JPH1123624A - Method for measuring harmonic in power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for measuring the harmonic characteristics on the upstream side of a power system by injecting currents of two frequencies, higher and lower than an interesting harmonic and not equal to integer times of the basic frequency of the system, in which the harmonic characteristics are measured inexpensively through a small and simple arrangement by lowering the voltage class of an apparatus being injected with the current of both frequencies. SOLUTION: A harmonic injecting point (a) is set on the lower voltage side than a harmonic measuring point (b) of a system 1 and currents of two frequencies f1 , f2 , higher and lower than an interesting harmonic of an object to be measured and not equal to integer times of the basic frequency of the system, are injected as intermediate harmonic currents into an injecting point (a) from a current injector 16. Current and voltage having the frequencies f1 , f2 are then detected at a measuring point (b) and the admittance of an equivalent circuit is determined, respectively, for the intermediate harmonic having the frequencies f1 , f2 in the upstream of the measuring point (b). The admittance 10 of an equivalent circuit 9 is then determined from both admittances by interpolation for the interesting harmonic in the upstream of the measuring point (b) and the harmonic characteristics are measured for the interesting harmonic in the upstream of the measuring point (b) being set in the upstream of the injecting point (a).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power system harmonic measurement method for measuring characteristics (harmonic characteristics) of a higher harmonic of interest than a power system harmonic measurement point.

[0002]

2. Description of the Related Art In transmission and distribution systems of power systems, it is important to reduce harmonics.

Meanwhile, the frequency of the harmonic is an integer multiple of the system fundamental frequency f _s, the frequency of a typical fifth harmonic is 5 × f _s.

The reduction of harmonics is performed by estimating the level of the harmonics and installing a filter having an appropriate frequency.

[0005] In order to predict the voltage level of the harmonic, etc., the connection point of the filter equipment of the power system is set as the harmonic measurement point, and the higher (upstream) and lower (downstream) harmonics of this measurement point are measured. It is necessary to grasp the characteristics and find its equivalent circuit.

The harmonic equivalent circuit can be regarded as a parallel circuit of admittance expressed by Norton's theorem and a current source.

[0007] The Transactions of the Institute of Electrical Engineers of Japan, B, 101, 8
No., p. 451-458, (Showa 56-8) discloses that when obtaining a harmonic equivalent circuit for the fifth harmonic of a distribution line, the voltage and current of the fundamental wave of the system are measured, and the admittance of the equivalent circuit is determined from the results. It describes that the magnitude and phase of the current source are calculated and estimated.

[0008]

According to the harmonic measurement method described in the above-mentioned publication, the nth harmonic of interest (frequency n
× f _s ), the harmonic admittance and the magnitude and phase of the harmonic current source are estimated and determined from the measurement results of the fundamental wave voltage and current of the system. Therefore, the admittance of the harmonic equivalent circuit is determined. Cannot be determined with high accuracy.

That is, in the case of the conventional harmonic measurement method, the admittance and current source of the equivalent circuit for the target harmonic to be measured are not actually measured and found, but the fundamental wave is measured based on the fundamental wave measurement information. Since the magnitude (vector value) of the harmonic of interest is merely estimated from the magnitude (vector value), its equivalent circuit cannot be accurately determined.

As a result, it is not possible to accurately grasp the harmonic characteristics of the power system and provide an appropriate filter, etc.
Good reduction of the harmonic level becomes difficult.

Therefore, the present applicant has filed Japanese Patent Application No. 8-31019.
According to the application of No. 2, currents at non-integer multiple frequencies (intermediate harmonic currents) of the fundamental wave above and below the measurement harmonic (harmonic of interest) are injected into the harmonic injection points of the power system. Based on the voltage of the injection frequency at the injection point and the measured results of the current at the injection frequency flowing above and below the injection point, the upper and lower harmonics of the injection point of the
Find the admittance of the equivalent circuit of the injection frequency on both lower sides,
It has already been invented to determine the admittance of the equivalent circuit of the harmonic of interest by such interpolation processing and to find the equivalent circuit of the harmonic.

In this case, the current of the injection frequency is a current of a non-integer multiple frequency of a fundamental wave which does not originally exist in the system,
Since the admittance of the equivalent circuit with respect to the injection frequency can be determined with high accuracy by actual measurement, the harmonic characteristics of the target harmonic can be accurately grasped using the result.

However, in the measurement method of the above-mentioned application, since the harmonic injection point and the harmonic measurement point are the same point, for example,
When measuring the higher harmonic characteristic of the system, the harmonic injection point must be set to a higher voltage upper bus or the like.

In this case, since the harmonic injection point has a high voltage, it is necessary to sufficiently increase the voltage class (insulation class) of the device for injecting the intermediate harmonic current into this injection point.
Moreover, it is necessary to take sufficient protective measures.

[0015] Therefore, there is a problem that the apparatus becomes large and complicated and expensive, and it is not possible to accurately measure the harmonic characteristics of the system upper side inexpensively with a small and simple configuration.

According to the present invention, when the current of the intermediate harmonic of two frequencies f ₁ and f ₂ sandwiching the harmonic of interest is injected to measure the higher harmonic characteristic of the system, the current of both intermediate harmonics is measured. It is an object of the present invention to reduce the voltage class required for the device to be injected, and to enable inexpensive measurement with a small and simple configuration.

[0017]

In order to solve the above-mentioned problems, a method for measuring harmonics of a power system according to the present invention comprises the steps of:
A harmonic injection point is set on the lower low-voltage side from the harmonic measurement point of the system, and the current injection device connected to this harmonic injection point places the n-th target harmonic of interest at the harmonic injection point. frequency f 2 frequency of the non-integer multiple of _{s f 1, f 2 (f} 1
<N × injected respectively f _s <current f ₂₎ as an intermediate harmonic currents, frequencies f _1, f ₂ each current harmonic measurement points, higher than the harmonic measurement point by detecting the voltage frequency The admittance of the equivalent circuit for each of the intermediate harmonics of f ₁ and f ₂ is determined, and the admittance of the equivalent circuit for the harmonic of interest higher than the harmonic measurement point is determined from both admittances by interpolation and determined. The harmonic characteristic of the higher harmonic of interest from the higher harmonic measurement point set is measured.

Therefore, the current injection device in which the harmonic injection point is set on the lower low-voltage side of the harmonic measurement point and injects the current of the intermediate harmonics of the frequencies f ₁ and f ₂ into the harmonic injection point is a harmonic injection device. The voltage class can be lower than when the point is the same as the harmonic measurement point, and the protection circuit and the like can be simplified. Therefore, the current injection device can be made small and simple in configuration and inexpensive.

[0019] Then, by injecting an intermediate harmonic current of a frequency f _1, f ₂ is not originally present in the system from the current injection device in harmonic injection point, the frequency f ₁ in the harmonic measurement point, f
₂₎ The current and voltage of the intermediate harmonic are detected, and based on this detection, the admittance of the equivalent circuit for both intermediate harmonics higher than the harmonic measurement point is determined. Determines the admittance of the equivalent circuit for the harmonic of interest and measures its harmonic characteristics, so it is inexpensive with a small and simple configuration, and the harmonic of interest higher than the harmonic measurement point set above the harmonic injection point High-precision measurement of harmonic characteristics of a wave can be performed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. FIG. 1 shows, for example, 77
FIG. 3 is a single-line diagram showing a case where the harmonic characteristics of the kV high-voltage bus 2 are measured by injecting a current into the lower-voltage low-voltage 6.6 kV distribution bus 3.

Power is distributed to the high voltage bus 2 via a circuit breaker 4, an upper line impedance 5, an upper substation (secondary substation) transformer 6, a 22 kV second high voltage bus 7, and a distribution substation transformer 8, for example. The bus 3 is connected, a harmonic injection point a is set near the secondary side of the transformer 8 of the distribution line 3, and a harmonic measurement point b is set near the primary side of the transformer 8.

[0022] At this time, the power system 1 there are various harmonics of integral multiples of the system fundamental frequency f _s, comprising a high-pressure bus 2 for n-th focused harmonic measured (n × f _s) Expressed by Norton's theorem, the upper equivalent circuit 9 is a parallel circuit of the admittance 10 and the current source 11.

Note that the equivalent circuit 12 below the harmonic injection point a for the target harmonic is also a parallel circuit of the admittance 13 and the current source 14 when expressed by Norton's theorem.

The current injection device 16 of the harmonic measuring device 15 is connected to the harmonic injection point a.
Is to measure repeated harmonic characteristic, the frequency f ₁ of the non-integer multiple of the system fundamental frequency _{f s, f 2 (f 1} <n × f s <
Injecting the currents I ₁ and I ₂ of the intermediate harmonic of f ₂ ) into the harmonic injection point a in a fixed time sequence is repeated, for example, in a cycle of 30 minutes.

At this time, it is possible to measure whether the currents I ₁ and I _{2 of} the intermediate harmonic are synchronous or asynchronous with the system power supply. Since it is practical to perform digital frequency analysis such as FFT, it is practically necessary to form the currents I ₁ and I ₂ in synchronization with the system power supply.

[0026] Thus, for example, harmonic synchronization device that is not shown the measuring device 15 is provided, forming a synchronization control signal of the synchronous devices that multiplied frequency synchronized with the system voltage of the system fundamental frequency f _s of the distribution bus 3 Then, the synchronization control signal is supplied to the current injection device 16 and the current injection device 1
Reference numeral 6 forms currents I ₁ and I ₂ of intermediate harmonics of frequencies f ₁ and f ₂ by PLL synchronous oscillation based on a synchronous control signal.

Further, the currents I ₁ and I ₂ of the formed intermediate harmonics are sequentially output for a predetermined time, for example, by a timer operation, and injected into the harmonic injection point a every 30 minutes.

Assuming that the harmonic of interest is the fifth harmonic (n = 5), the currents I ₁ and I ₂ of the intermediate harmonics are, specifically,
For example, 4.5 harmonics shifted from the focused harmonic by 0.5 harmonic, and 5 harmonics.
The current is set to five harmonics.

The currents I ₁ and I _{2 of} the intermediate harmonic injected into the harmonic injection point a are currents at frequencies that do not originally exist in the power system 1. Even with the device described above, measurable levels of intermediate harmonic currents I ₁ and I ₂ can be secured on the upper and lower sides of the harmonic injection point a.

The equivalent circuit of the high voltage bus 2 for the intermediate harmonics of the frequencies f ₁ and f ₂ as viewed from the harmonic measurement point b, and the lower equivalent circuit of the distribution system 3 as viewed from the harmonic injection point a are Norton's. Expressed by the theorem, each of them has only the admittance similar to the admittances 10 and 13 of the equivalent circuits 9 and 12.

For the sake of simplicity, it is assumed that the line impedance 5 and the like are ignored, the higher order than the harmonic measurement point b is represented by the equivalent circuit 9, and the harmonics are divided from the harmonic injection point a. Assuming that currents at frequencies f ₁ and f ₂ flowing through the measurement point b in the upper direction are I _iu (i = 1, 2) and the voltage thereof is V _iu (i = 1, 2), the harmonic measurement point b The admittance Y _iu (i = 1,
2) is obtained from the operation of the following equation (1).

[0032]

[ _Expression 1] Y _iu = I _iu / V _iu

Further, if the admittance Y _iu (= Y _1u , Y _2u ) for the intermediate harmonics of the frequencies f ₁ and f ₂ is obtained, the simplest method is to perform, for example, an interpolation calculation of (Y _1u + Y _2u ) / 2. the admittance 10 of the equivalent circuit 9 for focus harmonics of the intermediate frequency n × f _s is obtained as Y _{u (n).}

When the admittance Y _u ( _n ) of the target harmonic is determined, based on the actual measurement of the current I ( _n ) and the voltage V ( _n ) of the target harmonic flowing through the harmonic measurement point b, the target harmonic is measured. The current source 11 of the equivalent circuit 9 is obtained as a current source I _Gu ( _n ) from the following equation (2).

[0035]

## EQU2 ## I _Gu ( _n ) = I ( _n ) -V ( _n ) × Y _u ( _n )

The admittance Y _iu and the admittance Y _u ( _n ) obtained from the operation of the expression ( ₁ ) and the current source I _Gu ( _n ) obtained from the operation of the expression (2) are obtained when the upper side is viewed from the high voltage bus 7. For example, the admittance Y _u ( _n ) and the current source I _Gu ( _n ) can be calculated by converting the value of the upper side from the high voltage bus 2 based on the transformer 6 transformation ratio and the like. Good.

The admittances Y _iu , Y _u ( _n ) and the current source I _Gu ( _n ) can be determined more accurately by taking into account the voltage drop due to the line impedance 5 and the like.

The admittance Y _u ( _n ) and the current source I _Gu
In order to obtain ( _n ), etc., the instrument transformer 1
7 is connected, an instrument current transformer 18 is provided near the upper side of the measurement point b, and the voltage at the harmonic measurement point b and the system current flowing through the measurement point b are measured. .

The measured output of the voltage of the instrument transformer 17 and the measured output of the current of the instrument current transformer 18 are supplied to the A / D converter 19 of the harmonic measuring device 15, and this A / D converter is used. Numeral 19 samples and converts them into digital measurement data.

At this time, the sampling of the A / D converter 19 needs to be performed at a timing synchronized with the system fundamental wave in order to accurately perform the subsequent frequency analysis.

Therefore, the synchronization control signal of the synchronization device is A /
It is transmitted to the D converter 19 as a measurement command signal, and based on the timing control of the measurement command signal, when the intermediate harmonic currents I ₁ and I ₂ are injected into the harmonic injection point a, A /
The D converter 19 samples the measurement outputs of the instrument transformer 17 and the instrument current transformer 18 in synchronization with the system fundamental wave, that is, both intermediate harmonics.

The sampling frequency of the A / D converter 19 is sufficiently higher than the frequencies f ₁ and f ₂ .

In this embodiment, the equivalent circuit 1 for the target harmonic lower than the harmonic injection point a is described.
In order to obtain and identify the admittance 13 and the current source 14 also, an instrument current transformer 20 is provided on the injection line of the current injection device 16, and this current transformer 20 is connected to the intermediate harmonic injection current I ₁ , Measures I ₂ and outputs A / D
It is sampled by the converter 19.

Then, each measurement data of the A / D converter 19 is supplied to the signal processing device 21, and the signal processing device 21
Are obtained by digital frequency analysis such as DFT analysis and FFT analysis of the system voltage of the instrument transformer 17 and the system current of the instrument current transformer 18, the frequency f _{1 of} the harmonic measurement point b included in each measurement data, f ₂ The voltage V of each intermediate harmonic
_iu and the current I _iu are detected.

The data of the voltage V _iu and the current I _iu are supplied to the arithmetic processing unit 22. The arithmetic processing unit 22 calculates the admittance Y _iu from the calculation of the equation (1) based on the voltage V _iu and the current I _iu. Ask.

Next, the arithmetic processing unit 22 by the interpolation calculation using the admittance Y _iu, admittance 10 of interest harmonics, i.e. admittance Y _u determines the _(n), higher than the harmonic measurement point b The harmonic characteristics of the high voltage bus 2 are measured.

In the present embodiment, the current source 11 is also determined by measuring the harmonic characteristics, and the equivalent circuit 9 is completely identified.

Therefore, when the harmonic measuring device 15 detects the end of the current injection of the intermediate harmonic by stopping reception of the synchronous control signal or the like, the frequency of the signal processing device 21 based on the measurement data of the A / D converter 19 is detected. The current I ( _n ) and the voltage V ( _n ) of the harmonic of interest existing in the power system 1 are actually measured by analysis.

[0049] Then, the determined admittance Y _{u (n)} and the actually measured current I _(n), based on the voltage V _(n), the processing unit 22 is current for interest harmonics from the calculation of the foregoing equation 2 the source 11 is determined as the I _{Gu (n),} the admittance Y _{u (n)}
And the current source I _Gu ( _n ) and the equivalent circuit 9 is completely identified.

In order to identify the equivalent circuit 12 lower than the harmonic injection point a, the arithmetic processing unit 22 outputs the current I _iu ,
The voltage V _iu is converted into a value viewed from the harmonic injection point a, and I _1d = I based on the converted current I _iu , that is, the currents I _1u and I _2u and the actually measured injection currents I ₁ and I _{2. 1} -I
_1u, the calculation of I _2d = I ₂ -I _2u, frequency f ₁ diverted to lower the harmonic injection point a, f ₂ intermediate harmonic current I _1d, seek I _2d.

Further, the voltages V _1d , V _2d of the lower frequencies f ₁ , f ₂ of the harmonic injection point a based on the injection of the intermediate harmonic currents I ₁ , I ₂ are converted into the converted voltage V _iu (= V _1u , V _2u ), the currents I _1d , I _2d and the converted voltages V _1u ,
Based on V _2u , by the same operation as the operation of the expression of Expression 1,
Admittance Y _id (i = 1,2) of an equivalent circuit for intermediate harmonics of lower frequencies f ₁ and f ₂ below harmonic injection point a
Also ask.

Then, similarly to the admittance 10, the admittance 13 of the harmonic of interest, ie, the admittance Y, is obtained by interpolation using the admittance Y _id.
d ( _n ) is determined, and lower harmonic characteristics of the distribution system 3 are measured.

Further, based on the admittance Y _d ( _n ) and the current I ( _n ) and voltage V ( _n ) of the harmonic of interest, the current source 10 I _gd ( _n ), and the equivalent circuit 12 is identified by the admittance Y _d ( _n ) and the current source _IGd ( _n ).

Each time the current of the intermediate harmonic of the frequencies f ₁ and f ₂ is injected, the admittances Y _u ( _n ), Y _d ( _n ), current sources I _Gu ( _n ), I _Gd ( _n ) is found,
The latest equivalent circuits 9 and 12 on the upper and lower sides of the target harmonic are repeatedly identified.

Further, the result is displayed on the display unit 23 in the form of an equivalent circuit diagram as shown in FIG.
The information is stored in the storage unit 24 as recording information.

Since the harmonic injection point a is set to the distribution bus 3 on the low voltage side lower than the harmonic measurement point b of the high voltage bus 7, the voltage class of the current injection device 16 is changed to the harmonic injection point a
And the harmonic measurement point b can be made lower than when they are set to the same point, so that the size can be reduced and the protection circuit configuration can be simplified.

Therefore, currents I ₁ and I ₂ of intermediate harmonics of frequencies f ₁ and f ₂ which do not originally exist in power system 1 flow, so that the current capacity of current injection device 16 is reduced and its size is reduced. In addition to the above, the current injection device 16 can be further reduced in size and simplified based on the reduction in the voltage class, and the current injection device 16 can be reduced in cost with an extremely small and simple configuration.

For this reason, a small, simple, and inexpensive harmonic measuring device 15 is provided with a harmonic measuring point b above the harmonic injection point a, and the harmonic characteristic of the target harmonic higher than the measuring point b is obtained. Can be accurately measured.

Further, in this embodiment, the data used for the measurement of the higher harmonic characteristics than the harmonic measurement device b is diverted, and at the same time as this measurement, the data lower than the harmonic injection point a is used. Harmonic characteristics of the target harmonic can also be accurately measured.

Incidentally, the A / D converter 19, the signal processing device 21, and the arithmetic processing device 22 can be realized by software of a computer.
The converter 19, the signal processing unit 21, the arithmetic processing unit 22, the display unit 23, and the storage unit 24 can be formed by one computer device such as a so-called portable personal computer.

The measurement outputs of the instrument transformer 17 and the instrument converters 18 and 20 may be transmitted to the A / D converter 19 by radio.

The harmonic injection point a and the harmonic measurement point b can be arbitrarily set in the power system 1 so that the harmonic injection point a is located below the harmonic measurement point b.

For this reason, for example, a harmonic measurement point b is set in the distribution system 3 and a harmonic injection point a is set in the secondary side of the lower pole transformer, so that higher harmonic characteristics including the distribution system 3 can be obtained. The measurement can be performed by injecting a current from the lower side, and the present invention can be applied to measurement of higher harmonic characteristics than an arbitrary point of the power system 1.

At this time, the frequencies f ₁ and f ₂ may of course be set to appropriate intermediate harmonic frequencies which are non-integer multiples of the system fundamental frequency f _s sandwiching the target harmonic.

In an actual system, the intermediate harmonic currents I ₁ and I ₂ are injected for each phase to provide equivalent circuits 9 and 12.
Will be identified.

[0066]

The present invention has the following effects. Since the harmonic injection point a is set to a lower low voltage side than the harmonic measurement point b, the voltage class of the current injection device 16 for injecting the intermediate harmonic current of the frequencies f ₁ and f ₂ into the harmonic injection point a is set to This can be lower than when the wave injection point a is the same as the harmonic measurement point b, and the protection circuit and the like can be simplified.

For this reason, the current injection device 16 can be made compact and simple in construction and inexpensive.

[0068] Then, by injecting an intermediate harmonic current of a frequency f _1, f ₂ of the harmonic injection point a does not exist originally line 1 from the current injection unit 16, the frequency f ₁ in the harmonic measurement points b, f The current and voltage of the intermediate harmonic ₂ are detected, and based on this detection, the admittance of an equivalent circuit for both intermediate harmonics higher than the harmonic measurement point b is obtained, and the harmonics of the harmonic of interest are calculated from both admittances. It is possible to determine the admittance of the equivalent circuit 9 for the harmonic of interest higher than the wave measurement point b and measure its harmonic characteristics.

For this reason, a small and simple configuration is inexpensive,
It is possible to perform highly accurate measurement of the harmonic characteristic of the target harmonic higher than the harmonic measurement point b set above the harmonic injection point a.

[Brief description of the drawings]

FIG. 1 is a circuit connection diagram according to an embodiment of the present invention.

[Explanation of symbols]

 1 Power system 9,12 Equivalent circuit 10,13 Admittance 11,14 Current source a Harmonic injection point b Harmonic measurement point

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Nishimura, 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Nissin Electric Co., Ltd.

Claims (1)

[Claims] 1. A harmonic injection point is set to a lower voltage side lower than a harmonic measurement point of a system, and a current injection device connected to the harmonic injection point focuses on the harmonic injection point at the nth order of a measurement target. Harmonics (frequency nxf
_s ) Two frequencies f that are non-integer multiples of the system fundamental frequency f _s
1, f ₂ and respectively injected _{(f 1 <n × f s} <f 2) the current of the intermediate harmonic currents, the frequency f _1, f ₂ respectively current of the harmonic measuring points, detects a voltage The admittance of an equivalent circuit for each of the intermediate harmonics of the frequencies f ₁ and f ₂ higher than the harmonic measurement point is obtained, and the equivalent circuit for the target harmonic higher than the harmonic measurement point is obtained from both admittances. The admittance of the power system is determined by interpolation calculation, and the harmonic characteristic of the target harmonic higher than the harmonic measurement point set at the higher harmonic injection point is measured. Wave measurement method.