                                                          ELECTRICAL PARAMETERS

Resistance Values

Whilst E24 values are preferred, other values are readily available at no additional cost.

Resistance Tolerance

± 20%, ± 10% and ± 5% available as standard.

Resistivity Range - ρ

3 Ohm cm to 30000 Ohm cm

ρ = R x A/L,   where R = Resistance Value

Temperature Coefficient - TCR

-0.05% to -0.15% per °C Temperature Rise depending on Resistivity Value.

TCR = 0.16 x e -(log ρ / 1.4) - 0.135     (% / °C Temperature Rise)

Voltage Coefficient - VCR

-0.5% to -7.5% / kV / cm

VCR = -0.62 x ρ 0.22   (% / kV / cm)

For ρ domain 10 to 7500 Ohm cm

Inductance

This is negligible (nH) and the resistors may be described as non-inductive. In practice the inductance of connecting leads will be greater than that of the resistors.

Dielectric Constant (Permittivity) εr

This is very difficult to measure and will vary according to material resistivity.

As an order of merit :     єr  ≈  5

Maximum Working Voltage Withstand per cm of Disc Length (V wk)

 Volts (rms) SF6 V wk = 1.00 x (R/t x A/L) 0.335 kV/cm } t Domain 10 to 50 ms ↑ AIR V wk = .87 x (R/t x A/L) 0.3 kV / cm t = Insertion time in ms ρ Domain 10 to 7500 Ohm cm Volts (Impulse) SF6 V wk = 8.0 x 1.2 √ Log (R/2.54 x A/L) kV / cm 1.2 / 50 µs Waveform AIR V wk = 4.3 x 1.2 √ Log (R/2.54 x A/L) kV / cm 1.2 / 50 µs Waveform AIR V wk = 3.0 x Log (R/2.54 x A/L) kV / cm 50 / 1000 µs Waveform ↓ AIR V wk = 1.5 x (Log (R/2.54 x A/L)) 1.25 kV / cm 100 / 10000 µs Waveform

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