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Protection Against Fire Substation

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    with fire associated with power transformers or oil-filled reactors, where the consequences can be particularly serious and extensive because of the large volume of oil that can catch fire and spread widely (Fig). For more details on protection against fire 

     

    • Limiting the damaged area and minimizing damage as far as possible
    • Extinguishing the fire in and around the transformer

     

    Limitation of the Damage Zone

     

    This can be done in various ways

     

    Oil Containment

    A bunded area should be provided around the transformer to prevent the spread of any oil that may escape from the transformer tank. These days this is frequently required by law simply because of the environmental effect of oil escaping into the ground and contaminating watercourses. From the fire limitation point of view, the oil passing into the collection tank will normally pass through a flame trap, the simplest form being stone chippings laid on top of a metal grid such that as the burning oil passes through the stone, the flames cannot pass through.

     

    Separation

    Many utilities limit the damage from transformer fires simply by separation. One method of achieving this is that a fire damage zone is calculated based upon experience with oil fires in a bund. Provided that no equipment associated with a bay other than the transformer bay itself and no common  substation equipment encroaches into this fire damage zone, then no further protection is provided.

     

    Fire Walls

    Where it is not possible to achieve satisfactory separation, then the construction of a fire wall to protect the equipment that would have fallen into the fire damage zone should be done. This wall will need to be higher than the highest oil-containing part of the transformer 

     

    Provision of Mobile Firefighting Equipment

    Placing in an area close to where the transformers are located mobile firefighting equipment such that if the fire is detected early enough, it can be extinguished quickly before it spreads

     

     

    Fire Blocks in Trenches

    Fire blocks should be located in trenches/ducts in close proximity to the transformer to prevent the spread of burning oil that can damage the insulation of the cables contained within them. These fire blocks will usually consist of sand.

     

    Physical Separation of the Control Circuits

    The control circuits should be located at some distance from the power circuits such that they can remain intact for some time in the event of a serious fire on the power circuit.

     

    Extinguishing of the Fire

    When designing the substation, allowance should be made for access for public firefighting vehicles to the transformer locations. In some cases consideration can be given to the provision of purpose-designed fire-extinguishing equipment associated specifically with the transformer. This may
    use water deluge, water spray, foam, or other methods. Usually when such equip-ment is fitted, it will be associated with fire detection devices such as heat and smoke detectors that will automatically trigger the fire-extinguishing equipment.

     

    Fences

    Fences are usually provided around high-voltage substations. The legal requirements for such fences may vary significantly from country to country. This short section will deal with the external fences and also any fences required within the overall substation area.

     

    External Fences

    From the safety point of view, the main purpose of the external fence is to prevent the general public from approaching too close to the electrical conductors and equipment for safety. In order to achieve this, fences must be separated from live equipment by a distance at least equal to the horizontal safety distance such that someone outside of the fence has the same degree of protection as those inside. The fence will normally be a
    minimum of 2 m in height, but in some countries, this minimum height will be greater. Unfortunately in this modern age, the fences around a substation are also required to prevent unauthorized access to the substation and in some cases to prevent vandalism to the equipment located inside. In some countries in the worst areas for intrusion and vandalism, the fences around substations also incorporate electric fencing over and above the basic fence, and the level of security of such fences can be the same as that used for prisons

     

     

    Internal Fences

    There are occasions within substations where the insulation clearance height has not been achieved, and so it is not permissible to allow people to access these areas. This is quite often the case with filter equipment where the capacitor stacks may be mounted at ground level. In these cases it is normal to erect a fence around this equipment which will normally be the minimum height accepted by the utility. In order for it to be safe to access the area within this fenced-off enclosure, the equipment inside the enclosure should normally be dead, isolated, and earthed. To ensure that this is the case, electromechanical interlocks may be used to ensure that the gate cannot be opened until the relevant earth switch is closed and conversely the earth switch cannot be removed until the gate is secured and locked.

     

    Reference: Substation Design CIGRE

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