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What Type of Capacitor is Best for High Voltage?

Capacitors are passive components that store electric charge. They are used with circuits operating at various voltage levels to filter signals, couple stages, bypass noise and more. Selecting the right capacitor for an application requires matching its electrical traits to the expected voltages. For circuits with elevated voltages above 500V, specialized capacitors are needed to reliably perform without breaking down over time.

This guide will examine the most suitable capacitor varieties used in high voltage environments and their distinguishing properties.

Defining High Voltage Circuits

First, what constitutes “high voltage” when it comes to capacitors? Here are some voltage ranges and applications considered high voltage:

Over 500V – Industrial controls, power supplies, lasers, scientific equipment 1-100kV – X-ray/MRI machines, particle accelerators, broadcast transmitters
**100-1,000kV ** – Heavy utility transmission lines, railways, large electric motors

Circuits operating constantly at these DC or AC peak voltage levels require robust, non-conductive dielectrics in their capacitors to resist steady electrical pressure without catastrophic failure through arcing or dielectric breakdown.

Now let’s survey specific capacitor types suitable for high voltage reliability.

Polypropylene Film Capacitors

Polypropylene capacitors offer stable, long-lasting AC and DC performance well-suited for high voltage circuits up to 10kV.

Dielectric – Polypropylene film has high dielectric strength, rated typically 5000V/mil (2kV/mm) thickness. This allows thinner films to reach high voltage ratings from 1kV to over 30kV.

Benefits

  • Extremely low leakage current
  • Low dielectric losses
  • High reliability and consistency
  • Self-healing property repairs minor arcs
  • Operate from -55°C to 125°C

Applications – Stage/studio gear, guitar amps, power transmitters, converters, particle accelerators, lasers, pulsed klystron modulators.

Polypropylene capacitors handle high voltage DC filtering, coupling and energy storage across diverse fields.

Polyethylene Naphthalate Capacitors

Related to polypropylene caps, polyethylene naphthalate (PEN) also provides robust performance under high voltage loads.

Dielectric – Stacked layers of thin 4-10um PEN film allow rated voltages from 1kV to 140kV in a compact case size. Withstands up to 8000V/mil.

Benefits

  • Extremely low loss. Near zero leakage current.
  • Moisture resistant construction
  • High energy density – more capacitance per volume
  • Operational range from -55°C to 125°C

Applications – MRI/NMR machines, laser modulators, broadcast transmitters, power supplies, X-ray generators, pulsed applications.

Polyphenylene Sulfide Film Capacitors

Polyphenylene sulfide (PPS) film capacitors meet demanding high temperature, high voltage environments.

Dielectric – Heat-resistant PPS film rated to 200°C ambient retains capacitance at temperature extremes. Multiple film layers achieve working voltages over 10kV.

Benefits

  • Tight capacitance tolerance
  • Very high ripple current ratings
    -Low thermal coefficients for stability
  • Compact SMD or leaded styles
  • No known wear-out mechanisms

Applications – Geophysical monitoring equipment, military & avionics systems, downhole petrochemical tools, surveying instruments, high temperature auto electronics near hot engines.

PPS Keeping circuits stable up to 200°C in 9,000 hour lifetimes qualifies these caps for unrelenting conditions.

Mica Capacitors

Stacked sheets of mica mineral dielectric backed by thin metallic foil makes mica capacitors robust to 15kV+.

Dielectric – Muscovite mica offers a dielectric strength of 1,000V/mil (40V/um) while maintaining stability across wide temperature and frequency ranges.

Benefits

  • Tolerates high heat to 500°C
  • Extremely low loss factor
  • Withstands high intermittent currents
  • High Q factor benefits radio tuning circuits
  • Operates for decades without aging

Applications – Vacuum tube radios/audio gear, RF transmitters, industrial generators and power supplies, magnetron tubes, radar equipment.

Mica sheets withstand huge voltage spikes in microwave components owing to mica’s properties.

Ceramic Capacitors

Advanced ceramic composites baked at high temperature achieve superb dielectric strength for smaller case sizes up to 30kV.

Dielectric – Proprietary formulations like glass/mica fillers in an epoxy resin matrix keeps leakage current low at high temperatures while withstandingVoltage gradients above 50V/mil ( 2kV/mm) in some types.

Benefits

  • Compact SMD styles for pulse applications
  • Multi-layer construction for high capacitance density
  • Rugged performance from -55°C to 200°C
  • Flexible termination styles
  • High peak current ability

Applications – Sparking ignition systems, laser pumps, beam charging packs, industrial & medical RF generators.

Ceramic caps handle rapid high voltage discharges across 3,000V to 30kV ranges in advanced systems.

Oil Filled Capacitors

Submerging rolled metallized film or paper dielectric capacitors in mineral oil boosts voltage handling past standard film caps for ratings between 600V and 100kV.

Dielectric – The impregnating oil penetrates capacitor windings, displacing air pockets. This prevents corona discharge or arcing up to 30kV while the oil’s high breakdown voltage bolsters the dielectric strength to around 300V/mil.

Benefits

  • Helps cool internal hot spots
  • Seals out environmental moisture and contaminants
  • Much higher energy density than dry types
  • Large capacitance values available

Applications – High power RF generators, MRI machines, broadcast transmitters, power line conditioning, induction heating, laser power supplies.

The oil flood technology pushes voltage capabilities higher for these inexpensive workhorse AC filtering capacitors.

Pulse Discharge Capacitors

Specialized capacitors built to quickly absorb and discharge high amplitude current spikes above 50kV within nanoseconds for short bursts.

Dielectric – Thin metallized film layers stacked with intervening electrodes allows extremely fast charging/discharging across film. Dielectrics are often PPS, PP, PEN, mica, paper rated to handle repeated 20kV+ transients.

Benefits

  • Repeated peak current pulses over 150A
  • Rapid nanosecond discharge time
  • Compact cylindrical aluminum cases
  • Charge/discharge cycles > 500,000+

Applications – Medical defibrillators, particle accelerators, free electron lasers, EMP simulators, UV irradation systems, nuclear stimulation technology.

When electric currents need intense microsecond spikes at 20kWs, specialized pulse discharge capacitors are the choice.

Choosing the Best Variety

With this survey of high voltage capacitors, hopefully the ideal type for your demanding application is clearer. Matching dielectric film strengths, temperature requirements, loss factors, leakage current tolerance and other traits to expected electrical loads and circuit conditions leads to the most optimal reliable capacitor selection. Consider the environment conditions, operational lifespan, peak voltages/currents, durability to rapid charge/discharge rates and any size constraints before purchase. Engineer partnerships with vendors also aids picking the right part number. With an adequately rated capacitor chosen, your high voltage circuit will smoothly filter, couple or bypass unwanted interference for years of service.

Frequently Asked Questions

Questions on selecting an appropriate high voltage capacitor? Here are some answers to common queries:

What capacitor has the highest voltage rating?

Specialized pulse power capacitors can be rated over 100kV utilizing proprietary ceramic, polymer film or even liquid dielectric materials. They are built for extremely fast high amplitude discharge applications.

Is there a maximum voltage ceramic capacitors can handle?

Practical usage limits for ceramic caps is around 30-50kV, beyond which porosity, thickness and material rigidity poses challenges, though cutting edge laboratory versions have reached over 500kV.

Do mica capacitors have high voltage ratings?

Yes, mica caps working voltages frequently fall between 1-20kV thanks to mica’s innate dielectric strength, with some reaching 50kV or higher using stacked sheets and special construction techniques.

Can I use multiple capacitors in series for higher voltage?

Series capacitor strings help split voltage loads across each capacitor. But impedance differences can unbalance currents, and one failed cap shorts all, requiring voltage balancing resistors across each or redundant series blocks.

Which dielectric offers the greatest dielectric strength?

Advanced ceramics hold the records – barium strontium titanate composites used commercially achieve strength over 10,000V/mm. Novel graphene, diamond and boron nitride research dielectrics reach up to 12,000-100,000V/mm.

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