JPH06294826A - Effective/reactive current measuring method - Google Patents

Abstract

PURPOSE:To accurately measure effective/reactive currents in a short time by an algorithm for equalizing a product of sampling times and sampling time at the time of reading to an integer-fold of a standard period of a commercial power source wave. CONSTITUTION:An amplifier Amp amplifies a secondary loading end voltage of a current transformer CT by a predetermined gain. This signal wave output Sig is input to an A/D converter of a computer Comp, set to a predetermined voltage by a transformer Tr from a commercial power source S, and a reference signal wave Ref as voltage and phase references is also input to the converter. The Comp discretely reads (samples) both the signals, calculates via a predetermined algorithm when it reads predetermined number, and displays a measured value on a display unit Disp. In order to rapidly measure via the computer, it is necessary to read (sample) the input signal in a necessary minimum shortest time and to accurately calculate a discrete sampled measured value in as short time as possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring an earth leakage current of an electric wiring and an effective / ineffective component flowing in a load device.

[0002]

2. Description of the Related Art Conventionally, as a method for measuring active / reactive currents, a voltmeter / ammeter / wattmeter is connected to an electric line for measurement, or disclosed in JP-A-61-213676. There is known a method of measuring a live line without opening the line, such as the "leakage current measuring method".

[0003]

The method of measuring by connecting a voltmeter / ammeter / wattmeter to an electric line has a problem that the measurement cannot be performed as a live line and it takes time and time.
In the invention described in the above-mentioned JP-A-61-213676, it is possible to perform measurement as it is with a live wire, but it is necessary to slightly improve a conventional commercially available clamp type current transformer, in addition to computer measurement. In addition, there are drawbacks such as the need to output a control signal from a computer and the series of processings need some time. An object of the present invention is to solve the above problems of the conventional method for measuring active / reactive current, and to provide an active / reactive current measuring method capable of accurately measuring and processing active / reactive current in a short time. is there.

[0004]

In order to achieve the above object, the present invention applies a unique algorithm to a program in computer measurement processing, and the program is applied to a current transformer / amplifier / reference signal transformer / The present invention is incorporated into a computer including an AD converter and a measurement value display to constitute the active / reactive current measuring method of the present invention.

The contents of the algorithm applied to the present invention are as follows. (1) Input the measured signal voltage of the load current through the current transformer or amplifier and the reference signal voltage of the commercial voltage to each port of the AD converter of the computer and read it by the computer to obtain the vector value of the load current. An algorithm that sets each constant such that the product of the number of samples N at the time of reading and the sample time t is equal to an integral multiple of the standard period T of the commercial power wave, depending on the measuring system.

(2) In the calculation processing of the above computer, the phase of the reference signal voltage by the commercial voltage is utilized by using the addition theorem in the trigonometric function and the relational expression of the coordinate axis rotation,
An algorithm that finds the phase difference from the commercial voltage wave and finds the phase of the measured current on the reference complex plane coordinates.

[0007]

According to the present invention, the active / reactive current of the current to be measured is measured and processed by using the computer program created based on the above algorithm. In the present invention, the reading time of each signal voltage is shortened as much as possible, and the series expansion of the trigonometric function necessary for calculating each angle for obtaining the phase difference is not necessary, so that the calculation processing time is significantly saved. Can be achieved.

[0008]

EXAMPLES Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples without departing from the gist of the present invention.

FIG. 1 shows a hardware system constituting the present invention. In FIG. 1, CT is a current transformer, and Amp is an amplifier that amplifies the secondary load end voltage of the current transformer CT to a predetermined gain. This signal wave output Sig is input to CH1 of the AD converter of the computer Comp. From the commercial power source S, a transformer Tr sets a predetermined voltage,
Reference signal wave Ref as a reference of voltage and phase is AD
Input to CH2 of the converter. In the computer Comp, both signals are read discretely (sampling), and if a predetermined number is read, calculation processing is performed by a predetermined algorithm and the measured value is displayed on the display device Disp.

The purpose of this measurement is to measure the vector value of the current flowing through the primary line of the current transformer CT in this system. What is needed as a measuring instrument is that the hardware configuration is as simple as possible, that it can be handled easily, and that measured values can be displayed quickly.

In order to speedily perform the computer measurement process, the input signal can be sampled and read in the minimum necessary short time, and the discrete sample measurement value can be accurately calculated in the shortest possible time. An effective / reactive current measuring method that satisfies these two points will be described.

First, the effective / reactive current measuring method described in claim 1 will be described. Generally, there is a DFT (discrete Fourier transform) algorithm or an FFT (fast Fourier transform) algorithm as a mathematical method for calculating the amplitude and phase of a specific frequency by a computer in a voltage (or current) whose peak value fluctuates with time. . On the other hand, the commercial power supply is constantly fluctuating in its effective value and frequency around the standard value. Therefore, the above FFT algorithm is usually applied to the spectrum analysis of commercial waves.

By the way, the frequency fluctuation of the commercial wave is about 0.1 Hz per 10 Sec, centering on the standard value.
In this state, if the reading of the computer is within a short time of several times the commercial wave period, it is found that the error is practically allowable even if it is regarded as a standing wave and is calculated. The relational expression of the discrete Fourier analysis of the standing wave is shown by the following expression.

[0014]

[Equation 1]

In this case, if the sampling number N is N≈∞, the spectrum of all orders is accurately calculated. But,
In this case, even in the spectrum calculation process of the fundamental wave of the commercial wave, it is necessary to sample for a long time due to the characteristics of the AD converter, which is not practical. Here, x _{k = N} at the sample k = _N, and Xη at the sample k = 0 at x _{k = 0}
If the envelope of the waveform during this period is periodic, X η
Will be accurately determined. This means that the sampling time Δt may be selected so that the number N is small.

An actual example of this is shown in FIG. In FIG. 2, circled dots represent the signal under measurement (CH1), and dots (•) represent the reference signal (CH2). It can be seen from FIG. 2 that the amplitude of the 7th order (that is, the commercial frequency) of the wave having a frequency of 1/7 of 60 Hz of the commercial wave is equal when k = 0 and k = N = 90. If this relation is shown by a general formula, it is as follows. N × Δt = n · T where N: number of samples Δt: sample time T: standard period of commercial wave n: integer.

Next, the effective / reactive current measuring method described in claim 2 will be described. In the above, "the number of samples N at the time of reading and the sample time t
It has been stated that each sample (X η) read by the “algorithm in which each constant is set so that the product of is equal to an integral multiple of the standard period T of the commercial power wave” is shown in FIG. Then, when each of these Xη is subjected to COS conversion and SIN conversion, the real and imaginary parts of the (apparent) input signal voltage at the time of observation at this time are obtained, and the square root of each sum of squares of the input signal voltage is obtained. Amplitude value. The following is a mathematical description.

[0018]

[Equation 2]

Further, this input signal is the measured signal component made up of the load current and the reference signal R made up of the power supply voltage.
As described above, there are two types of ef.
The reference signal voltage is not normally in phase with the power supply line voltage. Therefore, it is necessary to know in advance the absolute phase of the reference signal voltage (the phase where the power supply line voltage is 0 degree) from the current in phase with the standard line voltage. This correction angle is set to β (in this β, CH1 to C of AD conversion are
The signal voltage reading time difference between H2 is also included).

Therefore, the usual way of finding the absolute phase of the signal voltage to be measured will be described by mathematical expressions. Apparent measured signal voltage phase: φ _a φ _a = tan ⁻¹ (AXηs / AXηc) where AXηs: cos converted value of measured signal voltage AXηc: sin converted value of measured signal voltage Apparent reference signal voltage Phase: φ _b φ _b = tan ⁻¹ (BXηs / BXηc) where BXηc: reference signal voltage cos conversion value BXηs: reference signal voltage sin conversion value Absolute phase correction angle: β However, reference signal voltage absolute The phase is advanced. Absolute phase of the measured current: The _{Φ a Φ a = φ a -φ} b + β In this equation, the calculation of trigonometric functions (in this case tan ^-1), is required each time. In the case of calculation by a computer, there is a drawback that the calculation processing time is extremely long because the calculation is performed by expanding the series. An algorithm devised to eliminate this drawback is based on mathematical contents based on "additive theorem in trigonometric function and relational expression of coordinate axis rotation" described below.

FIG. 3 is a coordinate and vector relationship diagram for explaining the mathematical theory. First, the symbols in FIG. 3 are explained: coordinate axes X, Y: complex plane coordinates with the line voltage taken as the X axis coordinate axes x, y: coordinates during observation Ref: voltage proportional to the power supply line voltage (for example, 3% V) , And a reference signal value I ₀ having a specific phase difference: a calibration signal value S ₀ : a standard current value (for example, 3 mA) when the power supply line voltage is in phase and the power supply voltage is a standard value. Measurement signal value β: Phase difference between power supply voltage and Ref α: Apparent phase of Ref at the time of observation θ: θ = α−β Expanding the mutual relationship of the vectors in FIG. 3, (by the addition theorem) cos θ = cos ( α-β) = cos α · cos β + s
in α · sin β sin θ = sin (α−β) = sin α · cos β-c
osα · sinβ where cosβ and sinβ are cosβ and si because β is an eigenvalue that is originally determined by the hardware system.
nβ is also an eigenvalue.

Cos α = BC / (BC ² + BS ² ) ^1/2 ≡CA sin α = BS / (BC ² + BS ² ) ^1/2 ≡SA However, BC is a scalar value BS of cos of Ref at the time of observation. : Scalar value of sin of Ref at the time of observation. Also, the coordinate of the point P (same as the measured signal value sig) is calculated from the coordinates x _p, y _p at the time of observation to the absolute coordinate X by the relational expression of the coordinate axis rotation. _When converted into _{p and} Y _p , X _p = x _p · cos θ + y _p . sin θ = XAC Y _p = −x _p · sin θ + y _p . cos θ = YAS When the formula of the addition theorem of the previous formula is put and arranged, X _p = (x _p · cos α + y _p .sin α) · cos β
+ (X _p · sin α−y _p .cos α) · sin β Y _p = (− x _p · sin α + y _p .cos α) · cos
β + (x _p · cos α + y _p · sin α) · sin β Here, when the standard voltage of Ref is set to 3 V, X
Normalize _{p and} Y _p .

Assuming that these are XAR and YAX, XAR = 3 / (BC ² + BS ² ) ^1/2 · X _p = 3 · XA
C ・ CA / BC YAX = 3 / (BC ² + BS ² ) ^1/2・ Y _p = 3 ・ YA
S · SA / BS, that is, in the calculation process for obtaining the standardized measured signal value, it is not necessary to calculate all trigonometric function values, so that the time for computer calculation processing can be greatly shortened.

As an example of a computer program to which the algorithm used in the present invention is applied, a basic program described below is shown. 10 REM "IA" 20 CLEAR, & H1FE0: DEF SEG = & H1FE0 30 BLOAD "AD.BIN": ADCON = 0 40 DIM A (100), B (100) 50 FOR N = 0 TO 89 60 AD% = 0 70 CALL ADCON (AD%) 80 AE% = 1 90 CALL ADCON (AE%) 100 A (N) = AD% 110 B (N) = AE% 120 NEXT N 130 DIM C (100), S (100) 140 FOR N = 0 TO 89 150 C (N) = COS (.48869219 # * N) 160 S (N) =-SIN (.48869219 # * N) 170 NEXT N 180 FOR N = 0 TO 89 190 AC = AC + ((( A (N) / 4096 * 10) -5) * C (N)) 200 AS = AS + (((A (N) / 4096 * 10) -5) * S (N)) 210 BC = BC + ((( B (N) / 4096 * 10) -5) * C (N)) 220 BS = BS + (((B (N) / 4096 * 10) -5) * S (N)) 230 NEXT N 240 VA = 2 / 90 * SQR (1/2) * SQR (AC * AC + AS * AS) 250 VB = 2/90 * SQR (1/2) * SQR (BC * BC + BS * BS) 260 IAO = (VA / VB) * 3 270 CA = BC / SQR (BC * BC + BS * BS) 280 SA = BS / SQR (BC * BC + BS * BS) 290 XAC = (AC * CA + AS * SA) *. 993560226 # + (AC * SA-AS * CA) *. 1
13305236 # 300 YAS = (-AC * SA + AS * C
A) *. 9935602226 # + (AC * CA + AS *
SA) *. 113305236 # 310 XAR = 3 * XAC * CA / BC 320 XAX = 3 * YAS * SA / BS 330 PHD = (ATN (XAX / XAR) /6.2
83185307 #) * 360 340 LPRINT “AC =” AC, “AS =” A
S, "BC =" BC, "BS =" BS 350 LPRINT 360 LPRINT
”::::::::::::::::::::::::
::: "370 LPRINT" VA = "VA," VB = "V
B 380 LPRINT 390 LPRINT ”!!!!!!!!!!!!!!!
!! !! !! !! !! !! !! !! !! !! !! !! !! "400 LPRINT" IAO = "IAO ,," XA
R = “XAR,” XAX = ”XAX 410 LPRINT 420 LPRINT” $$$$$$$$$$$$$
$$$$$$$$$$$$$ "430 LPRINT" PHD = "PHD 440 END In the above, line numbers 50 to 120 are 90-time sampling readings of the measured signal voltage and the reference signal voltage. ~ 170 lines are the creation of COS conversion and SIN conversion tables, and 0.488 of 150,160 lines.
69219 is 2π · η / N = 2π × 7/90. 1
Lines 90 to 220 are Fourier transforms.

Lines 240 to 320 are the algorithm relating to (2) described in the above-mentioned "Means for solving the problem", and the constants (0.993) in lines 290 and 300.
560226 and 0.113305236) are COSβ and SINβ determined by this hardware.

FIG. 4 shows the results of the test results measured by the above program, and FIG. 5 shows the measurement circuit. From this result, it can be seen that if Ir: Ic is up to about 1:20, it is a slight error and can be sufficiently put to practical use. The measurement processing time is within 1 second.

[0027]

Since the present invention is constructed as described above, it has the following effects.

Since the predetermined algorithm is applied to the computer program, the effective and reactive current components of the commercial wave can be accurately measured in a short time with the minimum necessary hardware configuration.

[Brief description of drawings]

FIG. 1 is a hardware system constituting the present invention.

FIG. 2 is an example showing the relationship of each constant of the present invention with an actual waveform.

FIG. 3 is a vector diagram of each signal wave for explaining the theory of the present invention.

FIG. 4 is an example of test result results in which the entire system of the present invention is applied.

FIG. 5 is a measurement circuit for the test of FIG.

Claims (2)

[Claims] 1. A vector of a load current, which is obtained by inputting a measured signal voltage of a load current through a current transformer or an amplifier and a reference signal voltage of a commercial voltage to each port of an AD converter of the computer and reading it by the computer. Depending on the system that measures the value, the number of samples N and sample time during reading △
An effective / reactive current measuring method in which an algorithm in which each constant is set so that the product of t becomes equal to an integral multiple of the standard period T of the commercial power wave is applied to a computer program. 2. A phase difference between a reference signal voltage due to a commercial voltage and a commercial voltage wave is obtained by using an addition theorem in a trigonometric function and a relational expression of coordinate axis rotation, and the phase of a measured current is used as a reference complex plane. The active / reactive current measuring method according to claim 1, wherein the algorithm obtained on the coordinates is applied to a computer program.