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Measurements and modeling of the frequency behavior of residual current devices- from 4 Hz to 40 kHz
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-5558-7708
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-6074-8633
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-4004-0352
2022 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 209, article id 108052Article in journal (Refereed) Published
Abstract [en]

Residual current devices (RCDs) are a common means of protection against shock due to indirect contact in low voltage (LV) systems. Due to the increasing penetration of power electronics equipment in LV systems, higher amounts of waveform distortion at a broad range of frequencies, from dc, subharmonics up to hundreds of kHz (supraharmonics), are expected to be present both during normal operation and during faults. The standardization committees and manufacturers have responded to this challenge by proposing different types of RCDs that are expected to function under given conditions of fault current waveform. However, subharmonic and supraharmonic frequency components are not considered in the standards for most of the RCD types. This article studies the effect of these frequency components on RCDs type AC, A, B and F. An assessment is made in terms of two types of RCD failure: blinding and nuisance tripping, for which both magnitude of the current and breaking time is considered. A frequency mapping of the RCDs is performed, and an assessment of these results based on the frequency-dependent response of the human body to currents is performed. Finally, a frequency model for RCDs type A, F and B is developed.

Place, publisher, year, edition, pages
Elsevier, 2022. Vol. 209, article id 108052
Keywords [en]
Frequency response, Harmonics, Leakage current, Power quality, Residual current devices, Supraharmonics
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-90583DOI: 10.1016/j.epsr.2022.108052ISI: 000797729900001Scopus ID: 2-s2.0-85129532678OAI: oai:DiVA.org:ltu-90583DiVA, id: diva2:1656954
Funder
Swedish Energy Agency
Note

Validerad;2022;Nivå 2;2022-05-09 (sofila);

Funder: Energiforsk

Available from: 2022-05-09 Created: 2022-05-09 Last updated: 2023-09-05Bibliographically approved
In thesis
1. On the supraharmonics in single-phase and three-phase installations
Open this publication in new window or tab >>On the supraharmonics in single-phase and three-phase installations
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Society has increasingly started depending on the continuity of internet services, the interruption can be crucial for vital societal functions. It is therefore important to maintain continuous and reliable operations of e.g., installations housing sensitive IT (Information Technology) loads. The establishment of a data center attracts huge investments, thereby boosting the economy. The electrical load within the data center is more structured with a similar type of load, i.e., power supplies supplying the servers connected repetitively. They also use power-conditioning equipment such as an uninterruptible power supply (UPS), which ensures uninterrupted power to the servers. The power supplies use switching techniques to modulate and condition the power supplied to the IT load. The switching residues from the power supplies are often in the frequency range from 2 kHz to 150 kHz, known as supraharmonics. The switching frequency of power electronic converters and power line communication are identified as the main contributors to supraharmonics. The increase in the number of power electronic converters in the power system has sparked interest in supraharmonics. Limited standards are available on the magnitude of supraharmonics allowed in the system. For installations that house multiple power converters, prior knowledge about the propagation and consequences of the supraharmonics can be an advantage in increasing their reliability. This work is focused on supraharmonics within data centers, but the results of the study can be applied to other installations.

The data centers are usually three-phase installations where single-phase devices, i.e., servers are distributed over three phases. To understand the holistic view of the system, it is important to understand the spread of supraharmonics in phase, neutral, and protective earth conductors. A perspective on the behaviour of supraharmonics in three-phase installation is presented in this work. The focal point of the work is the summation of supraharmonics in the neutral conductor and conductor crosstalk. The behaviour of the device connected in single-phase installation and when the same devices are spread over three phases may differ depending on the design of the installation. Since the focus is on a greater number of devices, analysis for the change in the magnitude of supraharmonics in a neutral conductor with the change in the number of devices is also undertaken. The IT workload in a data center changes continuously, thus a constant unbalance in the electrical load between the three phases can exist. The thesis aims to understand the factors influencing the change in supraharmonic magnitude and propagation in phase and neutral conductors according to a balanced and unbalanced voltage supply and loading conditions. The presence of a supraharmonic emitting load in one phase can cause interference on the adjacent phase due to conductor crosstalk. Crosstalk leads to the propagation of supraharmonics between the phases. The work focuses on the parameters influencing the crosstalk phenomena for supraharmonics. Among the parameters studied, the type of cable used in an installation and the cable length is dominating. The measurement of supraharmonic emission from the device connected as single-phase and connected as three-phase would differ because of crosstalk.

A large number of servers in data centers connected close by may lead to an increased leakage current. The composite leakage current can comprise subharmonics, harmonics, and supraharmonics. This can cause unwanted tripping of the residual current device (RCD), which is installed for human protection. The work aims to understand the impact of the composite residual current on the operation of the residual current devices.

The main contributions of this work are summarized as:

• A sensitivity analysis is presented based on the parameters impacting the propagation of supraharmonics for different operating modes of a UPS.

• A characterization of supraharmonics emission from different devices according to their time and frequency varying behaviour.

• A mathematical model to predict the change in the supraharmonic emission in the neutral conductor.

• An increased understanding of the behaviour of supraharmonics for constant powerloads under voltage reduction conditions in three-phase installations.

• Introduction and definition of the terms induced primary emission and induced secondary emission to explain conductor crosstalk for supraharmonic emission.

• A mathematical model to show the factors influencing the magnitude of induced primary emission and induced secondary emission.

• The frequency response of RCDs of type AC, A, B, and F under residual currents comprising pure tones and composite currents is presented by measurements andmodeling.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023. p. 70
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electric Power Engineering
Identifiers
urn:nbn:se:ltu:diva-96668 (URN)978-91-8048-321-6 (ISBN)978-91-8048-322-3 (ISBN)
Public defence
2023-05-30, Hörsal A, Luleå tekniska universitet, Skellefteå, 09:00 (English)
Opponent
Supervisors
Available from: 2023-04-20 Created: 2023-04-19 Last updated: 2023-09-05Bibliographically approved

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Sutaria, JilEspin Delgado, AngelaRönnberg, Sarah

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