Specifications

impregnating or trickle resins. Smooth surface, therefore good machineability, Low moisture

absorption, good chemical resistance. Dielectric strength: 7 – 24 kV. Used widely as Slot

insulation, slot closure, layer insulation. Triflexil is available in sheets, rolls, strips, and in

thicknesses from 0.25 mm.

Film paper : Polyester film is a flexible, strong and durable film with right balance of properties

making it suitable for many industrial applications. It is Insulation class E (120 °C) material. In

motor applications, certain types of polyester film are used for ground insulation as slot liners

and wedges, as well as phase insulation. Polyester film is a tough general purpose film which is

semi-transparent with thickness ranging from 0.075 mm or above. Generally it has a tensile

strength of an average 210 MPa, highly resistant to moisture and most chemicals. It is able to

withstand temperatures ranging from extremes –70°C to150°C. Since it contains no plasticizers,

film does not brittle with age under normal conditions. Dielectric Strength is 2,5 to 20 kV/mm.

Melinex, Mylar, Teonex are some of the trade names of the films used.

Press Board : It is a mixture of cellulous and old cloth and is manufactured in short lengths. It is

also called as Fuller board. It is similar to a press pan paper. It is available from 0.1 to 0.8 mm

thickness of wire and 1 to 3 mm thickness of plates. Insulation class A (105 °C). Brown colour,

non-glazed (mat), glazed (polished) on both sides. Dielectric strength is 11 kV/mm. It is used as

slot insulation, Core insulation, Separator, Used under bamboo sticks.

Empire cloth : It is made by using cotton or silk cloth dipped in varnish. It is yellow or black in

colour. It cannot withstand high heat, but flexible and can withstand high moisture. It has good

mechanical and dielectric strength. Used as cover for armature winding, slot insulation along

with leathroid paper, Insulation paper between coils, in between small transformer windings.

Bamboo sticks : During running of motor, the coils may be come out from the slots due to

centrifugal force. This is avoided by inserting bamboo sticks at the top side of the slots. The

sticks are made to size depending on the slot size. Hard trees are used for making these sticks.

Paper : It is prepared from wood pulp and manila fibres beaten and rolled into sheets. Its dielectric

strength is 4 to 10 kV/mm thickness. It is moisture absorbent and so is particularly suitable for

impregnation. Electrical properties are quite good. It is rarely used in un impregnated condition

but can be used successfully under oil. It catches fire at 125

C so that the temperature of any

paper insulated apparatus is limited to about 100

Wood : The dielectric constant of wood varies in the range 2.5 to 2.7. Dry resistivity is in the

order of 10

to 10

ΩΩ

Ω cm. It can withstand a voltage gradient of 40 kV/mm in service. These

properties vary over a wide range , depending on the type of wood, seasons of cutting, grain

direction, and especially the water content. Used for slot wedges, Papers, etc.,

Asbestos board : Its dielectric strength is 3 to 4.5 kV/mm thickness. It is highly moisture absorbent.

Its strength increases by impregnation but heat resistance and non-inflammability reduces. It

melts at 1500

C. It is neither mechanically strong nor flexible. Purified fibres with clay filler have

better electric strength. Asbestos electrical insulating paper is supplied in thickness of 0.2 to 1.0

mm and, depending on its thickness, has a minimum breakdown voltage from 0.9 to 2.4 kV. It is