Objectives

20NRM03 DC Grids

Objectives

The overall goal of this project is the traceable measurement and characterisation of PQ parameters to support standardisation in further development and future use of DC grids. The specific objectives of the project are:

  1. To develop on-site measurement equipment and to capture dynamic voltage and current signals in real low voltage DC (LVDC) grids, at voltage and current levels up to 1 kV and several hundreds of amperes, respectively, with target uncertainties below 0.1 % taking into account the presence of AC ripple and other disturbances.

  2. To analyse on-site measurement data in real LVDC grids to obtain a set of DC power quality (PQ) parameter definitions and electricity meter test waveforms, and to develop reference systems for measuring DCPQ parameters and DC energy taking into account the presence of defined PQ disturbances.

  3. To define equipment specifications and methods for PQ “compatibility level” and “planning level” surveys in LVDC grids for DC parameters such as in-rush current, voltage dips, voltage and current ripple.

  4. To contribute to a revision of EN 50160 by providing the data, methods, guidelines and recommendations, which are necessary for the standardisation of voltage characteristics of public electricity supply, to CLC TC8X WG1. To contribute to a revision of IEC 62053-41 by providing the data, methods, guidelines, and recommendations, which are necessary for the standardisation of DC electricity metering, to IEC TC13 WG11. In addition, to contribute to the standards development work of the technical committees IEC TC85 WG20 and IEC SC77A WG9. Outputs should be in a form that can be incorporated into the standards at the earliest opportunity and communicated through a variety of media to the standards community and to end users (e.g. electric suppliers for general public and industrial applications).

Progress beyond the state of the art

On-site DCPQ parameter measurements (Objective 1)

The number of DC trial grids worldwide is growing rapidly, but the behaviour of PQ phenomena in DC grids is not yet adequately understood. Consequently, standardisation is still in its infancy and the corresponding measurement techniques need to be developed. The preceding project 16ENG04 MyRailS made a first step towards measuring specific DCPQ events between railway supply systems and rolling stock, but further work is needed.

This project is going beyond the state of the art by developing new measurement systems with new trigger mechanisms to detect PQ events associated with DC grid applications. Subsequently these systems will then be used for measurements in real-world DC trial grids in order to collect actual DCPQ events in real DC grids.

 

Traceability for DCPQ parameters (Objective 2)

Traceable reference systems for AC PQ are well established in NMIs and accredited laboratories, however, these do not apply to DC. New amplifiers, transducers, and data analysis techniques are under development in this project as those used for AC usually cannot be used for DC.

In this project, new DCPQ reference systems are being realised to provide traceability for DCPQ. To do this the project has identified DC-specific PQ parameters such as current and voltage ripple, inrush currents, voltage fluctuations, and short circuit events, together with new traceable calibration methods, procedures and uncertainty budgets. The results will then be fed back to CLC TC8X WG01 for a future extension of the presently AC-only EN 50160 so that it can include DC grids.

 

Test waveforms and reference systems for DC energy (Objective 2)

Currently, the metrological infrastructure for DC power under distorted conditions is largely missing. In addition, DC power is not yet listed among the calibration and measurement capabilities (CMCs) in the BIPM database. A first step was made towards developing this metrological infrastructure in the project 16ENG04 MyRailS for initial railway-specific parameters with an intended 0.1 % uncertainty. However, this level is insufficient for application in DC grids.

This missing metrological infrastructure is being built in this project by (i) developing new reference systems for DC energy, (ii) performing an inter-comparison of these new reference systems, and (iii) proposing new CMCs with target uncertainties below 0.01 % in the presence of DC-grid related disturbances. These new reference systems will be demonstrated for use by calibrating electricity meters using waveforms covering a wide range of applications including high-current EV charging. This demonstration should provide the necessary input and information for IEC TC13 WG11 regarding a future update of the IEC 62053-41 on DC metering.

 

Equipment specifications and methods for PQ level surveys (Objective 3)

Despite the existence of several LVDC trial grids in different countries, the definition of DCPQ compatibility levels is currently hampered by a lack of knowledge and reliable measurement methodology. This project is going beyond the state of the art by developing special equipment and methods to conduct the required surveys for setting compatibility levels, that will be used as the basis of future “planning level” surveys carried out by utility companies in order to manage the PQ levels in LVDC networks.