Condition monitoring is essential for transformer maintenance, environmental legislation and Insurance assessments are encouraging routine testing of units.
The analysis of electrical oils serves a pivotal role in the maintenance and upkeep of transformers, switchgears and tap-changers. Transformer oil analysis is a service that gives the engineer ample time to arrange a production stop or an oil/unit change when it suits. The service has been developed specifically to apply to all types and sizes of transformers filled with mineral or silicon insulating oil. Using analytical programs the system interprets the lab results, identifies the type of fault and determines the probable time to failure, in some instances up to 4 years in advance of a developing problem.
Transformer test methods
Polychlorinated biphenyl (PCB) analysis
PCB’s where realised in the 1970’s during the oil crises to bulk up the transformer oils. Due to the high toxicity of PCB’s it is now legislation to know the PCB content of your transformer oil.
Dissolved gas analysis (DGA)
Dissolved gases in transformer oils are inherent gases and gases that form due to the breakdown of the paper or oil under stress or degradation. With regular DGA testing the following problems can be detected months in advance
- Loose connections
- Breakdown in cellulose
- Partial discharge
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.
Why is important to determine the moisture content in transformer oil?
- To determine if there are any leaks in the transformer
- Increase in moisture indicates insulating paper degradation
- Determine if decrease in insulating strength is due to high water content in the transformer oil.
Total acid number (TAN)
TAN is the quantity of base (mg of KOH) that is required to neutralise acid constituents in 1g of sample. An increase in acid indicates that sludge formation is beginning to occur or is occurring.
Dielectric strength is the voltage at which breakdown of the oil occurs. Insulating power decreases as the amount of contaminants in the transformer oil increases so the insulating quality of the oil can be predicted.
Furancis are degradation 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
- Water (moisture)
- Oil oxidation