ABB’S new Onboard Dc-grid optimizes fuel consumption
The vast majority of oceangoing vessels are built to get from Port A to Port B as quickly as possible. Their engines run at a steady clip and all support systems, including the onboard electrical grid, are calibrated accordingly.
But offshore drillships and support vessels spend a lot of time at low speeds or floating in place, what is known as “dynamic position,” resulting in inefficient electricity delivery. ABB’s new Onboard DC-Grid — the first exclusively directcurrent system in the industry — could fix that.
“There are forces such as water and wind that will move the vessel from the position,” said Ismir Fazlagic, Global Product and Solution manager for ABB. “The thrusters and propellers are running on very low load, but the fixed speed engine, which is not designed for these types of loads, needs to consume more fuel to handle those loads.”
Fixed speed engines have a narrow window for optimal fuel consumption — usually between 75 percent and 85 percent of the load. Dynamic position load is well below that.
“The DC-Grid enables us to run the engines and generators on variable speed operation, so we’re able to optimize fuel consumption throughout speed and load curve,” Fazlagic said. “The biggest load in a vessel is the engine, so the engine needs optimization. It’s consuming the fuel.”
Variable speed operation of the engine can save up to 20 percent in fuel, cut emissions and reduce maintenance. It could result in up to a 30 percent reduction in weight from obsolete equipment.
Ships have historically used AC/DC grids, where alternating current runs through a direct current link to change frequencies. An all-DC system was impossible previously because of the costly and bulky breakers required.
“We have developed technology to achieve protection and selectivity with basically no breakers,” Fazlagic said. “Instead of having the DC link in the drives, we have DC distribution throughout the entire vessel. The fuel consumption of the engines will not be at the very narrow window; the optimal fuel consumption is widened through entire load range.” Ford Gunter is a freelance writer in Houston.