IEEE 433:2022

Revision Standard - Active.
Described in this recommended practice are very low frequency withstand and diagnostic tests that are performed on the stator windings of ac electric machines.

This document describes very low frequency (VLF) testing of ac electric machines. It covers acceptance testing of new machines in the factory or on-site after erection. Also covered is the routine maintenance testing of machines that have been in service. In order to facilitate communication and comparison among investigators, this document recommends that the VLF used be 0.1 Hz ±10%. For ac electric machines, voltages between 3.3 kV to 30 kV are considered to be high voltage machines.
The purpose of this recommended practice is as follows:
a) To provide a uniform procedure for testing the stator (armature) insulation of ac electric machines with VLF voltage, in order to obtain consistent results.
b) To recommend constants for relating VLF tests to power-frequency and direct-voltage tests to obtain equally effective test levels.
c) To describe VLF test equipment and wave shape.
d) To define terms that has specific meaning in VLF testing.