Electricity: motive power systems – Induction motor systems – Braking
Patent
1986-09-17
1988-06-28
Smith, Jr., David
Electricity: motive power systems
Induction motor systems
Braking
318760, H02P 324
Patent
active
047542110
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a device for braking an asynchronous motor, specifically by applying a direct current obtained from an AC voltage source through rectification to the field windings of said motor.
Previously known solutions for braking an asynchronous motor by means of a direct current applied to the field windings thereof are disclosed in e.g. German Offenlegungsschrifts Nos. 2,214,731 and 3,040,035. In these solutions, the duration of the braking is based on the setting of the braking time, which leads in inaccurate stops and resettings of the braking time if the speed of rotation of the motor and/or the fly mass connected to the armature is changed. Solutions for the elimination of the above disadvantages are disclosed in e.g. U.S. Pat. No. 4,392,098, German Offenlegungsschrift No. A1 3,110,841 and European Patent Specification No. A2 41,191, in which the control of the supply of a braking current to the field windings of a cage induction motor is effected by utilizing the frequency of the voltage induced in the field winding, the voltage induced in the field winding or the current induced in the field winding. These solutions have frequently led to relatively expensive technical realizations including a plurality of structural elements.
The object of the present invention is to provide a method and a device which enable a controlled braking of asynchronous motors irrespective of any changes in the speed of rotation of the motor and/or in the fly mass connected to the armature thereof and which can be used for starting and braking of single-phase, two-phase or multi-phase asynchronous motors.
The invention is mainly characterized by these features which are set forth in the enclosed claims.
The invention will be described in the following by means of certain embodiments thereof with reference to the attached drawings, wherein
FIG. 1 shows a circuit diagram of a device for starting and braking of a delta-connected squirrel cage motor supplied from a three-phase net,
FIG. 2 shows a circuit diagram of a device according to another embodiment of the invention for starting and braking of a delta-connected squirrel cage motor supplied from a three-phase net,
FIG. 3 shows a circuit diagram of a braking current control unit included in the device according to FIG. 2,
FIG. 4 shows a circuit diagram of a device provided with a safety relay and intended for connecting and controlling a braking current to a star-connected squirrel cage motor supplied from a three-phase net,
FIG. 5 shows a circuit diagram of a device for connecting and controlling a braking current to a squirrel cage motor supplied from a two-phase net,
FIG. 6 shows a circuit diagram of a device for connecting and controlling a braking current to a delta-connected capacitor motor supplied from a one-phase net,
FIG. 7 shows a circuit diagram of a device for connecting and controlling a braking current to a star-connected capacitor motor supplied from a one-phase net,
FIG. 8 shows a circuit diagram of a device for connecting and controlling a braking current to a capacitor motor supplied from a one-phase net, and
FIG. 9 shows the curveform of a the generator voltage generated by the embodiment of FIG. 1.
Similar components are indicated by the same references in all figures.
FIG. 1 shows terminals R, S, T, N of a three-phase net and delta-connected field windings 1, 2, 3 of a squirrel cage motor. To start the motor the terminal S is by a press-button switch 13 connected to the terminal N through a press-button stop switch 14, a press-button emergency switch 15, a contact 23 of a braking current relay 28 and a coil 7 of an operation current relay 27, whereby the operation current relay picks up, the contact 8 thereof is opened and the contacts 9, 10, 11 connect phase voltages from the terminals R,S,T to the terminals 6, 5, 4 of the field windings 1, 2, 3, the coil 7 obtaining a hold current through contacts 14, 12, 15, 23. To brake the motor the hold current circuit of the operation current relay 27 is disconnected by means of the press-button
REFERENCES:
patent: 2929977 (1960-03-01), Choudhury
patent: 3678353 (1972-07-01), Marchi
patent: 3708734 (1973-01-01), Rowe
patent: 3866097 (1975-02-01), Anzai et al.
patent: 4115727 (1978-09-01), Gross
patent: 4151453 (1979-04-01), Suzuki et al.
patent: 4181197 (1980-01-01), Tanabe et al.
patent: 4334181 (1982-06-01), Schroeder
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