I am sailing on a modern DP 2 diesel electric Platform Supply Vessel. This has 4 Diesel Alternators feeding a Bus Bar that can be split for DP2 Operations. In turn each Bus bar supplies a tunnel bowthruster an Azipul aft and half the auxiliary systems.
Recently we were running on 2,3 & 4 D/As steaming out to location, Bus Bar tied, when No 2 D/A started to take load off the other two generators, the Bus Bar split automatically and the Alarm Monitoring system came up with about 5 pages of alarms and half the systems tripped! Everything was reset and we continued as normal, this happened again a few hours later, in total 3 times that day. The fault did not become permanent or display any symptoms that we were able to track down, so we quarantined No 2 D/A and reported that we only had 3 D/As available for use. We had no further problems and after a long struggle we were able to get the makers men down with lap tops and special software to interrogate all the control systems, after 2 seperate visits by 2 Technicians they eventually determined the cause of the problem.
The D/As run Isochronously (constant speed, no Droop) in order to do this the control computer on each D/A receives a kw signal from its feed into the switchboard, all the D/As talk to each other, the Power Management System and lots of other Electronics and computers around the ship, and their Electronic Governors send an appropriate signal to the fuel rack actuator to maintain an equal load. If the kw signal moves outside the expected range the control system FOR THAT ENGINE ONLY, goes into a "Back Up" mode. It takes measurement of Fuel Rack angle, Charge air pressure, Turbocharger and engine RPM exhaust temperatures etc and compares them wiith a "Power Map" derived from the Test Bed Data, to calculate the load on the engine.
All the engines then use the calculated value from that D/A in conjunction with the measured values of the other generators to maintain load sharing.
Eventually it was determined that we had an intermittent fault in the kw measurement system for No 2 D/A and the problem was caused when the engine went into back up mode.
The kw measurements had been set up incorrectly, there was a 10% scalar error in converting the milli amp signal from the kw Transducer into kw inside the engine's computer. This meant that the engines thought they were producing 10% more power than they really were. When the kw sensor from No 2 D/A failed that automatically meant that it tried to increase load by 10% In addition it was found the fuel rack sensor (the principal part of the load guestimatation system) had been set up incorrectly and that was also causing No 2 D/A to take too much load. Once the difference in load, measured at the switchboard, between Alternators, reaches 10% for 10 seconds the Bus Tie Breaker automatically trips.
Our Technical Department think that 2 spanner monkeys like me can operate these ships, they took the ETOs off a year ago to save money, it is not saving them so much now.
I think I know what Jolly Jack's comments will be!
It is always better to ask a stupid question than to do a stupid thing.