An active high-voltage divider and phase shifter

Abstract

An instrument combining the functions of an active high voltage divider and a phase shifter designed to yield small phase-angle uncertainties within 20 JLrad is described. It is based on a circuit employing a feedback amplifier and a controlled source. The presence of the controlled source greatly reduces the potential for dynamic instabilities of the feedback loop and effectively eliminates the errors associated with the finite gain of the amplifier. Design and construction details and the results of the accuracy evaluation are presented.

An active high-voltage divider with 20 μV/V uncertainty

“…For example, note the approaches described in [2], [3]. The method described in [1] uses the concept of a controlled voltage source, phase-locked to the input hv signal, that is inserted on an open-loop basis in the low-voltage arm of the divider to add to the amplifier output, as in the complete circuit of Fig. 1.…”

“…The controlled source is implemented as an additional feedback amplifier and signaladder circuits [1].…”

“…The previous circuit described in [1] requires two hv capacitors which are available in some capacitor structures as dual low voltage electrodes coupled to the same hv electrode. To accommodate most existing hv capacitors having a single low voltage electrode, an alternative was developed as shown in Fig.…”

“…In a related earlier development [1], an active divider with polystyrene capacitors in the low-voltage arm and a feedback amplifier enhanced with a controlled source was built and used as a standard for calibration of test equipment to measure transformer losses. Ten years of successful use of that equipment and the stability of its components prompted the reexamination of this approach with a possibility of advancing its accuracy and versatility.…”

Extension of voltage range for power and energy calibrations

“…The bridge is optimized for operation at 120 V and 5 A. Calibrations at other voltages and currents are possible using scaling transformers within the power bridge. To further extend the voltage range to 600 V, it was decided to investigate an amplifier-compensated resistive divider technique, similar to that successfully applied to high-voltage capacitive dividers [2]. The goal was to develop a multi-ratio divider for voltage ratios to 600 V/120 V having a relative uncertainty within 5 V/V.…”