Corona protection

Von Roll is a leading company in the field of corona protection for electrical high-voltage machines. Electrical stress control measures are an essential component of any high-voltage machine. Von Roll has developed a number of products, namely:

  • Conductive and semi-conductive tapes (CoronaShield® C or SC)
  • Conductive and semi-conductive varnishes  (CoronaShield® P)
  • Conductive mastics 
  • Conductive sheets (Conductive Vetronite)

Electrical stress control measures are an essential component of any high-voltage machine. Von Roll has developed conductive and semi-conductive tapes under the trade names CoronaShield® C and CoronaShield® SC.

These tapes can be applied as:

  • External corona protection - within the slot
  • End corona protection - outside the slot
Conductive and semi-conductive tapes


Electrical stress control measures are an essential component of any high-voltage machine. Von Roll has developed conductive and semi-conductive varnishes under the trade names CoronaShield® P.

These varnishes can be applied as:

  • External corona protection - within the slot
  • End corona protection - outside the slot
Conductive and semi-conductive varnishes

To control the electrical field at the conductor stack and to prevent partial discharges (corona), also in any cavities that may exist, we recommend using conductive mastic as internal corona protection.

Conductive mastic is used as a filler in conductor strands of Roebel bars at the points where conductors cross over. The material contains mainly mica powder, epoxy resin and conductive filler material.

Conductive mastic

Von Roll offers conductive glass fabric laminate according to G-11 standards under the name Conductive Vetronite.

Conductive Ripple springs are manufactured from molded prepreg composite material. They help to  stabilize and protect contents of the generator armature. Cut into narrow strips, they are flattened between wedge and contents of stator slots so that if wedge becomes loose or dislodged, product expands to fill void. Springs hold coils and insulation in place against magnetic field forces of generator and provide Class F insulation properties, withstanding continuous temperatures to 150°C.

Conductive sheets