The development of semiconducting fiberglass tapes LSP-O, their properties, and their use for anti-corona protection of high voltage windings

Semiconducting fiberglass tapes were developed in order to achieve a stable, heat-resistant, chemically homogeneous semiconducting material with electrical resistance, which would be independent of the probability of the distribution of semiconducting fillers (such as carbon-black or SiC) in the dielectric binders, and in order to avoid the influence on the material resistance of the binder thickening degree during manufacture of the winding and the aging in operation. The semiconducting properties of fiberglass were achieved by introducing metal oxides into the glass mixture. This material does not contain the capacitive interlayers in its semiconducting structure and does not overheat under a high frequency voltage component. It is expedient to use it for anticorona system of the windings, which have been exposed to voltage with high frequency harmonics. Semiconducting fiberglass tapes can be obtained with a preassigned value with magnitude of dispersion of the resistance within half an order of magnitude, either as low resistance semiconducting tape LSP-O-1 for slot parts anti-corona protection or high resistance semiconducting tapes LSP-O-2 for the end turns of high voltage windings. The resistance remains stable up to 180 C. The tapes LSP-O can be produced with thickness of 0.1; 0.15; 0.2 mm. Tapes LSP-O-2 have been applied as high resistance layers for anti-corona protection at seven turbo generators 300 MW with windings of 20 kV, which have been successful in operation for more then 25 years. Tapes LSP-O-1 have been widely used as anti-corona protection for slot parts in smaller generators and high voltage motors with windings of 6.0 10.5 kV, which were manufactured by VPI process "Monolit", because insulation compounds penetrate easily through the tapes. Tapes LSP-O have the highest stability to the action of the cycles of cryogenics temperatures. This material remained with the same ranges of the magnitude of electrical resistance at 77K, and at 4.2K too, w- - hen traditional semiconducting composite materials lost their conductivity. It was discovered that the LSPO began to take on some non-linearity of electrical resistance from electrical field stress at 4.2K.