JPH01255488A - Starting device for squirrel-cage induction motor - Google Patents

Abstract

PURPOSE:To permit arbitrary and optimum setting of a starting voltage command pattern, by a method wherein the starting voltage command pattern is generated by synthesizing a command signal in accordance with values set in an initial starting period voltage setter, a voltage increasing rate setter and an initial voltage continuing time setter. CONSTITUTION:A function generator 13 generates a starting voltage commanding pattern synthesized by the combination of command signals in accordance with set values set in an initial starting period voltage setter 9, an initial voltage continuing time setter 10 and voltage increasing rate setter 11. A gate control circuit 14 outputs a trigger signal to the gate of a thyristor 12 based on a starting voltage command pattern in the function generator 13 and controls the thyristor 12 so as to impress a primary voltage, which becomes a starting voltage impressing pattern, on a cage rotor type induction motor 1. According to this method, the generation of a starting peak current in the cage rotor type induction motor may be restrained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a starting device for a squirrel-cage induction motor, and more specifically to a starting control device for controlling the primary voltage of a squirrel-cage induction motor using a thyristor. The present invention relates to a starting device for a squirrel-cage induction motor in which a starting voltage command pattern can be arbitrarily selected and the starting voltage can be changed to suppress starting peak current.

[Conventional technology]

For example, in a small squirrel cage induction motor of 5 kW or less, the starting current does not become very large. Therefore, there is no problem in adopting a direct starting method in which the motor is directly connected to the power source using a switch and the full voltage is applied to the motor to start the motor. However, in larger induction motors, a starting peak current that is 6 to 8 times larger than the rated current flows, so the applied voltage at starting is lowered and the full voltage is applied only after the motor rotation speed has increased. It is common that the engine enters the normal operating state. Such starting voltage control methods include the starting compensator method by switching the taps of an autotransformer, the star-triangle starting method by switching to a delta connection after a Y connection, and the Condorfer method.
There are starting methods, reactor starting methods, etc. According to such a starting method, since the starting voltage can be increased stepwise, the starting peak current flowing through the squirrel cage induction motor can be suppressed.

On the other hand, if the direct start method is adopted in a system that is equipped with a diesel generator for private power generation and is designed to supply power to several squirrel cage induction motors, the generation of a large starting peak current will cause the generator to overflow. A voltage drop may occur, causing a temporary drop in the rotational speed of the motor that is already in operation, resulting in inconveniences. In order to eliminate such drawbacks, it is necessary to suppress the voltage drop within an acceptable range, and conventionally, diesel generators have been selected whose capacity is considerably larger than the total load capacity for continuous operation. Therefore, the reality is that power generation equipment must be installed that has an excessive capacity that is not required during rated operation. This kind of thing is not limited to when equipped with a generator.
The same applies when power is being supplied from a power receiving transformer. If the above-mentioned starting peak current can be made smaller than that in direct-on starting, the capacity of the generator and power receiving transformer can be reduced, making it possible to downsize and reduce the cost of equipment. Even when adding a new electric motor, there is no need to change the power supply capacity based on the starting current.

[Problem to be solved by the invention]

The various starting methods described above require tap switching. Furthermore, since there is a contactor for switching, there is a possibility of welding, and wear and tear occurs due to long-term use, resulting in problems that require frequent maintenance and inspection.

On the other hand, it is well known that thyristors have recently been widely used to control the primary voltage of electric motors. A gate signal for a thyristor is generated based on the speed command signal, and the voltage applied to the squirrel cage induction motor is controlled by the thyristor to perform speed control. In some cases, thyristors are also used for voltage control during starting. As described above, primary voltage control using a thyristor has become easier, but the change in starting voltage generally has a linear or S-logical starting characteristic. However, in order for the setting to match the load of the motor,
The current situation is that it is not necessarily easy to set up.

The present invention was made in view of the above-mentioned problems, and its purpose is to suppress the generation of starting peak current when starting a squirrel-cage induction motor, so that when a generator is provided, the capacity of the generator is reduced to a power receiving transformer. When power is supplied from An object of the present invention is to provide a starting device for a squirrel-cage induction motor that can easily adjust the starting voltage according to the starting torque required by the invention.

In particular, it is desirable to be able to easily set a starting voltage command pattern that obtains a starting voltage application pattern that is suitable for various loads driven by an electric motor so that it can be arbitrarily and nearly optimal each time. This is its main purpose.

[Means to solve the problem]

The present invention is applicable to a starting device for an induction motor that uses a thyristor to control the primary voltage of a squirrel-cage induction motor. a starting initial voltage setting device 9 that sets the starting voltage, a voltage rising rate setting device 11 that sets the rising rate of the starting voltage from the above-mentioned initial value, and a starting initial voltage setting device 9 and a voltage rising rate setting device 11 that set the starting voltage according to the setting values. A function generator 13 that generates a starting voltage command pattern for making the primary voltage applied to the squirrel cage induction motor 1 a desired starting voltage application pattern by synthesizing command signals, and a starting voltage 1 command pattern in the function generator 13. The present invention is configured to include a gate control circuit 14 that causes a thyristor 12 to apply a primary voltage forming a starting voltage application pattern to the squirrel cage induction motor l using a trigger signal based on the above.

In addition to the starting initial voltage setting device 9, the voltage increase rate setting device 11, and the gate control circuit 14, there is also an initial voltage duration setting device 10 that sets the time for which the starting initial voltage continues, the starting initial voltage setting 9, and the initial voltage. By combining the command signals according to the values set by the duration setting device 1 and the voltage increase rate setting device 11, a starting voltage command pattern is created that makes the primary voltage applied to the squirrel cage induction motor 1 a desired starting voltage application pattern. The structure includes a function generator 13 for generating a function.

[For production]

Turn each knob of the starting initial voltage setting device 9, initial voltage duration setting device 10, and voltage increase rate setting device 11. Based on the set value, the function generator 13 generates a starting voltage command pattern that is a combination of the respective command signals. A trigger signal is output from the gate control circuit to the gate of the thyristor 12 in accordance with this starting voltage command pattern.

In response to the signal, the thyristor 12 applies a temporary voltage to the motor that provides a desired starting voltage application pattern, that is,
A constant voltage power supply is converted to a variable voltage power supply.

Since the secondary voltage changes and rises at a specified rate of increase from the initial starting voltage, which is lower than in the case of the direct-on starting method, the starting peak current does not increase, and the current required to start the load can be generated. I can do it. If the inertia is large and starting torque is required and it takes a long time to start, for example, leave the setting device 9 or 10 set at a certain value and change the setting value of the voltage increase rate setting device 11 to make it take a longer time. is applied to increase the pressure, that is, reduce the rate of increase. Depending on this setting, different starting voltage command patterns are generated by the function generator 13, and if starting suitable for the load is obtained, each setting device 9, 10
．． 11 is fixed, and from now on, the squirrel cage induction motor 1
is started with a starting voltage application pattern based on the selected starting voltage command pattern.

On the other hand, if the initial voltage duration setting device 10 is not required, the starting voltage command pattern based on the setting values only of the starting initial voltage setting device 9 and the voltage increase rate setting device 11 is set by the function generator 1.
Generate in 3. This also allows the primary voltage to be set to the desired starting voltage application pattern to the thyristor 1, as described above.
2 can be added to the electric motor.

〔Effect of the invention〕

According to the present invention, since the starting voltage gradually increases from a certain initial voltage within a range that does not interfere with starting the load, the generation of large starting peak current in squirrel cage induction motors is suppressed, and soft starting is possible. becomes. Therefore, the capacity of the generator and the capacity of the receiving transformer can be small, and the load is not shocked at startup. Furthermore, if there are other loads being supplied with power from the same power source, a decrease in rotational speed due to a voltage drop in the power source due to the starting peak current can be avoided. Since the starting voltage command pattern in the function generator can be changed by changing the setting values of each setter, the starting voltage application pattern can be arbitrarily selected by looking at the starting situation of the load. When the load driven by the electric motor changes, adjustments can be made accordingly, and nearly optimal starting can be achieved. In addition, there is no need to change taps for starting adjustment, and as a stationary starter device, maintenance and inspection efforts can be significantly reduced, and the device is small, lightweight, and inexpensive. I can do it.

On the other hand, if a starting voltage command pattern similar to the above can be obtained without providing an initial starting voltage setting device, and if such a pattern is acceptable depending on the load, then the configuration of the starting device can be reduced and the It can be an inexpensive device.

〔Example〕

The starting device for a squirrel cage induction motor according to the present invention will be explained in detail below.

Figure 2 is a standard circuit diagram for feeding and driving squirrel-cage induction motors m and 1. Normally, power supplies R, S, and T each have a circuit breaker 2, an electromagnetic contactor 3, and a thermal relay 4. A control unit 5 for control is connected to it. A switch 6 for commanding start and stop, an indicator light 7, and a signal light 8 are provided. The control unit 5 includes, for example, volume type small resistors 9, 1.0.
11 are attached in total, each functioning as a starting initial voltage setting device, an initial voltage duration setting device, and a voltage increase rate setting device.

FIG. 1 is a block diagram of the overall configuration of the starting device shown together with a schematic system diagram, showing the control unit 5 that outputs trigger pulses to the thyristor 12 in response to setting commands from each of the setting devices 9, 10, and 11 mentioned above. . The control unit 5 comprises a function generator 13 and a known gate control circuit 14.

The above-mentioned starting initial voltage setting device 9 specifies the initial value of the starting voltage by setting a resistance value, and as shown in FIG.
It can be set arbitrarily, and if it is set to 100%, it will be the same as when starting directly. For example, by setting the resistance value,
A command signal voltage of +V2, v3, . . . is determined and is used as an input signal for function generation in the function generator 13.

The initial voltage duration setting device 10 defines the time period during which the starting initial voltage continues, and the time period for maintaining the starting initial voltage set by the starting initial voltage setting device 9 is set to 0, for example.
t+, t2. shown in FIG. 3(b) in the range of ~10 seconds.
It can be arbitrarily selected, such as t3... Note that a known electronic timer may be employed as this initial voltage duration setting device 10.

The voltage increase rate setter 11 sets the starting voltage increase rate β1. from the initial value. β2. β3... is determined by the starting initial voltage setting device 9 and the initial voltage duration setting device 10 from the point P [see FIG. 3(d)] to the point P determined by the starting initial voltage setting device 9 and the initial voltage duration setting device 10, almost linearly as shown in FIG. 3(C). It is designed to realize a voltage rise that rises to a certain angle, and can be selected within the range of 90 to 30 degrees, for example.

The function generator 13 generates a combination of command signals shown in FIGS. 3(a) to 3(C) according to the values set by the starting initial voltage setting device 9, the initial voltage duration setting device 10, and the voltage increase rate setting device 11. A starting voltage command pattern is generated that makes the primary voltage applied to the squirrel cage induction motor 1 a desired starting voltage application pattern, as shown by the solid line in FIG. 3(d) synthesized by the above. In addition, Fig. 3 (e) and (f)
The portion from point P until reaching the rated voltage may be deformed to form a polygonal line or curve as shown in FIG.

The gate control circuit 14 is composed of a phase control circuit 15 and a gate trigger circuit 16, and outputs a trigger signal to the gate of the thyristor 12 based on the starting voltage command pattern in the function generator 13, and outputs a trigger signal to the gate of the thyristor 12, which becomes the starting voltage application pattern. The thyristor 12 is controlled so as to apply voltage to the squirrel cage induction motor l.

According to the configuration described above, the squirrel cage induction motor 1 can be started in the following manner. First, the resistance values are changed by turning the respective knobs of the starting initial voltage setting device 9, initial voltage duration setting device 10, and voltage increase rate setting device 11 to make temporary settings. For example, a starting voltage command pattern as shown in FIG. 3(d) is generated by the function generator 13. Starting switch 2, 3. 6, squirrel cage induction motor 1
A voltage is applied to the starting voltage application pattern as shown in FIG. 4(a). At this time, a starting current as shown in FIG. 5(a) flows, and the mechanical device driven by the squirrel cage induction motor 1 is started. If you need to increase the starting torque,
If you want to shorten the acceleration time, use the starting initial voltage setting device 9.
If the starting voltage is slightly lowered, the starting voltage application pattern becomes as shown in FIG. 4(b), and the starting current changes as shown in FIG. 5(b). For example, if the starting voltage control as shown in Fig. 4(C) results in a current pattern as shown in Fig. 5(C),
The accelerating current becomes almost constant, and there is no starting peak current, and its maximum value is equal to the direct starting current (shown in Figure 6).
(6 to 8 times the rated current), it is much smaller (1.5
~3 times). Note that when the motor reaches its rated rotational speed, the load current suddenly settles down to the load current.

By such setting work, starting of the electric motor 1 suitable for optimum starting is realized. In this state, each setting device 9, 1.
If the setting position of the 0.11 knob is fixed, the motor 1 will be started in accordance with the starting voltage application pattern based on the unique starting voltage command pattern generated by the function generator 13 from now on. That will happen.

In particular, the starting initial voltage setting device 9 can independently and easily set the starting initial voltage commensurate with the starting torque to an extent that does not generate excessive starting peak current.
0 and the voltage increase rate setting device 11 can be set independently. Diesel generators are usually equipped with an automatic voltage regulator (AVR), so even if the generator voltage drops due to the generator's weekly actance, the automatic voltage regulator will function after a slight time lag and the voltage will be increased. will be restored to its original state. However, if the voltage specified by the starting initial voltage setting device 9 is maintained for the time set by the initial voltage duration setting device 10, the voltage drop can be kept low against the subsequent increase in starting current. can be demonstrated.

That is, it is possible to have a constant initial voltage portion up to point P in FIG. 3(d) and to adjust the period.

As can be seen from the explanation of the above embodiments, a starting voltage corresponding to the starting torque is applied at the beginning of a certain period of time, and the starting voltage gradually increases within a range that does not interfere with starting the load. The occurrence of a large starting peak current in the engine is suppressed, and soft starting is possible. In addition, the generator capacity and power receiving transformer capacity can be small, and the load will not be shocked at startup. Even if there are other loads on the same power source, a decrease in rotational speed due to a voltage drop in the power source due to the starting peak current can be avoided. The above starting voltage control can be changed by changing the settings of each setting device, so for example, if the inertia is large and starting torque is required and it takes time to start, operate one of the setting devices above, If a function generator generates a starting voltage command pattern according to the starting voltage command pattern, the starting voltage application pattern can be arbitrarily selected while checking the starting condition of the load. If the load driven by the motor changes, adjustments can be made accordingly, making it possible to achieve near-optimal starting. In addition, there is no need to change taps, which was required each time the conventional starting method is started, and as a stationary starting device, maintenance and inspection efforts can be significantly reduced, and the device is small, lightweight, and inexpensive. I can do it.

By the way, the duration set by the initial voltage duration setting device 10 may be set to zero seconds depending on the type of load, so the initial voltage duration setting device 10 may not be necessary. In such a case, only the starting initial voltage setter 9 and the voltage increase rate setter 11 are provided, and the function generator 13 generates a command pattern of the combined starting voltage based on these set values. . This also makes it possible to apply a primary voltage from the thyristor 12 to the motor in a desired starting voltage application pattern similar to the above shown by the solid line in FIG. In this case, there is an advantage that the configuration of the starting device is simple.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the starting device for a squirrel cage induction motor according to the present invention, Figure 2 is a standard circuit diagram of the starter, and Figure 3 is a standard circuit diagram of the starting device.
Figures (a) to (c) are function generation command signal diagrams corresponding to the setting values in each setting device, Figures 3 (d) to (f) are examples of starting voltage command patterns in the function generator, and Figure 4 (a) )～(
c) is the starting voltage application pattern applied to the squirrel cage induction motor, Figures 5 (a) to (C) are the starting current change diagrams of the motor corresponding to the starting voltage application patterns, and Figure 6 is the starting voltage application pattern in the case of direct-on starting. The starting current pattern, FIG. 7, is the starting voltage command pattern when the initial voltage is not continued. 1.-Squirrel cage induction motor, 9-Starting initial voltage setting device (volume type small resistor), 10-Initial voltage duration setting device (volume type small resistor, electronic timer), 11-
Voltage increase rate setting device (volume type small resistor), 12~
Thyristor, 13-function generator, 14-gate control circuit. Patent applicant Toyo Kiden Co., Ltd. Agent Patent attorney Katsutoshi Yoshimura (and one other person) Light 3 Figure (a)
) Fig. 3 (C) Fig. 3 (b) Fig. 3 (d) Fig. 3 (e) 10 = 1 1 Fff Dark No. 6 Fig. History 1 Fermentation Fig. 3 (1), 1 Fig. 7 Fig. 1 Time rA

Claims (2)

[Claims] (1) A starting device for an induction motor that uses a thyristor to control the primary voltage of a squirrel-cage induction motor includes an initial starting voltage setting device that sets the initial value of the starting voltage, and a starting voltage setting device that sets the starting voltage from the initial value. By combining a voltage increase rate setting device that sets the rate of increase, and a command signal according to the setting values from the starting initial voltage setting device and the voltage increase rate setting device, the primary voltage applied to the squirrel cage induction motor is applied to the desired starting voltage. A function generator that generates a starting voltage command pattern to form a starting voltage command pattern, and a trigger signal based on the starting voltage command pattern in the function generator to apply a primary voltage that becomes a starting voltage application pattern to the squirrel cage induction motor using a thyristor. 1. A starting device for a squirrel cage induction motor, comprising: a gate control circuit for controlling the noise; (2) In addition to the starting initial voltage setting device, the voltage increase rate setting device, and the gate control circuit according to claim 1, an initial voltage duration time setting device for setting the time for which the starting initial voltage continues; A starting voltage command pattern that sets the primary voltage applied to the squirrel cage induction motor to the desired starting voltage application pattern by combining command signals according to the settings from the setting device, initial voltage duration setting device, and voltage increase rate setting device. A starting device for a squirrel-cage induction motor, comprising: a function generator that generates .