Transformer oil analysis is a crucial aspect of electrical maintenance, ensuring the reliability and efficiency of oil-filled electrical equipment. However, the accuracy of this analysis begins long before the laboratory testing process—it starts with proper sampling. The choice of container and adherence to best practices play a significant role in obtaining reliable results.

The Importance of Proper Sampling

Laboratories follow strict procedures and standards to maintain compliance with industry certifications and requirements. However, even the most advanced laboratory can only provide accurate results based on the quality of the sample it receives. If a sample is taken incorrectly, stored improperly, or collected in a contaminated container, the results may be compromised. This can lead to incorrect diagnoses and costly maintenance decisions.

Recommended Sampling Containers

In South Africa, the standard container for transformer oil sampling is a one-liter tin. However, alternative containers may be used under specific circumstances:

1. Glass Bottles

Certain mining operations require the use of clear glass bottles for security reasons. While glass is suitable for sampling, it presents safety risks due to its fragility. Breakage during transport or handling can pose hazards to both field personnel and laboratory staff.

2. Plastic Containers

Plastic containers are generally discouraged because they can interfere with most laboratory tests. However, they are acceptable for Polychlorinated Biphenyls (PCB) analysis. For this purpose, WearCheck provides 100 ml single-use plastic bottles, which are responsibly discarded after testing to ensure environmental compliance.

3. Gas-Tight Syringes

For Dissolved Gas Analysis (DGA), gas-tight syringes offer excellent repeatability, particularly for transformers with high gas levels, such as those in wind and solar farms. However, these syringes hold only 30 or 50 ml of oil—insufficient for comprehensive testing—and are more expensive than tins. They are also fragile and prone to breaking during sampling, transport, or handling in the laboratory.

Why New Tins Matter

WearCheck strongly recommends using new tins for each sample. While this increases sampling costs, it helps prevent contamination-related issues. A recent case study illustrates the risks of reusing tins: a client noticed a slight increase in PCB values, which was traced back to a second-hand tin. The history of reused tins is often unknown, and residual contaminants can skew moisture and dielectric readings. This can lead to unnecessary oil purification or replacement, costing clients significant amounts of money.

Best Practices for Transformer Oil Sampling

To ensure accurate results, the sampling process must be conducted with precision. Here are some key best practices:

1. Clean the Sampling Container with Transformer Oil

A client in the Northern Cape reported finding water in the flanges from which samples were taken. This underscores the importance of flushing the sampling container with oil from the transformer to remove potential contaminants.

2. Avoid Reusing Sampling Tubes

Residual water or PCB contamination from previously used sampling tubes can compromise results. Clients should work with reputable service providers who follow stringent protocols to prevent cross-contamination.

3. Rely on Trained Technicians

Improper sampling techniques, even minor mistakes, can lead to incorrect diagnoses and costly consequences. Engaging trained professionals ensures that samples are taken correctly, stored properly, and handled according to industry best practices.

Conclusion

Proper sampling is the foundation of accurate transformer oil analysis. By using the correct containers, maintaining cleanliness, and ensuring trained professionals conduct the sampling, clients can trust the integrity of their oil analysis results. Cutting corners in the sampling process can lead to misdiagnoses, unnecessary maintenance, and financial losses. Investing in proper sampling practices is an essential step toward effective transformer maintenance and long-term operational reliability.