HEARING EDITION
                                                                         REPORT PHASE 1
                                                                          14th January 2002              Page 1 of 3


Oil-filled components in power plants are dangerous, hazardous objects in which serious explosions and fires
can occur. In particular large power step-up transformers in underground power plants are a primary area of
focus. The SEBK highlights the explosion potential and the consequences of incidents that can be considered
as being out of control.

Risk means “the rate of probability multiplied by the consequence”. Although comprehensive measures are
given increasing priority in the power sector, incidents always occur. Therefore power stations to be designed
in order to provide as good sectioning as possible in order to provide both explosion and fire barriers.

Directly or indirectly electrical faults are the predominant cause of incidents in power plants. Minor or
insignificant failures may develop or may cause serious incidents and they can spill over to more important
plant functions and result in a disaster occurring.

Failures in high voltage or high-energy circuits or components, such as short circuits, are subject to special
attention. Incorrect manual operation may cause the development of a serious incident if no automatic back-up
safety functions are provided. Particular high-risk areas are transformers, oil-filled cables, cable connections
and other oil-filled components. Primary causes of incidents include mechanical stresses, a lack of maintenance
and a lack of inspection. Faults in minor important components or outbreaks of fire may affect high-risk
components or areas. Component failures are normally found to result from manufacturing defects/weaknesses,
incorrect operation or aging.

Hacker and High Power Microwave (HPM) technology represents a worsening of the safety risk. The
Internet and the increasing use of automatic and software based systems increase the possibilities of entering
power control networks.

Cable joints represent a potentially high safety risk as well. The termination of cables into a connection
chamber filled with oil represents a substantia l explosion potential. Insulation material defect caused the
disaster at Tonstad power station in 1973.

Risk levels for personnel and material assets as well as the consequences of these risks are considerable higher
in underground electric power plants than in plants located above ground. The establishment of escape routes
is a major problem in the design of underground power plants. safety measures.

After the de-regulation of the Norwegian power marked, the operational mode has been changed
dramatically in the majority of plants. The present level of knowledge that is available concerning the aging
processes in power transformers is not satisfactory despite many years of research and operating experience.
Both the paper and the oil are the weakest components in the insulating devices inside the transformer. These
are obviously the components in the aging process of transformers. The researchers agree that it is no
satisfactory way whereby the transformer oil can be replaced in order to improve the condition and increase
the remaining lifetime of the transformer since any such improvement seem to be marginal.

In spite of a lack of quantitative statements it seems clear that the water content of the paper increases
dramatically the decomposition speed of the insulation. Additionally, the operating temperature, the average
temperature and the hot-spot temperature inside the transformer and its duration all have a major influence of
the decomposition of the paper.

The development of gasses caused by decomposition of the insulating oil and its pressure expansion seems to
be the most important factor in a fault situation. If an ignition source then occurs as a result of an electrical or
                                                                      HEARING EDITION
                                                                       REPORT PHASE 1
                                                                        14th January 2002              Page 2 of 3

other fault then the resulting damage due to combustion and associated danger to personnel will be
In the power sector not enough focus has been placed on acceptable risk as being a steering factor as well as
risk evaluations connected to various safety measures despite the fact that acceptable risk has been the subject
of lessons and references. Long and dangerous escape routes in a poor environment and in dangerous
circumstances. Large fire-loads without the possibility of relieving pressure to the free atmosphere. Much
smoke develops during a fire and is difficult to ventilated away from the area. Enormous amounts of energy
are released into a confined space

The Norwegian Ministry of Defense has defined accept criteria for individual risks and group risks within
their areas of responsibility. In the power sector, however, the authorities, represented by the Energy
department, have not brought this subject into the arena for discussion and clarification.

Everybody makes mistake in their daily work and all systems have to intercept them, automatically and
systematically, in order to avoid consequential damages. All mistakes must be reported and included in the
maintenance work. If a mistake is not reported or the operator try to hide the mistake, then the mistake will
become much more serious.

Measures that can warn power station attendants prior to an explosion occurring are very limited. An abnormal
operational status, fault signals and noise might be the only early warning prior to an explosion occurring.To
reduce risk of explosion is fundamental.

The environmental aspects related to the SEBK project are Halon used as extinguishing and suppression
remedy and transformer oil pollution

A number of accidents have occurred in Norway and abroad where oil mist was the cause of an explosion.
Some are reported in this report. Examples of research and work out in the field of safety risk are reported as

Suppression/quenching of an explosion during it is development and fire extinguishing have an important

The status of the extinguishing equipment market at present is fragmented and unstable. There is a multitude of
methods, means, products, consultants and suppliers. The market is inundated with opinions and attitudes.
However it is necessary to treat this complicated area with a degree of caution and respect and to adopt a
practical, down-to-earth approach.

Extinguishing a fire in an underground power station presents a number of special challenges where a variety of
factors come into play. The fires that occur have different features depending on the fire load supporting the fire
and the time that has elapsed since the fire started. Further, it is necessary to have sufficient knowledge with
regard to the materials that can burn and how the fire is likely to develop

There is no medium available today that has all of those features. However, they provide good guidance when
the choice of extinguishing medium is made.

There has been a long-term trend towards using water (alone or with additives) as an extinguishing medium for
all types of fires. This means that attention has been paid to the use of water in this report.

When water mist is considered as an extinguishing medium it is necessary to differentiate between actions
against fire and those against explosion. The drop size is important when fire extinguishing and when water
damage is to be avoided.
                                                                      HEARING EDITION
                                                                       REPORT PHASE 1
                                                                        14th January 2002              Page 3 of 3

According to the partial report by GexCon it is, with a high degree of certainty, likely that in the first phase
of an explosion spray systems, especially water spray, create much turbulence thus an uncontrolled
development. It is reasonable to be cautious and view the present situation with some scepticism.

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