Abstract
Insulation of all electrical machinery is practically in the form of organic compounds that contain water as part of their make-up. Excessive temperature tends to dehydrate and oxidize the insulation and make it become brittle and disintegrate under vibration and shock. The insulation lifespan of turbo generators deteriorates slowly at low temperatures and more rapidly at high temperature. Economic factors, such as initial cost, replacement cost, obsolescence, and maintenance, are of prime importance when determining the years of useful service desired for the electrical insulation. Generator digital protection- fault diagnosis test was carried out to find out the cause of insulation breakdown on the turbo generator unit 411G3. The experimental procedure consists of an insulation resistance test, meggering (time-resistance absorption test), and pendulum over-speed test. A thorough investigation was conducted to identify all the stator bars that constituted the Red phase and other connections. Voltage drops on these stator bars were measured and values were used to detect ground faults which were rectified via an intelligent protection scheme.
Highlights
Electrical insulation testing involves dielectric strength testing and insulation resistance measurement
Insulation Resistance (IR) test of the Stator conducted with AC Powered–Series 1megger; 1000V injected; 390C StarPoint disconnected condition for fault is shown in table 1
The results reveal IR test is very effective in detecting ground faults in turbo generators
Summary
Electrical insulation testing involves dielectric strength testing and insulation resistance measurement. The addition of modified varnish with a high thermal conductivity coefficient to the insulation material does not yield any deterioration of its electrical properties. [1, 2] works reveal the electro-physical properties of a new type of high-efficiency heat conducting insulation for turbo generators with air and hydrogen cooling They further stated that the addition of modified varnish with a high thermal conductivity coefficient to the insulation material does not yield any deterioration of its electrical properties. The thermal insulation coefficient of the modern mica-based composite ranges between 0.25 and 0.30 W/(m K), while copper and steel are 1500 and 300 greater respectively [5] This implies that mica based insulation acts as a heat barrier resulting in limiting the efficiency of the cooling system and, the specific power carrying capacity of an electric machine. The recommended minimum insulation resistance for field and armature windings is determined from the following employing a 500 V Megger: -
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