In Amersfoort/Netherlands Yokogawa Europe has in October 2015 introduced to Power Electronics Europe the world’s first non-governmental ISO17025 accreditated lab for power measurements up to 100 kHz. Only four national institutes so far cover this frequency range. This is in addition to its established capability for providing high-accuracy calibration at 50 Hz, especially at very low power factors (down to 0.0001) and at high currents and its efforts starting in 1991 for internal ISO9001 accreditation.

“Due to more inverterized power systems such as drives or solar inverters, particularly with the growing focus on renewable energy markets and the need to optimize energy efficiency while complying with international standards on power quality, especially at low power factors, there is a growing demand for calibrated power mesurement and test system. In addition, the inverters used in renewable energy systems are switching at higher speeds: a scenario that introduces harmonics at higher frequencies”, commented Erik Kroon, Yokogawa's Metrology Expert.

Thus power measurements have to be correct to meet the exacting requirements of modern design. Their power meters need to be calibrated at the frequencies present in their specific application and not just at 50 Hz. However good the calibration result at 50 Hz, it does not say anything about high-frequency performance. Frequency is just one factor being addressed in the calibration of power meters. Whereas in the past it was sufficient to list voltage and current measurements in a power meter’s data sheet, today’s power environment needs to address variables such as phase shift, power factor and the effects of distorted waveforms – which today are included in the instrument specifications.

Calibration of instruments delivered to customers is done mostly over night in an automated process. The calibration lab itself is located in a temperature/humidity stabilized room, where the master instruments run 24 h/7 d without switching off. Low-current measurements (up to 20 A) are provided via highly accurate (ppm tolerance rage) in-house made shunts, whereas higher currents are measured via in-house made current transducers (high-permeability cores, special winding).

Regarding instruments, in the efficiency validation stage of inverters for instance, the key factors that need to be tested are power analysis, conversion efficiency, harmonics, and in automotive applications perhaps the battery charge and discharge process. For tests of this type, the instrument of choice is the power analyser, offering high precision, high accuracy, high stability, and the ability to carry out calibrated measurements. Yokogawa's WT3000E Power Analyzer offers 0.01% of reading 0.03% of range. It is the enhanced version of the industry standard WT3000. Along with high accuracy it provides a broad bandwidth of DC, and 0.1Hz to 1 MHz. The high measurement accuracy will provide engineers with the test data needed to evaluate power consumption and energy loss more precisely.

In addition to the dedicated instruments, engineers and R&D professionals are also looking for hybrid instruments that can be used at all stages of the development cycle. When the power consumed by the load varies at start-up of a motor, it may be necessary to measure power at much shorter intervals. A specific requirement is the time-based measurement functionality of an oscilloscope combined with the accuracy of a power analyzer. Such precision power scopes offer flexibility, accuracy and wide bandwidth, allowing for drawing the range of power readings needed to optimize the efficiency of boost-circuits and inverters. Yokogawa's PX8000 Power Scope brings transient analysis and high time-based accuracy to electrical power measurements. Its combination of accurate power measurements over precise time intervals is vital for analyzing energy loss and efficiency in high speed switching devices.

In addition to wide-band and high accurate power-meter calibration systems, the state-of-the-art calibration laboratory also includes systems for calibrating oscilloscopes, recorders and optical products, and is therefore capable of calibrating a wide range of instruments in the test & measurement industry. “Future requirements due to even higher switching frequencies of SiC and GaN power stages in solar inverters of power power supplies will be covered step-by-step”, Kroon said. AS

More in our upcoming printed issue.

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