ZnO Zinc Oxide Varistor Discs


Our Silicon carbide varistors are made from about 90% silicon carbide of different grain sizes and 10% ceramic binder and additives. The raw material is formed into various SiC variable resistor geometric dimensions and then sintered under specific atmospheric and ambient conditions at a high temperature creating the repeatable nonlinear resistor characteristics. A layer of brass is then flame sprayed onto the SiC varistor as an electrical contact. Other standard metalized contacts include Aluminum, Copper, Nickel, and Silver. In the case of disks, an electrical connection is created by clamping a metal plate to each side of the non linear resistor disk using a tie rod. Large assemblies in the case of disks are fashioned using metal plates with tab connections on each side of these nonlinear resistor disks to create series and parallel stacks of SiC variable resistors to provide appropriate
overvoltage protection for high power. Smaller variable resistor disks simply have tinned copper wires soldered to the brass layer and can be further processed to include a dielectric coating. Silicon Carbide varistor geometries are manufactured to suit the electric values required by varying the OD, ID, thickness, and length. Our manufacturing process yields good voltage dependences and high energy absorption.
Key features of Silicon Carbide Varistors
  • Self-Healing.
  • Used in Air/ Oil/ SF6 Environments.
  • Configurable into Single or Modular Assemblies.
  • Extremely High Ampacity.
  • High Surge Energy Rating.
  • 100% Active Material.
  • Repeatable Nonlinear Resistor Characteristic.
  • High Voltage Withstand.
  • Essentially Non-Inductive.


Below is a list of our standard diameter variable resistor disks 37, 45, 60, 80, 95, and 150mm: Energy absorption per SiC variable resistor disks ranges up to 122,290J. This allows the configuration of nonlinear resistor disk assemblies with extremely high energy absorption ratings in the tens of Mega-Joules.
SiC Varistor Disk Mechanical Parameters




Outside Diameter


37 to 150 mm

Inside Diameter


10 to 30 mm



2 to 25 mm

Standard SiC Varistor Disk Specifications
Disk Size Characteristic Curves Disk Specifications
37mm OD Disk 37mm U/I Curves 37mm Chart
45mm OD Disk 45mm U/I Curves 45mm Chart
60mm OD Disk 60mm U/I Curves 60mm Chart
80mm OD Disk 80mm U/I Curves 80mm Chart
95mm OD Disk 95mm U/I Curves 95mm Chart
150mm OD Disk 150mm U/I Curves 150mm Chart
SiC Varistor Electrical Parameters
Item Range
Operating Temperature Range -40 to 150°C
TCV (Typical Temperature Coefficient of Voltage) -0.12 to 0.18 %/°C
TCI (Typical Temperature Coefficient Current) 0.5 to 0.8 %/°C
Specific Heat Capacity Approximately 2 J/cm³/°C
Thermal Conductivity 0.07 W/cm² . °C/cm
Inductance nH’s (non-inductive)

SiC Varistor Disk Applications

  • Generator protection - protect synchronous power generator damage during a shutdown. Discs absorb high energy in the field winding of a generator exciter. These are used both permanently and switched in protection to discharge the energy stored in the field coil of the generator acting as an excitation field limiter.
  • Magnet coil field discharge of large industrial electromagnetic lifting magnets.
  • Mitigate transient damage produced during the de-excitation of a synchronous motor by reducing the field current fast as possible, minimizing short-circuit current as part of an excitation field limiter.
  • Switch contacts with inductive load.
  • High switch-off voltages in transformers.
  • Mains overvoltage from lightning, inductive or capacitive coupling.