INSTITUTION OF DIAGNOSTIC ENGINEERS

Text Box: Shipyard trials and tribulations David Atkinson MIDiagE preceded his article with the following comment. "My experiences on the ship I have mentioned here were extraordinary; the ship was very well advanced in all aspects of diagnostic and electronic equipment on board. Nagasaki was a fantastic place to stay. It was also a good experience to work alongside the Japanese MHI engineers in the "yard" and at sea. They were very helpful and courteous to fellow officers and myself. A few years ago I joined a 300,000-ton VLCC being built out in Nagasaki in Japan. I was signing on as the ship's Electro Technical Officer along with the Chief Officer. Two of us flew out from the UK in early March and met up with the Chief Engineer of the new ship. We arrived about a month ahead of the rest of the Officers and Filipino Crew. We worked all week including Saturdays but had Sunday off for sightseeing. We visited both the old and the new Atomic Bomb Museums, the new one opening in April 1996. Nagasaki is steeped in history besides the atomic bomb, Thomas Glover, the famous British Engineer who brought a lot of new technology to Japan in the 1800’s including shipbuilding, railways and telephone systems to name but a few. Puccini's plaque and a statue of “Madam Butterfly” are also to be found in Glover Gardens. The City is surrounded by many hills. The City trams are very cheap to travel on. We stayed at the Holiday Inn just off the centre of Nagasaki City and had to commute every morning by taxi to the Mitsubishi Shipyard some distance away. We were issued boiler suits, hard hat, shoes and our own designated bicycle by the shipyard; the cycle journey was about a mile and a half out to the fitting out berth. The accommodation on the ship was still in the process / of being built but most of the engine-room machinery had been installed including our new shaft generator. The main engine was a Mitsubishi diesel engine type 7UEC85LSII developing some 33,000 bhp at 69.5 RPM. Reaction fins were fitted just forward of the propeller to increase prop efficiency. The electrical system comprised of three Bergen diesels producing 900KW each 440V at 60 Hz. The generators speed was 720 rpm. Our new shaft generator was rated at about 800-850KW max. It comprised of the main shaft unit which was connected to a series of converter cabinets and line reactor and the output drove a synchronous condenser, which was primarily an AC motor driving a generator at 1800 rpm producing 440V at 60hz. The rotating excitation diodes were exactly the same for all the engine room electrical generators. I met the installation/ commissioning engineer, a German by the name of Hans. Our ship was the second one of a series of five to be built at the same yard. Hans showed me round the systems and we did a series of air gap checks round the main shaft generator rotor to check droop clearance, we also walked round the rest of the machinery. He mentioned in passing that the first ship of the series had developed a problem with the shaft generator's synchronous condenser; all the rotating diodes on the excitation unit on the first vessel had been failing with monotonous regularity. He said that we were to conduct tests as soon as ours was up and running. We were the test bed to diagnose the problems on this system. The shaft generator was designed to take full ships load and operated from 35 rpm on the main shaft which produced 5 power up to around 57 rpm which produced 100 power. It was generally considered that the generator was under powered for the job in hand and should have been a 1MW unit. Our first tests were not too encouraging and we had our first failures. It was decided that Hans and myself were to go on the builder's trials, virtually unheard of for first time out. We were the only Europeans amongst a whole ship full of Japanese shipyard personnel, living on pot noodles and sleeping rough. We left port on the Bergen diesels and conducted load-sharing exercises with these. There was an excellent generator management system, which also dealt very well with proportional load sharing. On our way out to the trial grounds we prepared, the ship for its first speed run. At 35-40 rpm on the main engine, we ran up the synchronous condenser and as engine speed came up we left one diesel generator and proportioned the load between itself arid the shaft Generator. On our first full speed trial run we transferred the load onto the shaft generator and took the Diesel off line. We ran for about 10-15 minutes conducting checks, when suddenly - the lights went out. We had blacked out after a very short run. The synchronous condenser diodes were found to have failed. These were replaced and they later failed again. We had a serious problem. Our next ship trial was some weeks later. The main trial proved no different, except this time we rigged up test monitoring and recording equipment to try and ascertain why it kept failing. Our first failure was recorded and we wondered if there was an electrical spike causing the failure. All the cabinets and the condenser were checked including all terminations but still failure. The shipyard decided lo have a further ship trial to try to gel to the bottom of this problem but to no avail. Hans and I were no further on. He said to me one day "Dave, you are looking at a downed German" - he had a good sense of humour even in those trying times he needed it. I asked him if the system had been fully tested back in Germany and he thought it had. We had to sail for the Arabian Gulf without a functioning shaft generator. The generators manufacturer had been on the case and sent out an extra hand to help. Eventually some bright spark came out with the answer. We had sent the defective diodes back lo Germany to be lab tested. It was discovered they were failing physically and not electrically. The diodes had failed due lo centrifugal forces being exerted upon them far above their design limit. They were fine ticking over at 720 rpm on the Bergens but when the speed went up to 1800 rpm on the synchronous condenser, the forces were too great. We called off Singapore to pick up the new engineer and the correct diodes. New physically stronger diodes were installed and no further problems arose. The shaft generator ran as sweet as a nut for the rest of the trip to the Arabian Gulf right up to the time I left the ship in the US Gulf. I sailed on two further sister ships and encountered no more problems with these shaft generators. More R & D should have been done before these machines were unleashed; having said that it proved to be an excellent system and was very economical to run, reducing the maintenance on the Bergen diesels which were only used during manoeuvring and in port. David Atkinson MIDiagE member 9834  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

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