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Arnaud Magnier

Vice President at SERGI Transformer Protector

The TRANSFORMER PROTECTOR (TP) prevents transformer explosions, and thus fire. To ensure such level of safety, SERGI TRANSFORMER PROTECTOR (SERGI) has been investing for more than twenty years in research, development and testing. Today, with more than 2,800 installations worldwide and a 100 percent success in protecting transformers, the company is also in position to provide customers with a Liability Insurance of 15 Million-Euros.


SERGI has its headquarters in France, near Paris. As of Today, it is a company of more than 100 employees worldwide, operating two entities in France, one in India, one in Brazil, USA of course, and Peru. SERGI has two manufacturing facilities, one in France and the other in the USA. The U.S. facility was established because of the large SERGI customer base in USA and Mexico. SERGI sells approximately 400 TRANSFORMER PROTECTOR (TP) per year, averaged over the past three years.

A long journey to the ultimate safety

SERGI was created in the 1950s by Electricité de France (EDF), the French owned electricity generation, transmission and distribution company, which needed a solution for extinguishing fires caused by transformer explosions. At that time, SERGI used to design and manufacture a system called “Drain and Stir” to extinguish transformer fires.
In the beginning of the 1990s, the company decided to invest in preventive technologies to prevent transformer explosions, and thus avoid oil fires. SERGI was a small business of around ten employees then and only few people were dedicated to manufacturing the “Drain and Stir” fire extinguishing system, while the remaining staff were mainly researchers. This solely explain the strong, permanent, outstanding and up-to-date SERGI policy in R&D investments.
In line with this new approach, since 1995 SERGI conducted an intensive R&D program which led in 1999 to the first TRANSFORMER PROTECTOR (TP) patent application and the first TP on-site installation was done in Italy one year later.
In France, EDF implemented the TP for the first time in 2007.

As a manufacturer of the former “Drain and Stir” fire extinguishing system, in the 1990s SERGI invested in R&D to develop an efficient solution to prevent transformer explosions, rather than extinguishing oil fires.

Abundance of simulations and prototyping

To first explain the phenomenon, transformers explode primarily because of internal electrical arcs resulting from failure of electrical insulation. When occurring, electrical arcs generate immediately a large gas volume in the sealed transformer tank. These gases produce a first dynamic pressure peak reflecting inside the tank, creating pressure waves. Within milliseconds, the pressure waves superimpose to create static pressure, meaning that pressures become uniformly applied on the entire tank leading to explosion and fire.
Since 1995, SERGI developed its own numerical solvers to simulate the behavior and properties of electrical arcs, the associated gas generation inside transformer oil, first dynamic pressure peak propagation, pressure wave creation and static pressure build up inside transformer tanks. These investigations allowed SERGI to understand the transformer explosion phenomenon and design the TP to be activated, depending on arc location and transformer size, within 0.5 to 20 milliseconds by the first dynamic pressure peak to avoid transformer explosion before static pressure increases.

Over time, the SERGI R&D knowledge on these phenomena has improved significantly, thanks to information gathered during successful TP activations, enabling R&D solvers to steadily improve, resulting in increasingly accurate numerical simulations.

Once the R&D numerical solvers were operational, SERGI decided to perform TP validation tests. These were conducted in two different programs. A first series of 28 live tests was conducted in 2002 at the EDF High Voltage Laboratory, Les Renardières, three years after filing of the patent application.
These 28 live tests were performed on small transformers, but the main objective was to validate the concept only, proving that the TP was functional and depressurizing the transformer before static pressure built-up.

Having validated the concept, the next step was to seek a high voltage laboratory that would accept the ignition of powerful electricals arc inside transformers on live test conditions to observe the TRANSFORMER PROTECTOR (TP) behavior. CEPEL, the Brazilian High Voltage Laboratory, accepted the SERGI challenge with electrical arcs energies of up to 2.5 Mega Joules. Three different transformers were fitted with the TP and 34 live tests were performed, with several levels of arcs energies in various transformer tank locations to make sure the TP would avoid transformer explosion without tank deformation.
These two successful test campaigns led to a worldwide recognition since no other companies up-to-now has performed such an extensive program. These live tests became a trigger for utilities and transformer owners to fully protect their transformers and update their technical specifications to include the TP. Therefore, between 2002 and 2017, SERGI can claim that the TP is the sole proven solution to prevent transformer explosion and fire.

Risks of transformer explosion

Currently, transformer explosions and fires are common occurrences. An article published by the “German Federal Ministry for Nuclear Safety and Nature Conservation” refers to two main transformer explosions every day in the USA only, ref. “Reliability of Main Transformers, H.P. Berg, N. Fritze, RT&A # 01 (20), (Vol.2) March 2011”.
There are many negative factors and consequences related to transformer explosions. One of the main risks is the power outage, complete plant destruction, human injuries and lethal consequences. Recently, there was a case in Nepal where two people died because of a transformer explosion. In another case, ten people died and nearly 200 were injured in Saudi Arabia due to the fire caused by a short circuit involving a transformer. There are hundreds of similar cases.
Environmental issues are another important risk and efforts to avoid pollution caused by the spreading of oil. For example, in the USA, a utility was fined several hundred million USDs because of the oil spillage into an adjacent river. Finally, the question of reputation for the utilities is also important; obviously, companies would like to avoid publicity linked to explosions, oil fire and pollution.

The TP lifetime liability coverage has been multiplied by a factor of 30 over 10 last years, up to 15 Million EUR, because the TP lifetime coverage had never been activated, meaning the TRANSFORMER PROTECTOR has never failed.
We help our customers avoid severe consequences relating to transformer explosions, such as loss of production, human injuries and lethal consequences, environmental pollution, etc.

In this regard, it is worth mentioning that all TRANSFORMER PROTECTOR commissioned by SERGI come with a TP lifetime Liability Insurance of 15 Million EUR. From 500,000 EUR when first set; the TP lifetime liability coverage has been multiplied by a factor of 30 over 10 last years because the TP lifetime coverage had never been activated, meaning the TRANSFORMER PROTECTOR has never failed.

As of today, twenty-three TP activations have been reported, meaning that these transformers were prevented from explosion and even more critical consequences. Ten cases happened in the last three years, and two are very recent, one in Namibia (to be disclosed soon), the other in Kazakhstan. NamPower, the Namibian utility, has already provided SERGI with a Certificate of Successful Activation. For Kazakhstan, we are yet to receive an official certificate from the end-user.
We emphasize that up to now all transformers were back to service after a TP activation.

The TRANSFORMER PROTECTOR has a lifetime at least as long as the transformer it is protecting. The requirements for maintenance are based on transformer shut down with the replacement of critical parts scheduled at the same time.

Why do customers come to us?

There are three typical channels customers get in touch with SERGI. The most common is following a recommendation from the client’s insurance broker. An interesting case is an on-going project in France in the nuclear sector.

It is very common that customers approach us following a recommendation from their insurance company

Another common case is when SERGI is approached by companies willing to reduce the risk of transformer explosions. For example, we have installed several units at ArcelorMittal’s steelworks. According to ArcelorMittal, a transformer explosion leads to a subsequent loss of production, which results in losses of USD Millions per day. Compared to the TP cost investment, it is obvious that protecting the transformers with the TP is cost-effective.
The third channel appears to be a direct contact with utilities for inclusion of the TP in their technical specifications. In this case, usually companies are performing a risk assessment and the most critical transformers are protected first. Obviously, utilities which have experienced transformer explosions are more willing to learn about transformer protection because they are fully aware of all consequences. Customers with such experiences are very interested in learning more about the SERGI research and the TP technology.

What else can SERGI provide?

The SERGI core business philosophy is to continuously develop our understanding and quantification of all phenomena pertaining to electrical arcs inside transformer oil and their consequences on transformer tank rupture. As customers are increasingly aware of SERGI’s experience in this domain, the SERGI Research Department (RD) is often call for investigations, mainly by companies having experienced transformer explosions or transformers fleets vulnerable to failure. In this case, the SERGI RD simulates the transformer faults and propose solutions based on Fluid Structure Interaction simulations. Often, these simulations lead to customer technical specification modifications for transformer design and related equipment.
The subsequent SERGI activity is the TRANSFORMER PROTECTOR (TP) design and manufacturing. SERGI can also provide supervision and maintenance services and, upon client request, extend to turn-key projects, but SERGI is mainly a research, engineering and manufacturing company.
In a variety of countries around the world, end-users susceptible to transformer failures request SERGI to approve the TP position and configuration on their transformers because of the safety the TP provides. Therefore, SERGI uses its R&D numerical solvers, to ensure that the provided protection is correctly sized and positioned for each transformer.
The TP positioning and location is decided on a case-to-case basis. When installing the TP on a new transformer, SERGI works directly with transformer manufacturers to select the best sizing and locations. On existing transformers, the configuration is adapted based on the available manholes or openings. For example, in some cases it is not possible to adapt the TP ideal configuration, so this may require installation of additional Depressurization Sets on transformer to make sure that we can achieve the most reliable solution to ensure that the TP will depressurize the transformer before static pressure increases.
Whenever SERGI deals with configurations never simulated in the past, the Research Department uses “in-house” simulation software to calculate and identify an ideal sizing and configuration for the TP installation. However, having protected more than 2,800 transformers so far, the need for such simulations is much less frequent than before, leading to reduced delivery time.

Future prospects

Currently, the SERGI Research and Development Departments are developing new products similar to the TRANSFORMER PROTECTOR, which are intended for smaller transformers. The TP current design is not very suitable for small transformers. This new product has already been installed in some end-user sites and is planned to be launched at global scale shortly.

SERGI is developing new products similar to the TRANSFORMER PROTECTOR for small transformers

In the medium-term, SERGI is looking at expanding and increasing its worldwide network by establishing branches in different countries. For example, in Africa, Middle East, and some Asian countries. Another key of success is to pass the FM Global Certification started by SERGI several years ago. This is a long process due to the lack of standards for transformer protection. Well-known insurance companies can also perform product accreditation.
It is also important to highlight that the TRANSFORMER PROTECTOR concept has been recognized by the National Fire Protection Association and included in the NFPA editions since 2005 as part of their 850 civil codes. This was an important achievement in the last decade.


Arnaud Magnier joined SERGI in 2006. Previous to joining Sergi, he worked for EADS (the European Aerospace and Defense Group, nowadays Airbus) and AREVA subsidiaries. His background is in engineering.


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