Concentrações de hidrogénio e acetileno

In January 2007, the transformer experienced a sudden rise in the

concentrations of Hydrogen and Acetylene. Hydrogen increased from 84ppm to

200ppm and Acetylene increased from 27ppm to 96ppm over a period of about

48 hours. The measurement frequency increased from every 4 hours to every

hour as the TRANSFIX measured concentrations exceeded the alarm levels. In

this case, the customer had set alarm levels and used Caution and Alarm Modes

to accelerate the frequency of measurement as the gas concentrations

increased. The load on the transformer was reduced and the gas concentrations

remained relatively constant for 4 days. Then the load was increased again and

the Hydrogen concentration increased to 280ppm and the Acetylene increased to

158ppm. The transformer was temporarily taken off-line and degassed. When

the load was increased again, the concentrations of Hydrogen and Acetylene

rapidly increased. The transformer was degassed again, and once more the

concentrations of Hydrogen and Acetylene increased with load. At this point, a

replacement transformer became available and the faulty transformer was safely

taken out of service.

The value of the on-line monitoring provided by TRANSFIX is clearly seen here,

as the fault that developed was not the same as had been seen in the long-term

condition of the transformer. The fault that occurred in January 2007 developed

rapidly and might have led to catastrophic failure of the transformer if there had

not been on-line monitoring in place.

CASE STUDY 2

In this case, the TRANSFIX was installed in December 2006 on a transformer

with high levels of Hydrogen (510ppm), Methane (1711ppm) and Ethylene

(641ppm) and Ethane (1047ppm). The gas levels remain fairly constant under

constant load conditions, and then began to rise rapidly on 21 January 2007.

The transformer load was removed on 7 February, and the gas levels stabilised,

although the transformer was still energised at this time. In this case, the

transformer operator had taken a decision to remove load from the transformer

based on the on-line DGA measurements. The rapid rise in the gas levels over a

period of a few days shows that on-line monitoring has advantages over manual

sampling as rapidly developing events can be detected.

The transformer operator