Overview Silicon Carbide (SIC) varistors are high-performance nonlinear resistors engineered for robust overvoltage suppression in demanding industrial environments. Unlike conventional linear resistors, SIC varistors exhibit a highly voltage-dependent resistance: their impedance drops sharply as voltage increases, enabling instantaneous clamping of transient surges and absorption of large energy pulses within microseconds.
Key Features
- Nonlinear Voltage-Current Characteristic: Follows the power-law relationship I=A⋅Uk , where the exponent k typically ranges from 3 to 5, ensuring rapid response to voltage spikes.
- High Energy Absorption Capacity: Capable of safely dissipating tens to hundreds of kilojoules, making them ideal for protecting inductive loads such as motor excitations, electromagnets, and large generator fields.
- Excellent Thermal Shock Resistance: Constructed from sintered silicon carbide with ceramic binders, these components withstand extreme thermal cycling without degradation.
- Flexible Configuration: Units can be connected in series, parallel, or series-parallel arrays to meet specific voltage, current, and energy requirements.
- Fast Response Time: Reaction time under 1 microsecond, ensuring immediate protection against fast transients.
Typical Applications
- Suppression of switching surges in high-inductance circuits
- Contact protection for relays and contactors by reducing arc energy
- Rapid demagnetization of large hydro and thermal turbine generators
- Surge protection for power electronics and static excitation systems
- Overvoltage clamping in DC and rectified AC systems
Technical Advantages
- Operates effectively under both transient-only and continuous voltage conditions
- Negative temperature coefficient (approx. –0.005/°C) requires thermal stability consideration in continuous-duty designs to prevent thermal runaway
- Available in multiple physical sizes and voltage ratings to suit diverse engineering needs
- Stable performance across wide ambient temperature ranges (up to 125°C total component temperature)
Design Considerations When used in continuously energized circuits, total temperature rise—comprising ambient, steady-state power dissipation, and transient energy heating—must remain below 125°C. Accurate power loss calculation under non-sinusoidal waveforms (e.g., rectified or thyristor-controlled voltages) is essential and can be performed by integrating energy over small time intervals using the nonlinear I-V relations
Conclusion SIC varistors represent a proven, reliable solution for industrial-grade nonlinear resistor applications requiring high energy handling, fast response, and long-term durability. Their unique material properties and scalable architecture make them indispensable in modern power systems where equipment protection and operational continuity are critical.
