It hardly ever happens; but if it does, it can end badly: a transformer fire after a flashover. A new passive protection system from MR protects operators from serious damage in such cases.
Faults in transformer windings, bushings, and on-load tap-changers, in which large amounts of energy are released, are extremely rare. If they do occur, however, high pressure is created by an electric arc that vaporizes the surrounding insulating liquid. If the process is uncontrolled, the consequences can be serious. In general, transformer tanks and protection systems, including those of on-load tap-changers (OLTCs), are prepared for this: In the event of a fault, they release pressure as controlled as possible to minimize the impact on the environment.
However, there is potential for optimization to reduce the risk even further, especially for the rare events with release of very high energies. For this reason, designs and protection systems have been and continue to be improved, for example with robust transformer tanks. In the event of an arc fault in the transformer tank, the energy released is dissipated by deformation of the tank which has been proven to be the most effective measure against fire after a high-energy arc fault.
MR has developed the BPS –Burst Prevention System® as a supplement for robust transformer tanks. The overall result is a transformer that minimizes the effects of such damaging events, which can be of great importance for operators of energy infrastructure as well as for industrial companies, and anywhere where space is limited.
Cover Reinforcement
The engineers at MR have scrutinized and reinforced all relevant parts of the OLTC, from the cover to the gear unit, screw connections, flow relay, sight glass, and pressure relief valve for directional oil drainage. Computer simulations show that the BPS can handle disturbances of up to 10 megajoules in 80 milliseconds and 50 bar pressure (see the illustration belowto see exactly how this works).
Five scenarios where the additional passive protection of BPS is particularly worthwhile:
Valuable
components
in the Vicinity

Valuable
components
in the Vicinity
An explosion can damage nearby components and set them on fire. Additional passive protection is therefore particularly recommended where there is valuable infrastructure nearby, such as in substations for high-voltage direct current (HVDC) transmission.
Sensitive
Ecosystems

Sensitive
Ecosystems
For transformers close to bodies of water or in nature reserves, a BPS prevents massive environmental pollution and high clean-up costs in the event of oil leaks.
Offshore
Facilities

Offshore
Facilities
Infrastructure that is difficult to reach, such as offshore facilities, benefits from the lower risk because it would be difficult and take a long time to fight fires in case of emergency at such locations.
Transformers
in Buildings

Transformers
in Buildings
In steelworks and other factories, transformers are often located inside of buildings, and an explosion here would be a major hazard for employees and could even damage the building itself.
Urban
Environments

Urban
Environments
The more people who live near a transformer, the higher the risk of someone being injured or suffering smoke inhalation in the event of a disaster. A BPS helps to prevent such situations.
The BPS was validated not only using numerous simulations, but also in a test with a real arc in cooperation with the Chinese Electric Power Research Institute (CEPRI) where the engineers subjected a test transformer equipped with the BPS to the stress of a 5.6 megajoule arc within 50 milliseconds. The BPS withstood the subsequent, rapidly increasing pressure of around 40 bar, thereby convincing a Chinese grid operator to retrofit the first transformers in the field.
What happens when it happens:
1.
Electric Arc

Electric arcs occur when insulation sections are overloaded. While most arc flashovers are harmless, there are also severe ones with energies of several megajoules. In this example, we are assuming such a high-energy arc.
2.
Pressure Development

The brief, immense heat causes the surrounding insulating oil to vaporize and expand due to the resulting gas. A pressure relief device opens automatically at the top of the OLTC cover and releases the oil and pressure. In our example, however, this is not enough, and the pressure becomes so great that it expands the walls of the OLTC housing.
3.
Reinforced Cover
Normal Cover
Internal Relief

A reinforced BPS cover withstands the pressure which instead breaks open the bottom of the OLTC housing and escapes into the transformer. The flexibility of the transformer tank is such that it absorbs all the energy without oil escaping uncontrollably. If necessary, the transformer’s pressure relief device releases oil into a pan which allows the environment to remain unaffected.
Explosion

If the pressure increases too much or too suddenly, the OLTC cover bursts, releasing a surge of oil and steam which can ignite and contaminate the surroundings.

YOUR CONTACT PERSON
Do you have any questions about the BPS — Burst Prevention System®?
Martin Guth is here for you:
M.Guth@reinhausen.com