Transformer diagnosis

What is the transformer condition diagnosis?

The diagnosis of the transformer is carried out through a series of inspections, actions and tests with which a global vision of the condition of the transformer is obtained, both external and internal, which allows the adoption of the corresponding preventive and corrective actions that guarantee the maximum availability of the facility. The following apply:

• Visual inspection.
• High definition infrared thermography.
• Ultrasonic inspection.
• Dissolved gas analysis (DGA) of the insulating liquid.
• Physicochemical analysis (FQ) of the insulating liquid.
• Vibrations measurement.
• Noise measurement.

Who performs the inspection?

On-site inspection at the facility is carried out by engineers with extensive experience in work in electrical generation facilities and, particularly, in the techniques applied in the inspection. The analytical tests of the insulating liquids (mineral oil, silicone, ester) are carried out by chemical personnel with extensive experience in the laboratory. Insulating liquid sampling is carried out by our staff during the inspection.

What security measures are adopted?

The inspection is carried out only if the environmental conditions are suitable (absence of rain, snow, wind and low humidity); safety distances to active parts are maintained at all times. The staff has the following protection elements: safety helmet, hearing protector, glasses, dielectric boots, electric field detector, voltage detector, gloves against mechanical risks and nitrile gloves.

What equipment is available for inspection?

The instruments available to carry out the on-site inspection are the following:

• High definition infrared thermographic camera.
• Ultrasonic inspection equipment.
• Devices for insulating liquid sampling.
• Absolute pressure transducer.
• Thermometer for liquids.
• Thermohygrometer.
• Vibration meter.
• Sound level meter.
• Binoculars.
• Photographic camera.
• Current clamp.
• Anemometer.

The following equipment is available for the analysis of the insulating liquid samples:

• Acid and base meter.
• Moisture meter by coulometric Karl Fischer.
• Dielectic breakdown voltage (100 kV).
• Dielectric loss tangent meter.
• Particle counter.
• Dissolved gas analizer (DGA).
• Analytical balance.
• Viscosímeter.

Sampling for analysis of gases dissolved in the insulating liquid (DGA) and in the Buchholz relay is always done with a glass syringe, using stainless steel adapters to the transformer sampling valve. In case of urgency of the results, the analysis can be carried out directly at the client's own facility.

How important is liquid insulating sampling for FQ and DGA analysis?

If the analysis of the dissolved gases and that of the physicochemical characteristics of the insulating liquid are the most reliable tools to verify the internal condition of the transformer and that of its insulating liquid, respectively; the taking of the samples is the most important part of the whole process, since it depends on it that the result of the analysis is a true reflection of the condition of the transformer and not the product of the contaminants present in samples poorly taken by personnel without preparation, experience and the appropriate equipment, which will inevitably lead to false diagnoses.

Is other equipment examined during the inspection?

Although the main object of the inspection are the main power transformers, the following elements of the substation are also inspected: voltage and current transformers, lightning and surge arresters, switches, disconnectors, auxiliary services transformers, etc. On these elements, thermography and ultrasound techniques are basically applied.