Silicon Carbide Varistor Discs

ABOUT SILICON CARBIDE VARISTORS

Excitation field limiter six disc sic varistor assembly
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
Nonlinear resistor two disc sic varistor assembly
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 dependencies 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.
Silicon carbide varistor disc
Silicon resistor tube

SiC DISK VARISTORS

Variable resistor disc
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
   

Description

Abbreviation

Range

Outside Diameter

Do

37 to 150 mm

Inside Diameter

Di

10 to 30 mm

Length

L

2 to 25 mm

Non linear resistor sic disc dimension diagram
 
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 - protects 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 as 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.
Generator protection sic varistor assembly

ROD AND TUBE SILICON CARBIDE VARISTORS

Sic assembly 32 disks 60mm od ferrule end
These non linear resistors (varistors) are made from SiC and have high power dissipation and high energy absorption. This series of nonlinear resistors are manufactured in rods and tubes with outside diameters ranging from 6 to 30mm and lengths up to 600mm. The non linear Resistors may be connected in series or parallel for various fields of application. Brass is the standard metallization, but these are also available in aluminum, copper, and zinc. They can operate up to 150C continuously and have essentially zero inductance.
Silicon resistor tube
 
Mechanical Parameters - Rod and Tube Silicon Carbide Varistors
   
Description Abbreviation Range
Outside Diameter Do 6 to 30 mm
Inside Diameter Di 0 to 8 mm
Length L 50 to 600 mm
Density N/A 1.9 g / cm³ to 2.0 g / cm³
 
Electrical Parameters - Rod and Tube Silicon Carbide Varistors
   
Item Range
Operating Temperature Range -40 to 150°C
Ohmic Range 500 to 17 x 106 Ω/cm
Maximum Pulse Residual Voltage 4.3 x 1.2√(log(R x A x l)) kV/cm
Specific Heat Capacity Approximately 2 J/cm³/°C
Inductance nH’s (non-inductive)
 
Rod and Tube Silicon Carbide Varistors Technical Specifications
   
Outside Diameter (mm) Inside Diameter (mm) Maximum Length (mm) Material Type Maximum Volume (cm3) Maximum Watts @ 20°C Maximum Joules @ 20°C (1) Tau (s)
6.7 0 200 6770 42.1 38.6 1290 45
25 0 600 64 471.2 301.3 66714 221
30 0 600 64 565.5 361.5 96068 266
 
Rod - Silicon Carbide Varistors Material Specification – Outside Diameter 30mm x Length 300mm
 
Maximum Length (mm) Maximum Volume (cm3) Material Type Maximum Watts@ 20°C Maximum Joules @ 20°C Tau (s) Heat Capacity (J/ (kg x K) Thermal conductivity (W/ cm² x K) Temperature coefficient (1/K)
300 2120.6 6770 259.3 51718 199 856 0.00611 -2.85E-04
300 2120.6 64 180.8 48034 266 917 0.00492 -1.84E-04
300 2120.6 82 226.7 323 1.4 6 0.00617 -1.05E-10

SiC Varistor Rod and Tube Applications

  • Generator protection - protect synchronous power generator damage during a shutdown. Rods or tubes 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.

MOV VARISTORS / ZnO VARISTORS WITH LEADS

Mov varistors disk leads
We offer a large range of radial leaded disk metal-oxide varistors (MOV’s) manufactured with 90% of ZnO. These mov’s range from voltage up to 1100VDC and maximum energy absorption of 230 Joules. Radial leaded MOV varistor disks come in diameters of 5 mm, 7 mm, 10 mm, 14 mm, and 20 mm.
Mov's disc 75mm leads

List of Standard MOV Varistors / ZnO Varistors

Series Disk Size Specification Chart
5M 5mm 5M - Chart
7M 7mm 7M - Chart
10M 10mm 10M - Chart
14 M 14mm 14M - Chart
20 M 20mm 20M - Chart
Sic disk 125sd leads

ZnO BLOCK VARISTORS

ZnO varistor enclosed
These are high-energy absorption industrial Metal-Oxide Varistors (MOVs) designed to provide surge protection in heavy industrial applications. They feature solid terminals for safe wire connections and a case providing complete electrical isolation from the MOV disk. Our non linear resistors in this block package (block varistors) feature superior creepage and clearance to minimize voltage breakdown along the package surface and provide complete electrical isolation of the MOV disk assembly.
List of Standard Non Linear Resistors - Block Varistor Values
Series Disk Size Specification Chart
40M 37mm 40M - Chart
60M 60mm 60M - Chart
80M 80mm 80M - Chart
Mechanical Layout - Non Linear Resistors - Block Varistor
Block varistor dimensions

SILICON RESISTOR - SI-METAL CERAMIC COMPOSITE RESISTORS

Silicon resistor tube
Silicon resistors (Si-Metal) are silicon metal linear resistors that extend the operating temperature of standard ceramic composite resistors to a continuous rating of 350°C and short durations rating of 390°C. The unique construction of silicon resistors allows for the highest continuous power rating and high energy absorption. Silicon metal linear resistor failures occur at 600°C and above. Common geometries of silicon metal linear resistors are rods and tubes of varying sizes. As with other ceramic composite resistors, silicon resistors may be connected in series or parallel for various total energy, electrical values, and power ratings.

Silicon Resistor - Silicon Metal Linear Resistor Tube Specifications