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Before electronic VFDs were developed, the speed of wound-rotor 3-phase induction motors was controlled by schemes involving variable resistance inserted in series with the rotor windings or connecting the rotor windings to additional machines (Kramer and Scherbius drives). There were also schemes in which variable frequency was generated by driving an AC generator with some other type of variable speed machine such as a DC motor, eddy-current coupling drive, or a mechanical speed changer (continuous variable transmission).

In many cases, a DC motor, eddy-current coupling drive, or a mechanical speed changer was used to drive machines directly without using AC motors. However wound rotor motors could be built with higher power ratings than other machines, and could be controlled using a lower power rotor rotor powercircuit control. That was one reason to use those schemes.

Variable-speed AC generator machines were also used to control large quantities of small synchronous motors used for making synthetic fiber. The first solid-state electronic variable speed drives were developed by Borg Warner under contract for DuPont for synthetic fiber spinning applications.

Also, small induction and brushless synchronous motors controlled that way could safely be installed in explosive atmosphere areas.

Before the invention of the transistor, vacuum tubes, mostly thyratrons, were used for variable-speed control of DC motors, eddy-current coupling drives, wound-rotor induction motor drives and perhaps some variable frequency drives.

Before electronic VFDs were developed, the speed of wound-rotor 3-phase induction motors was controlled by schemes involving variable resistance inserted in series with the rotor windings or connecting the rotor windings to additional machines (Kramer and Scherbius drives). There were also schemes in which variable frequency was generated by driving an AC generator with some other type of variable speed machine such as a DC motor, eddy-current coupling drive, or a mechanical speed changer (continuous variable transmission).

In many cases, a DC motor, eddy-current coupling drive, or a mechanical speed changer was used to drive machines directly without using AC motors. However wound rotor motors could be built with higher power ratings than other machines, and could be controlled using a lower power rotor rotor power control. That was one reason to use those schemes.

Variable-speed AC generator machines were also used to control large quantities of small synchronous motors used for making synthetic fiber. The first solid-state electronic variable speed drives were developed by Borg Warner under contract for DuPont for synthetic fiber spinning applications.

Also, small induction and brushless synchronous motors controlled that way could safely be installed in explosive atmosphere areas.

Before the invention of the transistor, vacuum tubes, mostly thyratrons, were used for variable-speed control of DC motors, eddy-current coupling drives, wound-rotor induction motor drives and perhaps some variable frequency drives.

Before electronic VFDs were developed, the speed of wound-rotor 3-phase induction motors was controlled by schemes involving variable resistance inserted in series with the rotor windings or connecting the rotor windings to additional machines (Kramer and Scherbius drives). There were also schemes in which variable frequency was generated by driving an AC generator with some other type of variable speed machine such as a DC motor, eddy-current coupling drive, or a mechanical speed changer (continuous variable transmission).

In many cases, a DC motor, eddy-current coupling drive, or a mechanical speed changer was used to drive machines directly without using AC motors. However wound rotor motors could be built with higher power ratings than other machines, and could be controlled using a lower power rotor circuit control. That was one reason to use those schemes.

Variable-speed AC generator machines were also used to control large quantities of small synchronous motors used for making synthetic fiber. The first solid-state electronic variable speed drives were developed by Borg Warner under contract for DuPont for synthetic fiber spinning applications.

Also, small induction and brushless synchronous motors controlled that way could safely be installed in explosive atmosphere areas.

Before the invention of the transistor, vacuum tubes, mostly thyratrons, were used for variable-speed control of DC motors, eddy-current coupling drives, wound-rotor induction motor drives and perhaps some variable frequency drives.

Source Link
user80875
user80875

Before electronic VFDs were developed, the speed of wound-rotor 3-phase induction motors was controlled by schemes involving variable resistance inserted in series with the rotor windings or connecting the rotor windings to additional machines (Kramer and Scherbius drives). There were also schemes in which variable frequency was generated by driving an AC generator with some other type of variable speed machine such as a DC motor, eddy-current coupling drive, or a mechanical speed changer (continuous variable transmission).

In many cases, a DC motor, eddy-current coupling drive, or a mechanical speed changer was used to drive machines directly without using AC motors. However wound rotor motors could be built with higher power ratings than other machines, and could be controlled using a lower power rotor rotor power control. That was one reason to use those schemes.

Variable-speed AC generator machines were also used to control large quantities of small synchronous motors used for making synthetic fiber. The first solid-state electronic variable speed drives were developed by Borg Warner under contract for DuPont for synthetic fiber spinning applications.

Also, small induction and brushless synchronous motors controlled that way could safely be installed in explosive atmosphere areas.

Before the invention of the transistor, vacuum tubes, mostly thyratrons, were used for variable-speed control of DC motors, eddy-current coupling drives, wound-rotor induction motor drives and perhaps some variable frequency drives.