JPH077977A - Motor overload protector - Google Patents

Abstract

PURPOSE:To operates a thermal relay when an abnormal starting current flows and to shut OFF a current by providing a thermal relay bypass circuit for connecting one end of an AC unit to the other end through a third A contact and a second current regulating resistor. CONSTITUTION:First A contact 11a1-third A contact 11a3, first B contact 11b1, second B contact 11b2 of an auxiliary relay are, in addition to a thermal relay 7, provided in a controller 13. When a start pushbutton switch 9 is closed, a circuit of the switch 9, a stop phshbutton switch 10 and a contact 7-1 of the relay 7 is formed from a power source 8 for an operation, and a switch 5-1, contacts 5a1-5a3 of an electromagnetic contactor 5 are closed. As a result, the unit 5-1 is closed so that a current flows from a three-phase power source 1 to a motor 2 through a witch 4-1 of a breaker 4 for wiring, the switch 5-1, a motor is started to generate a motor starting current I0 proportional to a current of a motor circuit 3 in an AC unit 6, and the current is branched to a current I1 and a current I2 in the controller 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor overload protection device for interrupting a circuit of the electric motor when the electric motor is overloaded when starting the electric motor.

[0002]

2. Description of the Related Art Conventionally, a thermal relay has been used as an overload protection device for an electric motor. When an overcurrent flows through the electric motor, the temperature of the thermal relay rises to a predetermined temperature or higher, and the function of a bimetal or the like causes the electric motor to operate. The circuit breaker that opens and closes the circuit is opened to protect the motor from being overloaded.

However, when the weight or diameter of the load rotated by the electric motor is large, the starting time until the rotational speed of the electric motor reaches a predetermined rotational speed becomes long, and the starting current flowing during this starting time also has a large current value. become. In order to prevent the thermal relay from opening the circuit of the electric motor with such a starting current, a bypass circuit is provided in the thermal relay, and when the electric motor is started, the bypass circuit is closed to prevent the load current from flowing to the thermal relay. After the start-up is completed, the bypass circuit is automatically opened and a load current is passed through the thermal relay to protect the motor from overload.

An example of such a conventional motor overload protection device will be described with reference to the circuit diagram of FIG. 5. In the middle of the motor circuit 3 connecting the three-phase power source 1 and the motor 2, wiring is provided. The switch 4-1 of the circuit breaker 4 and the switch 5-1 of the electromagnetic contactor 5 are connected in series.
The circuit breaker 4 for wiring prevents the accident by opening the switch 4-1 to shut off the current when an abnormally large current such as a short circuit flows. The electromagnetic contactor 5 is used for starting and stopping the normal electric motor 2. When the operating current flows through the electromagnetic contactor 5, the opening / closing part 5-1 is closed and the operating current flows through the electromagnetic contactor 5. When it disappears, the opening / closing part 5-1 is opened, and its action will be described in detail later.

Reference numeral 6 denotes a current transformer, which produces a current proportional to the current of the motor circuit 3 flowing through the motor 2 and causes the current to flow through the thermal relay 7. The thermal relay 7 is provided with a bimetal or the like, and opens the contact 7-1 when the temperature rises above a predetermined temperature.

Reference numeral 8 is a low-voltage operating power source. The operating power source 8 includes a start push button switch 9 which is closed when it is pressed, a stop push button switch 10 which is opened when it is pressed, and a contact 7-1 of the thermal relay 7. , The electromagnetic contactor 5 is connected in series. The start push button switch 9 is connected in parallel with a contact 5a1 which is closed when current is flowing through the electromagnetic contactor 5 and is opened when no current is flowing through the electromagnetic contactor 5. It forms a holding circuit.

The electromagnetic contactor 5 is further provided with contacts 5a2 and 5a3 which are closed when a current flows through the electromagnetic contactor 5 and open when no current is flowing through the electromagnetic contactor 5, and a contact 5a2.
Is connected in series with the timer contact 12-1 and the auxiliary relay 11 to the operating power supply 8, and the contact 5a3 is connected in series with the timer 12 to the operating power supply 8.
The timer 12 is designed to open the timer contact 12-1 which has been closed until a predetermined time elapses after the contact 5a3 is closed and energized, and the timer 12 is energized. To timer contact 12-
The fixed time until 1 is opened is set to be the starting time until the electric motor 2 starts and the current value decreases to the rated current value. This starting time becomes longer when the weight and diameter of the load are large.

The auxiliary relay 11 has an A contact 11a.
Therefore, it is connected to the current transformer 6 in parallel with the thermal relay 7. The A contact 11a is closed when a current flows through the auxiliary relay 11 and is excited, and the A contact 11a is closed.
It opens when there is no current flowing in 1 and it is demagnetized.

The operation of the conventional motor overload protection device shown in FIG. 5 will be described below.

When the start push button switch 9 is pressed and closed to start the electric motor 2, the start push button switch 9 closed from the operating power supply 8 and the stop push button switch 1 closed.
0, a circuit of the contact 7-1 of the thermal relay 7 which is closed is formed, a current flows through the electromagnetic contactor 5, and the opening / closing part 5-1 and the contacts 5a1, 5a2, 5a3 are closed.

When the opening / closing section 5-1 is closed, a current flows from the three-phase power source 1 through the opening / closing section 4-1 of the closed circuit breaker 4 and the closed opening / closing section 5-1 to the electric motor 2 and the electric motor 2 starts. At this time, the current transformer 6 produces a current proportional to the current of the motor circuit 3.

When the contact 5a1 is closed, the start push button switch 9 is released and the start push button switch 9 is released.
Even if is opened, the self-holding circuit of the contact 5a1 keeps the current flowing in the electromagnetic contactor 5, so that the electric motor 2 continues to rotate.

By closing the contact 5a2, the contact 5a2 closed from the operating power source 8 and the closed timer contact 1
The auxiliary relay 11 is excited via 2-1 and the A contact 11
a closes to form a bypass circuit of the thermal relay 7, and the current from the current transformer 6 does not flow in the thermal relay 7.

Further, by closing the contact 5a3, the timer 12 is energized. After a certain period of time, the timer contact 12-1 opens and the auxiliary relay 11 is demagnetized.
The contact 11a opens and the current from the current transformer 6 causes the thermal relay 7
Comes to flow.

When the electric motor 2 is overloaded in the state after the start and the current flowing through the electric motor 2 exceeds the rated current value,
The temperature of the thermal relay 7 rises above a predetermined temperature and the contact 7-
1 will open. When the contact 7-1 opens, the electromagnetic contactor 5
Current that had been flowing to the switch was cut off, opening / closing section 5-1 and contact 5a
1,5a2,5a3 will be opened. And opening and closing part 5
When -1 is opened, the electric current of the electric motor 2 is cut off, and the overload protection of the electric motor 2 is performed.

For a certain period of time until the motor 2 starts and the current value drops to the rated current value, the A contact 11a is closed to form a bypass circuit of the thermal relay 7, and the thermal relay 7 has a current transformer. The reason why the current from 6 does not flow is to prevent the thermal relay 7 from malfunctioning due to the starting current.

[0017]

However, since the above-described conventional motor overload protection device forms the bypass circuit of the thermal relay 7 when the electric motor 2 is started, the electric motor is abnormal when the electric motor 2 is started. Even if the starting current flows, if the current value is equal to or smaller than the characteristic value of the circuit breaker 4 for wiring, the current of the electric motor 2 is not cut off, and the abnormal starting current affects the life of the electric motor or burns the electric motor. Could lead to

The present invention overcomes these drawbacks of the prior art,
Prevent the thermal relay from operating at normal starting current,
It is an object of the present invention to provide an electric motor overload protection device which operates a thermal relay to cut off the electric current of an electric motor when an abnormal starting current flows.

[0019]

SUMMARY OF THE INVENTION An electric motor overload protection device of the present invention comprises an electric motor, a current transformer that produces a current proportional to the electric current flowing through the electric motor, and an electromagnetic contactor that opens and closes the circuit of the electric motor. A thermal relay that opens the electromagnetic contactor when a current flows and the temperature rises above a predetermined temperature; an auxiliary relay that excites for a certain period of time after the current flows through the electric motor and demagnetizes after the certain period of time; A first A contact, a second A contact, and a third A contact which are closed when the relay is excited and opened when the auxiliary relay is demagnetized; and the auxiliary relay which is opened when the auxiliary relay is excited A first B contact and a second B contact that are closed when is demagnetized, and a first current adjusting resistor for distributing a current corresponding to the rated current at the time of starting the electric motor and flowing the current to a thermal relay. Thermally relay the remaining current A second current adjusting resistor for flowing by bypassing the first A from one end of the current transformer
A circuit connecting the other end of the current transformer via a contact, a first current adjusting resistor, a first B contact, a thermal relay, and one end of the current transformer to the second B contact, a second A circuit connecting the first B contact and the thermal relay via the A contact of the second contact and the second current adjusting resistor and the first B contact.
Connecting circuit between the B contact and the second A contact, and the other end of the current transformer from one end of the current transformer through the third A contact and the second current adjusting resistor. And a thermal relay bypass circuit to be connected.

[0020]

The current generated from the current transformer at the time of starting the electric motor is distributed to the thermal relay by allocating the current corresponding to the rated current.
Of the current adjusting resistor and the second current adjusting resistor for flowing the remaining current by-passing the thermal relay,
The abnormality is detected by increasing the current split to the first current adjusting resistor and flowing to the thermal relay.

After the start-up time of the electric motor has elapsed, the first current adjusting resistor and the second current adjusting resistor are disconnected, and all the current generated from the current transformer flows to the thermal relay. The abnormal current comes to be detected.

[0022]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, in which the same parts as those in the conventional device shown in FIG.

In the present invention, a part of the control device 13 shown in FIG. 1 is added. The control device 13 includes the same thermal relay 7 as the conventional one, as well as the first A contact 11a1 of the auxiliary relay 11.
The second A contact 11a2 and the third A contact 11a3, and the first B contact 11b1 and the second B contact 11 of the auxiliary relay 11
b2 and are provided. Of these, the first A contact 11
a1, second A contact 11a2, third A contact 11a3
Is closed when the auxiliary relay 11 is excited and opened when the auxiliary relay 11 is demagnetized. The first B contact point 11b1 and the second B contact point 11b2 are the auxiliary relay points 11b1 and 11b2.
It is opened when is excited and closed when the auxiliary relay 11 is demagnetized. Further, the control device 13 includes a first current adjusting resistor 14 and a second current adjusting resistor 1
5, a converter 16 is provided.

Then, the other end of the current transformer 6 is passed from the one end 6a of the current transformer 6 to the first A contact 11a1, the first current adjusting resistor 14, the first B contact 11b1, and the thermal relay 7. 6b
And a circuit 17 connecting the first and second B contact points 11b2, 11a2, and a converter 16 from one end 6a of the current transformer 6, and connects the first B contact point 11b1 and the thermal relay 7 to each other. A circuit 18, a connection circuit 19 connecting the first current adjusting resistor 14 and the first B contact 11b1 between the second B contact 11b2 and the second A contact 11a2, and a current transformer. A thermal relay bypass circuit 20 is formed which connects the other end 6b of the current transformer 6 from the one end 6a of 6 through the third A contact 11a3 and the second current adjusting resistor 15.

As will be described below, the circuits of these control devices 13 basically allow only the rated current of the electric motor 2 to flow through the thermal relay 7 when the electric motor is started, and detect the amount of increase in this electric current value. The abnormal current at the time of starting the motor is detected by.

Next, the operation of FIG. 1 will be described.

When the start push button switch 9 is pushed and closed as shown in FIG. 2 to start the electric motor 2, the start push button switch 9 and the stop push button switch 1 are operated from the operation power source 8.
0, the circuit of the contact 7-1 of the thermal relay 7 is formed, and the current flows through the electromagnetic contactor 5, and the opening / closing part 5-1 and the contacts 5a1 and 5
a2 and 5a3 will be closed.

Even if the start push button switch 9 is opened by releasing the hand from the start push button switch 9 by closing the contact 5a1, the electromagnetic contactor 5 is caused by the self-holding circuit of the contact 5a1.
Since the state in which the current flows is maintained, the electric motor 2 continues to rotate.

When the contact 5a2 is closed, the contact 5a2 from the operating power source 8 and the closed timer contact 12-1.
The auxiliary relay 11 is excited via the
Is closed to energize the timer 12. When the auxiliary relay 11 is excited, the first A contact 11a1 and the second A contact 11a1 of the auxiliary relay 11 are excited as shown in FIG.
The contact 11a2 and the third A contact 11a3 are closed, and the first B contact 11b1 and the second B contact 11b2 of the auxiliary relay 11 are closed.
Will open.

When the switch 5-1 is closed, a current flows from the three-phase power source 1 to the electric motor 2 through the switch 4-1 of the circuit breaker 4 and the closed switch 5-1. The electric motor 2 starts. At this time, the current transformer 6 produces a motor starting current I ₀ proportional to the current of the motor circuit 3.

When the electric motor is started, is the end 6a of the current transformer 6
Electric motor starting current I₀ Is a current I in the controller 13.
₁ And current I₂ And the current I₁ Is the first
A contact 11a1, first current adjusting resistor 14, connection circuit
Path 19, second A contact 11a2, converter 16, thermal relay
Flows through the transformer 7 to the other end 6b of the current transformer 6, and the other current I ₂ 
Is the third A contact 11a3 and the second current adjusting resistor 1
After passing through 5, the current flows to the other end 6b of the current transformer 6.

As described above, the thermal relay bypass circuit 20 is provided for the thermal relay 7 of the overload protection device for the electric motor 2, and the first current adjusting resistor ₁ is provided in the circuit through which the current I ₁ flows.
4 and the current I ₂ flows through the thermal relay bypass circuit 2
The second current adjusting resistor 15 is inserted in 0.
Then, by appropriately setting the resistance values of the first current adjusting resistor 14 and the second current adjusting resistor 15, respectively, the current I ₁ is made a current value corresponding to the rated current of the electric motor 2 and the thermal relay. Current I flowing to 7 and exceeding the rated current I
₂ does not pass through the thermal relay 7 and the thermal relay bypass circuit 20
It was made to flow to.

In this case, the thermal relay 7 having the same characteristics as the conventional one
In order to be able to use, the current I ₁ is the same as the rated current of the motor 2 (rated working current of the thermal relay 7), and the motor starting current I ₀ from the current transformer 6 is a current value that can be calculated in advance. Is. Therefore, the resistance value of the first current adjusting resistor 14 is R ₁ , and the second current adjusting resistor 1 is
If the resistance value of 5 is R ₂ ,

[Equation 1] I ₀ = I ₁ + I ₂ I ₁ = {R ₂ / (R ₁ + R ₂ )} × I ₀ I ₂ = {R ₁ / (R ₁ + R ₂ )} × I ₀ is satisfied. determining the resistance value R ₁ of the first current adjusting resistor 14, the resistance value R ₂ of the second current adjusting resistor 15 as.

The converter 16 in the controller 13 corrects the current I ₁ at the start of the motor so that the thermal relay 7 having the same characteristics as the conventional one can be used. As shown in FIG. _{When 1} becomes a certain value or more, the current I flowing to the thermal relay 7 is rapidly increased, and the current is detected by the thermal relay 7 so that it can be surely judged that the electric motor 2 is in the overload state. It is a thing.

When the thermal relay 7 detects the overload of the electric motor 2 at the time of starting the electric motor of FIG. 2, the contact 7-1 is opened and the current flowing in the electromagnetic contactor 5 is cut off, and the opening / closing part 5-1 is opened. The electric current of the electric motor 2 is cut off to protect the electric motor 2 from overload.

At the beginning of starting the electric motor, a current flows in the state shown in FIG. 2 described above, but when the preset fixed time T ₁ has passed, the timer contact 12-1 which has been closed until then opens, so that the auxiliary relay. 11, the first A contact 11a1, the second A contact 11a2, and the third A contact 11a3 are opened as shown in FIG. 1, and the first B contact 11b and the second B contact 11b are opened.
The contact 11b2 is closed.

Therefore, the current from the one end 6a of the current transformer 6 passes through the second B contact 11b2, the connection circuit 19, the second B contact 11b2 and the thermal relay 7 and the other end 6b of the current transformer 6 is reached. Flow into the thermal relay bypass circuit 20, and the current no longer flows into the thermal relay bypass circuit 20, and the current becomes the current route in the normal operating state.

The current state generated by the current transformer 6 from the start of the electric motor to the normal operating state described above is shown in the graph of FIG. 4, and the current I _{2 in the} shaded area is the thermal relay at the start. This is a part that allows the bypass circuit 20 to flow, and the dotted part is a part that flows to the thermal relay 7.

[0040]

The present invention makes it possible to detect an abnormal starting current larger than a preset starting current by making the thermal relay function even at the time of starting the electric motor, thus protecting the entire operating period of the electric motor. As a result, the reliability of the electric motor overload protection device is significantly improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a state at the time of starting the electric motor.

FIG. 3 is a graph showing characteristics of a converter.

FIG. 4 is a graph showing a current value from when the electric motor is started to when it is in a normal operating state.

FIG. 5 is a circuit diagram of a conventional device.

[Explanation of symbols]

 2 Electric motor 5 Electromagnetic contactor 6 Current transformer 6a One end 6b The other end 7 Thermal relay 11 Auxiliary relay 11a1 First A contact 11a2 Second A contact 11a3 Third A contact 11b1 First B contact 11b2 Second B contact 14 First resistor for current adjustment 15 Second resistor for current adjustment 17 Circuit 18 Circuit 19 Connection circuit 20 Thermal relay bypass circuit

Claims (1)

[Claims] 1. An electric motor, a current transformer that produces a current proportional to a current flowing through the electric motor, an electromagnetic contactor that opens and closes a circuit of the electric motor, and the electromagnetic device when the temperature of the electric current rises above a predetermined temperature. A thermal relay that opens a contactor, an auxiliary relay that is excited for a certain period of time after a current flows through the electric motor, and degaussed after the certain period of time has elapsed, and a auxiliary relay that is closed when the auxiliary relay is excited and the auxiliary relay is demagnetized. A first A contact, a second A contact, and a third A contact that open when the auxiliary relay is energized, and a first B contact that opens when the auxiliary relay is deenergized and closed when the auxiliary relay is demagnetized. No. 2 B contact, the first current adjusting resistor for distributing the current corresponding to the rated current to the thermal relay when starting the motor, and the remaining distributed current for bypassing the thermal relay. Second for
Current adjusting resistor and one end of the current transformer from the first
A contact, a first current adjusting resistor, a first B contact, a circuit connecting the other end of the current transformer via a thermal relay, and one end of the current transformer to the second B contact, A circuit connecting the first B contact and the thermal relay via a second A contact, and the second B contact between the first current adjusting resistor and the first B contact. And a connection circuit connecting between the second A contact and
A thermal relay bypass circuit connecting one end of the current transformer to the third A contact, the second current adjusting resistor and the other end of the current transformer. Load protection device.