CHAPTER 5 APPLICATIONS OF INSULATING MATERIAL • Temperature Classification for Insulating Materials • Application of Insulating Materials in electrical apparatus: In Power Transformer In Rotating Machines In Circuit Breaker In Power Capacitors In High Voltage bushing In Small Machines 1
There are four principal areas where insulation must be applied 1.Between coils and earth (phase to earth) 2.Between coils of different phases (phase to phase) 3.Between turn (inter-turn), and 4.Between the coils of the same phase (inter coil) 2
• Insulating material must be able to withstand electrical stresses, in addition to it should be able to withstand certain other stress namely during manufacture, storage and operation. • The performance of the insulation depends on its operating temperature. The higher temperature, the higher will be the rate of its chemical deterioration. 3
The insulating materials are grouped into different classes with temperature limit : - Organic materials: Class O : 90 0 C and Class A : 105 0 C - Inorganic materials :Class B : 130 0 C ; Class C : No Specific Limit 4
The insulating materials are grouped into different classes with temperature limit : - Organic materials: Class O : 90 0 C and Class A : 105 0 C - Inorganic materials : Class B : 130 0 C ; Class C : No Specific Limit 5
IEC (International Electrotechnical Commission ) Class Y (Paper, cotton, Silk,natural rubber,etc) : 90 0 C Class A ( Same class Y but impregnated) : 105 0 c Class E (Polyethlene terephthalate) : 120 0 C Class B (Mica and Fiberglass) : 130 0 C Class F ( same class B but with alkyd and epoxy based resin) : 155 0 C Class H (like class B with silicone rubber, polymide film) : 180 0 C Class C (As class B but with non organic binder, teflon, and high temperature polymers) : above 180 0 C 6
APPLICATIONS IN POWER TRANSFORMERS The Transformer insulation is divided into: a). Conductor or turn to turn insulation; • using directly organic enamel on conductor for smaller rating. • Using paper or glass type wrapped on the rectangular conductors. b). Coil to coil insulation, • Kraft paper is used in smaller transformer • Pressboard, glass fabric, or porcelain are used in the case of higher rating transformer. 7
c). Low voltage coil to earth insulation , Normally consist of solid tubes combined with liquid or gas filled spaces. d). Low voltage coil to low voltage coil insulation, Generally of the insulation system used in oil- filled transformers consist of oil impregnated pressboard. e). High voltage coil to ground insulation, Same at c. 8
The winding Insulation is normally made of paper. Cellulose board is also used as internal insulation in liquid-filled transformers. Cellulose insulation is impregnable with the insulating fluid of transformers. 9
Conductor insulations is usually paper, in the form pressboard. Insulating board is made of wood or mixture of wood and cotton. Cast resin also used as insulating system at lower voltage rating. Higher temperature systems, employ synthetic fluid Gas Insulated Power Transformers use sheet aluminum conductors for windings, a polymer film for turn-turn insulation. 10
Insulation of Dry type transformers is now using prepress (manufactured using the following baking materials: glass fibres, Nomex, Aramid paper etc. 11
APPLICATIONS IN ROTATING MACHINES Usually insulation has been used for machines are mica. Mica available in the form of very thin splitting. The selection of the right material depends on the power rating and the conditions under which it operates. Polyester film with or without impregnation being used for slot insulation. A Particularly important of the machines are the insulation of rotors and stators. The main insulation of the stators have always been mica based. For the support between the winding bars, slots and the core lamination used glass fiber reinforced epoxy. 12
APPLICATIONS IN CIRCUIT BREAKERS Low voltage breakers use synthetic resin mouldings to carry the metallic part. For higher temperature ceramic parts are used. Medium and High voltage, nowadays using SF6 Gas Medium voltage use vacuum as insulating medium. Gas Mixtures CB SF6 gas causes environmental effect and expensive Several gas mixture such SF 6 / N 2 has dielectric strength, is 80% of pure SF 6 but the short circuit rating is normally lower (reduce to 40 kA from 50 kA) 13
Table The Various Insulating Material For High Voltage Switchgear • Epoxy Resins Low pressure castings for bushings, Switchgear, bus-bars, instruments transformer. • Epoxy Resins bonded For components such as arc control devices, CB glassfibre • Poly ester resins Insulating lever for CB and phase barrier plate in switch board. • Porcelain Insulators and bushings of power transformer • Sysnthetic resin bonded Bushings, arc chambers, etc paper • Nylon Injection mouldings for arc control devoces in CB • Silicone rubber Filling for moulded joint boxes in SF 6 insulated CB 14
APPLICATIONS IN CABLES The physical properties required for wire and cable insulation depend on the type of application. have good elongation, tensile strength and toughness, so that will withstand handling during installation and service Have a low dielectric constant and power factor but high dielectric strength and insulation resistance. Have excellent resistance to ageing at high temperature Have very low water absorption. Not become stiff and brittle when operate at low temperature 15
The main type of insulations used in the cable industries are paper, rubber, plastic and compressed gas. Paper insulated lead sheathed cables are still used because of the reliability, high dielectric strength, low dielectric loss, and long life. Low and medium voltage (up to 3.3 kv), polyvinylchloride (PVC), Polyethylene and cross-linked Polyethylene (XLPE) is most used. PVC is not suitable for high voltage because High dielectric constant and high loss Polyethylene has low dielectric constant and low loss but high dielectric strength. The best material for high voltage and high temperature is teflon (PTFE) which can be employed up to 250 0 C 16
3.6/6 ~ 18/30kV XLPE/DSTA/PVC Power Cable 1-Conductor 2-Conductor shielding ( Semi-conducting layer ) 3-Insulation 4-Insulation shielding ( Semi-conducting layer ) 5-Metallic shielding 6-Fillers 7-Binder tape 8-Separation sheath 9-Steel tape armour 10-Outer sheath 17
PVC INSULATED CABLES 18
APPLICATION IN POWER CAPACITOR • Normally made using impregnated paper dielectric. • Made of several layers of insulation paper of adequate thickness and aluminum foil of 6 microns thickness as electrodes interleaved and wound. • Properties required for the insulation paper for capacitor applications are high dielectric, low dielectric strength, low dielectric loss, high dielectric constant, uniform thickness, and minimum conducting particles. • The impregnates for power capacitors should have high dielectric Strength, high dielectric constant, good chemical and thermal stability and adequate viscosity for efficient conduction heat. 19
The Concept of The Dielectric in paper and all paper film In Capacitor 20
APPLICATIONS IN FRACTIONAL HORSE POWER MOTORS Small Generator : The insulation system must guarantee reliability, combined with good processing capability, mechanical strength an tolerance to severe short thermal stress while in operation. Kind of application the following materials have been found to have excellent insulation properties, viz. presspaper reels, NMN multilayers (made of nomex and polyester film) as well as saturated DMD (made from non-woven polyester and polyester film). Small size motors : Kinds of Polymers have been developed and are beeing widely used as insulating materials. 21
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