Soft starting device for motors

Claim 2

A soft starting device for motor comprising a three-phase induction motor with a squirrel-cage rotor, at least two silicon controlled rectifiers connected in antiparallel with each other and in series between the primary winding of said motor and one phase of a three-phase power source, impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and phase control circuit means providing small conduction angles for said rectifiers upon application of a source voltage to said motor, said phase control circuit means including means to automatically increase said conduction angles continuously, said phase control circuit means being connected between the power source sides of said rectifiers and the other ends of said impedance elements, and impedances of said impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced.

Claim 3

A soft starting device for motors comprising a three-phase induction motor with a squirrel-cage rotor, two silicOn controlled rectifiers connected in antiparallel with each other and in series between the primary winding of said motor and one phase of a three-phase power source, impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other ends of said impedance elements, impedances of said impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said silicon controlled rectifiers, resistors connected in series between output terminals of said rectifier circuit, a transistor having its base connected to the junction point of said resistors and its collector to the negative output terminal of said rectifier circuit, a diode connected between the emitter and base of said transistor, and a further resistor interposed between said junction point of said resistors and the emitter of said transistor.

Claim 4

A soft starting device for motors comprising a three-phase induction motor with a squirrel-cage rotor, two silicOn controlled rectifiers connected in antiparallel with each other and in series between the primary winding of said motor and one phase of a three-phase power source, impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other ends of said impedance elements, impedances of said impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said silicon controlled rectifiers, resistors connected in series between output terminals of said rectifier circuit, a transistor having its base connected to the junction point of said resistors and its collector to the negative output terminal of said rectifier circuit, a diode connected between the emitter and base of said transistor, and a further resistor interposed between said junction point of said resistors and the emitter of said transistor.

Claim 5

A soft starting device for motor comprising a three-phase induction motor with a squirrel-cage rotor, two silicon controlled rectifiers connected in antiparallel with each other and in series between the primary winding of said motor and one phase of a three-phase power source, impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other ends of said impedance elements, impedances of said impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said silicon controlled rectifiers, first and second resistors connected in series between output terminals of said rectifier circuit, a transistor having the base thereof connected to the junction point of said first and second resistors through a third resistor, a fourth resistor connected between the emitter of said transistor and the negative output terminal of said rectifier circuit, a first capacitor connected between said negative output terminal and the base of said transistor, and a fifth resistor and a second capacitor connected between the collector of said transistor and the positive terminal of said rectifier circuit.

Claim 6

A soft starting device for motor comprising a three-phase induction motor with a squirrel-cage rotor, two silicon controlled rectifiers connected in antiparallel with each other and in series between the primary winding of said motor and one phase of a three-phase power source, impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other ends of said impedance elements, impedances of said impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said silicon controlled rectifiers, first and second resistors connected in series between output terminals of said rectifier circuit, a transistor having the base thereof connected to the junction point of said first and second resistors through a third resistor, a fourth resistor connected between the emitter of said transistor and the negative output terminal of said rectifier circuit, a first capacitor connected between said negative output terminal and the base of said transistor, and a fifth resistor and a second capacitor connected between the collector of said transistor and the positive terminal of said rectifier circuit.

Claim 7

A soft starting device for motors comprising a three-phase induction motor with a squirrel-cage rotor, two silicon controlled rectifiers having anodes and cathodes thereof connected in antiparallel and connected in series between the primary winding of said motor and one phase of a three-phase power source, first and second impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other terminals of said first and second impedance elements, impedances of said first and second impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said rectifiers, a varistor connected between said input terminals, third and fourth resistors connected in series between output terminals of said rectifier circuit, a first transistor having its base connected to the junction point of said third and fourth resistors and its collector to the negative output terminal of said rectifier circuit, a diode connected between the emitter and base of said first transistor, a fifth resistor interposed between the junction point of said third and fourth resistors and the emitter of said first transistor, a second transistor having the base thereof connected to said junction point of said third and fourth resistors through said fifth resistor, a sixth resistor connected between the emitter of said second transistor and the negative output terminal of said rectifier circuit, a first capacitor connected between said negative output terminal and the base of said second transistor, a seventh resistor and a second capacitor connected between the collector of said second transistor and the positive output terminal of said rectifier circuit, an eighth resistor connected between the emitter and collector of said second transistor, a third transistor having the base thereof connected to the collector of said second transistor, a third capacitor connected between the collector of said third transistor and said negative output terminal, a ninth resistor connected between the emitter of said third transistor and said positive output terminal, a variable resistor interposed between the collector of said third transistor and said positive output terminal, a unijunction transistor having the emitter thereof connected to the collector of said third transistor, and a pulse transformer having two secondary coils each connected between the cathode and gate of each of said two silicon controlled rectifiers and a primary coil connected to the base circuit of said unijunction transistor.

Claim 8

A soft starting device for motors comprising a three-phase induction motor with a squirrel-cage rotor, two silicon controlled rectifiers having anodes and cathodes thereof connected in antiparallel and connected in series between the primary winding of said motor and one phase of a three-phase power source, first and second impedance elements respectively connected at one end each thereof with the other two phases of said three-phase power source, and a phase control circuit adapted to provide small conduction angles for said rectifiers upon application of the source voltage to said motor and then to automatically increase said conduction angles continuously, said phase control circuit being connected between the power source sides of said rectifiers and the other terminals of said first and second impedance elements, impedances of said first and second impedance elements and said phase control circuit connected in star with respect to said three-phase power source being balanced, said phase control circuit further including a rectifier circuit having input terminals to which are applied a voltage of the same phase as the voltage applied to said rectifiers, a varistor connected between said input terminals, third and fourth resistors connected in series between output terminals of said rectifier circuit, a first transistor having its base connected to the junction point of said third and fourth resistors and its collector to the negative output terminal of said rectifier circuit, a diode connected between the emitter and base of said first transistor, a fifth resistor interposed between the junction point of said third and fourth resistors and the emitter of said first transistor, a second transistor having the base thereof connected to said junction point of said third and fourth resistors through said fifth resistor, a sixth resistor connected between the emitter of said second transistor and the negative output terminal of said rectifier circuit, a first capacitor connected between said negative output terminal and the base of said second transistor, a seventh resistor and a second capacitor connected between the collector of said second transistor and the positive output terminal of said rectifier circuit, an eighth resistor connected between the emitter and collector of said second transistor, a third transistor having the base thereof connected to the collector of said second transistor, a third capacitor connected between the collector of said third transistor and said negative output terminal, a ninth resistor connected between the emitter of said third transistor and said positive output terminal, a variable resistor interposed between the collector of said third transistor and said positive output terminal, a unijunction transistor having the emitter thereof connected to the collector of said third transistor, and a pulse transformer having two secondary coils each connected between the cathode and gate of each of said two silicon controlled rectifiers and a primary coil connected to the base circuit of said unijunction transistor.