High Impulse Voltage and Current Measurement Techniques by Klaus Schon

Author:Klaus Schon
Language: eng
Format: epub
Publisher: Springer International Publishing, Heidelberg

Various types of resistors come into consideration for a resistive impulse voltage divider. As high-voltage resistor for large voltage dividers, a resistance wire of NiCr or CuNi wound in a meandering manner is commonly used; this is woven with textile threads into a resistance web of width up to 1 m. The resistance web can be manufactured either as a flexible one several meters long or stiff one, cast in a rigid form as rod or tube. Small damping resistors as well as large impulse voltage dividers with the highest rated voltages can be rationally made out of them. Due to the meander-like arrangement of the resistance wire, one attains a large reduction of the inductance. The remaining inductance per unit length of the resistance web lies in the range of less than 1 μH/m up to 30 μH/m. By an optimal layout of the meandering, the effect of the inductance is at least partially compensated by the capacitances of the parallely arranged sections of wires [19]. In yet another type of construction of the high-voltage resistor, a resistance wire is wound around a carrier tube. For reduction of the inductance, two windings each wound in the opposite direction are arranged as a bifilar winding [20].

For “fast” voltage dividers with rated voltages of less than 500 kV, even series-connected low-inductive individual resistors are made use of. Carbon film resistors have a good high-frequency behaviour and high impulse withstand voltage. The carbon film deposited on an insulating body, however, must not indicate any incised helical or partially helical groove with which usually a prescribed resistance value shall be obtained. At the border line between the finished groove and the surrounding carbon film, discharges might set in leading to a flashover and damage of the carbon film. Film resistors have the disadvantage that in comparison to the wire-wound resistors their current loading capability is much less. The required higher current rating is obtained by each series resistor being made up by a parallel connection of a large number of resistors. In the parallel connection, the total inductance is also further reduced. Even better frequency behaviour is shown by the chip and ceramic resistors, in which the resistance layer is brought out on a quartz substrate. Carbon composition resistors connected in series can also be used [21]. A report is available in [22, 23] on the application of low-ohmic liquid resistive dividers with NaCl or CuSO4 solutions for the measurement of short voltage impulses in the 100 kV range. The high temperature coefficient, however, prevents the use of liquid dividers for higher accuracy requirements.

Usually, the low-voltage part is located in a shielded box and consists of a parallel connection of individual resistors in order to obtain a higher current loading and a lower inductance. As a rule, the resistors in the high-voltage part and the low-voltage part are similar in construction, so that they have the same thermal behaviour but are differently loaded. The principle of the compensated voltage divider well-known in low-voltage

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