JPH0660915B2 - Reverse-phase current measuring device - Google Patents

Description

The present invention relates to an anti-phase current measuring device, and in particular, an anti-phase current measurement capable of accurately measuring an anti-phase current flowing through a three-phase AC circuit. It is related to the device.

[Conventional technology]

Generally, a three-phase balanced current usually flows in a three-phase AC circuit, but for example, when the load is unbalanced or an accident such as a short circuit or a ground fault occurs. A three-phase unbalanced current may flow to the generator in the circuit. The unbalanced current includes positive-phase, negative-phase, and zero-phase currents.The negative-phase current in this current causes eddy currents on the rotor surface of the generator. As a result, the rotor may be damaged or a torque having a frequency component twice the power supply frequency may be generated. When this reverse-phase current is excessive, the rotor burns out due to a significant temperature rise,
Alternatively, the rotor material may deteriorate. For this reason, measuring the reverse-phase current is an important technical matter in a three-phase AC circuit including a generator.

Now, the currents of the U, V, and W phases are _U , _V , and
_{Assuming W} , the anti-phase current ₂ is expressed by the following equation (1).

The above equation (1) is transformed into the following equation (2).

However, ₀ is for zero phase. Now, assuming that this zero-phase component ₀ is ignored, the following equation (3) is obtained.

FIG. 5 is a schematic configuration diagram of a conventional anti-phase current measuring device using an anti-phase filter for measuring the anti-phase current ₂ . A reverse-phase current measuring device of this type is described in, for example, Leaflet L-33401 (Mitsubishi TOQ-2-D type reverse-phase overcurrent relay) manufactured by Mitsubishi Electric Corporation. In FIG. 5, the U-phase coil (4) and the resistor (8) are provided on the first leg (1) of the iron core. A V-phase coil (5) is provided on one side (2A) of the second leg (2) of the iron core with a gap,
A W-phase coil (6) is provided on the other side (2B). An output coil (7) is provided on the third leg (3) of the iron core.

Next, the operation will be described. The anti-phase filter in the above conventional example is designed to obtain an output proportional to the anti-phase current ₂ by generating the sum of the component proportional to _U and the component proportional to j ( _V − _W ). is there. In the conventional example shown in FIG. 5, a magnetic flux having the same phase as _U is generated in the iron core first leg (1) provided with the U-phase coil (4). Further, the V-phase coil (5) provided on one side (2A) of the iron core second leg (2) and the W-phase coil (6) provided on the other side (2B) are opposite to each other. Since it is wound in the opposite direction, a magnetic flux proportional to j ( _V - _W ) is generated in it.

Therefore, since both the magnetic flux proportional to _U and the magnetic flux proportional to j ( _V − _W ) pass through the third leg of the iron core (3), it is wound around the third leg of the iron core (3). A voltage proportional to the combined magnetic flux will be induced in the output coil (7).

[Problems to be solved by the invention]

The conventional anti-phase current measuring device has the above-mentioned configuration, and a part of the magnetic flux generated by the U-phase coil (4) leaks to the iron core second leg (2) and the V-phase coil ( 5) and part of the magnetic flux generated by the W-phase coil (6) is the first leg (1) of the iron core.
The magnetic flux passing through the third leg (3) of the iron core is no longer exactly proportional to the anti-phase current. For example, even if the anti-phase current is set to zero and only the positive-phase current is applied, the magnetic resistance is reduced. Since there is an imbalance in the core, some magnetic flux passes through the third leg (3) of the iron core, and a voltage is output as if a reverse-phase current were present. Therefore, there is a problem that the measurement error becomes large in the range where the reverse-phase current is small.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to obtain an anti-phase current measuring device capable of accurately measuring an anti-phase current flowing through a three-phase AC circuit. .

Further, in addition to the above-mentioned object, another invention of the present invention is an anti-phase system which eliminates an error based on distortion of a current waveform when a three-phase alternating current from a measurement object contains a harmonic component. The purpose is to obtain a current measuring device.

[Means for solving problems]

An anti-phase current measuring device according to the present invention includes an AD converter that samples a three-phase alternating current from a measurement target at a predetermined time interval and converts it into corresponding digital data, and a three-phase alternating current in one cycle. Select the maximum digital data as the peak value data, calculate the phase angle data between each phase based on the apex angle of the triangle having the peak value data of each phase as three sides, and to the peak value data and the phase value data. It is provided with a digital processing device for calculating the anti-phase current based on the above.

Further, a negative-phase current measuring device according to another invention of the present invention,
In the above, a low-pass filter for individually removing the harmonic components of the three-phase alternating current from the measurement target is provided.

[Work]

According to the present invention, the maximum digital data in one cycle of the three-phase alternating current is selected as the peak value data by the digital processing device, and the peak value data of each phase is based on the apex angle of a triangle having three sides. Then, the phase angle data between each phase is calculated, and the anti-phase current is calculated based on the peak value data and the phase angle data.

Further, according to another invention of the present invention, prior to the selection of the current peak value data, the harmonic component contained in the three-phase alternating current from the measurement target is removed.

〔Example〕

FIG. 1 is a block diagram showing a schematic configuration of an anti-phase current measuring device according to an embodiment of the present invention. In FIG. 1, (11) is an AD converter and each phase current is inputted.
_For digital transformation of _U , _V , _W , (1
2) is a digital computer in which a required data processing program is incorporated, and (13) is a storage device for storing data to be processed and data as a result of the processing.
Reference numeral (14) is a printing device, for example, for printing out the resulting data. The digital processing apparatus according to the present invention comprises a digital computer (12) and a storage device (13) in this embodiment. FIG. 2 is a flow chart for explaining the data processing program executed in the above embodiment. In FIG. 2, the current peak value is detected in step (S50), the current phase angle based on the current peak value is calculated in step (S51), and then the current peak value and the current are calculated in step (S52). The required anti-phase current is calculated from the data of both the phase angle. FIG. 3 is a vector diagram of a three-phase alternating current for explaining the operation of the above embodiment.

Next, the operation of the above embodiment will be described. The three-phase alternating current ( _U , _V , _W ) from the measurement target is set to an appropriate level via, for example, an appropriate current transformer (not shown). These three-phase AC currents ( _U , _V , _W ,)
The converter (11) samples at a predetermined time interval and converts it into a corresponding digital amount. Here, in step (S50) of FIG. 2, the current peak value is detected in a so-called peak hold mode. That is, it is determined whether the new data output from the AD converter (11) with the predetermined sampling period is larger than the currently held data, and the maximum at that time is determined. Data will be retained. Crest value data for each phase obtained in this way | I
_U |, | I _V |, | I _W | is used in step (S51). By the way, there is a relationship between these three-phase alternating currents (ignoring the zero-phase current) as shown in the vector diagram of FIG. In FIG. 3, the vector of each phase current forms a triangle, and when their crest values, that is, the lengths of the three sides of the triangle are known, the apex angle of the triangle is It is given by equation (4).

Now, assuming that the U-phase current vector _U is taken as the angle reference, the phase angle θ _UW between _U and _W or _U and _V
The phase angle θ _{UV between and} is given by the following equation (5).

The peak value data and the phase angle data thus obtained are used in step (S52). Here, if _U is taken as the angle reference, the above equation (1) for the negative phase current ₂ is expressed as the following equation (6).

The peak value | I ₂ | of the anti-phase current I ₂ is expressed by the following equation (7).

here, In step (S52) of FIG. 2, the calculation of the above equation (7) is performed, and the peak value | I ₂ | and the effective value are calculated for each cycle of the negative phase current _2. Will be calculated.

The storage device (13) stores the required data such as the peak value of each phase current and the negative phase current. These data are used for the analysis of the time course of the negative phase current and various average values. , Used for statistical processing to calculate standard deviation, etc.

Further, the printing device (14) prints out the reverse phase current value and other required data obtained in this way at appropriate time intervals.

FIG. 4 is a block diagram showing a schematic configuration of a reverse phase current measuring device according to another embodiment of the present invention. In FIG. 4, a low-pass filter (40) is provided between the object to be measured (not shown) and the AD converter (11) for each three-phase AC current supply line. This is similar to that of the embodiment of the present invention in FIG. Some measurement targets include harmonic sources such as power transistors and thyristors. In such a case, the three-phase AC current may be distorted and the final measurement result may be incorrect. . The other embodiments described above are for dealing with such a case.

〔The invention's effect〕

As described above, the negative-phase current measuring device according to the present invention samples the three-phase alternating current from the measurement object at predetermined time intervals and converts it into corresponding digital data.
The D converter and the maximum digital data in one cycle of the three-phase alternating current are selected as the peak value data, and the phase between the phases is based on the apex angle of the triangle having the peak value data of each phase as three sides. Since the digital processing device for calculating the angle data and calculating the anti-phase current based on the peak value data and the phase angle data is provided, the anti-phase current can be accurately measured, and the power generation in the three-phase AC circuit can be performed. If the damage to the machine can be prevented in advance, it has an effect.

Further, according to another invention of the present invention, by providing the low-pass filter in the preceding stage of the AD converter, it is possible to remove harmful harmonic components generated from the measurement target,
It is possible to prevent the occurrence of errors and the deterioration of accuracy due to the mixing of harmonic components.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a reverse phase flow measuring device according to an embodiment of the present invention, and FIG. 2 is a flow chart diagram for explaining a data processing program executed in the above embodiment. , FIG. 3 is a vector diagram of a three-phase alternating current for explaining the operation of the above embodiment, and FIG.
FIG. 5 is a block diagram showing a schematic configuration of an anti-phase current measuring device according to another embodiment of the present invention, and FIG. 5 is a block diagram showing a schematic configuration of a conventional anti-phase current measuring device. (11) is an AD converter, (12) is a digital calculator, (1
3) is a storage device, (14) is a printing device, and (40) is a low-pass filter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-59175 (JP, A) JP-A-57-199422 (JP, A) JP-B-56-35825 (JP, B2)

Claims (2)

[Claims] 1. An AD converter for sampling a three-phase alternating current from a measurement object at predetermined time intervals and converting it into corresponding digital data, and a maximum digital data in one cycle of the three-phase alternating current. Select as high-value data, calculate the phase angle data between each phase based on the apex angle of the triangle having the crest value data of each phase as three sides, and calculate the anti-phase current based on the crest value data and the phase angle data. An anti-phase current measuring device having a digital processing device for calculating. 2. A low-pass filter for individually removing harmonic components of a three-phase alternating current from a measurement target, and an AD conversion for sampling the output current from the low-pass filter at predetermined time intervals and converting it into corresponding digital data. And the maximum digital data in one cycle of the three-phase alternating current is selected as the peak value data, and the phase angle data between the phases based on the apex angle of the triangle having the peak value data of each phase as three sides. And a digital processing device for calculating an anti-phase current based on the peak value data and the phase angle data.