6FA Generator Major Overhaul

8/11/2019 6FA Generator Major Overhaul

1/17

ENERGIESLAVERA

6FA Generator MO and Transformer depolarization

6FA Generator Major Overhaul and Transformer

Depolarization - Lavera Energies


2/17

ENERGIESLAVERA


Equipment :

2 turbines GE frame 6 FA/6B 109 MW elec

2 HSRG with post combustion, output steam flowpower 240t/h at 80 bars

Cogeneration - Lavra Energies


3/17

ENERGIESLAVERA


6FA Generator identity card

Constructor : Alsthom

Power : 68,9 MVA

Voltage : 11,5 kV,

Speed 3 000 tr/h,

52 300 FFH in 2011


4/17

ENERGIESLAVERA


Generator MO strategy

Diversity in approach and practice in use internationally :

Source : Generator maintenance inspection and test programmes, working group


5/17


6/17

ENERGIESLAVERA


Extraworks

The bearings generator side and gear box side are damaged : High temperature impacts, one hole detected

For both bearings clearance out of range

Replacement of the bearings and several bolts

Clearance adjusted to 0,6 mm on the base of the new calculation Rotor alignment between load gear and the generator on the base of the

new clearance value.


7/17

ENERGIESLAVERA


Extraworks

The slot wedges are moving excessively :

Risks of damages to the rotor windings

Vibration risks during the start up

AEW and Alsthom advice to remove retaining rings and

resize the slot wedges So the rotor balancing becomes necessary


8/17

ENERGIESLAVERA


Extraworks

High pollution at the windings surface above the

retaining rings :

dry cleaning


9/17

ENERGIESLAVERA


Some global figures

Cost

MO order : 128 k

Scaffolding for the rotor 12 k

Exciter maintenance 18 k

CSF maintenance 8 k Craning 8 k

Retaining rings removal/balancing 76 k

Miscellaneous 10 k

TOTAL 260 k

Planning

Base : 6 weeks

Extraworks 6 weeks

TOTAL 12 weeks


10/17

ENERGIESLAVERA


Extent of problem transformer depolarization

The report of the working group A2-32, Copper Sulphide inTransformer Insulation describes the issue

The problem of copper sulphide in transformer insulation is quiteold. However, it is only in the last 15 years that it has gotten very

much attention, No one has a really good grasp of the extent of the problem.

Estimates vary, but we can estimate the number of sulphide-related failures are in the range 50 to 100.

Transformers from several different manufacturers have beeninvolved, and also several different suppliers of oi l.

The connection with corrosive sulphur in oi ls implemented 10-15years before became evident.

There is a correlation between e.g.high disulphide contents in

general (and DBDS content in particular) and the formation ofcopper sulphide. This is complex, and far from well understoodtoday.


11/17

ENERGIESLAVERA



Copper sulphide is a semiconductor. It will normally not be good

to have such a substance in the insulation. But the presence of

copper sulphide will not necessarily lead to failure. It will surely

depend on the amount, as well as the location.

It seems that basically we have 2 main routes:

1 Progressively lowered insulation withstand as copper sulphide

penetrates the insulation. The paper get more or less

impregnated. In the end it is not insulation any more.

2. However, it may not always be necessary to have very large

amounts of sulphide or failures to occur.

There may be other failure modes as well. Failures often destroy

the evidence , leaving the field open for speculation


12/17

ENERGIESLAVERA



The approach is to use chemical analysis, to detect the presence

of potentially harmful sulphur species.

Some are known to be relevant, such as DBDS content, or total

disulphide content.

The important thing to know, is that such tests may not in

themselves be enough for assessing if an oil is potentially

harmful or not.


13/17

ENERGIESLAVERA


Mitigation technique

Four techniques exist : additives

Oil treatment (for example depolarization)

Oil exchange

Modified operating conditions

The selective depolarization process is used in Italy and France

since summer 2005, to remove DDBS and reduce corrosiveness.

We applied this technology to treat the Lavera transformer.


14/17

ENERGIESLAVERA


Depolarization task

Contractual points : Dalkia started the specific audit / campaign since 2007 for all transformers

The contractual points / warranty are defined via specific global contract

13 days off-load treatment maximum

50 k cost

DDBS concentration at the end < 10 mg/kg

DDBS concentration after 6 months < 10 mg/kg. In case of deviation, thesupplier will achieve the additional treatment free of charge

Historic : 56,7 mg/kg DDBS before and 9 mg/kg after the depolarization

31 mg/kg after 6 months (additional depolarization implemented)

Now i ts OK since 12 months

Leaks on the transformer seal during the start-up, Immediate seals replacement

3 months later the preventive thermograph control discovered the hotpoint on the transformer connections (154 C instead of 45C)

Decision to stop the machine (5h)

Connection cleaning, bol t replacement

Proper bol t and nut torque process

Start up and new thermograph control => OK


15/17

ENERGIESLAVERA


Thermograph report


16/17

ENERGIESLAVERA


Hot spot on the connections


17/17

ENERGIESLAVERA


Thank you for your attention

6FA Generator Major Overhaul

Documents

Transcript of 6FA Generator Major Overhaul