JP3930845B2 - Automatic return method of motor protection device - Google Patents

Description

  The present invention relates to an automatic return method for a motor protection device, and more particularly to an automatic return method for a motor protection device for protecting an AC electric motor used as a drive source for utility or auxiliary equipment of factory equipment. It is.

  The motor as described above is provided with a motor protection device (overcurrent protection device) including a motor breaker and a thermal relay as a protection device for avoiding motor burnout due to an abnormal increase in load. The motor breaker is a device that immediately cuts off the current when an overcurrent such as a short circuit current is detected, and the thermal relay is a device that cuts off the current when the temperature rise due to energization reaches a predetermined level.

  When an abnormality occurs during operation and the motor is overloaded, the thermal relay normally operates to cut off the current and protect the motor. In the past, when such an abnormality occurred, an operator went to the site each time and the thermal relay was manually reset. However, since such a manual return method takes a long time to respond, the line may be stopped due to a response delay.

As disclosed in Patent Document 1, it is conventionally known to incorporate an automatic return function into a circuit breaker. However, when the automatic return function as shown in Patent Document 1 is incorporated in the motor protection device, the motor may be repeatedly started up to the set number of times without removing the abnormality, and the motor may burn out. For this reason, conventionally, it has been impossible to incorporate an automatic return function into a motor protection device used in a factory.
JP-A-10-322878

  The present invention solves the above-described conventional problems, can surely prevent motor burnout due to an increase in load, and can automatically prevent line breakage by the motor protection device. It was made to provide a method.

The present invention made to solve the above problems is an automatic return method of a motor protection device including a motor breaker, a thermal relay, and a calculation unit , and the thermal relay is within a set time from when the overload is interrupted. Until the number of overload cutoffs reaches the set number of times, the operation of automatically returning the thermal relay after the elapse of the time necessary for cooling the motor winding is repeated, but the number of overload cutoffs within the set time exceeds the set number of times. Sometimes, the automatic recovery function is stopped as a serious failure, and when the number of overload interruptions within the set time does not exceed the set number, the set time is counted again from the last overload interruption within the set time. And the count of the number of interruptions within the set time is started.

It should be noted that resetting when a serious failure occurs is preferably performed in an electric room that manages the motor power supply.

  According to the present invention, when the motor load increases and the thermal relay performs overload interruption, the timer is started, and when the time for the motor winding to cool down due to the motor operation stop has elapsed, The relay is automatically reset. For this reason, since it is not necessary for the worker to go to the site and manually return the thermal relay as in the conventional case, the line is not stopped due to a response delay.

Such automatic return of the thermal relay is repeated until the set number of overload interruptions within a certain time from when the thermal relay first performs overload interruption. However, if the interruption and start-up are repeated many times without removing the cause of the overload, the temperature of the motor winding gradually increases and reaches the dielectric breakdown region as shown in FIG. 1, and the motor may burn out. There is. Therefore, in the present invention, when the number of overload interruptions within a predetermined time after the thermal relay performs overload interruption exceeds the set number of times, the automatic return function is stopped as a serious failure. For this reason, if the set time and the set number of times are appropriately set according to the characteristics of the motor, a motor burnout accident can be reliably prevented. Further, when the number of overload interruptions within the set time does not exceed the set number, the count of the set time and the count of the number of interruptions within the set time are repeated from the last overload cutoff within the set time. Therefore, the motor burnout accident can be prevented more reliably than simply resetting the timer when the set time elapses.

  FIG. 2 is a diagram illustrating the configuration of the embodiment of the present invention. In FIG. 2, reference numeral 1 denotes an AC motor used as a drive source for utility or auxiliary equipment of factory equipment. On the power source side, a motor comprising a motor breaker 2, an operation contactor 3, and a thermal relay 4. A protection device 5 is connected. The motor breaker 2 is a device that immediately cuts off the current when a large current such as a short circuit current is detected as described above. The thermal relay 4 is a device that cuts off the current when the temperature rise of the bimetal or the like reaches a predetermined level due to the overcurrent.

  As shown in FIG. 3, the protection curves of the motor breaker 2 and the thermal relay 4 are set to be above the starting characteristics of the motor 1. Further, for overload currents below the starting (restraining) current, protection coordination is achieved so that the thermal relay 4 operates before the motor breaker 2 as in the conventional case.

  In the present invention, the motor protection device 5 is provided with an automatic return unit 6. The automatic return unit 6 includes a counter 7 that counts the number of times that the thermal relay 4 performs overload interruption, a timer 8 that operates when the thermal relay 4 performs overload interruption, a calculation unit 9, and a thermal relay. 4 return operation sections 10. Below, the automatic return method of the motor protection apparatus of this invention is demonstrated.

  When the load of the motor 1 equipped with such a motor protection device 5 increases and the thermal relay 4 performs the first overload interruption, the timer 8 starts operating and the counter 7 counts the number of overload interruptions. To do. If the count number is less than the set number of times, for example, 3 times, the calculation unit 9 outputs a return signal to the return operation unit 10 to automatically return the thermal relay 4. However, immediately after the thermal relay 4 is operated, as shown in FIG. 1, the temperature of the motor winding has risen to a dangerous area, so it is not preferable to immediately restart the motor 1 by automatically returning the thermal relay 4 automatically. . Therefore, the return time is counted by the timer 8 and automatically returned after the time necessary for cooling the motor windings. Thus, since the motor 1 is restarted simultaneously with the automatic return of the thermal relay 4, the line stop can be avoided.

  However, if the number of overload interruptions within a set time, for example, one hour from when the thermal relay 4 performs the first overload interruption exceeds the set number (for example, 3 times), a mere temporary increase in load There is a high possibility that some sort of failure has occurred. In such a case, if the automatic return is repeated, the motor 1 may be burned out. Therefore, in such a case, the calculation unit 9 determines that a serious failure has occurred, stops the automatic return function, sends a signal to the electrical room that manages the motor power supply, and the operator removes the failure on site. Thereafter, the counter 7 and the timer 8 are reset in the electric room, and the normal operation is resumed.

In addition, as shown in FIG. 4, when the fourth overload cutoff is not performed within a set time, for example, 1 hour after the first overload cutoff, a temporary load increase occurs instead of a serious failure. It should be judged that it has only occurred. In this case, instead of simply resets the timer 8, so as to count the final setting time overload blocking within the set time, it is preferable to count the blocking times within the set time. As a result, it is possible to reliably prevent a motor burnout accident rather than simply resetting the timer when the set time has elapsed. The above flow is shown in FIG.

  As described above, according to the present invention, when the thermal relay 4 performs an overload interruption, it is not necessary for the worker to go to the site and manually return the thermal relay as in the prior art. Is not invited. When the number of overload interruptions within a certain time after the thermal relay performs overload interruption exceeds the set number, the automatic return function is stopped as a serious failure. For this reason, a motor burnout accident can be reliably prevented.

It is a graph which shows the temperature change of a motor winding. It is a configuration explanatory view of an embodiment of the present invention. It is a cut-off operation characteristic figure of a motor breaker and a thermal relay. It is a graph of overload interruption. It is a flowchart of an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 2 Motor breaker 3 Driving contactor 4 Thermal relay 5 Motor protection device 6 Automatic return part 7 Counter 8 Timer 9 Calculation part 10 Return operation

Claims (2)

A motor protection device automatic recovery method that includes a motor breaker, thermal relay, and calculation unit . When the thermal relay performs an overload cutoff, the number of overload cutoffs within the set time is limited to the set number of times. The operation to automatically return the thermal relay after the elapse of the time required for cooling the battery is repeated, but if the number of overload interruptions within the set time exceeds the set number, the automatic return function is stopped as a serious failure, and the setting If the number of overload interruptions within the time does not exceed the set number, the counting of the set time and the number of interruptions within the set time are started again from the last overload interruption within the set time. A method for automatically returning a motor protection device.   2. The method of automatically returning a motor protection device according to claim 1, wherein the reset when a serious failure occurs is performed in an electric room that manages the motor power supply.

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