Particle Count and Filming Compounds (PC/FC)
Standard Test Method for Particle Count Using Automatic Optical Particle Counters, ASTM D6786, used in conjunction with microscopic ferrography
This testing should be done on equipment where moving parts are in contact with insulating oil, such as in Load Tap Changers (LTCs). Following Particle Count analysis (described separately), microscopic ferrography is used to visually identify the particles seen in the oil. Ferrous metals can be differentiated from non-ferrous types. Arcing spheres can be identified, in contrast to filming compounds (polymeric varnish that can form on electrical contacts). This test can help identify misaligned moving parts. Cutting and shearing wear can be identified and large arcing spheres can be a sign of misaligned contacts or shorts, depending on if they are copper or iron. It is strongly recommended that a dissolved gas analysis be performed at the same time to help identify possible faults.
The microscopic ferrography part of the testing starts with the generation of a ferrogram. A ferrogram is a special microscope slide that is designed to trap particles from the oil. During the generation of the ferrogram, the slide sits over a magnetic field that will cause the ferrous particles to align with the magnetic field. As the oil flows over the slide, the particles are also distributed by size. The slide is then flushed with a fixer and dried. Once dried, the slide is examined under a microscope by a trained technician and the particles are identified. Identification of the size, shape, and composition of the particles is vital for proper interpretation of the conditions in the unit being tested.
This testing should be done on equipment where moving parts are in contact with insulating oil, such as in Load Tap Changers (LTCs). Following Particle Count analysis (described separately), microscopic ferrography is used to visually identify the particles seen in the oil. Ferrous metals can be differentiated from non-ferrous types. Arcing spheres can be identified, in contrast to filming compounds (polymeric varnish that can form on electrical contacts). This test can help identify misaligned moving parts. Cutting and shearing wear can be identified and large arcing spheres can be a sign of misaligned contacts or shorts, depending on if they are copper or iron. It is strongly recommended that a dissolved gas analysis be performed at the same time to help identify possible faults.
The microscopic ferrography part of the testing starts with the generation of a ferrogram. A ferrogram is a special microscope slide that is designed to trap particles from the oil. During the generation of the ferrogram, the slide sits over a magnetic field that will cause the ferrous particles to align with the magnetic field. As the oil flows over the slide, the particles are also distributed by size. The slide is then flushed with a fixer and dried. Once dried, the slide is examined under a microscope by a trained technician and the particles are identified. Identification of the size, shape, and composition of the particles is vital for proper interpretation of the conditions in the unit being tested.