The measurement of lightning or even switching impulse voltages demands
a much higher bandwidth as already discussed in section 3.6.2. The decrease
of C
e by very carefully adapted ‘shielding’ or potential grading methods is
limited, although a reduction by a factor of about 5–10 seems possible. But this
is not enough. There is only one practical solution, i.e. to reduce the value of
R by some orders of magnitude. Let us assume that we have to build a resistor
divider with T ³ T0 D 50 nsec, still introducing an amplitude error υ of 10
per cent for linearly rising voltages chopped at Tc D 0.5 µsec (see eqn (3.53)).
Thus the product RCe becomes 300 nsec according to eqn (3.79). Let the
resistance be about 2 m in height, providing a lightning impulse withstand
strength of about 1000 kV. Without excessively large top electrodes for forced
shielding, C0e is about 10 pF/m and thus R ³ 300 ð 109/20 ð 1012 D 15 k.
This is indeed the order of magnitude which can be used for voltage dividers
applicable for the measurement of lightning impulse voltages. This low value
of a resistance will load the impulse generators, but this resistive load is
tolerable if the discharge resistors within the generator are adapted. A large
increase of the rated voltage is, however, not possible. The reduction of Ce
by huge shielding electrodes becomes impractical as the dimensions must
increase with the divider’s height. Thus the response time with the resistance
value unchanged increases proportional to Ce or the product HC0e. Response
The measurement of lightning or even switching impulse voltages demands
a much higher bandwidth as already discussed in section 3.6.2. The decrease
of C
e by very carefully adapted ‘shielding’ or potential grading methods is
limited, although a reduction by a factor of about 5–10 seems possible. But this
is not enough. There is only one practical solution, i.e. to reduce the value of
R by some orders of magnitude. Let us assume that we have to build a resistor
divider with T ³ T0 D 50 nsec, still introducing an amplitude error υ of 10
per cent for linearly rising voltages chopped at Tc D 0.5 µsec (see eqn (3.53)).
Thus the product RCe becomes 300 nsec according to eqn (3.79). Let the
resistance be about 2 m in height, providing a lightning impulse withstand
strength of about 1000 kV. Without excessively large top electrodes for forced
shielding, C0e is about 10 pF/m and thus R ³ 300 ð 109/20 ð 1012 D 15 k.
This is indeed the order of magnitude which can be used for voltage dividers
applicable for the measurement of lightning impulse voltages. This low value
of a resistance will load the impulse generators, but this resistive load is
tolerable if the discharge resistors within the generator are adapted. A large
increase of the rated voltage is, however, not possible. The reduction of Ce
by huge shielding electrodes becomes impractical as the dimensions must
increase with the divider’s height. Thus the response time with the resistance
value unchanged increases proportional to Ce or the product HC0e. Response
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