JPH1123629A - Method for measuring harmonic of power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the harmonic characteristics of a power system by setting harmonic measuring points on a plurality of branches in the in the downstream or upstream of a harmonic injecting point of a system and determining the admittance of an equivalent circuit for an interesting harmonic in the downstream or upstream of these measuring points. SOLUTION: Based on the output from an synchronizing unit 13, currents of two frequencies f1 , f2 , higher and lower than an interesting harmonic and not equal to integer times of the basic frequency of the system, are injected as intermediate harmonic currents into a harmonic injecting point 9 from a current injector 11 and a harmonic measuring unit 15 is provided at each harmonic measuring point (b) in the downstream or upstream of the injecting point (a) of a system 1. The unit 15 analyzes the frequency of current and voltage at each measuring point (b) in synchronism with the output from the synchronizing unit 13. Current and voltage having the frequencies f1 , f2 are then detected at a measuring point (b) based on the analysis and the admittance of an equivalent circuit is determined for the intermediate harmonic. The admittance of the equivalent circuit is then determined from both admittances by interpolation for the interesting harmonic in the downstream and upstream of each measuring point (b) and the harmonic characteristics are measured for the interesting harmonic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a characteristic (harmonic characteristic) of an n-th harmonic (harmonic of interest) in a plurality of branches or the like lower or higher than a predetermined harmonic injection point of a power system. The present invention relates to a method for measuring harmonics of an electric power system for individually measuring the following.

[0002]

2. Description of the Related Art Conventionally, in power transmission and distribution systems,
It is important to reduce harmonics.

[0003] From the viewpoint of reducing harmonics, it is also important to suppress the level of harmonics in each customer to a certain level or less. The nth-order (n = 1, 2,..., Integer) harmonic (nth harmonic) is an integral multiple of the system fundamental frequency fs, and a typical fifth harmonic frequency is 5 × fs. It is.

[0004] The reduction of harmonics is performed by estimating a harmonic level (voltage level) and attaching filter equipment of the frequency to a capacitor equipment.

[0005] When predicting the harmonic level, it is necessary to find out the lower harmonics (downstream) of the power system, for example, from the connection point of the filter equipment, and to find its equivalent circuit (harmonic equivalent circuit). Yes, at that time, if the lower than the connection point is branched to a plurality of systems or customer equipment,
It is necessary to grasp the harmonic characteristics for each branch of the system or for each customer.

By the way, when this harmonic equivalent circuit is expressed by Norton's theorem, it can be regarded as a parallel circuit of admittance 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), when obtaining a harmonic equivalent circuit for the fifth harmonic of the distribution line system,
It describes that the voltage and current of the fundamental wave of the system are measured, and the admittance of the harmonic equivalent circuit, the magnitude and phase of the current source, etc. are calculated and estimated from the results.

[0008]

When a harmonic equivalent circuit of a power system is obtained by the harmonic measurement method described in the above-mentioned journal, the fundamental voltage and current values of the system are measured, and the harmonic admittance is measured from the measurement result. Since the size and phase of the harmonic current source are estimated, it is not possible to accurately determine the admittance of the harmonic equivalent circuit of the power system.

That is, in the case of the conventional harmonic measurement method, the admittance and current source of the harmonic of interest are not determined from the actual measurement results, but are determined from the magnitude (vector value) of the fundamental wave based on the measurement information of the fundamental wave. Since only the magnitude (vector value) of the harmonic of interest is estimated, the harmonic equivalent circuit cannot be obtained with high accuracy.

For this reason, it is not possible to accurately determine the lower harmonic characteristics of the power system, for example, below the connection point of the filter equipment, to provide an appropriate filter equipment, and to reduce the harmonic level satisfactorily.

Therefore, the present applicant has filed Japanese Patent Application No. 8-31019.
According to the application of No. 2, a current having a non-integer multiple of the fundamental wave above and below the measurement harmonic (harmonic of interest) is injected into the harmonic injection point of the power system, and the voltage of the injection frequency at the injection point is injected. And admittance of an equivalent circuit for the injection frequency on each of the upper and lower sides of the harmonic of interest for lower or higher than the injection point of the system, based on the actual measurement results of the injection frequency current flowing in the upper and lower injection points. It has already been invented to determine the admittance of the equivalent circuit for the harmonic of interest by means of these interpolation processes and measure the harmonic characteristics.

In this case, the current at the injection frequency is a current having a frequency that is a non-integer multiple of the fundamental wave that does not originally exist in the system, and the admittance of the equivalent circuit of the injection frequency can be accurately determined by actual measurement. Higher harmonic characteristics of harmonics can be accurately grasped.

However, according to the measurement method of the above-mentioned application, the harmonic injection point coincides with the harmonic measurement point, and only the harmonic characteristics of the entire lower or upper system of the injection point can be measured.
For example, there is a problem that it is not possible to individually measure the harmonic characteristics of a plurality of branches below the injection point.

It is a technical object of the present invention to be able to individually measure the harmonic characteristics of each branch or the like lower or higher than the harmonic injection point.

[0015]

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 current injection device is connected to the harmonic injection point of the system, and based on the output synchronized with the system fundamental wave of the synchronizer, the current injection device places the n-th target harmonic of interest (frequency n × fs) at the harmonic injection point. ) Are injected as intermediate harmonic currents at two frequencies f ₁ and f ₂ (f ₁ <n × fs <f ₂ ), which are non-integer multiples of the system fundamental frequency fs. Harmonic measurement points are set for a plurality of lower or upper branch paths, etc., and a harmonic measurement device is provided for each harmonic measurement point, and the measurement current and measurement for each harmonic measurement point are performed by each harmonic measurement device. The voltage is frequency-analyzed in synchronization with the output of the synchronizer, and by this frequency analysis, the current and voltage of each of the frequencies f ₁ and f ₂ at each harmonic measurement point are detected, and the lower or higher frequency is measured from each harmonic measurement point etc. for the frequency f _1, the middle harmonic of f ₂ Obtain the admittance of the circuit, determine the admittance of the equivalent circuit for the lower or upper harmonic of interest at each harmonic measurement point from each of these admittances, determine the admittance of the equivalent circuit, and measure the harmonic characteristics of the harmonic of interest. .

Therefore, based on the output of the synchronizer, the intermediate harmonics of the frequencies f ₁ and f ₂ which do not exist in the system which is a non-integer multiple of the frequency fs synchronized with the system fundamental wave from the current injection device to the harmonic injection point. Wave currents are injected respectively.

Also, for example, a harmonic measurement point is set in each branch of the measurement object below the harmonic injection point, and a harmonic measurement device is provided at each measurement point.

Then, the measurement current and the measurement voltage at each harmonic measurement point are frequency-analyzed by this measuring device, and the currents of the intermediate harmonics of the frequencies f ₁ and f ₂ at each harmonic measurement point are calculated.
The voltage is detected, and based on this detection, the admittance of the equivalent circuit with respect to the intermediate harmonics of the frequencies f ₁ and f ₂ of each branch to be measured is individually obtained for each branch.

Furthermore, by interpolation using the admittance of an equivalent circuit of the intermediate harmonics of frequencies f _1, f _2, it is calculated admittance of an equivalent circuit of the interest harmonics between the frequencies f _1, f ₂ The harmonic characteristics of the determined harmonic are individually and accurately measured with respect to each of the lower branches of the determined harmonic injection point.

Therefore, for example, the characteristic of the harmonic of interest can be individually and accurately measured with respect to a plurality of branches below the harmonic injection point or each customer.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. (First Embodiment) First, a first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an equivalent circuit in a single line notation of the power system 1 to be measured. In the figure, a is selected at an appropriate position of the power system 1, for example, at a position to which a filter device for reducing harmonic current is connected. This is the harmonic injection point.

The power system 1 has various harmonics having a frequency n × fs (n is an integer of 1, 2,...) Which is an integral multiple of the frequency fs of the system fundamental wave. The upper (upstream) position on the left side as viewed from the harmonic injection point a is in a state where the upper equivalent circuit 5 is connected via the transimpedance 2, the upper line impedance 3, and the circuit breaker 4, for example.

The lower part (downstream) on the right side of the harmonic injection point a is branched into a plurality of branches, for example, and the equivalent circuits 6 of the respective branches are connected in parallel.

At this time, if the equivalent circuits 5 and 6 are expressed by Norton's theorem, the upper equivalent circuit 5 can be regarded as a parallel circuit of the admittance 7 and the current source 8, and the lower equivalent circuits 6 also have respective admittances. 9 and the current source 10 can be regarded as a parallel circuit.

It is to be noted that, particularly, each of the lower current sources 10 does not usually have a current source, but is generated due to current distortion or the like due to a load.

Then, a predetermined harmonic of the power system 1 such as the fifth harmonic (n = 5) is set as a target harmonic, and the circuit constant of the lower equivalent circuit 6 for the target harmonic that changes every moment is individually determined. In order to measure the respective harmonic characteristics, the current injection device 11 having a PLL control oscillator configuration is connected to the harmonic injection point a.

Further, the secondary side output of the instrument transformer 12 connected to the power system 1 is supplied to a synchronizer 13, and the synchronizer 13 forms a synchronization signal synchronized with the system fundamental wave.
This synchronization signal is used as an injection command signal via a communication cable 14 as a wired communication means, for example, as a current injection device 11
Is supplied periodically or continuously.

Based on the supply of the synchronizing signal, the current injection device 11 operates in synchronization with the system fundamental wave, and has two non-integer multiples of the system fundamental frequency fs sandwiching the harmonic of interest, ie, the frequency of the harmonic of interest. An intermediate harmonic current of lower and upper frequencies f ₁ , f ₂ (f ₁ <n × fs <f ₂ ) on the lower and upper sides of n × fs is output for a predetermined period, for example, at every 30-minute measurement cycle. Inject at injection point a.

Assuming that the target harmonic is the fifth harmonic (n = 5, frequency 5 × fs), the current of the intermediate harmonic of the frequencies f ₁ and f ₂ is, for example, 0% from the target harmonic. 4.5 harmonics shifted by 4.5 harmonics (n = 4.5, frequency 4.5 × f)
s), 5.5 harmonics (n = 5.5, frequency 5.5 × fs)
These are currents at frequencies that do not originally exist in the power system 1.

Then, the currents I ₁ and I ₂ of the intermediate harmonics of the frequencies f ₁ and f ₂ injected into the harmonic injection point a and flowing thereunder are lower # 1,..., # M−1, # The flow is divided into m branch paths of m at a ratio corresponding to the respective load states.

Due to this branching, the respective branches pass through the intermediate harmonic currents I ₁₁ ,..., I _1m-1 , I _1m of the frequency f ₁ , and the intermediate harmonic voltages V _{11 ,.} , V _{1 m} is generated, similarly, the middle harmonic current I ₂₁ of the frequency _{f 2, ..., I 2m-} 1,
I _2m flows and the voltage of the intermediate harmonic V ₂₁ ,..., V _2m-1 ,
V _2m is generated.

[0032] At this time, since the intermediate harmonic frequency f _1, f ₂ does not exist originally power system 1, the frequency f _1, f ₂
The equivalent circuit expressed by Norton's theorem for each branch of is equivalent to a circuit having only the admittance 9 excluding the current source 10 from the equivalent circuit 6.

Therefore, for example, in the branch road # 1,
By measuring the current I ₁₁ and the voltage V ₁₁ of the intermediate harmonic frequency f _1, the number of the admittance Y ₁₁ Katsuki of the equivalent circuit 1
Can be easily and accurately obtained from the calculation of the expression.

[0034]

## EQU1 ## Y ₁₁ = I ₁₁ / V ₁₁

The admittance Y ₂₁ of the equivalent circuit for the intermediate harmonic of the frequency f ₂ is also obtained by the same operation as the operation of the equation (1).

When the admittances Y ₁₁ and Y ₂₁ of the intermediate harmonics of the frequencies f ₁ and f ₂ are obtained, the simplest method is, for example, an interpolation calculation of (Y ₁₁ + Y ₂₁ ) / 2. The admittance 9 for the target harmonic of the frequency n × fs is obtained as the admittance Y ₁ (n).

Further, when the admittance Y ₁ (n) of the harmonic of interest is determined, the measured values I ₁ (n) and V ₁ (n) of the current and voltage of the harmonic of interest flowing through the branch of # 1 are obtained. based from calculation of expression 2 the current source 10 Katsuki equivalent circuit 6 of interest harmonics, obtained as a current source I _G1 (n).

[0038]

[Number 2] _{I G1 (n) = I 1} (n) -V 1 (n) · Y 1 (n)

The values of the admittance 9 and the current source 10 for the harmonic of interest are determined for the remaining branches 6 from the same measurements and calculations as those of the branch 6 of # 1.

Therefore, in this embodiment, a harmonic measurement point b is set at each branch end of each branch path 6.

When measuring the harmonic characteristics of each branch 6 sequentially, for example, when measuring the branch 6 of # 1,
The harmonic measuring device 15 which is independent and independent of the current injection device 11 is #
The first branch 6 is located at the harmonic measurement point b.

Next, the primary side of the instrument transformer 16 of the harmonic measuring device 15 is connected to the harmonic measuring point b, and an instrument current transformer 17 is provided near the lower side of the measuring point b.
The voltage at the harmonic measurement point b and the system current flowing through the measurement point b are measured.

Then, the detection output of the system voltage of the instrument transformer 16 and the detection output of the system current of the instrument current transformer 17 are sent to the A / D converter 19 provided in the measurement circuit section 18 of the harmonic measurement device 15. The data is supplied, sampled by the A / D converter 19, and converted 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 at the time of the current injection of the intermediate harmonic at the harmonic injection point a in order to accurately perform the subsequent frequency analysis. is there.

For this reason, the synchronizing signal of the synchronizing device 13 is transmitted to the A / A
The signal is transmitted to the D converter 19 as a measurement command signal, and based on the timing control of the measurement command signal, when an intermediate harmonic current of frequencies f ₁ and f ₂ flows into the harmonic injection point a, the A / D The converter 19 samples the detection output of the instrument transformer 16 and the instrument current transformer 17 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 .

Then, the measurement data of the system voltage and the system current output from the A / D converter 19 are supplied to the signal processing device 21. The signal processing device 21 performs the DFT analysis and the FFT.
The digital frequency analysis such as analysis, system voltage, the voltage V ₁₁ of frequency f _1, f ₂ each intermediate harmonics of the harmonic measurement point b contained in the measurement data of the system _current, V ₂₁ and the current I _11, I ₂₁ is detected.

The data of the voltages V _11, V ₂₁ and the currents I ₁₁ , I ₂₁ are supplied to the arithmetic processing unit 22,
Based on the voltage V _11, V _21, current I _11, I _21, the number 1
The admittances Y ₁₁ and Y of the branch 6 of # 1 are calculated from the calculation of the expression
_Ask for ₁₂ .

At this time, since the intermediate harmonics of the frequencies f ₁ and f ₂ do not originally exist in the power system 1, the admittances Y ₁₁ and Y ₂₁ can be accurately obtained even if their injected current amounts are small.

Therefore, the current injection device 11 may be a small device having a small current capacity, and the entire device configuration can be reduced in size, weight, and cost.

Next, the arithmetic processing unit 22 calculates the admittance 9 of the target harmonic of the branch 6 of # 1, that is, the admittance Y ₁ (n), by the above-described interpolation operation using the admittances Y ₁₁ and Y _21. Then, the harmonic characteristic of the branch 6 of # 1 is measured.

In the present embodiment, the current source 10 is also determined by measuring the harmonic characteristics, and the equivalent circuit 6 is completely identified.

Therefore, the harmonic measurement device 15 stops receiving the synchronization signal from the synchronization device 13 or the like, so that the frequencies f ₁ , f
_When the end of the current injection of the _second harmonic is detected, the A / D
The current I ₁ (n) and the voltage V ₁ (n) of the harmonic of interest existing in the branch 6 of # 1 are actually measured by the frequency analysis of the signal processing device 21 based on the measurement data of the converter 19.

Further, based on the determined admittance Y ₁ (n) and the actually measured current I ₁ (n) and voltage V ₁ (n), the arithmetic processing unit 22 calculates the value of # 1 from the calculation of the equation (2). determining a current source 10 for focusing the harmonic branch 6 as a current source I _G1 (n), the admittance Y ₁ (n) and the current source I _G1 (n) to identify the equivalent circuit 6 completely.

Each time the current of the intermediate harmonic of the frequencies f ₁ and f ₂ is injected, the admittance Y ₁ (n) and the current source I _G1 (n) are obtained in the same manner as described above. The latest equivalent circuit 6 for the target harmonic of the branch 6 is 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.

When measuring the other branch path 6,
A harmonic measurement device 15 is provided at the harmonic measurement point b of the branch 6 to be measured, and based on the synchronization signal transmitted from the synchronization device 13 via the communication cable 20 by this device 15,
As in the case of the branch path # 1 described above, the admittance 9 and the current source 10 for the target harmonic are determined, and the equivalent circuit 6 is identified.

Therefore, the current injection device 11 is used as a common current injection device, and each of the lower branches 6 of the harmonic injection point a is provided by the harmonic measurement device 15 separate from the current injection device 11.
Each harmonic characteristic can be measured individually.

At this time, a current of an intermediate harmonic of frequencies f ₁ and f ₂ , which does not originally exist, is injected into the power system 1, and from the measurement result, the frequency n × fs (f ₁ <n × fs <f ₂ ) Since the admittance 9 and the current source 10 for the target harmonic are determined and the equivalent circuit 6 is identified, the harmonic characteristics of each branch 6 can be accurately measured based on actual measurement.

The A / D converter 19, signal processing device 21, and arithmetic processing device 22 of the harmonic measurement device 15 can be realized by software of a microcomputer.

Therefore, the harmonic measuring device 15 can be formed by a so-called portable personal computer or the like except for the instrument transformer 16 and the instrument current transformer 17, and the harmonics of each branch 6 to be measured can be formed. It can be easily carried to the measurement point b.

When the harmonic characteristic is measured collectively for a part or all of each branch 6, the harmonic measurement device 1 is placed at the harmonic measurement point b of each branch 6 to be measured.
5 may be provided to simultaneously measure the respective harmonic characteristics of each branch 6 to be measured.

Incidentally, the synchronizer 13 and the current injection device 1
1, of course, the communication means of the synchronization signal with the harmonic measuring device 15 may be various means of wireless and wired.

In addition, the synchronizer 13 may be located at any position in the power system 1, and in some cases, the synchronizer 13 may be formed integrally with the current injection device 11 or the harmonic measurement device 15. Is, for example, the communication cable 14 or 20
There is an advantage that can be omitted. Further, the interpolation calculation of the arithmetic processing unit 22 may be a calculation of a weighted average or the like.

Next, the harmonic injection point a and the harmonic measurement point b can be arbitrarily set in the power system 1 according to the purpose of measurement.

When the harmonic injection point a is supplied from a plurality of higher systems, the higher harmonic measurement point b is set individually for each higher branch, and the same measurement and calculation as in FIG. 1 are performed. By doing so, the admittance and the current source of the equivalent circuit similar to the equivalent circuit 6 are individually determined for each higher-level system as in the case of each branch path 6 in FIG. 1, and the equivalent circuit is identified with high accuracy. be able to.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a case where the present invention is applied to the measurement of the harmonic characteristics of each customer. In this case, a harmonic injection point a is set at the power supply end of the distribution substation 25 of the power system (distribution system) 1 ′, The receiving end of each customer 26 to be measured by the system terminal is set to the harmonic measurement point b.

In FIG. 2, the same reference numerals as those in FIG. 1 denote the same or corresponding components, and reference numeral 27 denotes a power receiving point of the customer 26.

When the current of the intermediate harmonic having the frequencies f ₁ and f ₂ is injected from the current injection device 11 to the harmonic injection point a, the harmonics are measured by the harmonic measurement device 15 provided at the harmonic measurement point b. As in the case of 1, the admittance and current source of the equivalent circuit for the target harmonic in each customer 26 are determined, and the equivalent circuit is fixed.

From this result, each customer 26 can make a self-diagnosis as to whether or not the own facility is a source of harmonics and take necessary measures.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. Figure 3 is the highest level of the bus M ₁ from the bus M ₂ lower through each bank transformers Tr, ..., is applied to the harmonic measurement of M _3, M _4, power system 1 that branches ... binary " Show the case.

In this case, for example, when measuring the harmonic characteristics of each of the lower systems l ₁ , l ₂ , l ₃ ,... Below the bus M ₄ , for example, the measurement target between the buses M ₃ , M ₄ Subsystem l
Harmonic injection point a on the load side of bank transformer Tr close to ₁
Set to set the harmonic measurement point b on the load side of the bank transformer Tr between the busbar M ₄ and lower lines l ₁ to be measured.

Then, an intermediate harmonic current having frequencies f ₁ and f ₂ is injected from the current injection device 11 to the harmonic injection point a,
As in the case of FIG. 1, the admittance and current of the equivalent circuit for the target harmonic of the lower system l ₁ are determined by the harmonic measurement device 15 provided at the harmonic measurement point b, and the equivalent circuit is determined. Identify.

When a plurality of sub-systems of the bus M ₄ are collectively measured, a harmonic measurement point b is placed on each load side of the bank transformer Tr between the bus M ₄ and each sub-system to be measured. Set the harmonic measurement device 1 at each harmonic measurement point b.
5 can be provided, and in this case, the harmonic characteristics of each lower system can be collectively measured using the current injection device 11 in common.

[0075]

The present invention has the following effects.
You. Based on the output of the synchronizer 13, the current injection device 11
At the harmonic injection point a, the frequency synchronized with the system fundamental wave
Frequency f which does not originally exist in the system of non-integer multiple of fs₁, F
_TwoOf each of the intermediate harmonics of
Harmonic meter on the branch, etc. of the measurement object below the harmonic injection point a
Measurement points b are set, and a harmonic measurement device 15 is installed at each measurement point b.
The measuring device 15 measures the electric power at each harmonic measurement point b.
Analysis of current and measured voltage, and frequency f at that point₁,
f_TwoCurrent and voltage of each intermediate harmonic of
Therefore, based on this detection, the frequency of each branch
f₁, F _TwoOf the equivalent circuit for the intermediate harmonics
Can be obtained individually for each branch path.

[0076] Further, by interpolation using the admittance of an equivalent circuit of the intermediate harmonics of frequencies f _1, f _2, and calculates the admittance of an equivalent circuit of the interest harmonics between the frequencies f _1, f ₂ Since the determination has been made, the harmonic characteristics of the lower harmonics of interest can be individually and accurately measured for each lower harmonic measurement point below the harmonic injection point a.

Therefore, for example, for each branch or each customer below the harmonic injection point b, the characteristic of the harmonic of interest can be individually and accurately measured.
The same effect can be obtained when each harmonic measurement point b is provided above the harmonic injection point b.

[Brief description of the drawings]

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

FIG. 2 is a circuit connection diagram according to a second embodiment of the present invention.

FIG. 3 is a circuit connection diagram according to a third embodiment of the present invention.

[Explanation of symbols]

 1, 1 ', 1 "power system 11 current injection device 13 synchronizer 15 harmonic measurement device 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 current injection device is connected to a harmonic injection point of a system, and based on an output synchronized with a system fundamental wave of a synchronizer, an n-th focus of a measurement object from the current injection device to the harmonic injection point. System fundamental frequency fs sandwiching harmonics (frequency n × fs)
F ₁ , f ₂ (f ₁ <n × fs <f
₂ ) Inject the currents respectively as intermediate harmonic currents, set harmonic measurement points on a plurality of branches or the like lower or higher than the harmonic injection point of the system, and respectively set the respective harmonic measurement points. A harmonic measuring device is provided, and the harmonic current is measured by the harmonic measuring devices in synchronization with the output of the synchronizer. Detecting the current and voltage of each of the frequencies f ₁ and f ₂ at a point to determine the admittance of an equivalent circuit for intermediate harmonics of the frequencies f ₁ and f ₂ lower or higher than the respective harmonic measurement points; Interpolating and determining the admittance of the equivalent circuit for the lower or upper harmonic of interest of each of the harmonic measurement points from the both admittances, and determining the harmonic characteristics of the harmonic of interest. Harmonic measurement method of the power system characterized by.