01/12/2005

HUMIDITY MEASUREMENTS DURING ELECTRIC TRANSFORMER INSULATION


Aplein Ingenieros, S.A. and the American manufacturer XENTAUR that produces measurement transmitters for moisture in liquid and gas have signed a distribution agreement for their equipment in Spain.

Based on the registered HTFTM (Hyper-Thin-Film) technology for aluminium oxide sensors, they provide a reliable solution for the measurement of moisture and dewpoint in gases and liquids in applications for measuring moisture in electric substation transformers.

The main moisture measurement applications during electric substation maintenance are as follows:

1. Measurement of the humidity in sulphur hexafluoride-filled (SF6) breakers.
2. Measurement of the humidity in nitrogen-filled (N2) transformers.
3. Measurement of the humidity in air and nitrogen during transformer start-up or restart-up.
4. Measurement of the humidity in oil-filled transformers.


All electrical equipment that is manipulated is filled with some form of insulation: air, SF6, N2 or oil. These insulators must be completely dry since it is well-known that water and electricity do not mix well. The presence of humidity can cause failures, short circuits, explosions and very expensive maintenance procedures.


Xentaur portable XPDM model.

This is recommended for moisture measurement applications where breakers are filled with sulphur hexafluoride (SF6), in the transformer nitrogen blanket, where the operator purges a small sample of nitrogen by means of the instrument, waiting one or two minutes for stabilisation and then performing the measurement.
The XENTAUR XPDM model provides significant advantages over other dewpoint measuring equipment because of its response speed, portability and minimum gas consumption.


                                  XPDM with filter and regulator option.


The main characteristics of this equipment are:
- Portable analyser
- The lightest and smallest analyser on the market
- Low gas sample consumption
- Response time for 10 ppmV (-60ºC dp): < 1 minute
- Robust construction
- Contamination resistant due to its internal drying chamber
- Options: Carrying case, various connectors, regulator and filter.


Self-Drying ESS Xentaur Model.

Recommended for transformer putting-into-operation applications.
The Sample Extraction System (SES) has a modular design and can be configured to accommodate almost any measurement requirement. It is manufactured from high quality materials and the system complies with all station standards. The system includes a moisture sensor that remains completely dry when the equipment is not actually in use. It incorporates a desiccant cartridge that is easy to change in the field and which eliminates undesired contaminants and moisture with practically no maintenance.

The system is ideal for station or mobile applications. This system enables evacuation times to be significantly reduced, providing savings in energy and resources.

The sampling technique is unique and avoids long recovery times, drift and premature sensor failure.


Xentaur model HDT for liquids (transformer oil)

The hybrid dewpoint transmitter, model HDT, is a HART self-powered loop transmitter that can be employed in all transformer oil applications with its new sensor for liquid measurements.

The Xentaur facilities have their own liquid laboratory, which researches and develops sensors for measuring water vapour in liquids.

The main primary standard for measuring the water vapour content in liquids is the JKarl Fischer (KF) evaluation. Aplein Ingenieros, S.A. and Xentaur also market this type of laboratory analyser.

Xentaur employs a secondary measurement method based on Al2O3 technology for moisture measurements in transformer oil; these sensors measure the changes in water vapour partial pressure. Water vapour partial pressure is directly related to the concentration in parts per million by weight (ppm w) by means of the Henry non-dimensional proportionality constant. In oil transformers the Henry constant is essentially dependent on temperature. When the temperature increases, the capacity of the oil to hold water also increases, but the moisture concentration remains the same.



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