JPH0736449Y2 - Motor load protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a motor load protection device, and more particularly to a device for protecting a motor load by detecting a current flowing through the motor.

[Prior Art] Conventionally, as a motor load protection device of this type, for example, there is a thermal relay as described below.

The thermal relay protects the motor itself,
At the same time, it also protects the load. In this thermal relay, this thermal heater is heated by the current flowing in the thermal heater inserted in the power supply line of the motor, that is, the current consumed by the motor load, and this heat is used to drive the bimetal to mechanically Separate the contact mechanism,
It protects the motor and the load by shutting off overcurrent and confined current flowing through the motor.

[Problems to be solved by the invention]

However, this thermal heater has a long operating time from the occurrence of overcurrent or restraint current to the actual opening of the contacts and interruption of these currents. Therefore, due to the large current generated during this operating time, the motor However, there was a problem that the output torque of was increased and the load was damaged.

For example, a thermal heater is used for a motor that drives a belt conveyor in a factory production line, but when foreign matter is caught in a chain that transmits the driving force of the motor to the belt conveyor, a binding current is generated, The chain was cut by the excessive torque output from the motor before the thermal heater was operated, or the shear pin connected to the motor output shaft was damaged. As a result, the production work using the belt conveyor had to be stopped until the time required to replace the chains and the shear pins, resulting in great damage.

[Means for solving problems]

The present invention was made to solve the above problems,
From the detection circuit that detects the current flowing in the thermal heater inserted in the motor power supply line as a voltage using the resistance of this thermal heater, the comparison circuit that compares this voltage with the reference voltage, and this comparison circuit And a relay that stops the power supply to the power supply line of the motor in response to the signal.

[Action]

The detection of overcurrent, restraint current, etc., and the stop of the power supply to the motor are performed in a short time by the electrical processing of the electronic circuit.

〔Example〕

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.
The figure is this wiring diagram.

In FIG. 2, reference numeral 1 is a three-phase AC motor that drives a load, and the R-phase, S-phase, and T-phase three-phase AC power supplies are power supply lines 2,
It is input via 3,4. Relay contacts 5a, 5b, 5c, which will be described later, are connected to the power supply lines 2, 3, 4 to connect the relays 5a, 5b.
Thermal heaters 6 and 7 having low resistance components are inserted in power supply lines 2 and 4 between c and the motor 1. Reference numeral 8 is a motor load protection circuit described later, which inputs power from power supply input terminals 8a and 8b connected to R and S phases on the power supply side of relay contacts 5a and 5b of power supply lines 2 and 3, respectively. , Both ends of the R-phase thermal heater 6 are connected to the shock detection terminal 8c and the common terminal 8d, and flow to the thermal heater 6.
That is, the current that drives the load of the motor 1 is input as voltage. Further, the S phase of the power supply line 3 is connected to the rotation detection terminal 8e, and the voltage indicating the rotation state of the motor 1 generated between this terminal 8e and the common terminal 8d is input. The relay contacts 5a, 5b, 5c, the thermal heaters 6, 7 and the motor load protection circuit 8 constitute a motor load protection device.

FIG. 1 is a block diagram showing the internal structure of the motor load protection circuit 8.

In the figure, 8c is the above-mentioned shock detection terminal, and the voltage to the common terminal 8d generated at this terminal 8c is input to the high-pass filter 9 and the commercial frequency component is removed and output. The output voltage is input to the amplifier circuit 10,
The amplification factor is determined and amplified according to the current that normally flows through the load connected to the motor 1. The high-pass filter 9 and the amplifier circuit 10 are detection circuits that detect the load current of the motor 1 as a voltage. The amplified voltage is compared circuit 11
And is compared with the reference voltage from the reference voltage generation circuit 12. This reference voltage is predetermined by the adjustment resistor,
For example, if the voltage generated at both ends of the thermal heater 6 due to the normal load current of the motor 1 is 100%, it is 10% at 100% intervals.
It is predetermined within the range of 0 to 1000%.

The comparison circuit 11 compares the input voltage from the amplification circuit 10 with the reference voltage from the reference voltage generation circuit 12 and outputs it as a signal when the voltage from the amplification circuit 10 is larger. The output voltage from the amplifier circuit 10 is input to the indicator drive circuit 13, the indicator 14 which is a level meter blinks, and the current amount of the load current of the motor 1 is displayed in real time.

The signal output from the comparison circuit 11 is input to the low pass filter 15, and the motor 1 detected from the shock detection terminal 8c is detected.
The high-frequency noise is removed from the overcurrent and the restricted current flowing in the motor, that is, the signal indicating that the motor shock has occurred. This low-pass filter 15 forms an integrating circuit with an adjusting resistor and a capacitor, and by adjusting the time constant of the rise time of the above-mentioned signal with this adjusting resistor, it is possible to cope with different noise depending on the type of load of the motor 1. become. For example, the rise time is made variable within the range of 0 to 0.1 seconds. The shock signal from which the noise has been removed in this way is input to the AND circuit 16,
The signal from the timer circuit 17, which will be described later, is ORed and output, and the output signal is input to the relay drive circuit 18 to open the relay contacts 5a, 5b, 5c, and stop the power supply to the motor 1. Let The relay contacts 5a, 5b, 5c and the relay driving circuit 18 form a relay.

Further, the signal from the timer circuit 17 is output as follows. That is, a voltage corresponding to the rotation state of the motor 1 generated at the rotation detection terminal 8e is input to the high-pass filter 19 to remove the commercial frequency component, and this voltage is amplified by the amplifier circuit 20.
Amplified by and input to the dead zone generation circuit 21. This dead zone generation circuit 21 detects the level of the input voltage,
It outputs a signal only when a voltage above a certain level is input. This is because when the motor 1 starts up or when it stops together with the dynamic brake, the current flowing in the power supply lines 2, 3 and 4 more than the normal time is detected as a voltage of a certain level or higher, and when the motor 1 starts up or stops. It detects and outputs this as a signal.

When a signal is output from the dead zone generation circuit 21, the timer circuit
The signal normally output from 17 will not be output for a certain period of time. That is, the AND circuit 16 for inputting the output signal from the timer circuit 17 is provided so that the motor load protection circuit 8 does not erroneously detect a large current at the time of starting or stopping the motor 1 as an overcurrent or a constraint current. It is a thing. The above-mentioned fixed time is set according to the type of the motor 1 and the type of the dynamic brake, and is variable within the range of 0 to 10 seconds, for example. Further, at the same time, the signal output from the dead zone generation circuit 21 is input to the low pass filter 22 having the same configuration as the low pass filter 15 described above to remove noise and drive the stop detection output relay drive circuit 23. .
This circuit 23 is for confirming the stop of the motor 1, and for example, drives a relay that lights a lamp to confirm the stop.

Incidentally, reference numeral 24 is a push switch which is a b contact, and is for preventing a detection signal from being erroneously output when the amplification factor of the amplifier circuit 10 is set.

In such a configuration, if an abnormality occurs in the load of the motor 1, an overcurrent or a restricted current flows in the power supply lines 2, 3, and 4. These currents are detected by the detection circuit as voltages using the resistance of the thermal heater 6, and are compared with the reference voltage by the comparison circuit 11, so that the motor shock is instantaneously detected, and the relay is driven to the motor 1. The power supply is stopped immediately. This series of operations is different from mechanical ones that use bimetals for work, and because the electronic circuits are all electrically operated, the operation time is short and excessive torque applied to the motor load is It is suppressed and damage to the motor load is avoided.

It is known that a low resistance is inserted in the power supply line of the motor to detect the current flowing in the load from the voltage drop of this low resistance to protect it from overcurrent. When a resistor is used, it is difficult to set a value because the resistance is small, and it is difficult to obtain a resistor having a desired resistance. Also, since a large current flows, it is necessary to increase the current capacity, and it is difficult to obtain a low resistance that satisfies all the characteristics. However, when the thermal heater is used as a resistor instead of the conventional heater as in the present invention, the thermal heater is originally designed to be inserted into the power supply line of the motor, so the resistance value is sufficiently low and the current is low. An optimal low resistance resistor having a large capacity can be obtained.

[Effect of device]

As described above, according to the present invention, the current flowing in the thermal heater inserted in the power supply line of the motor is detected as a voltage by the detection circuit, and this voltage is compared with the reference voltage by the comparison circuit to relay the power supply line. Open the circuit,
By stopping the power supply to the motor,
The detection of overcurrent and restraint current, and the stop of power supply to the motor are performed by electrical processing by an electronic circuit, so the operating time becomes shorter and the output torque of the motor increases and load is If it is damaged, it has the effect of solving the problem. Therefore, for example, the production work using the belt conveyor can be performed as planned without delay.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a wiring diagram thereof. 1 …… Motor, 2,3,4 …… Power supply line, 5a, b, c ……
Relay contacts, 6,7 ... Thermal heater, 8 ... Motor load protection circuit, 9 ... High pass filter, 10 ... Amplification circuit, 11 ... Comparison circuit, 12 ... Reference voltage generation circuit, 18 ...
Relay drive circuit.

Claims (1)

[Scope of utility model registration request] 1. In a motor load protection device using a thermal heater inserted in a power supply line of a motor, a detection circuit for detecting the load current of the motor flowing through the thermal heater as a voltage, and a detection circuit from the detection circuit. A comparison circuit that compares a voltage with a preset reference voltage and outputs a signal when the voltage from the detection circuit is higher than the reference voltage; and a power supply to the power supply line that is driven by the signal from the comparison circuit. A motor load protection device comprising a relay for stopping.