Abstract: A medium voltage adjustable frequency drive includes an input isolation transformer having a three-phase input and a three-phase output, a converter having a three-phase input electrically connected to the three-phase output of the input isolation transformer and an output providing a direct current bus, an inverter having an input electrically connected to the output of the converter and a three-phase output, and a pre-charge circuit. The pre-charge circuit includes a ferro-resonant transformer circuit having a primary winding structured to input a low voltage and a secondary winding structured to output a medium voltage and provide a constant current source. The pre-charge circuit also includes a medium voltage diode bridge having an input receiving the medium voltage from the secondary winding of the ferro-resonant transformer circuit and an output structured to provide the constant current source to the direct current bus.

Abstract: A medium voltage adjustable frequency drive includes an input isolation transformer having a three-phase input and a three-phase output, a converter having a three-phase input electrically connected to the three-phase output of the input isolation transformer and an output providing a direct current bus, an inverter having an input electrically connected to the output of the converter and a three-phase output, and a pre-charge circuit. The pre-charge circuit includes a ferro-resonant transformer circuit having a primary winding structured to input a low voltage and a secondary winding structured to output a medium voltage and provide a constant current source. The pre-charge circuit also includes a medium voltage diode bridge having an input receiving the medium voltage from the secondary winding of the ferro-resonant transformer circuit and an output structured to provide the constant current source to the direct current bus.

Abstract: An electrical bus isolation system includes a pair of bus bar supporting members, each of which includes a first substantially flat surface portion configured to retain a first bus bar, and second and third substantially flat surface portions each disposed on opposite sides of the first surface portion, and defining an offset in height from the first surface portion. The second and third surface portions are configured to retain opposite lateral sides of a second bus bar when the pair of supporting members are operatively engaged, with corresponding second and third surface portions facing each other such that the first bus bar is retained in a fixed position relative to the second bus bar in a parallel spaced relationship thereto and at a distance determined by the offset in height. An air gap between the bus bars electrically isolates the bus bars and prevents corona discharge between the bus bars.

Abstract: An electrical bus isolation system includes a pair of bus bar supporting members, each of which includes a first substantially flat surface portion configured to retain a first bus bar, and second and third substantially flat surface portions each disposed on opposite sides of the first surface portion, and defining an offset in height from the first surface portion. The second and third surface portions are configured to retain opposite lateral sides of a second bus bar when the pair of supporting members are operatively engaged, with corresponding second and third surface portions facing each other such that the first bus bar is retained in a fixed position relative to the second bus bar in a parallel spaced relationship thereto and at a distance determined by the offset in height. An air gap between the bus bars electrically isolates the bus bars and prevents corona discharge between the bus bars.

Abstract: There is disclosed a direct current motor drive system comprising a direct current motor operable in a forward motoring mode receiving current from a power source and in a reverse inversion mode providing inversion current to the power source. The drive system includes a converter for controlling motor operation. The converter converts alternating current, received from the power source, to direct current. The converter supplies direct current across terminals of the motor when operating in the forward motoring mode. The system includes an inversion fault current limiter for limiting inversion fault currents associated with motor operation in the reverse inversion mode without effecting the supply of current to the motor in the forward motoring mode. The inversion fault current limiter is electrically connected in series between the converter and one armature terminal of the motor. The inversion fault limiter includes a diode switch connected in parallel with a resistor.

Abstract: In a drive system for a grinding mill the load torque plus frictional torque may increase considerably as a loaded mill is inched from its rest position and will suddenly decrease when the load tumbles or cascades. The applied torque or driving torque must increase at a corresponding rate and should also decrease when the load cascades. If the applied torque exceeds by a significant amount the load torque plus frictional torque, a destructive hammering will occur in the gear train and this will be generally proportional to the excess of applied torque for a synchronous motor drive. The drive system has a DC source which is commutated by a commutating device to provide a low frequency stepped alternating voltage to the stator windings of the synchronous motors of the drive system for inching. The output of the DC source has an alternating current component which varies as the difference between the applied torque and the load torque plus frictional torque.

Abstract: A speed control for a DC motor drive having regenerative braking and a field reversing control, has a field current feedback circuit which includes a modifier to change the feedback signal in accordance with the saturation curve of the field to provide a feedback signal representing field strength or field flux. Because motor field strength is regulated as a function of the required field strength, the control tends to make the speed of response independent of actual field strength. Also, a feedback signal is provided which is a function of the product of actual field strength and desired armature current, i.e., related to torque, and this controls the speed signal so that the gain of the speed regulating amplifier is inversely proportional to field strength. This allows drive operation at reduced field strength while maintaining the response.

Abstract: This invention relates to a system for protecting an amortisseur winding during the starting of a synchronous motor. The system compares the actual slip frequency of the accelerating motor with predetermined slip frequencies. These predetermined slip frequencies are each associated with a timer which measures successive time segments. Each timer is stopped when the actual slip frequency, which decreases as rotor speed increases, is less than the associated predetermined slip frequency. When the timer is stopped a successive timer is started. In this manner the acceleration of the motor is broken up into time segments. The initial timer is started when the motor starts. The final timer is stopped when the rotor field current is applied to bring the motor into synchronism. Should any timer be permitted to have its timed segment expire before being stopped, the motor is shut down. There is also provided a thermal memory which receives information from the expired timer as to its associated slip frequency.

Abstract: A control circuit for an electrical precipitator having a high voltage transformer with a bridge rectifier between the secondary of the transformer and the high voltage precipitator electrodes. The control circuit includes a pair of oppositely poled main thyristors in the primary circuit with a firing arrangement to trigger the main thyristors to maintain desired conditions at the electrodes. The primary circuit does not require a current limiting reactor to limit primary current when a spark discharge takes place at the electrodes. A pair of auxiliary thyristors are each connected in series with a capacitor. Each capacitor and the respective auxiliary thyristor form a branch and these two branches are each connected in parallel with the main thyristors. A rectifier is connected to keep the capacitors charged in opposing directions.