Professional engineers are responsible for designing electrical and mechanical systems, but as an EA assisting the engineering staff, you need to be familiar with the methods, materials, and terminology used to design and construct these systems. EA Basic Chapter 10 Electrical Systems and Plans introduced this topic. This lesson will expand on that beginning, so you may find it helpful to review that lesson before beginning this one. This lesson will also present material on water distribution and sewage collection systems that are exterior to buildings. Some of the materials and terms used in the design and construction of these exterior systems are the same as those used for building plumbing within the footprint of a structure. Therefore, you may also find it helpful to review EA Basic Chapter 9, Mechanical Systems and Plans.
When you have completed this lesson, you will be able to:
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1.0.0 Electrical Power System
2.0.0 Water Supply and Distribution 3.0.0 Wastewater Systems Summary Review Questions |
As you learned in EA Basic Chapter 10, a complete electrical distribution system brings power from the generating plant to the power consumers through substations, feeders, and transformers to a building’s premises by overhead power poles or underground lines. In addition, this delivery network is considered to consist of two parts: the transmission system and the distribution system. Figure 6-1 shows a typical electrical power system, including the transmission and distribution systems. To recap your knowledge of the two systems, begin with the transmission system. Figure 6-1 — Typical electrical power system.
Refer to Figure 6-1. Note that the starting point for electrical power transmission is at its place of origin, or generating station (not part of the transmission system), which may use fossil fuel, water flow pressure, solar energy, wind energy, geothermal heat, or, in some locations, nuclear energy to drive turbine generators. Energy generated in larger stations from fossil fuel, water pressure, and nuclear energy is generally in the range of 13,200 to 24,000 volts, but that voltage is insufficient for economical transmission over long distances. 6-4 Therefore, the generating station’s transmission substation raises the voltage to transmission levels (138,000 to 765,000 volts). A substation contains transformers, switches, and other equipment used to raise or lower voltages to appropriate levels, and protect the substation, transmission lines, or distribution feeders against faults. Usually run overhead, structures with attached insulators support the high voltage energized transmission lines (transmission circuits) that transmit large bulks of power over relatively long distances. In locations where overhead high-voltage lines are not practical or permissible, transmission lines may be run underground. As shown in Figure 6-1, towers support the transmission lines (circuits) that deliver power from the transmission substation at the generating plant to customers located along the route. Throughout its length, when necessary, transmission circuits are equipped with additional substations that lower the voltage to reduced transmission (or subtransmission) levels. In addition to transmission substations, transmission circuits also have distribution substations that further reduce the voltage to required distribution levels. This is where the distribution system begins.
The distribution system is the segment of the electrical power system that connects the transmission system to the user’s equipment at a usable voltage. Figure 6-2 shows the principal elements of a distribution system. It includes:
Figure 6-2 — Elements of a power distribution system. A power distribution system may be an overhead line (less costly), or an underground cable system such as those required near an airfield. This lesson will present information mainly on the overhead distribution system; it is the more common of the two systems. 6-5
The distribution substation transforms the transmission voltage to the proper distribution voltage and protects the substation and transmission lines against faults occurring in the feeder circuits. At advanced bases, the source of power may be generators connected directly to distribution centers (Figure 6-3). This eliminates the need for substations because the generator’s output is a usable voltage. Figure 6-3 — Example of advance base generators. MUSE Power Plants supporting Operation Sea Signal, Guantanamo Bay, Cuba.
1.2.2 Primary Feeders
Refer again to Figure 6-2. In a distribution system, primary feeders are those conductors that transfer power from the distribution substations’ step-down transformers to the distribution centers. They may be overhead or underground, and arranged as radial, loop, or network systems.
1.2.2.1 Radial Distribution System
Figure 6-4 is a schematic example of a radial distribution system. 6-6 In radial distribution, primary feeders take power from the distribution substation to the load areas by way of subfeeders and lateral-branch circuits. Because it is the simplest and least expensive to build, it is also the system most commonly used. It is not, however, the most reliable system; a fault or short circuit in a primary feeder can result in a power outage to all users on the system. Figure 6-4 — Example of a radial distribution system. Power service on a radial system can be improved by installing automatic circuit breakers that reclose at predetermined intervals, but if the fault continues after a predetermined number of closures, the breaker will be locked out until the fault is identified and cleared; then service can be restored.
1.2.2.2 Primary Loop (or Ring) Distribution System
Figure 6-5 is a schematic example of a loop (or ring) distribution system. Loop distribution starts at a distribution substation, runs through or around an area serving one or more distribution transformers (load centers), and returns to the same substation. More expensive to build than the radial system, the loop system is more reliable and may be justified in areas where continuity of service is required, for example, at a medical center. Figure 6-5 — Example of a loop (ring) distribution system. In the loop system, circuit breakers sectionalize the loop on both sides of each connected distribution transformer. A fault in the primary loop is cleared by the breakers in the loop nearest the fault, and power is supplied the other way around the loop without interruption to most of the connected loads. If a fault occurs in a section 6-7 adjacent to the distribution substation, the entire load can be fed from one direction over one side of the loop until repairs are made.
1.2.2.3 Network System
Figure 6-6 is a schematic example of a network distribution system, the most flexible type of primary feeder system. It provides the best service reliability to the distribution transformers or load centers, particularly when the system is supplied from two or more distribution substations. Power can flow from any substation to any distribution transformer (load center) in the network system. In addition, the network system is more flexible about load growth than both the radial or loop systems. Service can readily be extended to additional points of usage with relatively small amounts of new construction. While the network system is more reliable and flexible, it does require large quantities of equipment and is, therefore, more expensive than the radial system. Figure 6-6 — Example of a network distribution system.
1.2.3 Primary Mains
Refer to Figure 6-8. Primary feeders supply power to primary mains. In overhead pole installations, primary mains are always installed below the feeders. The primary mains, through fused or automatic cutouts, provide power to distribution transformers. Note the cutouts in Figure 6-8, one on each primary line; they contain the fuses that protect the transformer against overload and short circuits.
1.2.4 Distribution Transformers
Most electrical equipment in the Navy uses 120/208 volts. However, the usual primary voltage on Navy shore installations is 2,400/4, 160 volts. 6-8 Figure 6-7 — Various types of transformers. Therefore, a distribution transformer is used to reduce (step down) the high primary voltage to the equipment utilization norm of 120/208 volts. There are three general types of single-phase distribution transformers (Figure 6-7, Views A-C). The conventional type requires a lightning arrester and fused cutout on the primary phase conductor feeding it. The self-protected (SP), or lightning-protected (LP), type has a built-in lightning protector. The completely self-protected (CSP) type has a lightning arrester and current-overload devices, so it requires no separate protective devices. Figure 6-8 shows one of various different types of transformer arrangements and installations. Regardless of the type of installation or arrangement, transformers must be protected by fuses or circuit breakers and lightning protection either as separate items or as part of the internal design.
1.2.5 Secondary Mains
Refer to Figure 6-8. Secondary mains (circuits) are lines that carry power from the secondary side of the transformer through a distribution system to supply the electrical loads. They may or may not be on the same pole with the feeder lines. If they are on the same pole, they may be on a crossarm below the feeder lines or on spool racks attached to the side of the pole below the feeder lines. Secondary circuits may have several wires (service drops) connected to various buildings to serve their electrical needs, or a transformer or transformer bank may be located at a building site where a large load is in demand.
1.2.5.1 Single Phase
Refer to Figure 6-8. Single-phase secondary mains (circuits) usually supply current for electrical lighting loads, small electric appliances, and small (1 horsepower and under) single-phase electric motors. The secondaries consist of two hot conductors and one neutral conductor. 6-9 In overhead construction, these conductors are mounted on the bottom crossarm on a pole or on spools attached to the side of a pole. One transformer will feed this circuit if the required load is not too heavy. Where the load is heavy or where several buildings are served, a bank of three transformers may feed the circuit. The normal voltage of a single-phase circuit is 120 volts from either of the energized conductors to the neutral, or 240 volts across the two energized conductors.
1.2.5.2 Three Phase
Some facilities, such as motor pools, industrial shops, and water and sewage plants, have equipment using three-phase motors, which require three-phase power. Three-phase transformer banks are installed to supply this power (Figure 6-7, View D). If a number of buildings in the area require three-phase power, cluster-mounted threephase secondaries may be installed to extend in two or three directions, with service drops extending from the secondary to the buildings. 6-10 Figure 6-8 — Pole-mounted feeders, primary mains, transformers, secondaries. 6-11
1.2.6 Service Drops
Each building requiring electric current must have a lead-in conductor, known as a service drop, comprised of two, three, or four individual conductors, or a single cable containing the required number of conductors. A typical service drop is connected to a secondary main to provide service to a small load. However, where a transformer bank services a building requiring a large power load, the secondary main becomes the service drop since it feeds current to one load only. Most Navy buildings are not metered, but when there is a need to know how much electricity is being consumed, a meter can be installed at the service drop ahead of the main switch to the building.
Like any other electrical circuit, a power-distribution circuit needs devices to provide control and protect the system from influences (internal or external) that could damage the circuit or injure personnel.
Refer to Figures 6-8 and 6-9. A distribution cutout is used to protect the distribution system or the equipment connected to it. Distribution cutouts are used with transformers, capacitors, and cable circuits, and at sectionalizing points on overhead circuits. The air switch and the oil switch are two types of switches used in power distribution (Figure 6- 9). Both devices are used to connect or disconnect a portion of the power distribution system. The air switch is used for the overhead section of the distribution system; the oil switch is used with underground portions. Figure 6-9 — Examples of distribution cutout switches. 6-12 Used for overload protection, reclosers are designed to open a circuit in an overload condition and then automatically reclose the circuit. Reclosers come in single- or three-phase models and can be pole mounted or installed in a substation (Figure 6-10). Figure 6-10 — Example of a recloser. Oil, air, gas, and vacuum circuit breakers are available in a number of designs, all used to switch electric circuits and equipment in and out of the system (Figure 6-11). They may be operated manually or by remote control, or be automatically set to meet a predetermined condition or electrical failure in the system. Figure 6-11 — Examples of vacuum circuit breakers. 6-13
Refer to Figures 6-8 and 6-12. Lightning arresters serve a dual purpose. First, they provide a point in the circuit where a lightning impulse can pass to earth through a ground wire without injuring line insulators, transformers, or other connected equipment. Second, arresters prevent any follow-up power current from flowing to ground. Lightning arresters must be installed on the primary side of all substations, distribution centers, distribution transformers, and capacitor banks. Figure 6-12 — Examples of lightning arresters.
An overhead electrical distribution system needs a structure specially designed to support the weight of the conductors and all the equipment mounted on the structure. Figure 6-13 — Examples of conductor supports. A conductor support’s design must also meet required clearances from the ground to the conductors and distances between conductors. Metal towers, metal poles, reinforced concrete poles, and wood poles are all commonly used, depending on the voltage being conducted (Figure 6-13). This course will discuss only poles. 6-14
Poles used in the Navy can be reinforced concrete, metal (steel or aluminum), or wood, but concrete and metal poles should only be used when economics or special considerations warrant their use.
Poles are available in various types of wood depending upon the species of trees available in a local area. In the United States, the southern yellow pine, western red cedar, and the Douglas fir are the most commonly used species. The length and circumference of poles vary, which may also be dependent on the species of tree. Poles are typically available in 5-foot incremental lengths with top circumferences varying in 2- inch increments. Therefore, poles are available in 30-, 35-, and 40-foot lengths, with top circumferences of 27-, 25-, 23- inches, and so on (Figure 6-14). A pole of given species, length, and top circumference is then classified by the circumference of the pole measured at a point 6 feet up from the butt. The class identifies the strength of the pole, which is its ability to resist loads applied 2 feet from the top. Classes are numbered from 1 to 10, with 1 being the strongest. Figure 6-14 — ANSI classification of western red cedar poles. Wood poles are used mostly in distribution systems and light-duty transmission lines. The class of pole used depends on the pole’s intended purpose, such as line pole, corner pole, or transformer pole. A pole’s required length is determined, in part, by clearances required for the voltage of the circuits, the number of circuits, and the location of the pole in relation to streets, railroads, buildings, and so forth. Another factor in pole selection is the requirement of clearances to provide safe working conditions for linemen working on the lines. All clearances have minimum requirements set by the American National Standards Institute (ANSI) and the National Fire Protection Association (NFPA). These requirements are specified in the National Electrical Safety Code (NESC), ANSI C2-87, and the most recent edition of the National Electrical Code® (NEC®). Engineers also consider local conditions when determining the length of poles; poles located in densely popular high-traffic areas need to be higher than those poles in sparsely populated rural areas. 6-15 In the Navy, all wood poles must be a minimum length of 30-feet while transformer poles must be 35-feet minimum. MIL-HDBK-1004/2A (UFC 3-550-03N), Power Distribution Systems provides additional guidance regarding the heights and classes of poles for use in the Navy.
Where a wood pole’s life is shortened by local conditions, concrete poles are preferred; they may be solid or hollow (Figure 6-15). Solid concrete poles are made in a trough form with steel reinforcing rods running lengthwise. Hollow concrete poles are made by placing the concrete and reinforcing rods into a cylinder/core combination form of the desired length and taper, adding the concrete and then removing the forms. The hollow type is lighter than the solid type, and provides an access to make connections through the pole to underground cables or services. This allows the wires to be concealed and protected from the weather. Figure 6-15 — Example of a hollow concrete pole. The exterior form of concrete poles can be changed to meet almost any need, functional or aesthetic. Gains (cut notches) for crossarms and holes for bolts can be cast in the pole. Pole steps can be cast into the face of the pole, or pre-threaded holes for steps can be installed. Concrete poles are stronger and last longer than wood poles, but they are also expensive to make and install. However, the rising cost of wood poles, their treatment process, maintenance costs, and greater landscaping concerns have brought concrete poles into increased use.
4.1.3 Metal Poles
Metal poles are either steel or aluminum. Steel poles are not used in ordinary power-line distribution circuits except for unusual circumstances, such as where high stress or heavy load may be placed on the pole. Aluminum poles are only used for lightweight distribution, such as for streetlights.
1.4.2 Guying of Poles
Poles must have sufficient strength to carry heavy conductors and pole-mounted equipment. This is where proper anchoring and guying are essential to help support poles, especially in sandy or swampy ground. Guys also help to counteract added strains caused by the elements, such as gravity, high winds, snow, and ice. 6-16 Various types of guy anchors have been developed to hold imposed loads securely in varying soil conditions (Figure 6-16). Figure 6-16 — Examples of various guy anchors. 6-17 There are many different uses of guys, and each usage has its own terminology. 1. Down guys — the most common type of guys; wire is run from the top of the pole to an anchor in the ground with different variations such as the following:
• Side guy — used to reinforce a pole line against the side pull of conductors developed at curves, angles, or sharp turns in the line (Figure 6-17). Figure 6-17 — Typical side guy.
• Terminal down guy — usually placed at the end of a pole line to counterbalance the pull of the line conductors; sometimes also called a corner guy (Figure 6-18). Figure 6-18 — Typical terminal down guy. 6-18
• Corner guy — used where there is a directional change in the line (Figure 6-19). Figure 6-19 — Typical corner guy.
• Line guy — installed in a straight pole line where an unusual stress or strain comes from farther down the pole line or where there is a chance the conductors may break and cause excessive damage; often installed in pairs, line guys are also called storm guys (Figure 6-20). Figure 6-20 — Typical line (storm) guy. 6-19 2. Head guys — wire is run from one pole to the next pole down the line. Head guys are used to transfer the load supported by one line pole to another (Figure 6-21). Figure 6-21 — Typical head guy. 3. Push brace — used where a pole is too small to be self-sustaining and cannot be guyed. Push braces are used in marshy or sandy soils where anchors cannot be firmly embedded. The upper end of the brace is bolted to the pole (Figure 6-22). Figure 6-22 — Typical push brace. 6-20
1.4.3 Laying Out of Pole Lines NAVFAC NFGS-16302, Overhead Electrical Work provides information on materials, specifications, and construction methods needed to design pole lines. When designing and constructing a pole line, there are a number of points to consider. As an EA preparing construction drawings or performing surveying operations, you may be directly involved in some of the considerations. The following is intended as familiarization so you will understand why an engineer plans a line along a specific course:
• Use the shortest possible route. — The shortest route is usually the least expensive. Run the line as straight as possible from one point to another.
• Follow highways and roadways as much as possible. — This makes it easier to build, inspect, and maintain the line. As much as possible, locate the line on only one side of the road and on the side least cluttered with other lines and trees. If trees line the road, consider locating the line a short distance away from the road; trees are preserved, trimming is minimized, falling trees cannot cause outages, and maintenance is simplified.
• Follow the farmer’s property or section lines. — Normally not a major concern in the military, but the engineer may have to consider bomb ranges and other such areas. If railroad tracks run through the area, follow them since the path has already been cut.
• Route in the direction of possible future loads. — The route should go as close to new load centers as possible.
• Avoid going over hills, ridges, swamps, and bottom lands. — Hills and ridges are subject to lightning storms; swamps and bottom lands are subject to flooding. Following these routes also makes it difficult to deliver materials and provide line maintenance.
• Avoid disrupting the environment. — The engineer should consider environmental impact, codes and regulations, as well as aesthetics to select routes that cause the least disturbance. <p>1.5.0 Electrical Distribution Drawings When your tour rotation takes you to a construction battalion or the engineering division of a public works department, you may need to assist the engineering officer in preparing electrical distribution drawings of the following types. 1.5.1 Electrical Distribution Plans The type and extent of information placed on an electrical distribution plan will depend on the purpose of the plan. Figure 6-23 shows a general distribution plan for a Navy activity taken from that activity’s master plan. This plan shows the routes of the distribution circuits, but it only identifies them as aboveground or belowground. Note that the majority of electrical distribution is underground in this case since the location is an airfield. For this plan, you would need to find the master plan for a narrative description of the circuits. 6-21 Figure 6-23 — Typical master plan drawing of electrical distribution system. 6-22 This type of drawing is of little use to an engineer or lineman in the field who requires specific information about the distribution system. For field use, as opposed to planning use, you need to prepare a detailed electrical distribution plan using the proper electrical symbols found in ANSI Y32.9. While a detail plan may appear similar to Figure 6-23 (a detail plan shows all buildings, facilities, and distribution routing), it should also include the following information as applicable:
• Source of power (power plant, public utility line, substation, standby generator with electrical data)
• Number, type, and size of underground conduit or cable ducts; size, number, voltage, and type of cable
• Location, dimensions, and description of splice boxes where cable runs are made without installed ducts
• Identification and description of all electrical manholes and handholes by location, identification number, type, dimensions, with top and invert elevations
• Descriptions of all transformer vaults, aboveground or belowground, with dimensions, top and invert elevations, numbers, type, and electrical data
• Electrical data for all substations
• Location and type of all sectionalizing switches
• Number, size, type, and voltage of all overhead conductors
• Location, identification, material, class, and height of all poles
• Number and rating of all pole-mounted transformers
• Street-lighting systems, light standards, type, and rating of lights
• Number, size, voltage, and type of street-lighting circuits
• Notes of any buildings containing street-lighting transformers and control equipment together with type and rating of transformers To simplify a drawing with this much information, it is common practice to place much of it in an appropriate schedule. For example, on a plan for an overhead distribution system, you need only show the location and an identification number for the poles. Then in a pole schedule sorted by identification number, you can list the material, class, and height of the poles. 1.5.2 Site Plans As presented in EA Basic, a site plan furnishes the essential data for laying out a proposed facility. It shows property boundaries, contours, roads, sidewalks, existing and proposed buildings or structures, references, and any other significant physical features, such as existing utility lines. Small, uncomplicated buildings can often include all proposed electrical and other new utility lines on the site plans. However, for the average facility, rather than inclusion on the site plans, it is common practice to prepare separate utility plans for addition to the project plan’s plumbing and electrical division(s). 6-23 Figure 6-24 shows a simple electrical site plan and the routing of a new 13.8-kilovolt (kV) primary service line to a new dining facility. The new service is tapped to an existing 13.8-kV overhead primary feeder (note the absence of poles along the new line), runs down existing pole Number 126, and then runs underground to a new padmounted 75-kilovoltampere (kVA) transformer located next to the new facility. Figure 6-24 — Typical electrical site plan. A competent Construction Electrician or contractor could install this new service line from only the site plan but would have to prepare additional drawings or sketches to show the work crew the specific details. Therefore, to provide a better description of the installation and convey the specific intent, the electrical designer prepares additional electrical details. 1.5.3 Electrical Details Detail drawings should clarify the exact requirements of a project. In providing details for the installation shown in Figure 6-24, the designer begins at the existing pole and works towards the new transformer pad. Refer to Figure 6-25, a detail of the existing pole. This detail leaves little doubt about the requirements at the pole. It shows the existing pole, crossarm, 13.8-kV feeder, and required clearance distances for a new crossarm with associated equipment. It also shows that the new circuit taps the existing conductors and then runs to three new 10-ampere fused cutouts on the new crossarm before running to the new cable terminals and lightning arresters mounted directly to a new bracket on the pole. 6-24 Figure 6-25 — Detail 1- pole detail from electrical site plan. 6-25 Figure 6-25 (also called Detail 1) also shows that the new three-wire shielded cable connects to the cable terminators and runs down the pole. Now refer to Figure 6-26 (Detail 2). From the pole, the cable is then run at a specified distance underground to the new transformer pad. Figure 6-26 — Detail 2- cable-trench detail from electrical site plan. The run must be over 40-inches deep to the top of the encasing concrete with 3-inches minimum concrete cover over a split 4-inch fiberduct. Finally, refer to Figure 6-27 (Detail 3), a detail of the pad the designer included in the working drawings. These details leave little doubt about the job requirements at the transformer pad either. Location, finish grade, dimensions, and ground rod location/wiring are all included. However, other information could also be included when deemed necessary for clarification: specified material requirements for the concrete, cables, or conduit; specified procedures for backfilling the trench and placing the concrete. Any other information necessary for a full understanding of the material and installation requirements should also be shown on the drawings or in the project specifications. 6-26 Figure 6-27 — Detail 3- transformer pad detail from electrical site plan. These examples of electrical transmission and distribution systems, distribution plans, and electrical details should leave you in a better position to aid the engineering officer or other design engineers. To increase your knowledge and become an even more valuable asset to yourself and the Navy as an accomplished Engineering Aid, further your studies by reading other publications, including the CE NRTCs and commercial publications, such as The Lineman’s and Cableman’s Handbook by Kurtz and Shoemaker.
| Test Your Knowledge 1. A complete electrical power system includes all of the associated equipment necessary to supply power from a generation point to the _____. |
Again referring to the EA Basic course, Chapter 9 states that a water supply system consists of all the facilities, equipment, and piping used to obtain, treat, and transport water for a water distribution system; a distribution system is a combination of connected pipes that carry the supplied water to the users. This section will cover water distribution to familiarize you with the elements of a water distribution system and the information required on distribution drawings. The engineering officer is responsible for selecting a water source, determining the methods of developing the source, and designing the supply and distribution system, but you need to have a general knowledge of the subject so, as a technician, you will be better able to assist.
The Navy’s first preference is to obtain potable water from nearby public sources, but that is not always possible. The following briefly discusses the different types of water sources, source selection and development, and the need for water treatment. 2.1.1 Water Sources Rain is the principal source of water, and it is classified based on where it collects and is accessible as either surface water or groundwater. Surface water is rain that runs off the ground into streams, rivers, and lakes. Historically, it is the most easily accessible and hence the most common source used for a water supply. However, its availability depends on the amount of rainfall an area receives. In areas of substantial rain, the quantity of surface water may be plentiful, but in dry areas or during a drought, the supply may be minimal or significantly reduced. Groundwater is rain (or surface water) that percolates through the soil and collects as an underground source. As water seeps through the soil, it eventually meets an impervious stratum (a layer of earth, usually rock, that the water cannot penetrate) and forms a water level known as the water table. The depth of the water table (the distance from the ground surface to the water level) and the depth of the underground body of water itself can vary considerably with the amount of rainfall. During a drought, the water table may lower; during a rainy season, it will probably rise. As your studies of soil formations pointed out, the stratum where groundwater can accumulate is irregular, not a continuously flat plane. Therefore, unless and until groundwater is confined, it flows over the irregular stratum and is nearer the surface in some places than in others. Where this groundwater flows near the surface and the ground area is low, the water may flow out as a spring, or if there is no exit, it may seep out and create a swampy area. Alternatively, groundwater may become entrapped between impervious layers and build up enough water pressure to create an artesian well if the stratum is penetrated by drilling or by a natural opening. In some regions of the world, neither surface water nor groundwater is available to support the local need; there, alternative sources are necessary. Rain itself can be an alternative source with large catchment areas constructed (usually on the side of a mountain or hill facing the prevailing rainfall) to collect rain and store it for future use. In 6-28 other areas, snow and ice may be an alternative source. Still another source, although costly to develop for use, is seawater that has the salt removed by desalination. 2.1.2 Selection and Development of Water Sources The engineer must consider three primary factors when selecting a water source for development: quantity, reliability, and quality. The water quantity factor must consider the amount of water available at the source balanced against the amount of water demanded. The amount of water available at the source will depend on variables: amount of precipitation, size of drainage area, geology, ground surface, evaporation, temperature, topography, and artificial controls. Water demands are estimated using per capita requirements and other controlling factors: fire protection, industrial use, lawn sprinkling, construction, vehicles, and water delivered to other activities. Water reliability is one of the most important factors the engineer considers when selecting a source. A reliable water source is one that will supply the water quantity factor for as long as required. To determine reliability, the engineer studies data such as hydrological data, to determine the variations that may be expected, and geological data since geological formations can limit the flow of water. Water quantity and reliability may be affected by laws regulating and controlling water rights, which vary considerably from state to state and country to country, so legal advice may be necessary when selecting a water source. Water quality is the third primary factor the engineer must consider when selecting a source. Practically all water supplies have been exposed to pollution of some kind, either natural or manmade. Therefore, to ensure that water is potable and palatable, it must be tested for any impurities that could cause disease, odor, foul taste, or bad color. In most cases, any water source will require treatment to remove impurities through various filtration and sedimentation processes, and in nearly all cases, it will be disinfected using a chemical agent, usually chlorine. Once the engineer has selected the water source, development can begin. Developing a water source includes all work that increases the quantity, improves the quality, or makes the water more readily available for treatment and distribution. In developing the source, the engineer may propose constructing dams, digging or drilling wells, or any other improvements to increase the quantity and quality of the water. For more detailed information on water source selection, development, and treatment, refer to NRTCs UT Basic and UT Advanced. For NAVFAC guidance, refer to MILHDBK-1005/7A (UFC 3-230-19N), Water Supply Systems. 2.2.0 Distribution System Elements and Accessories A water distribution system includes a number of elements including the following:
• Distribution mains — pipelines that make up the distribution system. Their function is to carry water from the water source or treatment works to users.
• Arterial mains — distribution mains of large size. They are interconnected with smaller distribution mains to form a complete gridiron system. 6-29
• Storage reservoirs — structures used to store water. They also equalize the supply or pressure in the distribution system. A common example is an aboveground water storage tank.
• System accessories — system accessories include the following: o Booster stations — used to increase water pressure from storage tanks or low-pressure mains o Valves — control the flow of water in the distribution system by isolating areas for repair or by regulating system flow or pressure o Hydrants — designed to allow water from the distribution system to be used for fire-fighting purposes o Meters — record the flow of water in a part of the distribution system o Service connections — used to connect individual buildings or other plumbing systems to the distribution system mains o Backflow preventers — used to prevent flow through potential cross connections. A cross-connection is any connection between a potable and non-potable water system through which a contaminating flow can occur.
Carefully planned distribution systems lay out pipes in a grid or belt system. Large pipes divide the community or base into several blocks each, with smaller connected pipes serving the streets within the grid. If possible, the network is planned so the whole pipe system consists of loops, and no pipes come to a dead end. Then water can flow to any point in the system from two or more directions, eliminating the need to cut off the water supply for maintenance work or to repair breaks (Figure 6-28). 6-30 Figure 6-28 — Typical water distribution system site plan. Older water systems frequently were expanded without planning and developed into a treelike system (Figure 6-29, View A), that is, a single main that decreased in size as it left the source and progressed through the area with smaller pipelines branching off and dividing again much like the trunk and branches of a tree. A treelike system is not a desirable system. The size of the main line limits the system’s expansion, and the many dead ends, where water remains for long periods, cause undesirable tastes and odors in nearby service lines. 6-31 Figure 6-29 — Examples of branch and grid distribution systems. MIL-HDBK-1005/7A (UFC 3-230-19N), Water Supply Systems provides specific guidance to follow when planning the location of mains. Generally, if possible, mains should be located clear of other structures, as well as adjacent and parallel to streets but not within roadways. Also if possible, mains should be separated from other utilities to ensure the safety of potable water and lessen interference with other utilities during maintenance.
Shutoff valves in water mains at various locations allow sections to be taken out of service for repairs or maintenance without significantly curtailing service over large areas (Figure 6-30). In long supply lines, valves should be installed at intervals no greater than 5,000 feet, and no greater than 1,500 feet in main distribution loops or feeders. All branch mains connecting to feeder mains or feeder loops should have valves installed as close to the feeders as practical so branch mains can be taken out of service without interrupting the supply to other locations. Valve spacing of 500 feet may be appropriate for areas where water demand is great or when dependability of the distribution system is particularly important. Figure 6-30 — Typical water main valve. 6-32 At the intersection of distribution mains, the number of valves required is normally one less than the number of radiating mains; the omitted valve is the one that supplies flow to the intersection. As much as possible, shutoff valves should be installed in standardized locations (specific northeast corner of an intersection or a certain distance from the centerline of a street), for easier location in emergencies. Figure 6-31 — Typical water main valve precast vault. All buried small- and medium-sized valves should be installed in valve boxes. For large shutoff valves (30-inch diameter and larger), it may be necessary to surround the valve operator or the entire valve within a vault or manhole to allow repair or replacement (Figure 6-31).
MIL-HDBK-1008C (UFC 3-600-01) Fire Protection for Facilities Engineering, Design, and Construction provides criteria for fire hydrants. Street intersections are the preferred locations for fire hydrants because fire hoses can be laid along any of the radiating streets. Hydrant locations should be a minimum of 6 feet and a maximum of 7 feet from the edge of a paved roadway surface. If a hydrant is more than 7 feet from a paved edge, it may be necessary to provide ground stabilizing or paving next to the hydrant to accommodate fire-fighting equipment. Hydrants should not be placed closer than 3 feet to any obstruction and never in front of entranceways. In general, hydrants should be at least 50 feet from a building and never closer than 25 feet to a building, except where building walls are blank firewalls.
The following provides general information on the contents of water distribution plans and details.
A water distribution plan should show the following information at a minimum:
The design engineer will determine the varied and numerous details to be included in a set of construction drawings for a water distribution system. For example, you may need to prepare plans, elevations, and details for a new water storage tank, thrust block details, trench details for underground piping, details for aboveground pipe supports, or plans and details for valve boxes, vaults, and so forth.
| Test Your Knowledge 2. The _____ is responsible for selecting a water source.
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In addition to drawings of electrical and water distribution systems, as the engineering officer’s assistant, you may need to prepare detailed drawings of wastewater systems as well. This section provides a brief overview to familiarize you with the elements and structures used in wastewater systems, and the general content requirements for wastewater system drawings.
A wastewater system is a collection of sewer pipes and pumps designed to convey domestic and industrial wastes, and transport them to a wastewater treatment plant. These systems are intended to safeguard public health by preventing diseaseproducing bacteria, viruses, and parasites from getting into groundwater or drinking 6-34 water systems. Figure 6-32 provides a diagram of the main elements of a typical wastewater collection system. Figure 6-32 — Diagram of a typical wastewater collection system. The following is a description of the various elements and structures used in a wastewater system:
• Sanitary sewer — carries mostly domestic wastes but may carry some industrial waste; NEVER designed to carry storm water or groundwater. (Storm sewer systems are designed and constructed separately from the sanitary sewer system.) Sanitary sewer system piping includes the following: o Building, or house sewer — service-connection pipe that connects an individual building to the wastewater system. Commonly made of concrete, cast iron, or plastic, this pipe is 4 inches or larger in diameter and the smallest pipe in a wastewater collection system. All other pipes must be a MINIMUM of 8 inches in diameter. o Lateral sewer — pipe that receives discharge from house sewers o Submain, or branch sewer — pipe that receives waste from two or more lateral sewers o Main, or trunk sewer — pipe that takes discharge from two or more submains or from a submain plus laterals o Intercepting sewer — pipe that receives wastewater from more than one main, or trunk sewer 6-35 o Relief sewer — sewer built to relieve an existing sewer that has an inadequate capacity
• Lift station — location where wastewater is pumped through a pipe, called a force main, to higher elevation gravity pipes. Note: most piping in a wastewater system is gravity piping designed to flow by gravity action at a rate of not less than 2 feet per second. Where gravity flow is not practical or possible, a lift station is constructed to pump wastewater to a higher level. Unlike gravity piping, force mains always flow completely filled and under pressure.
• Inverted siphon — pipes that dip below the designed gradient of the gravity pipes and are used to avoid obstacles, such as open-cut railways, subways, and streams; designed to flow full and under pressure (Figure 6-33). Not a true siphon, an inverted siphon may have one or more pipes and is designed to flow at a rate of at least 3 feet per second to keep the pipe(s) clear of settling solids. It should have manholes constructed at both ends for maintenance. Figure 6-33 — Typical inverted siphon.
• Manhole — a concrete or masonry structure used for inspection and maintenance of sewer lines (Figure 6-34). The bottom portion of a manhole is usually cylindrical and has an inside diameter of at least 4 feet. The upper portion usually tapers to the street or ground surface and is fitted with a cast-iron cover. For proper sewage flow, the bottom of the manhole slopes toward a built-in channel that has a depth of three fourths of the diameter of the sewer pipe. Manholes are usually spaced 300 to 400 feet apart for sewers up to approximately 60 inches in diameter. They are also required at all locations where sewer lines intersect, or change direction, grade, or pipe size. Figure 6-34 — Typical manhole. 6-36
MIL-HDBK-1005/8A (UFC 3-240—02N) Domestic Wastewater Control provides design guidance for wastewater systems. The design engineer begins with a careful study of the serviced area to determine the types and quantities of sewage to be handled. Based on the average daily use of water per person, a typical value is 100 gallons per person per day. Water use is not constant, however; it is greater in the summer than in the winter, and greater during the morning and evening than in the middle of the day or at night. Consequently, the average daily flow (based on the average utilization) is multiplied by a peak flow factor to obtain the design flow. Typical peak flow factors range from 4 to 6 for small areas down to 1.5 to 2.5 for larger areas. Sometimes, to obtain the estimated design flow, the engineer may also add an allowance for unavoidable infiltration of surface and subsurface water into the lines. A typical infiltration allowance is 500 gallons per inch of pipe diameter, per mile of sewer, per day. From the types of sewage and the estimated design flow, the engineer can tentatively select the types, sizes, slopes, and distances below grade for the piping. Then preliminary drawings of the wastewater system can be prepared. The preliminary drawings should include both plans and profiles, along with all buildings, roads, waterways, utilities, geology, and so forth that may affect the design. You may be called upon to assist in preparing the preliminary plans. Topographic maps of sufficient detail, if available, may be used in selecting the routing of the proposed system. However, when maps are not available or to ensure sufficient detail, you may be required to conduct topographic and preliminary route surveying for the system Final design may begin following acceptance of the preliminary design. During this phase, adjustments to the preliminary design should be made as necessary, based upon additional surveys, soil analysis, or other design factors. The final design should include a general map of the area showing the location of all sewer lines and structures. It should also provide ground elevations, detailed plans and profiles, pipe sizes and slopes, location of any appurtenances and structures such as manholes and lift stations, and should include construction plans and details for those appurtenances and structures.
Your position as a senior Engineering Aid carries with it, of course, greater responsibility, and depending on the personnel level of a Battalion or Public Works Center, you could be assigned to fill the Assistant Engineering Officer’s billet in duties if not in title. From that assignment, you could be responsible for the development of many drawings that include electrical, water, and wastewater distribution systems. Relatively all structures that personnel use or occupy require one, and usually all, of these systems. The more familiar you are with the general terms, descriptions, functions and purposes of the materials and equipment, the more accomplished you will be as a skilled EA capable of supervising the engineering division to professionally produce any required drawings.
1. Which of the following items is NOT part of a power transmission system? A. Power generating plants B. Circuits carrying large bulks of high-voltage power C. Subtransmission substations D. Primary feeders 2. In which of the following manners are transmission circuits most often run? A. Overhead on poles or towers B. Direct-buried C. Underground in cable duct D. All of the above 3. For which of the following purposes are substations used in an electrical power system? A. To step up voltage only B. To step up or step down voltage C. To provide protection against faults D. Both B and C 4. At what location in a power system does the distribution system begin? A. Generating plant B. Distribution substation C. Distribution center D. Distribution transformer 5. Which of the following items are NOT part of a typical power distribution system? A. Circuit breakers B. Service entrances C. Service drops or laterals D. All of the above 6-38 For questions 6 through 9, refer to the table below then select the type of feeder system that best matches the characteristic given. 1. Radial System 2. Loop System 3. Network system 6. Starts and ends at the same distribution substation. A. 1 B. 2 C. 3 D. 4 7. Least costly but most unreliable type of feeder system. A. 1 B. 2 C. 3 D. 4 8. Uses subfeeders and branch circuits to take power to load centers. A. 1 B. 2 C. 3 D. 4 9. Readily adaptable to future requirements. A. 1 B. 2 C. 3 D. 4 10. Conductors used for connecting distribution transformers to the feeder circuit are called _____. A. distribution mains B. secondary mains C. primary mains D. service drops 11. The primary purpose of a distribution transformer is to _____. A. increase voltage to primary distribution levels B. protect the primary feeders against overloads C. protect secondary feeders against overloads D. decrease voltage to utilization levels 6-39 12. What overhead circuits carry power from the transformer to the customer through one or more service drops? A. Single-phase primaries only B. Single- or three-phase primaries C. Single-phase secondaries only D. Single- or three-phase secondaries 13. Which of the following control or protective devices should the electrician open to neutralize an underground branch circuit in the distribution system? A. Air switch B. Oil switch C. Recloser D. Distribution cutout 14. Which of the following locations require lightning arresters? A. All substations B. Primary side of all transformers C. All distribution centers and capacitor banks D. All of the above 6-40 For answering questions 15 through 20, refer to the figure below. 15. What type of distribution line is identified by the letter “A”? A. Primary feeder B. Primary main C. Secondary main D. Service drop 16. What type of distribution line is identified by the letter “B”? A. Primary feeder B. Primary main C. Secondary main D. Service drop 17. What type of distribution line is identified by the letter “C”? A. Primary feeder B. Primary main C. Secondary main D. Service drop 18. What is the device identified by the letter “D”? A. Insulator B. Lightning arrester C. Fused cutout D. Circuit breaker 6-41 19. What is the device identified by the letter “E”? A. Recloser B. Circuit breaker C. Air switch D. Fused cutout 20. Of what type are the shown transformers? A. Completely self-protected B. Self-protected C. Conventional 21. In an electrical power system, the supporting structures for the conductors must be designed to _____. A. support the weight of the conductors B. support the weight of all transformers or other equipment mounted on the support C. provide required clearances from the ground to the conductors and between the conductors D. All of the above 22. Which of the following circumstances provides the best justification for placing an electrical distribution system underground rather than overhead? A. When the system to be installed would impede airfield traffic B. When underground installation is justified on the basis of initial construction cost only C. When an economic analysis shows that construction and long-term maintenance costs are less for underground installation D. When the system is to be installed in an area subject to major termite damage 23. On which of the following factors does the availability of wood poles at any given naval installation depend? A. Strength B. Species C. Size D. Class 24. For which of the following reasons might an engineer select a Class 2 pole rather than a Class 5 pole when designing an overhead distribution system? A. When a longer pole is needed to obtain necessary clearances B. When a stronger pole is needed to support the loads that will be applied to the pole C. When a pole having a smaller butt circumference is required due to local conditions on the ground D. When the design loads are less than those requiring a Class 2 pole 6-42 25. Which of the following criteria must be considered when an engineer determines the required length of a wooden power distribution pole? A. Local conditions B. Clearances required for the voltage of the circuits C. Clearances required for safety and working clearances D. All of the above 26. Under what circumstances would the Navy use aluminum poles? A. For ordinary power-line distribution circuits B. For poles on which high stress or heavy loads may be placed C. For lightweight distribution, such as streetlights D. For landscaping concerns For questions 27 through 29, refer to the table below then select the type of pole guy or support that can be used to best satisfy the condition given. 1. Side guy 2. Terminal down guy 3. Head guy 4. Push brace 27. Used to transfer loads from one pole to another. A. 1 B. 2 C. 3 D. 4 28. Used at the end of a pole line. A. 1 B. 2 C. 3 D. 4 29. Used when guy anchors are impracticable. A. 1 B. 2 C. 3 D. 4 30. Which of the following factors is/are important for an engineer to consider when selecting the route for a new overhead distribution line? A. Future maintenance economy B. Trends in population growth C. Distance and terrain conditions D. All of the above 6-43 31. You are preparing a preliminary site plan for a new public works maintenance facility. On this site plan, the electrical design engineer requires information such as the location, identification, and class of existing distribution poles; the location, identification, and capacity of existing transformers and the size, type, and voltage of existing overhead and underground conductors. In what source(s) should you look first to find this information? A. The station’s electrical distribution drawings or plans B. The surveyor’s field books C. The station master plan D. The electrical site plans for all surrounding buildings or facilities 32. Electrical manholes are identified on electrical utility drawings by _____. A. number and type only B. symbol, dimensions, and elevation C. identification number, location, type, dimensions, and top and invert elevations D. number, type, and complete electrical data 33. What element of a pole schedule is keyed to the plan of an overhead distribution system’s drawings? A. Identification number B. Pole classification C. Drawing symbol D. Pole location 34. In what division of the drawings should you look to find the size, type, and voltage of the service laterals leading to the building when using the as-built construction drawings of a large Navy building? A. Civil B. Architectural C. Mechanical D. Electrical 35. Which of the following information for the construction of a reinforced concrete transformer vault would more likely be found in the construction specifications rather than the construction drawings? A. Dimensions of the vault B. Slump and strength requirements for the concrete C. Capacity of the transformers to be housed in the vault D. Number and type of conduit leaving the vault 6-44 36. In general, the earth’s most common source for supplying water is classified as _____. A. surface water B. subsurface water C. groundwater D. rainwater 37. The term “water table” refers to the _____. A. upper level of groundwater collected over an impervious stratum B. lower level of groundwater collected over an impervious layer of earth C. distance from the ground surface to the upper level of groundwater collected over an impervious stratum D. distance from the ground surface to the lower level of groundwater collected over an impervious layer of earth 38. With the exception of rainfall, which of the following factors has the greatest influence on the water table in any given geographic region? A. Clay or sandy soils B. Surface runoff C. Soil permeability D. Subsurface geology 39. What is the preferred source of potable water on Navy or Marine Corps installations? A. Artesian wells and springs B. Public reservoirs C. Catchment basins D. Natural lakes and streams 40. A water source that supplies sufficient water for unlimited time is said to be _____. A. plentiful B. potable C. reliable D. palatable 41. The two most important factors that influence water quantity within a given area are _____. A. geology and rainfall B. availability and demand C. population growth and climate D. topography and geology 6-45 42. What action must first be taken before the quality of a water source can be deemed suitable for human needs? A. Testing B. Filtering C. Treating D. Disinfecting 43. To make water potable and palatable, water treatment may include _____. A. filtration B. chlorination C. sedimentation D. All of the above 44. Which of the following descriptions best defines a water supply system? A. All of the piping used to transport water B. All of the piping, reservoirs, and system accessories used to transport and store water C. All of the facilities, equipment, and piping used to obtain, treat, and transport water D. A combination of connected pipes that carry supplied water to its users 45. Large size water lines that interconnect with smaller distribution mains are called _____ mains. A. trunk B. arterial C. branch D. feeder 46. What system accessories are used for fire-fighting purposes? A. Valves B. Hydrants C. Booster stations D. Backflow preventers 47. Which of the following components should be used to protect against nonpotable water contaminating the water system? A. Booster valve B. Main-line meter C. Backflow preventer D. Service connection 6-46 48. What type of branch is best for water distribution? A. Loop B. Tree C. Cross D. Lateral 49. At what distance from the feeder should a shutoff valve be installed on branch mains? A. 25 feet B. 50 feet C. 75 feet D. As close as possible 50. In general, hydrants should be at least _____ feet from a building and never closer than _____ feet to a building. A. 25, 3 B. 50, 25 C. 75, 50 D. 100, 50 For questions 51 through 54, refer to the table below then select the system element or structure that best satisfies the condition given. 1. Main sewer 2. Submain sewer 3. Building sewer 4. Force main 5. Inverted siphon 51. May be less than 8 inches in diameter. A. 1 B. 2 C. 3 D. 4 52. May receive discharge from two or more laterals. A. 1 B. 2 C. 3 D. 5 53. Designed to flow full and under pressure. A. 1 only B. 1 and 4 C. 4 only D. 4 and 5 6-47 54. Also called a trunk sewer. A. 1 B. 2 C. 3 D. 4 55. In general, what minimum rate of speed, in feet per second, should wastewater move for gravity piping gradient? A. 1 B. 2 C. 3 D. 4 56. What system elements or structures should be placed at all locations where wastewater piping changes direction, grade, or size? A. Force mains B. Inverted siphons C. Manhole D. Intercepting sewers 57. To expedite flow, a sanitary sewer design can include storm water runoff. A. True B. False 58. What two factors are sometimes combined by addition when an engineer determines the design flow of a sewer line? A. Daily flow and peak flow B. Average usage and daily flow C. Peak flow and infiltration allowance D. Daily flow and infiltration allowance 59. How many gallons of water per day form the baseline for average daily flow/per capita in wastewater system design? A. 75 B. 100 C. 150 D.