The most important feature of transformers in silicone insulation, which gives them an advantage over devices in resin insulation, is the completely non-explosive character of the structure.
Explosions of devices in resin insulation (transformers and voltage transformers) usually occur as a result of long-term development of interwinding short circuits in high and low voltage windings, which cause long-term overheating of the internal insulation and release of large quantities of gases.
Gases accumulate inside the transformer’s casting and their pressure gradually increases, up to the point where an explosion occurs. It leads to the destruction of the transformer and other equipment installed in its immediate vicinity. Initially, the short-circuit current is so low that it does not activate the fuses – the explosion of transformers in resin insulation usually occurs earlier, before the fuses start to operate! That is why this phenomenon is so dangerous when it comes to transformers in resin insulation.
In the case of silicone castings, this risk does not exist. If the pressure inside the casting increases excessively, a local rupture of the casting occurs and the accumulated gas is released. This way, the risk of an explosion, which can be extremely dangerous for people (for example in mines), is avoided.
An additional advantage of transformers in silicone insulation over transformers in resin insulation is their extraordinary resistance to external environmental impact – silicone rubber used as insulation of power equipment has high electro-insulating properties and an extraordinary resistance to external environmental conditions, such as very high (+200 °C) and very low temperatures (–100 °C), humidity or vibrations. Moreover, silicone rubber has low flammability and does not react with most of the aggressive substances found in the air in mines or industrial facilities.
Silicone rubber retains its elasticity even in very low temperatures and does not break under the stresses that can occur as a result of temperature differences between the inside and the outside of the casting. By contrast, in the case of resin transformers left in very low temperatures for a long period of time and then put into service this can be a real danger.
The materials, silicone rubber and, among others, NOMEX™ and Thermoflux™, ensure durability and very low flammability of high voltage and low voltage coil interwinding insulation and of main insulation.
UNICORE® cores with very low energy loss ensure minimum idle losses and appropriately selected cross-sections of winding wires with high thermal resistance (200 °C) guarantee low active load losses.