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Description / Abstract:
The intent of this standard is to establish a uniform method by
which the thermal endurance of electrical insulation systems for
dry-type specialty and general-purpose transformers can be
compared. These insulation systems are intended for use in the
types of transformers described in NEMA ST 1-1988 1 and NEMA ST
20-1992. In general, these dry-type transformers are used with the
primary windings connected to secondary distribution circuits of
600 V nominal and below.
Thermal degradation generally is one of the principal factors
affecting the function of most insulating materials. It is the
principal environmental factor in this standard. Other
environmental factors such as vibration, thermal shock, and
moisture are included to simulate operating conditions. These
factors have been chosen in such a way as to develop and promptly
disclose any significant weakness during the temperature aging of
an insulation system.
This standard provides a statistical method for establishing a
life-temperature relationship for an insulation system. This
life-temperature relationship is relative. To have any
significance, it must be supported by adequate field service data
or it must be compared to similar life test data for insulation
systems with known field-service reliability.