Abstract: Methods of testing a multilevel inverter include selectively pulsing (i.e., attempting to turn on) at least one of the inner and outer switches of the inverter and determining a status of at least one of the inner switches, the outer switches and the neutral clamping diodes of the inverter based whether the pulsed at least one of the inner and outer switches desaturates. The pulsing may be preceded by charging the DC bus to a predetermined voltage magnitude that is less than a nominal working voltage magnitude of the DC bus, e.g., the predetermined voltage magnitude may be around 50% or less of the nominal working voltage magnitude.

Abstract: An apparatus includes a plurality of DC buses and a plurality of inverter circuits, respective ones of which are coupled to respective ones of the plurality of DC buses. The apparatus further includes a control circuit configured to generate a representative DC voltage signal based on DC voltage signals for respective ones of the DC buses, to generate a first modulation control signal from the representative DC voltage signal, to generate second modulation control signals for the respective inverter circuits from the representative DC voltage signal and the first modulation control signal that are normalized based on the DC voltage signals for the buses and the representative DC voltage signal, and to modulate the inverter circuits responsive to respective ones of the second modulation control signals. The representative DC voltage signal may represent a maximum of the DC voltages for the respective DC buses.

Abstract: A reduced voltage starter for electric motors comprises a controller, and a plurality of semiconductor switches to selectively connect a power source to a motor. The controller is configured to apply a first voltage ramp to provide a controllable fraction of the full line voltage to the motor, while maintaining a current flow to be within a programmable current limit during motor startup. The controller is further configured to implement a bumpless force transition, by applying a second voltage ramp when the speed of the motor is below the rated motor speed, and force transition criteria correlated with overheating of the semiconductor switches and/or a connected load are met.

Abstract: A reduced voltage starter for electric motors comprises a controller, and a plurality of semiconductor switches to selectively connect a power source to a motor. The controller is configured to apply a first voltage ramp to provide a controllable fraction of the full line voltage to the motor, while maintaining a current flow to be within a programmable current limit during motor startup. The controller is further configured to implement a bumpless force transition, by applying a second voltage ramp when the speed of the motor is below the rated motor speed, and force transition criteria correlated with overheating of the semiconductor switches and/or a connected load are met.

Abstract: An apparatus includes a plurality of DC buses and a plurality of inverter circuits, respective ones of which are coupled to respective ones of the plurality of DC buses. The apparatus further includes a control circuit configured to generate a representative DC voltage signal based on DC voltage signals for respective ones of the DC buses, to generate a first modulation control signal from the representative DC voltage signal, to generate second modulation control signals for the respective inverter circuits from the representative DC voltage signal and the first modulation control signal that are normalized based on the DC voltage signals for the buses and the representative DC voltage signal, and to modulate the inverter circuits responsive to respective ones of the second modulation control signals. The representative DC voltage signal may represent a maximum of the DC voltages for the respective DC buses.

Abstract: A converter of a variable frequency drive (VFD) is operated in a ramp-up mode to produce an AC output voltage for accelerating a motor. A loading of the converter is determined concurrent with the ramp-up mode. Transfer of the motor to a bypassed mode is conditioned on whether the determined loading in the ramp-up mode meets a criterion. In some embodiments, conditioning transfer to the bypassed mode comprises foregoing transition to the bypassed mode based on a comparison of the determined loading to an underloading threshold.

Abstract: An apparatus includes a magnetometer-based current sensor (e.g., a Hall-effect or fluxgate-based current sensor) configured to sense a magnetic field generated by a current in at least one conductor connecting a motor drive output to a motor and to responsively produce a first current sense signal and a magnetometer-based voltage sensor (e.g., a Hall-effect or fluxgate-based voltage sensor) configured to sense a magnetic field generated in response to a voltage of the at least one conductor and to responsively produce a first voltage sense signal. The apparatus further includes a signal conversion circuit configured to receive the first current sense signal and the first voltage sense signal and to generate a second current sense input and a second voltage sense input for provision to a current sense input and a voltage sense input, respectively, of a motor protection relay that protects the motor.

Abstract: A motor starter apparatus includes an enclosure, a bypass contactor configured to be installed in the enclosure and configured to selectively couple a power source to a motor, and a reduced voltage soft starter (RVSS) circuit assembly (e.g. a wheeled truck) configured to be installed in the enclosure, to be coupled to the power source and to apply a variable voltage to the motor. The bypass contactor is configured to preserve a connection of the bypass contactor to the power source and the motor when the RVSS circuit assembly is removed from the enclosure.

Abstract: A motor starter apparatus includes an enclosure, a bypass contactor configured to be installed in the enclosure and configured to selectively couple a power source to a motor, and a reduced voltage soft starter (RVSS) circuit assembly (e.g. a wheeled truck) configured to be installed in the enclosure, to be coupled to the power source and to apply a variable voltage to the motor. The bypass contactor is configured to preserve a connection of the bypass contactor to the power source and the motor when the RVSS circuit assembly is removed from the enclosure.

Abstract: A motor starter includes a plurality of semiconductor switches configured to couple respective phases of an AC power source to respective phases of a motor and a control circuit configured to configured to selectively operate the semiconductor switches to gradually increase a voltage applied to the motor, to determine root mean square (RMS) current values of a current of the motor as the voltage increases, and to cause the semiconductor switches to apply a full voltage or a more steeply ramping voltage to the motor responsive to the RMS current values meeting a criterion.

Abstract: An apparatus includes a magnetometer-based current sensor (e.g., a Hall-effect or fluxgate-based current sensor) configured to sense a magnetic field generated by a current in at least one conductor connecting a motor drive output to a motor and to responsively produce a first current sense signal and a magnetometer-based voltage sensor (e.g., a Hall-effect or fluxgate-based voltage sensor) configured to sense a magnetic field generated in response to a voltage of the at least one conductor and to responsively produce a first voltage sense signal. The apparatus further includes a signal conversion circuit configured to receive the first current sense signal and the first voltage sense signal and to generate a second current sense input and a second voltage sense input for provision to a current sense input and a voltage sense input, respectively, of a motor protection relay that protects the motor.

Abstract: An electrical system (2) includes a transformer (16) coupled to an AC source (6) that provides a main AC voltage, the transformer having a number of sets of primary windings (18) and secondary windings (20), and a charging module (32) structured to generate a magnetizing AC voltage. The charging module is structured to selectively provide the magnetizing AC voltage to: (i) one of the number of sets primary windings, or (ii) one of the number of sets secondary windings. The magnetizing AC voltage is such that responsive to the magnetizing AC voltage being provided to one of the sets of primary windings or one of the sets of secondary windings, one or more of the sets of primary windings will be magnetized in a manner wherein a flux of the one or more of the number of primary windings is in phase with the main AC voltage provided from the AC source.

Abstract: A switchgear unit includes an enclosure having a first compartment and a second compartment and a fuse assembly mounted on a wall that separates the first compartment and the second compartment, the fuse assembly comprising a fuse housing disposed in the second compartment and accessible from the first compartment via an opening in the wall. The fuse assembly may include a cover configured to separate a fuse in the fuse housing from the first compartment and that is removable to provide access to the fuse from the first compartment. The fuse assembly may further include a power input terminal supported by the fuse housing and accessible from the second compartment and a switch disposed in the first compartment and configured to electrically connect the power input terminal to the first fuse connection terminal.

Abstract: An improved cable assembly includes at least a first elongated signal-carrying cable and a protector that has an elongated covering apparatus that is connected with the signal-carrying cable. The covering apparatus has a resilient portion having a number of corrugations. The signal-carrying cable is received within the covering apparatus, and the resilient portion is moved from a free state to a collapsed state. The signal-carrying cable and the covering apparatus are received at least partially in an uncured quantity of potting compound, and the compound is then permitted to cure.

Abstract: An improved cable assembly includes at least a first elongated signal-carrying cable and a protector that comprises an elongated covering apparatus that is connected with the signal-carrying cable. The covering apparatus comprises a resilient portion having a number of corrugations. The signal-carrying cable is received within the covering apparatus, and the resilient portion is moved from a free state to a collapsed state. The signal-carrying cable and the covering apparatus are received at least partially in an uncured quantity of potting compound, and the compound is then permitted to cure.