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A sampling current ratio measurement system has been developed to calibrate the voltage dependence of ratio error and phase displacement of current transformers (CTs) used for medium-voltage (MV) and high-voltage (HV) applications. The influence of voltage-induced leakage current on the apparent ratio error and phase displacement of the reference circuit was unambiguously demonstrated using a novel measurement method. Measurement results for voltages up to 24 kV show that the observed leakage current is purely capacitive and caused by the shielded cable capacitance of the HV cable used to feed the current. The maximum ratio error and phase displacement were found to be about 100 parts in 106 and $100~\mu $ rad for the smallest current of 100 A used for these investigations. Since these values scale linearly with the applied voltage and inversely proportional with current, the assumption of negligible voltage dependence used in other reference systems presented in literature is questionable. Using the corrected reference circuit, a commercial class 0.2S MV CT with 2500-A nominal current was calibrated at voltage levels up to 24 kV. The voltage dependence of ratio error and phase displacement for primary currents up to 500 A was demonstrated to be capacitive as well, with a maximum impact on the current ratio of almost 0.9% for a primary current of 100 A (corresponding to 3.6% at 1% of nominal current). This value is beyond the limits of in-force standards, which emphasizes the necessity of implementing voltage dependence testing in those standards. [ABSTRACT FROM AUTHOR]

AC–DC measurements have been performed on a commercial thermal transfer standard (TTS) using a pulse-driven ac Josephson voltage standard with a small cryostat enabling shorter voltage leads. A 20 mV RMS output voltage was chosen, close to the maximum value that can be obtained without lowfrequency compensation (at a sigma-delta code amplitude of about 10 %) and close to the upper limit of the TTS in its 22 mV range. The measured deviation at higher frequencies, which is due to the length of the voltage leads, was an order of magnitude smaller than was observed before with a normal cryostat. The observed square dependence on the signal frequency and cable length follows exactly the expected behavior. All results agree well with the calibrations performed using a micropot reference system. Furthermore, the influence of other cables and equipment was investigated. The measurement results can be quantitatively understood both in terms of a lumped circuit description and in terms of reflected waves. [ABSTRACT FROM AUTHOR]

A sampling current ratio measurement system has been developed, tested, and validated for the accurate complex ratio measurement of ac current transducers. Calibrations can be performed for primary currents up to 10 kA with typical expanded uncertainties of 5\cdot 10^\mathrm \mathbf -6 in magnitude and 5 $\mu $ rad in phase ( $k=2$ ). A unique property of the system is the use of digitizers for sampling of the secondary current signals and step-down transformers with a large number of current ratios. Therefore, the system does not require the current transducer under test to be a current transformer having a nominal ratio equal to the reference current transformer. Furthermore, it allows for the accurate calibration of a large variety of different current transformers and other types of current transducers. A bilateral comparison between VSL and NRC confirms the stated uncertainty. [ABSTRACT FROM PUBLISHER]

A measurement setup is developed for the accurate ratio measurement of ac current transformers (CTs) for primary currents up to 5 kA. A unique property of the system is the use of high-quality digitizers for sampling of the secondary current signals and step-down transformers with different current ratios. This allows for accurate comparison of CTs even when their nominal ratios are not equal. The calibration results of the key components in the setup show that the sampling current ratio bridge has a ratio uncertainty of better than 2 \muA/A in magnitude and 0.8 \murad in phase for CT-under-test current ratios that do not differ by more than a factor of 5 from one of the ratios in the reference CT. The linearity of the bridge for input currents changing between 1% and 120% of nominal input current is better than 4 \muA/A in magnitude and 0.5 \murad in phase. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents results of an international comparison of two quantum AC voltage standards based on pulse-driven Josephson arrays. The two systems differ in several hardware and software characteristics as well as in the level of automation, features which can influence the accuracy of transferring the quantum-standard voltage value to a calibrated instrument. The comparison was performed at 100mV, 20mV and 12mV, at frequencies between 2.5kHz and 100kHz. An electronically-aided thermal transfer standard was used as a travelling standard. At the most accurate voltage and frequency point, 100mV at 2.5kHz, both laboratories agreed to better than 1 part in 106. [Copyright &y& Elsevier]

We have developed a home-built vibrating reed (VR) electrometer. The heart of the meter is a VR capacitor, which excels in a stable and low input leakage current of only 8 aA with a 2 aA noise for a 1 h measurement. This paper demonstrates that this makes the instrument ideal for the characterization of subtle charge effects in, for example, connectors and cables. The exceptional sensitivity of the electrometer is proven in a measurement of the leakage resistance of an air gap capacitor which results in a value of Rleak = (8.8 ± 0.3) · 1017 Ω, obtained at a test voltage of only 10 V. Calibration of the system with both a picoampere and a picocoulomb generator shows that the instrument has an accuracy of 15 parts in 106 (k = 1) at a current of 1 pA. As far as we are aware, this is the best uncertainty for a room temperature electrometer published so far. [ABSTRACT FROM AUTHOR]

A high accuracy current source has been developed for the generation of very small currents (below 200 pA) based on applying a linear voltage ramp to a capacitor. Using software-controlled compensation for the nonlinearity of the voltage ramp, a stable current can be reached within a few seconds. A voltage ramp within typically 10.10-6 of any desired value between less than 1 mV/s and several hundreds of mV/s can be realized. Using a high quality air-dielectric capacitor, currents below 200 pA can be generated With an uncertainty of 20 μA/A (k = 2), with a lower limit 0f 2.0 aA (k=2). [ABSTRACT FROM AUTHOR]