Thomas L. Nelson

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate AC programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 muV/V (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.

Error and Transient Analysis of Stepwise-Approximated Sine Waves Generated by Programmable Josephson Voltage Standards

We are developing a quantum-based 60 Hz power standard that exploits the precision sinusoidal reference voltages synthesized by a programmable Josephson voltage standard (PJVS). PJVS systems use series arrays of Josephson junctions as a multibit digital-to-analog converter to produce accurate quantum-based dc voltages. Using stepwise-approximation synthesis, the system can also generate arbitrary ac waveforms [i.e., an ac programmable Josephson voltage standard (ACPJVS)] and, in this application, produces sine waves with calculable root mean square (rms) voltage and spectral content. The primary drawback to this ACPJVS synthesis technique is the uncertainty that results from switching between the discrete voltages due to finite rise times and transient signals. In this paper, we present measurements and simulations that elucidate some of the error sources that are intrinsic to the ACPJVS when used for rms measurements. In particular, we consider sine waves synthesized at frequencies up to the audio range, where the effect of these errors is more easily measured because the fixed transition time becomes a greater fraction of the time in each quantized voltage state. Our goal for the power standard is to reduce all error sources and uncertainty contributions from the PJVS-synthesized waveforms at 60 Hz to a few parts in 107 so that the overall uncertainty in an ac power standard will be a few parts in 106.

Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards

We are implementing a new standard for 60 Hz power measurements based on precision sinusoidal reference voltages from two independent programmable Josephson voltage standards (PJVS): one for voltage and one for current. The National Institute of Standards and Technology PJVS systems use series arrays of Josephson junctions to produce accurate quantum-based DC voltages. Using stepwise-approximation synthesis, the PJVS systems produce sinewaves with precisely calculable RMS voltage and spectral content. We present measurements and calculations that elucidate the sources of error in the RMS voltage that are intrinsic to the digital-synthesis technique and that are due to the finite rise times and transients that occur when switching between the discrete voltages. Our goal is to reduce all error sources and uncertainty contributions from the PJVS synthesized waveforms to a few parts in 10 7 so that the overall uncertainty in the AC-power standard is a few parts in 106

Precision differential sampling measurements of low frequency voltages synthesized with an AC Programmable Josephson Voltage Standard

Sampling is a promising technique for comparing the stepwise-approximated sine waves synthesized by an AC Programmable Josephson Voltage Standard to the sinusoidal voltages of a secondary source at low frequencies (a few hundred hertz or less). This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high purity sine wave voltages by comparing them to quantum-accurate waveforms.

NIST support of phasor measurements to increase reliability of the North American electric power grid

The importance of developing better tools for observing the status of the North American power grid is described. Focus is on the performance of the phase measurement units being deployed to give the raw data for this improved observability. How the availability of this information would have appeared during the August 2003 power blackout is described. IEEE is developing a standard for these units but no calibration service is available to use as a common reference to assure the interchangeability of units from different manufacturers. The program under way at NIST to develop such a calibration service and the coordination with the power industry to develop a guideline for performing these calibrations is presented. The future directions of work in this area are given

NRC-NIST intercomparison of calibration systems for current transducers with a voltage output at power frequencies

Summary form only given. A number of international comparisons of current transformer calibrations at power frequencies were conducted in the past. However, all of them were done with a secondary current output of 5 A. This intercomparison of current transformer calibration systems between the National Research Council of Canada and the National Institute of Standards and Technology, USA, is done with a primary current range of 100 A and a secondary output signal of voltage range of 10 V. The comparison is implemented with a transfer standard consisting of a modified commercial current-comparator-based transimpedance with the output voltage adjustable in magnitude and phase within a range of /spl plusmn/1 percent.

Extension of voltage range for power and energy calibrations

A special purpose ac voltage divider system having voltage ratios of 600 V, 480 V, 360 V, and 240 V to 120 V has been developed to extend the voltage range of primary electric power calibrations from 120 volts to 600 volts at power frequencies of 50 and 60 Hz. The system consists of a special two-stage resistive divider compensated with an active circuit, thereby reducing the error contributions to below 1 /spl mu/V/V. The developmental goal to realize ac voltage scaling within 5 /spl mu/V/V uncertainty in a device verifiable with dc resistance ratio measurements has been attained.

A system to measure current transducer performance

A special purpose ac current transducer measurement system capable of intercomparing transducers with ac output voltage ratios from 1:1 to 50:1 has been developed to extend the range and accuracy of current transformer, current shunt, and mutual inductor calibrations at power frequencies of 50 Hz and 60 Hz. The system consists of a two-stage binary inductive voltage divider, an amplifier-aided two-stage current transformer, a precision shunt, a wideband buffer, and a commercial, sampling digital multimeter (DMM). When comparing current transducers with ac output voltage ratios of 1:1 to 50:1, the system attains an overall relative standard uncertainty of the ratio of 10/sup -5/ to 10/sup -4/, respectively. The basic system can be used to calibrate transducers with input currents of 0.1 A to 200 A (RMS) and can be extended to measure devices handling input currents up to 15 kA.

A 600 V AC Voltage Amplifier for Power Measurements

A voltage amplifier composed of three cascaded -10:1 gain sections has been developed to extend the voltage range of primary electric power calibrations from 120 to 600 V over the 50-400-Hz frequency range. The gain and phase errors of each amplifier section are continuously measured and corrected in situ using a permuting impedance measurement technique. The amplifier design approach, measurement principles, and initial performance results are presented.

NIST coordination of smart grid interoperability standards

The National Institute of Standards and Technology has efforts underway to accelerate the development of interoperability standards to support the future modernized “Smart Grid” electric grid or energy delivery network characterized by a two-way flow of electricity and information, capable of monitoring and responding to changes in everything from power plants to customer preferences to individual appliances. Through a high-visibility, rapid, and open process that brought together the Smart Grid community, including utilities, equipment suppliers, government and consumers of electricity, NIST has developed and published its Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0 [1], to create the basis for prioritizing, coordinating and accelerating the development of standards in private-sector standards setting organizations, including international standards development organizations such as the International Electrotechnical Commission (IEC) and the IEEE.