Vacuum Degassing connected with existing GC to automate the DGA Procedure

Electrical abnormalities in transformers are exhibited by gas in the oil and evaluated by a DGA, which allows a detection of two different types of failures: electrical and thermal faults, whereby each type of failure can be subdivided into three different categories according to the international standard IEC 60599. DGA became a well known and approved technique in recent decades, although different
techniques of dissolved gas analysis and its interpretation exist.

As a first step for an evaluation of the actual condition of Transformer insulating system
usually a dissolved gas analysis is used, because failures inside the transformer lead to a
degradation of the liquid insulation in such a way that different so called failure gases are
produced, thus the compound of the gases, which is characteristic for different failure types,
enables an identification of the failure cause.
Therefore from the gases that are dissolved in the insulating liquid, which usually consists of
a mineral based insulating oil, an assessment of the strains that have been provoked insulation
degradation, is possible. By such an analysis both thermal and electrical overstressing
becomes evident, thus allowing an early information about condition of your Transformer

With the new TOGA system the analysis is done automatically in 2 steps with high selectivity
and accuracy.
1. Degassing of the taken oil sample through vacuum extraction (according to IEC 60567 [2])
2. Dissolved gas analysis by gas chromatography with TCD (thermal conductivity detector),
FID (Flame Ionization detector) and Methanizer or your excisting GC.
Both steps, which are explained in more details in the follwoing, are synchronized by a microcontroller,
which guarantees a fast and reliable measurement routine.
Also possible is the use of an excisting GC

Vacuum Degassing
A new invented vacuum degassing method (Patent pending DE 102 52 652 4) degases the oil
sample in multiple periods. After the extraction by a 4 step vacuum pump the gases are
enclosed in a vacuum chamber where they are separated. The gases are evacuated from the
vacuum chamber with a vacuum pump, therefore a very high sensitivity can be reached.
In- and outlet of the oil sample as well as the switching valve are microprocessor controlled
and a linear pressure sensor measures online the total gas content (TGC), which is an
important parameter concerning bubbling.
The injection of the gas samples into the gas chromatograph is made via a fixed mounted
tansfer pipe but also an additional port for a withdrawal of gas samples is installed.
The analysis of the dissolved gases is done after the automatic injection in an automatic
sample loop of the gas chromatograph.

With the automatic Injection the VDU gives an start signal that the GC to analyse the injected
gas.

An additional modification we also could use our Automatic sampler to contain 16 syringes to
run the system over night.