JPS6240928B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control and protection device for a (three-phase) induction motor that controls the speed by controlling the phase of one or two phases of three-phase primary voltage.

Conventionally, as a method for controlling the speed of a three-phase induction motor, a method based on phase control of the primary voltage using an electric valve such as a thyristor has been often used because of its ease of use. And especially among the above methods,
A method using three-phase balanced control is often used, but recently, a method using one-phase or two-phase phase control is being used from the viewpoint of reducing the number of elements and simplifying the control circuit. However, when the speed of the induction motor is controlled by controlling the phase of one or two phases, there is a risk that the open phase protection device among the control protection devices for the three-phase induction motor may malfunction. These problems will be described below with reference to the operation of a conventional control protection device.

FIG. 1 shows a configuration example of a speed control device using one-phase phase control of a three-phase induction motor. In the figure, IM is a three-phase induction motor, PHC is configured by connecting control rectifying elements such as thyristors in antiparallel, and
A phase (voltage) control device that controls the voltage applied to the U phase of the IM primary winding from the three-phase power supply R, S, and T. D detects an open phase state using the terminal voltage of the three-phase induction motor IM. This is an open-phase protection device that operates the breaker NFBI. Moreover, F and R are electromagnetic contactors for switching the rotational direction provided in the primary circuit of the three-phase induction motor IM, respectively. In such a configuration,
We have now introduced a disconnector NFBI and a three-phase induction motor IM.
When either of the electromagnetic contactors F and R, which specify the rotation direction of the three-phase induction motor IM, are turned on, V, W of the three-phase induction motor
The line voltages of three-phase power supplies R, S, and T are applied between the two phases. In such a state, when a firing signal is given to the phase control device PHC, a voltage corresponding to the firing angle is applied to the U phase, which generates a rotating magnetic field in the three-phase induction motor IM and generates torque. arise. At this time, when the firing phase given to the phase control device PHC is narrowed down, that is, when the speed reference signal is not generated or when the speed setting is small, the three-phase induction detected by the open phase protection device D The voltage of the motor IM becomes unbalanced, causing the open-phase protection device D to malfunction, and as a result, the breaker NFBI opens, causing the operation of the three-phase induction motor IM to stop even though there is no open-phase accident. There is a drawback.

The present invention was made in order to solve the above-mentioned problems, and its purpose is to prevent unnecessary operation stoppage of the motor without malfunction in the event of an open phase state during speed control of a three-phase induction motor. An object of the present invention is to provide a control and protection device for an induction motor that operates only in the case of a one-phase or two-phase open-phase accident such as a short circuit or disconnection, and is capable of reliably protecting a three-phase induction motor from an open-phase accident. .

In order to achieve the above object, in the present invention, one phase or two phases of the three-phase primary voltage applied to the three-phase induction motor through the breaker, the magnitude of which increases over time to a predetermined value. The speed of the three-phase induction motor is controlled by performing phase control based on the deviation between the speed reference voltage that increases to The three-phase primary voltage and the speed reference voltage are compared, and as a result, if the three-phase primary voltage is smaller than the speed reference voltage, an open phase fault in one or two phases of the three-phase primary voltage is detected and the system operates. The present invention is characterized in that it includes an open-phase protection device that opens the shield circuit breaker using the operation output.

First, the concept of the present invention will be described.

Three-phase primary voltage control, especially one-phase and two-phase control, is used to prevent inrush current when starting a three-phase induction motor. The system is such that the full voltage is applied after a certain period of time. While the motor is starting, the voltage of one or two phases is in an open phase state depending on the speed reference voltage, so in the case of the conventional open phase protection device mentioned above, There is a risk that an open phase will be detected. On the other hand, the voltage applied to the motor with respect to the speed reference voltage has the following relationship. That is, when the speed reference voltage is zero, one-phase voltage is applied, and when the speed reaches the rated speed, three-phase full voltage is applied. In addition, during this period, when comparing the speed reference voltage and the motor voltage using three-phase full-wave rectified DC voltage, it is considered that they are proportional. Further, when one phase is open, the motor voltage is considered to be zero if the speed reference voltage is zero, and if the speed reaches the rated speed, it is considered that the motor voltage is in a 1Φ applied state. FIG. 5 shows these relationships.

In other words, in FIG. 5, the horizontal axis is the speed reference voltage,
On the vertical axis, the solid line shows the motor voltage during normal and open phase conditions. Now, from this figure 5, when detecting the change in the motor voltage during normal operation and when one phase is open, if a reference voltage proportional to the speed reference is used, then by comparing this reference voltage and the motor voltage, it is possible to detect the normal When, within all speed references, the motor voltage exceeds the reference voltage. On the other hand, when one phase is open, the motor voltage falls below the reference voltage regardless of the speed reference range. Therefore, the magnitude relationship between the motor voltage, that is, the three-phase primary voltage, and the speed reference voltage is compared, and as a result, since the three-phase primary voltage is smaller than the speed reference voltage, there is a lack of three-phase primary voltage in all speed ranges. Phase faults can be detected.

Hereinafter, an embodiment of the present invention based on the above-mentioned concept will be described with reference to the drawings. Second
The figure shows in block form an example of the configuration of a control protection device for a three-phase induction motor equipped with an open-phase protection device according to the present invention, and the same parts as in FIG. This will be omitted and only the different parts will be described here. In the figure, SG is a speed detector that detects the speed of the three-phase induction motor IM,
The output is sent out as a speed voltage signal called WR. WC is a speed deviation detector which inputs the speed voltage signal WR and the speed reference voltage signal WS and detects the deviation thereof; P is an ignition signal generator which receives the output deviation signal DW of the speed deviation detector WC; A firing signal based on the deviation value is given to the phase (voltage) control device PHC to control the firing angle of the anti-parallel connected thyristors. Further, D inputs the three-phase terminal voltage of the three-phase induction motor IM and the speed reference voltage signal WS, and detects an open-phase accident such as a short circuit or disconnection based on the comparison results.The details will be described later. The open phase protection device is configured so that its operation opens the shield breaker NFBI.

FIG. 3 shows a detailed configuration example of the phase loss protection device D described above. In the figure, BR consists of bridge-connected diodes and is connected to the three-phase induction motor.
The rectifier circuit that rectifies the three-phase terminal voltage of IM, and IA, is an insulated smoothing amplifier that insulates and smoothes the output voltage of rectifier circuit BR, and sends out its output as a voltage signal V _WBR . Also, AT is the speed reference voltage signal mentioned above.
An attenuator that inputs WS and adjusts its voltage value.
The output is sent out as an open phase state determination reference voltage signal _VWS via a limiter DWL to which an upper limit voltage value _VWSO is set. Furthermore, CL is a comparator whose normal input terminal receives the output V _WS of the limiter DWL, and its inverting input terminal receives the output V _WBR of the isolation smoothing amplifier IA, and compares the two. As a result, the magnitude of the signal V _WBR becomes the signal V _WS
The configuration is such that a positive output signal V _CL is sent out as an operation signal of the phase loss protection device D when the output signal V CL is smaller than .

Next, the operation of the control and protection device for a three-phase induction motor will be described with reference to FIGS. 4a and 4b.
Now, when starting and controlling the three-phase induction motor IM, first of all, when either the magnetic contactor F or R, which specifies the rotation direction of the three-phase induction motor IM, is turned on, the three-phase induction motor
Line voltages of three-phase power supplies S and T are applied between the two phases V and W of IM. Meanwhile, speed deviation detector WC
is the speed voltage signal WR of the speed detector SG and the time t.
A speed reference voltage signal WS that increases with the passage of time is introduced, and its deviation is detected to generate a speed deviation signal DW.
is applied to the ignition signal generator P, and an ignition signal based on the deviation value is sent to the phase (voltage) controller PHC.
given to. Then, the firing angle of the anti-parallel thyristor of the phase control device PHC is controlled by this firing signal, and a voltage corresponding to this firing angle is applied to the U phase. This generates a rotating magnetic field in the three-phase induction motor IM, which starts and speeds it.
On the other hand, in this case, simultaneously with the above control, the speed reference voltage signal WS and the three-phase terminal voltage signal of the three-phase induction motor IM are applied to the open phase protection device D. First, the three-phase terminal voltage signal is rectified by the rectifier circuit BR, then insulated and smoothed through the insulated smoothing amplifier IA, and then applied to the inverting input terminal of the comparator CL as the voltage signal V _WBR . In addition, the speed reference voltage signal WS has its voltage value adjusted by an attenuator AT, and is then passed through a limiter DWL having an upper limit voltage value V _WSO to the normal rotation input terminal of the comparator CL, where the open phase state determination reference voltage signal V Added as _WS . In this case, the output voltage signal V _WBR of the insulated smoothing amplifier IA and the limiter DWL from the start time t=0 to the start completion time are
The open phase state determination reference voltage signal V _WS is the output signal of
The change in is as shown in FIG. 4a, and this is added as an input to the comparator CL. As a result, the magnitude of each signal V _WBR and V WS is compared in the comparator CL, but in this case, the magnitude of each signal V WBR and V _WS is compared.
Since the signal V _WBR is larger than the signal V _WS in the range of 0≦t≦t ₃ , the output signal V _CL is the fourth
As shown in FIG. b, a signal of negative polarity is sent out (not sent out as an actual output). Therefore, the comparator CL, that is, the open-phase protection device D, does not operate, and as mentioned above, when the three-phase induction motor IM starts up and there is an open phase during speed control, the disconnector NFBI is accidentally opened. It never happens. On the other hand, if an open phase fault such as a short circuit or disconnection occurs at the above time _t3 , the magnitude of the signal V _WBR , which is the input signal of the comparator CL, becomes smaller than the signal V _WS as shown in Figure 4a. As the output signal V _CL , a positive polarity signal is sent out as shown in FIG. 4b. Therefore, in this case, the comparator CL, that is, the phase loss protection device D, operates, detects the voltage drop due to the phase failure, and then disconnects the circuit.
NFBI is opened and open phase protection is performed.

In this way, the three-phase induction motor IM can be disconnected.
The U phase of the three-phase primary voltage applied via the NFBI and the electromagnetic contactors F and R is connected to a speed reference voltage signal WS whose magnitude increases to a predetermined value as time t passes, and a speed detector SG. The speed of the three-phase induction motor IM is controlled by performing phase control based on the deviation value from the speed voltage signal WR detected by the three-phase induction motor IM.
Voltage signal V _WBR obtained by rectifying, insulating, and smoothing the three-phase terminal voltage of IM and the speed reference voltage signal mentioned above.
A comparator CL compares the magnitude with the open-phase state determination reference voltage signal V _WS obtained by attenuating and limiting WS, and as a result of the comparison, the magnitude of the signal V _WBR is smaller than the signal V _WS . The device is equipped with an open-phase protection device that detects an open-phase accident such as a short-circuit or disconnection, and operates to open the above-mentioned breaker NFBI.

Therefore, it is possible to reliably determine whether the drop in the three-phase terminal voltage of the three-phase induction motor IM is due to its starting speed control or to an open phase such as a short circuit or disconnection. It is possible to eliminate the drawbacks of the prior art in which a malfunction of the open-phase protection device D causes the disconnector NFBI to open and the operation is stopped during start-up control. As a result, it is possible to reliably protect the three-phase induction motor IM from open-phase accidents, and
It becomes possible to perform extremely reliable speed control.

It should be noted that the present invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist thereof.

For example, in the above embodiment, the case where one phase of the three-phase primary voltage is phase-controlled has been described, but the present invention is not limited to this, and can be similarly applied to a case where two phases are phase-controlled. Also,
If the output signal of the comparator CL in the above V _CL is configured not only to open the breaker and the disconnector NFBI, but also to operate various brake circuits (not shown) at the same time, the three-phase induction motor IM and its load can be made safer. It is something that can be protected.

As explained above, according to the present invention, when an open phase occurs during speed control of a three-phase induction motor, unnecessary operation of the motor is prevented without malfunction, and one-phase or two-phase It is possible to provide an extremely reliable induction motor control and protection device that operates only in the case of an open-phase accident and can reliably protect a three-phase induction motor from an open-phase accident.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional three-phase induction motor control device, Fig. 2 is a schematic configuration diagram showing an embodiment of the present invention, and Fig. 3 is a detailed configuration of the open phase protection device in Fig. 2. The figures shown in FIGS. 4a and 4b are diagrams for explaining the operation of the same embodiment, and FIG. 5 is a relational diagram for explaining the idea of the present invention.

Claims (1)

[Claims] 1. One or two phases of the three-phase primary voltage applied to the three-phase induction motor via the breaker, and the speed reference voltage whose magnitude increases to a predetermined value with the passage of time and the three-phase induction The speed of the three-phase induction motor is controlled by performing phase control based on the deviation from the speed voltage of the motor, wherein the three-phase primary voltage applied to the three-phase induction motor and the speed reference voltage As a result, the three-phase primary voltage is smaller than the speed reference voltage, so it operates by detecting an open-phase fault in one or two phases of the three-phase primary voltage, and uses this operating output to detect the above-mentioned A control protection device for an induction motor, comprising an open-phase protection device that opens a disconnector.