JP2000188824A - Open-phase detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an open-phase detecting circuit which can be readily applied to protection of a machine, such as a three-phase rotating machine operated by a three-phase AC power supply. SOLUTION: This detecting circuit comprises current transformers(CT) 1 or transformers(PT) which are connected with a three-phase power source, a rectifying circuit 2 which full-wave rectifies three outputs of the current transformers 1 or the transformers, an average voltage divider circuit 4 for averaging the output of the rectifying circuit, and a comparator circuit 5 which compares an divider circuit output with a rectifying circuit output, and detects the current open-phase or voltage open-phase of each phase of the three phases. Thereby open-phase generated in the upstream side and the downstream side of current or voltage can be detected easily and surely. This open-phase detecting circuit has no adjusting parts at all, can be constituted of the same circuit for rotating machines from small capacity to large capacity, and enables cost reduction from the use of common components and high volume production.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase loss detection circuit, and more particularly to a phase loss detection circuit suitable for use in a device that is supplied with power from a three-phase AC power supply such as a pump operation control device.

[0002]

2. Description of the Related Art A pump or the like generally operates by receiving a three-phase AC power supply. For example, a power supply is opened due to a poor connection of one or more phases, or a short circuit is caused by insulation deterioration. This causes a so-called phase loss, which hinders driving. Therefore, if a so-called open phase occurs, it is necessary to detect it promptly and take appropriate measures. However, conventional operation control devices for pumps, for example, generally include an overcurrent detection device or a non-voltage detection device, but it is difficult to detect even if an open phase occurs in these detection devices. Met. For this reason, there is a problem that the device is deteriorated after long-time use without noticing the existence of the open phase.

Conventionally, a CT is connected to a device that operates by receiving a supply of three-phase AC power, and the output is full-wave rectified, so that a pulsation output is obtained in the case of an open phase. It has been known that the current open phase can be detected. Similarly, it has been known that by connecting a PT and performing full-wave rectification on the output, a pulsation output can be obtained in the case of a phase loss, whereby a voltage phase loss on the upstream side can be detected. However,
These open-phase detection circuits have a complicated circuit configuration, require adjustment of signal levels, and are not always easy to use.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can be easily applied to protection of equipment such as a three-phase rotating machine that operates by receiving a three-phase AC power supply. It is an object to provide a possible phase loss detection circuit.

[0005]

SUMMARY OF THE INVENTION An open-phase detecting circuit according to the present invention comprises a current transformer (CT) or a transformer (PT) connected to a three-phase power supply and three current transformers or transformers. A rectifying circuit for full-wave rectifying the output of the rectifying circuit, an average voltage dividing circuit for averaging and dividing the output of the rectifying circuit, and a comparing circuit for comparing the output of the average voltage dividing circuit with the output of the rectifying circuit. It is characterized by detecting a current missing phase or a voltage missing phase of each phase.

According to the present invention described above, the current or voltage of the three-phase power supply line is detected by CT or PT, and is subjected to full-wave rectification. A DC having a ripple is output. The average voltage dividing circuit further averages and divides the output of the full-wave rectifier circuit to obtain a DC output whose level is sufficiently lower than the substantially flat effective value. Therefore, in a normal state, the output of the comparison circuit does not generate an open-phase detection pulse because the three-phase full-wave rectified output is sufficiently higher than the output of the average voltage dividing circuit even if a ripple component exists. And when an open phase occurs, the three-phase full-wave rectified output generates a large pulsation,
There is a time when the output drops below the output of the average voltage dividing circuit, and a comparison circuit compares the two outputs to generate an open-phase detection pulse. According to the above-described circuit configuration, the phase loss can be detected by the three-phase full-wave rectifier circuit, the average voltage dividing circuit, and the comparison circuit. Therefore, the phase loss can be detected with a relatively simple circuit configuration and without adjustment. Can be detected.

It is preferable that two of the current transformers or the transformers are connected to a three-phase power supply line by V connection. Thus, CT and PT for one phase can be omitted, and a phase loss detection circuit can be configured at lower cost.

Further, in the open phase detection circuit according to the first aspect, it is preferable that an output signal of the comparison circuit is connected to a CPU. This makes it easy and reliable to observe the number of pulses, the pulse interval, the time during which the pulses are continuously output, and the like using a microcomputer or the like generally used in the control device and the like. Missing phase can be detected.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

It is well known that there are (a) V connection, (b) Y connection, and (c) Δ connection as shown in FIG. 1 as a method of connecting a current transformer (CT). Similarly, it is well known that there are (a) V connection, (b) Y connection, and (c) Δ connection as shown in FIG. 2 as a connection method of the transformer (PT). FIG.
In the V connection and the Y connection, a current proportional to the current (I ₁ , I ₂ , I ₃ ) flowing in each of the R, S, and T phases is measured by an ammeter.
(A ₁ , A ₂ , A ₃ ). The Δ connection is R, S,
T is proportional to the current (I ₁ , I ₂ , I ₃ ) flowing in each phase, and the vector-combined current is converted to an ammeter (A ₁₂ , A ₂₃ , A ₃₁ )
Flows to Similarly, in FIG. 2, voltages U, V, and W proportional to the voltages of R, S, and T are generated at the u, v, and w terminals.

FIG. 3 shows an example of a circuit configuration for detecting an open phase by detecting only two of the three phases (V connection). The signal detected by the CT 1 is full-wave rectified by the full-wave rectifier circuit 2, converted into a direct current, and amplified by the operational amplifier 3. The signal is averaged by an average voltage dividing circuit 4 to form a signal divided at a certain ratio. This average voltage dividing circuit 4 includes an operational amplifier 3
, A DC voltage lower than the output level of the operational amplifier and containing no pulsation component is output.
Then, this output and the output of the operational amplifier 3 are compared by a voltage comparator (comparator) 5. Further, the output pulse is converted to an appropriate output level using the pulse level conversion circuit 6.

FIG. 4 shows waveforms of input / output signals of the voltage comparator. In a normal state, as shown in FIG. 4A, the voltage of the signal amplified by the operational amplifier is always higher than the voltage of the averaged divided signal. Therefore, the output of the voltage comparator is always at the low level, and the open-phase signal is at the low level. However, when one-phase or two-phase current loss occurs, the voltage of the signal amplified by the operational amplifier 3 has a waveform as shown in FIG. That is, the pulsation component increases compared to the normal state. On the other hand, in the average voltage dividing circuit 4,
Since the average is obtained including the large pulsation, the magnitude of the output signal hardly relates to the magnitude of the pulsation. For this reason, when a phase loss occurs, the output voltage of the full-wave rectifier circuit pulsates greatly, and becomes partially lower than the voltage of the output signal of the average voltage dividing circuit. Therefore, the output of the voltage comparator outputs a pulse. As a result, the phase loss signal becomes High and is output. The signal level is adjusted by the pulse level conversion circuit 6 and output to an external control circuit (not shown).
In FIG. 4B, the pulse interval t is about 10.0 in a 50 Hz area.
msec, about 8.3 msec in a 60 Hz area.
Further, since the circuit is a current phase loss detection circuit, it is possible to detect an unbalanced phase loss due to insulation degradation on the load side when the voltage is normal.

In the above-described circuit configuration, an example is shown in which two CTs are used to connect by V connection. However, three CTs are used to connect in Y connection as shown in FIG. As shown in FIG. 6, the connection may be made in a Δ connection. Even in a Y or Δ connection in which CT is connected to all three phases, V in FIG.
Open phase can be detected in the same way as connection. Further, by using PT in place of CT of the open-phase detection circuit and performing full-wave rectification on the detection signal in the same manner and performing signal processing in the same manner as described above,
Similarly, a voltage open phase can be detected.

Even if a V connection is used as shown in FIG.
In addition, not only the detected phase (R phase and T phase in FIG. 3) but also the missing phase (S phase in FIG. 3) can be detected. For this reason, compared to the Y connection or Δ connection shown in FIG. 5 or FIG. 6, the cost for one CT and the number of wiring steps can be reduced.

Further, for example, the CP
In the case where U is used, the pulse level conversion circuit 6 is omitted as shown in FIG.
7 may be taken into the external interrupt input. From the number of pulses of the output signal of the voltage comparator 5, the pulse interval, the time during which the pulses are continuously output, and the like, it is possible to determine whether or not the phase is totally open using the CPU. As a result, not only the component cost can be reduced by omitting the pulse level conversion circuit 6, but also erroneous detection due to instantaneous imbalance such as rapid voltage fluctuation can be prevented. Since there is no adjustment portion (for example, a variable resistor) and no portion greatly affected by temperature, the above-described simple circuit configuration can be applied to protection of various rotating machines from small capacity to large capacity. . Therefore, the present invention can be applied to operation control devices for rotating machines such as pumps and fans, all with the same circuit configuration, and it is expected that components can be used in common and mass production will reduce costs.

[0016]

According to the present invention, the current of a three-phase rotating machine,
And the phase loss detection circuit of the voltage, the current signal of each phase,
The following effects can be expected by using a configuration in which the output obtained by full-wave rectification of the voltage signal and the output obtained by dividing the output obtained by full-wave rectification into an average voltage are compared. That is, open phases generated on the upstream side and the downstream side of the current or the voltage can be easily and reliably detected. And, this open phase detection circuit,
There is no adjustment part, and all the rotating machines from small capacity to large capacity can be configured with the same circuit, and common use of parts and cost reduction by mass production can be expected.

Further, the open-phase detecting circuit has a C
It can be composed only of T or PT, and the cost can be further reduced by reducing the component cost and the number of wiring steps. In addition, the voltage comparator output signal of the current and voltage open phase detection circuit is directly connected to the external interrupt input of the CPU, and the number of pulses of the detection signal, the pulse interval, and the time during which the pulse is continuously output. And so on. As a result, it is possible to reduce the number of components and prevent a malfunction due to a sudden voltage change or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing various connection methods of CT, (a) showing a V connection, (b) showing a Y connection, and (c) showing a Δ connection.

FIGS. 2A and 2B are diagrams showing various connection methods of PT, where FIG. 2A shows V connection, FIG. 2B shows Y connection, and FIG. 2C shows Δ connection.

FIG. 3 is a circuit diagram showing an open phase detection circuit according to the embodiment of the present invention.

4A and 4B are diagrams showing waveforms of respective parts, where FIG. 4A shows a normal state and FIG. 4B shows a phase loss state.

FIG. 5 is a diagram showing an open phase detection circuit at the time of Y connection.

FIG. 6 is a diagram showing an open phase detection circuit at the time of Δ connection.

FIG. 7 is a circuit diagram of an open phase detection circuit when the output of the voltage comparator is connected to a CPU.

[Description of Signs] 1 Current transformer (CT) 2 Full-wave rectifier circuit 3 Operational amplifier for signal amplification 4 Average voltage dividing circuit 5 Comparator (voltage comparator) 6 Pulse level conversion circuit 7 CPU

Continued on the front page (72) Inventor Yasuyuki Tadokoro 4-1-1, Motofujisawa, Fujisawa-shi, Kanagawa Prefecture Ebara Densan Co., Ltd. (72) Inventor Manabu Watanabe 4-1-1, Motofujisawa, Fujisawa-shi, Kanagawa Prefecture F-term in Ebara Densan (reference) 5G004 AA02 AB02 BA06 CA04 DA01 DB01 DB02 DC05 5G058 BB01 BC11 CC04 CC08 5H410 BB02 CC04 DD04 DD06 FF03 FF05 FF11 FF22 LL13 LL14 LL20

Claims (2)

[Claims] A current transformer (CT) connected to a three-phase power supply;
Or, a transformer (PT), a rectifier circuit for full-wave rectification of three outputs of the current transformer or the transformer, an average voltage divider circuit for averaging and dividing the output of the rectifier circuit, and the average voltage divider An open-phase detection circuit comprising a comparison circuit for comparing a circuit output with the output of the rectifier circuit, wherein the open-phase detection circuit detects a current open phase or a voltage open phase of each of the three phases. 2. The phase loss detection circuit according to claim 1, wherein an output signal of the comparison circuit is connected to a CPU.