JP3205451B2 - Electric energy measuring device - Google Patents

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 the amount of electric power for monitoring overpower.

[0002]

2. Description of the Related Art The measurement of the amount of electric power on an electric circuit has been widely performed in order to grasp the state of the electric circuit and to perform an alarm at the time of overpower.

[0003] As a technique for measuring the electric energy, an electronic watt-hour meter that converts the frequency of a voltage and a current, integrates the frequencies, and accumulates the accumulated energy to calculate an integrated electric energy is known. Are known.

[0004] Further, there is known a technique in which a harmonic component is independently sampled and processed in parallel with a fundamental component to detect a harmonic component of the electric energy.

[0005]

According to the above-described technique for calculating the integrated electric energy, it is not possible to detect a harmonic component, so that it is not possible to give an alarm such as occurrence of a failure due to an increase in high-frequency current.

On the other hand, according to the technology for processing the fundamental wave component and the harmonic component in parallel, the configuration of the device for processing the component becomes complicated, resulting in an increase in the size and cost of the device.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power measuring device capable of obtaining a harmonic component as well as a fundamental component with a simple device configuration.

[0008]

To achieve the above object,
The present invention provides a sampling unit for sampling a voltage and a current of a monitored circuit at a timing of a given sampling signal, a storage unit for accumulating a voltage value and a current value of the monitored circuit sampled by the sampling unit, and A processing unit for calculating the electric energy of the monitored circuit from the voltage value and the current value of the monitored circuit stored in the means, wherein the processing device is capable of detecting a harmonic component on the monitored circuit. A sampling signal having a period T1 is output to the sampling means for an integral multiple of the frequency of the fundamental wave on the monitored circuit. Means for outputting a sampling signal of a sampling period T2 capable of detecting a component to said sampling means for a predetermined period; Temporary power calculation for obtaining the distorted wave power on the monitored circuit and the fundamental wave power on the monitored circuit from the current value and the voltage value sampled by the sampling circuit in accordance with the sampling signal of the sampling period T1 stored in the storage device. means and, stored in the storage means, a current value sampled at the sampling means by the sampling signal of the sampling signal and the sampling period T1 of the sampling period T2, a current value per time interval T2 of the voltage value Calculating means for calculating the electric energy on the monitored electric circuit by correcting the integrated value of the voltage value using the ratio between the fundamental power and the distorted wave power obtained by the temporary electric energy calculating means. The present invention provides an electric energy measuring device characterized by the following.

[0009] Further, the present invention provides,
In such an apparatus, a sampling period T capable of detecting a harmonic component on the monitored circuit is used instead of the processing apparatus.
1 is output to the sampling means for an integer multiple of the frequency of the fundamental wave on the monitored circuit, and the sampling period T at which the fundamental component on the monitored circuit can be detected.
Means for continuously outputting the second sampling signal to the sampling means for a predetermined period including a period for outputting the sampling signal of the sampling cycle T1, and the sampling means according to the sampling signal of the sampling cycle T1 stored in the storage means. Means for obtaining the distorted wave power on the monitored electric circuit from the current value and the voltage value sampled in the above, and a period in which the sampling signal of the sampling cycle T1 stored in the storage means is output.
A provisional power calculating means for obtaining a fundamental wave power on a monitored circuit from a current value and a voltage value sampled by the sampling means in accordance with the sampling signal of the sampling cycle T2; By correcting the integrated value of the current value and the voltage value sampled by the sampling means by the sampling signal using the ratio between the fundamental wave power and the distorted wave power obtained by each of the power calculation means, the current value on the monitored electric circuit is corrected. Provided is an electric energy measuring device, which is constituted by using a processing device provided with an operation means for calculating an electric energy.

[0010]

According to the electric energy measuring apparatus of the present invention, the sampling of the period T1 and the sampling of the period T2 are performed by the common sampling means. And the period T
A current value sampled by the sampling of 1;
From the voltage value, the distorted wave power on the monitored circuit during the period in which the sampling signal of the sampling period T1 is output is obtained, and the current value and the voltage value sampled by the sampling means at time intervals T2 during the same period are obtained. The fundamental power on the monitored electric circuit is determined, and the integrated value of the current value and the voltage value sampled by the sampling means at each time interval T2 is calculated using the fundamental power and the distorted wave power determined by the temporary power amount calculating means. The power amount on the monitored electric circuit is calculated by making correction using the ratio of.

As described above, according to the present invention, the electric energy on the monitored electric circuit is obtained by taking into account the harmonic components by simple processing using common sampling means. Accordingly, it can be realized with a simple device configuration.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below by taking an example of application to a power supply monitoring device.

A power supply monitoring apparatus 100 according to the present invention is provided for each transformer 200 provided in a factory or plant, for example, as shown in FIG. The amount is monitored, and in the event of an abnormality, an alarm is displayed and the monitoring room 30 is connected via the communication line 500 in the factory.
This is notified to the monitoring apparatus 400 of No. 0.

Next, FIG. 2 shows the configuration of the power supply monitoring apparatus 100 according to the present embodiment.

In this embodiment, the power supply monitoring apparatus 100 is described as measuring and monitoring the power of a three-phase three-wire power line.

In the figure, reference numeral 1 denotes a transformer (hereinafter referred to as "PT") for extracting a voltage of a three-phase three-wire power line to be measured, and 2 denotes a voltage obtained by the PT to lower the voltage. (Hereinafter referred to as “internal PT”).

Reference numeral 3 denotes a current transformer (hereinafter referred to as "CT") for extracting a current of the three-phase three-wire power line to be measured, and reduces the current obtained by CT to a lower current. (Hereinafter referred to as “internal CT”).

Next, reference numeral 5 denotes a zero-phase current transformer (hereinafter referred to as "ZC") for extracting the ground fault current of the three-phase three-wire power line to be measured.
T ") where the internal CT4 and the zero-phase current transformer Z
The current obtained by CT5 is converted into a voltage value through a current-voltage conversion circuit.

Each AC voltage taken into the unit in this manner is amplified by an amplifier circuit 6 and converted into a rectangular wave by a sample-and-hold circuit (hereinafter referred to as an "SH circuit") 7, and is converted into a digital signal. The waveform is easily converted.

However, actually, since the target is a three-phase three-wire power line, PT1, internal PT2, CT3, internal CT
4, the amplification circuit 6, the SH circuit 7, etc. are provided for three systems.

On the other hand, a central processing unit (hereinafter referred to as "CP
U) 8 outputs a signal for selecting one of the aforementioned AC voltages, and an analog multiplexer (hereinafter referred to as “M”).
PX ") and select one of the AC voltages. The selected AC voltage is converted into a digital signal by an analog / digital conversion circuit (hereinafter, referred to as an “A / D converter”), passed through a buffer 11 and taken into a CPU 8, and then stored in a storage circuit (RAM) 12. You.

After repeating these series of operations a predetermined number of times, the CPU 8 performs an arithmetic operation on the data stored in the RAM 12 and outputs the result via a driver 14 to a display unit (in this embodiment, a seven-segment light emitting diode). (Using an element) 13 to display calculation results (voltage, current, harmonic current, ground fault current, active power, reactive power, power factor, active power, reactive power, etc.). If the calculation result indicates an abnormality, an alarm is issued by a lamp, a buzzer or the like provided outside via a relay 19, and the communication control device 20 connected to the communication port 16 is activated. This is notified to the monitoring device 400 in the monitoring room 300 via the communication terminal. In the figure, reference numeral 17 denotes an address decoder for selecting a peripheral circuit according to an address of the CPU 8, and 21 denotes a nonvolatile storage means ROM storing a program to be executed by the CPU 8.
(For example, EEPROM).

Hereinafter, the power supply monitoring apparatus 100 according to the present embodiment will be described.
Will be described.

In this operation, processing is performed using a sampling time interval T1 at which a harmonic component can be detected and a sampling time interval T2 at which a fundamental component can be detected. here,
The time interval T2 is a time interval that is an integral multiple of T1. , FIG.
2 shows a procedure of a power amount calculation process performed by the CPU 8 of the power supply monitoring device 100 in accordance with the program read from the ROM 21.

As shown, when starting the processing, the CPU 8 first executes the main flow shown in FIG. In this main flow, first, the internal timer is set to time T1 (step 301), and it is waited that the timer interrupt processing is performed a predetermined number of times M (step 302).

On the other hand, in the timer interrupt processing called by the internal timer at every time T1, as shown in FIG. 3B, a sampling pulse is given to each SH circuit 7.
By controlling the MPX 9, each AC voltage is fetched via the buffer 11 and written into the RAM 12 (step 401).
That is, sampling of each AC voltage to the RAM 12 is performed. In the timer interrupt processing, the number of times of processing (the number of times of sampling) is counted for each processing and set in a register in the CPU 8 (step 402).

In the main flow, when it is known from the register in the CPU 8 that the timer interrupt process has been performed M times (step 302), the count of the register is reset and the internal timer T2 is set (step 30).
3). From the AC voltage values sampled in the RAM 12 by the interrupt process T1, various measured values (current, voltage, ground fault current, harmonic voltage, current,
Ground fault current, etc.) (step 304).
The power W ^{* of the} distorted wave including the fundamental wave and the harmonics in this period and the power W1 of the fundamental wave are calculated (step 3).
05).

Next, the CPU 8 sets the internal timer T2 during this time.
It waits for the interrupt process called by the timer interrupt to be performed a predetermined number of times N (step 306).

On the other hand, steps 304 and 3 of the main flow
When the internal timer T2 interrupts the timer during the execution period of the internal timer T5, the CPU 8 uses the internal timer to execute the time T2.
Each time, the timer interrupt processing shown in FIG. 3B is executed.

In the main flow, the CPU 8
When the timer knows from the register that the timer interrupt process has been performed N times, it resets the count of the register (step 307). And the time interval T so far
From the AC voltage values sampled in the RAM 12 by sampling at 1 and T2, the instantaneous value W (t) of the power of the fundamental wave at each time interval T2 in the total period of sampling at the time intervals T1 and T2 is calculated. It is calculated (step 308).

The final power amount is calculated by multiplying the thus obtained ratio of W ^* and W1 by the integral value of each instantaneous value W (t) of the fundamental wave power (step 309).

Based on the thus obtained electric energy, ground fault current, harmonic current, and the like, the display on the display unit 13, the display of the alarm, the output of the alarm by the relay 19, and the output to the monitoring device 400 are performed. A notification is made (step 310), and the process returns to step 301.

Now, in such an operation, the time T1 set in step 301 and the number M determined in step 302, the time T2 set in step 303 and the number N determined in step 306 are set as follows. I do.

That is, as shown in FIG.
It is time to sample various AC currents and voltages at a high frequency enough to detect the maximum order harmonic current to be obtained. M is the original (designed) frequency of the three-phase AC power on the three-phase three-wire power line. That is, the number of times of sampling various AC currents and voltages in one cycle period of the fundamental wave and at the time interval T1. T2 and N are sampling time intervals at which fluctuations in current and voltage at the frequency of the fundamental wave on the three-phase three-wire power line can be obtained with constant accuracy. Are set to sample various AC voltages during the cycle period. However, as described above, the time interval T2 is set to be an integral multiple of the time interval T1.

Accordingly, as shown in FIG. 4, sampling is performed at a time interval T1 for one cycle of the frequency of the fundamental wave of the three-phase AC power, and then for a plurality of cycles, a time interval T
2 is performed. This sequence is repeated.

From the sampling values obtained by such sampling, as shown in FIG. 5, the currents I1, I2, I3 and the voltages E1, E2, E3 of the three power lines of the three-phase three-wire power line at each sampling point. Is found.

Next, the calculation of each instantaneous value W (t) of the power performed in step 308 is performed as follows. That is,
In this calculation, not only the AC voltage values sampled at the time interval T2 but also the sampling values at the timing corresponding to the sampling at the time interval T2 among the AC voltage values previously sampled at the time interval T1 are used. . In this way, the fundamental power can be corrected based on the harmonic power during the same period, and the final power amount can be obtained.

If the CPU 8 has sufficient capacity, the above processing may be performed as follows using two internal timers, time T1 and time T2, simultaneously. That is, the power W ^{* of the} distorted wave is obtained by operating the internal timer at time T1 for one period of the fundamental wave,
It is obtained by using the sample value obtained by the interrupt processing by the internal timer of No. 1. Then, the internal timer at the time T2 is operated for a plurality of periods including one period during which the internal timer at the time T1 is operating, and the internal timer at the time T2 is operated during the one period operating in parallel with the internal timer at the time T1. The fundamental wave power W1 is obtained using the sample value obtained by the interrupt processing by the timer.
Further, each instantaneous value W (t) of the fundamental wave power is a sample value obtained by interrupt processing by the internal timer at time T2 during a plurality of cycle periods including one cycle period operating in parallel with the internal timer at time T1. Is determined using However, in this case, it is necessary to ensure that the interrupt processing by the two internal timers does not temporally collide during one cycle period in which the internal timer at the time T1 and the internal timer at the time T2 are operating in parallel.

The measurement of the power value of such a distorted wave is described in detail in “Revised AC Circuit” (published by Tokyo Denki University, Koichi Uno and Naokichi Isobe).

As described above, according to the present embodiment, since the power amount is continuously obtained by the low frequency sampling, the power amount can be calculated accurately while following a load having a large fluctuation. Since the waveform can be intermittently accumulated by the high-frequency sampling and the detailed frequency analysis can be performed, the harmonic current can also be measured. Furthermore, since the load of computation is greatly reduced as compared with the case where sampling and computation processing are performed using both frequencies, high-performance, high-cost CPUs are not used.
Calculation of the above-described various measured values other than the integrated power amount and the harmonic current can also be performed.

As shown in FIG. 2, the hardware configuration of the power supply monitoring apparatus 100 according to the present embodiment is no different from the case where only the electric power is continuously monitored by low frequency sampling. .

The embodiment of the present invention has been described above.

Although the present embodiment has been described with reference to a case where a three-phase three-wire type power line is to be measured, the present invention can be similarly applied to a case where a power line by another power transmission system is to be measured. . Further, in the present embodiment, a case where the present invention is applied to power monitoring in a substation facility has been described, but the present embodiment can be similarly applied to power measurement in various other uses.

In this embodiment, sampling at a high frequency (at the time interval T1) is performed only for one period of the fundamental wave, but may be performed for a plurality of periods.

In the present embodiment, the ratio between the fundamental wave power obtained from the sampling value during the high frequency sampling period and the distortion wave power is used. The fundamental power obtained from the sampling value in the low frequency sampling period or the ratio of the fundamental power obtained from the sampling value in the period obtained by combining the high frequency sampling period and the low frequency sampling period may be used. However, the accuracy in these cases is expected to slightly deteriorate. In addition, a certain effect can be expected even if only the instantaneous values of each voltage and current of the fundamental wave power, which are corrected by the ratio between the fundamental wave power and the distorted wave power, use only those in the low frequency sampling period.

[0046]

As described above, according to the present invention, a harmonic component as well as a fundamental component can be obtained with a simple device configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a monitoring system using a power supply monitoring device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a power supply monitoring device according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a power measurement operation according to the embodiment of the present invention.

FIG. 4 is a timing chart showing sampling timing of the power supply monitoring device according to the embodiment of the present invention.

FIG. 5 is a diagram showing an alternating current and an alternating voltage obtained by sampling of the power supply monitoring device according to the embodiment of the present invention.

[Explanation of symbols]

 1, 2 transformer 3, 4, 5 current transformer 6 amplifier circuit 7 sample and hold circuit 8 CPU 9 analog multiplexer 10 analog / digital conversion circuit 11 buffer 12 RAM

Continuing on the front page (72) Inventor ▲ Taka ▼ Naohiro Kamo 46-1 Tomioka, Nakajo-cho, Kitakanbara-gun, Niigata Prefecture Industrial Machinery Division, Hitachi, Ltd. 46-1 Hitachi Industrial Equipment Division (56) References JP-A-63-221258 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 21/00-22 / 00 G01R 11/00-11/66

Claims (3)

(57) [Claims] 1. Sampling means for sampling the voltage and current of a monitored circuit at the timing of a given sampling signal; storage means for accumulating the voltage and current values of the monitored circuit sampled by the sampling means; A processing unit for calculating the electric energy of the monitored circuit from the voltage value and the current value of the monitored circuit stored in the storage unit, wherein the processing device can detect a harmonic component on the monitored circuit. Outputting a sampling signal of the sampling period T1 to the sampling means for an integral multiple of the frequency of the fundamental wave on the monitored electric circuit;
Then, a means for outputting a sampling signal of a sampling period T2, which is a sampling period that is an integral multiple of the sampling period T1 and capable of detecting a fundamental wave component on the monitored circuit, to the sampling means for a predetermined period; The accumulated sampling period T1
Temporary power calculating means for obtaining the distorted wave power on the monitored circuit and the fundamental wave power on the monitored circuit from the current value and the voltage value sampled by the sampling means in accordance with the sampling signal, and stored in the storage means. , Sampling period T2
The temporary power calculating means determines the integrated value of the current value and the voltage value at each time interval T2 of the current value and the voltage value sampled by the sampling means by the sampling signal of the sampling period T1 and the sampling signal of the sampling period T1. A power calculating device for calculating the power on the monitored circuit by correcting using a ratio between the fundamental wave power and the distortion wave power. 2. Sampling means for sampling the voltage and current of the monitored circuit at the timing of a given sampling signal; storage means for accumulating the voltage value and current value of the monitored circuit sampled by the sampling means; A processing unit for calculating the electric energy of the monitored circuit from the voltage value and the current value of the monitored circuit stored in the storage unit, wherein the processing device can detect a harmonic component on the monitored circuit. Outputting a sampling signal of the sampling period T1 to the sampling means for an integral multiple of the frequency of the fundamental wave on the monitored electric circuit;
Means for continuously outputting a sampling signal of a sampling period T2 capable of detecting a fundamental wave component on the monitored electric circuit to the sampling means for a predetermined period including a period of outputting the sampling signal of the sampling cycle T1, and accumulating in the storage means Sampling period T1
Means for obtaining the distorted wave power on the monitored circuit from the current value and the voltage value sampled by the sampling means according to the sampling signal, and the period during which the sampling signal of the sampling period T1 stored in the storage means is output. A temporary power calculating means for obtaining a fundamental power on the monitored circuit from a current value and a voltage value sampled by the sampling means in response to a sampling signal of a sampling cycle T2; Period T2
By correcting the integrated value of the current value and the voltage value sampled by the sampling means by the sampling signal of the above using the ratio between the fundamental wave power and the distorted wave power obtained by each of the power calculation means, And a calculating means for calculating the amount of power. 3. A step of sampling the voltage and current of the monitored circuit at an integer multiple of the frequency of the fundamental wave on the monitored circuit at a sampling period T1 capable of detecting a harmonic component on the monitored circuit. The voltage and current of the monitoring circuit are sampled at a sampling period T2 at which the fundamental wave component on the monitored circuit can be detected, and between the sampling, the voltage and current sampled at the sampling period T1 are used. Obtaining a harmonic component of the time interval T2 of the sampled voltage and current values
Obtaining a fundamental wave component on the monitored electric circuit from each voltage and current value.