Power measurement apparatus

The present invention relates to a power measuring instrument that measures the power of a circuit in a distribution board or the like using a current transformer (CT).

Conventionally, a current transformer has been used when measuring the electric power of a circuit in a distribution board provided in a facility such as a house or a building. Generally, a power measuring instrument is connected to the receiving circuit of the current transformer, and the power measuring instrument inserts a burden resistor into the circuit connected to the current transformer, and the voltage across the load resistor is inserted. Is detected to measure the current value and perform power calculation.

Here, the functional configuration of the conventional power measuring instrument will be described with reference to FIG. 7. The power measuring instrument 100 includes a current detection unit 101, a voltage detection unit 102, and a power calculation unit 103. The multiplication unit 103a provided in the power calculation unit 103 powers (W) based on the current value detected by the current detection unit 101 connected to the current transformer (CT) 104 and the voltage value detected by the voltage detection unit 102. Performs power value calculation such as. The transmission circuit unit 103b outputs the calculation result of the multiplication unit 103a as a measured power value.

In the power measuring instrument 100, the current value detected by the current detection unit 101 has a predetermined threshold value T as a noise countermeasure._hIf it is less than, it determines that zero current, peristaltic prevention performance is set not to start the power calculation is constant. Further, in the power measuring instrument 100, the current value (actually the effective value) detected by the current detection unit 101 is the threshold value T for determining the start of the power calculation._hWhen the above (also referred to as "starting current") is reached, it has the ability to start power calculation. The threshold T_hIs determined by a predetermined ratio (very small level) of the rated current of the power measuring instrument 100. For example, when the rated current is 100 A and the predetermined ratio is 0.3%, the threshold value T_hIs set to 0.3A.

By the way, there is disclosed a power measurement system in which a power measuring instrument provided with a current detecting means and a voltage detecting means can be attached to and detached from a breaker (see, for example, Patent Document 1).

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2009-103538</text></patcit></p>

<p num="0007"> However, in the processing circuit of the power measuring instrument 100, various external noises derived from thermal noise in the amplifier circuit and the resistor, radiated radio, magnetic field, etc. are actually generated, and as a result, the noise is superimposed on the current signal. I have something to do. The noise includes high frequencies and is white noise that vibrates irregularly in the vertical direction.</p><p num="0008"> Here, the influence of noise on the conventional power measuring instrument 100 will be described with reference to FIG. As shown in FIG. 8A, the voltage waveform input to the voltage detection unit 102 is a sinusoidal waveform having an effective value of AC voltage of 100 V and a frequency of 50 Hz. Further, since the load 105 is de-energized at 0 A, the current waveform input to the current detection unit 101 is not detected as shown in FIG. 8 (b). Then, when external noise as shown in FIG. 8C is generated in the current detection unit 101, the current waveform output from the current detection unit 101 is shown in FIG. 8B as shown in FIG. 8D. The current waveform is obtained by superimposing the noise shown in FIG. 8 (c) on the current waveform shown in FIG.</p><p num="0009"> At this time, depending on the noise level, the current value measured by the current detection unit 101 is the threshold value T._h(0.3A in FIG. 8) is exceeded, and the power calculation in the power calculation unit 103 is erroneously started. That is, although no current actually flows through the load 105, the measured power value is output from the power measuring instrument 100 (the power measuring instrument 100 is latent) depending on the noise level. As a result, there is a problem that the accuracy of the measured power value output from the power measuring instrument 100 deteriorates.</p><p num="0010"> The present invention has been made in view of the above problems, and an object of the present invention is to provide a power measuring instrument capable of outputting a more accurate measured power value even when external noise or the like is superimposed on a current signal. To do.</p>

<p num="0011"> In order to achieve the above object, the present invention includes a voltage detection unit that detects a voltage signal from a circuit, a current detection unit that detects a current signal based on an output from a current transformer attached to the circuit, and a current detection unit. In a power measuring instrument including a power calculation unit that calculates the power of the circuit by multiplying each signal of the voltage value and the current value detected by the voltage detection unit and the current detection unit, the calculation is performed by the power calculation unit. A measurement control unit that obtains the amount of power accumulated over a predetermined time, and when the amount of power exceeds a predetermined threshold, controls the power value after exceeding the threshold to be output as a measured power value. It is characterized by being prepared.</p><p num="0012"> In this power measuring instrument, the predetermined threshold value is the amount of power obtained by multiplying the rated voltage of the power measuring instrument by a predetermined ratio of the rated current of the power measuring instrument and integrating the power value obtained in a predetermined time. It is preferable to have.</p><p num="0013"> In this power measuring instrument, the predetermined threshold value is preferably a value obtained by multiplying the electric energy by a power factor value based on the phase difference between the current waveform and the voltage waveform.</p><p num="0014"> In this power measuring instrument, it is preferable that the rated voltage is calculated based on the actual measured voltage value measured by the voltage detection unit.</p><p num="0015"> In this power measuring instrument, the measurement control unit further determines based on a predetermined threshold value determined by multiplying the current value detected by the current detecting unit and a predetermined ratio of the rated current of the power measuring instrument. When the current value exceeds the predetermined threshold value, it is preferable to control so that the power value after exceeding the threshold value is output as the measured power value.</p><p num="0016"> In this power measuring instrument, it is preferable that the measurement control unit performs the control with respect to the starting current.</p>

<p num="0017"> In the power measuring instrument according to the present invention, the measurement control unit has a power amount at a predetermined time and a predetermined threshold value T._hThe amount of electric power is a predetermined threshold value T_hIf it exceeds, the measured power value is controlled to be output. Therefore, in the present invention, even if external noise or the like is superimposed on the current signal or voltage signal, the measured power value can be output more accurately.</p>

<figref num="1">It is an overall block diagram of the electric power measurement system which concerns on embodiment of this invention.</figref><figref num="2">It is a functional block diagram of the power measuring instrument provided in the power measuring system as above.</figref><figref num="3">(A) Voltage waveform input to the voltage detection unit of the power measuring instrument, (b) Current waveform input to the current detection unit of the power measuring instrument in a state where external noise is not generated, (c) The current. It is a figure which shows the current waveform output from a detection part, and (d) the power waveform calculated by the power calculation part of the power measuring instrument.</figref><figref num="4">(A) Voltage waveform input to the voltage detection unit, (b) Current waveform input to the current detection unit, (c) Current waveform detected by the current detection unit in a state where external noise is generated, ( d) It is a figure which shows the current waveform output from the current detection unit, and (e) the power waveform calculated by the power calculation unit.</figref><figref num="5">(A) The voltage waveform input to the voltage detection unit, (b) the current waveform input to the current detection unit when the load is energized, and (c) the current detection unit in a state where external noise is generated. It is a figure which shows the current waveform detected in (d), (d) the current waveform output from the current detection unit, and (e) the power waveform calculated by the power calculation unit.</figref><figref num="6">It is a flowchart which shows the operation procedure of the power measuring instrument.</figref><figref num="7">It is a functional block diagram of a conventional power measuring instrument.</figref><figref num="8">(A) Voltage waveform input to the voltage detection unit of the conventional power measuring instrument, (b) Current waveform input to the current detection unit of the power measuring instrument, (c) The current detection in a state where external noise is generated. It is a figure which shows the current waveform output from the part, (d) the power waveform calculated by the power calculation part of the power measuring instrument.</figref>

(Embodiment) The electric power measuring instrument according to the embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a power measurement system in which the power measuring instrument according to the present embodiment is used. The power measurement system S includes a distribution board 1, current transformers 2a and 2b, a power measuring device 3, a monitoring device 4, a load 5, and breakers 6a to 6c. This power measurement system S monitors the power consumption of various loads 5 such as lighting fixtures and personal computers that receive power from the distribution board 1 in a general house or office building, and "visualizes" the power. Has been realized.

The distribution board 1 has a main circuit that receives commercial power supplied from the outside to the inside of a building or a house to the primary side via an electric wire 7 such as a three-phase three-wire system, and an electric circuit branched from the secondary side of the main circuit. It is provided with a plurality of branch circuits interposed therein. In addition to lighting equipment and personal computers, various loads 5 such as air conditioners and IH equipment are connected to each branch circuit. Further, the breaker 6a is a main breaker connected to the electric wire 7 of the main circuit, and the breaker 6b is a branch breaker arranged in a plurality of branch circuits branched from the main circuit.

The current transformers 2a and 2b (collectively, the current transformer 2) reduce the current of each circuit at a constant rate and supply the current to the power measuring instrument 3 via the signal line 8 which is a dedicated cable. In the present embodiment, the current transformer 2a is installed to periodically measure the main current flowing through the main circuit through which a relatively large current flows, and in this figure, it is attached to two electric wires of the main circuit wiring. It is penetrated and connected to the power measuring instrument 3 by a signal line 8. The current transformer 2b is installed to periodically measure the branch current flowing through each branch circuit through which a relatively small current flows, and is attached to a predetermined position of the electric wire of the branch circuit. It is connected by the signal line 8. The current detecting means is not limited to the current transformer 2, and for example, another current sensor including a Hall element, a shunt, or the like may be used.

The power measuring instrument 3 is connected to the current transformer 2, has a burden resistor to be inserted into a circuit connected to the current transformer 2, and measures the electric power of the circuit in which the current transformer 2 is installed. The power measuring instrument 3 outputs the measured power value to the monitoring device 4 via the communication line. The power measuring instrument 3 is installed at a predetermined position in the distribution board 1.

The monitoring device 4 is a dedicated personal computer or the like having a monitor, and is a monitoring unit that manages and displays the power information of each branch circuit. The monitoring device 4 is connected to the power measuring instrument 3 via a network, collects data on the power usage of each load 5, and displays a graph or the like for data analysis. Then, the monitoring device 4 automatically records data on power usage every hour or day, for example, and collectively manages energy via a network connected to the power measuring instrument 3 to efficiently use power. Realize "visualization".

The load 5 is a lighting fixture having a drive voltage of 100 V or 200 V connected to a branch circuit, a personal computer, and various electric devices such as an air conditioner and an IH device.

Next, the functional configuration of the power measuring instrument 3 according to the present embodiment will be described with reference to FIG. The power measuring instrument 3 includes a current detection unit 31 that detects a current from the signal of the current transformer 2, a voltage detection unit 32 that detects a voltage signal of the circuit, and a current in the current detection unit 31 and a voltage in the voltage detection unit 32. A power calculation unit 33 that calculates power based on each signal is provided.

The current detection unit 31 is an adder circuit that adds a predetermined value to the burden resistor 311 inserted in the circuit connected to the current transformer 2, the filter 312 that passes the signal of the predetermined frequency band, and the current signal that has passed the filter 312. 313 is provided.

The voltage detection unit 32 is connected to the electric wire 7 via a breaker 6c or the like shown in FIG. 1 at a terminal, and includes a voltage step-down circuit 321, a filter 322, and an addition circuit 323. The voltage step-down circuit 321 steps down the voltage, the filter 322 passes a voltage signal in a predetermined frequency band, and the adder circuit 323 biases the voltage signal appropriately so that the voltage waveform is in the range of 0 to 5 V, for example. Call.

The power calculation unit 33 is supplied to the load 5 connected to the electric wire 7 to which the current transformer 2 is attached, based on the current measured by the current detection unit 31 and the voltage detected by the voltage detection unit 32. It is a microcomputer that calculates electric power. The power calculation unit 33 includes an A / D conversion unit 331, 332, a multiplication unit 333, a measurement control unit 334, and a transmission circuit unit 335.

The A / D conversion unit 331 converts the analog signal received from the voltage detection unit 32 into a digital signal. The A / D conversion unit 332 converts the analog signal received from the current detection unit 31 into a digital signal. The multiplication unit 333 is a circuit that multiplies the signals output from the A / D conversion units 331 and 332, that is, calculates the electric power (W). In this way, the power calculation unit 33 converts the voltage value and the current value from the analog signal to the digital signal, and performs the calculation processing with the digital value.

The measurement control unit 334 calculates the electric energy (W · s) obtained by integrating the power (W) calculated by the multiplication unit 333 in a predetermined time (for example, 10 ms). Further, in the measurement control unit 334, the calculated electric energy is set to a preset "predetermined threshold value T"._hIf it exceeds, the power value such as the power and the amount of power after that time is controlled to be output to the management device 4 or the like via the transmission circuit unit 335 as the measured power value. To do.

This "predetermined threshold T_hWas calculated by multiplying, for example, the "rated voltage (for example, 200V)" of the power measuring instrument 3 and the "predetermined ratio (for example, 0.3%) of the rated current (for example, 100A)" of the power measuring instrument 3. It becomes the amount of electric power. Therefore, the measurement control unit 334 uses the "predetermined ratio of rated current" used for the start determination of the conventional power calculation as the "predetermined threshold value T" in the power measuring instrument 3 according to the present embodiment._hCan be used for the calculation of. Therefore, it is possible to control the output of the measured power value at the same energization level without making the calculation circuit in the power calculation unit 33 unnecessarily complicated.

The measurement control unit 334 can perform the control with respect to the starting current. In this case, the measurement control unit 334 has noise resistance by using the control for preventing the dive of the power measuring instrument 3 and determining the starting current. Accurate dive prevention and starting current judgment can be performed.

The transmission circuit unit 335 has, for example, a two-wire serial communication circuit compliant with RS485 or the like, and transmits a measured power value to a monitoring device 4 capable of communicating with each other via a connected communication line.

Next, the voltage waveform, the current waveform, and the power waveform detected by the power measuring instrument 3 according to the present embodiment will be described with reference to FIGS. 3 to 5.

First, examples of voltage waveforms, current waveforms, and power waveforms in a state where a current of about 1 A is applied to the load 5 and no external noise is generated in the current detection unit 31 are shown in FIGS. 3 (a) to 3 (d). ). As shown in FIG. 3A, the voltage waveform input to the voltage detection unit 32 is a sinusoidal waveform having an effective value of AC voltage of 100 V and a frequency of 50 Hz. Further, as shown in FIG. 3B, the current waveform input from the current transformer 2 to the burden resistor 311 of the current detection unit 31 is a sinusoidal waveform having an effective value of AC current of 1A and a frequency of 50 Hz. Here, since the processing circuit of the current detection unit 31 is not affected by external noise, the current waveform input to the addition circuit 313 is the same waveform as that of FIG. 3 (b) as shown in FIG. 3 (c). Become. Next, the measurement control unit 334 (or the multiplication unit 333) calculates the power waveform shown in FIG. 3D based on the voltage value and the current value output from the A / D conversion units 331 and 332. In this case, the measurement control unit 334 sets the preset "predetermined threshold value T" for the amount of electric power (that is, the area indicated by the diagonal line A) in a predetermined time (for example, 20 ms)._h, So the output of the measured power value is controlled to start.

Next, FIGS. 4 (a) to 4 (e) show examples of a voltage waveform, a current waveform, and a power waveform in which external noise is superimposed on the current detection unit 31 when the load 5 is de-energized at 0 A. .. As shown in FIG. 4A, the voltage waveform input to the voltage detection unit 32 is a sinusoidal waveform having an effective value of AC voltage of 100 V and a frequency of 50 Hz. Further, as shown in FIG. 4B, the current waveform input from the current transformer 2 to the burden resistor 311 of the current detection unit 31 is not detected. Then, when external noise as shown in FIG. 4C is generated in the circuit of the current detection unit 31, the current waveform output from the current detection unit 31 is as shown in FIG. 4D, as shown in FIG. 4 (d). The current waveform is obtained by superimposing the noise shown in FIG. 4 (c) on the current waveform shown in b). Next, the measurement control unit 334 (or the multiplication unit 333) calculates the power waveform shown in FIG. 4 (e) based on the voltage waveform shown in FIG. 4 (a) and the current waveform shown in FIG. 4 (d). To do. In the power waveform shown in FIG. 4 (e), positive and negative values are randomly generated in the power, and the amount of power calculated in one cycle period (20 ms) (that is, the region indicated by the diagonal line B) is , It is canceled by plus or minus, and it becomes almost 0. Therefore, in the measurement control unit 334, the amount of electric power at a predetermined time is "a predetermined threshold value T."_hIs not exceeded, and the output control of the measured power value is not performed.

Next, FIGS. 5A to 5E show examples of a voltage waveform, a current waveform, and a power waveform in which external noise is superimposed on the current detection unit 31 when a minute current is applied to the load 5. Shown. As shown in FIG. 5A, the voltage waveform input to the voltage detection unit 32 is a sinusoidal waveform having an effective value of AC voltage of 100 V and a frequency of 50 Hz. Further, as shown in FIG. 5B, the current waveform input from the current transformer 2 to the burden resistor 311 of the current detection unit 31 has a minute wave height and is a sine waveform having a frequency of 50 Hz. Then, when external noise as shown in FIG. 5 (c) is generated in the circuit of the current detection unit 31, the current waveform output from the current detection unit 31 is as shown in FIG. 5 (d). The current waveform is obtained by superimposing the noise shown in FIG. 5 (c) on the current waveform shown in b). Next, the measurement control unit 334 (or the multiplication unit 333) has a power waveform as shown in FIG. 5 (e) based on the voltage waveform shown in FIG. 5 (a) and the current waveform shown in FIG. 5 (d). Is calculated. In this case, the measurement control unit 334 sets the preset "predetermined threshold value T" for the amount of electric power (that is, the area indicated by the diagonal line C) in a predetermined time (for example, 20 ms)._h, So the output of the measured power value is controlled to start.

Next, the operation procedure of the measurement control unit 334 will be described with reference to the flowchart shown in FIG. First, the measurement control unit 334 calculates the electric energy in a predetermined time based on the current value input from the current detection unit 31 and the voltage value input from the voltage detection unit 32 (S61). Next, in the measurement control unit 334, this electric energy amount is set to a predetermined threshold value T set in advance._h(S62), the threshold value T is determined._h(Yes in S62), the output of the measured power value is commanded (S63).

As described above, in the power measuring instrument 3 according to the present embodiment, the measurement control unit 334 has a power amount in a predetermined time and a predetermined threshold value T._hThe amount of electric power is a predetermined threshold value T_hIf it exceeds, the threshold T_hThe power value after that exceeds is controlled to be output as the measured power value. With this configuration, the power measuring instrument 3 can avoid the influence of noise superimposed on the current or voltage detection signal, and even if external noise or the like is superimposed on the current signal or voltage signal, a more accurate measured power value is output. it can.

(First modification) A first modification of the present embodiment will be described. In this modification 1, the measurement control unit 334 provided in the power measuring instrument 3 has a threshold value T._hThe rated voltage used in the calculation of is calculated based on the actual measured voltage value measured by the voltage detection unit 32.

Generally, the voltage fluctuates depending on the supply state from the electric power company, the type of the load 5, the measurement conditions, and the like. Therefore, some power measuring instruments 3 have a wide range of measured voltage (for example, 100 to 440 V). Therefore, in such a power measuring instrument 3, the threshold value T is based only on the preset rated voltage._hIf is set, the output control of the measured power value may not be performed accurately.

Therefore, in the present modification 1, the measurement control unit 334 determines the rated voltage based on the actual voltage value detected by the voltage detection unit 32, and sets the rated voltage to the predetermined threshold value T described above._hUsed for setting calculation of. In this way, the threshold value T is based on the actually measured rated voltage._hBy deriving the threshold value T_hCan be set more accurately. Further, since the rated voltage can be made to follow the actually measured voltage, the threshold value T_hCan be updated periodically, and a more accurate measured power value can be output based on the actual operation of the power measuring instrument 3.

(Second modification) A second modification of the present embodiment will be described. In the second modification, the measurement control unit 334 uses the threshold value T described above._hIn the calculation of, the value of the power factor based on the phase difference between the current waveform and the voltage waveform is multiplied.

This means that even if the voltage waveform and the current waveform are the same, the power value will be different when the phase θ of the voltage and the current is different, that is, when the power factor is different. Therefore, in the power measuring instrument 3 according to the present modification 2, "a predetermined threshold value T" is used._hBy multiplying the power factor in the setting calculation of "", the electric energy of the predetermined time calculated by the measurement control unit 334 and the "predetermined threshold value T"_hThe amount of deviation from "" can be reduced. Therefore, in the power measuring instrument 3 according to the present modification 2, a more accurate measured power value can be output based on the actual operation of the power measuring instrument 3.

(Third variant) A third modification of the present embodiment will be described. In the third modification, the measurement control unit 334 executes the output determination of the measured power value by the OR determination of the control shown in the first embodiment or the conventional control method. That is, the measurement control unit 334 further multiplies the current value detected by the current detection unit 31 by a predetermined ratio of the rated current of the power measuring instrument 3 to obtain another threshold value T._hTo determine. Then, in the measurement control unit 334, the current value is the threshold value T._hIf it exceeds, the threshold value T_hThe multiplication unit 333 and the like are controlled so as to output the power value after exceeding the above as the measured power value. Therefore, in the present modification 3, when noise does not occur in the current or the like, it can be basically based on the start determination of the conventional power calculation, and the calculation load in the power calculation unit 33 can be reduced.

The present invention is not limited to the configuration of the above embodiment, and various modifications can be made without changing the gist of the invention. Further, in order to achieve the above object, the present invention can be a power measurement method in which characteristic constituent means included in the power measuring instrument are steps, or can be realized as a program including those characteristic steps. .. The program is not only stored in a ROM or the like, but can also be distributed via a recording medium such as a USB memory or a communication network.

1 distribution board 2a, 2b current transformer 3 Power measuring instrument 4 Monitoring device 5 load 6a, 6b, 6c breaker 7 Electric wire 8 signal line 31 Current detector 32 Voltage detector 33 Power calculation unit 331,332 A / D converter 333 Multiplying part 334 Measurement control unit 335 Transmission circuit section S power measurement system