JPH0527326B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a ground fault protection relay installed in a power distribution substation, and more particularly to a ground fault protection relay that eliminates the influence of residual zero-sequence voltage. BACKGROUND ART Earth fault protection relays, such as earth fault directional relays and earth fault overvoltage relays, detect earth faults using changes in zero-sequence voltage. Problems to be Solved by the Invention There is always a residual zero-sequence voltage in the power system. This residual zero-sequence voltage is caused by the unbalance of the ground capacitance of each phase. For example, as shown in Fig. 3, the ground capacitance C _a ,
When C _b and C _c have the same value C and the ground capacitance of phase a changes to C + C' by coupling capacitor C', the zero-sequence voltage
V ₀ (neutral point voltage V _N ) is |V ₀ |=C′/3C+C′E _a = |V _N |. The influence of the unbalanced capacitor C' on this zero-sequence voltage V ₀ is shown in Figures 4A and 4B when the a-phase ground fault resistance R _F = 0 to 10KΩ, C = 0.4μF, and C' = 0.3μF. is expressed by voltage V ₀ and phase angle θ between V ₀ and zero-sequence current I ₀ . In the figure, the solid line shows the zero-sequence voltage 3V ₀ and phase angle θ with respect to the ground fault resistance R _F with balanced ground capacity without capacitor C', and the broken line shows the phase angle θ of a, b, and c when capacitor C' is present. The zero-sequence voltage 3V ₀ and phase angle θ are shown when one phase is grounded. Similarly, in Fig. 4C, the solid line indicates the zero-sequence current I ₀ at the balanced ground capacity (without C').
The dashed line indicates the zero-sequence current at each phase ground fault when unbalanced.
Indicates I ₀ . As shown in these figures, due to the unbalanced ground capacity, a difference appears in the phase angle θ of the zero-sequence voltages V ₀ and V ₀ due to the ground fault phase, and this is especially large in the region where the ground fault resistance R _F is large. The difference appears. For this reason, in the case of a ground fault relay whose operation range is indicated by diagonal lines in the figure, ground faults can be detected sufficiently with a setting value of 30V (A in Fig. 4) in the case of balanced ground capacity, but in the case of unbalanced ground faults, the b-phase R _F = 7K due to ground fault
In the range of Ω or more, the setting value must be set to 20V or less, resulting in a decrease in sensitivity. This setting value 20V
This also exceeds the tap range of a small ground fault relay that detects ground faults with large ground fault resistance R _F. Similarly, regarding the phase angle θ, the relay sensitivity is reduced in the case of an unbalanced ground fault. Means and Effects for Solving Problems The present invention makes it possible to detect ground faults with high sensitivity even in systems with unbalanced ground capacity, and the difference between the zero-sequence voltage at the time of a fault and the zero-sequence voltage at a normal state is The relay is configured to detect ground faults based on changes, and to reduce variations in zero-sequence voltage V ₀ and phase angle θ due to differences in ground fault phases, as well as system unbalance and ground fault resistance values. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The change amount detection circuit 1 of the zero-sequence voltage V ₀ detects the zero-sequence voltage
Detect the change amount ΔV ₀ using V ₀ and the reference amount V _o as input,
The ground fault detector 2 detects a ground fault based on this amount of change ΔV ₀ . The reference amount V _o is set to a healthy phase-line voltage, and for example, to detect an a-phase ground fault, it is set to a line-to-line voltage of the b and c phases. The detection circuit 1 is composed of 3 to 11. The inner product/divider 3 calculates an inner product between the current reference amount _Vo and the zero-phase voltage _V0 , and divides the inner product result by the square of the magnitude of the voltage _Vo . The data obtained by this inner product/divider 3 is given by the following equations (1) and (2) for V _o and V ₀ : V _o = √2V _N sin (ωt + φ + θ) ... (1) V ₀ = √2V ₀ sin(φt+φ) ……(2) Vector inner product is current value V _N (T), V ₀ (T) and electrical angle 90
From the previous voltage V _N (t-Δt), V ₀ (t-Δt) to 1/2 {V _N (T)・V ₀ (T)+V _N (t-Δt) V ₀ (t-Δt)
} = 1/2 {√2V _N sin (ωt+φ+θ)・√2V ₀ sin
(ωt+φ) +√2V _N sin(ωt+φ+θ−90°)・√2V ₀ sin(
ωt+φ−90゜)｝ =V _N V ₀ {sin(ωt+φ+θ)) sin(ωt+φ)+co
s(ωt+φ+θ)cos(ωt+φ)} =V _N V ₀ {sin(A+θ)sinA+cos(A+θ)cosA} However, A=ωt+φ =V _N V ₀ cos(A+θ−A) =V _N V ₀ cosθ , the value M ₁ divided by the square of the _magnitude of the voltage Vo (V _N ² ) is M ₁ =V ₀ /V _N cosθ (3). Similarly, the other inner product/divider 4 calculates the inner product of the voltage V ₀ and the reference quantity V _o ′ obtained by delaying the reference quantity V _o by 90 degrees by the phase shifter 5 to the square of the magnitude of V _o ′. Perform the calculation divided by. In this case, V _o ′=√2V _N sin (ωt+φ+θ−90°) ……(4), so the vector inner product is V _N V ₀ sinθ, and V _N ²
The value M ₂ divided by is given by the following formula. M ₂ =V ₀ /V _N sinθ ...(5) Next, the calculation results of inner product/divider 3 and 4 M ₁ , M ₂
are delayed by an integer multiple of 360 degrees in electrical angle by passing through shift registers 6 and 7, respectively, and the current reference amounts V _o ,
Multipliers 8 and 9 are used to multiply the resultant V _o ', respectively, and adder 10 adds the resultant products. This addition result V ₀ ' is given by the following equation (6). V ₀ ′=V _o M ₁ +V _o ′M ₂ =√2V ₀ cosθ・sin(ωt+φ+
θ) +√2V ₀ sinθcos(ωt+φ+θ−90°)=√2V
₀ sin(ωt+φ)……(6) This calculation result V ₀ ′ means that the past zero-sequence voltage value can be reproduced as the current zero-sequence voltage, and it is not affected by the difference in sampling frequency and system frequency. do not have. Next, the subtracter 11 subtracts the zero-sequence voltage V ₀ ′ and the current zero-sequence voltage V ₀ , and the subtraction result ΔV ₀ (=V ₀ −
V ₀ ′) is given to the ground fault relay 2 as a zero-sequence voltage change. Here, the relationship between the sampling of the voltages vo _{and v0} and the calculations of each part of the detection circuit 1 will be explained below with reference to FIG. The inner product/divider 3 calculates the zero-sequence voltage v ₀ (T) at time t, the healthy phase-line voltage v _o (T), and the voltage v ₀ (t
V _N V ₀ cosθ is calculated by calculating at the time t using -Δt) and v _o (t-Δt), and to find V _N ² , v _o (T) and v _o (t-Δt ) to find. V _N ² = 1/2 {v _o (T) v _o (T) + v _o (t-Δt) v _o (t-Δ
t)} On the other hand, the inner product/divider 4 calculates the voltage v _o ′(T) at time t,
We need v ₀ (T) and the voltage before Δt _v o ′ (t−Δt), v ₀ (t−Δt), but since v _o ′ is the voltage v _o shifted by 90 degrees, Voltage v _o (t-Δt), v _o (T) and v _o (t-
2Δt) and v ₀ (t−Δt). The calculation at time t is obtained from the shaded area in FIG. V _N V ₀ sinθ=1/2 {v _o ′(T)v ₀ (T)＋v _o ′(t−Δt)
v ₀ (t-Δt)} = 1/2 {v _o (t-Δt) v ₀ (T)+v _o (t-2Δt) v ₀
(t-Δt)} Next, the past zero-sequence voltage v ₀ ' and the current zero-sequence voltage v ₀
In order to obtain the change amount Δv ₀ from the subtracter 11, the zero-sequence voltage v ₀ ' needs to be an integral multiple of 360 degrees in electrical angle. Therefore, in Fig. 5, in order to subtract the voltages v ₀ ' and v ₀ at time (t+4Δt), the calculated values (V ₀ /V _N ) cos θ and (V ₀ /V _N ) sin θ 360 degrees earlier are transferred to the shift register 6. , ₇ , and the voltage _is
Multiply v _o and v ₀ by multipliers 8 and 9, respectively, and adder 10
By adding the voltage v ₀ ' to the time (t+
4Δt). Therefore, according to this embodiment, as shown in FIG. 3, the line voltage of the healthy phases (phases B and C) is used as the reference value v _o to detect the a-phase ground fault, and the change amount detection circuit 1 The change ΔV 0 between the zero-sequence voltage v ₀ ′ before the ground fault and _the zero-sequence voltage v ₀ after the earth fault is obtained by , and the ground fault is detected by comparing this change ΔV ₀ with the set value. , zero-sequence voltage
The residual zero-sequence voltage included in V ₀ ′, V ₀ is changed by the change ΔV ₀
It is possible to detect ground faults removed from In Figure 3, the line voltage of the healthy phase is V _b = V ₀ + E _b ……(7) V _c = V ₀ + E _c ……(8) V _b −V _c = E _b −E _c = E _bc … ...(9) This becomes the voltage with the zero-sequence voltage V ₀ component removed. Also, regarding the zero-sequence current I ₀ , even if V ₀ ′=10V, the zero-sequence current change I ₀ ′=0.02A,
Since the sensitivity is small compared to the relay sensitivity, a change detection circuit is not required. An example of calculation of the zero-phase voltage V ₀ ′ and the change amount ΔV ₀ by the change amount detection circuit 1 is shown in the table below. In addition, in the circuit shown in Figure 3, E _a , E _b , E _c = 6600/√3(V), and ground resistance R _N
= 10000Ω and a phase grounding resistance R _F = 2KΩ and C (=C _a =
Table 1 shows the case of C _b = C _c ) = 5μF, and C with R _F = 8KΩ.
= 1.2μF is shown in Table 2, and in each table, the coupling capacitor C' is shown for each sample of 0, 0.05C, 0.1C, and 0.2C.

【table】

【table】

【table】

[Table] Furthermore, FIG. 2 shows the absolute value of each zero-sequence voltage in the calculation example shown in Table 1. As is clear from these tables and Figure 2, despite changes in the conditions of the coupling capacitor C', fault resistance R _F , and ground capacitance C, as long as the difference between the zero-sequence voltage V ₀ and V ₀ ' is taken, the residual zero By removing the influence of phase voltage, ground faults in each phase can be detected with high sensitivity. Effects of the Invention As described above, according to the present invention, ground faults are detected from the amount of change in zero-sequence voltage, so regardless of the presence of residual zero-sequence voltage due to system imbalance, the magnitude of ground fault resistance,
This has the effect of reducing zero-sequence voltage variations and phase angle variations due to differences in ground fault phases, allowing highly sensitive ground fault detection.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a graph showing an example of zero-sequence voltage calculation based on the present invention, Figure 3 is an equivalent circuit diagram of a three-phase power system, its ground capacity and ground fault resistance, Figures 4A, 4B, and 4 C is a diagram showing fluctuations in zero-sequence voltage V ₀ , phase angle θ, and zero-sequence current I ₀ due to unbalanced ground capacitance in FIG. 3, and FIG. 5 is a time chart for explaining the operation of the change amount detection circuit. . 1... Change amount detection circuit, 2... Earth fault relay,
3, 4... Inner product/divider, 2... Phase shifter, 6, 7
...shift register, 8, 9...multiplier, 10...
...Adder, 11...Subtractor.

Claims (1)

[Claims] 1. Calculate the inner product of the zero-sequence voltage V ₀ obtained by sampling from the three-phase power system and the line-to-line voltage V _o of the healthy phase at the same time among the three phases, and use this calculated value as The first inner product, which is calculated by dividing the voltage V _o by the square value.
Divider 3 performs an inner product calculation between the zero-sequence voltage V ₀ and a voltage V _o ′ obtained by delaying the line voltage V _o by 90 degrees, and divides this calculated value by the square value of the voltage V _o ′. The second dot product,
The calculation results of the divider 4 and the inner product/divider are each expressed in electrical angle.
first and second shift registers 6 and 7 that delay by an integral multiple of 360 degrees; a first multiplier 8 that multiplies the line voltage _Vo by the output of the first shift register 6; and the second The output of the shift register 7 of
a second multiplier 9 that multiplies V _o ′; an adder 10 that adds the calculation results of both multipliers to obtain the past zero-sequence voltage V _{0 ′} ; a subtracter 11 that subtracts the zero-sequence voltage V ₀ ' from the adder to obtain the amount of change ΔV ₀ in the zero-sequence voltage; a ground fault relay 2 that detects a ground fault from the amount of change ΔV ₀ obtained in the subtracter; A ground fault protection relay characterized by comprising: