JPS59175393A - Protecting device of motor - Google Patents

Abstract

PURPOSE:To prevent the unintentional stop of one motor and the stop of a plant by predicting the overload state of the motor and operating the other motor. CONSTITUTION:Load predicting means (a) samples a load current of a motor during the operation at the prescribed period to predict and calculates the load current by the rate of change from the sampling value of previous time at the next sampling time, and applies it to a register (e). Overload discriminating means (b) outputs an overload discrimination signal when the value predicted by the means (a) is the set value or larger. Preliminary motor operation instructing means (c) applies an operation command to the preliminary motor if the predicted value of the previous sampling time is the set value or higher when the overload discrimination signal is outputted. Load rate calculating means (d) obtain a load rate from the load current when a plurality of motors are operated and applies a stop command to one motor when the load rate is within the set value.

Description

[Detailed Description of the Invention] [Summary of the Invention] When controlling the number of a plurality of electric motors, the present invention provides that if the regular motor is overloaded even if the operating level of the standby motor has not been reached, the standby motor This invention relates to an electric motor maintenance device that issues a driving command to a regular motor and causes it to run in parallel with a regular motor to prevent overloading of the regular motor and the resulting damage to the motor.

[Technical background of the invention and its problems]

Figure 1 shows an example of motorized ladder protection coordination in general industry. In the figure, a and b are the load currents at steady state when there are grains of ￫＄j+轡, C is the rated current of the motor, and d%
e are the operating values of the instantaneous and anti-timed elements of the overcurrent relay. Normally, the operating value of the inverse time limit element is set to about 110% of the evening motor rated current during the time period when the motor does not operate due to the starting current of the motor. In the above setting, since the starting characteristics of the motor are taken into consideration, the inverse time characteristic of the long time limit does not work easily against overcurrents in the small area or the basin, and the child girder does not work well for protection against large currents. There is no protection.

Generally, when level control in a water tank or the like is performed using a plurality of electric motors (for example, a regular use motor and a standby electric motor), the normal use electric motor usually performs the first operation, and the standby electric motor is on standby. When the level position rises and the regular-1-motor cannot process it, it reaches the operation level of the standby motor, and the standby Thj i
Issue an operation command to machine h, operate the standby motor, and use it regularly.
The standby motors operate in parallel. After parallel operation, when the level decreases, the regular or standby electric motor is generally stopped according to a predetermined sequence.

On the other hand, when the regular movable machine is in operation, even if the operating level of the standby motor has not been reached, if the regular movable machine becomes overloaded due to load fluctuations such as disturbances, the regular movable machine will be overloaded due to the above-mentioned time maintenance coordination characteristic. , it detects that the motive is: I is a thief and stops it.

As a result, the process has to be started up from the beginning, which not only results in a loss of time but also may damage the equipment.

[Purpose of the invention]

The purpose of the present invention is to reduce the power consumption by causing the standby motor to operate completely according to the operation command, even if the standby motor has not reached the operating level, if the main motor is likely to overload or exceed the Fi overload tolerance. An object of the present invention is to provide a protection device for a motor that prevents unnecessary stoppage during overload and burnout caused by continued overload.

[Summary of the invention]

The present invention relates to a protection device for a motorized motor which can share the load with each other in seconds.As shown in Fig. 2, the load current of an operating motor is sampled at regular intervals, and each sampling is based on the previous sampling value. A load prediction means a predicts and calculates the load current at the next sun 19fufu based on the rate of change of If the predicted value is equal to or higher than the set value as a result of the determination by the load determining means, a means C for issuing an operation command to the standby machine on the condition that the predicted value at the time of the previous sampling was equal to or higher than the set value, and operation of the plurality of electric motors. By providing a load factor calculation means d which calculates the load factor from the load current and issues a stop command to one of the motors if the load factor is less than a predetermined value, the overload state of the motor can be prevented. The system predicts this in advance and activates a standby machine to share part of the load in order to prevent burnout due to overload.

Note that e in the figure is a register that holds the predicted value from the previous sampling. f is frost, motor operation control circuit, motor 1
A control signal is given to the switch 3 to stop the operation.

A current transformer 4 detects the current flowing through the motor 1.

[Embodiments of the invention]

The present invention will be explained in detail below with reference to an embodiment shown in the drawings.

In FIG. 3, a 1.1l-It electric motor is capable of sharing the load with each other and is connected to a busbar via a power fuse 2 and a switch 3, such as an ML magnetic contactor.

Note that the power fuse 2 and electromagnetic contactor 3 may be replaced with a breaker depending on the load capacity or power supply capacity, or in the case of a smaller capacity, a no-fuse breaker and an electromagnetic contactor in the control center. 4 is a current transformer that detects the load current of a motor, for example, a rust conduction motor l.

A conventional overcurrent relay 5, an auxiliary current transformer or transducer 6, a current changeover switch 7, an ammeter 8, etc. are connected to the secondary side of the current transformer 4. 9 is the second
The load current of the motor 1 is inputted through the current transformer 4 and the auxiliary current transformer 6 in the motor protection device having the calculation function shown in the figure. Here, the electric motor 1 is used to drive a valve used for controlling the water level of a water tank, etc., and a level detector 10 such as a lightning rod or pole rod is provided to detect the operating level of the electric motor 1.

FIG. 3 shows an example of a predictive overload calculation method. The current I in the figure corresponds to the motor rated load current S in FIG. 1, and is a function of time I (t).

IN is the motor rated current, and is the motor rated current CK in Figure 1.
handle. t is the current time, t is a sampling time 61 seconds before the current time, and t is a sampling time 61 seconds after the current time. Predicted current I at time t!
is calculated using the following equation based on the current electrician and the amount of change Δ■ in the first lightning current at a sampling time ΔT a certain time later.

ΔWork'=I+lhWork×ΔT This calculation is performed by the load prediction means a shown in FIG. 2 in the maintenance device 9.

Then, the overload determining means determines whether or not this predicted current value is greater than or equal to a preset value.

Figure 3 shows the possibility that the predicted current value of the electric motor will increase beyond the rated current, but the temperature rise of the motor is
Since there is a thermal time constant, the circuit breaker is not immediately tripped at this point t, but processing is performed after determining whether the temperature rise of the motor is within the permissible temperature rise of the motor, that is, within the permissible overload operation limit. This judgment criterion is determined by the standby machine operation commanding means C, with the condition that the predicted value at the previous sampling is greater than or equal to the rated value. Here, the sampling time ΔT is determined by the system including the #1 machine.

As a result of the above judgment, when a predetermined judgment criterion is met, a driving command is issued from the motor operation control circuit f to the standby motor to perform parallel operation with the regular motor. Normally used during parallel operation, the load factor f1 is calculated from the load condition using the load factor calculation means d, and when the load factor decreases to the point where one motor can supply the load, one motor is continuously operated to reduce the base load. Supply and stop the nine city transit trains that have been running until now.

FIG. 4 shows a flowchart showing the flow of the above operation, and this operation +d is executed by each means shown in FIG. Limit checks of operating conditions are performed using the level position and load current value. The level position limit check is the same as the conventional method, but the overcurrent limit check is
The load current after 61 seconds is predicted based on the current load current.

That is, it is determined whether the load current after 61 seconds is on an increasing trend. As a result, if there is a possibility that the load current exceeds the overload capacity, the standby motor is operated even if the level position has not reached the standby motor operation start position.

Next, calculate the load factor of the regular and standby motors operating in parallel, and when the load factor decreases to the point where the standby motor can supply the load, continue operating the standby motor to supply the base load, and then Stop the paddle.

The reason why the backup motor is operated continuously instead of the regular motor is to keep the operating time and maintenance of the rectangular motor at the same level and to improve the reliability of motor operation.

As described above, according to the present invention, the operating state of the electric motor can be grasped, and the electric motor can be protected from overloading.

The retention device has a first-stage alarm and a second-stage trip mechanism, and an alarm is issued when a certain load rate is exceeded, and a backup motor operation command is issued (after a certain period of time from this point onwards). However, if the load factor decreases after a certain period of time, this circuit is reset.

The trip command signal is issued when there is a possibility that the overload operation of the plotter will be out of tolerance. During parallel operation of regular and standby motors, if the load factor of both motors increases and there is a possibility that the overload capacity will be exceeded, take measures to stop the motors on the process side and install a breaker. trip to protect the motor. In addition, if the regular machine is still overloaded and the standby machine is lightly loaded, an alarm will be issued to notify that the regular machine is overloaded, and at the same time a signal will be issued (for example, by opening/closing a valve), so the backup machine will be alerted. It is possible to perform load migration.

Since this arithmetic device is equipped with a contact circuit, there is no wear on the seven contacts compared to a contact circuit, and the delay in operation time is negligible.

Generally speaking, in order to operate the WL motor with high efficiency, the load factor must be ρ.
It is better to start operation of the standby motor, but based on the premise that the standby motor operates in coordination with the regular motor, it can be set not only when the standby motor is overfied or overloaded, but also when a certain load factor is exceeded. . In addition, in the explanation, the spare 115.
Although the operation mode to the ilj machine has been described, the operation mode can also be changed from the standby electric motor to the regular electric motor by switching the operation mode. Although the description has been limited to a level signal as an operation command signal for a standby motor, it can also be applied to a process such as a pressure signal.

In addition to automatic operation, which issues a run command to the standby motor when a certain set load factor is reached, it also issues a run command to the standby motor to prevent the standby motor from operating, for the purpose of protecting the motor. , it is possible to stop the electric *lJ machine currently in operation.

The present invention can be used not only to grasp the operating status of the electric motor but also for maintenance monitoring.

〔Effect of the invention〕

As described above, according to the present invention, for several electric motors whose loads can be known to each other, by predicting an overload state of one of the electric motors and operating the other electric motor, one electric motor can be operated. It is possible to prevent inadvertent stoppage of the electric motor in an overloaded state and the resulting stoppage of the plant.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating overcurrent fAi' and protection coordination of a conventional induction motor using a relay, FIG. 2 is a block diagram showing the present invention, and FIG. 3 is a diagram according to the present invention. FIG. 4 is a diagram showing an example of a predictive overload calculation method according to the present invention, and FIG. 5 is a flowchart showing the operation of the present invention. 1...Electric motor 2...Power fuse 3.
・・Magnetic contactor 4・・Current transformer 5・・Overcurrent relay 6・・Auxiliary current transformer or transducer 7・・Current selection switch 8・・Hair flow puller 9・・Calculation function Protective device 10...Level detection everyone; (7317) Agent Patent attorney Noriyuki Chika (
(1 person) Figure 1: To Figure 2/C/Ha Figure 3: B Figure 4: bt t tz -rB1

Claims (1)

[Claims] In a protection device for multiple motors that can share the load with each other, the load current of the operating motor is sampled at regular intervals, and for each sample, the load current at the next sampling is predicted and calculated based on the rate of change from the previous sampling value. a load prediction means; an overload determination means for determining whether the value predicted by the load prediction means is greater than or equal to a set value; A means of giving an operation command to a standby machine on the condition that the predicted value or a set value is exceeded, and a method of calculating the load factor from the load current of multiple motors when operating multiple motors, even if this load factor is less than the planned value. A motor maintenance device comprising load factor calculation means for giving a stop command to one of the motors.