: Fluid Testing Packages for Electrical Asset Management

What is DGA testing?

Dissolved Gas Analysis is the most critical tool for analysis in predictive/preventative transformer maintenance plan by testing by the transformer fluid.

The insulating fluids used in transformers and related equipment are used because of their high dielectric strength and chemical stability. However, conditions and faults within the equipment will lead to chemical degradation of the fluid. The intensity of the fault or action determines the nature and degree of the degradation. The fault breakdown products are low molecular weight gaseous compounds that are soluble in the fluid. Analysis of which gases are present, the amount of each, and the ratios to each other are used to determine which fault processes are present in the equipment.

Common gases determined in DGA testing of transformer oil

DGA provides the current condition within the equipment by detecting thermal and electrical faults. This may indicate a need for additional diagnostic or electrical testing or evaluation during manufacture or warranty.

After determining the gases present, interpretation of the data can be done in several ways.

Key Gas Analysis

This method is a qualitative interpretation based on determination of fault types from “key gases” formed at different temperatures.

Ratio Analysis

This is a statistical determination of the ratios of certain gases to each other to further define fault types and thermal or arcing severity of the faults occurring.

Graphical Analysis

This interpretation involves plotting specific gases graphically in nomograms, triangles, or pentagons using intersecting points to indicate areas where the fault conditions are most probable.

Rate of Generation

This evaluation involved tracking the change between successive analyses in concentration of gases indicated. This can involve a change or delta between 2 analyses or using linear regression analysis over several points of applicable data. This can indicate severity and rate of progression of the faults occurring.

Unit Specific and Historical Tracking

These methods of interpretation are enhanced further with specific knowledge of the operating conditions of the equipment involved and historical records of the gases’ levels over time and those conditions. That’s why IEEE has developed a permanent anonymous database to further the industry’s effort to refine DGA data.