|
In Part 1 of this series on sampling, we discussed what information is necessary to make a correct diagnosis of the state of your electrical equipment. In Part 2 we discussed some of the issues involved in obtaining a good and representative sample. In Part 3 we will review appropriate sample containers.
The following table lists various sample containers and highlights their main characteristics. For a more comprehensive list, see ASTM D923 Appendix X2.
Container Type |
Comments |
Glass Syringe |
- Best container for DGA (dissolved gas analysis).
|
Clear Glass Bottle |
- Sample can be visually inspected.
- The water content of the sample is usually not impacted (see further below).
|
High Density Polyethylene (HDPE) Bottle |
- Durable and lightweight.
- Good container for regular oil quality tests and furans.
- Not good for water measurement, since the plastic walls are permeable.
|
Welded Seam Metal Can (Flexible-sided) |
- Durable.
- Can be used for DGA and water content if filled to overflowing and then capped.
- However, must open cap to retrieve contents for DGA and some gas concentrations (particularly hydrogen) may be reduced as a result.
- Can’t view contents.
- Note: Soldered seam metal cans have often been confused with welded seam cans. The flux used in soldered seam cans may severely impact the properties of the sample.
|
Seamless Aluminum Can |
- Very durable.
- Can be used for DGA and water content if filled to overflowing and then capped.
- However, must open cap to retrieve contents for DGA and some gas concentrations (particularly hydrogen) may be reduced as a result.
- Can’t view contents.
|
Particle-free Bottle |
- Convenient for particle count testing, since specifically prepared to have a low background level of particles.
|
Stainless Steel Sampling Cylinder |
- Extremely durable.
- Can’t view contents.
- Heavy to ship.
|
Regarding containers for Karl Fischer Moisture Analysis, S. D. Myers has found that a glass bottle functions as an excellent container for moisture analysis if all of the following conditions are met:
- Before sampling, the capped bottle is kept dry by using a desiccant tablet (discarded immediately before sampling).
- The glass bottle has a metal cap with a Teflon liner.
- When sampling, the bottle is filled to the very top (if possible), in order to minimize the gas space in the bottle.
- The KF Moisture test is the first test performed out of the bottle – i.e., the first time the bottle is opened after sampling is for the KF Moisture test.
Using proper sample containers will help insure that your samples are representative of the actual conditions inside your electrical equipment, enabling proper diagnosis to extend the life of your transformer.
|
|
