6.9-kV drive strengthens ABB’s medium-voltage drive portfolio

ABB says it has the world’s first multilevel, fuseless, medium-voltage AC drive to meet the growing number of applications driven by standard motors up to 6.9 kV. The ACS 5000 drive is rated from 5 to 24 MW and can be applied to standard industrial motors (asynchronous and synchronous) found in pulp and paper, power generation and similar applications.

The ACS 5000 inverter unit combines several proven technologies developed by ABB for efficiency, reliability, performance and size. The technologies include the Multilevel-Fuseless Voltage Source Inverter (VSI-MF) design, the direct torque control (DTC) motor control platform, IGCT power semiconductors, the latest generation of ABB’s power block and the elimination of traditional fuses.

VSI-MF. The VSI design allows efficient and smooth switching operations, free from torque pulsations, over the entire speed range. The VSI provides full torque even from zero and very low speed. Its near-unity input power factor has a positive effect on plant power supply.

However, the biggest advantage is that the design has an optimum number of switching levels providing a multilevel output waveform. To get a sinusoidal voltage to the motor, the number of switching levels would have approach infinity. However, too many switching levels decrease reliability and efficiency because the number of components increases. ABB says the ACS 5000 design has enough switching levels to enable the use of standard motors while the same time keeping the parts count to a minimum.

This allows the use of standard motors up 6.9 kV, rather than the traditional custom engineered motor, without compromising reliability. When combined with DTC and IGCTs, the drive offers the highest system efficiency.

Motor control platform. DTC means fast and accurate process control along with low energy consumption. DTC uses motor torque and flux as control variables to achieve higher accuracy than other technologies, says ABB. gives the highest torque and speed performance as well as lowest losses ever achieved in medium-voltage drives.

Power semiconductors. The drive uses IGCTs, the most advanced power semiconductor switching device available and which combines the best of two traditional technologies: the fast switching of IGBTs with the proven reliability and low losses of GTOs. IGCTs result in low parts count, leading to less complexity and a more efficient and reliable drive. IGCTs also account for the extremely high efficiency the drive. The over-all converter efficiency, including cooling and auxiliaries, is over 98%.

Power block. The IGCTs are used in a device called the Power Electronic Building Block (PEBB). The PEBB replaces complex power electronic circuits with a single, multi-function device. The use of IGCTs enables a lower parts count, a compact mechanical structure and high power density. As a result, the size for complete system for a given power rating has been  educed by 50% compared to other available solutions. By combining several PEBBs, higher voltages can be reached, enabling reliable and efficient operation of motors up to 6.9 kV.

Fuseless. The ACS 5000 does not use medium-voltage power fuses, which are known to unreliable, costly and subject to ageing. Instead IGCTs provide faster and more reliable protection of power components. If an overcurrent occurs, a small coil senses the fault and responds within 25 microseconds — about 100 times faster than fuses. A design feature of the IGCT absorbs all the energy from the fault current and avoids damage to other devices in the inverter. In contrast, with a traditional drive, can take about five milliseconds to trigger the fuse and break the circuit, long enough to cause damage to other devices within the drive.

ABB Switzerland Ltd., www.abb.com

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