| Types of Surface Insulation Resistance and Typical Applications |
| AISI Insulation Designation |
Description |
Typical Applications |
| C-O |
The natural oxide surface which occurs on flat-rolled silicon steel which gives a slight but effective insulation layer sufficient for most small cores and will withstand normal stress-relief anneal of finished cores by controlling the atmosphere to be more or less oxidizing to the surface. |
Fractional horsepower motors, pole pieces and relays, small communication owner transformers and reactors. |
| C-2 |
An inorganic insulation which consists of a glass-like film which forms during high temperature hydrogen anneal of grain-oriented silicon steel as the result of the reaction of an applied coating of MgO and silicates in the surface of the steel. This insulation is intended for air-cooled |
Wound-core, power frequency devices,distribution transformers, saturable rectors and large magnetic amplifiers. |
| C-3 |
An enamel or varnish coating intended for air-cooled or oil immersed cores.The interlamination resistance provided by this coating is superior to the C-1typed coating which is primarily utilized as a die lubricant. The C-3 coating will also enhance punchability;is resistant to normal operation temperatures; but will not withstand stress-relief annealing. |
Air-cooled, medium-sized power and distribution transformers; medium-sized continuous duty, high efficiency rotating machinery. Can be oil-cooled. |
| C-4 |
A chemically treated or phosphate surface intended for air-cooled or oil-immersed cores requiring moderate levels of insulation resistance. It will withstand stress-relief annealing and serve to promote punchability. |
Applications requiring insulation similar to C-3 and a stress-relief anneal. Used extensively for small stamped laminations that require higher resistance than provided by annealing oxides. |
| C-5 |
An inorganic insulation similar to C-4 but with ceramic fillers added to enhance the interlaminar resistance. It is typically applied over the C-2 coating on grain-oriented silicon steel. Like C-2, it will withstand stress-relief annealing withstand stress-relief annealing atmosphere. |
Principally intended for air-cooled or oil-immersed cores which utilize sheared laminations and operate at high volts per turn. Also finds applications in apparatus requiring high levels of interlaminar resistance. |
| Anti-stick(no AISI Designation) |
An inorganic insulation similar to C-4 |
A superior surface treatment providing improved magnetic quality and protection against sticking of laminations during the quality annealing of semi-processed material. |
