CIRCULAR LETTER NO : CL/TEC/07004 SECTION : TECHNICAL DATE OF ISSUE : 18/06/07 SUBJECT : TROUBLES WITH PRIMARY SOURCES OF ELECTRICAL POWER Recently several failures of electrical generators and in one case prime mover occurred on board of our managed vessels. 1. 47,000 chemical tankers Several reports were received about unacceptable low insulation of generators. One vessel reported low insulation of stator winding. First signs were noticed on 20.01.07, but faultfinding was unsuccessful due to very short periods of low insulation. Finally, 22.02.07 they found that the reason of low insulation on MSBD is Generator N1. The cause of low insulation in generator could not be found immediately and suggestion was to the damage of windings. However further careful inspection by crew shown damage of cable's insulation in terminal box (caused by friction), which was rectified by crew 28.02.07.

Fig. 1Damaged cable insulation in the terminal box of generator. Sister vessels were informed about the problem and requested to carry out unscheduled inspection of their generators. All involved vessels reported that inspection was done, however another sister vessel reported that from 22.03.07 they experience problems with low insulation, which was normal on stopped generator or running idle, but low insulation appeared while loading at the level about 350 kW. Again crew failed to find the reason immediately, but after all possible parts were removed from the generator for the most close inspection on 30.03.07 it was revealed that air guide wall (situated on the drive-end side) loosen and have touches with stator winding. It was secured back by means of point welding with necessary precautions, and generator put back in operation.

Fig.2 Secured air guide wall Inspection on sister vessel revealed the same defect, which was rectified in advance prior complete failure of generator. Another vessel reported about low insulation indication on MSBD and failure of excitation system on one of the generators. Damaged parts were replaced by spares available onboard and generator put back in operation.

Fig.3 Damaged transformer of excitation system One of the reasons of damage crew reported as poor soldering quality of wires and due to this the main cause due to loosen wires on terminals. The last two cases described above clearly shown that even after request for unscheduled close inspection of generators and establishing of proper maintenance and supervision on generating sets, this task was carried out mostly in formal way, without proper attitude from the crew.

2. LNG carrier One of our LNG carriers experienced blackout due to failure of steam generating plant and therefore turbo alternators were shut down. Vessel is equipped with stand-by diesel generator and emergency diesel generator. Stand-by diesel generator was started, however generator was not excited. Arrangements were done for power feedback from ESBD to MSBD in order to start boiler plant. Further faultfinding of diesel generator shown that one wire for field winding burnt due to loosen contact on terminal.

Fig.4 Damage caused by loosen terminal. Operation of diesel generator was restored, other generators on this and sister vessel were inspected and connections re-tightened. 3. 159,000 oil tanker During routine inspection of ER in UMS period, Duty Engineer noticed wrong load sharing between working generators N1 and N2. Attempts to share load manually by means of regulator’s remote control on MSBD and locally from regulating knobs on Woodward are failed. Stand by diesel generator N3 was started and connected. The following load sharing was achieved: AE N1 about 480 kW, AE N2 and AE N3 about 200 kW (unstable) each. Frequency started to rise and reached 62.5 Hz. Decision was taken to disconnect ACB of generator N1 manually, in order to avoid blackout caused by high frequency trip. After generator was disconnected, overspeed protection activated, however fuel rack was kept by jammed governor and engine continued to run. Two minutes later AE N1 was stopped by means of closing fuel supply. Internal inspection of engine revealed the following damages: cylinder liners N1 and N3 had broken lower edges, pistons 1, 3, 6 damaged, cylinder heads 1, 3, 6 had surface damages, including intake and exhaust valves, crankcase filled with water from cooling system.

Fig.5 Damaged liner Fig.6 Damaged piston

Fig.7 Cylinder head After investigations vessel reported the damage reason as failure of governor Woodward UG8.

Fig.8 Governor of prime mover

However mentioned mechanical failure could be only the reason of malfunction and such serious damages to the diesel engine could be avoided if crew properly assessed the consequences of their actions. 4. 72,000 tanker This vessel is equipped with microprocessor controlled air circuit breakers. Recently she reported problems with one of the circuit breakers. Generators N1 and N3 worked in parallel, after load was transferred to generator N1 and generator N3 was disconnected, blackout occurred. Investigation shown that generator N1 was tripped due to overcurrent (current in each phase was about 1900A, while setting for protection is 1200A), although load did not exceed 500 kW. After further investigation it was noted that measuring device of ACB shows incorrect values of measured current, twice more than real, but source of trouble was not determined. From this time generator N1 was not able to operate in stand alone mode. Five days later Micrologic controller was removed from ACB for further investigation, and after reinstallation back it was found that currents being measured correctly. The reason of troubles was defined as bad connection between Micrologic unit and measuring circuit. Actions to be taken: - Unscheduled inspection of generators should be carried out, all connections to be re-tightened, proper securing of all cables and internal components to be verified. Job C41-01-AE to be reported and properly logged. - Electrical generating equipment is recognized as critical equipment, therefore it should be maintained and operated properly. Periodic maintenance and regular supervision of generator sets should be established onboard, under control of Chief Engineer. Inspections and maintenance should include both windings area of generators (through available openings) and terminal boxes. - Training with Engine staff regarding operation and control of generating plant in emergency situations to be arranged. Every Engineer Officer to be familiar with manual operations required for synchrozing/connection/disconnection of generators and to be aware about consequences of improper actions.