J. Hällström

Metrology for high voltage direct current

HVDC energy transmission is crucial for a successful uptake of renewable energy sources in the grid. A research program is described, intended to provide metrology support for the needs of HVDC energy transmission. This program will provide improvements for the present HVDC metrology infrastructure: accurate measurement of HVDC, determination of losses in HVDC systems, on-site power quality measurements at HVDC substations, and DC metering. It is a combined effort of 7 European national metrology institutes, one university and one industrial partner.

Traceability and Characterization of a 1000 kV HVDC Reference Divider

This paper presents the characterization of a resistive high-voltage dc (HVDC) reference divider and methods to establish traceability. The divider is designed for use as a laboratory reference for calibration of HVDC measuring systems up to 1000 kV. Targeting a measurement uncertainty of 20 μV/V at full voltage has put a focus on the temperature coefficients of the resistors, elimination of humidity dependence, and control of leakage currents in the high-voltage arm. A scale factor calibration against a 50 kV divider at 10 kV leads to an expanded uncertainty of 15 μV/V.

Optimizing Temperature Coefficient and Frequency Response of Rogowski Coils

This paper describes a new method for optimizing both Rogowski coil’s temperature coefficient and its high frequency response. The proposed scheme is based on finding a value for coil termination resistance and for its temperature coefficient, which result in negligible change of coil output voltage versus temperature while still allowing for any damping ratio desired. The method is tested in a proof-of-concept setup with an openable, rigid Rogowski coil. The result shows that a well-damped LC-resonance of the coil is possible without having to make a compromise with temperature coefficient and vice versa. The proof-of-concept measurement is done for a broad temperature range around room temperature and works for any range where the coil‘s temperature expansion is sufficiently linear. At the same time, the frequency response is preserved, giving an extension of at least an order of magnitude with respect to previous work.

A reference merging unit and calibration setup for sampled values over Ethernet

This paper describes a reference digitizer - or a merging unit in the context of prevalent standards - for producing a stream of traceable sampled values over Ethernet. The device is based on an earlier custom digitizer design. A measurement setup for calibrating other equipment is built around the digitizer and Ethernet hardware including a network timing source. The digitizer has built-in functionality for time synchronicity in the lab and in remote locations. A field measurement campaign is planned for on-site calibration of electrical grid equipment in a live network environment.

Precision loss measurement of reactive compensation components by sampling voltage and current

This paper describes the setup of sampling-based high voltage measuring systems for reactive compensation components recently developed at VTT and PTB. First measurements show an agreement within 10-4 between both measuring systems. Both a phantom power source emulating reactors and capacitors with adjustable losses, and a set of real reactive components were measured. Measurements were performed with stable 53 Hz frequency and variable 50 Hz power frequency. The measuring systems are developed within the frame of the European project “ELPOW - Metrology for the Electrical Power Industry”.

Bilateral high voltage ac peak and rms value comparison up to 150 kV between VTT and PTB

This paper describes the measuring systems, setup and results of an rms and peak ac high voltage comparison performed at PTB in 2015. The three measuring systems are based on different principles. VTT system is a compressed gas capacitor based voltage divider together with a sampling voltmeter and signal processing. PTBs systems are based on the measuring of loading current of high voltage compressed gas capacitors. Differences in measured peak and rms voltages according to IEC 60060-1:2010 were less than 50 μV/V for all measured voltage levels. This comparison is a follow-up to resolve the differences that arose during EURAMET.EM-S33 comparison.

A three-phase calibration and field measurement setup based on a custom digitizer

This paper describes a new three-phase power measurement setup to be used as a national power standard in Finland. A custom 6-channel digitizer was previously developed for the purpose together with measurement software, which can be extended at will to accommodate new analyses. The setup can easily be moved outside the lab for field measurements. Voltage attenuators are custom-made at VTT and different types of current sensors can be selected for use depending on current levels and location. Uncertainty budget is currently being made for the setup.

International comparison of current transformer calibration systems up to 10 kA at 50 Hz frequency

Current transformers (CTs) are precision devices that scale high currents down to values that can be easily handled by measurement equipment. To support CT applications in revenue metering, a comparison on AC current transformer calibration systems was performed among 15 European national metrology institutes using a precision CT as the travelling device. The first comparison results for the transformation ratios (4, 5, 6, 8, 10) kA/5 A of the travelling CT at nominal burden of 5 VA and 15 VA indicate good agreement between the participating laboratories. The main differences are found for phase displacement, at least partly caused by the instability of the traveling standard.