Insulation system - AbsoluteAstronomy.com

The insulation system for wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

s used in generator

Generator

Generator may refer to:* Electrical generator* Engine-generator, an electrical generator, but with its own engine.* Generator , any of several closely related usages in mathematics.Computing:...

s, electric motors, transformers

Transformers

A transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling.Transformer may also refer to:* ASUS Eee Pad Transformer, an Android 3.2 Honeycomb tablet computer manufacturer by Asus...

, and other wire-wound electrical components is divided into different classes by temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

and temperature rise. The insulation system is sometimes referred to as insulation class. The different classes are defined by NEMA

Néma

Néma is a town in southeastern Mauritania, close to the border with Mali. It is located at around . It is the capital of Hodh Ech Chargui Region and of the Néma Department....

, Underwriters Laboratories

Underwriters Laboratories

Underwriters Laboratories Inc. is an independent product safety certification organization. Established in 1894, the company has its headquarters in Northbrook, Illinois. UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing...

(UL), and IEC

IEC

-Organisations:* Independent Electoral Commission * Independent Electrical Contractors, a U.S. national trade association.* Institut d'Estudis Catalans , a Catalan academic institution....

standards.

IEC 60085 class	NEMA Class	NEMA/UL Letter class	Maximum hot spot temperature allowed	Typical materials
Y			90°C	Unimpregnated paper, silk, cotton, vulcanized natural rubber, thermoplastics that soften above 90 C
A	105	A	105°C	Organic materials such as cotton Cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal.... , silk Silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity... , paper Electrical insulation paper Electrical insulation papers are paper types that are used as electrical insulation in many applications due to pure cellulose having outstanding electrical properties... , some synthetic fibers
E			120°C	Polyurethane, epoxy resins, polyethylene terpthalate, and other materials that have shown usable lifetime at this temperature
B	130	B	130°C	Inorganic materials such as mica, glass fibers, asbestos Asbestos Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals... , with high-temperature binders, or others with usable lifetime at this temperature
F	155	F	155°C	Class 130 materials with binders stable at the higher temperature, or other materials with usable lifetime at this temperature
H	180	H	180°C	Silicone elastomers, and Class 130 inorganic materials with high-temperature binders, or other materials with usable lifetime at this temperature
200		N	200°C	As for Class B,and including teflon
220	220	R	220°C	As for IEC class 200
		S	240°C
250			250°C	As for IEC class 200. Further IEC classes desiganted numerically at 25 °C increments.

The maximum hot-spot operating temperature is reached by adding the rated ambient temperature of the machine (often 40°C), a temperature rise, and a 10 °C hot-spot allowance. Electrical machines are usually designed with an average temperature below the rated hot-spot temperature to allow for acceptable life. Insulation does not suddenly fail if the hot-spot temperature is reached, but useful operating life declines rapidly; a rule of thumb is a halving of life for every 10 °C.

Older editions of standards listed materials to be used for the various temperature classes. Modern editions of standards are proscriptive, only indicating that the insulation system must provide acceptable life at the specified temperature rise.

In large machines, different systems may be used according to the predicted temperature rise of the machine; for example, in large hydroelectric generators, stator windings may be Class B but the more difficult to cool rotor winding may be Class F.

Further reading