The tests monitor various aspects of the transformer:
Oil condition - moisture, acid content and dielectric strength
Internal working - dissolved gas analysis (DGA)
Paper condition - furanic analysis
Contaminants - PCB and corrosive sulphur
1. Moisture Analysis
Why is it important to determine the moisture content in transformer oil?
To determine if there are any leaks in the transformer
Increase in moisture accelerates insulating paper degradation
To determine if decrease in insulating strength is due to high water content in the transformer oil
Paper and oil degradation
2. Total Acid Number
(TAN) TAN is an indication of the acidity of the oil. High acidity will cause oil degradation and sludge formation which will cause paper degradation, cooling problems and internal corrosion.
3. Dielectric Strength
Dielectric strength is the voltage at which the electric breakdown of the oil occurs. By analysing the voltage the amount of contaminants and the insulating quality can be predicted.
4. Dissolved Gas Analysis
(DGA) Dissolved gases in transformer oils are inherent gases and gases that form due to the breakdown of the paper, oil under stress or degradation, or mechanical faults.
4(A). With regular DGA testing the following problems can be detected months in advance
Breakdown in insulation
Furanics are degradation by-products of the insulation paper found in transformers.
Analysing furanics is important in predicting the degradation of the insulating paper
The following will destroy insulation paper
6. Corrosive Sulphur
Corrosive sulphur forms acidic conditions in transformers. This is a vital test as DGA, MAD and furanic tests may indicate normal operation even when failure is imminent. If corrosive sulphur oil is found, oil will need to be replaced.
7. Polychlorinated Biphenyl (PCB) Analysis
PCBs were released in the 1970's during the oil crisis in order to bulk up transformer oil volume. Due to the high toxicity and environmental impact of PCBs it is now been legislated to know the PCB content of your transformer oil.