On-site BDV testing or Laboratory BDV testing?
The relative merits of on-site and laboratory testing have long been debated by engineers and the debate is still going on. The underlying issue is that test results are greatly influenced by contamination. There are those who argue that this means it is better to test on-site because, if a sample has to be bottled and the bottle sent to a laboratory, there will always be doubt about whether the bottle was cleaned adequately before use and whether it was sealed sufficiently well to guard against contamination in transit.
Others will point out that testing on site provides no guarantees against contamination, as the most likely time for a sample to be contaminated is while it is being collected. They may also argue that, if a sample is sent to a laboratory, it will be tested by a skilled technician who will follow all of the procedures needed to ensure accurate results. Conversely, tests carried out on site are performed under less-than-ideal conditions and often under significant time pressure, which may lead to errors.
On-site testing undeniably has the benefit of immediacy. If a suspicious result is obtained, it is usually possible to repeat the test without delay and, if the problem is confirmed, the affected transformer can, at least in principle, be taken out of service immediately.
There is no clear answer to the question of whether on-site or laboratory testing is best. It is really a matter for individual users to decide which approach best suits their particular circumstances.
