You can refer to national standard or guidelines such as ENA DOC 18-2008 – Interim Guideline for the Fire Protection of Electricity Substations
which illustrated below some related sections.
The provision of safety clearances and space for equipment handling in outdoor switchyards goes a long way towards providing adequate separation to prevent a fire from spreading to other equipment. Additional consideration should, however, be given to:
• Transformer locations and separation
• The possible violent failure of VT's, CT's etc.
• The location of gantry structures
• Overhead lines / feeder conductors
• Access for fire fighting
• Control of spilt oil
• Possible propagation of fire along cable trenches
• Good housekeeping
8.4.1. General Remarks
Buildings should comply with the Building Code of Australia (BCA) requirements. The fire protection section of BCA adopts the general approach of prescribing requirements on the following criteria:
(a) The USE to which the building is put (ie the "Class" of Building)
(b) The HEIGHT of the building above ground (ie the "rise in storeys")
(c) The LOCATION of the building (ie whether inside or outside a designated "fire zone")
Fire zones are established by local authorities and generally relate to areas of sizeable commercial or business development. It is usual for a higher degree of inbuilt fire protection to be required in such zones.
The BCA requirements also incorporate the concepts of a "fire source feature" and an "effective distance".
A "fire source feature" represents a theoretical burning building emitting heat radiation. Major factors involved with the spread of fire are the intensity of heat radiation, the geometrical relationship and the distance apart of buildings.
The "effective distance" between a fire-source feature and a proposed new building determines what precautions are required to guard against the spread of fire and the undue heating of structural members by radiation.
The BCA does not address the specific problems of electricity substations. However, the broad principles are applicable and local authorities are likely to press for the most stringent interpretation for substations in highly developed locations.
Substation buildings can be deemed as Class 8 buildings if they are not pole mounted, kiosk, padmount or modular type substations and should comply with the BCA, Section C generally and, in particular, clause C2.13 “Electricity Supply System”.
8.4.2. Buildings Adjacent to Transformers
Where buildings are not adequately spaced from transformers and barrier walls have not been constructed, then the following precautions are recommended:
There should be no windows facing the transformer
The wall and any doors should be a minimum two (2) hour fire rated construction. A higher fire rating may be justified depending on the outcome of a risk assessment which would consider;
• Likely response time of the Fire Brigade
• Access / ease of extinguishing fire
• Post fire performance of structure
The roof and eaves construction should be either of fire resistant construction or be shielded from radiated heat by the wall (see Figure 5). However, a fire analysis may determine that the roof and eaves also need to be fire rated depending on the incident radiant heat flux. This will be dependant on the height of the fire and the height of the wall/roof.
8.4.3. Emergency Exits
Each switchroom, cable basement etc. should be arranged to provide safe exit for personnel should any item of plant fail violently, or ignite.
This would usually be achieved by providing two (2) exits towards opposite ends of each room.
The disabling effects of smoke and fumes should be considered.
The provision of adequate ventilation and illuminated EXIT signs and emergency lighting can help under such circumstances.
8.4.4. Segregation of Rooms
The extent of fire segregation within a substation building will depend largely on:
• The size of the building
• The importance of the substation to the network or the consequences of a major fire
• The type of equipment housed
In general, larger substations will be divided into a number of separate rooms which can fairly easily be fire-segregated by the use of appropriate building methods.
It should be remembered that roof spaces should also be segregated to control the spread of fire or the collapse of the roof onto otherwise undamaged equipment.
Cable basements should be segregated from switch and control rooms. All cable penetrations of walls or floors should be sealed to prevent the spread of fire, smoke and corrosive fumes liberated by burning PVC. The fire stop should be at least 100 mm thick.
Good housekeeping is an important factor in preventing fires. Particularly during equipping stages, all rubbish, off-cuts of insulation etc. should be regularly cleaned-up.
Flammable materials such as oil, jointing compound, cleaning fluids, paint etc., should be stored in a safe manner preferably remote from electrical plant.
8.4.6. Fire Detection and Alarm Systems
The objective of a fire detection and alarm system is to provide early notice of a fire so that prompt action may be instigated to minimize the damage.
Fire alarm systems are now generally installed at zone substations and also in larger bulk supply and transmission substations. The coverage provided may be limited to special hazard areas(control panels, switchrooms, cable basements etc.) or may cover the whole substation building.
The application of detection and alarm systems to outdoor substation equipment is quite rare. The considerations which may lead to their installation in any type of substation would include:
• BCA regulation (eg if substation is combined with another building which requires alarms).
• Particular hazards (eg at an industrial site).
• Remoteness (ie where there are no neighbours to raise the alarm or where alarms would avoid an undue delay in attendance of a fire brigade).
• Supply reliability (ie where the consequences of a substation fire would justify the cost of installation and maintenance of an alarm system).
Fire alarm signals, where provided, are normally sent direct to the System Control Room and need to be separated from other substation alarms so that fire brigade and electrical operation staff can be alerted at the same time. Alternatively, a parallel alarm can be provided direct to the fire brigade.
Details of various types of detection and alarm systems are given in Section 9 of this Guideline.
8.4.7. Fire Fighting Systems
As with detection and alarm systems, fixed fire fighting systems are only installed in selected locations, in determining if a system should be installed, similar considerations would apply, plus:
• the consequences of a fire spreading from unit to unit, or its effect on the building.
• the lack of adequate access to fight a fire with mobile equipment.
Details of various types of fire fighting systems are given in Section 10 of this Guideline.