scope:

This guide makes suggestions on testing the dielectric strength of the insulation separating the various turns from each other within multi-turn form-wound coils to determine the acceptability of the coils. Typical ratings of machines employing such coils normally lie within the range of 200 kW to 100 MW. Test voltage levels described herein do not evaluate the ability of the turn insulation to withstand abnormal voltage surges, as contrasted to surges associated with normal operation. These suggestions apply to the following:

a) Individual stator coils after manufacture

b) Coils in completely wound stators of original manufacture

c) Coils and windings for rewinds of used machinery

d) Windings of machines in service to determine their suitability for further service (preventivemaintenance testing)

The repetitive voltage surges (spikes) associated with Adjustable Speed Drives (ASDs) are not addressed here.

Purpose

This guide will address the following:

a) Define surge/impulse testing as applied to the windings of an electric machine;

b) Review the service conditions which affect or change voltage levels in a coil;

c) Recommend devices suitable for measuring surges, with precautions to avoid erroneous results;

d) Describe various points in time at which surge testing should be performed;

e) Present suggested surge test levels for form-wound multi-turn coils.