Control failure

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Big Pete
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Control failure

Postby Big Pete » Fri Aug 22, 2014 11:44 pm

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!

BP
It is always better to ask a stupid question than to do a stupid thing.

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JollyJack
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Re: Control failure

Postby JollyJack » Sat Aug 23, 2014 8:07 pm

No need to say it then. :) Electronic control of machinery is very reliable, it can be relied upon to fail and make megabucks for the manufacturer on specialist repair, updates and spare parts.
Discourage incest, ban country "music".

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JK
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Re: Control failure

Postby JK » Sun Aug 24, 2014 12:55 pm

Thank the EPA world. I wonder in the scheme of things, how much a ship pollutes as compared to, say, the oilfields!?

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Big Pete
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Re: Control failure

Postby Big Pete » Sun Aug 24, 2014 11:41 pm

Be thankful you do not live in the European Union, our fearless leaders have just announced an energy saving law, banning most vacuum cleaners/ Hoovers that are in the best buy lists by limiting the maximum power consumption and introducing a plan to reduce the limit even further in the future.
They have already done this with washing machines and Dishwashers, generally the result is that they all take longer to complete a washcycle, so no energy saving overall.
They have also, several years ago, banned hot water filling to these machines, so if you have been environmentally friendly and invested in Solar Hot Water Panels, log burning stoves or Heat Pumps, you still have to fill the machines with cold water and heat it Electrically!!
None of these self styled "Environmentalists" have a clue.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: Control failure

Postby JK » Mon Aug 25, 2014 1:25 am

Light bulbs here and they were replaced by the curly ones that have a bit of mercury inside.Now a entire watercourse can be polluted. Big money is running the show and all they give a fK about is their pocket.

Personally I think we are doomed as a species to a huge population crash and we better start treating the native tribes better as they will be the survivors.

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Big Pete
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Re: Control failure

Postby Big Pete » Mon Aug 25, 2014 11:33 pm

We have spiral compact Fluorescent lamps over here too.
The old incandescent filaments lamps were banned a couple of years ago. However, Rough Service Filament lamps were classed as being for industrial use and so are legally available, a lot of people buy them instead.
The Greenies are now trying to move us to LED lamps at £10 each.

Going back to the original thread, I find it interesting that in these days of quality control ISM etc, that Wartsila didn't pick up their failure to commission the plant properly, nor did the Shipyard, Class, MCA, Owners Representatives, FMEA Auditors etc when the ship was built, nor was it picked up later at Annual or intermediate Surveys. I suspect that the system is so complicated that everyone left it to Wartsila to set up and test and took their word for it that everything was O.K., because nobody else understood the system.

BP
It is always better to ask a stupid question than to do a stupid thing.

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Big Pete
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Re: Control failure

Postby Big Pete » Fri Aug 29, 2014 12:10 am

I have just seen a newspaper article saying that the EU are planning to ban high powered hairdryers, kettles, WiFi Routers and all sorts of other electrical equipment.
These people really are insane Boiling water in a a kettle with a lower power will take longer, therefore more heat will be lost by radiation, conduction and convection from the kettle during boiling. Everyone with the slightest Technical/ Engineering background knows that it will take exactly the same amount of energy to raise the temperature of say one litre of water to boiling point, irrespective of the rate at which the energy is applied. It is more efficient to do it quickly!!

BP
It is always better to ask a stupid question than to do a stupid thing.

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JollyJack
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Re: Control failure

Postby JollyJack » Tue Sep 09, 2014 7:21 pm

LED lights, the only answer. They wer on special at around $6 each in Central Supplies, so I bought abot 40 to change all the buls in both houses! Looking forwar to lower power bills!

Heating effect is quantified as I r (squared). These LED lights burn cold! No heat waste, garunteed 6 years, with unit exchange, bloody amazing
Discourage incest, ban country "music".


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