TransformerCare Unit
Status monitoring
Specifying the gas formation rate of the transformer
The transformer gas formation rate (ml/day or ppm/year) is determined via the
gases collected which flow from the gas withdrawal connection (23) in the lower
section of the degasification and dewatering unit.
The gases are collected in the gas sampling bag over a certain period, and then
analyzed in a gas chromatograph.
The gas quantity is determined in ml/day for each gas (including gases in the air) via
the total volume of collected gases and the time measured for filling. The oil quantity
in the transformer can then be used to determine the gas formation rate in
ppm/year.
The gas quantity in ml/day or ppm/year represents the gas formation rate in the
transformer or the air gases which enter via the expansion vessel, provided:
The gas content in oil remains "unchanged" - that means that the gas
content in the oil reaches a relatively constant condition, whereby the
quantity of dissolved gases can be assumed to be constant over time. This
status is never fully reached as the conditions such as the load and
temperature change constantly.
The gas content has reached relatively low values so that the majority of the
gases are removed by the TCU, and accordingly only a negligible quantity
escapes through the expansion vessel.
The time required to reach these balanced conditions depends on the initial
condition, e.g. the oil quantity, the initial gas content (e.g. was the TCU degasified
before installation) or whether the transformer is open or closed.
The air gases oxygen and nitrogen generally reach a constant level after just 8
circulations (15 m³ / week).
Gases with higher Bunsen coefficients such as acetylene or carbon dioxide take
longer to reach a balanced state.
This is particularly due to the fact that degasification of the insulating oil can cause
an imbalance between the gas concentration in the oil and the cellulose, which
means that the gases must first migrate from the cellulose (solid insulation) into the
oil, before they can be removed.
HYDAC FILTER SYSTEMS GMBH
en
Page 43 / 64
BeWa TCU 3472805b en 2011-07-05.doc
2011-07-05
Summary of Contents for TCU Series
Page 63: ...Notes ...
