MacGregor's 'Soft Start' Benefits Powerful Electric Motors

MacGregor, part of Cargotec, has introduced a new electric starter cabinet for hydraulic hatch cover power units on bulk carriers and general cargo ships. It features an intelligent “soft-start” function that avoids starting current peaks and reduces stresses on mechanical and hydraulic components.

"A ship has a closed electrical system and so current peaks may cause disturbances elsewhere in the system. Therefore when high-powered motors are introduced into hydraulic systems, it is important that the starting process is carefully controlled," said Mika Åback, MacGregor Technical Manager, Control Systems. "For a heavy-duty electric motor the starting current peak can be up to ten times its operating current at its nominal running output power, and so it is important to reduce this demand peak on the ship's electrical supply."

Soft-start technology significantly reduces starting peaks to around four times a motor's nominal running output power. It replaces the existing standard solutions, which are direct on line starting, or optional stepped starting via Star Delta technology.

For convenient operation, MacGregor offers an optional small remote control unit which allows the operator to start up and shut down the hydraulic pump unit (HPU) remotely. This can save a lot of time when the HPU is situated well away from the control stands.

Safety is paramount and there should always be at least two people involved in hatch cover operations. "As standard we provide an emergency stop button on the opposite side of the hatchway to the control stand," he noted. "This will shut down the HPU when activated. As an option we offer a confirmation button, again located on the opposite side of the hatch to the control position. This replaces the standard emergency stop button, and it must be pressed and held down throughout the whole operation, ensuring that two people are always involved in hatch cover movements.

"An additional advantage is that the hydraulic system is pressurised only when the button is held down," Åback said. "This reduces the number of start/stop sequences, which slows down the oil's chemical aging process and prolongs the components' working life. It is also energy efficient, because the motors only work at full capacity during hatch operation."

The new starter unit is intended both for newbuild applications and for retrofit to existing hatch cover operating systems. It also has a data logging facility, accessible to MacGregor engineers for service and diagnostic purposes.

macgregor.com