JP2001251754A - Direction discriminating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a direction discriminating method which accurately performs direction discrimination in a short time. SOLUTION: A voltage waveform is presumed sinusoidal with the same frequency as the power source. According to the measured sampled voltage and sampled periods, a voltage waveform composed of an amplitude and a phase, by which the error between the presumed voltage waveform and a sampled voltage becomes minimum is presumed by the method of least squares, and a current waveform is similarly presumed. The direction of a short circuit and the direction of power are discriminated by the phase difference between the presumed current waveform and voltage waveform. Accordingly, voltage waveform and current waveform can be presumed from the measured values obtained without using any filter. Delays produced by a transient characteristic by a filter are prevented, and direction can be discriminated accurately in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a protective relay for protecting a power system from an accident or the like.
In particular, the present invention relates to a direction discriminating method used for a direction relay for discriminating a power direction, a short circuit direction, and the like.

[0002]

2. Description of the Related Art FIG. 7 is an explanatory diagram showing the phase characteristics of a conventional short-circuit direction relay shown in, for example, "Protective Relay Engineering" (edited by the Institute of Electrical Engineers of Japan, Ohmsha, published in 1980, page 129). In the determination of the power direction or the short circuit direction, the direction is determined based on the phase current and the line voltage. As a combination method, a 90 ° lead connection method (Ia to Vab) in which the current leads by 90 ° with respect to the voltage and a 30 ° lead connection method (Ia to Vac) in which the current leads by 30 ° are frequently used. . As the short-circuit direction relay, the phase characteristics are determined so that all three-phase short-circuits and two-phase short-circuits can be detected. A 30 ° delay is selected as the maximum sensitivity angle on a standard basis. In the power directional relay, the maximum sensitivity angle is set so that the maximum sensitivity can be obtained when the power factor is 1. In the ground fault direction relay, the direction is determined based on the zero-phase current and the zero-phase voltage,
The maximum sensitivity angle is selected according to the neutral grounding method.

[0003] Next, a method for determining a phase difference between a current and a voltage and determining a direction from the phase difference will be described. For example, when the combination of the current and the voltage is advanced by 90 ° and the maximum sensitivity angle is selected to advance by 30 ° based on the voltage, the phase difference β-α between the current and the voltage is determined by the difference of VIcos (β-α-30 °). The sign indicates the short-circuit direction. VIcos (β-α-30
°) is expressed by Equation 1, and VI sin (β−α), V
It can be seen that Icos (β-α) can be obtained. VIcos (β−α−30 °) = VIcos (β−α) cos (30 °) + VIsin (β−α) sin (30 °) (Equation 1)

"Electric Joint Research, Vol. 41, No. 4, Digital Relay, issued in January 1986", p.
Table 1-3 shows typical examples of the phase difference calculation method.
FIG. 8 is an explanatory diagram showing a phase difference calculation method of the product type C method, which is one of the representative examples. Assuming that the current waveform and the voltage waveform are sine waveforms having the same frequency as the power supply frequency, Expression 2 is obtained when the voltage amplitude is V, the phase is α, the current amplitude is I, and the phase is β. However, the sampling period is 30 electrical degrees
Is the case. _{v m = v (t) =} Vsin (ωt + α) v m-3 = v (t-90 °) = Vsin (ωt + α-90 °) = -Vcos (ωt + α) i m = i (t) = Isin (ωt + β) _{i m-3 = i (t} -90 °) = Isin (ωt + β-90 °) = -Icos (ωt + β) ( equation 2) Thus, as shown in equation _{3, v m, v m-} 3, i m, i VIcos (β−α) and VIsin (β−α) can be obtained from _m−3 . _{v m · i m + v m} -3 · i m-3 = Vsin (ωt + α) · Isin (ωt + β) + Vcos (ωt + α) · Icos (ωt + β) = V · Icos (β-α) v m-3 · i m + v _m · im _-3 = Vcos (ωt + α) · Isin (ωt + β) + Vsin (ωt + α) · Icos (ωt + β) = V · Isin (β−α) (Equation 3)

[0005]

Since the conventional direction discriminating method is configured as described above, as shown in FIG. 1, it is assumed that the private generator 2 and the commercial system 1 are interconnected and used. Under severe circumstances, if the voltage drops due to an accident such as a lightning strike on the commercial system 1 side, it is necessary to disconnect the interconnection point at high speed to protect the important load on the private generator 2 side There is. On the other hand, when an accident occurs on the line on the side of the private generator 2, if the connection point and the accident line are cut off at high speed, the voltage becomes unstable, and in the worst case, the private generator 2 goes down. there is a possibility. Therefore, the interconnection point should not be disconnected in order to continue stable operation of the private generator 2. In addition, there is a possibility that the private generator 2 may go down due to the influence of the accident, and even if the private generator 2 goes down, the important load of the healthy line is continuously operated.
The interconnection points should not be disconnected. Therefore, when a voltage drop occurs in the commercial system 1 at the time of an accident or the like, it is necessary to quickly determine the short-circuit direction and the power direction at the interconnection point.
In order to continue the operation of the important load, it is necessary to disconnect the interconnection point within one cycle after the occurrence of the accident, so it is necessary to determine the direction within one-fourth cycle considering the operation time of the breaker. is there. However, in the conventional direction determination method, since the calculation is performed on the assumption that the current waveform and the voltage waveform are only sine waveforms having the same frequency as the power supply frequency, a harmonic component included in the current waveform and the voltage waveform is filtered using a filter. And DC components are removed. For this reason, it is necessary to consider the delay due to the transient characteristics of the filter.
There has been a problem that accurate determination cannot be made in a short time of / 4 cycle or less.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a direction discriminating method for accurately discriminating a direction in a short time.

[0007]

A direction discriminating method according to the present invention uses a least-squares method according to a voltage waveform assumed to be a sine waveform having the same frequency as a power supply frequency, a measured sampling voltage value, and a sampling period. A voltage waveform estimating step of estimating a voltage waveform composed of an amplitude and a phase in which an error between the voltage waveform and the sampling voltage value is minimized,
According to the current waveform assumed to be a sine waveform having the same frequency as the power supply frequency, the measured sampling current value, and the sampling period, the least square method is used to calculate the amplitude and phase that minimize the error between the current waveform and the sampling current value. A current waveform estimating step of estimating a current waveform, a phase difference calculating step of calculating a phase difference between the estimated current waveform and the estimated voltage waveform, and a power direction or a short circuit direction according to the calculated phase difference. And a direction determining step of determining.

In the direction discriminating method according to the present invention, in the current waveform estimating step, taking into account the direct current component of the current, the current waveform estimating step is performed according to the current waveform assumed to be the sum of a sine waveform having the same frequency as the power supply frequency and a constant value. Thus, the current waveform is estimated.

In the direction discriminating method according to the present invention, in the current waveform estimating step, the current waveform is assumed to be a sum of a sine waveform having the same frequency as the power supply frequency and a linear function in consideration of the DC component of the current. Accordingly, the current waveform is estimated.

A direction discriminating method according to the present invention is based on a theoretical formula including impedance based on Ohm's law, a measured sampling voltage value, a sampling current value, and a sampling period. An impedance estimating step of estimating an impedance that minimizes an error between a voltage value calculated by substituting a value and a sampling voltage value, and a direction determining step of determining a power direction or a short-circuit direction according to the estimated impedance. It is a thing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a power system diagram showing an accident detection device using a direction discriminating method according to Embodiment 1 of the present invention. In the figure, 1 is a commercial system, 2 is a private generator,
Reference numeral 3 denotes an accident detection device which is provided at an interconnection point between the private generator 2 and the commercial system 1 and which disconnects the interconnection point at high speed in accordance with the direction in which the accident occurs. FIG. 2 is a block diagram showing a direction discriminating apparatus using the direction discriminating method according to the first embodiment of the present invention. In FIG. 2, a voltage waveform 11 is assumed to be a sine waveform having the same frequency as the power supply frequency. A voltage waveform estimating unit (voltage waveform estimating step) for estimating a voltage waveform having an amplitude and a phase that minimizes an error between the voltage waveform and the sampling voltage value according to the least square method according to the sampling voltage value and the sampling cycle; Is the amplitude and phase at which the error between the current waveform and the sampling current value is minimized by the least square method according to the current waveform assumed to be a sine waveform having the same frequency as the power supply frequency, the measured sampling current value, and the sampling period. Current waveform estimating section (current waveform estimating step) for estimating a current waveform composed of
Reference numeral 3 denotes a phase difference calculation unit (phase difference calculation step) for calculating a phase difference between the current waveform estimated by the current waveform estimation unit 12 and the voltage waveform estimated by the voltage waveform estimation unit 11;
Denotes a direction discriminating unit (direction discriminating step) for discriminating the power direction or the short-circuit direction according to the phase difference calculated by the phase difference calculating unit 13.

Next, the operation will be described. First, the voltage waveform estimating unit 11 and the current waveform estimating unit 12 will be described in detail. FIG. 3 is an explanatory diagram showing a current waveform estimation method and a voltage waveform estimation method. In the figure, x represents a sampling voltage value measured at a predetermined sampling time, and * represents a sampling current value measured at a predetermined sampling time, and represents a sampling voltage value and a sampling current value measured without using a filter. Contains a harmonic component, and if the phase difference between the current and the voltage is directly calculated from the measured sampling voltage value and sampling current value, the phase difference will include a large error. Therefore, first, the same frequency as the power supply frequency omega ₀ is not included the voltage waveform harmonics sinusoidal waveform (v
Assume that (t) = Vsin (ω ₀ t + α)).
In this assumed voltage waveform, the amplitude V and the phase α are unspecified, but the error between the assumed voltage waveform and the sampling voltage value is minimized by the least square method according to the measured sampling voltage value and sampling period. The amplitude V
And the functions (Vcosα, Vsinα) of the phase α are specified, and the voltage waveform is estimated from the specified functions. Similarly, the current waveform does not include the current waveform harmonics power frequency omega ₀ and the same frequency of the sinusoidal waveform (i
(T) = Isin (ω ₀ t + β)), and an amplitude at which an error between the assumed current waveform and the sampling current value is minimized by the least square method according to the measured sampling current value and sampling period. The functions (Icosβ, Isinβ) of I and phase β are specified, and the current waveform is estimated from the specified functions.

Hereinafter, the voltage waveform estimating unit 11 will be specifically described. Put as Equation 4 in order to approximate the voltage waveform at the same frequency of the sine wave power supply frequency omega _0. v (t) = Vsin (ω ₀ t + α) (Equation 4) In order to simplify the equation, c = Vcosα and d = Vsinα
Equation 4 is replaced with Equation 5. v (t) = Vsin (ω 0 t) cosα + Vcos (ω 0 t) sinα = c · sin (ω 0 t) + d · cos (ω 0 t) ( Equation 5) k = 1, ···, as n, The calculated value v _tk and the measured value v (t
The error s ^{2 of} _k ) is set as in Equation 6.

(Equation 1) C and d that minimize the error s ² are obtained from the simultaneous equations 7.

(Equation 2)

When the simultaneous equations 7 are solved for c and d, functions f and g for obtaining c (= Vcosα) and d (= Vsinα) from the sampling time and the sampling voltage value can be obtained as shown in Expression 8. Therefore, the voltage waveform estimating unit 11 performs the calculation of Expression 8. _{Vcosα = f (t 1, ···} , t n, v t1, ···, v tn) Vsinα = g (t 1, ···, t n, v t1, ···, v tn) ( Formula 8) The result of actually obtaining the functions f and g is Expression 9.

(Equation 3) As a result, the obtained c (= Vcos α) and d (= V
By substituting sinα) into Equation 5, a voltage waveform having the same frequency as the power supply frequency ω ₀ containing no harmonic component shown in Equation 4 and having the specified amplitude V and phase α is estimated. can do. On the other hand, the same calculation as that of the voltage waveform estimating unit 11 is performed for the current waveform estimating unit 12.

Next, the phase difference calculator 13 for voltage and current will be described. The phase difference between the voltage and the current is calculated by the Vsin obtained by the voltage waveform estimating unit 11 and the current waveform estimating unit 12 with respect to the phase difference β-α between the current and the voltage.
Expression 10 is executed using α, Vcosα, Isinβ, and Icosβ to obtain VIsin (β−α), VIcos (β
−α) is calculated. VI sin (β−α) = I sin β · V cos α−I cos β · V sin α VI cos (β−α) = I cos β · V cos α + I sin β · V sin α VIsin (β-α), VIcos
The direction of short circuit and the direction of power are determined from the calculated value of (β−α).

As described above, according to the first embodiment, the voltage waveform is assumed to be a sine waveform having the same frequency as the power supply frequency, and the least square method is used in accordance with the measured sampling voltage value and sampling period. Estimate the voltage waveform consisting of the amplitude and phase that minimizes the error between the assumed voltage waveform and the sampling voltage value, and estimate the current waveform in the same way, and calculate the phase difference between the estimated current waveform and the voltage waveform. Since the short-circuit direction and the power direction are determined, even if the voltage waveform or the current waveform contains a harmonic component, the harmonic component is determined from the sampling voltage value and the sampling current value measured without using a filter. Is the sine waveform of the same frequency as the power supply frequency that does not include the voltage and current waveforms whose amplitude and phase have been specified. It is not necessary to consider delays due to the transient characteristics of filter can be a precise direction determination in a short time.

Embodiment 2 FIG. In the second embodiment, the current waveform estimating unit 12 according to the first embodiment considers the DC component of the current and assumes that the current is a sum of a sine waveform having the same frequency as the power supply frequency ω ₀ and a constant value. The current waveform is estimated according to the waveform. The configuration other than the current waveform estimating unit 12 is the same as that of the first embodiment. The current waveform is a sine waveform having the same frequency as the power supply frequency ω ₀ and a constant value a.
To approximate as the sum of i (t) = I sin (ω ₀ t + β) + a (Equation 11) In order to simplify the equation, c = I cos β and d = I sin β
Equation 11 is replaced with Equation 12. i (t) = I sin (ω ₀ t) cos β + I cos (ω ₀ t) sin β + a = c · sin (ω ₀ t) + d · cos (ω ₀ t) + a (Equation 12) where k = 1,... , The calculated value _itk and the measured value i (t
The error s ^{2 of} _k ) is set as in Expression 13.

(Equation 4) C, d, and a that minimize the error s ² are obtained from the simultaneous equations 14.

(Equation 5)

When the simultaneous equations 14 are solved for c, d, and a, c (= Icos β) and d (= Isin β) are obtained from the sampling time and the sampling current value as shown in Expression 15.
Can be obtained. Therefore, the current waveform estimating unit 12 performs the calculation of Expression 15. _{Icosβ = f (t 1, ···} , t n, i t1, ···, i tn) Isinβ = g (t 1, ···, t n, i t1, ···, i tn) ( Formula 15) The results of actually obtaining the functions f and g from the simultaneous equations 14 will be omitted because they are complicated equations, but calculations are easy because only the third-order simultaneous equations are solved.

As described above, according to the second embodiment, in addition to the first embodiment, the DC component of the current is taken into consideration.
Since the current waveform is estimated assuming that it is the sum of a sine waveform of the same frequency as the power supply frequency and a constant value, use a filter even if the current waveform contains harmonic components or DC components. From the measured sampling current value, estimate a current waveform that does not include harmonic components, has a sine waveform of the same frequency as the power supply frequency with the DC component added, and whose amplitude and phase are specified. Therefore, it is not necessary to consider the delay due to the transient characteristics of the filter, and the direction can be accurately determined in a short time.

Embodiment 3 In the third embodiment, it is assumed that current waveform estimating section 12 in the first embodiment is a sum of a sine waveform having the same frequency as power supply frequency ω ₀ and a linear function in consideration of the DC component of the current. The current waveform is estimated according to the current waveform. The configuration other than the current waveform estimating unit 12 is the same as that of the first embodiment. Equation 16 is used to approximate the current waveform as the sum of a sine waveform having the same frequency as the power supply frequency ω ₀ and a linear function (at + b). i (t) = I sin (ω ₀ t + β) + at + b (Equation 16) In order to simplify the equation, c = I cos β and d = I sin β
Equation 16 is replaced with Equation 17. i (t) = I sin (ω ₀ t) cos β + I cos (ω ₀ t) sin β + at + b = c · sin (ω ₀ t) + d · cos (ω ₀ t) + at + b (Equation 17) k = 1,..., n The calculated value _itk and the actual measured value i (t
The error s ^{2 of} _k ) is set as in Expression 18.

(Equation 6) C, d, a, and b, which minimize the error s ² , are represented by the simultaneous equations 19
Is obtained.

(Equation 7)

When the simultaneous equations 14 are solved for c, d, a, and b, c (= Icos β) and d (= Isin) are obtained from the sampling time and the sampling current value as shown in Expression 20.
Functions f and g for determining β) can be obtained. Therefore,
The current waveform estimating unit 12 performs the calculation of Expression 20. _{Icosβ = f (t 1, ···} , t n, i t1, ···, i tn) Isinβ = g (t 1, ···, t n, i t1, ···, i tn) ( Formula 20) The results of actually obtaining the functions f and g from the simultaneous equations 19 will be omitted because they are complicated equations, but calculations are easy because only the fourth-order simultaneous equations are solved.

As described above, according to the third embodiment, in addition to the first embodiment, the DC component of the current is taken into consideration.
Since the current waveform is estimated assuming that it is the sum of a sine waveform of the same frequency as the power supply frequency and a linear function, a filter is used even if the current waveform contains harmonic components or DC components. From the sampling current value measured without
It is a sinusoidal waveform with the same frequency as the power supply frequency with the DC component added, without the harmonic components, and the current waveform with the specified amplitude and phase can be estimated. There is no need to consider, and accurate direction determination can be made in a short time.

Embodiment 4 FIG. 5 is a block diagram showing a direction discriminating apparatus using a direction discriminating method according to Embodiment 4 of the present invention. In FIG. 5, reference numeral 21 denotes a theoretical equation including impedance based on Ohm's law, a measured sampling voltage value, An impedance estimating unit (impedance estimating unit) for estimating an impedance that minimizes an error between a voltage value calculated by substituting the sampling current value into a theoretical formula by the least square method according to the sampling current value and the sampling cycle and the sampling voltage value. Steps) and 22 are direction discriminating sections (direction discriminating steps) for discriminating the power direction or the short-circuit direction according to the impedance estimated by the impedance estimating section 21.

Next, the operation will be described. First, the impedance estimating unit 21 will be specifically described. Current,
With respect to the voltage, R and L satisfying Expression 21 based on Ohm's law are obtained.

(Equation 8) Expression 21 is integrated into Expression 23, and both sides of Expression 21 are integrated, and Expression 21 is rewritten as Expression 23.

(Equation 9) R · x _i + L · y _i in Expression 24 is a calculated value of a voltage integral value calculated by substituting the sampling current value into the right side of Expression 23, and Z _i in Expression 24 is an integral value of the sampling voltage value. Is the measured value of the integrated voltage value
An error s ² between the calculated value and the actually measured value is set as in Expression 24.

(Equation 10) R and L that minimize the error s ² are obtained from the simultaneous equations 25.

[Equation 11]

When R and L are obtained from the simultaneous equations 25, Equation 2 is obtained.
6 is obtained. Therefore, the impedance estimating unit 21 performs the calculation of Expression 26. In the above, the method of integrating R and L so as to minimize the error between the calculated value of the voltage integrated value and the actually measured value has been described.
May be used as it is, and R and L may be obtained such that the error between the calculated value of the voltage and the actually measured value is minimized.

(Equation 12)

The direction discriminating section 22 discriminates a short circuit direction and a power direction from the calculated values of R and L obtained by the impedance estimating section 21. For example, when the voltage is the line voltage and the current is the difference between the phase currents, the calculated impedance is the distance measurement impedance of the distance relay, and the phase characteristic as shown in FIG. 6 is obtained. Therefore, (Ia-Ib to Vab), (Ib-I
c-Vbc) and (Ic-Ia-Vca), in the case of at least one combination in which both R and L are negative, in the opposite direction,
If there is no combination in which both R and L are negative, a method of determining the forward direction can be considered.

As described above, according to the fourth embodiment, the least squares method is used according to the theoretical formula including impedance based on Ohm's law, the measured sampling voltage value, the sampling current value, and the sampling period. Since the impedance that minimizes the error between the voltage value calculated by substituting the sampling current value into the theoretical formula and the sampling voltage value is estimated, and the short-circuit direction and the power direction are determined based on the estimated impedance, the voltage Even if the waveform or current waveform contains harmonic components or DC components,
The impedance can be estimated from the sampling voltage value and sampling current value measured without using a filter, and there is no need to consider the delay due to the transient characteristics of the filter, and accurate direction discrimination can be performed in a short time. it can. In addition, since it does not depend on the frequency, the present invention can be applied even when the voltage waveform or the current waveform has a frequency variation.

[0028]

As described above, according to the present invention, the voltage is determined by the least square method according to the voltage waveform assumed to be a sine waveform having the same frequency as the power supply frequency, the measured sampling voltage value, and the sampling period. A voltage waveform estimating step of estimating a voltage waveform composed of an amplitude and a phase that minimizes an error between the waveform and the sampling voltage value; a current waveform assumed to be a sine waveform having the same frequency as the power supply frequency; a measured sampling current value; A current waveform estimating step of estimating a current waveform composed of an amplitude and a phase that minimizes an error between the current waveform and the sampling current value by a least square method according to the sampling period, and an estimated current waveform and an estimated voltage A phase difference calculating step of calculating a phase difference from a waveform, and a direction of determining a power direction or a short circuit direction according to the calculated phase difference Since it is configured to include a separate process, even if the voltage waveform or the current waveform contains a harmonic component, the harmonic component is included from the sampling voltage value and the sampling current value measured without using a filter. It is a sinusoidal waveform with the same frequency as the power supply frequency that is not specified, and can estimate the voltage and current waveforms whose amplitude and phase have been specified. Thus, an effect of being able to determine a proper direction can be obtained.

According to the present invention, in the current waveform estimating step, taking into account the DC component of the current, the current waveform is determined according to the current waveform assumed to be the sum of a sine waveform having the same frequency as the power supply frequency and a constant value. Because it was configured to estimate the waveform, even if the current waveform contains harmonic components and DC components, from the sampling current value measured without using a filter,
It is a sinusoidal waveform with the same frequency as the power supply frequency with the DC component added, without the harmonic components, and the current waveform with the specified amplitude and phase can be estimated. There is no need to consider, and an effect that an accurate direction determination can be made in a short time is obtained.

According to the present invention, in the current waveform estimating step, taking into account the direct current component of the current, the current waveform is assumed to be the sum of a sine waveform having the same frequency as the power supply frequency and a linear function. Since it was configured to estimate the current waveform,
Even if the current waveform contains a harmonic component or a DC component, the sampling current value measured without using a filter indicates that the harmonic component is not included and the power supply frequency with the DC component added is the same. It is a sinusoidal waveform of frequency, and the current waveform whose amplitude and phase are specified can be estimated, and there is no need to consider the delay due to the transient characteristics of the filter, and the effect of being able to accurately determine the direction in a short time is obtained. can get.

According to the present invention, the sampling current value is substituted into the theoretical formula by the least square method according to the theoretical formula including impedance based on Ohm's law, the measured sampling voltage value, the sampling current value, and the sampling period. An impedance estimating step of estimating an impedance that minimizes an error between the calculated voltage value and the sampling voltage value, and a direction determining step of determining a power direction or a short-circuit direction according to the estimated impedance. Therefore, even if the voltage waveform or the current waveform contains a harmonic component or a DC component, the impedance can be estimated from the sampling voltage value and the sampling current value measured without using a filter. It is not necessary to consider the delay due to transient characteristics, It is possible to discrimination. Further, since the frequency waveform does not depend on the frequency, an effect that can be applied even when the voltage waveform or the current waveform has a frequency variation is obtained.

[Brief description of the drawings]

FIG. 1 is a power system diagram showing an accident detection device using a direction determination method according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a direction discriminating apparatus using a direction discriminating method according to Embodiment 1 of the present invention;

FIG. 3 is an explanatory diagram showing a current waveform estimation method and a voltage waveform estimation method.

FIG. 4 is an explanatory diagram illustrating a direction determining unit according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram showing a direction discriminating apparatus using a direction discriminating method according to Embodiment 4 of the present invention.

FIG. 6 is an explanatory diagram showing a direction determining unit according to a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing phase characteristics of a conventional short-circuit direction relay.

FIG. 8 is an explanatory diagram showing a phase difference calculation method of a product C method.

[Explanation of symbols]

1 commercial system, 2 private generator, 3 accident detection device,
11 voltage waveform estimating section (voltage waveform estimating step), 12 current waveform estimating section (current waveform estimating step), 13 phase difference calculating section (phase difference calculating step), 14, 22 direction discriminating section (direction discriminating step), 21 impedance Estimation unit (impedance estimation step).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G033 AB03 AB07 AD14 AF03 2G035 AA15 AB07 5G058 EF02 EF03 EG01 EG02 EG13 EH01 EH02

Claims (4)

[Claims] A voltage waveform assumed to be a sine waveform having the same frequency as a power supply frequency, a measured sampling voltage value,
A voltage waveform estimating step of estimating a voltage waveform having an amplitude and a phase in which an error between the voltage waveform and the sampling voltage value is minimized by a least square method according to the sampling cycle, and a sine waveform having the same frequency as the power supply frequency. A current waveform for estimating a current waveform composed of an amplitude and a phase that minimizes an error between the current waveform and the sampling current value by the least squares method according to the current waveform assumed to be present, the measured sampling current value, and the sampling period. An estimating step, a phase difference calculating step of calculating a phase difference between the current waveform estimated by the current waveform estimating step and the voltage waveform estimated by the voltage waveform estimating step, and a phase calculated by the phase difference calculating step. A direction determining step of determining a power direction or a short circuit direction according to the phase difference. 2. The current waveform estimating step estimates a current waveform according to a current waveform assumed to be a sum of a sine waveform having the same frequency as the power supply frequency and a fixed value, taking into account the DC component of the current. 2. The method according to claim 1, wherein: 3. The current waveform estimating step estimates a current waveform according to a current waveform assumed to be a sum of a sine waveform having the same frequency as the power supply frequency and a linear function in consideration of a DC component of the current. 2. The method according to claim 1, wherein the direction is determined. 4. A method of substituting a sampling current value into a theoretical expression by a least squares method according to a theoretical expression including impedance based on Ohm's law, a measured sampling voltage value, a sampling current value, and a sampling cycle thereof. And a direction determining step of determining a power direction or a short-circuit direction according to the impedance estimated by the impedance estimating step. Direction determination method.