UTILITIES II

SUBCOURSE II CORRESPONDENCE COURSE SUBCOURSE 389 9 II States Army Engineer School 9 NID 906 material in this subcourse employed in the design water supply distribution and sewage collection and of operations such as depots hospitals replacement depots the like require fairly extensive construction rehabilitation necessary and operation of systems are responsibilities of units While this course not make you an expert it will sufficient basic information enable you to function as an staff officer or commander in communications zone of a theater of four lessons and an as follows 1 Electric Power Systems Electrical Water Distribution Systems Sewage credit hours are allowed for subcourse will not be limited as to the of hours you may spend in the or the examination furnished Figures 14 16 18 lesson 4 IMPORTANT NOTICE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70 DISREGARD ALL REFERENCES TO THE 75 REQUIREMENT 1 POWER SYSTEMS ASSIGNMENT Attached memorandum REQUIRED None OBJECTIVE To teach you the characteristics functions of electric power MEMORANDUM CURRENT AC SYSTEMS reasonably reliable and adequate of electric power is always installations The required of electric power systems the combat areas to the larger permanent installations in the Maximum use should be made of in order to save time and Where no existing power is capable of producing from watts to 300 kilowatts are used in combinations that there will be an adequate supply of power any one of them fails CURRENT DC SYSTEMS direct current is a current which the condition of a constant has a constant magnitude and in the same direction at all fig 1 Use of DC current for first flows in one direction the loop then reverses and in the other direction at recurring intervals Most systems are of the alternating type To understand how this of current is produced a simple generator will be described this generator consists of north and south magnetic pole and a of wire fixed so it can rotate the poles fig 2 Current induction As the loop between the poles a current direction when the first 180 are being turned and in the direction when the next 180 are being turned The of current occurs when loop cuts the magnetic lines of flowing from the north to the pole When the loop reaches the point the maximum number lines are being cut and the induced is at a maximum When 1 Direct current minute to produce a frequency of cycles per second A more common of generator in use today is multipole generator which produces rpm Figure 3 shows a 2 Simple two pole AC loop reaches the 180 degree point is no longer cutting any lines and current is zero One complete of the loop constitutes one because the current has gone zero to maximum value twice as in figure 2 Frequency frequency The most common in use in the United is 60 cycles per second A two pole generator would have 3 Schematic diagram of four AC generator revolution of the loop two cycles To produce at 1800 rpm half as fast as two pole type POTENTIAL SYSTEMS most common type of system for potential type where the is kept as constant as and the current varies with in loads This system is subdivided into direct and current of which as stated the direct current not be discussed The systems employ another known as three phase Previously described were two pole and multipole generators produced alternating current 4 Three phase current because only one source induced current one loop or coil used between the poles Now by three coils or loops current is in each one by the poles and resulting effect is three single currents acting in the same as shown by figure 4 Note the illustration shows a much sequence of impulses than the illustration of single phase The difference may be to the action of a two gasoline engine single phase as against a six cylinder three phase current The phases or cylinders used the the power output This is the only advantage of three phase as will be shown later current however is not obsolete by three phase current type of current has its own application which is based on type of load to be served The arrangements of single phase three phase currents are used in systems two wire three wire three wire four wire NOTATION are identified by the number phases and wires and the voltage the wires For example 6 shows a single phase three 120 240 volt system The correct for this system is 1 3W A three phase four wire system would be shown as 3 120 208V PHASE equipment or buildings 5 1 120V system 6 1 120 240V system 7 3 120V system only lighting loads For purposes two wire service is but for heavier loads three service must be used Two wire systems 1 2W In single phase two wire system fig one of the two wires from the is connected to the ground is called the ground wire or the The other wire is called the wire Normally the voltage between these wires is 120 Sometimes locally available 1 generators will be designed for a voltage In such a case can be used to step down voltage to 120 volts In this the current in one wire is to the current in the other Typical 1 2W 120V loads are and most equipment requiring power Three wire systems 1 3W In system there are two voltages which provide the advantage simultaneously obtaining a high for heavy loads and a lower for lighter loads Figure 6 the three wire single system Volt