JPH0248888Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overload protection device for a power supply device for a motor, and particularly to an overload detection device suitable for a power supply device whose load is a group of motors in the textile and paper industries.

In general, power supplies such as thyristor inverters that use an electric motor as a load often require a capacity design that can withstand the starting current of the electric motor, requiring a high capacity margin, and various methods have been proposed as a countermeasure. . In the textile industry, etc., it is required to control the speed of a large number of electric motors with high precision, but since there is no need to increase response speed, permanent magnet motors are used and many variable frequency power supplies are installed in one variable frequency power supply. By sequentially starting each motor in a time-sharing manner as a motor power source, the starting current of each motor can be 10 to 20 times the rated current, and the ratio of starting capacity to continuous current capacity as seen from the power supply device can be kept low. ing.

In this way, in order to improve equipment efficiency by sequentially starting multiple motors with one power supply, the overload capacity of the conventional power supply was determined simply by the motor start time and its current. If the starting current and time increase due to an increase in motor capacity such as higher speeds, overloading will be repeated each time the motor is started.If the overload capacity is simply determined from the current and starting time, unless the design is designed to allow for a large margin, overloading will occur. There is a risk that the system will go down. This system down causes great damage in line control in textile and paper manufacturing industries, so it is desirable to reliably avoid system down and reduce the capacity of the power supply device.

This invention was made in view of the above circumstances,
In a power supply device for a system that sequentially starts multiple electric motors, there is an overload condition while starting the electric motor, and an overload condition that causes intermittent starting repetitions in which the motor is in a normal load condition from the end of starting the motor to the start of the next electric motor. By detecting overload time as a double integral value of the load state and each time below the state,
It is an object of the present invention to provide an overload protection device that can appropriately detect overload of a power supply device and can continue operation until the overload reaches the practical allowable limit of the device.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

As shown in Figure 1, the guaranteed overload capacity of the power supply to be protected is designed to be 30 seconds for load currents up to 200% of the rated current, and 60 seconds for load currents up to 150% of the rated current. The overload detection device according to the present invention has the configuration shown in FIG.

In Fig. 2, the load current signal I detected from the output section of the power supply device (not shown) to be protected is connected to a comparator 1 that detects a load current state of 100% or more, and a load current signal I that detects a load current state of 150% or more. It is used as a comparison input of comparator 2 that detects. The detection output of the comparator 1 is made into the gate open signal of the AND gate 3 and the gate open signal of the AND gate 5 through the inverter 4, and the gate open inputs of the AND gates 3 and 5 receive the pulse output of a constant frequency pulse generator 6. are used as the count-up (UP) and count-down (DOWN) inputs of the up-down counter 7.
The counter 7 obtains an output OUT ₁ when the count up to the certain value is reached, and this output OUT ₁
is used as an operation command for a 150% overload display relay 8 provided in the central monitoring room and an operation command for an overload display relay 10 through an OR gate 9.

The detection output of the comparator 2 is simultaneously established with the detection output of the comparator 1 and becomes the gate open signal of the AND gate 11 and the gate open signal of the AND gate 13 through the inverter 12. The pulse output of the pulse generator 6 is used as the count-up input and count-down input of the up-down counter 14. counter 1
4 gets the output OUT ₂ when the count up to the certain value is reached, and this output OUT ₂ is 200%
Operation of overload display relay 15 and OR gate 9
The operation command for the relay 10 is issued through the signal.

In this configuration, when the overload current I is greater than or equal to 100% and less than 150%, the comparator 1 detects an overload and opens the gate of the AND gate 3, and the counter 7 counts the output pulses of the pulse generator 6. The count-up operation (integration of time in an overload state) is performed as an up input, and when a set count value (a value corresponding to an integrated value of 60 seconds in FIG. 1) is reached, relays 8 and 10 are operated. but,
If the starting current decreases and the load current I becomes a value lower than 100% (below the set overload range) before the counter 7 counts up to a certain value, the AND gate 3 is closed and the AND gate 5 is closed. The gate is opened, and the counter 7 performs a countdown operation (subtraction from the time integrated value in the overload state) from the count value up to that point, and maintains the state at count zero.

Similarly, when the load current I is 150% or more, in parallel with the operation of the counter 7, the overload detection of the comparator 2 causes the counter 14 to count up, and the relays 15 and 14 count up to a certain value. When the overload reaches a value lower than 150%, the counter 14 counts down and maintains the state at zero.

Here, the counter 7 is set to 60 seconds in FIG. 1 and the count value until output OUT ₁ is obtained as shown in FIG. Double integration is performed by subtracting the integrated value by the time during which the current is within the rated current range, and this integrated value is the value equivalent to 60 seconds.
Detect overload when N ₁₀₀ is reached. Similarly, the counter 14 indicates that the count value until obtaining the output OUT ₂ has reached a value corresponding to 30 seconds in Figure 1 in the range of 150% or more of the load current by double integration of the overload time and the time below. Detect with. The setting values for obtaining the outputs of counters 7 and 14 are set to 1/2 that of counter 14 as compared to that of counter 7.

Therefore, intermittent overloads in systems that sequentially start many motors with large starting currents can be detected by double integration of the overload state time and the less than 100% load current. During normal load, overload detection can be adapted to the state of recovery from an overload state, such as eliminating the temperature rise of the power supply due to the previous overload, and enables overload detection close to the actual overload tolerance of the power supply. Make it. In other words, it is possible to design the power supply device with a small overload tolerance margin, and it is possible to reduce the cost of the power supply device.

In addition, by inputting the count-up and count-down of the counters 7 and 14 from a pulse generator with a different frequency, it is preferable to adjust the integration time constant during overload and below to the thermal time constant of the power supply device. Overload detection occurs.

Also, overload detection ranges from 100% to 150% and 150%
This example shows the case where the overload is divided into two ranges from % to 200%, but three or more circuit units consisting of a comparator, a counter, a relay, and an up/down switching circuit are prepared to detect the overload by subdividing it into three or more ranges. By doing so, the current overload condition can be appropriately displayed and the supervisor can be informed, and it is easy to appropriately operate or automatically control the time intervals of the sequential starting of the electric motors.

If an overload detected in this way causes a large amount of damage due to a system failure in the textile industry, etc., the power supply unit should not be stopped immediately upon detection of an overload, as shown in Figure 4. Power supply device 16
Temperature sensor 18 of main thyristor cooling fin 17 of
power supply 16, such as a thermal pre-failure detection signal by
The power supply is stopped only when the limit of failure occurrence is detected. In this way, the operation of the power supply unit is not stopped immediately when an overload is detected, but is stopped from the permissible temperature limit value of the cooling fin, etc. In addition to the temperature rise due to overload due to load current, cooling fin failure etc. Parallel protection from other failure causes is also possible.

As described above, according to the present invention, in a system that efficiently uses a power supply device by sequentially starting a large number of electric motors, such as those used in the textile industry, intermittent overload conditions and load conditions below the above conditions can be treated separately. Since overload time is detected by double integration of time, overload detection is compatible with the overload tolerance of the power supply device. In addition, instead of immediately stopping the system when an overload is detected, the system can continue operating as if it were a minor failure until it reaches the allowable limit of the power supply, making it suitable for overload protection in the textile industry and the like. In addition, by detecting the actual permissible limit such as the temperature of the element cooling fin, which is the maximum temperature, when stopping the operation of the power supply unit, protection is provided that takes into consideration the ambient temperature of the cooling fin, and protection devices such as the cooling fin against failure of the cooling system. Cooperation results in appropriate overload detection.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram illustrating the overload capacity of a power supply device for a motor, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a time chart for explaining the operation of Fig. FIG. 4 is a main part configuration diagram for explaining overheat protection of the power supply device. 1, 2...Comparator, 6...Pulse generator, 7,
14...Up-down counter, 8, 10, 15
...Overload detection relay, 17...Cooling fin, 1
8...Temperature detector.

Claims (1)

[Scope of utility model registration request] In a motor power supply device that sequentially starts multiple electric motors as a load, when the motors are repeatedly started intermittently, the time in the overload state that reaches the set overload range is accumulated, and the time during which the overload falls below the set overload range is calculated. It is equipped with an overload detection circuit that performs double integration by subtracting time from the integrated value and obtains an overload detection output when this double integrated value exceeds the overload time in a predetermined overload range. Features: Overload protection device for electric motor power supply.