Enel Bargi power plant explosion. How the disastrous accident occurred: the possible reconstruction

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What happened inside the Bargi power plant, on Lake Suviana, in the Tuscan-Emilian Apennines, “is unthinkable”. Vittorio Rubino, a Filctem Cgil territorial official from Bologna who is following the situation closely, has no doubts. A tragedy that has profoundly affected the employees of the plant, who in recent days are engaged alongside the firefighters and the police in rescue operations inside the plant. Two of them also took part as representatives of their colleagues in the general strike called by CGIL and UIL but they preferred to leave Piazza Maggiore without speaking to journalists. Enel was asked in a series of emails addressed to workers “not to make statements to people outside the company and to avoid media engagement” with respect to what happened on Tuesday afternoon, says the trade unionist.

The first hypotheses circulated after the accident

If Enel employees now prefer to remain silent, in the immediate aftermath of the accident some reconstructions emerged among them immediately. Someone was talking about turbo-alternators in commissioning (starting), just replaced and the hypothesis that during a maneuver some sort of failure of the alternator output had occurred, hence the short circuit with a power of 100 Mega-watts, which then it would have physically exploded the transformer and turbine. The explosion would have been so violent that it broke through the turbine and let water enter the power plant, according to the hypothesis circulated.

Even more dramatic is the testimony of one of the first rescuers to arrive in Bargi, reported by Rai, which speaks of an “impressive disaster”. “An alternator exploded on floor 8”, he says, also speaking of “a series of subsequent explosions”.

Rumors and hot stories on which it is difficult to build technical hypotheses to understand what happened. What is certain is that “Enel has always been very rigorous in its procedures”, underline several trade unionists.

Bargi power plant: how the most powerful plant in Emilia Romagna works

What work has been done?

Fundamental to reconstructing what happened is to understand what type of work was carried out inside the power plant where some external companies had been working for some time. The works management was also entrusted to a technician not employed by Enel. From what was known, the mechanical components of the system, i.e. turbine and alternator, would have been overhauled and rearranged, while the oleo-pneumatic controls which are used to open and close the switches and operating controls have been installed from scratch. The short circuit could therefore have arisen from these newly replaced parts, or from incorrect operations or even from a design error. All hypotheses that the Bologna Prosecutor’s Office, with a pool of experts, will have the difficult task of examining.

The expert confirms the first reconstructions

To try to reconstruct what happened Today consulted a technician expert in the maintenance of hydroelectric plants who actually considers the hypotheses circulated among the employees plausible. “When there are short circuits, the electromagnetic forces that are released are enormous – he explains -. For this reason, the electrical machinery is equipped with protections that have the purpose of detecting and immediately interrupting the fault”. It is not excluded, however, “being in the commissioning (start-up) phase that the protections were in some way not calibrated or functioning correctly. Moreover, being a new machine, therefore tested in the factory, the fault was unlikely”. In fact, according to the reconstructions circulated among the employees, the fault would not have been on the machine, but on the point where the machine is connected to the cables, which is a notoriously weak point in the system, as the technician points out.

A giant that pulls the alternator and the turbine

According to the expert, practically nothing would have exploded. “The alternator has three phases separated by insulating material – he explains – When the insulating material fails or a bolt is tightened badly and two phases come into contact, there is a ‘short circuit’, i.e. the electrical circuit closes very much sooner than it should. The electrical resistance goes to zero and the currents become enormous.”

The passage of current between two conductors causes electrodynamic forces whose intensity is not easily imaginable. In practice, due to these forces, the alternator was ‘yanked’ with enormous power. “Since it is rigidly connected to the turbine – explains the technician – it tore it from its seat and the water came out, flooding the premises”. Once the water entered the power plant, it may have wet the circuits, causing other short circuits and generated fire.

In simple words, it is as if there had been a giant pulling the alternator and the turbine and tearing them from their foundations or twisting them all. This is the comparison that the expert draws. “The start-up phase is the most dangerous of all – he adds – because the works are not finished, so there are people around the construction site, and the plant is not yet completely ready”.

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Some technical elements to clarify

There hydraulic turbine it is a mechanical device, made of steel or cardboard, capable of transforming the kinetic and/or pressure energy of a liquid into mechanical energy available to a shaft capable of driving a further device such as, for example, an electric generator. Their efficiency is high, often above 90%, which is why they are highly appreciated, even if their installation requires different infrastructures.

L’alternator is a rotating electric machine based on the physical law of electromagnetic induction (or Faraday) that converts the mechanical energy supplied by the prime mover into electrical energy in the form of alternating current generated by the rotor shaft.

The transformer it is a static electric machine, operating in alternating current and based on the phenomenon of electromagnetic induction. There are various types of transformers, generally suitable for changing the voltage values ​​between the input and the output, conserving the electrical power.

 
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