Importance of Dehydration of Transformer Oil.

1. Transformer Oil Purification
/ Filtration Process /
Procedure

2. In this article you will understand
transformer oil purification
process, steps and methods
involved in oil purification process.

3. Transformer oil purification is a
process to remove sludge,
dissolved moisture and dissolved
gases from the oil.

5. Before we move to process details,
Lets see why transformers need
purified oil?
As discussed in details Advantages of
transformer oil filtration in post why
transformer oil filtration is required?
Here we will see in brief advantages
for transformer oil purification:

7. •Improved insulation properties of the oil and hence
the other media like paper/cellulose insulation.
•Better the insulation of transformer, longer the
life of the transformer and lesser the breakdown of
the transformer.
•Longer the life of the transformer asset, good
returns on investment of the asset.
•Lesser breakdowns and failure of the transformer
results in uninterrupted power supply.

8. For good performance of transformers we
require filtration machines designed and
manufactured with standards.
At TransfoTech. Engineering, we use Oil
purification machines with International
prescribed Standards (BIS, NEMA, IEEE,
IEE, ASTM, ASME, IEC) for good
performance of transformer.

10. Transformer Oil Purification Procedure
Transformer is one of the main asset in
the electrical power industry which
needs to be maintained for guaranteed
uninterrupted power transmission in
order to get assured revenue benefits.
Transformer life mainly depends on the
quality of oil volume it contains.
Regular transformer oil filtration assures
long and consistent results from the
transformer.

11. Transformer oil purification is a process to
remove sludge, dissolved moisture and dissolved
gases from the oil.Transformer oil conditioning
may also include to some extent improving the
acidity of the oil.
A good oil purification system is able to deliver
filtered oil with parameters as per the standard
specification.

12. However, this revival of the oil by oil filtration
plant to standard oil parameters is based on
the quality of unprocessed oil and its initial
process.
In case the unprocessed oil does not match
the standard oil parameters, then the effort
of transformer oil filtration is all in vain.
Alternate method of regeneration of
transformer oil should be adopted in this
case.

13. Here we shall look at the method of the
transformer oil filtration by vacuum type
dehydration and centrifuge type removal of
solids and water separation.
Transformer oil conditioning is a stream line
oil filtration process of sludge purification,
moisture removal and gas removal.
The first step in this serial process is to raise
the oil temperature to a desired level,
generally up to 65 Deg C. This aids to give the
oil latent heat which later aids to dissociate
the moisture and gases from oil in the
degassing chamber.

14. Additionally the viscosity of the oil drops
which aids in better filtration to some extent.
Recommended heater design should consider
an area of heating of about 1 to 2 W/sq.cm. In
the transformer oil purification plant, the
heating system is protected against over
pressure built up and excess temperature rise.
The second step of transformer oil
purification plant is removal of sludge and
dirt from the transformer oil.
Two methods have been used for removal of
the sludge:
• Removal of sludge by filter candles. and/or
• Removal of sludge by centrifuging action.

15. Transformer oil filtration using filter
candles in the transformer oil purifier
machine can further be classified as:
 Filtration using the classical edge filter
 Filtration of transformer oil using the
depth type filter.
Both methods of cartridge type filtration
are prevalent and owe certain advantages
and disadvantages.

16. The edge type filter system can be cleaned and be
reused for at least three to four times,
however, cleaning and fitting of the edge filters
involves considerable time and human effort.
This system is robust to handle large quantity of
sludge. Edge filters can be cleaned by reverse
pressurized dry air/nitrogen flow in order to
remove the contamination.
After de-sludging the paper stack is removed and
dried in oven/ bright sunlight and reused. This
operation demands experience and skill set.

17. New trends and technology in the market
have driven transformer oil filter machines
to use filter cartridges instead edge type paper
stacked filters.
These cartridges are similar to those of the water
filter cartridges and can be selected from a
variety of purification range say from 500 micron
to 0.5 micron size.
The advantage using these cartridges over the
edge filter is:
 No moisture storage, since the filter media used
can be non-hygroscopic.
 Easy to replace with less human effort and easy
availability.

18. An alternate method used for dirt
separation from oil is centrifuge.
Routine transformer oil filtration or transformer oil
conditioning is often confused with transformer oil
centrifuging.
Transformer oil centrifuging is all together a
different technology and has a little impact on
improving the oil parameters.
Centrifuges used for separation of dirt from the
transformer oil can be slow speed type
centrifuges that do not require additional electric
motor to spin the centrifuge cone at high speed.

19. However, the dirt separation from oil with
such centrifuging has limitations since these
centrifuges cannot remove the dirt less than 10
micron level.
Thus a power driven centrifuge becomes evitable
which scales up the cost of the oil conditioning
machine.
Only advantage of the centrifuges is that the recurring
cost of changing filter elements is saved.
Power driven centrifuges can remove water from the
oil that is in free form but not the dissolved moisture.
Manufacturers of power driven centrifuge also often
do not guarantee removal of moisture to a level less
than 5 ppm

20. The third step in the oil filter machine is
dehydration of transformer oil and degasification
of the transformer oil.
These processes of dehumidification of
transformer oil and removal of gasses are executed
in the degassing chamber. The dissolved water oil
separation or dissolved gas oil separation is
possible at reduced pressure, i.e. vacuum, due to
difference of boiling point of water, gas and
transformer oil.

21. In the process of separation of gases from the
oil it becomes important to retain the aromatic
hydrocarbons so that the original properties of
the oil are retained.
When the water level in the oil is above
saturation level of the transformer oil, oil is
observed in free water.
Removal of free water can be done by power
driven centrifuge or by coalescing principle,
where the later is more effective and
economical in practice.

22. With the different processes involved in the
transformer dehydration and degasification
plant it is evident that the processes should be
neatly designed to tame different oil volumes to be
filtered.
With increasing power demands and scaled up
voltages transformer oil filtration is becoming more
and more demanding and sophisticated. With the
advent of new technology now the water activity or
the water content in the transformer oil is
measurable online and methods of laboratory
testing like the titration method are becoming
limited.

23. At Transfo Tech. Engineering,
we understand the requirements of the oil
filtration and are committed for resulting a good
transformer performance. Feel free to contact
us, we shall be happy to help you and provide
you a quick response.
At Transfo Tech. Engineering, we understand
the requirements of the oil filtration and are
committed for resulting a good transformer
performance. Feel free to contact us, we shall
be happy to help you and provide you a quick
response.

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KARACHI
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