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4. HEATING, VENTILATION AND AIR-CONDITIONING
4.1 Air Circulation
The correct air circulation or number of air changes per hour is essential to ensure comfort of substation operations and maintenance personnel. The number of air changes depends on the number of personnel and size of the room but a minimum of four fresh air changes per hour is recommended. In addition, it’s necessary to prevent the build-up of dangerous gases such as may occur in a battery room using vented cells. Typical air changes per hour for different substation building areas are listed below:
FIG. 9 Methods of earthing.
Power system earth (green/yellow) PE(green/yellow) PE(green/yellow) PE(green/yellow) Exposed conductive parts Exposed conductive parts TN Neutral and protective functions combined in a single conductor throughout system.
TN Neutral and protective functions combined in a single conductor in a part of the system.
TN Separate neutral and protective conductors throughout system.
TT Power system. IT Power system.
Substation Area Air Changes per Hour
MV and/or HV switch rooms 4_8 (30_60 for smoke removal) LVAC and/or DC switch rooms 4_8 Control and relay rooms 4_8 Battery rooms 6_10 Control and communication rooms 4_8 (overpressures via a filter may be specified to prevent ingress of dust into sensitive equipment partly depending on the equipment enclosure protection (IP) rating and need for adequate heat dissipation) Offices 4_8 Toilet and wash rooms 10_12 Mess room 10_12 Corridors 3_6 Consider a 21/3.3 kV transformer housed in a transformer pen (7.5 mx 6mx11.7 m). The maximum ambient conditions are 28_ C and the design engineer has specified a maximum pen air temperature of 34_ C. The trans former enclosure has louvres to the atmosphere along one side (6.0 m3 10.0 m) with 30 m2 open space. Air circulation is assisted by a ducted ventilation system. What air flow is necessary to maintain the trans former pen within the specified upper temperature limit?
The necessary ventilation calculations may be based upon the 'Sol-Air' temperature concept as described in Section A2 (pages 69 and 70) of the Chartered Institute of Building Services Engineers (CIBSE) Guide together with the derivations. The formulae are incorporated into a spreadsheet program to give the number of air changes required. As an alternative the total summer maximum heat gain may be determined by using W/m^2 figures as described in Section 4.2.3. The necessary ventilation air flow heat transfer QV is then calculated with a simple thermal heat balance equation:
For practical purposes c?/3,60050.33. It should also be noted that the major element of the heat gain in this example will arise from the trans former losses rather than the solar heat gain through the building fabric.
All ductwork must be designed in conjunction with the fire safety engineers in order to ensure that the fire zoning is reflected in the ductwork.
Zonal control is usually achieved by using automatic fire dampers where ductwork passes through floors or across fire zone walls. Dampers should have 1- or 2-hour ratings and be released from a fusible link or by a solenoid interconnected into the fire detection system. This is especially important where migration of smoke from one zone to another could be a substantial hazard. The need for zonal control also applies to cable trenches running through different fire zones within the substation building.
4.2 Air-Conditioning
4.2.1 Introduction
The internationally recognized standard used for the design of Heating, Ventilation and Air-Conditioning (HVAC) is that produced by the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE). However, in the UK the standards usually acknowledged are those produced by the Chartered Institute of Building Services Engineers (CIBSE). This is a specialist subject and therefore only a brief introduction is given in this section such that the power engineer can correctly specify requirements and understand the terminology used by HVAC engineers.
Areas of substation buildings should be air-conditioned in the following ways:
Substation Area | HVAC Requirements
Switchgear rooms Ventilation with air tempering to prevent the formation of condensation on cooled surfaces is the ideal approach. The most controllable solution is to temper the supply air using electrical or low pressure water coils. Alternatively, the switchgear should be specified to operate at ambient temperatures up to 40_ C and 90% relative humidity with ratings calculated accordingly and panel heaters should be installed to prevent condensation and freezing.
LVAC and/or DC switch rooms -- As for MV and HV switchgear rooms.
Control and relay rooms HVAC. If because of economies switchgear and control and relay panels and operators' desks are all provided together in a single room, then air-conditioning will be required.
Battery room
Extract ventilation with high quality acid fume resistant fans.
Control and communication rooms Manufacturer's standard light current equipment often demands a stringent environment. Such sensitive equipment should be maintained typically at 20_C and 50% relative humidity.
Offices -- HVAC to between 20_ C and 25_C with relative humidity maintained between 40% and 60% for comfort.
Toilet and wash rooms Extract ventilation fans with supply air drawn in through transfer grilles to ensure smells don’t enter the working area.
Mess room Extract ventilation discharging to the outside with air transfer grilles as described for the toilet and wash rooms. Possible HVAC depending on budget.
Corridors
Air-conditioning if in a manned substation where people are frequently moving between rooms.
Note: Depending on the volumes of the rooms and therefore the volume of air to be moved to achieve the desired air changes per hour when applying air-conditioning, noise may be an issue. As well as continually occupied spaces, account must be taken of operatives working in substations, switch rooms, etc., during maintenance periods. In the UK the CDM Regulations (require that a noise assessment be made to ensure that the Noise at Work regulations are not breached during periods of occupancy.
4.2.2 Calculation Methodology
Calculating the cooling load involves estimating and compensating for the heat gains associated with radiation from equipment (usually taken under full load conditions and including lighting) and people in the room plus solar radiation effects. The cooling load consists of the 'sensible' load associated with the cooling required to maintain the desired temperature and the 'latent' load which is necessary for dehumidification and the release of latent heat of vaporization. Detailed calculations therefore involve the orientation of the room walls relative to the sun, wall, window, ceiling and floor materials and thickness, coefficients of heat transmission (K factors in W/m^2 _ K), tempera ture difference, air infiltration, the number of people (that produce heat and moisture), and the heat produced from equipment.
Because of the traditional dominance of North American manufacturers in this field, air-conditioning plant capacity is often described in imperial units of BThU/hour, being the measure of heat removal; 1 BThU is the amount of heat required to raise the temperature of 1 pound of water by 1_F (12,000 BThU/hour is equivalent to 3,024 kcal/hour).
Note that 12,000 BThU/hour is called 1 ton of refrigeration (to freeze 1 ton of ice per 24 hours).
1kW 53,413 BThU 1kW 5860 kcal 1 kcal53.968 BThU
4.2.3 Simplified Cooling Load Estimate for Window-Mounted Air-Conditioners
It’s sometimes necessary for the substation engineer to have a rough estimate of the air-conditioning requirements before detailed calculations are made. The room dimensions are recorded. Doors and windows are assumed closed to reduce unnecessary infiltration and exhaust only when necessary or under smoky conditions. All windows and glass areas exposed to direct sun light are assumed to have blinds, awnings or shades and an additional heat gain is added where windows face summer afternoon sun. Roofs exposed to direct sunlight are assumed to have at least 50 mm insulation material and all false ceiling space is assumed to be well ventilated with outside air. A further heat gain is added to compensate if this is not the case. The cooling load estimations given in TBL. 5 are then made.
For example, consider a control and relay room in a normally unmanned Middle East distribution substation 10.8 m long x 7.3 m wide x 4.1 m high.
Air-conditioning is a specified requirement and the initial rough estimated cooling load would be:
Floor area=78.85 m2 Control room volume=323.25 m^2 Temperature to be maintained in range 25_C63_ C New energy codes in the UK specify maximum coefficients of heat transmission (K values in W/m^2 _K) for different constructions and materials together with typical heat requirements (q in W/m^2) for various types of building. As an initial estimate, assume the cooling load requirement from the table giving simplified estimations above is 320 W/m^2 giving a cooling requirement of 320378.85525 kW. This may be checked against a slightly more rigorous approach taking into account individual solar and equipment heat gains:
m^2 W/m^2 Total, W (a) Windows and doors under direct sunlight (i) South a direction 25.55 2x0 5,877 (ii) East direction (double door) 5.37 26 1,397 (b) Outer walls under direct sunlight 38.91 50 1,946 (c) Other outer walls 74.21 25 1,855 (d) Flat roof 78.85 60 4,731 (e) Floor 78.85 9 710 (f) Lighting 720 (g) Equipment 6,300 23,536W a
This assumes a location north of the tropics.
Window-mounted 24,000 BThU air-conditioning units are standard Electrical Supply Utility store items. 23,536W523.536 33,413 BThU 580,316 BThU.
Therefore, number of units required 580,316/24,000 53.3. Therefore four window mounted units would be sufficient. Following such a calculation the building civil engineers or architects would then become involved for more accurate estimations and to detail the aesthetic appearance of the system. Such estimations assist in the sizing of the substation auxiliary transformers at the early planning stages of a project.
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TBL. 5 Simplified Cooling Load Estimations for Window Air-Conditioner Selection Type of Use W/h/m^2 Floor Area BThU/h/ft^2 Floor Area Notes Control and relay rooms (load depends on manning level and heat emissions from equipment) 250_380 75_120 Minimum fresh air requirement per person depends on outside temperatures and level of pollution (smoking, etc.). Use 20 m^3/h per person for outside temperatures 0_25_ C and assumption that smoking is not allowed.
Offices 200 60 Mess room 160_200 50_60 Allow 300 W per person Corridors 100 30
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4.2.4 Air-Conditioning Plant
'All-refrigerant' air-conditioning systems are normally sufficient for substation control buildings. The advantages of such systems are that they are compact, cheap and simple to install. However, they require a relatively high level of maintenance, have a relatively short working life, and single package units may be noisy. The classification is confined to 'single package' room air-conditioners and 'split' systems in which the cooling effect is produced by refrigerant gas being compressed and passed through an evaporator whereby it absorbs heat. Single package units are typically sized up to 24,000 BThU and split units up to 64,000 BThU with air volume flows of 200-1,000 m^3/hour. The units come complete with controls and protective devices. In the single package unit air is drawn through a filter into the unit by a centrifugal fan. The air is cooled as it passes over the evaporator cooling coil and discharged into the room. The most common form of such units is window mounted. A room thermostat actuates the system. Such units may also contain an electric heating element (ratings between 1 and 4 kW) for use as a fan heater in winter conditions.
In a 'split' air-conditioning system the condenser and evaporator sections are supplied separately, usually for interconnection by means of flexible pre charged refrigerant piping with quick connection fittings. The condenser is mounted outside the building (to reduce noise and allow heat loss to the outside air) while the evaporator section with a fan may take the form of a free-standing console mounted inside the room being air-conditioned. A suitable water piping system is necessary to carry condensate to an external drain or soakaway.
Local 'air-handling' units supplied with cooling water or direct refrigerant expansion as the cooling medium coupled with electric or low pressure hot water (LPHW) heater elements using a fan fresh air supply are used for the larger substation buildings. Supply and return ductwork provides a uniform air distribution within the different areas being served. Such units may be provided with humidifiers, efficient air filtration and can generally control the internal environment within close limits of temperature and humidity.
'Fully ducted' air systems connected to a central substation air-handling unit are used where a number of similar rooms are to be air-conditioned or where space prohibits the installation of air-handling units adjacent to the air-conditioned area. It’s essential to adequately filter all input or make-up air in order to avoid dust build-up and possible premature equipment failure.
Energy efficiency is increased by recirculating a proportion of already cooled or heated substation building air back into the air-conditioning system. The disadvantage of all air-ducted systems is the space requirement for the ducts.
Larger 'all-water' plants are unlikely to be necessary for substation buildings. Piped, heated or chilled water derived from a central refrigerant or boiler plant is circulated to different parts of the building. Fan coil heat exchanger units dissipate the heating or cooling effect via air grilles in duct work into the rooms.
4.3 Heating
Heating is not normally required in climates where the minimum ambient temperature does not fall below 15 C although units may be installed where close control of temperature and humidity is necessary. The following methods are available:
'Air heater' batteries using electrically heated elements operated in stages, or low pressure hot water coils, located in air-conditioning ductwork.
'Electric space heating' from room heaters.
LPHW space heating using radiators fed by circulating hot water.
Normally the air heater option would be used in conjunction with an air-conditioning scheme. The heat gains from personnel, switchgear and control equipment are not normally taken into account when sizing heating plant so as to cater for conditions when the substation is not operational. Anti-condensation heaters with ratings of a few tens of Watts are often specified for installation within switchgear and control panels.
5. FIRE DETECTION AND SUPPRESSION
5.1 Introduction
Heat, fuel and oxygen are required together for a fire to exist. Removal of any of these components will extinguish the fire. The fire safety philosophy is to:
1. Safeguard personnel.
2. Maintain the functional state of the substation.
Substations have a comparatively low fire risk because the designs are such as to introduce little chance of an internal fire spreading to an adjoining property or causing danger by smoke contamination. However, certain equipment (traditional bulk oil or low oil volume indoor switchgear installations) and materials (transformer oil, cable joint compounds, solid forms of insulation, etc.) may ignite and therefore fire detection and suppression systems should be incorporated. Further, special precautions have to be taken concerning the spread of fire caused by oil leakage from transformers or the oil filled types of switchgear. This section describes general fire detection and suppression schemes for substation installations covering fires originating from transformers, switchgear, control and protection equipment and cables
5.2 Fire Extinguishers
Hand or trolley mounted fire extinguishers are the cheapest form of manual fire extinguishing. Such extinguishers should be mounted in the substation control or switchgear building as well as in the switchyard. The types of commonly available fire extinguishers and their usage under different conditions are as shown in TBL. 6. See BSEN3, BS7863:1996 and BS5306.
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TBL. 6 Commonly Available Fire Extinguishers and Their Usage
Type Color Code Bands | Application Extinguishing Action Water| Red Fires involving wood and other solid, organic- or carbon-based material.
Cools fuel to below the temperature at which sustained flaming occurs.
CO2 Black Mainly electrical equipment fires.
Cools and makes the atmosphere inert.
Dry powder Blue Flammable liquid fires/electrical fires.
Inhibits the chemical reactions in the flames.
Halon (BCF) a Green Flammable liquid fires, electrical fires and fires in carbon-based solids.
Same as dry powder but also has a cooling effect.
a Halon has now been effectively banned for future installations because of its ozone depletion potential. The EU regulation 2037/2000 required mandatory decommissioning of existing halon fire extinguishing systems by December 31, 2003. There are a number of inert gas products that can be used instead. Use of fluorinated gases, some of which are also currently available as an alternative, is controlled by an EU directive EC842/2006.
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5.3 Access, First Aid and Safety
5.3.1 Access
The exits from substation control and switch rooms must always be kept clear. Panic release bars should be fitted to the doors such that the doors will quickly open outwards from the inside by pressure against the release bar.
Doors should be sized greater than 750 mm x 2,000 mm and areas at the rear of switchboards should not be less than 12 m from an exit. Doors between equipment containing bulk oil should have a 2-hour fire resistance rating.
Two exits should always be included in the layout design (especially in switchgear rooms containing switchboards greater than 5 m long) such that escape is possible by at least two different routes from any area in the sub station building. In this way the chance of personnel being cut off from an exit by the fire is reduced. Emergency lighting fittings should be installed over each exit.
5.3.2 First Aid and Signage
Fire and emergency signage should be installed in accordance with the appropriate national standard. A sample of signs in accordance with BS5378 and BS5499 is shown in FIG. 10. It should be noted that in accordance with the European Regulations and the UK Health and Safety Executive rulings it’s necessary to examine the risks associated with any engineering design. The Electricity at Work Regulations require precautions to be taken against the risk of death or personal injury from electricity in work activities. Basic first aid kits (first aid dressings, medication, eyewash, blankets, etc.) and safety barriers to screen off work areas should therefore be available on the substation site. Signage describing the actions to be taken in the event of electrical shock should also be clearly on display.
It should be noted that modern legislation requires a risk assessment to be made of the activities to be performed in the substation building or com pound and the standards, directives and regulations given in TBL. 7 are important.
FIG. 10 Fire and emergency signs.
5.3.3 Good Housekeeping
Manual or automatic fire detection and suppression systems must be regularly maintained to ensure their effectiveness. A regime of maintenance checks must be included in the substation operations procedures. In addition, regular disposal of waste materials (e.g. oil cleaning rags, etc.) must be enforced together with careful removal of smoker's materials or a ban on smoking (especially important in cable basements).
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TBL. 7 Relevant European Standards, Directives, or Regulations
Standard, Directive or Regulation | Description | Notes
UK Fire Precautions Act 1971 Covers emergency lighting UK local authorities or fire officers will look for emergency lighting compliance with BS5266 Part 1: 1988.
89/106/EEC The Construction Products Directive Concerned with products used in construction. Introduces six essential requirements:
_ mechanical resistance and stability
_ safety in case of fire
_ hygiene, health, and environment
_ safety in use
_ protection against noise
_ energy, economy, and heat retention
89/659/EEC The Framework Directive General enabling directive.
89/654/EEC The Workplace Directive Covers a broader range of premises than the UK Fire Protections Act; imposes legal obligations for compliance upon the employer or Electrical Supply Utility rather than the Fire Authority and applies retrospectively.
92/58/EEC The Safety Signs Directive Legalized in the United Kingdom by the safety signs and signals regulations 1996.
Introduces new symbols for safety exit signs replacing those previously defined in BS5499 Part 1: 1990. For example, pictograms rather than wording are introduced onto signs, and an exit sign shows a 'running man' with an arrow pointing toward a symbol for a door.
EC 842/2006 On Certain Fluorinated Greenhouse Gases Covers control, containment and recovery of Fluorinated Gases (F gases).
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5.4 Fire Detection
5.4.1 Manual Call Points
The fire may be detected by personnel manning or working on the substation site at the time of the fire. The alarm may therefore be raised by the breaking of glass at a manual call point. These should be mounted at approximately 1.4 m above floor level and located on exit routes both inside and outside the sub-station building so that no person need to travel more than approximately 30 m from any position in the building in order to raise the alarm.
5.4.2 Sensors
Two types of detector or sensor are found in substation applications:
1. Heat detectors
Depending upon the type these sense changes in the thermal environment very locally or in the immediate vicinity of the unit. Bimetallic strips and thermistors are commonly used devices in such sensors. Maximum mounting heights depend upon the grade of the detector but lie in the range 6-13.5 m. In order to differentiate between the normal temperature changes and fire conditions the sensors detect the temperature above a preselected limit and the rate of rise of temperature (which will be rapid in the case of a fire) in order to initiate an alarm or automatic fire suppression system.
2. Smoke detectors
These sense small particles of matter or smoke in the air which are the result of a fire. Ionization detectors work on the principle that the current flowing through an ionization chamber reduces when smoke particles enter the chamber. Electronic alarm circuitry detects this change and initiates the alarm.
Optical detectors note the scattering or absorption of light due to the smoke particles in a light beam. Maximum mounting heights are typically 10.5_15 m. It’s considered that optical types are best suited to detect slow smoldering fires where large smoke particles are formed and that ionization types are best suited for fast burning fires where small smoke particles are formed. Smoke detectors tend to give a faster response than heat detectors but may also be liable to give more false alarms. Because of this and since prediction of the fire type may not be possible both types of smoke detector are often found in a single installation together with heat detectors.
3. Radiation (flame) detectors
These detect ultraviolet or infrared radiation and are mainly suitable for supplementing heat and smoke detectors or as a general surveillance of a large switchyard area.
5.5 Fire Suppression
It’s important to avoid anomalous operation of a fire detection and suppression system. Therefore a 'double knock' system is usually employed where two sensors have to detect the alarm before the suppression system is activated. Radial circuits are used with the detectors effectively cabled in parallel together with an 'end-of-line' resistor. The circuit is monitored for both short circuit (typically less than 1,000 Ohm) and open circuit conditions and a maintenance alarm raised if the circuit is out of tolerance. Sensor circuits are arranged on a 'zonal' basis in order to isolate the fire into certain areas. For example, the substation switchgear room may be split into two, both physically (with a fire wall) and electrically (with a bus-section switch).
Each half of the switchboard would then be covered by a separate zone of the fire detection and suppression system. In a similar manner the control and relay room might also be covered by a separate zone of protection. The zone where the fire has occurred is indicated on the fire detection control panel. The panel sends signals to alarm sounders to alert personnel and to send signals to the automatic fire extinguishing systems or to shut down the HVAC plants that could spread the fire. Both inert gas and CO2 gas systems require the rooms to be enclosed. 'Fire stopping' is the term used to describe the sealing of small openings in fire barriers. Ventilation louvers should be fitted with temperature sensing or remote controlled closing devices. It’s not considered essential for modern gas insulated switchgear to be housed in rooms with fire suppression systems.
Halon 1301 gas, previously used as a fire extinguishing medium in sub stations, is an ozone layer depleting gas and most electrical supply utilities now ban its use. There are available a number of inert gas mixtures of argon, nitrogen and carbon dioxide, and also a heavily fluorinated compound with the generic term HFC227ea, any of which is used as a replacement.
(HFC227ea breaks down to give hydrofluoric acid under severe fire conditions, and as an F gas is covered by EC842/2006.) Alternatively, the older CO2 flooding systems (which require a larger concentration of gas for the same extinguishing effect) may be used.
Gas bottles are suspended from the ceiling in the room being protected, or a central set of cylinders with a piping system to ceiling mounted nozzles in the different rooms may be employed. The required concentration of gas to extinguish the fire, while small, is considered dangerous to personnel. It’s therefore considered necessary to avoid personnel being in the zone during gas discharge.
This is an absolutely essential requirement for CO2 flooding since the necessary 28% CO2 gas concentrations will be lethal. A door/gas suppression system interlock is therefore necessary such that the suppression system is deactivated whilst maintenance staff are working in the room. In addition a delay between alarm and suppression activation is built into CO2 flooding systems.
Water sprinkler systems may be employed in cable basements. The normal sprinkler has a liquid-filled glass bulb valve that is activated by the expansion of the liquid and shattering of the glass. This is not sufficiently fast for cable fire protection. Therefore the glass ampoule is fitted with a 'percussion' hammer which is activated electronically from the smoke or heat detectors.
The fire resistant properties of cables are described in Section 12. Cables may be coated with protective paints and mastics to reduce fire risk without affecting cable current-carrying thermal capacity. Intumescent coatings swell up over an elevated temperature range to form an insulating foam layer.
Automatic water spray systems may be used for transformer protection in outdoor areas where the gas would leak away. The oil is contained in a bund as part of the transformer civil works installation design. The water spray cools the oil to a temperature below its fire point at which sustained flaming can occur. Other techniques involve oil temperature sensors within the transformer. Upon activation the transformer is electrically isolated and a small proportion of oil drained from the core. Dry nitrogen gas is then injected at the base of the transformer which bubbles through the oil causing mixing, heat transfer within the oil and lowering of oil temperature.
5.6 Cables, Control Panels and Power Supplies
It makes sense to ensure that the cabling associated with the substation fire detectors is both flame retardant and flame resistant if it’s to operate successfully and reliably initiate an alarm. Mineral insulated copper sheathed cable is therefore favored. An oversheath is not essential, but if used should preferably be LSF and colored red to differentiate from other services.
Other types of 0.5 mm^2 or 1.0 mm^2 minimum cross-section (depending upon load) copper conductor PVC or EPR insulated cables should only be used in conjunction with a suitable conduit, trunking or ducted system.
Control panels with key access should be located in an area of low fire risk close to the entrance of the substation building or guard house. The panels should display the status of each protected zone, detector faults (insulation or loop resistance, detector removal, rupture of any fuse or operation of protection devices associated with the system) and power supply. A fire alarm must take precedence over any other indication that the control panel may be giving. Key switch isolation facilities must be available for maintenance and test functions. The audible alarm generated within the control panel may be both locally and remotely sounded.
The fire alarm system should have its own battery-backed power supply with sufficient autonomy (say, 1 or 2 hours) for correct operation upon loss of AC supply and to provide an evacuation alarm for at least 30 minutes upon fire detection. The connection to the AC power source must be clearly labeled 'Fire alarm: don’t switch off' and arranged such that continuity of supply is ensured. On larger substation sites it may be possible to integrate the fire alarm system with any local standby generation.
6. SECURITY
Substations are often located in remote locations and such facilities are unlikely to have permanent staffing. Typically, physical security to prevent damage to plant from unauthorized human intrusion or from animals will involve:
_ delay/deterrence,
_ detection,
_ threat assessment,
_ communication, and,
_ response.
The normal approach to substation security (and other transmission and distribution system components) is to first carry out an identification of the critical nature of the infrastructure involved. The process for such a risk-assessment methodology should take into account the possibilities for loss mitigation from plant redundancy or transmission and distribution systems operations. Critical infra structure may be defined as being that which if severely damaged or destroyed would have a service impact on a large number of customers for an extended period of time and to cause a significant risk to public health and safety.
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TBL. 8 Risk Approach to Security Installation
Security Measure/Level of Risk High Medium Low Fencing X X X Card keys X Special locks X X X Security patrols X CCTV X Door/gate monitors X X Motion/vibration/pressure pad detectors X X
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Such physical security is, in any case, an essential part of substation design (see Section 3) in order to assist in preventing safety accidents to utility personnel or unauthorized intruders. Of course, an intruder may have a variety of motives, other than just vandalism, for climbing transmission towers or entering a substation. These could include:
_ damage or tampering with/operating plant so as to cause damage, stealing,
_ posing a threat or
_ creating publicity.
Depending on the level of security required to match the importance or critical nature of the facility, security measures could include:
_ fencing, gates and barriers;
_ unique keying systems (smart locks, access cards, etc.);
_ security patrols;
_ authorized personnel identification (photo ID, etc.);
_ entry monitors and alarm systems;
_ perimeter alarms and surveillance systems (CCTV, etc.);
_ lighting (Section 2 above);
_ signage (see FIG. 10).
The application of such a risk-based approach to security will enable a rational distribution of resources to different substations within the network as illustrated in TBL. 8.
REFERENCE
1. North American Electric Reliability Council (NERC). Security guidelines for the Electricity Sector. 2004.