A fast capacitive voltage monitor for low impedance pulse lines

Accurate and reliable electrical measurements are critical issues in high voltage transmission lines for pulse power generators. Capacitive voltage monitoring is a well established technique which is widely used in this type of device. The monitor can operate in the pure capacitive division, or self-integrating mode for direct monitoring of the voltage or as a Ddot probe to measure the time rate of change of voltage. Difficulties exist in trying to improve the high frequency response of these monitors in the environment of a low impedance pulse line with water dielectric. The ultimate goal in capacitive voltage monitoring is a simple design, with good high frequency response, convenient attenuation ratio and long time constant measurement capability. Here we propose a new design for a capacitive voltage monitor which, in principle, satisfies most of the above requirements and is particularly suitable when applied to low impedance high voltage transmission lines. Above all, the design is intrinsically matched to the characteristics of the output cable and simple to implement. In the following, the basic schemes of the capacitive monitor are first discussed in order to highlight the problems with high frequency design. The new design is then presented together with details of construction. Finally, the properties of the proposed monitor obtained from calculation, and circuit simulation are demonstrated.