Standard Capacitors, Coupling Capacitors & Non-Inductive Resistors
The reference components a PD or impulse circuit is built on
A partial discharge measurement is a comparison between the object and everything else in the circuit. If the coupling capacitor discharges at 5 pC, a 3 pC defect in the object is invisible. The same logic governs impulse shaping: a resistor with parasitic inductance distorts the front of a 1.2/50 µs wave no matter how good the generator behind it is.
Coupling capacitors reach 1,200 kV in eight standard capacitance values from 80 pF to 25,000 pF, insulated in epoxy resin or mineral oil, with partial discharge below 1 pC and 20 µV at rated voltage. SF₆ standard capacitors run from 2 kV to 1,600 kV and 20 pF to 50,000 pF, with PD from 2 pC or less at low voltage to 10 pC or less at EHV, and a dissipation factor of 1 × 10⁻⁵. Non-inductive resistors are built in nickel-chromium from 10 kV to 2,400 kV and 100 A to 200 kA, in thirteen standard values from 10 Ω to 50 kΩ, rated from 1 kJ to 300 kJ with tolerance from ±0.5%.
Why it matters
Nickel-chromium non-inductive construction eliminates the parasitic inductance that distorts impulse waveshapes at high frequency.
A low-PD coupling capacitor is the difference between measuring the object's discharge and measuring your own circuit.
A dissipation factor of 1 × 10⁻⁵ on the SF₆ standard capacitor lets a tan δ bridge resolve the object rather than the reference.
Resistors from 1 kJ to 300 kJ and 100 A to 200 kA cover impulse shaping and high-current shunt duty from one component family.
Tolerance from ±0.5% means front and tail times land where the calculation said they would, shot after shot.
Ratings
Coupling capacitors — voltage: Up to 1,200 kV
Coupling capacitors — capacitance: 80 pF to 25,000 pF in eight standard values
Coupling capacitors — PD level: <1 pC and 20 µV at rated voltage
Coupling capacitors — insulation: Epoxy resin or mineral oil
SF₆ standard capacitors: 2 kV to 1,600 kV rated; 20 pF to 50,000 pF; PD ≤2 pC (LV) to ≤10 pC (EHV); tan δ 1 × 10⁻⁵
Non-inductive resistors — voltage: 10 kV to 2,400 kV
Non-inductive resistors — current: 100 A to 200 kA
Non-inductive resistors — values: 10, 12, 15, 70, 115, 230, 300, 400, 500, 600, 1,000 Ω, 25 kΩ and 50 kΩ
Non-inductive resistors — waveforms: 1.2/50 µs, 250/2500 µs and 8/20 µs
Non-inductive resistors — energy: 1 kJ to 300 kJ
Non-inductive resistors — tolerance: From ±0.5%
Humidity: <90% without condensation
Standards
IEEE C57.124
IEEE Std 1434
IEC 60270
IEC 60060-1/-2
ABNT NBR 5356 for South American projects
Applications
Partial discharge measurement circuits
Tan δ bridge reference standards
Impulse generator front and tail shaping
Burden resistors for CT and VT testing
High-current shunts
Questions engineers ask
What partial discharge level does the coupling capacitor itself contribute?Below 1 pC and 20 µV at rated voltage on the coupling capacitors, and 2 pC or less at low voltage rising to 10 pC or less at extra high voltage on the SF₆ standard capacitors. That headroom is what allows a complete IEC 60270 circuit to resolve discharge activity in the object rather than in the measuring branch.
Why does a non-inductive resistor matter in an impulse circuit?Front and tail times are set by resistance working against the generator and load capacitance. Any series inductance adds an oscillatory component the standard does not allow. Nickel-chromium non-inductive construction keeps the element resistive across the frequency content of a 1.2/50 µs, 250/2500 µs or 8/20 µs wave, with tolerance from ±0.5%.
Technical documentation
Download HVEX Coupling Capacitors for Partial Discharge Tests datasheet (English, PDF)
Download HVEX Non-Inductive Nickel-Chromium Resistors datasheet (English, PDF)
