From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH): “Time-reversal methods can make power transformers more reliable”

From The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH)

Leila Ueberschlag

Engineers at EPFL’s Electromagnetic Compatibility Laboratory have developed a revolutionary method for detecting and locating partial discharges, which disrupt the functioning of power transformers.

Transformers play a central role in power distribution systems, making it possible to carry electric power over long distances with minimal risk and losses. They’re crucial for ensuring the stability and reliability of power grids. When problems occur in transformers, grid operators need to be able to detect them rapidly and determine exactly where they’re located. “Sometimes, disturbances known as partial discharges occur inside a transformer,” says Farhad Rachidi, adjunct professor at EPFL and head of the Electromagnetic Compatibility (EMC) Laboratory. “If operators don’t do anything to fix them, the discharges can result in serious damage over time and even cause the transformer to explode.”

Time-reversed equations

There are a number of systems that can detect partial discharges, but they aren’t very effective in pinpointing where they originate. “With our method, engineers can locate the source of a partial discharge and act quickly to solve the problem,” says Hamid Reza Karami, scientist at the EPFL EMC Lab. “It’s based on a fairly recent technique called time reversal which stems from the ‘reversibility’ of physics equations. Just about all physics equations have a time variable and consider it as a value going forward. But most equations also work with its negative. So our technique entails replacing the “t” variable in physics equations which represents time with its negative: “–t”. Theoretically that allows us to go back in time.”

Reconstructing waves in the opposite direction

Partial discharges inside a transformer generate two kinds of waves: acoustic and electromagnetic. In the EPFL system, the waves are captured by a sensor and converted into digital format. An algorithm then analyses the waves and feeds them into a computer model of a transformer. The model reconstructs the waves by working backwards, in the opposite direction of travel, until it reaches the source of the discharge. That gives engineers precise information on where the discharge comes from.

Rachidi’s team is developing their technology jointly with Sparks Instruments, a Fribourg-based company that supplies systems for detecting partial discharges, and with HEIG-VD. “EPFL’s Technology Transfer Office put us in touch with the people at Sparks,” says Rachidi. “We also received support from enable, an EPFL program to encourage R&D, which allowed us to test and validate our system. Our technology has now been patented and we’re working with Sparks to find the best way to take it to market.”

Huge potential

Time-reversal-based methods have considerable potential in a host of applications – and this isn’t the first breakthrough by Rachidi and the engineers at his lab. In 2018, they patented an application that can locate short circuits in power grids in record time. “We were the first to use time reversal for this kind of application,” he says. And they’re applying their knowledge in other fields too: “We’ve filed a patent application for a system that can pinpoint the origin of cardiac arrythmia, and we’re working with Prof. Marcos Rubinstein and his group at HEIG-VD to develop a device that can locate lightning.”

See the full article here .


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The Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH) is a research institute and university in Lausanne, Switzerland, that specializes in natural sciences and engineering. It is one of the two Swiss Federal Institutes of Technology, and it has three main missions: education, research and technology transfer.

The QS World University Rankings ranks EPFL(CH) 14th in the world across all fields in their 2020/2021 ranking, whereas Times Higher Education World University Rankings ranks EPFL(CH) as the world’s 19th best school for Engineering and Technology in 2020.

EPFL(CH) is located in the French-speaking part of Switzerland; the sister institution in the German-speaking part of Switzerland is The Swiss Federal Institute of Technology ETH Zürich [Eidgenössische Technische Hochschule Zürich] (CH). Associated with several specialized research institutes, the two universities form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles Polytechniques Fédérales] (CH) which is directly dependent on the Federal Department of Economic Affairs, Education and Research. In connection with research and teaching activities, EPFL(CH) operates a nuclear reactor CROCUS; a Tokamak Fusion reactor; a Blue Gene/Q Supercomputer; and P3 bio-hazard facilities.

ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École Polytechnique Fédérale de Lausanne](CH), and four associated research institutes form The Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales] (CH) with the aim of collaborating on scientific projects.

The roots of modern-day EPFL(CH) can be traced back to the foundation of a private school under the name École Spéciale de Lausanne in 1853 at the initiative of Lois Rivier, a graduate of the École Centrale Paris (FR) and John Gay the then professor and rector of the Académie de Lausanne. At its inception it had only 11 students and the offices were located at Rue du Valentin in Lausanne. In 1869, it became the technical department of the public Académie de Lausanne. When the Académie was reorganized and acquired the status of a university in 1890, the technical faculty changed its name to École d’Ingénieurs de l’Université de Lausanne. In 1946, it was renamed the École polytechnique de l’Université de Lausanne (EPUL). In 1969, the EPUL was separated from the rest of the University of Lausanne and became a federal institute under its current name. EPFL(CH), like ETH Zürich (CH), is thus directly controlled by the Swiss federal government. In contrast, all other universities in Switzerland are controlled by their respective cantonal governments. Following the nomination of Patrick Aebischer as president in 2000, EPFL(CH) has started to develop into the field of life sciences. It absorbed the Swiss Institute for Experimental Cancer Research (ISREC) in 2008.

In 1946, there were 360 students. In 1969, EPFL(CH) had 1,400 students and 55 professors. In the past two decades the university has grown rapidly and as of 2012 roughly 14,000 people study or work on campus, about 9,300 of these being Bachelor, Master or PhD students. The environment at modern day EPFL(CH) is highly international with the school attracting students and researchers from all over the world. More than 125 countries are represented on the campus and the university has two official languages, French and English.


EPFL is organized into eight schools, themselves formed of institutes that group research units (laboratories or chairs) around common themes:

School of Basic Sciences
Institute of Mathematics
Institute of Chemical Sciences and Engineering
Institute of Physics
European Centre of Atomic and Molecular Computations
Bernoulli Center
Biomedical Imaging Research Center
Interdisciplinary Center for Electron Microscopy
MPG-EPFL Centre for Molecular Nanosciences and Technology
Swiss Plasma Center
Laboratory of Astrophysics

School of Engineering

Institute of Electrical Engineering
Institute of Mechanical Engineering
Institute of Materials
Institute of Microengineering
Institute of Bioengineering

School of Architecture, Civil and Environmental Engineering

Institute of Architecture
Civil Engineering Institute
Institute of Urban and Regional Sciences
Environmental Engineering Institute

School of Computer and Communication Sciences

Algorithms & Theoretical Computer Science
Artificial Intelligence & Machine Learning
Computational Biology
Computer Architecture & Integrated Systems
Data Management & Information Retrieval
Graphics & Vision
Human-Computer Interaction
Information & Communication Theory
Programming Languages & Formal Methods
Security & Cryptography
Signal & Image Processing

School of Life Sciences

Bachelor-Master Teaching Section in Life Sciences and Technologies
Brain Mind Institute
Institute of Bioengineering
Swiss Institute for Experimental Cancer Research
Global Health Institute
Ten Technology Platforms & Core Facilities (PTECH)
Center for Phenogenomics
NCCR Synaptic Bases of Mental Diseases

College of Management of Technology

Swiss Finance Institute at EPFL
Section of Management of Technology and Entrepreneurship
Institute of Technology and Public Policy
Institute of Management of Technology and Entrepreneurship
Section of Financial Engineering

College of Humanities

Human and social sciences teaching program

EPFL Middle East

Section of Energy Management and Sustainability

In addition to the eight schools there are seven closely related institutions

Swiss Cancer Centre
Center for Biomedical Imaging (CIBM)
Centre for Advanced Modelling Science (CADMOS)
École Cantonale d’art de Lausanne (ECAL)
Campus Biotech
Wyss Center for Bio- and Neuro-engineering
Swiss National Supercomputing Centre