JPS6132518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor overload prevention device for a turbo compressor.

As shown in Fig. 1, the conventional method for preventing overload of the motor of a turbo compressor 1 is to reduce the electric power (or current) of the motor that drives the turbo compressor 1.
is measured with a wattmeter (or ammeter) 2, and
The controller 3 converts the air pressure into an adjustment signal of 0.2 to 1.0 Kg/cm ² , while the discharge pressure controller 4 converts the compressor discharge pressure into an air pressure adjustment signal of 0.2 to 1.0 Kg/cm ^{2 .}
At the same time, it selects the lower of the two air pressure signals from the controller 3 and the discharge pressure controller 4, sends it to the selector 5 which outputs it, and selects which of the two signals. There is a method in which the suction damper 6 is activated by the lower signal to control the electric power, but this method uses an analog type controller 3 that converts the electric signal of electric power or current into an adjustment signal of air pressure. This has the disadvantage that the entire control system is expensive. Furthermore, since there is normally no discharge pressure before the compressor is started, the discharge pressure regulator 4 outputs a fully open signal for the suction damper 6, and the power controller also outputs a fully open signal, so the suction damper 6 is fully open. However, it is necessary to control the compressor so that the suction damper 6 is closed at startup, and after a low load startup, the suction damper 6 is gradually opened to increase the compressor load. Therefore, conventionally, as shown in FIG. 1, it is necessary to provide a function generator 7 whose output gradually changes when the compressor receives a start signal (for example, a contact 8 of a motor start switch).

This function generator is expensive, and in conventional equipment, it is used only when starting the turbo compressor, making it uneconomical.It also includes a current and analog signal converter to keep the motor current below a set value. An analog controller 3 must also be provided, which is also uneconomical.

In addition, because conventionally used current controllers perform fixed value control, they respond to current changes in response to temporary voltage fluctuations in the motor current system and temporarily fluctuate the capacity of the compressor, causing disturbances to the process. There was a drawback.

This invention was made to eliminate the above-mentioned drawbacks, and uses a signal generator that detects motor overload using a current detection switch and generates an analog signal in response to this on-off signal. This method performs overload prevention control by adjusting the suction damper, but this method involves controlling the suction damper to gradually open at startup and controlling the opening degree of the suction damper to prevent overload of the motor. An object of the present invention is to provide an overload prevention device that can be configured at low cost, which can be used for both purposes with one signal generator, does not respond to small changes in motor current, and can prevent disturbances to the process. It is.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, 11 is a turbo compressor, 12 is a suction damper provided on the suction side of the turbo compressor 11, and the capacity of the turbo compressor 11 is determined by the opening amount of a valve (not shown) in this suction damper 12. is controlled.

13 is an electric motor that drives the turbo compressor 11;
4 is a current detector for the electric motor 13.

Reference numeral 15 denotes a current detection switch, which is operated by inputting the output signal of the current detector 14, and the output contact H is activated when the current value of the motor 13 increases, for example, at the rated value, as shown in FIG. When the current exceeds 103%, it becomes closed, and when the current decreases, it becomes open when it is below 100%, and when the current increases, the contact L is closed until the rated value of 100°C, and when it exceeds 100%, it becomes open. When the current decreases to 97% or less, it closes, and the operation of both contacts has hysteresis.

The opening/closing operating points of each of the contacts L and H described above can be set as desired.

16 receives an electrical on-off signal and changes from 0.2 to 1.0
The air pressure signal generator 17 outputs an air pressure signal of Kg/cm ² , which detects the discharge air pressure of the turbo compressor 11, and decreases the output if the discharge pressure exceeds the set value, and increases the output if it is below the set value. 18 is a selector.

The air pressure signal generator 16 is connected to the current detection switch 15
It has a function of increasing (or decreasing) the output at a constant speed while the contact signal is closed when receiving a command contact signal from the contact signal, and maintaining the output signal at that time when the contact signal is open.

A pneumatic signal generator 16 is provided between the instrument air supply source 19 and the selector 18.

When a signal is applied to terminal A of this pneumatic signal generator 16, the output decreases and the suction damper 12 is opened.
When a signal is applied to terminal RO, the output increases and the suction damper 12 is closed.

20 is a flow rate controller, 21 is an atmospheric discharge valve,
When the output from the turbo compressor 11 increases, the opening degree of the atmosphere discharge valve 21 is adjusted based on the output of the flow rate controller 21 to discharge unnecessary air to the atmosphere.

23 is a first time contact that closes (turns on) when the motor 13 stops and opens (off) after a certain period of time after starting; 24 represents a second time contact that operates in the opposite direction to the first time contact 23; be.

The first time contact 23 is connected in parallel to a contact H that is turned on when the current of the motor 13 is higher than a predetermined value, and the second time contact 24 is connected in series to a contact L that is turned on when the current of the motor 13 is lower than a predetermined value. has been done.

When the electric motor 13 is stopped, the discharge pressure is less than the set value of the discharge pressure regulator 17, and the output of the regulator 17 increases and becomes a signal to fully open the suction damper, but in the above-mentioned device, the contact 23 is on. Therefore, the signal generator 16 outputs a signal that completely closes the suction damper 12, and the selector 18 outputs a signal that completely closes the suction damper 12.
The output signal is selected, and the suction damper 12 is fully closed.

Now, when the motor 13 is started, the contact L is on, and after a certain period of time after starting, the contact 23 turns off and the contact 24 turns on, causing the signal generator 16 to switch the suction damper 12 until the motor current reaches 100%. It continues to output a signal in the direction of gradually opening.
As the capacity of the turbo compressor increases, the discharge pressure also begins to rise, but the output of the signal generator 16 remains unchanged until the output of the signal generator 16 reaches the set value of the discharge pressure controller 17.
8. However, the discharge pressure is
7, the output signal of the controller 17 becomes smaller than the output of the signal generator 16, is selected by the selector 18, is connected to the suction damper, and the discharge pressure controller 17 controls the suction damper. Next, this operation will be explained in detail.

After startup, the electric motor 1 of the turbo compressor 11
If the current in 3 is less than 97% of the rating, contact L
is on, and the signal generator 16 continues to increase the signal in the direction of fully opening the suction damper 12. This signal is applied to the selector 18. On the other hand, a pressure adjustment signal is given to the selector 18 from the discharge pressure regulator 17, but immediately after the compressor is started, the pressure has not reached the set value of the discharge pressure regulator, so this pressure regulation signal is set to the maximum value, In other words, it is at a level where the suction damper is fully open. Therefore, the selector 18 selects the signal from the signal generator 16 and applies it to the suction damper to increase its opening, thereby increasing the capacity of the compressor and increasing the discharge pressure. When the discharge pressure reaches the set value of the discharge pressure regulator 17, the output signal of the regulator 17 begins to decrease and eventually becomes smaller than the output signal of the signal generator 16 (i.e., in the direction of closing the suction damper). Therefore, the selector 18 gives the signal of the lower commanded opening of the suction damper 12, that is, the signal of the discharge pressure regulator 17, to the suction damper 12, and the capacity of the turbo compressor 11 is adjusted by the signal of the discharge pressure regulator 17. will be done.

However, when the air consumption amount of the load 22 becomes larger than the discharge amount of the turbo compressor 11, the discharge pressure decreases and the signal of the discharge pressure regulator 17 increases. That is, a signal in the direction to open the suction damper 12 is output. Therefore, the compressor power increases, and the electric motor 1
The current of 3 also increases. When the current value of the motor 13 becomes 103% or more of the rated value, the contact H of the current detection switch 15 is turned on, and the signal from the signal generator 16 decreases. That is, an output signal in the direction of closing the suction damper 12 is applied to the selector 18.

The selector 18 gives the damper 12 a signal in the direction of the lower commanded opening of the suction damper 12, that is, a signal from the signal generator 16. As a result, the suction damper 12 is operated in the closing direction, and the pressure is 100% regardless of the discharge pressure.
Reduce the motor power to . When the motor current is at the rated value
When it reaches 100%, the contact H turns off, the output signal of the signal generator 16 also stops at that position, and the suction damper 12 is also held at an opening such that the motor output is 100% or less.

When the consumption of the load 22 returns to normal and the motor current becomes 97% or less of the rated value, the contact L of the current detection switch 15 turns on, and the output signal of the signal generator 16 changes in the direction of opening the suction damper 12. Output a signal. On the other hand, the discharge pressure regulator 17 outputs a signal in the direction of closing the suction damper 12 upon recovery of the discharge pressure, and the suction damper 12 is controlled by the discharge pressure regulator 17 .
As described above, by selecting the signal from the discharge pressure regulator 10 and the signal from the signal generator 16 using the selector 18 to control the suction damper 12, the pressure of the system using the turbo compressor can be adjusted by the discharge pressure regulator 10. The suction damper 12 can be controlled to a desired value, and if the motor becomes overloaded, the suction damper 12 can be controlled by a signal from the signal generator 16 to prevent the motor from being overloaded.

Therefore, according to the present invention, overload can be prevented without stopping the electric motor while controlling the pressure in a system using a turbo compressor.

As described in detail above, according to the present invention, the signal generator 16 operates both when starting the electric motor and when controlling the overload of the electric motor, thereby increasing the operating efficiency of the signal generator and Since an expensive analog controller for regulating the current is not required, the overload prevention device for the turbo compressor can be made inexpensive.

Further, according to the overload prevention device according to the present invention,
Frequently occurring voltage fluctuations in the motor power supply system are generally within a few percent, so if the current detection switch settings H and L are set to 6%, the motor current change width due to voltage fluctuations will be 5%. % or less, and therefore no overload prevention operation is performed more than necessary, which has the advantage of causing fewer disturbances to the process compared to conventional devices.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of an overload prevention device for a turbo compressor motor, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of a current detection switch. 11...turbo compressor, 12...suction damper, 13
...Electric motor, 14...Current detector, 15...Current detection switch, 16...Signal generator, 17...Discharge pressure regulator.

Claims (1)

[Claims] 1. In an overload prevention device that controls the opening degree of a suction damper provided on the input side of a turbo compressor using the current of an electric motor that drives the turbo compressor, the current of the electric motor for driving the turbo compressor is detected. a signal from a first contact that opens and closes with a certain width of hysteresis when the current value of the motor reaches a preset upper limit value; A current detection switch outputs two contact signals, one is a signal from the second contact that opens and closes with hysteresis, and the other is connected in parallel with the first contact to start the compressor at low load.It closes when the motor stops, and closes after starting. a timer having a first timer contact that opens after a lapse of time; a second timer contact that is connected in series with the second contact and operates in the opposite direction to the first timer contact; and the first timer contact; The signals from the first contact and the second contact are input, and while either the first time contact or the first contact is closed, a signal is output to close the suction damper, while the second time contact and the second time contact a signal generator having a function of outputting a signal to open a reverse damper while both contact signals are closed, and holding an output signal at the time when both contact signals are opened, The output signal of the turbo compressor and the output signal of the discharge pressure regulator for the turbo compressor are input, the output signal corresponding to the lower opening of the suction damper is selected from both output signals, and this selected output signal is An overload prevention device for a turbo compressor motor, comprising: a selector for controlling the suction damper.