IEEE 433-1974

Design innovations and rating increases of rotating machines continuously increase the need to develop improved methods of testing insulation for serviceability. Research in the last 15 years evolved a method of 1/10 Hz overpotential testing to supplement traditional power-frequency testing and to complement direct-voltage testing. A background for VLF (very low frequency) testing is available in the technical literature. (See Section 11.) VLF testing permits advantageous application of more easily transportable equipment both in weight and size as compared to non-resonant power-frequency testing. This document provides a uniform method of VLF testing in order to obtain consistent results, accumulate meaningful experience, and lead to establishment of standards of test level. References as listed in Section 10. are necessarily those which have been issued at the time this document was written. When subsequent revisions of the references are issued, they should be used in place of those indicated unless, due to a change in scope, they no longer apply.

The purposes of this recommended practice are: 1) To deÞne terms that have a speciÞc meaning in VLF testing 2) To describe VLF-test equipment and wave shape 3) To provide a uniform procedure for testing the armature insulation of large ac machines with VLF voltage 4) To recommend constants for relating VLF tests to power-frequency and direct-voltage tests to obtain equally effective test levels. This document applies to large ac rotating machines rated at 10 000 kVA or greater and rated 6000 V or higher. It covers acceptance testing of new equipment in the factory or on-site after erection. This recommended practice also covers routine maintenance testing of machines that have been in service.

New IEEE Standard - Inactive-Withdrawn. Terms that have a specific meaning in VLF testing are defined, and VLF test equipment and wave shape are described. A uniform procedure for testing the armature insulation of large AC machines with VLF voltage is provided. Constants for relating VLF tests to power-frequency and direct-voltage tests to obtain equally effective test levels are recommended.