero-sequence voltage and current change detection means is locked when the disconnector is opened. Even if the circuit is opened, the ground fault direction relay will not make a false judgment.

Furthermore, in a system with a large residual amount, an abnormality may be determined based on the residual amount or phase that changes from time to time, but the present invention has the advantage of not causing an abnormality determination even in such a case.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention;
The figure is a configuration diagram of a conventional ground fault directional relay, and FIG. 3 is an equivalent diagram of a power distribution system for explanation. Reference numeral 1 denotes means for detecting a change in zero-phase current; 2, means for detecting a change in zero-phase voltage; 3 and 4, a change level detecting section; 5, a phase determining section; and 6, 7, an AND section.

Claims (1)

[Scope of utility model registration request] Each change in the zero-sequence voltage and zero-sequence current that occurs in the power system is detected by the change detection means, and each detected signal is output to the level detection section and the phase judgment section, respectively, when a trigger signal is applied. An operation output is generated when the output logical product of the level detection section and the phase determination section is established, wherein an AND signal of the trigger signal and the closing condition signal of the shimmer breaker is applied to each of the change detection means. A ground fault directional relay characterized by being configured as follows.