TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

Most environmental stress is caused by weather and by the surrounding environment, such as industry, sea, or dust in rural areas. The environmental stresses affect both mechanical and electrical performance of the line. Temperature The temperature in an outdoor station or line may fluctuate between –50°C and +50°C, depending upon the climate. The temperature change has no effect on the electrical performance of outdoor insulation. It is believed that high temperatures may accelerate aging. Temperature fluctuation causes an increase of mechanical stresses, however it is negligible when well-designed insulators are used. UV Radiation UV radiation accelerates the aging of nonceramic composite insulators, but has no effect on porcelain and glass insulators. Manufacturers use fillers and modified chemical structures of the insulating material to minimize the UV sensitivity. Rain Rain wets porcelain insulator surfaces and produces a thin conducting layer most of the time. T...

Good quality electric service requires that the voltage at the consumers’ premises be kept within an acceptable voltage range for satisfactory operation of consumer equipment. At the 120-volt level, this is 110–126 volts at the utilization point. It is customary for utilities to hold voltage at the customer meter location between 114 and 126 volts, which allows for a 4-volt drop to the utilization point in the residence. The location of the voltage extremes are usually at the first and last customer locations on the primary feeder. During peak load conditions the first customer usually receives the highest voltage and the last customer the lowest. The variations from light to heavy load at these locations will establish the voltage range for the circuit. As a first step in the control of voltage on such a circuit, most utilities will regulate the primary voltage at the substation. This takes care of variations in the voltage supplied to the substation and the variation on the fee...

The capacity of the distribution system is determined in most cases by the thermal ratings of the equipment. In more rural areas with low load density it may be determined by voltage limits. The distribution substation capacity depends on the size of transformers and the provision of an additional spare transformer. If a substation has two transformers, all load must be supplied by the remaining one if one fails. In this case, the substation capacity will depend on the capability of the remaining transformer to carry the load for the time required to replace the failed transformer, with the capacity being lower if the replacement time is longer. For substations with a single transformer, load is limited to what can be transferred to other substations at remote feeder tie points. The allowable primary feeder loading can be limited by the size of conductors used and the characteristics of the load supplied. If the load varies, higher maximum loads can be carried by the f...

Primary voltage in the “13 kV class” is predominating among United States utilities. The 4-kV class primary systems are older and are gradually being replaced. In some cases 34 kV is used in new, high-density-load areas. The three-phase, four-wire primary system is the most widely used. Under balanced operating conditions, the voltages of each phase are equal in magnitude and 120° out of phase with each of the other two phases. The fourth wire in these Y-connected systems is used as a neutral for the primaries, or as a common neutral when both primaries and secondaries are present. The common neutral is also grounded at frequent intervals along the primary feeder, at distribution transformers, and at customers’ service entrances. Rural and suburban areas are usually served by overhead primary lines, with distribution transformers, fuses, switches, and other equipment mounted on poles. Urban areas with high-density loads are served by underground cable systems, with distribution t...

All the energy that leaves the generating stations is not reflected in the bills sent to customers. The difference is attributable to two issues. The first is called unaccounted-for energy. This energy is not metered by the local utility and is usually due to theft of service. In some underdeveloped countries this category can be as much as 50% of the energy generated. The second is the losses in the system directly related to the electric characteristics of the delivery system. They are an important consideration when selecting new electric power policies, when locating new generating plants, when deciding what generator to run to supply the next increment of load, when deciding on the voltage level and conductor sizes for new transmission and when deciding on the amount of voltage support to provide. Losses occur in both lines and transformers. Line losses are directly related to the square of the value of the current (I2R).The greater the amount of electricity the delivery syste...

There are two types of load diversity—that of different peak loads between customer classes, and that of different peak loads at different hours of the day and days of the year. From continuously recorded demand data, a number of different demand measures may be derived.The most commonly metered measure of customer demand is individual customer maximum demand.This measure indicates the highest demand level incurred by the customer during any metering interval in a billing period. Due to varying types and uses of electrical equipment across customers, there are broad differences in the times that customers achieve their individual maximum demands. For example, one customer whose major use of electricity is outdoor light may regularly experience maximum demand in the late evening hours of the day; while a second customer, whose major requirement for electricity is for air conditioning, is more likely to experience a maximum demand during afternoon hours in the summer months. ...

(a) Coil winding The winding consists of coils wound on all the poles of the machine and connected together to form a suitable series or parallel circuit. The direction of the current in the alternate pole will be opposite so that when one pole is the North Pole, the other adjacent pole will be a South Pole. This produces the flux in the proper direction, completing the magnetic circuit from the North Pole to the South Pole through the iron cores of both the stator and the rotor. The coil may be wound on the stator or on the rotor, forming the salient or non-salient poles of the machine. The DC supply is given to these windings and they produce a field proportional to the magnitude of the current through the windings. If the poles are on the stator, a stationary field is produced in the air gap. (b) Commutator winding The commutator winding is on the rotor. The armature has open slots and the conductors are located in these slots and ...

There are usually many factors that impact on the selection of the structure type for use in an OHTL. Some of the more significant are briefly identified below. Erection Technique: It is obvious that different structure types require different erection techniques. As an example, steel lattice towers consist of hundreds of individual members that must be bolted together, assembled, and erected onto the four previously installed foundations. A tapered steel pole, on the other hand, is likely to be produced in a single piece and erected directly on its previously installed foundation in one hoist. The lattice tower requires a large amount of labor to accomplish the considerable number of bolted joints, whereas the pole requires the installation of a few nuts applied to the foundation anchor bolts plus a few to install the crossarms. The steel pole requires a large-capacity crane with a high reach which would probably not be needed for the tower. Therefore, labor need...

Contamination caused flashovers produce frequent outages in severely contaminated areas. Lines closer to the ocean are in more danger of becoming contaminated. Several countermeasures have been proposed to improve insulator performance. The most frequently used methods are: 1. Increasing leakage distance by increasing the number of units or by using fog-type insulators. The disadvantages of the larger number of insulators are that both the polluted and the impulse flashover voltages increase. The latter jeopardizes the effectiveness of insulation coordination because of the increased strike distance, which increases the overvoltages at substations. 2. Application insulators are covered with a semiconducting glaze. A constant leakage current flows through the semiconducting glaze. This current heats the insulator’s surface and reduces the moisture of the pollution. In addition, the resistive glaze provides an alternative path when dry bands are formed. The glaze shunts t...

Things to look for in an electrical drawing 1. The symbols shown for a device in a circuit represent its de-energized state when no power is applied. It is either a timer NO/NC contact or a relay NO/NC contact in a circuit. In addition, power devices such as circuit breakers and contactors are provided with NO and NC auxiliary contacts which are used for indicating the status of the device in signaling and interlocking circuits. 2. An electrical drawing has a sheet number and each sheet is divided into columns listed vertically as A, B, C, D and horizontally as 1, 2, 3, 4. This kind of matrix arrangement helps in quickly locating a particular device or contact in a sheet. Similarly, it is used to cross-reference a contact. 3. In order to identify different coils and their contacts a letter such as K1, K2 or C1, C2 is placed next to the circle of the coil. Contacts of the same contactor coil are shown with the same letter in the dra...

When a particular amount of power has to be transmitted over a certain distance the following aspects need to be considered to decide the best voltage. A lower voltage the need higher size conductors to withstand the high current is involved. There is a physical limitation to the size of conductor. Also, the percentage voltage drop may become excessive. A higher voltage will make the conductor size manageable and reduce the voltage drop (% value) but the cost of the line becomes high due to larger clearances needed. The best voltage will be one in which the total operational cost which the sum of the annualized capital cost (of the line) and the running cost due to power loss in the line is the lowest. In practice, it is found that transmitting bulk power over long distances is economical if done in the HV range. The actual voltage will vary based on the distanceand quantum of power. Distribution circuits where typically the amount of powe...

A transformer, unlike a motor, has no mechanical output (expressed in kW). The current flowing through it can vary in power factor, from zero PF lead (pure capacitive load) to zero PF lag (pure inductive load) and is decided by the load connected to the secondary. The conductor of the winding is rated for a particular current beyond which it will exceed the temperature for which its insulation is rated irrespective of the load power factor. Similarly, the voltage that can be applied to a transformer primary winding has a limit. Exceeding this rated value will cause magnetic saturation of the core leading to distorted output with higher iron losses. It is therefore usual to express the rating of the transformer as a product of the rated voltage and the rated current (VA or kVA). This however does not mean that you can apply a lower voltage and pass a higher current through the transformer. The VA value is bounded individually by the rated v...

When something occurs at one point in space because something else happened at another point, with no visible means by which the "cause" can be related to the "effect," we say the two events are connected by a field. In radio work, the fields with which we are concerned are the electric and magnetic, and the combination of the two called the electromagnetic field. A field has two important properties, intensity (magnitude) and direction. The field exerts a force on an object immersed in i t ; this force represents potential (ready-to-be-used) energy, so the potential of the field is a measure of the field intensity. The direction of the field is the direction in which the object on which the force is exerted will tend to move. An electrically charged object in an electric field will be acted on by a force that will tend to move it in a direction determined by the direction of the fiel...

This is the classic book on Power System Analysis. This has been the bible of electrical power systems for the past 44 years so don't leave home without it ! It is a classic well-written textbook that stresses the important fundmantals of power system analysis with clarity that I have not seen in any other power book. Although other books may be fatter and contain more details, this book remains the best by wisely avoiding falling in the often tempting trap of computational details of numerical techniques and remains faithful to the basic principles. The chapters are just of the right length with many examples and clear explanations. It feels so good for the student and the professor to cover each chapter in about a week. I have used this book as a student and as an instructor and my recommendation is this: stick with this original classic and avoid the imitations! You will never regret it ! - Amazon Review DOWNLOAD LINK

Application of audio-tone systems for protective relaying can be divided into two categories: Transformer and Circuit Breaker Failure Protection or Other Direct Trip Applications These applications are termed “direct transfer tripping.” The audio-tone system functions as the communication link to extend relay tripping circuits to remote circuit breaker locations. These type of direct transfer tripping applications have the greatest difficulty in meeting the relay demands. These systems, with few exceptions, cannot have fault detector supervision of the receivers and the security against undesired tripping rests solely with the audiotone equipment. Transmission Line Protection Audio-tone systems function as the communication link for pilot relaying schemes employed for transmission line protection. Transfer trip schemes, including direct underreaching, permissive underreaching, and permissive overreaching protection are used extensively with telephone channels. Direc...

There is no universal practice with respect to reenergizing a transformer that has been disconnected from the system by relay action that may have been caused by a transformer fault. Since no one would intentionally energize an internally faulted transformer, the differences in practice seem to be based on the lack of knowledge of where the fault was or whether there was a fault. Consider a transformer differential arrangement that includes external leads. A fault within the differential zone may not be an internal fault. If the transformer has a pressure relay, this may give indication of an internal fault. If not, one has to rely on the presence or lack of evidence indicating an external fault. In the absence of definite information that a fault was external, most operating companies will not reenergize the power transformer without a complete check. Now consider a form of transformer protection that includes just the transformer. This may be a differential relay (operating f...

The electrical windings and the magnetic core in a transformer are subject to a number of different forces during operation, for example a)Expansion and contraction due to thermal cycling b)Vibration c)Local heating due to magnetic flux d)Impact forces due to through fault current e)Excessive heating due to overloading condition on inadequate cooling These forces can cause deterioration and failure of the winding electrical insulation. Table 1 summarizes failure statistics for a broad range of transformer failure causes reported by a group of U.S. utilities over a period of years. The detection systems that monitor other transformer parameters can be used to indicate an incipient electrical fault. Prompt response to these indicators may help avoid a serious fault. For example a) Temperature monitors for winding or oil temperature are typically used to initiate an alarm requiring investigation by maintenance staff. b) Gas detection relays can detect the evol...

Electrical faults in oil-filled transformers usually generate gases, some of which are combustible. Many transformer faults in their early stages are incipient and deterioration is gradual, but sufficient quantities of combustible gases are usually formed to permit detection and allow corrective measures to forestall a serious outage. Depending on the transformer oil preservation system, the gas may either be dissolved in the oil or enter the gas space above the oil. In certain types of transf These relays are usually set to alarm for the presence of gas. It is common practice to draw off samples of oil or gas for periodic analysis of combustible gas content. If there is a gas space in the oil preservation system, it is possible to directly draw off a sample of the gas and perform an on-the-spot analysis with a portable gas analyzer. If there is no gas space in the transformer, it is necessary to analyze an oil sample for dissolved gas content by gas chromatography (see Be...

Because of the helical path of the strand layers there is more length of metal in a given length of stranded conductor than in a solid round conductor of the same AWG size, hence both the weight and dc resistance per unit length are increased. The amount of increase for all-aluminum conductors may be computed according to a method described in ASTM B 23 1, may be used. The tensile load on a conductor is not always equally divided among the strands. This effect can reduce the total load at which the first strand breaks as compared with that of a solid conductor of equal cross section. However, this effect is more than offset by the fact that the unit tensile strength of commercially cold-drawn wire generally increases as its diameter is reduced, as is evident by the comparison for H19 stranded conductor. According to ASTM Standards, aluminum conductors that are concentric-lay stranded of 1350 or 6201 alloys in the various tempers have their rated tensile strength (or minimum ra...

This checklist provides an assessment of the minimum requirements needed to safely operate and maintain electric power systems. Below is a sample provided in IIEE STD 902-1998. You may modify it to suit your needs. One-line diagram exists. Yes _____ No _____ One-line diagram is legible. Yes _____ No _____ One-line diagram is correct. Yes _____ No _____ All persons who operate the power system have easy access to the current one-line diagram. Yes _____ No _____ Equipment is labeled correctly, legibly, and in accordance with the one-line diagram. Yes _____ No _____ Persons who operate/maintain electrical equipment are trained for the voltage-class equipment they operate/maintain. Yes _____ No _____ De-energized procedures and equipment exist and are used. Yes _____ No _____ Energized work procedures exist and are followed. Yes _____ No _____ Equipment is grounded. Yes _____ No _____ Ground system is tested periodically. Yes _____ No _____ E...

The following is an alphabetical listing of the groups that provide procedures and specifications for electrical testing and maintenance: a) American National Standards Institute (ANSI); b) American Society for Testing and Materials (ASTM); c) Association of Edison Illuminating Companies (AEIC); d) Institute of Electrical and Electronics Engineers (IEEE); e) Insulated Cable Engineers Association (ICEA); f) InterNational Electrical Testing Association (NETA); g) National Electrical Manufacturers Association (NEMA); h) National Fire Protection Association (NFPA); i) Occupational Safety and Health Administration (OSHA).

Inspection and testing The condition of electrical equipment is generally affected by the atmosphere and conditions under which the equipment is operated and maintained. Water, dust, temperature, humidity, corrosive fumes, vibration, and other environmental factors can adversely affect electrical equipment. Electrical equipment life can be extended dramatically by simple precautions that promote cleanliness, dryness, tightness, and the prevention of friction. The thoroughness of maintenance procedures can be categorized into three different levels: Level 1-General inspection and routine maintenance; Level 2-Inspection, general tests, and preventive maintenance; Level 3-Inspection, speciÞc tests, and predictive maintenance. Testing would include a) Insulation tests; b) Protective device tests; c) Analytical tests (e.g., time travel analysis, dissolved gas analysis, infrared, and contact resistance); d) Grounding tests; e) Functional tests. The following ...

Uses of the single-line diagram The single-line diagram may be used in a number of important ways in operating and maintaining an industrial or commercial power distribution system. Frequently, the single-line diagram, with all of the listed information, becomes too crowded for information to be used effectively in some of the operating activities. In those instances, it is wise to produce a set of single-line diagrams, with each different diagram in the set containing the pertinent information that is required for a particular activity or set of activities. Some of the needs for special single-line diagrams are a)Switching functions. When the primary use of the diagram is to provide information to system operators for switching in order to isolate portions for maintenance or for load control, then only the data required to make the decisions necessary for system switching are included on the diagram. Sometimes, when the distribution system is complex, a separate ver...

The following characteristics should help to ensure accuracy as well as ease of interpretation: a)       Keep it simple. A fundamental single-line diagram should be made up of short, straight lines and components, similar to the manner in which a block diagram is drawn. It should be relatively easy to get the overall picture of the whole electrical system. All, or as much as possible, of the system should be kept to one sheet. If the system is very large, and more than one sheet is necessary, then the break should be made at voltage levels or at distribution centers. b)       Maintain relative geographic relations. In many cases, it is possible to superimpose a form of the one-line diagram onto the facility plot plan. This is very helpful toward a quick understanding of the location of the system's major components for operating purposes. It may, however, be more difficult to comprehend the overall system operation from ...

Abstract  In this paper, transmission line performance with voltage sensitive loads is studied. Three types of load, namely constant power, constant current and constant impedance loads are considered, individually as well as in a mixed combination, and it is shown that the transmission line loss is highest with the constant power load and lowest with the constant impedance load. The line loss for mixed load is higher than that for constant power load when the constant power component is more pronounced in the mixed load. Transmission lines constitute the arteries of an electric power system. The availability of a well-developed, high capacity system of transmission lines makes it technically and economically feasible to move large blocks of power over long distances. Usually, transmission line performance is studied by considering constant power loads. The variation of power and reactive power taken by a load with various voltages is of imp...

The recommended controller for SCADA systems is the programmable logic controller (PLC).  PLCs are general-purpose microprocessor based controllers that provide logic, timing, counting, and analog control with network communications capability. a. PLCs are recommended for the following reasons:  (1)  They were developed for the factory floor and have demonstrated high reliability and tolerance for heat, vibration, and electromagnetic interference. (2) Their widespread market penetration means that parts are readily available and programming and technical support services are available from a large number of control system integrators. (3) They provide high speed processing, which is important in generator and switchgear control applications. (4) They support hot standby and triple-redundant configurations for high reliability applications. b. A PLC consists of the required quantities of the following types of modules or cards, mounted ...

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Bioelectricity: A Quantitative Approach, is the new edition of the classic introductory text to electrophysiology. It covers many topics that are central to the field including: - electrical properties of the cell membrane - action potentials - cable theory - electrical stimulation - extracellular waveforms - cardiac electrophysiology - function stimulation (FES) The study of electrophysiology has progressed rapidly because of the precise, delicate, and ingenious experimental studies of many investigators. The field has also made great strides by unifying these experimental observations through mathematical descriptions based on electromagnetic field theory, electrochemistry, etc., which underlies these experiments. In turn, these quantitative materials provide an understanding of many electrophysiological applications through a relatively small number of fundamental ideas. DOWNLOAD E-BOOK HERE...

Analog controllers can be classified by the relationship between the error signal input to them and the control action they produce: a. Proportional (P) controllers produce an output that is directly proportional to the error signal.  A defining characteristic of P control is that the error signal must always be non-zero to produce a control action; therefore, proportional control alone cannot return the process to setpoint following an external disturbance. This non-zero error signal that is characteristic of P controllers is the steady-state offset. The adjustable value of the proportionality constant of a P controller is the gain.  The higher the gain, the greater the control action for a given error signal and the faster the response. An example of a P controller is a governor on an engine-generator operating in droop mode, in which the governor opens the fuel valve proportionately to the difference between the desired revolutions per minute (RPM...

In this paper we have developed an integrated wireless SCADA system for monitoring &  accessing the performance of remotely situated device parameter such as temperature, pressure, humidity on real time basis. For this we have used the infrastructure of the existing  mobile network, which is based on GPRS technique Supervisory Control and Data  Acquisition (SCADA) is a field of constant development and research. This project investigates on creating an extremely low cost device which can be adapted to many different SCADA applications via some very basic programming, and plugging in the relevant peripherals. Much of the price in some expensive SCADA applications is a result of using specialized communication infrastructure. The application of infrastructure, in the proposed scheme the cost will come down. Additionally the generic nature of the device will be assured. Wireless SCADA deals with the creation of an inexpensive, yet...