New Standard AC Drive Features Small Footprint

The world’s smallest medium-voltage AC drive, in terms of power and voltage compared to size, has been introduced by ABB Industrial Systems. It is designed to be purchased as a standard, off-the-shelf unit for water and wastewater pumping and aeration applications.

The world’s smallest medium-voltage AC drive, in terms of power and voltage compared to size, has been introduced by ABB Industrial Systems. It is designed to be purchased as a standard, off-the-shelf unit for water and wastewater pumping and aeration applications.

The ACS 1000 is a Direct Torque Controlled (DTC) drive that provides speed and torque control of motors rated from 400 to 6,000 horsepower in voltages 2.3, 3.3 and 4.16 kV. For example, a 2,400 hp, 3.3 kV air-cooled ACS 1000 measures only 118 inches long by 79 inches high by 35.5 inches deep.

A key target for the drive is retrofit applications, since only about 3 percent of medium-voltage motors are controlled by AC drives, according to ABB research.

The ACS 1000’s compact size is achieved with a new power semiconductor switching device known as an IGCT (Integrated Gate Commutated Thyristor). With such a device, a 4.16 kV IGCT drive requires only 12 power semiconductor devices in the inverter, compared to 24-60 devices needed by older drives.

The IGCT system can also operate without a “snubber” system — a capacitor and resistor network designed to limit the rate of change of voltage. Instead, the system uses a new power handling device, GCT (Gate Commutated Thyristor) and the device control circuitry (gate driver) in an integrated package. This leads to fewer components.

The ACS 1000 will be available in both air-cooled and water-cooled versions. It can be configured with either a separately mounted input isolation transformer or an integrated dry-type input isolation transformer. This gives installation flexibility and allows for the use of oil-filled transformers for mounting outdoors.

The system also features a new output voltage filter that produces a near perfect sinusoidal voltage waveform and overcomes many problems traditionally faced by medium-voltage motors. These include rate of change of voltage, which stresses the motor insulation, torque pulsations, voltage reflections and noise.

As the output voltage (and hence current) is sinusoidal, variable speed drive induced torque pulsations are eliminated. The pulsations can seriously damage loads. Another benefit of the sine wave output filter is the elimination of voltage reflections. As a result, the drives can be located some distance from the motors.

The filter also provides the compatibility link between the drive and any standard squirrel-case induction motor. There is no need for special motor insulation, and no derating of the motor is required.

A key consideration in the design of the ACS 1000 is that it is retrofit-friendly — it can be fitted onto existing motors, no matter whose they are,” said Scott Conner, director of medium voltage drives at ABB.

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