H2scan TM Catalog 2025 - Flipbook - Page 39
Aging Transformer Insulating Systems
Several conditions can accelerate the aging of transformer insulating systems. These conditions include
high operating temperatures, the presence of oxygen, moisture, and oil oxidation by-products. These factors
contribute to solid and liquid insulation breakdown, reducing mechanical strength, dielectric strength and
overall insulation performance.
Various fault gases are produced and dissolved in the oil as the insulation degrades. The nature and
concentration of these gases can provide valuable insights into the type and severity of the fault. One of the
most signi昀椀cant fault gases is hydrogen, generated during partial discharge, overheating and arcing events.
Available Detection Methods Used to Measure
Transformer Health – Hydrogen Sensing
The sudden appearance or increase in hydrogen levels can signal an active fault condition, prompting further
investigation. Even temporary spikes in hydrogen indicate potential issues such as overload or overheating
events, with insulating 昀氀uid reaching temperatures high enough to generate hydrogen.
Traditionally, the standard practice for transformer monitoring involves manual oil sampling for dissolved gas
analysis (DGA) at a set interval, typically every 12 months. However, this time-based maintenance can lead to
delays of one week to one month for lab results. During this waiting period, uncertainty about transformer
conditions persists for asset owners. Additionally, just as a camera captures a single frame of a much larger
event, a periodic, manual DGA sample supplies a single snapshot of the transformer. What it does not
supply is real-time information about its health.
Another type of inspection is visual, which provides valuable information regarding physical defects that might
be present in the transformer to record it and, if necessary, to indicate when corrective action is required. ANSI/
NETA recommends that visual inspections of transformers be conducted at least once a month. However, due
to labor constraints, it’s not uncommon for inspections to slip to just once a year.
Another form is 昀椀eld electrical testing. Industry standards recommend performing this type of test every
two to 昀椀ve years. However, the reality is that this type of testing might be performed every ten to 昀椀fteen years
instead, depending on the organization. Field electrical testing requires the transformer to be shut down or
de-energized. Since transformers supply the power that keeps businesses, residences and manufacturing
facilities operational, many companies on the industrial side, for example, cannot afford to shut down and
absorb such a critical hit to pro昀椀tability.
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