Transformer oil purifiers and filters can be of various designs due to use of force fields. Purifiers have differential characteristic depending to their irremovability during operation. After contamination the operating element can be recovered by mechanical cleaning and subsequent washing in gasoline or other liquid of similar composition.
Transformer oil purification systems are divided into six types depending on the force field nature:
- Clarifier tanks. Oil is purified from solid particles due to gravitational field forces. It is called sedimentation. It is one of the oldest and widely used methods for purification of oils which are stored in tanks.
- Centrifuges. Oil is purified from solid particles in centrifuges by centrifugal forces. Both clarifier tanks and centrifuges purify oil only from particles with density that exceeds the fluid density.
- Magnetic purifiers. Oil is purified from ferromagnetic particles (wearing of parts, metal chips etc.), by the fields of one or more permanent magnets. Theoretically it is possible to use electromagnets, but it complicates the construction of a purifier and reduces its reliability.
- Electrostatic purifiers. Oil is purified by electrostatic field forces. The contaminated oil passes through an electrode gap with constant current. Solid particles, that received a charge due to their friction against the fluid, are attracted to electrodes that have opposite signs.
- Ultrasonic purifiers. Oil is purified by sedimentation of large solid particles by their own weight. Under condition of – fluid flowing rate in the ultrasonic field must be lower than contamination particulates deposition rate. The drawback of this method is maintaining the required ratio between the speeds is not always possible in practice.
- Combined purifiers. Oil is purified by the use of simultaneously combined porous filtering materials and force fields, or as a result of interaction of several force fields of different nature. The combined purifiers, which contain paper filter cells with permanent magnets as well as purifiers with combined effect of gravitational field and inertia of solid particles under sharp change of fluid flow direction are most commonly used. Also it is possible to use paper filter cells together with centrifugal and ultrasonic fields.