Electric AC drives offer true ‘no loss’ operation

The company says that the Stadt Stascho drives are the first it has produced for which the ‘no loss’ claim can be made. The development, according to Stadt, has been progressed over a seven year period, and recent tests carried out by DNV proved that losses in the drives were negligible. This finding by an independent third-party tester, says Stadt CEO Halvard Slettevoll, allows the company to make the ‘no loss’ claim for the first time. Moreover, Slettevoll believes this is the first such range of drives in the industry that can verifiably claim no loss.

The key to the low loss concept is Stadt’s bypass switching technology. Although the company points out that zero loss was not the original goal when developing this. The main target was to reduce the complexity of the drive systems, and thereby to increase reliability, cutting the risk of downtime to a minimum. Stettevoll says that the no loss, as well as associated reductions in electrical disturbances (EMC and THD), and the ability to dispense with the need for propulsion transformers, giving rise to a more compact design, were welcome consequences of the development.

The high energy efficiency and zero losses are of no use, says Stadt, unless long-term trouble-free operation can be assured. Stadt believes its Stascho drives can be warranted for at least two years, as the company has documented evidence of its products giving constant and totally trouble-free operation for that period. This is something that cannot be guaranteed by other manufacturers, as many Norwegian shipowners are discovering, says Stettevoll. He points out that the more complex drive systems can seldom offer a total service life of any more that 10 years, in many cases somewhat less, whereas his experience points to the Stascho drives performing reliably, and without major maintenance, for 25 years or more.

The company points out that the concept of energy loss in propulsion systems is always debatable, and figures claimed as ‘low loss’ can vary from around 7% up to as much as 15%, and even these are hard to verify without special skills and equipment. Although Stadt has known for some time that its Stascho drives produced very low losses, it was reluctant to use the term ‘no loss’ until the statement could be verified by third party measurements. The actual quoted electrical losses for the Stascho drives amount to <0.03%, which is accounted for by copper losses and losses in the bypass breaker, and are therefore easy to verify and document.

The Stadt Stascho product range is available in power capacities from 100 kW at 230V up to 100 MW at 15 kV. The product line encompasses IGBT transistors, thyristors and bypass switching. The company believes that the market for electric ship propulsion systems is increasing rapidly, as energy prices increase and global attention turns towards addressing climatic and environmental issues. Stadt says that its electric propulsion system can contribute to reduction in fuel consumption and exhaust gas emissions from ships by up to 45%. Both gas- and diesel-electric solutions are possible with the system.

“The features and qualities in the new product represent a sustainable technology, environmentally friendly in all respects,” says Slettevoll.