GENERAL CHARACTERISTICS
HIGH VOLTAGE / AC USES
• The main applications include live line indicators, AC dividers, grading systems for power distribution network, protection for HV switches and power circuit breakers. Coupling, by-passing high frequency circuits also use HV ceramic disc capacitors.
• These applications require:
- a high internal resistance.
- a high dielectric strength.
- low or moderate losses at working frequencies (from 50 Hz up to 10 kHz).
The active power (or losses) being: Wa = 2ΠFC tg δ V2 = k (Ctg δ) (FV2)
This shows that improved performances are obtained when:
- Good dielectric properties (low tg δ) and
- No long term overvoltage are present and
- Capacitors free of “partial discharge” (corona) effect, up to rated rms voltage.
TPC is able to perform “discharge free test” and may guarantee a rate as low as 5 picocoulombs at Vrms upon request.
• High voltage capacitors for AC uses are mainly made of type II dielectrics. Most of these materials except strontium titanate exhibit a significant non-linearity. Consequently, the capacitance value depends on the voltage across the component and on the frequency of the applied signal.
HIGH ENERGY PULSES
• Laser pulses circuitry, high energy/high voltage test equipment (HV accelerators, physics research) require products especially adapted to their specific requirements.
• Because of the high energy involved, the design of the capacitors have to provide:
- a very low ESR (equivalent series resistance) to minimize the lossed energy.
W = ∫ ip (ESR 2) di
- a very low ESL (equivalent series inductance) to keep the correct pulse shape.Typically due to the design of the electrodes, the products exhibit:
- ESR: ~ 10 mΩ
- ESL: < 30 nH
- peak current up to 50 kA
- a high withstanding of very large dV/ dt or short signal rise time.
- a high energy density J J = 12
k εo εr E2 (with E = V/m)
even under high electric field, (implying that εr is very little voltage dependent).
Through the use of almost linear or non-voltage dependent capacitors, the stored energy can reach 50 to 100 J/liter for the HP/HW/HK products.
• To ensure these properties, traditional ferroelectric type II capacitors cannot be used due to their electrostrictive and piezoelectric properties. The capacitors use quasi “paraelectric”, strontium-based, ceramic material.
• The main applications are coupling, decoupling, multipliers circuits, HV DC power supplies, high voltage dividers.
