Transcript Refurbishment work prompted

POWER TRANSFORMER
REFURBISHMENT
S. Bhattacharya
Manager - Substations Department
Power Transformer is one of the few vital and single
most costliest equipment in any T&D network
Hence keeping Power Transformer in good health
and extending its service life have always remain
challenging tasks to the professional engineers,
specially in today's regulatory regime.
Refurbishment
It is a major overhauling work to restore a
transformer to healthy condition.
Sometimes, it also involves some degree of
upgrading / uprating.
To maximise service life and to enjoy consequent
financial benefits and reliability.
Refurbishment work usually
comprises different combinations of
Major overhauling involving core & winding inspection,
thorough washing and sludge removal
Re-clamping of winding
Drying out
Gasket replacement
Corrosion treatment and painting
Oil reconditioning or replacement
Terminal bushing replacement, if required
OLTC replacement, if required
Refurbishment drive
Condition assessment
Condition improvement
Condition assessment, through
Oil condition monitoring test, once a year
Insulation Resistance measurement, once in 3
years
Condition improvement, through
On-line filtration
Oil replacement followed by on-line filtration
Drying out followed by filling with new oil
On-site
By external heating and vacuum pulling
By hot air blowing and impedance heating
At repairers’ works
In vacuum drying oven / autoclave
Replacement of terminal bushing, OLTC etc. as
and when required.
Condition improvement of solid
and liquid insulation effected by
 Removal of sludge, foreign contaminants,
moisture extraction and degassing of oil
 Moisture removal from solid insulation
(most difficult task in the drive)
Refurbishment work prompted
Mostly by poor health
Sometimes by a suspected problem
Sometimes by age
Sometimes by an intended relocation
Sometimes along with repairing
Refurbishment Strategy
Poor oil condition but with acidity < 0.5 and satisfactory /
moderate IR values – on-line oil filtration
Both oil condition and IR values are low – attempts are
made for condition improvement through on-line oil
filtration
Poor IR values and oil condition, specially with acidity
>= 0.5 – oil replacement followed by on-line oil
filtration
Refurbishment Strategy
IR very poor and IR improvement through oil
replacement is marginal / not sustainable – on-site
drying out and oil replacement
During resiting, transformer with very low IR values
or aged / last refurbished 20-25 years back –
drying out at repairer’s works and oil
replacement
While carrying out any repair work – drying out and
oil replacement
Achievement
Power Transformer refurbishment is being carried out since
1962 and now-a-days, on an average, refurbishment of 5/6
transformers are carried out each year.
Out of a current population of 214 nos. of power
transformers, 40 transformers are serving over 50 years and
23 transformers are in the age group of 35 to 50 years as
against common life expectancy of 35 years.
Life extension on Refurbishment Supports
35
Estimated Life
0
10
20
30
Borrowed Life
40
50
60 Years
Barrackpore
D/S T2
23
Barrackpore
D/S T3
24
28
54
59
28
53
59
P. St. D/S
T2
15
Canal D/S
T2
Sinthia D/S
T1
13
18
39
22
33
44
41 44
53
Rep.
& Drying Out
Drying Out
Oil Replacement
20
26
33
43 45
Oil Filtration
Future Pathway
Objective : Life extraction from the present day
transformers to that extent as achieved in
case of transformers of yesteryears.
Through :
1. Using means for reducing oil deterioration, such as
Air-bag fitted conservator, Thermosyphonic filter and
insulating oil conforming to stringent specification.
Future Pathway
Objective : Life extraction from the present day
transformers to that extent as achieved in
case of transformers of yesteryears.
Through :
2. Carrying out periodical oil maintenance, guided by
traditional means of oil and transformers’ IR monitoring.
Future Pathway
Objective : Life extraction from the present day
transformers to that extent as achieved in
case of transformers of yesteryears.
Through :
3. Taking care of any abnormalities in their nascent stage,
practicing transformer monitoring through DGA.
Future Pathway
Objective : Life extraction from the present day
transformers to that extent as achieved in
case of transformers of yesteryears.
Through :
4. Attaching much more importance to insulation
condition improvement drives, timely, such as oil
filtration / oil replacement / drying out, most importantly
based on health monitoring and residual life assessment
adopting state-of-the-art tools / techniques.
Conclusion
Refurbishment is an essential requirement to extend /
maximise service life of transformer
State-of-the-art techniques / tools for condition
monitoring should be practiced for remaining life
assessment study and to select right transformer for
refurbishment at the right moment
Cost-benefit analysis should be made to ascertain viability
of the refurbishment work