TRANSFORMERS - Insulating Materials

 TRANSFORMERS

Transformer Full Load Amps (FLA)

The Full Load Amps is the rated continuous current carrying capacity of a transformer at a referenced ambient temperature and allowable temperature rise.  Insulating materials are below for information.

The total temperature rise of an

 OA 65∞C transformer, at a maximum ambient temperature of 40∞C,

Is 120∞C.This does exceed the transformer insulation rating of 105∞C, and is allowed by ANSI.

The Full Load Amps label is located on the top decade at 1000 seconds. The Full Load Amps label is shown on the base

(Lowest KVA) rating of the transformer.

Table – Insulating Materials

Insulation        Maximum Temperature                         Insulating Materials Class

Y                              90∞C                                                       Cotton, silk, paper, wood, cellulose, fiber

Without impregnation or oil-immersion

                                                                                                 Class Y impregnated with natural resins,

A                              105∞C                                                     cellulose esters, insulating oils, etc.,

                                                                                                also laminated wood, varnished paper

Hybrid A               110∞C                                                     Insulter Insulation, Kraft paper with epoxy

Binders activated under pressure

E                              120∞C                                                     Synthetic-resin enamels, cotton and paper

Laminates with formaldehyde bonding

B                              130∞C                                                     Mica, glass fiber, asbestos, etc., with suitable

                                                                                                  bonding substance; built-up mica,glass fiber 

                                                                                                  and  asbestos laminates                                                                               

F                              155∞C                                                     The materials of Class B with more

Thermally-resistant bonding materials

H                             180∞C                                                     Glass-fiber and asbestos materials, and

Built-up mica, with appropriate Silicone resins

C                              >180∞C                                                  Mica, ceramics, glass, quartz, and asbestos

                                                                                               without binders or with silicone resins of super     
                                                                                                      thermal stability                                                                                

Hybrid H                  220∞C                                                     NOMEX insulation, varnish dipped

And vacuum pressure impregnated (VPI)

Transformer Through-Fault Damage Curve

Liquid-Immersed Transformers

Defines thermal and mechanical through-fault damage curves for liquid-immersed

Transformers,

“If fault current penetrates the limits of the thermal damage curve transformer insulation may be damaged. If fault current penetrates the limits of the mechanical damage curve cumulative mechanical damage may occur. The validity of these damage limit curves cannot be demonstrated by test, since the effects are progressive over the transformer lifetime. They are based principally on informed engineering judgment and favorable, historical field experience.”

Through-fault current is passing for the 2 to 1000 seconds.