3. High water content in the oil
Please never forget
that
the water content in transformer oil always strongly varies with the transformer
temperature
therefore
a moisture diagnostic based on water-in-oil only
can
judge a „cold“ transformer (erroneously) as „dry“ and
a „hot“ transformer (erroneously again) as „wet“ !!!
therefore
any proper evaluation of the water contamination of a transformer should be described
by a temperature invariant value - it means by the water content in the cellulose
,
furthermore
single readings of the water content in the oil regardless of
a transformer temperature is, from the point of proper diagnostics, mostly misleading
!
Moreover, the high water content in the oil can be caused by measuring
errors.
On-line measuring methods:
- the oil sample is contaminated by the air humidity or free water during
the sampling procedure or in the lab
- measurement error is induced by acids
in aged oils – the standard
Karl Fisher ( KF) method reads not only diluted water in the oil as required
, but
the water in acids as well. The corresponding KF reading is therefore a lot
higher than the real water content in the oil – See L
- reading of the
water content in oil without checking the equilibrium conditions of a transformer
inevitably induces the wrong evaluation of the water content
in its cellulose materials
Off-line measuring of the water content in the cellulose e.g. by the RVM
or PDC method, are extremely time-consuming (transformer has to be long-term
disconnected ) and has , with the exception of the FDC method, a low precision
and repeatability.
Generally, a high water content in the cellulose implicates either a poor
maintenance or design errors:
- humidity strongly enters our transformer due to e.g. the wrong function
of the air dehydrator
- the oxidation of the cellulose continuously works as
a main internal source of the water
The recommended solution of the problem:
1) proper measuring and evaluation:
All mentioned measuring (virtual) errors can be very effectively suppressed
by the application of the new SIMMS method because :
- the measuring procedure a priori excludes any oil contamination – the
connection lines are evacuated at first and the oil is never exposed to the
atmosphere during the measuring procedure.
- reading shows the water content
in the bulk of liquid insulation - oil is continuously forced from the transformer
through the SIMMS and returns to
the transformer
- the SIMMS is during the reading hermetically connected to
the transformer - the air entry while negative pressure in the transformer
is therefore impossible
- the measuring distortion due acids is excluded – the
capacity sonde reads only the real humidity of the oil , the reading
is therefore independent
from the actual content of acids in the oil - for the experimental verification
of the last statement See www.ars-altmann.com \News\ The Oil-Moisture Diagnostic problem of aged transformers.
- The evaluation of equlibrium conditions is
based on long-term measuring of the oil humidity and the two temperatures
of the transformer and its corresponding
data set is in-situ evaluated by the lap-top.
Any proper conclusion
about the water contamination of a given transformer
must be based
only
on the averaged value of the water content in the cellulose !
See TRACONAL
2) The transformer dehydration
See FAQ – What kind of transformer dehydration
should be used ?
3) The preventative maintenance
See TRAFOSEAL
Under normal operational conditions only an effective hermetization of the
transformer quarantees the long-term suppression of external and internal
water
sources in a transformer.
The reason is simple - only the effective long-term suppression of the entry
of O2 and H2O into a protected oil-cellulose system effectively retards the
accumulation of the water in the cellulose and stops the internal production
of the water in the transformer.