Alternator Issues post bad weather/unit shutdown
Alternator Issues post bad weather/unit shutdown
(OP)
Hi all,
Can you explain the effects of a large imbalance between phases R-Y, R-B = 0.38 milli ohm Y-B = 4 ohm when a generator is ductored, IR/PI good.
Star bar disconnected, IR between phases good. Line to line ductor all 3 phases identical. Only when star bar connected is there an issue when ductoring.
Unit didn't trip on any protection type, severe weather to cut a long story short caused Shutdown and consequently seawater/lube oil to enter alternator enclosure/ submerge stator 1/4 way up, now drained down awaiting chemical clean.
Can this unit be ran once cleaned with the large imbalance as above? Could interturn failire be a cause?Surely the diff protection would have operated in this instance....?
Any thoughts on alternate tests to carryout to pin point route cause. Strange situation given it ran with no known issues/alarms prior to unit shutdown due the plant ESD.
Can you explain the effects of a large imbalance between phases R-Y, R-B = 0.38 milli ohm Y-B = 4 ohm when a generator is ductored, IR/PI good.
Star bar disconnected, IR between phases good. Line to line ductor all 3 phases identical. Only when star bar connected is there an issue when ductoring.
Unit didn't trip on any protection type, severe weather to cut a long story short caused Shutdown and consequently seawater/lube oil to enter alternator enclosure/ submerge stator 1/4 way up, now drained down awaiting chemical clean.
Can this unit be ran once cleaned with the large imbalance as above? Could interturn failire be a cause?Surely the diff protection would have operated in this instance....?
Any thoughts on alternate tests to carryout to pin point route cause. Strange situation given it ran with no known issues/alarms prior to unit shutdown due the plant ESD.






RE: Alternator Issues post bad weather/unit shutdown
RE: Alternator Issues post bad weather/unit shutdown
RE: Alternator Issues post bad weather/unit shutdown
RE: Alternator Issues post bad weather/unit shutdown
This we cannot understand, even when bolting together instead of using the star bar we get the abnomally as above, so ruling any issue with the star bar out.
Could an /insulation failure/short on 1 phase give rise to such an anomally?
Any thoughts.....!
RE: Alternator Issues post bad weather/unit shutdown
RE: Alternator Issues post bad weather/unit shutdown
Corrosion of the stator iron will occur quickly also of the copper conductors. If the unit was submerged for a long time in salt water (days or more) then it will be possibly unrepairable.Not to mention the simeltaneous damage to the rotor. If it is a brushless unit even more bad news...
rasevskii
RE: Alternator Issues post bad weather/unit shutdown
My apologies - 11kV, 60Hz, 10.5MW, rated, IR/PI tested at 5Kv. Insulation results suprisingly good, in ggig range. As you mention and as we have concluded the fact that the stator has been submerged in seawater/lube oil is a concern and will inherently impact on the sets integrity. It is a brushless type, submersion was on the lower stator part, rotor IR at 14 G ohm.
It is suggested that a chemical clean be carried out but how sure or advantageous this is given it was submerged for 3 days I don't no. Insulation breakdown is my concern and will a chemical clean remove all the impregnated interfaced mix.
Putting this part aside what is the consensus on running the unit with this large an imbalance/ possible effects or damage....! Rotor heating...! Again we have opinionated a no run response to our shore based team. Your thoughts would be appreciated.
RE: Alternator Issues post bad weather/unit shutdown
Also the air passages in the stator and the spaces between the laminations must still be full of water/oil that will be driven out as the unit is operated.
The best procedure would be to comtact the OEM or an established winding repair company for an opinion.
Also the rotating rectifier assembly and exciter field and armature may be affected.
IMHO it would not be advisable to consider running the unit on voltage until at least the OEM opinion is available.
Others here may comment?
rasevskii
RE: Alternator Issues post bad weather/unit shutdown
The IR also may look good at megger test voltages (5KV) but at full voltage there may an issue (fault) at the coil end(s) due the semiconducting tape/paint being salted over or otherwise no longer effective.
rasevskii
RE: Alternator Issues post bad weather/unit shutdown
We were also surprised with the IR/PI results given no treatment in terms of drying out using heaters/short cct operation.
The units ACH obviously incurred damage due to submersion and are inactive. Excitor assembly already backloaded given size.
In few words it's not looking good.
Best regards and thankyou for your posts.
RE: Alternator Issues post bad weather/unit shutdown
RE: Alternator Issues post bad weather/unit shutdown
BTW what is an ACH? Is this a Diesel? A lot of other equipment must have taken a hit also.
Enjoy your life on the platform and good luck!
rasevskii
RE: Alternator Issues post bad weather/unit shutdown
ACH -anti con heaters/space heaters.
Unit was running prior to ESD which caused unit trip and coincidently due to severe weather caused the lube oil cooler to rupture, oil/sewater migrating to the alternator enclosure via the unit DE/NDE bearings. Yes other cooler failures due to bad weather occurred.
We run on an unearthed system so no theoretical solid earth. Earth fault monitoring is implemented. No record of any elect protection operation, so assume migration of oil/water occurred after unit shutdown due to platform ESD.
Thanks again
RE: Alternator Issues post bad weather/unit shutdown
What sort of ductor are you using - a high current set or a little 1A / 10A type? Can you get a reasonably sensitive tong tester around the neutral bar?
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