Dowsil PMX-561 (also known as XIAMETER PMX-561 Transformer Liquid) is a Polydimethylsiloxane electrical insulating liquid introduced by Dow Chemical. It is a non-halogenated, additive-free, non-hazardous class transparent silicone fluid.

This product is primarily designed as a cooling and insulating medium for transformers and other electrical equipment, complying with international standards such as IEC 60836(Type T-1 Silicone) and ASTM D 4652-92. It maintains good electrical properties and operational capability over a wide temperature range, aimed at replacing traditional mineral oils to enhance equipment safety.

PMX-561 exhibits high thermal stability, oxidation resistance, and excellent fire-resistant characteristics, with an open cup fire point up to 370°C and a lower heat release rate than other Class K insulating liquids, featuring non-sludging properties. Furthermore, this material is compatible with various solid electrical insulating materials, with prominent environmental attributes (low net calorific value), classifying it as an intrinsically safe insulating fluid.

In addition to conventional oil-immersed high-voltage power transformers, due to its high fire point and enhanced safety, Dowsil PMX-561 is often applied in scenarios with strict fire safety requirements, such as urban rail transit (railway tunnels) traction transformers, underground substations, substations inside high-rise buildings, offshore platform equipment, and certain high-voltage switches and power capacitors.