How smarter power systems are making dynamic positioning ships more reliable

Dynamic positioning systems enable ships to maintain their position and heading automatically. ABB’s marine power solution has some clever ways to keep them up and running

Dynamic positioning (DP) systems enable ships to maintain their position and heading automatically. Originally, of interest to the offshore oil industry, DP has become a popular technology for a wide range of vessels from cruise ships and flotels through to cable-laying ships, cranes and supply vessels of all types.

The systems take data from a host of environmental sensors to determine the magnitude and direction of environmental forces affecting the ships position.

The DP systems creates a real-time model of the vessel in the water taking account of the wind and currents acting on the vessel and the location and effect of the thrusters. This and other data gathered from instruments such as the Gyrocompass allows the computer to calculate the required steering angle and thruster output for each thruster to position the vessel. An important part in the reliability of the system is played by the electrical system onboard and here’s why.

Why are the electrical systems important?

A DP system is only effective as long as the system is online. To calculate the actions needed to maintain and correct a vessel’s position, and apply the necessary forces through the thrusters, a robust and dependable electrical system is required.

The International Maritime Organization (IMO) categorizes dynamic positioning systems into three classes, depending on their robustness. A Class 1 vessel has no built-in redundancy. A single fault can knock out the system and for many operators this is not viable.

How much redundancy do most DP systems require?

Class 2 vessels, can continue to maintain their position even if something major like a generator, thruster or switchboard fails and Class 3 vessels, have a fully redundant system, so that when something static like a cable or pipe disconnects, then the ship’s positioning is unaffected. This means that a fire or flood in a single compartment of the ship will have no effect on the DP system.

What does this mean for the electrical system?

These ships need intelligent electrical systems with “closed bus ties” to enable any of the ships generators top power the DP system. And the electrical system should be able to do this without eating up the limited space on board.

So what’s the solution?

ABB has designed a marine power system to support the higher performance demands of DP vessels. It is a more space-efficient way of providing the redundancy required. Operating a DP vessel in closed bus tie configuration provides unquestionable benefits. By interconnecting the generators, a ship can burn 3-5 percent less fuel and can cut the maintenance costs – up to 30 percent. More over a closed bus tie power system provides superior tolerance to plant faults, increasing the overall system reliability.

What makes ABB’s marine power system different?

It’s a more intelligent approach to the challenges. We install and connect Emax 2 circuit breakers together using our Ekip Link Ethernet module, instead of traditional wiring, so we have immediate space savings and the simpler cabling cuts the commissioning time by about 60 percent. We also use the built-in sensing and intelligence of Emax 2 to detect faults and isolate them more effectively. The Emax 2’s logic node is very easy to customize.

Does ABB’s approach provide faster selectivity in the event of a fault?

Ekip Link can locate and isolate a fault more precisely. Wherever it occurs, it can be isolated in less than a tenth of a second. That is faster than normal selectivity methods, and that is really due to the precision of ABB’s node logic and the directional protection that the Emax 2 circuit breakers provide.

What happens in the event of a fault?

Our solution uses an embedded “logic zone discrimination” strategy to protect against over currents. If the circuit breaker sees a fault current enter the node and none of the other breakers see it exit, it means the fault is somewhere inside that node. That breaker opens and isolates the fault. If the fault current exits the node, the breaker sends a blocking signal to the other breakers in the node.

During setup, ABB’s software establishes the system nodes, gives each actor an IP address and defines which signals will be sent and received. It’s a really smart approach.