Conference Paper

Reference setup for the calibration of power transformer loss measurement systems

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Abstract

A reference system is developed for the calibration of power transformer loss measurement systems (TLMs). A crucial element in such calibrations is the availability of voltage and current signals with adjustable phase close to 90°, that is power factor near to zero, in order to apply a known and stable loss or reference power to the TLM. In the new reference system, digital signal processing is used to maintain the phase relation between the voltage (up to 100 kV) applied to the TLM and the generated current (up to 2000 A). Initial results indicate that phase uncertainties of better than 20 μrad can be obtained.

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... In the framework of a European Joint Research Project, both Van Swinden Laboratorium (VSL), Delft, The Netherlands, and Physikalisch-Technische Bundesanstalt (PTB), Brunswick, Germany, have developed reference setups with complementary approaches for the system calibration of TLMS [10], [11], in order to support the European power transformer manufacturer industry in meeting the Ecodesign requirements via readily available TLMS system calibration services with sufficiently high accuracy. After a description of the respective VSL and PTB reference setups, this paper gives the approach and results of a full comparison of these two setups. ...
... The following two sections describe the VSL and PTB reference setups, respectively, that each uses one of these two-generation approaches. Fig. 1 schematically depicts the VSL reference setup for TLMS system calibration [10] for voltages up to 100 kV and currents up to 2 kA. The three TLMS channels are placed in parallel (voltage) and series (current), respectively, with the current channels at ground potential, disconnected from the voltage channels. ...
... Any deviation in the measured phase angle from the set point φ set is subsequently used to adjust the mix of the phase shifted and the original voltage signal in the phaseshifting block of the first stage by φ until the measured phase equals φ set . Extensive fine-tuning of the DSP algorithms was needed to assure a low-noise phase relation of better than 5 μrad between current and voltage under most typical test conditions, i.e., with varying frequency and phase of the applied test voltage [10]. ...
Article
A unique comparison has been performed of two reference setups for the calibration of industrial power transformer loss measurement systems (TLMSs). The setups are developed by the Van Swinden Laboratorium (VSL), Delft, The Netherlands and Physikalisch-Technische Bundesanstalt (PTB), Brunswick, Germany, with the aim to calibrate industrial TLMS as a complete system, rather than just via its individual components, with an uncertainty better than 50 μW/VA, for voltages up to 100 kV, currents up to 2 kA, and power factors down to 0. The results of the comparison show excellent agreement of the PTB and VSL reference setups, both for the individual components as for the complete system. The phase agreement in the VSL and PTB component calibration results is better than (2 ± 5), (5 ± 12), and (10 ± 15) μrad for all calibration points in current ratio, voltage ratio, and power, respectively. In the full system comparison, the difference in the results of the VSL and PTB systems is less than 12 μW/VA for currents up to 1000 A and voltages up to 70 kV, with a -7 μW/VA difference averaged over all comparison measurements. This is well within the present 25 μW/VA measurement uncertainty of each of the VSL and PTB reference setups.
... The basic approach in the TLM system calibration is to simultaneously apply voltage and current to the TLM system with a stable, adjustable, phase between voltage and current in order to simulate a load with controllable loss to the TLM system. To this end, the Van Swinden Laboratorium (VSL) has developed a reference setup for TLM system calibration, suitable for onsite use at the premises of power transformer manufacturers, that can reach an uncertainty of 0.2 % ( = 2) at power factor ( ) of 0.01 [3]. This VSL system essentially is a digital implementation of the original analogue system of the National Research Council Canada (NRC) [4]. ...
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Full-text available
A reference setup for system calibration of industrial transformer loss measurement (TLM) systems consists of three main components, a voltage divider, current transformer and a power meter, and their phase displacements should each not be more than 10 μrad to achieve an overall system uncertainty of better than 20 μW/VA. We have extensively verified the uncertainty level of the current-comparator-based capacitive voltage divider (CVD) used in the TLM reference setup of the Van Swinden Laboratorium (VSL), both from the component level and the system as a whole. Different practical conditions relevant for on-site measurements are considered, e.g. measurement cable lengths, cable types and grounding. The verification measurement results show an agreement of better than (6 ± 6) ×10-6 in ratio error and (4 ± 6) μrad in phase displacement between the CVD component and system calibrations up to 100 kV. Requirements for achieving this agreement are adequate grounding of the CVD and the use of triax cable between the HV capacitor and the CVD low-voltage electronics in case large distances have to be covered on-site. The (4 ± 6) μrad agreement in phase displacement is well within the required 10 μrad limit for voltage measurements as part of on-site TLM system calibrations with 20 μW/VA overall uncertainty at low power factors.
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