JPS5828473Y2 - Starting device for squirrel cage motor - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a starting device for a squirrel cage induction motor operated under a load such as a compressor.

In general, the starting methods for squirrel cage motors include the full voltage starting method, the Y-△ starting method, the Condorfer starting method, the fusa starting method, and the -order resistance starting method, but other than the full voltage starting method, there are All of them have the disadvantage that the starting current is reduced due to reduced voltage starting, but the starting torque is also reduced, and it is necessary to switch from starting to operation manually or by using a timer mechanism, etc.

The present invention was developed in view of the above facts, and is a car that automates the changeover from startup to operation, gradually increases acceleration torque to suit the load such as a compressor, facilitates startup, and suppresses inrush current. The purpose is to provide a starting device for type motors, and we have adopted a primary resistance starting method in which a power thermistor with a heat sink is inserted in series with the line as the starter, and the temperature of the heat sink is detected by another thermistor to start the motor. The present invention is characterized in that it not only performs confirmation and protects the power thermistor from thermal damage, but also automates the switching from startup to operation.

An embodiment of the present invention will be described below with reference to the drawings. 1 is a three-phase power supply, 2 is an operation switch inserted between two phases of the three-phase power supply, 3 is a stop push button switch that opens when suppressed, and 4 closes when pressed. 5 is a first electromagnetic switch connected in series to the operation switch 2; 6 is a normally open first electromagnetic switch contact; the first normally open contact 7 is connected in parallel to the operation switch 4; A second, third and fourth normally open contact 8, 9.10 is connected to each phase of the three-phase power supply 1, respectively.

11゜12.13 is a first negative characteristic thermistor connected to each line of the three-phase power supply 1 via the second, third, and fourth normally closed contacts 8, 9, and 10 of the first electromagnetic switch. It is made up of large elements.

14 is a squirrel cage motor having delta-connected windings 15, 16, and 17; 18 and 19 are a second negative characteristic thermistor and a second electromagnetic switch connected in parallel to the first electromagnetic switch 5; The thermistor 18 is formed of a small self-heating element.

20 is a normally open second electromagnetic switch contact, the first normally open contact 21 is parallel to the second negative characteristic thermistor 18, and the second, third, and fourth normally open contacts 22, 23, and 24 are each three-phase. First electromagnetic switch provided on each line of power supply 1 Each normally open contact 8°9.1
0 and the first negative characteristic thermistor 11, 12.degree. 13 are connected in parallel.

Note that the first negative characteristic thermistor 11, 12.13 and the second negative characteristic thermistor 1d are installed on the same heat sink 25 and are thermally coupled.

The present invention adopts the primary resistance starting method as described above, and the primary resistance is the first negative characteristic thermistor 11.12.13.
are using.

The operation will be described below. When the operation push button switch 4 is turned on, the first electromagnetic switch 5 is energized and the first electromagnetic switch contact 6 is closed.

Since the first regular contact 7 is closed, the first electromagnetic switch 5 is self-held even after the switch 4 is opened.

Also, since the second, third, and fourth normally open contacts 8, 9, and 10 are closed, each winding 15°, 16, and 17 of the squirrel cage motor 14 is energized via the first negative characteristic thermistor 11, 12, and 13. ,
The squirrel cage electric motor 14 enters the starting state.

If the line current at that time is iLK, ILK is expressed by the following equation.

However, +1 to Ek is the line voltage of two adjacent phases of three-phase power supply 1, and ZA (T) is the first negative characteristic thermistor 1°12.1
The resistance value Z at the thermistor temperature T of 3 is the phase impedance of the windings 15, 16, and 17 of the squirrel cage motor 14.

As can be seen from Equation 1, the line current ILK is limited by the thermistor resistance value Z l (T).

Moreover, since ZA'(T) has a low thermistor temperature T immediately after starting, iLK can be suppressed to a small value.
The inrush current flowing into the windings 15, 16, 17 of the :: type motor 14 at the time of starting is suppressed and protected from burnout.

On the other hand, as ILK flows, the first negative characteristic thermistor 11
．． 12.13 generates self-heating and the thermistor temperature T rises, so the resistance value Zl(T) becomes smaller.

This relationship is expressed by the following equation.

Z1(T)-Aexp(B-)...
``-(2) However, in equation 2), A and B are constants.

In this way, as Zl(T) decreases, iLK increases, and if the current flowing through the windings 15, 16, and 17 is iZ, there is a relationship of 1z=fiLK, so IZ increases with starting, and the acceleration torque increases. increases, squirrel cage electric motor 1
4 makes starting easier.

Now, at the start of startup, the first electromagnetic switch 5 is excited, but the second negative characteristic thermistor 8 provided in series with the second electromagnetic switch 19 has a thermistor resistance value R because the thermistor temperature T is low.
(T') is large and the second electromagnetic switch 19 operates and contact 2
0 is set so that it does not become a closed circuit.

In addition, since the second negative characteristic thermistor 8 is made of a material that generates little self-heating, the thermistor resistance R (T) increases due to self-heating.
decreases and the second electromagnetic switch 19 does not operate.

The second electromagnetic relay 19 operates when the first negative characteristic thermistor 11, 12, 13 self-heats and the thermistor temperature T becomes a predetermined temperature T.

At this time, the first negative characteristic thermistor 1
1, 12.13 has been reduced to Z l (To), the line current ILK expressed by equation (1) has increased, and the acceleration torque of the squirrel cage motor 14 has been sufficiently increased.

The first negative characteristic thermistor 11°12.13 self-heats and the thermistor temperature becomes T.

As a result, the second negative characteristic thermistor 18 installed on the same heat sink 25 has a thermistor temperature of T'.

The thermistor resistance value R(T', o) becomes small enough to operate the second electromagnetic switch 19, and the second electromagnetic switch contact 20 closes.

As a result, the first normally open contact 21 is closed, thereby bypassing the second negative characteristic thermistor 18 and self-holding the second electromagnetic switch 19.

Also, when the second, third, and fourth normally open contacts 22, 23, 24 are closed, the first electromagnetic switch normally closed contacts 8, 9, 10 and the first negative characteristic thermistor 11, 12, 13 of each phase are closed. The series circuits of each are bypassed.

This means that the squirrel cage electric motor 14 has completed starting.

In the operating state, the eleventh second electromagnetic switch contacts 6, 20 are closed, and a current of +1/Z flows through the line current iLK to C-Lk, and each winding 15, 16, 17 of the squirrel cage motor 14 has three phases. Full voltage of power supply 1 is applied.

On the other hand, since no current flows through the first negative characteristic thermistor 1L12, 13, the heat sink 25 is naturally cooled.

In this way, in the present invention, the first negative characteristic thermistors 11, 12. which generate large self-heating are inserted as secondary resistances after the start of the engine.
13 thermistor temperature T is T.

This means that the line current iLK flowing through the first negative characteristic thermistor 11, 12.13 is now necessary for starting the squirrel cage motor. Detection is made by lowering the resistance value of the second negative characteristic thermistor 18, which is connected to the The windings 15 and 16 of the squirrel cage motor 14 are electrically disconnected from the three-phase power supply 1 and are connected in delta.
, 17 are designed so that the full voltage of the three-phase power supply 1 is applied to them, so that the switching from starting to operation is performed automatically, and the first negative characteristic thermistors 11, 12, and 13 generate more heat than necessary, resulting in thermal damage. It cannot be caused.

As described above, the present invention connects a squirrel-cage motor to a three-phase power supply through a first negative characteristic thermistor that generates a large amount of self-heating, and a second
By providing a negative characteristic thermistor and an electromagnetic switch that operates according to the resistance value of the second negative characteristic thermistor, the electromagnetic switch contact bypasses the first negative characteristic thermistor when the electromagnetic switch is operated. The second negative characteristic thermistor detects the completion of starting and automatically switches from starting to operation. The present invention provides a starting device for a squirrel cage motor that has high practical effects, such as blocking the current flowing through the negative characteristic thermistor and preventing the first negative characteristic thermistor from generating excessive heat and causing thermal breakdown.

[Brief explanation of the drawing]

The figure shows an electric circuit showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Three-phase power supply, 11, 12. 13... First negative characteristic thermistor, 14... Squirrel cage electric motor, 18... Second
Negative % thermistor, 19...Second electromagnetic switch, 20.
...Second electromagnetic switch contact.

Claims (1)

[Scope of utility model registration request] A squirrel cage motor is connected to a three-phase power supply via a first negative characteristic thermistor, and a second negative characteristic thermistor is provided which is thermally coupled to the first negative characteristic thermistor, and the resistance value of the second negative characteristic thermistor is determined according to the resistance value of the second negative characteristic thermistor. 1. A starting device for a squirrel-cage motor, characterized in that an electromagnetic switch is provided, and when the electromagnetic switch is operated, a contact of the electromagnetic switch bypasses the first negative characteristic thermistor.