By the beginning of the 1970s, nearly all U.S. manufacturers were using the vacuum pressure impregnation (VPI) process on form wound equipment and by the end of the decade, they were starting to offer the process on random wounds for toughduty service. In mid-1974, servicenters began using VPI on form coil jobs through 6.9 kV and doing all sIzes of random wounds on a selective basis.
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