JPH07134154A - Abnormal current detecting device for three-phase load - Google Patents

Abstract

PURPOSE:To precisely detect an interruption even when the current carried to a load is low. CONSTITUTION:The load current of a motor 1 is detected by transformers 2a-2c, the secondary currents of the transformers 2a-2c are subjected to three- phase full-wave rectification to generate a voltage in a resistor 5, which is then amplified by an amplifier 12, and converted into a digital voltage by an A/D converter 15, and reed relays 10a, 11 are ON/OFF according to the digital voltage to change the amplification factor of the amplifier 2. A DC voltage is generated from a DC generator 18 according to this digital voltage, the DC voltage is compared with the output voltage of the amplifier 12 by a comparing circuit 19, and an interruption is detected by the ON/OFF time ratio K2 of the output voltage of the comparing circuit 19, whereby the interruption can be precisely detected even when the load current carried to the motor 1 is low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormal current detector for a three-phase load, and more particularly to an improved detection of an open phase and an unbalanced load current of a three-phase load.

[0002]

2. Description of the Related Art A conventional three-phase load abnormal current detecting device is disclosed in Japanese Utility Model Publication No. 62-1159. In FIG. 9 showing this, R1 to R15 are resistors, 2a and 2c are current transformers, TR1 to TR4 are transistors, IC1 to IC3 are AND elements, IC4 is an OR element, IC5 is a comparison element, C1 to
C5 is a capacitor, RA is a relay, and E is a DC power source. The resistor R9 and the capacitor C1 form an integrating circuit, and the resistor R10 and the capacitor C2 form a differentiating circuit.

Next, the operation of the conventional three-phase load abnormal current detection device will be described. Now, when the load current is a balanced three-phase current, the overlapping angle of each phase is 60 °, and V4 of FIG.
As described above, the signals are turned on and off every 60 ° and converted into a triangular wave like V5 by the integrating circuit, and only the ripple voltage is detected by the differentiating circuit. The ripple voltage and the reference voltage are compared by the comparison element IC5, but since the reference voltage is higher, the transistor TR4 remains off.

Next, when the S phase is missing, the voltages V1 and V3
Becomes the same phase and the overlapping angle of each phase is 18 as shown in Fig. 10 (b).
It becomes 0 °. Therefore, the integrating circuit converts it into a triangular wave like V5, and only the ripple voltage is detected by the differentiating circuit. However, the ripple voltage is larger than in the case of the balanced three-phase current, so that the transistor TR4 is turned on and the open phase signal is output. It

When the phases of the three-phase currents are unbalanced, FIG.
Since the ripple voltage is larger than the balanced three-phase current as shown in (c), the transistor TR4 is turned on and the open phase signal is output.

However, since the voltage VR1 is generated across the resistor R1 by the output current of the current transformer and the current flows through the resistors R3 to R5 based on the voltage VR1, the transistor TR1 is used.
The base current IB1 of 1 is (VR1-VBE) / R3. Here, VBE indicates the base-emitter voltage of the transistor TR1. Therefore, at least in the range of VR1 <VBE,
Since the output current of the current transformer cannot be detected at all, accurate phase loss determination could not be performed. Furthermore, when the output current of the current transformer is very small, the base currents of the transistors TR1 to TR5 cannot be made to flow sufficiently, so that the transistors TR1 to TR5 cannot be used in the saturation region, and it is difficult to accurately determine the phase loss. Met.

Further, since the load current value itself is not detected by detecting the overlapping angle of the phase currents, it cannot be detected that the load current becomes an overcurrent.

Further, since the overlapping angle of each phase current is detected, it is difficult to detect when the phases of the load currents are the same and only the current values are unbalanced.

Further, since the ripple voltage is detected by the integrating circuit, it takes a long time to determine the open phase and unbalance of the load current.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional device. Even when the load current is considerably lower than the primary side rated current of the current transformer, the load current It is to detect open phase and unbalance accurately.

Another object is to easily detect the load current value at the same time while detecting open phase and unbalance of the load current.

Still another object is to easily detect that the load current values are unbalanced.

Another object is to detect open phase and unbalance of the load current at high speed.

[0014]

An abnormal current detection device for a three-phase load according to a first aspect of the present invention is an abnormal current for a three-phase load in which an abnormal current flowing from a three-phase AC power source to a three-phase load is detected by a current transformer. In the detection device, a three-phase full-wave rectification circuit for three-phase full-wave rectification of the secondary side current of the current transformer, an amplification means for amplifying the output voltage of the three-phase full-wave rectification circuit, and an output voltage of the amplifier are provided. A / D conversion means for digital conversion, amplification factor changing means for changing the amplification factor of the amplifier according to the output voltage value of the A / D conversion means, and DC voltage according to the output voltage value of the conversion means A direct current generating means for generating and a comparing means for comparing the output voltage of the amplifying means with the output voltage of the direct current generating means are provided, and an abnormal current flowing in the three-phase load is determined by the output waveform of the comparing means. It is what

A three-phase load abnormal current detection device according to a second aspect of the invention is a three-phase load abnormal current detection device in which an abnormal current flowing from a three-phase AC power source to a three-phase load is detected by a current transformer. A three-phase half-wave rectifying circuit for rectifying the secondary side current of the current transformer into a three-phase half-wave rectifying circuit, an amplifying means for amplifying the output voltage of the three-phase half-wave rectifying circuit, and an A / for digitally converting the output voltage of the amplifying means. D conversion means, amplification factor changing means for changing the amplification factor of the amplification means according to the output voltage value of the A / D conversion means, and DC voltage generated according to the output voltage value of the A / D conversion means And a comparison means for comparing the output voltage of the amplification means with the output voltage of the DC generation means, and an abnormal current flowing through the three-phase load is determined by the output waveform of the comparison means. To do.

A three-phase load abnormal current detecting device according to a third aspect of the present invention is a three-phase load abnormal current detecting device in which an abnormal current flowing from a three-phase AC power source to a three-phase load is detected by a current transformer. A three-phase full-wave rectifier circuit for rectifying the secondary current of the current transformer into a three-phase full-wave rectification circuit, an amplification means for amplifying the output voltage of the three-phase full-wave rectification circuit, and an A / D for digitally converting the output voltage of the amplifier. Conversion means, and voltage detection means for detecting that the output voltage value of the A / D conversion means is greater than or equal to a predetermined value,
Amplification factor changing means for changing the amplification factor of the amplifying means by the operation of the voltage detecting means, DC generating means for generating a DC voltage according to the output voltage value of the converting means, output voltage of the amplifying means and DC And comparing means for comparing the output voltages of the generating means, and determining an abnormal current flowing in the three-phase load based on the output waveform of the comparing means.

A three-phase load abnormal current detection device according to a fourth aspect of the present invention is a three-phase load abnormal current detection device in which an abnormal current flowing from a three-phase AC power source to a three-phase load is detected by a current transformer. A three-phase full-wave rectifier circuit for three-phase full-wave rectifying the secondary current of the current transformer, an amplifying means for amplifying the output voltage of the three-phase full-wave rectifying circuit, and an A / for digitally converting the output voltage of the amplifying means. D conversion means and amplification rate changing means for changing the amplification rate of the amplification means according to the output voltage value of the A / D conversion means are provided, and the output from the A / D conversion means flows to the three-phase load. It is characterized in that the current is calculated.

[0018]

According to the three-phase load abnormal current detection device of the first aspect of the invention, the three-phase full-wave rectifier circuit rectifies the secondary side current of the current transformer into three-phase full-wave rectification, and the amplifying means includes the three-phase full-wave rectification The output voltage of the wave rectifier circuit is amplified, the A / D conversion means digitally converts the output voltage of the amplifier, and the amplification factor changing means changes the amplification factor of the amplifier according to the output voltage value of the A / D converter, DC generating means is A
A DC voltage is generated according to the output voltage value of the D / D converter, and the comparing means compares the output voltage of the amplifier with the output voltage of the DC generator to determine an abnormal current flowing in the three-phase load based on the output waveform of the comparison circuit. To do.

According to the three-phase load abnormal current detection device of the second aspect of the invention, the three-phase half-wave rectifier circuit rectifies the secondary side current of the current transformer by three-phase half-wave, and the amplifier three-phase half-wave. Except for amplifying the output voltage of the rectifier circuit, the same operation as the above is achieved.

According to the three-phase load abnormal current detection device of the third aspect of the invention, the voltage detection means detects that the output voltage value of the A / D conversion means is equal to or higher than a predetermined value, and the amplification factor changing means Except that the amplification factor of the amplifier is changed by the operation of the voltage detecting means, the same operation as the operation according to the first invention is achieved.

According to the abnormal current detection device for a three-phase load of the fourth invention, the current flowing through the three-phase AC induction motor from the output of the A / D converter is calculated. The effect is almost the same as the effect.

[0022]

【Example】

Example 1. Hereinafter, the present invention will be described based on embodiments shown in the drawings. In the drawings, the same reference numerals as those used in the related art indicate the same or corresponding portions. In FIG. 1, reference numeral 1 is a load device connected to a three-phase AC power supply consisting of R-phase, S-phase, and T-phase, which is a three-phase AC induction motor (hereinafter referred to as a motor), and such a motor is generally referred to as three-phase. The load. Reference numerals 2a to 2c are current transformers for transmitting the currents flowing in the R, S, and T phases of the motor 1 to the secondary side at a predetermined current transformation ratio Kc.
Are connected in common at one end to form a star connection. Four
Is a three-phase full-wave rectification circuit consisting of diodes D1 to D6, and the output terminals of the current transformers 2a to 2c are diodes D1 and D, respectively.
2, connected to the anode side of D3. Reference numeral 5 is a resistor connected to the output of the three-phase full-wave rectification circuit 4, 6a is an operational amplifier element, the non-inverting input terminal is connected to one end of the resistor 5, and the inverting input terminal is the resistors 6, 8 , One end of 9,
A resistor 7 and a normally open contact 10 are connected to the output terminal of the operational amplification element 6a.
One end of a and 11a is connected and the other end of the resistor 7 is connected to the inverting terminal. The operational amplification element 6a and the resistors 7 to 9 constitute an amplifier 12 for amplifying the voltage across the resistor 5, and at the same time, the amplification factor changing means for changing the amplification factor α of the amplifier 12 by opening / closing the normally open contacts 10a, 11a. Are configured. The resistors 5 to 9 have resistance values R5 to R9, respectively.

Reed relays 10 and 11 respectively have normally-open contacts 10a and 11a. One end of the coil is grounded and the other end is connected to the drive circuits 13 and 14, respectively.
The other ends of the drive circuits 13 and 14 are the microcomputer 16
(Hereinafter, referred to as "microcomputer".) Interfaces (hereinafter, referred to as "I / F") 16d and 16e. Also, an amplification rate α which is a ratio of the input voltage Vi12 and the output voltage Vo12 of the amplifier 12. Is configured to have the following three types of amplification factors: First, the amplification factor αoff when the normally open contacts 10a and 11a are off is (R6 + R7) / R6,
The amplification factor α10on when the normally open contact 10a is on and the normally open contact 11a is off is (R6 + R7 // R8) / R6. The symbol // indicates a combined resistance in which the resistances are connected in parallel. That is, the combined resistance Rc is (R7R8) / (R7 + R8). Further, when the normally open contacts 10a and 11a are on, αon = (R6 + R7 // R8 // R9) / R6. Therefore, the amplification factor α has a relationship of αoff>α10on> αon.

Reference numeral 15 is an A / D converter having one end connected to the output end of the amplifier 12 and the other end connected to the I / F 16a,
Reference numeral 18 denotes a DC generator, the input terminal of which is connected to the I / F 16c, and is configured to generate a variable DC voltage that changes according to the output voltage value of the A / D converter 15. The inverting terminal of the operational amplification element 19 is connected to the output terminal of the amplifier 12, and the non-inverting terminal is connected to the output of the DC generator 18, forming a comparison circuit. The DC voltage Vdc generated from the DC generator 18 has the following relationship with the output voltage Vo12 of the amplifier 12. Amplifier 1 when three-phase balanced
Since the output voltage Vo12 of No. 2 is the same as the output waveform of the three-phase full wave as shown in FIG. 3 (b), the maximum value Vo12max and the minimum value Vo12min of the output voltage are Vo12min = (√3 / 2) Vo12max. Become. Therefore, Vdc = kVo12 and k <(√3 / 2). Actually, the k is determined in consideration of the power supply voltage fluctuation of the three-phase AC power supply.

Next, the operation of the first embodiment will be described with reference to FIGS. First, the case where a three-phase balanced current flows will be described. In FIG. 1, when the operation of the motor 1 is started, a load current flows from the three-phase AC power supply to the motor 1 and the load currents ILr, I of the R, S, T phases are changed by the current transformers 2a to 2c.
The current is transmitted to the secondary side by detecting Ls and ILt. The secondary currents ILr2, ILs2, ILt2 are the load currents IL on the primary side multiplied by Kc. Kc is a current transformation ratio, and if the primary side rated current is IN1 and the secondary side rated current is IN2, Kc = IN2
/ IN1. Secondary current I to the input of the three-phase full-wave rectifier circuit 4
Lr2, ILs2, and ILt2 flow, and in the section of 0 to π / 3, D1 of the diode D1, D3, and D5 group is similarly D
Since D6 of 2, D4 and D6 group is conducting, three-phase full-wave rectifier circuit 4
Output current Id is Id = iLr2-iLs2. ILr
2 and iLs2 represent vector representations of ILr2 and ILs2, respectively. Here, assuming that the reference vector is iLr2 = I, ILs2 is Iε- ^{j2 / 3π} . Therefore, the output current Id is Id = I-
Iε- ^{j2 / 3π} . When the output current Id flows through the resistor 5 and the voltage across the resistor 5 is Vr5, Vr5 = IdR5. Note that the output current Id is the current in the section of 0 to π / 3, and the output current Id is set every π / 3 section.
Flows.

Since the voltage Vr5 is input as the differential voltage of the operational amplification element 6a, the output voltage Vo12 of the amplifier 12 is Vo.
12 = αVr5, and the output voltage waveform becomes as shown in FIG. 3 (b). As shown in FIGS. 1 and 2, the output voltage Vo12 is A /
The D converter 15 reads the data every sampling time ts and converts it into a digital voltage value VDo, and at the same time I / F 16a
It is read into the microcomputer 16 through (step 101). The read duration tr is the frequency cycle of the three-phase AC power supply. The reading duration tr is the sampling time ts
, There is a relation of tr> ts. The digital voltage value Vdo is compared with a predetermined reference voltage value Vp (step 102). If Vdo> Vp as a result of the comparison, it is judged whether the reed relays 10 and 11 are off (step 103),
If it is in the off state, the reed relay 10 is turned on to close the normally open contact 10a to lower the amplification factor α10on, lower the output voltage V012, and lower the digital output voltage value VDo (step 104). Output voltage Vo12 is again A /
The digital voltage value VDo converted by the D converter 15 is read into the microcomputer 16 through the I / F 16a (step 101). The digital voltage value Vdo is compared with a predetermined reference voltage value Vp (step 102). If Vdo> Vp as a result of the comparison, it is judged whether the reed relay 11 is in the off state (step 105). If it is in the off state, the drive circuit 13 is operated to turn on the reed relay 11 and the amplification factor α.
It is further reduced as on, to the output voltage Vo12, and the digital output voltage value VDo is lowered (step 10).
6).

Next, the microcomputer 16 causes the digital voltage value V
Input a digital voltage to the DC generator 18 according to do,
As shown in FIG. 3 (c), the DC voltage Vdc is applied from the DC generator 18.
Is generated (step 107), the comparison circuit 17 compares the DC voltage Vdc with the output voltage Vo12 of the amplifier 12, and Vo12> Vdc. Therefore, as shown in FIG.
A DC output voltage Voc is generated from 7. The output voltage Voc is read into the microcomputer 16 (step 108). The microcomputer 16 determines whether the output voltage Voc is normal, that is, whether the on / off time ratio K2 = Ton / Toff becomes ∞ (step 109). Here, Ton means an H level voltage period, and Toff means an L level voltage period. Since the DC voltage is only Ton and Toff does not exist during three-phase balance, the on / off time ratio K2 becomes ∞, and it is determined that a normal three-phase balanced current is flowing to the motor 1 (step 111). First, the output voltage Vo12 of the amplifier 12 is converted from the digital voltage value Vdo to calculate the load current IL by the following equation. IL = Vo12 / (1-
ε- ^{j2 / 3π} ) × (1 / α) (step 115). The load current IL is the digital voltage value Vdo and the amplification factor αo.
A load current IL is obtained by providing a RAM having three types of current tables corresponding to ff, α10on, and αon, determining the RAM address by the digital voltage value Vdo and the amplification factor, and reading the contents stored in the RAM by the address. May be. As a result, the processing time is shortened as compared with the above example.

Further, when the output voltage of the amplifier 12 is equal to or higher than a predetermined value, the reason why the amplification factor α is decreased is to operate the operational amplification element 6a without saturating it and maintain the linearity. This is to increase the resolution of the A / D converter 15. That is, even if the number of bits of the A / D converter 15 is increased, the resolution cannot be increased if the input voltage is operated at a low level. The load current of the motor 1 can be normally detected by maintaining the linearity.

Further, the amplification factor of the amplifier 12 corresponding to the current corresponding to the operation of the motor 1 is set in advance and the amplification factor closest to the amplification factor is selected. Based on the selection, the on / off states of the switches 10 and 11 in the initial stage are set. Therefore, the settings of the switches 10 and 11 can be omitted.

Now, the operation when the S phase is lost will be described. In such a case, this is the same as applying a single-phase AC voltage between the R and T terminals, and the R-phase and T-phase current values and phases are the same. Therefore, the detected current of the current transformers 2a and 2c is IL
Then, the voltage across resistor 5 is Vr5 in the interval of 0 to π.
= KcR5ILsinθ, and the output voltage Vo12 of the amplifier 12
Becomes αVr5. That is, it becomes a single-phase full-wave waveform as shown in FIG. Vr5 is amplified by the amplifier 12, and steps 101 to 108 in the flowchart of FIG.
To execute. Since the output of the DC generator 18 is as shown in FIG. 3 (c), the output waveform of the comparison circuit 17 is as shown in FIG. 3 (d). From the value of the output voltage, the on / off time ratio K2 =
Ton / Toff is calculated to determine whether K2 is ∞ (step 109). In the case of the phase loss, the on / off time ratio K2 is not ∞, so the output voltage of the DC generator 18 is reduced by the command of the microcomputer 16 and it is again determined whether the on / off time ratio K2 is ∞ (step 110a). When the on / off time ratio K2 is ∞, it is determined that there is an imbalance (step 113). In the case of unbalance, as shown in FIG. 4B, the output voltage Vdc of the DC generator 18 is lowered, the output voltage Vo12 of the amplifier 12 becomes Vo12> Vdc, and the on / off time ratio K2
Because is ∞. If the on / off time ratio K2 is not ∞, it is determined that the phase is open (step 112).

A case where an unbalanced current is flowing will be described. Fig. 4 (a) shows the waveform of each phase of the unbalanced current, and Fig. 4 (b)
Shows the voltage Vr5 across the resistor 5. The both-end voltage Vr5 is amplified by the amplifier, and steps 101 to 108 in the flowchart of FIG. 2 are executed as in the three-phase balanced state. Microcomputer 1
6 is the on / off time ratio K2 based on the output value of the comparison circuit 17.
= Ton / Toff is calculated to determine whether K2 is ∞ (step 109). Next, if K2 is not ∞, it is determined whether K2 is a constant value (step 110). If an unbalanced current is flowing, Ton / Toff will be an irregular value. Therefore, it is determined as an unbalanced current (step 11
3).

Example 2. In the second embodiment, the output voltage Vo12 of the amplifier 12 is judged by an analog circuit and the amplification factor α of the amplifier 12 is changed. In FIG. 5, the voltage detectors 37 and 47 have the following configurations. Reference numerals 31 and 41 are operational amplifier elements that constitute the voltage detector, 32 and 33 are resistors that determine the comparison reference voltage Vpc3 of the operational amplifier element 31, and 42 and 43 are resistors that determine the reference voltage Vpc4 of the operational amplifier element 41. And 34 and 44 are resistors for supplying current to the bases of the transistors 36 and 46, respectively. One end of the normally open contact 10b is connected to the output end of the amplifier 12,
The other end is connected to the inverting terminal of the operational amplification element 41.
The comparison reference voltages Vpc3 and Vpc4 are the resistances 32 and 3, respectively.
If the resistance values of 3, 42, and 43 are R32, R33, R42, and R43, Vpc3 = {R33 / (R32 + R33)} Vc, Vpc4 = {R43
/ (R42 + R43)} Vc. Note that Vc is the power supply voltage of the analog circuit.

Next, the operation of the apparatus configured as described above will be described. It is almost the same as the first embodiment except for the following points. When a load current flows through the motor 1, a voltage Vr5 is generated in the resistor 5, and an output voltage of αVr5 is generated by the amplifier 12. First, if αVr5> Vpc3, the voltage detector 37
Operates to energize the reed relay 10. Therefore, the normally open contacts 10a, 10b are closed, and the amplification factor of the amplifier 12 is reduced to α10on. Furthermore, in the voltage detector 47, Vo12
If> Vpc4, the reed relay 11 is energized to close the normally open contact 11a to reduce the amplification factor of the amplifier 12 to αon. After that, almost the same operation as that of the first embodiment is performed according to the flowchart shown in FIG. Therefore, the reed relay 1
The difference in that the judgment of the operation of No. 1 is processed by software in the microcomputer in the first embodiment, but is processed by the voltage detectors 37 and 47 by analog circuits in the present embodiment. Therefore, higher speed processing is possible than the circuit of the first embodiment.

Example 3. An embodiment using a three-phase half-wave rectifier circuit will be described. The difference from the first embodiment is the same configuration except that the three-phase full-wave rectifier circuit is changed to a three-phase half-wave rectifier circuit. The operation of the third embodiment configured as described above will be described with reference to FIGS. 7 and 8. Figure 8
The steps 101 to 108 are substantially the same as those in the first embodiment. Here, when a three-phase balanced current is flowing, the output voltage of the amplifier 12 becomes as shown in FIG. 7 (a), the output waveform of the comparison circuit 19 becomes as shown in FIG. 7 (d), and the on / off time ratio K2
Is determined to be constant (step 109a). If constant,
Steps 111 and 115 are executed almost in the same manner as in the first embodiment. When the S phase is missing, the output voltage of the amplifier 12 becomes as shown in FIG. 7 (c), the output of the comparison circuit 19 becomes as shown in FIG. 7 (f), and it is determined whether the on / off time ratio K2 is constant. (Step 109a). From the above, the on / off time ratio K2 is not constant, so it is determined whether the output of the comparison circuit 19 has generated two pulses in one cycle (step 110a). In the case of the phase loss, two pulses are generated in one cycle, so it is determined that the phase is missing (step 112). Further, when an unbalanced current is flowing, the output voltage of the amplifier 12 becomes as shown in FIG. 7 (b), the output of the comparison circuit 19 becomes as shown in FIG. 7 (e), and it is judged whether the on / off time ratio K2 is constant ( Step 109a). From the above, the on / off time ratio K2 is not constant, so it is determined whether the output of the comparison circuit 19 has generated two pulses in one cycle.
(Step 110a). As a result, three pulses are generated in one cycle, so it is determined that an unbalanced current is flowing.
(Step 113).

The present invention is not limited to the configuration of the above-mentioned embodiment, and can be embodied by appropriately changing it without departing from the spirit of the invention. Although (1), the amplifier, the A / D converter, the DC generator, and the comparison circuit have been described as having a hardware configuration, they may have a software configuration having equivalent functions. (2) Although the operational amplifier 12 is used as the non-inverting amplifier, it can be configured as an inverting amplifier. Further, it may be a DC amplifier, for example, a balanced direct-coupled amplifier circuit. (3) Although the current transformer is used as the star connection, it may be V connection.

[0036]

According to the first aspect of the present invention, a three-phase full-wave rectifying circuit for three-phase full-wave rectifying secondary current of a current transformer, an amplifier for amplifying an output voltage of the rectifying circuit, and an output voltage of the amplifier. A / D conversion means for digitally converting the signal, an amplification factor changing means for changing the amplification factor of the amplifier according to the output voltage value of the A / D conversion means, and a DC voltage is generated according to the output voltage value of the conversion means. The direct current generating means and the comparing means for comparing the output voltage of the amplifier and the output voltage of the direct current generator are provided, and the abnormal current flowing in the three-phase load is determined by the output waveform of the comparing means. Even when the current is considerably lower than the rated current of the primary side of the current transformer, it is possible to obtain the effect of accurately detecting the open phase and unbalance of the load current.

A second aspect of the invention is a three-phase half-wave rectifying circuit for rectifying the secondary side current of a current transformer into a three-phase half-wave, an amplifying means for amplifying an output voltage of the rectifying circuit, and an A / D converting means. Amplification factor changing means for changing the amplification factor of the amplifier according to the output voltage value of
The direct current generating means for generating a direct current voltage according to the output voltage value of the converting means and the comparing means for comparing the output voltage of the amplifying means with the output voltage of the direct current generating means are provided, and the output waveform of the comparing means is used for the above. Since the abnormal current flowing through the three-phase load is determined, it is possible to obtain the effect of easily detecting the open phase and unbalance of the load current with high accuracy.

A third aspect of the present invention is a three-phase full-wave rectifying circuit for three-phase full-wave rectifying secondary current of a current transformer, an amplifying means for amplifying an output voltage of the three-phase full-wave rectifying circuit, and an amplifier. A / D conversion means for digitally converting the output voltage, voltage detection means for detecting that the output voltage value of the A / D conversion means is a predetermined value or more, and the amplification factor of the amplifier is changed by the operation of the voltage detection means. The comparison means includes an amplification factor changing means, a direct current generating means for generating a direct current voltage according to an output voltage value of the converter, and a comparing means for comparing the output voltage of the operational amplifying means with the output voltage of the direct current generator. Since the abnormal current flowing in the three-phase load is determined by the output waveform of, the effect that the open phase and the imbalance of the load current can be detected at high speed can be obtained.

A fourth aspect of the present invention is a three-phase full-wave rectifying circuit for three-phase full-wave rectifying secondary current of a current transformer, an amplifying means for amplifying an output voltage of the three-phase full-wave rectifying circuit, and the amplifying device. A / D conversion means for digitally converting the output voltage of the means, and the above A / D
A gain changing means for changing the amplification factor of the amplifier according to the output voltage value of the converting means is provided, and the current flowing to the three-phase load from the output of the A / D converter is calculated. The effect that the value of the load current can be easily detected simultaneously while detecting the phase and the imbalance is obtained.

[Brief description of drawings]

FIG. 1 shows an overall circuit diagram of the present invention.

FIG. 2 shows a flow chart of the present invention.

FIG. 3 is a diagram showing voltage waveforms at various portions according to the present invention.

FIG. 4 is a diagram showing voltage waveforms at various portions during an unbalanced current according to the present invention.

FIG. 5 shows an overall circuit diagram of another embodiment of the present invention.

FIG. 6 is a diagram showing voltage waveforms at various portions in another embodiment of the present invention.

FIG. 7 shows a flowchart of another embodiment of the present invention.

FIG. 8 shows a flowchart of another embodiment of the present invention.

FIG. 9 shows a conventional overall circuit diagram.

FIG. 10 is a diagram showing a conventional voltage waveform of each part.

[Explanation of symbols]

 1 Three-phase load 2a, 2b, 2c Current transformer 4 Three-phase full-wave rectifier circuit 12 Amplifier 15 A / D converter 18 DC generator 19 Comparison circuit 37, 47 Voltage detector

Claims (4)

[Claims] 1. A three-phase load abnormal current detection device for detecting an abnormal current flowing from a three-phase AC power supply to a three-phase load by a current transformer, wherein the secondary side current of the current transformer is three-phase full-wave rectified. Three-phase full-wave rectification circuit, amplification means for amplifying the output voltage of the three-phase full-wave rectification circuit, A / D conversion means for digitally converting the output voltage of the amplifier, and output voltage value of the A / D conversion means. Amplification factor changing means for changing the amplification factor of the amplifier according to the above, DC generating means for generating a DC voltage according to the output voltage value of the converting means, output voltage of the amplifying means and output voltage of the DC generating means An abnormal current detection device for a three-phase load, comprising: an abnormal current flowing through the three-phase load based on an output waveform of the comparison means. 2. A three-phase load abnormal current detecting device for detecting an abnormal current flowing from a three-phase AC power source to a three-phase load by a current transformer, wherein the secondary side current of the current transformer is three-phase half-wave rectified. Three-phase half-wave rectifier circuit, amplification means for amplifying output voltage of the three-phase half-wave rectification circuit, A / D conversion means for digitally converting output voltage of the amplification means, and output voltage of the A / D conversion means Amplification factor changing means for changing the amplification factor of the amplifying means according to a value, DC generating means for generating a DC voltage according to the output voltage value of the A / D converting means, output voltage of the amplifying means and DC An abnormal current detecting device for a three-phase load, comprising: comparing means for comparing output voltages of the generating means; and determining an abnormal current flowing through the three-phase load based on an output waveform of the comparing means. 3. A three-phase load abnormal current detection device for detecting an abnormal current flowing from a three-phase AC power supply to a three-phase load by a current transformer, wherein the secondary side current of the current transformer is three-phase full-wave rectified. Three-phase full-wave rectification circuit, amplification means for amplifying the output voltage of the three-phase full-wave rectification circuit, A / D conversion means for digitally converting the output voltage of the amplifier, and output voltage value of the A / D conversion means. Is a predetermined value or more, a voltage detecting means for detecting that the amplification factor of the amplifying means is changed by the operation of the voltage detecting means, and a DC voltage according to the output voltage value of the converting means. Direct current generating means,
An abnormality of the three-phase load, comprising: a comparing means for comparing the output voltage of the amplifying means and the output voltage of the direct current generating means, and determining an abnormal current flowing in the three-phase load based on the output waveform of the comparing means. Current detection device. 4. A three-phase load abnormal current detection device for detecting an abnormal current flowing from a three-phase AC power supply to a three-phase load by a current transformer, wherein the secondary side current of the current transformer is three-phase full-wave rectified. Three-phase full-wave rectification circuit, amplification means for amplifying the output voltage of the three-phase full-wave rectification circuit, A / D conversion means for digitally converting the output voltage of the amplification means, and output voltage of the A / D conversion means. An abnormality of a three-phase load, comprising: an amplification factor changing unit that changes the amplification factor of the amplification unit according to a value, and calculating a current flowing from the output of the A / D conversion unit to the three-phase load. Current detection device.