JPH07318595A - System for detecting change in quantity of ac electricity - Google Patents

Abstract

PURPOSE:To accurately detect the change in the quantity of AC electricity without being affected by frequency by obtaining the inner outer product values of the quantity of change of AC electricity of a power system with the quantity of reference electricity before and after the change with the quantity of AC electricity which does not change as a reference. CONSTITUTION:A present data of the volume of AC electricity to be detected, and a preceding data of a set time before from the current data, and a data of the quantity of AC electricity which are not affected by the change in the quantity of AC electricity, and a data preceding a set time from it are obtained. Then, the current inner product value between the quantity of AC electricity to be detected and the quantity of AC electricity which is not affected by the influence in the change of the quantity of AC electricity, the square value of the difference of the inner product value preceding a set time, and the sum of the square value of the difference between the current outer product value of the same of electricity, and the outer product value preceding a set time are obtained. Then, the square value of the amplitude value of the quantity of AC electricity which does not affect the change in the quantity of AC electricity is calculated and the value is multiplied by a setting value K. Then, the difference between the inner and outer product values preceding a set time is compared with the sum of the square value and the value obtained by multiplying a set value K.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a change amount of alternating current electricity for detecting a magnitude of a vector change amount of alternating current electricity of a power system with high accuracy.

[0002]

2. Description of the Related Art It is well known that a load current is constantly flowing through a power system, but in recent years, the system configuration has become complicated,
It is difficult to maintain balance even if the system is in a healthy state,
It has been reported that zero-phase and negative-phase voltage / current exist even at all times. Even under such a condition, it is necessary to reliably detect an accident. Therefore, when the amount of electricity generated at the time of an accident is very small, even if the always-present zero-phase or negative-phase electricity amount is superimposed on the electricity amount at the time of the accident, it is difficult to detect the magnitude of the electricity amount as it is. Is becoming.

[0003]

When an accident occurs in the power system, the amount of electricity in the system changes according to the aspect of the accident. In this case, if a load current is flowing, it will be superimposed on the fault current, and the current detection sensitivity will deteriorate. Therefore, there is a current change detection relay that cancels the load current.
Variation in this method, as shown in (1), the moment of the current instantaneous values i _m and its several cycles before the data i
The level of the difference value of _mM is detected.

[Equation 1] Δi _m = i _m −i _mM ……………… (1)

Now, when the current instantaneous value data is set as the following equation,

## EQU00002 ## i _m = I sin (ωt _m ) _imM = I sin (ω (t _m −M · T)) (M · ω _o T = M · 2πf _o / f _s = N · 2π) ... M = N · f _s / f _o (f _s : sampling frequency, T: sampling period)

The above formula (1) becomes the formula (2).

[Number 3] _{Δi m = i m -i mM =} 2I · sin ((ωM · T) / 2) · cos (ω (t m -M · T / 2)) = 2I · sin ((ωM · T) / 2) = 2I ・ sin (M ・ (ω _o + Δω) ・ T) = 2I ・ sin ((M ・ ω _o T + M ・ Δω ・ T) / 2) = -2I ・ sin ((M ・ Δω ・ T) / 2) …………… (2) (N: integer, ω = ω _o + Δω, ω _o : system fundamental frequency,
Δω: Frequency fluctuation)

Here, when the frequency of the alternating-current electricity quantity fluctuates during normal times, the electricity quantity which should be zero originally occurs as a change amount shown in the equation (2). For example, N = 1 (one cycle before)
(Since M = 12), Δω = 5%, f _s / f _o = 1
When 2,

[Expression 4] | Δi _m | = 2I · sin (M · Δω · T / 2) = 2I · sin (12 · 0.05 · π / 12) = 2I · sin (9 °) = 0.31 · I ………… (3), which results in a 31% error. The present invention has been made to solve the above-mentioned problems, and even if the frequency of the power system changes with respect to the fundamental frequency, the amount of change in the AC electricity amount is detected with high accuracy without being affected by the frequency. It is an object of the present invention to provide a method for detecting the amount of change in alternating-current electricity amount that can be performed.

[0007]

According to a first aspect of the present invention, there is provided a method for detecting a change amount of an alternating current electricity amount in a method for calculating a change amount of an alternating current electricity amount of a power system. Means and data for a certain time before it, and data for the amount of AC electricity not affected by changes in the amount of AC electricity and data for a certain time before that, and AC electricity to be detected Quantity and the squared value of the difference between the inner product value of the alternating current electricity quantity and the inner product value of the current electricity quantity which is not affected by the change of the alternating current electricity quantity, and the outer product value of the current electricity quantity and the outer product value of the same electricity quantity before the fixed time Second means for obtaining the sum of squared values of the difference and a squared value of the amplitude value of the AC electricity quantity that does not affect the change of the AC electricity quantity, and a predetermined set value K is set to the value. The third means to multiply, the value obtained by the second means and the third obtained It is obtained and a fourth means for comparing the magnitude of the value.

[0008] AC electric quantity variation detection method according to claim 2 of the present invention, in claim 1, as a first means, the AC electric quantity of sampling values (i _m to be detected, i
_{mk / 2} , i _mk ) and sampling values (i _mM , i _{mk / 2-M} ,) before a certain time (before time-series M sampling)
i _mkM ), and the sampling value (V _pm , V _pn ) of the AC electricity quantity that is not affected by the change in the AC electricity quantity, and the sampling value (V _pm-M ) before a certain time (before time-series M sampling). , V _{pm-k / 2-M} , V _pm-kM ), and as a second means, obtain the change in the AC electric quantity from the sampling value based on the following equation:

Equation 5] ^{_{(ΔI · V p) 2 =}} {(i mk / 2 · V pm-k / 2 - (i mk · V pm + i m · V pm-k) / 2) - (i mk / 2- _M · V _{pm-k / 2-M} − (i _mkM · V _pm-M −i _mM · V _pm-kM ) / 2} ² + {(i _m · V _{pm-k / 2} −i _{mk / 2} · V _pm ) − (i _mM · V _{pm-k / 2-M} −i _{mk / 2-M} · V _pm-M )} ² (4) In the third means,

[Equation 6] V _p ² = V _{pm-k / 2} ² −V _pm-k · V _pm (5) (m and M are sampling time series) (k is a sampling time series) The phase at the fundamental frequency is 18
The difference corresponding to 0 °) is calculated.

According to a third aspect of the present invention, there is provided a method for detecting a change in alternating-current electricity amount according to the first aspect, wherein as the electricity amount to be detected by the first means, zero which occurs when a one-line ground fault occurs in a three-phase power system. A healthy interphase voltage other than the ground fault phase is used as the phase voltage, the reverse phase voltage, the sum of the zero phase voltage and the reverse phase voltage, or the quantity of electricity that is not affected by the change in the quantity of electricity.

According to a fourth aspect of the present invention, there is provided a method for detecting a change in alternating-current electricity amount according to the first aspect, wherein the electricity amount to be detected by the first means is zero generated in a one-line ground fault in a three-phase power system. The normal interphase voltage other than the ground fault phase is used as the phase current, the reverse phase current, or the sum of the zero phase current and the reverse phase current, and the quantity of electricity that is not affected by the change in the quantity of electricity.

[0011]

The alternating current electricity amount variation detecting method according to claim 1, claim 2, claim 3, and claim 4 of the present invention does not affect the variation amount of the alternating current electricity amount of the power system before and after the change. Based on the electric quantity, the in-phase component and the quadrature component with respect to the reference electric quantity before and after the change are obtained by vector inner product and outer product calculation, and the sum of the squared values of the difference values before and after the change of each component is calculated. It was done like this. The formula is as shown in formula (6). That is, if the inner product and the outer product value of the detection target AC electricity quantity and the reference electricity quantity are calculated with high accuracy, it can be converted into a DC quantity that is not affected by time and the frequency of the power system, and changes in the AC electricity quantity Instead of directly calculating the minute, the change is calculated from the change in the inner product and outer product values.

[Formula 7] (ΔI) ² · V _p ² = {(I · V _p · cos (θ)) _m − (I · V _p · cos (θ)) _M } ² + {(I · V _p · sin (Θ)) _m − (I · V _p · sin (θ)) _M } ² …………………… (6) (m and M are sampling time series, M: before change, m: after change)

[0012]

FIG. 2 is a block diagram of a digital relay to which the system according to the present invention is applied. In FIG.
The AC current amount i and the voltage amount v converted and taken in from the power system at a predetermined level are first determined by the sample hold circuit S /
The signal is sampled at H and sequentially input to the analog / digital converter A / D via the multiplexer MPX.
The digital value converted by the analog / digital converter is input to the arithmetic unit CPU. The CPU has a schematic configuration for performing a predetermined operation determination calculation based on the present invention and outputting the result.

In FIG. 2, the outputs of the S / H circuit for the current i and the voltage v are i _m and v _m , respectively.
The same applies to digital processing in PU without distinction. Further, in the present invention, the processing content relating to the digital relay in the arithmetic unit CPU is of the alternating current electricity quantity change detection method.

FIG. 1 is a diagram showing the detection of a change in AC electricity according to the present invention.
It is a block diagram which shows one Example of a system. First the first hand
As step 1, sampling of the amount of AC electricity to be detected
Value (i_m, I_{mk / 2}, I_mk) And a certain time before that
Sampling value (before time series M sampling)
(I_mM, I_{mk / 2-M}, I_mkM), And said AC electricity
Sampling value of AC electricity quantity that is not affected by changes in quantity
(V_pm) And a certain time before that (time series M sampler)
Before sampling) (V_pm-M, V_{pm-k / 2-M}, V_pm-k
-M) And, in the second means 2, the sampling value
Then, the variation of the AC electricity is obtained based on the following equation.

[0015]

Equation 8] ^{_{(ΔI · V p) 2 =}} {(i mk / 2 · V pm-k / 2 - (i mk · V pm + i m · V pm-k) / 2) - (i mk / 2- _M · V _{pm-k / 2-M} − (i _mkM · V _pm-M −i _mM · V _pm-kM ) / 2} ² + {(i _m · V _{pm-k / 2} −i _{mk / 2} · V _pm ) − (i _mM · V _{pm-k / 2-M} −i _{mk / 2-M} · V _pm-M )} ²

In the third means 3, V _p ² = V _{pm-k / 2} ² −
V _pm-k · V _pm (where k is the sampling time series and the phase at the fundamental frequency is the difference between 180 and m) The square value of the reference electric quantity is multiplied by the set value K to calculate the fourth value. In the means 4, the second
Of the amount (ΔI) ² · V _p ² calculated by the means described above and the amount K (V _p ) ² calculated by the third means (ΔI) ² · V
_p ² > K · (V _p ) ² .

Next, the operation result of FIG. 1 will be verified.
Now, the electric quantity of the change detection target and the reference electric quantity that does not change are set to i and v, and the sampling time series is given by the following equation.

Equation 9] _{i m = I · sin (ωt} m), i mk = I · sin (ωt m -kωT) i mM = I M · sin (ωt m + φ-MωT) i mkM = I M · sin (ωt _m + φ-kωT−MωT) V _pm = V · sin (ωt _m + θ), V _pm-k = V · sin (ωt _m + θ−kωT) V _pm-M = V · sin (ωt _m + θ−MωT) V _{pm-kM = V · sin (} ωt m + θ-kωT-MωT)

Here, φ, θ and I _M are as shown below. φ: time (t _m -MT) time for the exchange amount i at t _m
Leading phase of alternating current amount i. θ: Leading phase of alternating current amount v with respect to alternating current amount i at time t _m . I _M: Time (t _m -MT) amplitude values of the alternating quantity i in (before the change).

The inner product value of the alternating current amounts i and v before the change is as follows (7)
It is as shown in the formula.

(10) (I · V _p · cos (θ)) _M = i _{mk / 2-M} · V _{pm-k / 2-M} − (i _mkM · V _pm-M + i _mM · V _pm-kM ) / 2 = I _M · V · {sin (ωt _m + φ−kωT / 2−MωT) · sin (ωt _m + θ−kωT / 2−MωT) −sin (ωt _m + φ−kωT−MωT) · sin (ωt _m + θ _{-MωT) -sin (ωt m + φ} -MωT) · sin (ωt m + θ-kωT-MωT)) / 2} = I M · V · [1/2 {cos (φ-θ) -cos (2ωt m + (φ + θ) -kωT-2MωT )} - 1/2 · {cos (θ-φ) · cos (kωT) -cos (2ωt m + (φ + θ) -kωT-2MωT)}] = I M · V · 1 / 2 · [cos (φ−θ) −cos (θ−φ) · cos (kωT)] = I _M · V · cos (φ−θ) · sin ² (kωT / 2) ………………………… (7)

The inner product value after the change is as shown in the following equation (8).

[Number 11] _{(I · V p · cos (} θ)) m = i mk / 2 · V pm-k / 2 - (i mk · V pm + i m · V pm-k) / 2 = I · V · [Sin (ωt _m −kωT / 2) · sin (ωt _m + θ−kωT / 2) − {sin (ωt _m −kωT) · sin (ωt _m + θ) + sin (ωt _m ) · sin (ωt _m + θ−kωT )} / 2] = I · V · [1/2 {cos (θ) -cos (2ωt m + θ-kωT)} -1/2 · {cos (θ) · cos (kωT) -cos (2ωt m + θ −kωT)}] = I · V · 1/2 · [cos (θ) − cos (θ) · cos (kωT)] = I · V · cos (θ) · sin ² (kωT / 2)] …… ………… (8)

Similarly, the outer product value of the alternating current amounts i and v is (9)
It is as shown in the formula.

(12) (I · V _p · cos (θ)) _M = i _{mk / 2-M} · V _pm-M −i _mM · V _{pm-k / 2-M} = I _M · V · {sin (ωt _{m + φ-kωT / 2-} MωT) · sin (ωt m + θ-MωT) -sin (ωt m + φ-MωT) · sin (ωt m + θ-kωT / 2-MωT)} = I M · V · [1 / 2 {cos (φ−θ) −kωT / 2) −cos (2ωt _m + (φ + θ) −kωT / 2-2MωT)} − ½ · {cos (θ−φ) + kωT / 2) −cos (2ωt _{m + (φ + θ) -kωT} / 2-2MωT)}] = I M · V · 1/2 · [cos ((φ-θ) -kωT / 2) - cos ((θ-φ) + kωT / 2)] = I _M · V · sin (φ-θ) · sin (kωT / 2) …………… (9)

The changed outer product value is as shown in the following expression (10).

(I · V _p · cos (θ)) _m = i _{mk / 2} · V _pm −i _m · V _{pm-k / 2} = I · V · [sin (ωt _m −kωT / 2) · sin (ωt _m + θ) −sin (ωt _m ) · sin (ωt _m + θ−kωT / 2)] = I · V · 1/2 {cos (θ + kωT / 2) −cos (2ωt _m + θ−kωT / 2) } -cos (θ-kωT / 2 ) + cos (2ωt m + θ-kωT / 2)}] = I · V · 1/2 · [cos (θ + kωT / 2) -cos (θ-kωT / 2)] = I・ V ・ sin (θ) ・ sin (kωT / 2) ……………… (10)

In the above, the first and second terms on the right side of the equation (8) become the following equations (11) and (12).

[Expression 14] {(I · V _p · cos (θ)) _m − (I · V _p · cos (θ)) _M } ² = {I · V · cos (θ) · sin ² (kωT / 2) −I _M · V · cos (φ−θ) · sin ² (kωT / 2)} ² = {V · sin ² (kωT / 2)} ² · {I · cos (θ) −I _M · cos (φ −θ)} ² …………………… (11) {(I ・ V _p・ sin (θ)) _m − (I ・ V _p・ sin (θ)) _M } = {I ・ V ・ sin (θ) · sin (kωT / 2) -I M · V · sin (φ-θ) · sin (kωT / 2)} 2 = {V · sin (kωT / 2)} 2 · {I · sin (θ ) −I _M · sin (φ−θ)} ² …………………… (12)

In equations (11) and (12), k is a time series whose phase is delayed by 180 ° from m at the fundamental frequency, so kω _o T / 2 = 90 °. In the above equation, the physical meaning of the amount indicated by the underlined portion has the relationship shown in FIG. In the figure, with respect to the reference electric quantity v, the vector quantity OM is the alternating current quantity i before the change and the phase angle is (θ−φ). The amount of alternating current i after the vector OF changes, and the phase angle is θ
Is. Therefore, the change amount of the alternating current amount is the vector MF.
Therefore, the in-phase component of the magnitude of the vector MF with respect to the reference electric quantity v is the equation (11), and the orthogonal component is represented by the underlined portion of the equation (12). Therefore, 2 of each of the equations (11) and (12)
By taking the sum of multiplications, the magnitude of the change MF can be obtained.

The magnitude of the change amount MF is calculated by the following equation (13).

Equation 15] ^{_{(ΔI · V p) m 2}} = {V · sin (kωT / 2)) 2 · [{sin (kωT / 2)} 2 · {I · cos (θ) -I M · cos (φ ^{-θ)} 2 + {I ·} sin (θ) -I M · sin (φ-θ)} 2] = * {V · sin (kωT / 2)} 2 · [(I-x 2/2) · {I · cos (θ) -I M · cos (φ- θ)} 2 + {I · sin (θ) -I M · sin (φ-θ)} 2 .................. (13) ( Note , = * Means approximately: x = ε · kω _o
T / 2 = ε · π / 2, which is ε = f / f _o -1 order)

Further, the third means 3 calculates the product of the square value of the magnitude of the amplitude value of the reference AC electric quantity v which does not change and the constant K. The square value of the magnitude of the amplitude value of the reference AC electricity amount v is as follows.

[Formula 16] V _pm ² = V _{pm-k / 2} ² −V _pm-k · V _pm = V ² · sin ² (kωT / 2)

Therefore, the fourth means 4 judges the magnitude based on the equation (14).

Equation 17] {V · sin (kωT / 2 )} 2 · [(I-x 2/2) · {I · cos (θ) -I M · cos (φ-θ)} 2 + {I · sin (θ) -I _M · sin (φ-θ)} ² ]> K · V ² · sin ² (kωT / 2) ………………………… (14)

Equation 18] ^{(I-x 2/2)} · {I · cos (θ) -I M · cos (φ- θ)} 2 + {I · sin (θ) -I M · sin (φ-θ) } ² ＞ K ……………… (15)

The above is the outline of the present invention. As can be seen from the expression (15), the change amount of the AC amount can be calculated without depending on the time width of the change, that is, the difference between the time series and M. Also, the influence of the fluctuation range of the frequency,

Equation 19] ^{er = x 2/2 · {} I · cos (θ) -I M · cos (φ-θ)} 2 x = ε · kω o T / 2 = ε · π / 2 ε = 5% even, er = 0.00308 · {I · cos (θ) -I M · cos (φ-θ)} 2 , and the is negligible.

In the above method, the zero-phase voltage, the negative-phase voltage, and the zero-phase + negative-phase voltage amount in the one-line ground fault are changed to the outside-ground fault phase, that is, the healthy phase voltage amount as the change-target electric quantity to be detected. By applying it as the amount of electricity that is not affected by, it is possible to detect accidents with high sensitivity without being affected by the zero-phase voltage and the reverse-phase voltage that are slightly present in the normal power system. FIG. 4 shows an (αβO) equivalent circuit of the Clark coordinate method when an α-phase one-line ground fault occurs.
In the figure, Z2 and Z0 represent the negative phase and zero phase impedances between the accident point F and the power source Ea. Between the current I _.alpha.F and I _OF flowing through the α circuits and O circuitry (zero phase) I _.alpha.F = -2I
Connected because of _OF . As can be seen from the figure, the β circuit component does not change in the one-line ground fault.

This β circuit component is a healthy phase voltage.

Equation 20] ^{_{i = (v a + a 2}} · v b + a · v c) / 3 ...... reverse-phase voltage _{i = (v a + v b} + v c) / 3 ......... zero-phase voltage (a: I · exp (J120 °)) v = v _bc · exp (j90 °) ……… Between healthy phases (between bc phases) Advance the voltage by 90 °

As with the voltage at the time of the fault, the amount of change in the amount of change in the amount of electricity is zero-phase current, negative-phase current in the one-line ground fault,
It is naturally possible to apply the zero-phase + negative-phase current amount outside the ground fault phase, that is, as the sound phase-to-phase voltage amount as the electric amount that is not affected by the change.

I = (i _a + a ² i _b + a _c ) / 3 ・ ・ ・ Negative phase voltage i = (i _a + i _b + i _c ) / 3 ・ ・ ・ ・ ・ ・ ・ ・ Zero phase voltage (a: Iexp) (J120 °)) Unit: 120 ° phase shift vector v = v _bc · exp (j90 °) ……… Healthy phase (bc phase) Voltage is advanced by 90 °

Further, as the amount of electricity to be detected, the amount of electricity level-converted from the power source in the electric power station synchronized with the power system to a predetermined amount of electricity is superposed on the alternating current circuit taken in by the digital relay to obtain a predetermined amount of electricity. The present invention can be applied even when an inspection is performed to check whether or not they are superposed. That is, if the electric current of the current circuit that superimposes the electric quantity in the inspection place is set as the electric quantity i to be detected and the voltage quantity that does not apply the electric quantity for inspection is treated as the reference electric quantity, the electric current is applied without depending on the current before applying the inspection. It is possible to calculate the magnitude of the checked electricity quantity with high accuracy.

[0033]

[Equation 22] i = iM + iTS iM: Current before application of inspection iTS: Electricity for inspection v = v () ……… () is the voltage of the representative phase. Volume 41 Issue 4 (Digital Relay)
Monthly issue) P72-Fig. 5-2-2.

[0034]

As described above, according to the present invention, the inner product and the outer product value with the reference amount of electricity before and after the change are calculated with reference to the amount of change of the amount of alternating current of the power system that does not change. Since it is configured to calculate the change in the inner product and the outer product, it is possible to calculate with high accuracy without being affected by the size of the time width to see the change and the change in the system frequency. It was

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment for explaining a frequency detection method according to the present invention.

FIG. 2 is a schematic configuration diagram of a digital relay to which the present invention is applied.

FIG. 3 is a diagram illustrating the principle of the present invention.

FIG. 4 is a diagram illustrating an application example of the present invention.

[Explanation of symbols]

 1 Sampling value capture unit 2 Change calculation unit 3 Constant setting unit 4 Change level determination unit S / H Sampling hold circuit A / D Analog / digital converter MPX multiplexer circuit CPU calculation unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Kurosawa No. 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Corporation Fuchu factory inside

Claims (4)

[Claims] 1. An AC electricity amount change detection method for calculating a change in the AC electricity amount of a power system, wherein current data of the AC electricity amount to be detected and data before a certain time from the data, and the AC electricity amount. Means for obtaining data on the amount of alternating current electricity that is not affected by changes in the amount of electricity and data for a certain time period before that, and alternating current electricity that is not affected by changes in the amount of alternating current electricity to be detected and the amount of alternating current electricity Sum of squared values of the difference between the inner product value of the current amount and the inner product value of the fixed amount of time before, and the squared value of the difference of the current outer product value of the same amount of electricity and the outer product value of the fixed amount before ((ΔI · V _p ) ² ) to obtain ² ), and a square value (V _p ) ² of the amplitude value of the AC electricity quantity that does not affect the change of the AC electricity quantity is calculated, and the value is multiplied by a predetermined set value K. Third means, the value obtained by the second means and the predetermined value obtained by the third means AC electric quantity variation detection method, characterized by comprising a fourth means for comparing the magnitude. 2. The first means includes sampling values (i _m , i _{mk / 2} , i _mk ) of the alternating-current electricity amount to be detected and sampling values (i _mM , _{imk / 2-M} , _imkM ), and the sampling value (V _pm , V _pn ) of the AC electric quantity that is not affected by the change of the AC electric quantity, and a predetermined time before that (time series M).
Sampling value (before sampling) (V _pm-M , V
_{pm-k / 2-M} , V _pm-kM ), and the second means obtains the variation of the alternating current electric quantity from the sampling value based on the following equation, and the following equation (1) (ΔI · V _p ) _{^{2 = {(i mk / 2}} · V pm-k / 2 - (i mk · V pm + i m · V pm-k) / 2) - (i mk / 2-M · V pm-k / 2-M _{- (i mkM · V pm-} M -i mM · V pm-kM) / 2} 2 + {(i m · V pm-k / 2 -i mk / 2 · V pm) - (i mM · V pm _{-k / 2-M-} i _{mk / 2-M} · V _pm-M )} ^{2 In} the third means, V _p ² = V _{pm-k / 2} ^2- V _pm-k · V
_pm (k is the sampling time series and the phase at the fundamental frequency is m
And a difference equivalent to 180 °) are calculated. 3. The quantity of electricity to be detected by the first means is
Zero-phase voltage or negative-phase voltage that occurs in a one-line ground fault in a three-phase power system, or the sum of zero-phase voltage and negative-phase voltage, and the amount of electricity that is not affected by changes in the amount of electricity 2. The method for detecting an amount of change in AC electricity according to claim 1, wherein the normal interphase voltage is used. 4. The electric quantity to be detected by the first means is
Zero-phase current or negative-phase current that occurs at the time of a one-line ground fault in a three-phase power system, or the sum of zero-phase current and negative-phase current, and the amount of electricity that is not affected by changes in the amount of electricity 2. The method for detecting an amount of change in AC electricity according to claim 1, wherein the normal interphase voltage is used.