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Factors That Affect Air Electrical Strength During Grass Fires

Question:

Describe about the potential impact of grass fires under High Voltage power lines. 

The forest as well as Agricultural areas often crossed by the bare power lines . The control of high amount of flames and dense smoke in the lines vicinity due to air electric strength and  in brazil, mexico, canada, USA, south africa, and australia the probability of ground fault was being considered. In the above countries fire in Forest, Grass, Sugar cane /Bush ravage of huge area which often put at risk the reliability of power line. The unusual danger in environment condition of Overhead line and During Persian gulf war Electrical or Electronic equipment were eminent. The outage of line due to occurance of Forest fires ,were seen at poland . The early on studies of fire in the electric field was being worked from malinowski ,haber in the year 1920. The effect of local fire on the air dielectric strength was examined at wroclaw university of  technology by Janat . The fundamental study take the machinery response for decreasing  the air electrical strength  in occurrence of fire. Further guidance for safety of  public and Firemen were worked out in considering the fire provoked flashover  with a consequence of hazardous situation.

The  decrese in electrical strength of air under control of flame and smoke can be clarify considering three factors:

Air density reduction due to high temperature

Electric charge generated by flame

Smoke particles

Ground fault occures ,when flames crop up in the surrounding area of phase conductor. However smoke might foul the insulators which lead to flashover in the existence of moisture content generate due to fire combating process. This may create hazardous voltage potentials in near by surrounding area of towers. Hence it is desirable to let alone the area of radious within 10 m from the tower position.Frequently , ground faults will not occures if propane gas flames are at 2 m  minimum length from phase conductors in case of  500 kV line. However, the safety distance of clearance should be increased ,when flame and intense smokes are combinedly present . For 400 kv line the distance of safety should maintained at a distance of 3 m from the position of phase conductor.

When ACSR conductors (aluminum stranded steel reinforced conductors) are being exposed /heated by the fires: mechanical strength of conductor reduced lesser than the new conductor rated value. However Zinc coating on steel strands can be detached and galvanic corrosion should be considered. This tendency of corrosion in Aluminum strands in the inner layer and in bare conductor strand. Forest fire is an significant factor in reduction of durability of ACSR conductors in use.

The no of flashover occurred due to Sugar cane fire which was seen hundreds of years ago in the South Africa. One strategies was being used to solve the setback is, the development of a device which detect existence of fire under the possibility of fire flashover. The extreme rise in temperature and float particle  generated by the fire near an live line initiate enhancement of Corona discharges,that creates significant rise in level of radio frequency noise wave. To discriminate between radio noise wave generated due to fire, conductor’s  corona discharge and polluted insulator’s noise due to dry and wet condition of weather . In most of the suitable dry weather , high noise signal generated by fire are being distinguished  from the noise produced by the conductors, corona and due to polluted insulators. 

Prevention Measures for Ground Faults and Insulator Fouling

The flashover of fire mechanism air act as an isolated medium because of its dielectric properties between the live conductors  and the ground placed below it. During occurance of fire the air properties get changed to smoke particles which filled the desired space between the ground and the transmission lines that could result in electric discharge /flashover that was occurred  . That normally refer to a lines fault/ flashovers. During fire induction flashover in power lines is extremely dynamic and complex also. Authors explained the phenomena in different source (sukhnandan , Hoch 2002). To prevent the spread of fire on transmission lines in which early on fire detection data is desired for Bushfire conference  occurred in 2006 ,Brisbane 6 to 9 June 2006 which was satellite based primary warn to fires that reduce fire /flashover in  transmission lines located and  provides additional information basing on the temperature as well as size. In past Eskom lines the manager was follow the information from local residential area about occurrence and position of fire.

In Fire underside Transmission lines, the ignition source of  fires play an vital role for  considering the calculation of fire risk.  In Fynbos occurance of fire is 20% and in  Kruger National Park the vegetation is 10% which are ignited through natural source like lightning where human play a major origin of fires according to (Bond 1997). Awareness and proper prevention as well as suppression of fire must  involve different program of fire management .National Veld as well as forest fire act ( 101- 1998) play an  important role in  communal involvement for doing well prevention and strategic suppression of fire. Most of the fire burn involved in South Africa cause by different activities which are crop harvesting  for example sugar cane, fire break preparation, burn of refuse and arson also. Cultural motive like the conviction , good grass fires will cause good quantity of  rains are essential evidence in case of rural areas. Grass fire will exceed amount of bushes and forest fires also, but the last are much spectacular and is reported as more extensive in  media . From the report that received on fires touching both electrical utility area and commercial forest industries area,  fire on grass will frequencies come into view which is higher in case of South Africa than countries like australia - south america and united states(US). In  forest area  approximately 90 thousand ha in the South Africa was reported 600 fires per year, where as in Australia’s forest of similar size only 36 fires were traced for same period of time (as Oosthuizen pers comm. of 2003). The fact was confirmed further by  report that received from  Australian powers utility and TransGrid. Outages that caused by bush fire, few lines outages due to grass fire. Lightning is the main source of power outage. The bushfire outage numbers are analogous to lightning but severe bushfires was only occured around once in every five year. (Turner-pers. comm.-2003). The fire which frequency is of  low intensity,i.e. the  grass fires in theSouth Africa is very high than the  above quoted case quoted.  

Impact of Fires on Aluminum Stranded Steel Reinforced Conductors

Methodology of Advanced Fires Information System

The Advance Fire Information System methodology (AFIS) was being developed like a service module of  Wide Areas of Monitoring Information Systems (WAMIS), that aimed to convey fire informations product to the researchers, the agency of Fire Protection  and Disaster managers in all over South Africa will bear the effective decisions maker for monitoring natural  fires and manmade fires also. AFIS is the initial close to real time Operational satellite monitoring  fires system in South Africa. The architecture of the system was generally based upon  MODIS Rapid -Response- Web of  Fire Mapping system that developed at (University of Maryland). The CSIR have recently developed the AFIS II that is running basing upon a fully operational compliant architectures(OGC).

The fire detection  satellite that perfectly designed, are capable of spoting very small fires over a large area regularly that does not subsist yet. The only choice is  making use of recent satellites which is near and middle infra- red spectral band  for detection of fires. Polar orbit satellites has the gain of detecting undersized fires but at a very minimum overpass frequencies, while the geostationary satellites has the advantage of regular views over a large area (with in every 15 minutes with the MSG), where as with a very low resolution, it can only detect large quantity of fires.  For making use of the benefit of high resolution image(MODIS) and regular view from the MSG, two satellites sensor has been united within AFIS.

The two satellites MODIS are  the polar orbit, that  moving around  North and Southern Poles of  each and every 98 minutes at the time when the earth is rotating  from the west to the east. The Terra scan in the South African regions between 10 to  11:30 am where as Aqua scan in afternoons between the time of 14:00 to 15:30 pm. Each of the present satellite also scan the region at the time of night (i.e.Terra at time -22:00 pm and the Aqua at- 03:00 am). Validation of the result indicate , many amount of  biomes with the minimum flaming (between800-1000K) fire dimension typically visible at 50% probability with the MODIS is in the order  100m² (Giglio L.- et al.- 2000).

A geostationary satellite  MSG is that scans the Africa continent in every 15 minutes in the direction  south to north . The biggest restriction is the coarse resolutions that  limits the detection of minute fires. Validation for the minimum Bush-fires conference occurred in( 2006) – Brisbane: 6 to 9 June( 2006) that  Provide satellite based early on warning of  the fires that  reduce the fire flashovers in South African transmission line detectable fire of size for the MSG in South Africa is now currently being for research. Validation in USA on a similar satellite was shown a detectable size i.e. in a region of 500m² but  angle of scan, Biome,position of sun , temperature of  land surface , cloud covering, amount of smokes  and wind’s direction that should be the last determination factor (Prins- et al.- 2001). The percentage of fires detected by AFIS before the fire flashover had occurred.

Detection and Prevention of Flashovers in Power Lines during Fires

Fires occure under the power lines may cause the  mid-span of  flashovers with a consequent risky step of potential. During the fire fighting activity the guiding standard for safety issues of the firemen are to be follows:

The action of fire fighting is in the area of operational power lines (without line de-energization) and is permitted if :

the fire that not get to the ground  affected areas underneath the wire,

the burning of fire under the wire

the gaps present between the wire and also in the top of the flame i.e.  larger than 3 m length(which is valid for a line of 400 kV )

  • If the fire of high flame is being detected in direct area of operational line, whose utility is to be  called for  de-energize the affected lines of power . For a period when the line get energized, the unsafe steps potential zones should be assessed  based on the table no 1.
  • The area of reach that within 10 m from the towers should be let alone at all the times to defend against the risks of the flashovers of the insulators under wet and polluted environment  that generated due to the flames,fire fighting and  dense smokes.
  • The electrical as well as mechanical deterioration of the line’s conductors which are to be taken into consideration.

Safety advices for the fires near the power lines ,for  safety, at the time when there are fires closed to the powerline that remember:

  • Keeping the personnel, vehicle and the attachment with a distance of at least 25m from powerline.
  • Electricity, particularly at a high voltage can be ‘jump’ across an air gap of several metres . This may means that, the direct contact with  high voltage wires will not mandatory for producing a potentially lethal result.
  • Smoke can be act as conductors. Fires that burning on / near the powerline region can significantly increased the scope of flashover occurance.
  • Don’t count up on the rubber tyres of  vehicles to stop flashover from happening.
  • Wires present on the powerlines can sag to lower end in times of maximum demand, higher temperature and high spread of fire, reduction of ground clearance level.
  • Don’t build up stocks, windrow or mound combustion material under a high voltage lines.
  • Exercise of cautions if use of powerline’s easements for the access of  fire locations  as convenient firebreak and as a split from commence  of  back burning operation or  a protection areas in firestorm. 

Electric fence system in urbanised environment-

  • That is initially published in year1832, Chapter no 7 of “Domestic –Manners- of -Americans”by  the author Fanny - Trolope who describes a pattern of wires which are connected with  electric machines that used to look after a display i.e. called as dorfeuille's Hell in natural history in Cincinnati, western museum which was invented by her which was published in year 1870, Chapter no- 22 of “Jules- Verne's 20000 Leagues- Under- the -Seas”,it will describes the Lightning- Bolt of Captain- Nemo i.e. electrification  structure act as a suspicious weapon. that published in year1889, Mark Twain's novels A Connecticut- Yankee in- King- Arthur's- Court, use of an electric fence for the defensive purpose.
  • David Wilson obtained US exclusive rights 343,939 in year 1886, combined protection, alarm bells and telephonic communications. He was constructed a 30-mile electric fence as experiment that energized by water wheeling in 1888, but it was not unbeaten.
  • In the year 1905,the Russian army were improved the electric fences during the Russo and Japanese -warsat the Port of Arthur. In the year of 1915, during (World War- 1),the Germany army was mounted a “Wire- of -the- Death”e. an electric fence that accompanied by a border line between Belgium -Netherlands that prevent illegal movement of public across the border areas. This fences cover 300 km , that consist of various strand of Copper wires, which backed with a barb wire and that energize thousand volts. An estimate of  3,000 human wounded were caused due the fence as well as there was destruction due to live stocks.
  • Electrical fences that were used for the control of  live stockin the US in early years 1930 and electrical fence technique to develop both the US and NZ.
  • Early applications of the electric fences for livelystock controling was being developed in 1936 to1937 by NZ originator Bill Gallagher.That built from a car ignited trembler coils , Gallagher was used a device that keep the horse from the scratch against car. Gallagher in later was started for improving and marketing the design. In 1962, a New Zealand inventors, doug Phillips invented the non-short able electrical fence i.e.which based on capacitance discharge. That considerably increase the range of electric fences that could  used from few hundred metres  35 km  and that reduce the cost of fence more than 80%. The non-short able electric fences that  implemented by Phillips by 1964 was pretend by different plastic products in NZ firms Waikato- of- Electric- Fence. The above ideas were being  replaced by ceramic with the plastic insulator. Different varieties of plastic insulator are  used on farms all over the world .
  • By the year1939,a public safety of concerns in the US was impelled the Underwriters' - Laboratoriesfor the publishment of  a bulletin on electrical shock from an electric fence,that leads to ANSI/UL level of standard No- 69 for the electric fences controllers.

In  year of 1969 ,Robert- B. Cox, who is a farmer of Adams Countys ,  Iowas , that was invented with an improved electric fences brackets and was being issued in United States of  Patent No- 3-516-643 on the date June 23rd, 1970. The bracket that improved the electrical fences that keeps the wire as high enough and above ground and is far enough  from the fences to permit the grass and the weeds that breed near the wires to be shear. The brackets that attached to posts by that may be known as Pivot -binds or  the torsion-lock. The weights of  bracket , the append insulators and the electrical wires that attached to insulators to the bind of the brackets to post.

  • Poly-ethyleneinsulator replace the porcelain insulator, in the begin of   Poly-ethylene is much more cheaper as compared to porcelain and is also less breakable.
  • Improvements of electric designs of fences energizer are often known as "charger" (i.e.USA) , "fencer" (in UK).
  • Changes of In case of some authority, with certain types of electric output for fence were illegal from ( 1950s /1960s). In another areas, signage required and other possible restrictions that  are limited by the usabilities. Many of the US cities that continues in having obsolete laws that prohibits electric fence to avoid agricultural fence from the entering  cities . Houston of Texas for an example will changed the order which prohibit electric fence in year 2008.
  • Introduction of a highly tensile (HT steel) fences wire in year 1970s in NZ and in 1980s in United States(US).
  • Beginning of a synthetic webb and a rope like fence material that woven with a fine conductive wire.
  • Designing of a moveable fences component, like Tumblewheel.  

References

Lanoie, R., Mercure, H.P.(1989). Influence of forest fire on power line insulation (paper 30.06 ,6th Int). New Orleans: Symposium on High Voltage Eng.

Vosloo, W.L., Holzhausen ,J.P., Britten, A.C.(1991). Journal Electrochemical Society: WIDLICKI Z , Wrocław Distribution Utility: private information . Research into the detection of fires under high voltage lines ,paper 41.12, 7th Int.

(1992, july). The Kuwait environment and its effects on electronic materials and components , pp. 2058-2066  .

Lawton, J., Weinberg, F.J. (1964). Proc. of the Royal Society.Maximum ion currents from flames and the maximum practical effects of applied electric fields, vol. 277 A, pp. 468-497 [6].

Janat, M.(1991). Ph. D. thesis: Wroclaw University of Technology. Influence of localized flame on dielectric strength of air

 Mousa, A.M.( 1990 jan). IEEE Trans. on power delivery. Protecting fireman against fire-induced flashovers, pp. 297-302 [8]  .

Fialkov, A.B., HOMANN , K.H. (2001 Nov). Combustion and Flame: WEST H.J.Large molecules, ions, radicals, and small soot particles in fuel-rich hydrocarbon flames part VI: positive ions of aliphatic and aromatic hydrocarbons in low-pressure premixed flame of nbutane and oxygen, pp. 2076-2090 .

Mulan, D.W. Mc.(1978). IEEE-PES Winter Power Meeting: New York 1978.Fire induced flashovers of EHV transmission lines, paper A 73-047-2 [10] .

Avila , J.L, Robledo,A.Martinez.(2001). Symposium on High Voltage Eng: ISH Bangalore .Effect of polarity on DC flame breakdown. , pp. 310-313.Int.

Xiang, Hu, Jiazheng,Lu , Xiangjun, Zeng, Hongxian, Zhang.(2010). Journal of Elec1ric Power Science And Technology. Analysis on transmission line trip caused by mountain fire and discussion on tripping preventing measures.

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