The world's first multi-level, fuseless, medium voltage AC drive, it is thought, has been launched by ABB to meet the growing number of applications driven by standard motors up to 6.9kV:
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| ABB's new ACS 5000 AC drive in cabinet. |
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Called the
ABB ACS 5000, the drive is rated from 5 to 24 MW and can be applied to standard industrial motors (asynchronous and synchronous) found in cement, mining and minerals, chemical oil and gas, marine, metals, pulp and paper, power generation and water and waste water treatment.
The ACS 5000 inverter unit combines several proven technologies developed by ABB that bring unprecedented levels of efficiency, reliability, performance and size. The technologies include the Multilevel-Fuseless Voltage Source Inverter (VSI-MF) design, the DTC motor control platform, IGCT power semiconductors, the latest generation of ABB's power block and the elimination of traditional fuses.
VSI-MF - power factor near unity:
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. It also has an input power factor near unity, which has a positive impact on the plants power supply.
However, the biggest advantage is that the design has an optimum number of switching levels, which provide a multilevel output waveform. In order to get a sinusoidal voltage to the motor, the number of switching levels would have to approach infinity. However, too many switching levels decrease reliability and efficiency because the number of components increases. The ACS 5000 design provides the optimal solution because it has enough switching levels to enable the use of standard motors while at the same time keeping the parts count to a minimum.
This allows the use of standard motors up to 6.9 kV, rather than the traditional custom engineered motor, without compromising reliability. When combined with DTC and IGCTs (see below) the drive offers the highest system efficiency.
Motor control platform:
The use of Direct Torque Control or DTC means fast and accurate process control along with low energy consumption. DTC uses motor torque and flux as control variables and can therefore achieve higher accuracy than other technologies. It 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 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 of the drive. The overall converter efficiency, including cooling and auxiliaries, is in excess of 98%.
Power block:
The IGCTs are used at the heart of the inverter, in a device called the Power Electronic Building Block (PEBB). This device 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 a high power density. As such, the size for a complete system for a given power rating has been reduced 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 6.9kV.
Fuseless:
The ACS 5000 does not use any medium voltage power fuses, which are known to be unreliable, costly and subject to ageing. Instead IGCTs are used to provide much 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.
It is a design feature of the IGCT that absorbs all the energy from the fault current. With ABB's fuseless protection philosophy there is no subsequent damage to other devices in the inverter.
In contrast, with a traditional drive, should a fault occur, it can take about 5 milliseconds to eventually trigger the fuse and break the circuit. So long is this delay that further damage could be inflicted on other devices within the drive - the so-called domino effect.
The picture shows ABB's new ACS 5000 AC drive in cabinet.
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