JPS6223221Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a motor protection device that protects the motor from locking and protects the motor from overload.

A conventional motor protection device has a configuration as shown in FIG. 1, in which a second overload relay 6 and a current limiter 5 are connected in series between a power supply 1 and a motor 2 connected to the power supply. A circuit 4 is provided, and a contact point 7c of a starting relay 7 that short-circuits the current limiter 5 after a predetermined time has elapsed since the motor is energized is connected in parallel to the current limiter. However, according to the above configuration, when the compressor is operating, the entire current of the main winding current and the auxiliary winding current flows through the second overload relay 6.
In order to prevent malfunction due to the main winding current, the operating characteristics of the overload relay must be set high, making it difficult to protect the motor when starting it.

This proposal was made in view of these shortcomings,
The following description will be made based on the embodiments shown in the figures.

1 is a power source, 2 is an electric motor connected to the power source, and the electric motor is housed in a compressor (not shown). 3 is a dome-mounted first overload relay that is connected between the power source 1 and point C of the electric motor 2, is attached to the jacket of the compressor, and is opened and closed depending on the temperature of the jacket. . 4 is power supply 1
and a current limiter 5 connected between the current limiter 5 and the R point on the main winding side of the motor 2, and a remote-type second overload relay that is attached to the current limiter and opens and closes according to the energized current. This is a series circuit with 6. The current limiter 5 is for limiting the current flowing through the main winding of the motor. 7 is a voltage type starting relay having a normally closed contact 7a and a normally open contact 7b;
The contact 7a has one end connected to the S point on the auxiliary winding side of the motor 2 via the starting capacitor 8, and the other end connected between the second overload relay 6 and the current limiter 5, The normally open contact 7b is connected in parallel to the series circuit 4 of the second overload relay 6 and the current limiter 5. 7L is a coil that energizes the starting relay 7, and is connected in parallel to the auxiliary winding of the motor 2. Reference numeral 9 denotes an operating capacitor provided in parallel with the series circuit of the normally closed contact 7a of the starting relay 7 and the starting capacitor 8.

In the motor protection device configured as described above, the normally closed contact 7 of the starting relay 7 is closed when the compressor is started.
a is closed, energizing the starting capacitor 8 and the running capacitor 9, and the normally open contact 7b of the starting relay 7 is open, connecting the second overload relay 6 and the current limiter 5. Electric motor 2 through
is energized and starts the compressor. In this case, the first overload relay 3 is also energized, but since the compressor jacket temperature is low, the first overload relay 3 attached to the jacket is difficult to operate. Yes, the motor winding protection is provided by the second overload relay 6.
It is done in Thereafter, as the rotation speed of the motor 2 increases, the voltage of the auxiliary winding increases, and when the voltage reaches a predetermined value, the starting relay 7 is operated by the coil 7L, and its normally closed contact 7a opens, and the normally open contact 7b
is closed. Therefore, the second overload relay 6
The main winding current flowing in the series circuit 4 with the current controller 5 is bypassed and the second overload relay 6
Only the auxiliary winding current is energized. The starting capacitor 8 is also disconnected from the auxiliary winding, and the motor 2 enters the operating state. When electric motor 2 enters the operating state,
Since the temperature of the outer jacket of the compressor becomes high, the first overload relay 3 attached to the outer jacket is in a state where it is easy to operate, and the motor 2 is in a restrained state or an overload state, and the temperature of the outer jacket becomes higher than the first overload relay. When the set temperature of the overload relay 3 of No. 1 is exceeded, its contacts are opened to cut off the power to the motor 2, and the starting relay 7 is deenergized and returned to its original state. Thereafter, when the first overload relay 3 becomes lower than its set value due to natural cooling, it automatically returns and closes, and the motor is started again.

It is also assumed that the electric motor 2 is in a locked state when the compressor is started. At this time, since the normally open contact 7b of the starting relay 7 is open, a restraining current flows to the second overload relay 6. However, since the second overload relay 6 is bypassed during the normal operating state of the compressor and only the auxiliary winding current is energized, there is no need to deal with the main winding current of the motor 2; The operating characteristics can be significantly reduced, and the current to the motor 2 is cut off by immediately responding to the above-mentioned restraint current.

In the above explanation, the first overload relay 3 is of a dome mount type and is attached to the outer cover of the compressor, and is operated by the temperature of the outer cover. Needless to say, it is also possible to directly sense the temperature of this motor by installing it on the motor.

As described above, the present invention includes a power source, a motor connected to the power source, a first overload relay that is provided between the motor and the power source and is activated by heat generated from the motor, and a first overload relay that is also connected to the motor and the power source. The second overload relay is equipped with a series circuit of a current limiter and a second overload relay provided between the two, and a starting relay that short-circuits the series circuit after starting the motor.
A large current is passed through the second overload relay only when the compressor is started, and the operating characteristics of the second overload relay are set to be as small as possible, thereby greatly improving the protection performance when starting the motor. Can be done.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing a conventional example, and FIG. 2 is an electric circuit diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Electric motor, 3... First overload relay, 5... Current limiter, 6... Second overload relay, 7... Starting relay.

Claims (1)

[Scope of utility model registration request] A power supply, a motor connected to the power supply, a first overload relay provided between the motor and the power supply and activated by heat generated from the motor, and a first overload relay also provided between the motor and the power supply. A protection device for a motor, comprising: a series circuit including a current limiter and a second overload relay; and a starting relay that short-circuits the series circuit after starting the motor.