This guide is intended to apply in general to large alternating-current rotating electrical machines rated at 10 000 kVA or more@ and operating at voltages of 6000 V and above. Purpose The purpose of this guide is to present information necessary to permit an effective evaluation of the insulation systems of large alternating-current rotating electrical machines. Such an evaluation can serve as a guide to the degree of maintenance or replacement which might be deemed necessary@ and also offer some indication of the future service reliability of the equipment under consideration.