Electrical Infrastructure in Remote Areas. A Review of Potential Threats to Safety and Sustainability

Transcription

1 Electrical Infrastructure in Remote Areas A Review of Potential Justin Buskmiller 1, Larry Bentley 2 and Jon Fripp 3, Subject Key Word: Energy Key Words: Electrical infrastructure, power supply, power outage, blackout, wire grade Abstract: A properly designed, constructed, and maintained infrastructure is vital to bringing safe and reliable electric power to a community. With well-maintained electrical distribution, a community's ability to adequately address other problems-including lighting, sanitation, and food preparation- greatly increases. Dependable electricity opens up better possibilities for communication (i.e. cell phones) and computers become viable to own. This paper illustrates common problems encountered in assessing a community's power grid, and discusses techniques to deal with these problems. Examples are taken from two assessment trips to San Mateo, Belize conducted by Texas A&M's EWB chapter. Introduction This paper contains basic information on assessment of electrical infrastructure for poor communities around the world. The topics covered include determining whether electrical connections are official or illegal, assessing proper wire size(or gauge), dangers of low hanging, poorly insulated and illegally spliced wires, and the importance of officially sectioning the power grid. Electrical standards and surveys are touched on, while supplemental power was not considered in the paper. When a team visits a community with a goal to improve electrical infrastructure, it is important to bring proper instruments to measure electrical current and voltage, binoculars (which are useful in estimating wire size and condition as well as assessing connections and transformer information from the ground), safety equipment (including electrical gloves, goggles, and lock out material as needed), along with electrical tape and other insulating tools. Most of all it is helpful to bring someone with experience in the field. Official Grid vs. Informal Splicing The first step in assessing a community s electrical infrastructure is determining which parts of the infrastructure are official and which parts are informal. Official sections 1 Mechanical Engineering Student, Texas A&M EWB 2 Electrical Engineer Technical Mentor, Southern Methodist University EWB and North Texas Professional EWB, 3 Civil Engineer Technical Mentor, Texas A&M EWB, North Texas Professional EWB, and Southern Methodist University EWB Page 1

2 typically have customers paying for their electrical power through a formal grid, while unofficial areas are generally created by members of the community on an ad-hoc basis to get electrical power without formal approval or payment. Both can feature similar problems, but the strategies for dealing with these problems are different. If a formal grid is inadequate, communication with the local government or electrical company is the first step towards improving the grid. On the other hand, if the community gets its power from illegally spliced wires, direct communication and work with the community itself is preferable. Contacting government or electric company representatives can easily result in disassembly of whatever informal grid the community already has, doing real damage to existing infrastructure and any relationship with the community. Contacting government or company officials should only be done with extreme care in this circumstance. The easiest way to determine if electrical power is drawn from an official grid is to check for electric meters: the presence of an electric meter confirms that the power is being officially drawn and possibly regulated, whereas its absence generally suggests the opposite. Note that in some communities electricity is purchased at a flat rate, meaning some official lines will not have meters. Unofficially spliced wires (discussed later in this paper) are also a clear indication of unofficial power consumption. Discretion must be used in determining whether a wire was illegally spliced. For instance, wires roughly netted together, as in Figure 5, are likely unofficially spliced. On the other hand, wires cleanly connected by a metal crimp or a tight twist are more likely to be official. Often, one area will include an official grid spliced illegally to numerous surrounding locations. Wire Gauge One common problem with inadequate electrical infrastructure is the use of interior grade wire for house-to-house connections. The small diameter of interior wire causes significant voltage drop over these relatively long distances. When determining wire gauge, use Eq. 1 below E= 2 x L x R x I (1) Where: E is voltage drop (volts, v) L is length (ft) R is electrical resistance (Ω per ft) I is current (amps) Change in voltage equals resistance times current, but in this example the length of wire is considered twice since the current travels from the power source to the home, then back to the source. Page 2

3 Figures 1 and 2 Site in San Mateo, Belize, January 2013): Note small diameter interior grade wire often brings electricity from house to house. As an example, using 500 feet of copper wire that carry 50 amps of current and 230 volts, the wire will lose (using resistances for #1 and #10 gauge from Table A1 in Appendix A, from interfacebus.com) #1 gauge wire: 2* *500*50 = 6.2 volts #10 gauge wire: 2* *500*50 = volts With a 230-volt line, the interior grade #10 voltage drop is more than 20%, compared to the large diameter #1 gauge voltage drop of under 3% (by NEC standards, a voltage drop of 5% or less is deemed acceptable). This example illustrates the importance of using large diameter wire, but note that these are sample calculations only and should not be used by unqualified personnel. A licensed electrician should be consulted. Furthermore, smaller wires will heat up more than larger wires with the same electric current, making them a greater fire hazard. Without large diameter wire some devices such as motors or microwaves will likely not function properly, wasting power; this equipment can also be damaged by the heat. Additionally, interior wiring often uses insulation that is easily damaged in the outdoors by sunlight, which causes it to crack off. The remaining bare wire is hazardous to community safety. While it would be best if an electrician were consulted, switching out undersized outdoor wires to 0(aka 1/0 or "one ought") AWG or 2 AWG (the typical 100 amp service wire gauge), while expensive, will decrease voltage loss hugely, along with brownouts and often blackouts. See the appendices for more information on AWG and IEC R-20 wire size. Page 3

4 Low Hanging Wires and Power Poles Wires strung from one house to the next rather than being secured with power poles may hang one or two feet off the ground, while higher wires may still be within arm's reach of adults. A related problem is the prevalence of unstable power poles. These poles will likely fail in adverse weather or over time under regular use. Failure of the poles or their connections to the wires will likely lead to more wires at ground level and disrupt power delivery to homes in the related area. This low height could be dangerous if the wires are carring a significant load. Voltage difference from wire to ground is what forces the current through the body (low voltage is almost never fatal). Magnitude of electric current through the body, caused by a voltage difference, generally determines whether electric shock is fatal. This is especially relevant in any wet environment. Wet skin has relatively low resistance, so a given voltage differential results in higher electrical current when wet skin touches a wire. Rainy or swampy communities are therefore at particularly high risk of electrocution. Figure 3 and 4 (EWB TAMU San Mateo, Belize, January 2013): Wires hanging from the bush on the left are dangerously low and poorly secured. Right, this wooden pole will likely not hold wires up through inclement weather. Properly insulating wires can be an effective short term solution since well-insulated wires present a far lower risk of electrocution, even at a low height. Note that ground fault interrupter breakers or residual current breakers can also be used to prevent accidental electrocution by wire contact; however, these are likely too expensive for use in many poor communities abroad. The ideal long-term solution is high, secure power poles. Page 4

5 Unofficial Splicing One problem in power supply illegally drawn off the official grid is improper splicing. This exposes conductors, which is a safety hazard as contact to these can result in injury or death. Additionally, careless splicing creates connections that weaken over time due to corrosion and may deliver very low current. Adding new homes onto an existing grid without making provisions to deliver more power to the town as a whole pushes consumption above what can be supplied. This causes the electricity to decrease or shut off for many houses in order to meet the demands in other areas. Splicing also causes dramatic fluctuations in electrical current supply, a phenomenon noted by the EWB TAMU team during January Figure 5 (EWB TAMU San Mateo, Belize, January 2013): This power pole in San Mateo has illegally spliced wires, contributing to blackouts and brownouts. Safety around splices can be improved by properly insulating spliced connections. Tight winding or use of metal crimps can also improve splice longevity and lower splice resistance, and use of anti-oxidation pastes can minimize corrosion on splices. As an additional note, generally power poles use three lines: the hot line, which carries power to households, the neutral line, on which current flows from households to the earth, and the ground wire, which draws hazardous voltages off electrical equipment. Ground and neutral wires should not connect together except in service areas; this rule is sometimes be neglected in suboptimal electrical infrastructures, and should be addressed. Sectioning Equipment should be in place to turn off single sections of the power grid for maintenance or emergencies. This allows for maintenance and improvement without Page 5

6 having to shut down the entire power grid. While it is possible to turn off "sections" of an informal power grid, without well-kept records parts of the grid may remain powered on, leading to hazards(injury and death) that can be avoided with a formal grid divided into clearly defined and recorded sections. Survey Unbalanced power distribution is a common problem and an electrical load survey often serves as the basis for making adjustments. The goal of an electrical load survey is to determine the average daily electrical load for each house. This may be a multistep process, as electrical load used by each home will likely increase as power infrastructure improves. As part of the survey, privately owned generators need to be accounted for and regulated. Each unit must have a noticeable off switch, as generators connected into the power grid can electrocute people working on power lines if they are not powered off (additionally, turning grid power on can damage generators connected to the grid). Power generator capability, wire diameter, and transformer locations should all be thoroughly noted and recorded on a map so that infrastructure weak points are easy to spot. Optimally, an expert electrician should be contacted to determine the strength of the infrastructure with this data and to lead improvement and expansion. Standards Throughout the process of improving electrical infrastructure, certain standards must be adhered to. The National Electric Code or International Electric Code provide reliable standards; see Appendix A for a tables detailing NEC/AWG wire gauge and comparing NEC/AWG sizes with IEC sizes. Supplemental Power Supplemental power-possibly generated with photovoltaic panels for street lights or security lighting has the advantage of being possibly completely separate from the grid, making wiring simpler. However, it is expensive. It should also be noted that large reliance on solar power requires the significant complication of power storage for use at night or when weather obscures the sun. This paper did not assess the viability of supplemental power. Conclusion Recall that before confronting problems the grid should be classified as official or unofficial to properly deal with problems. Wire size, height, and splice quality are all issues that can effect power efficiency and community safety. Sectioning the power grid and an electrical survey are important for maintenance and improvement. By applying to the above mentioned methods and standards, the electrical infrastructure of a Page 6

7 community can be improved. This will increase community safety and give the community access to a wide array of tools for sanitation, lighting, food preparation, and a number of other applications. While these guidelines can be useful, the best and safest way to improve electrical infrastructure is to consult licensed and experienced electricians who have past experience. Consult or hire an expert before moving forward on major projects if at all possible. References -Electrical current can be fatal: -Wet skin dramatically decreases the human body s resistance: -Table A: -Table B: Page 7

8 Appendix A: Tables Table A-1: AWG values, areas, and corresponding ohms per 1000 feet at various temperatures. Increasing gauge from 10 to 20 or 20 to 30 increases resistance by about a factor of 10, while moving up 3 gauge sizes approximately doubles resistance. Page 8

9 Table A-2: AWG and IEC R-20 wire size comparison. Page 9