JPH0246206Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to an open phase detection circuit that detects a disconnection of a coil in a three-phase motor, a disconnection of a lead wire, an open phase on the power supply side, etc.

B. Prior Art Generally, phase loss in a three-phase alternating current, such as in a motor, is detected by a circuit shown in FIG. In the figure, the outputs of current transformers T1, T2, and T3 that detect the current level of each phase are half-wave rectified by rectifiers D1, D2, and D3.
After being smoothed by smoothing circuits S1, S2, and S3,
Maximum value detection circuit M and comparators C1, C
2. The levels are compared with each other by C3, and the level of the smoothing circuit output of at least one phase is higher than the voltage obtained by dividing the maximum voltage Vmax of the three phases at a fixed ratio (usually set to 0.55 to 0.65). If the ratio is less than 0.55 to 0.65, the output of one of the comparators C1, C2, and C3 becomes H level, and it is determined that an open phase occurs. In the figure, R
1 and R2 are voltage dividing resistors. The conventional example shown in FIG. 5 has the following problems. In other words, the positional relationship between the current transformer and the disconnection point is the current transformer T1 and disconnection A in the Y connection in Figure 2a, or the positional relationship between the current transformer and the disconnection point in Figure 2b.
T1 and disconnection B in the Δ connection, or c in the same figure
In the case of T1 and disconnection E, the current level detected at T1 is zero, so it is extremely easy to determine an open phase. However, in a delta connection, the line current is detected by a current transformer. In case of internal disconnection i.e. second
In the case of the relationship between T1 and disconnection C in Figure b, or the relationship between T1 and disconnection D in Figure 2c, which is an external disconnection when detecting a phase current, current transformers T1, T2, Since an unbalanced current flows through T3 and only causes a difference in the current level of each current transformer, the standard for the phase ratio is set so that disconnection can be detected even in such a case. In that case, there was a problem that malfunctions were likely to occur when the power supply voltage varied. In particular, with the recent spread of coolers, the use of delta-connected motors has increased, and the power consumption has also increased, causing the power supply situation to worsen and the incidence of voltage imbalance at the receiving end to increase. Even if the voltage unbalance is only a few percent on the power supply side, the current unbalance rate can reach several tens of percent, so with the setting ratio as described above, there was a risk that this power supply fluctuation would be detected as an open phase.

As a countermeasure, as shown in Fig. 6, a switch SW is provided to switch the voltage dividing resistors R1 and R1'.
A method is used to prevent power supply fluctuations from being misinterpreted as an open phase by lowering the set ratio to approximately 0.1 when the power supply situation worsens. However, in this case, there was a drawback that an open phase in which one phase did not become zero, ie, a disconnection at C or D in FIG. 2, could not be detected.

C. Purpose The purpose of the present invention is to solve the above-mentioned problems and provide an open phase detection circuit that can detect an open phase without malfunctioning even if the power supply situation worsens.

D. Configuration The present invention includes a current transformer that detects the current level of each phase of a three-phase alternating current, a smoothing circuit that smoothes the rectified output of each current transformer, and a smoothing circuit that detects the maximum value of each smoothed output. It is equipped with a maximum value detection circuit and a comparator that compares the divided voltage of the maximum value detection circuit output with each of the above-mentioned smoothed outputs, and the smoothed output of at least one phase becomes lower than the above-mentioned divided voltage due to the occurrence of an open phase. In addition to the conventional circuit shown in FIG. 5, which is configured so that an open phase detection signal is output from the comparator when This circuit is equipped with an exclusive OR circuit that receives as input, a one-shot circuit that is triggered by the output of the exclusive OR circuit, and an OR circuit that receives the output of the one-shot circuit and the output of each comparator as input. By taking advantage of the fact that the currents in each phase are in the same phase or out of phase when the wire is disconnected as shown in D in Figure 2, and by monitoring the phase relationship of each phase, the system can be used without being affected by fluctuations in the current level. This makes it possible to detect phase loss.

E. Embodiment FIG. 1 shows an embodiment of the circuit of the present invention. In the figure, the outputs of current transformers T1, T2, and T3 that detect the current level of each phase of three-phase AC are half-wave rectified by rectifiers D1, D2, and D3, and are further smoothed by smoothing circuits S1, S2, and S3. is input into the maximum value detection circuit M. Maximum value detection circuit M
is the maximum level of the smoothed output.
Vmax is output, and this is divided into approximately 1/10 by voltage dividing resistors R1 and R2, and each comparator C1,
It serves as a reference voltage for C2 and C3. Each smoothed output is input to the other inputs of each comparator C1, C2, and C3. The configuration up to this point is exactly the same as the conventional example shown in Figure 5, except that the partial pressure ratio is 0.55 to 0.55.
The difference is that it is smaller than 0.66 but about 01. In the present invention, the rectifiers D1, D2,
Waveform shaping circuits H1 and H2 that shape the signal voltages of arbitrary two phases among the outputs of D3, an exclusive OR circuit E whose inputs are the outputs of both waveform shaping circuits H1 and H2, and exclusive OR A one-shot circuit W triggered by the output of the circuit E is provided, and the output of the one-shot circuit W and each of the above comparators C1,
The output of the OR circuit G which inputs the outputs of C2 and C3 is used as an open phase detection signal.

3 and 4 illustrate the operation of the circuit of the present invention. In FIG. 3, a shows the output of the waveform shaping circuit when there is no open phase, and the waveforms of each phase have a phase difference of 120° from each other. Third
Figures b to e show the output of the waveform shaping circuit in each case of open phase in Figure 2, where b is the case of disconnection A or B and the current level of one phase is zero, and c is the state where the current level of one phase is zero. In case C, the phase relationship of each phase is the same as a with no open phase, and in case d, the current flowing through each current transformer T1, T2, T3 is
It shows the state of being in phase or out of phase (in the figure, T1 and T2 are in phase and T3 is out of phase),
In case E, one phase is zero. For A, B, and E, where at least one phase is zero, it is possible to detect phase loss with a comparator circuit that sets the voltage dividing ratio of voltage dividing resistors R1 and R2 sufficiently small (approximately 0.1), and the problem can be solved. is the case of disconnections C and D, but as mentioned above, the phase relationship in C is the same as in case a without open phase, so detection is impossible, so the connection in Figure 2 b is useless. I'll make sure there aren't any. That is, when the motor is connected in a delta connection, the current transformers T1, T2, and T3 may be connected as shown in FIG. 2c. Furthermore, in the case of D, the three phases are in phase or out of phase, so by detecting this, it is possible to detect an open phase regardless of the current level.

Figure 4 shows the voltage waveforms at points A, B, C, and D in Figure 1 for each case D, and Figures a and b show the case where point D is disconnected. There is. When the two phases are in phase a, the output C of the exclusive OR circuit E becomes L level, and when the two phases are out of phase, the exclusive OR output C becomes H level as shown in figure b. Therefore, in either case a or b, no trigger signal is input to the one-shot circuit W, and its output D remains at the L level. Figure c shows the normal state, that is, the case where there is a phase difference between each phase, and the exclusive OR output C repeats HL at twice the frequency of the power supply, and Figure d shows the case where there is a phase difference between each phase.
This shows the case of E, where the exclusive OR output C repeats HL at the power supply frequency. Therefore, by setting the time constant of the one-shot circuit W to be slightly longer than the period of the power supply, the output of the one-shot circuit W can be maintained at the H level in cases other than case D of open phase. Note that the inverter I inserted on the output side of the one-shot circuit W is for inverting the one-shot output to match the logical value with the outputs of the comparators C1, C2, and C3; however, if the output of the one-shot circuit is used, this inverter can be omitted.

Effects According to the present invention, as mentioned above, in the case of an open phase where the current level of one phase becomes zero, the threshold value for determining the open phase can be lowered, and the phase current in the delta connection can be lowered. If there is an external disconnection during detection, 2 will be detected.
Phase loss can be detected regardless of the current level by utilizing the fact that the phases are in phase or out of phase, so malfunctions due to fluctuations in power supply voltage or drop in power factor can be prevented regardless of the wiring method. It has the advantage of being possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
Figures 2 a, b, and c are connection diagrams showing various cases of open phase, Figures 3 a to e are waveform diagrams for each case in Figure 2, and Figures 4 a to d are diagrams of each part in Figure 1. FIG. 5 is a block diagram of a conventional example, and FIG. 6 is a block diagram of another conventional example. T1, T2, T3...Current transformer, D1, D2, D
3... Rectifier, S1, S2, S3... Smoothing circuit,
M... Maximum value detection circuit, R1, R2... Voltage dividing resistor, C1, C2, C3... Comparator, H1,
H2... Waveform shaping circuit, E... Exclusive OR circuit, W... One shot circuit, I... Inverter, G... OR circuit.

Claims (1)

[Scope of utility model registration request] A current transformer that detects the current level of each phase of three-phase AC, a smoothing circuit that smoothes the half-wave rectified output of each current transformer, and a maximum value detection circuit that detects the maximum value of each smoothed output. , a comparator that compares the divided voltage of the maximum value detection circuit output and each smoothed output, means for detecting when any two phases are in phase or opposite phases, and the detection output of the means and the output of each of the above-mentioned comparators. 1. An open phase detection circuit comprising: an OR circuit whose input is an OR circuit.