Thermal insulation class (B/F/H)
The maximum permissible temperature of the insulation (130 / 155 / 180 °C).
Definition
The thermal insulation class defines the maximum temperature that a transformer’s insulating materials (varnishes, papers, resins) can withstand continuously without premature degradation. It is standardised by letters: class B (130 °C), class F (155 °C), class H (180 °C), among others.
This class directly governs the unit’s lifetime: lastingly exceeding the class temperature accelerates the ageing of the insulation and can lead to a breakdown. The choice of class follows from the expected heating (linked to the load and cooling) and the ambient service temperature.
A high class allows operation at a higher temperature, hence greater compactness or better tolerance to hot environments.
The ABL tip
For closed enclosures, hot environments or heavy loads, a higher insulation class (F or H) secures the lifetime. Tell us your ambient temperature and load profile: we choose the appropriate class.
