TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

Abstract  New terminology is introduced to make clear the relationship between harmonics and symmetrical components. Three-phase sets are classified in terms of symmetrical sets and asymmetrical sets. Subclasses are introduced with the names symmetrical balanced sets, symmetrical unbalanced sets, asymmetrical balanced sets and asymmetrical unbalanced sets to show that a threephase set can resolve to either one, two or three symmetrical component sets. The results from four case studies show that these subclasses and their resolution to symmetrical component sets improve understanding of harmonic analysis of systems having balanced and unbalanced harmonic sources and loads. Conclusions The table and paragraph given in Ref. 1 does not adequately describe the relationship between harmonics and symmetrical components, especially harmonic sources and does not cover unbalanced loads. In general authors of power system literature ignore the symme...

Introduction Sequence component analysis plays an essential role in analyzing power system faults and explaining some power system phenomena. It is very well known that negative sequence current could cause rotor damage, and that damage is highly detrimental to rotating machines such as motors and generators. IEEE Tutorial of the Protection of Synchronous Generators (95 TP 102) has the following statement in  section “Current Unbalance Protection”: “During unbalanced conditions, negative sequence current is produced.  The negative sequence current component rotates in the opposite direction from the rotor.” This statement is not quite correct. Positive, negative and zero sequence currents are linear combinations of  phase currents; thus, the vector of each sequence current rotates in the same direction as the phase current.   Usually, phase angle is measured with a reference, and the rotation of the negative sequence current g...

Written by the following Authors: ALI EBADI a.ebadi@stu.nit.ac.ir MOHAMMAD MIRZAIE  mirzaie@nit.ac.ir SAYYED ASGHAR GHOLAMIAN  gholamian@nit.ac.ir  Department of Electrical and Computer Engineering  Babol University of Technology  Babol, Iran  Abstract:  Because of various techno-economic benefits, three-phase induction motors are used extensively in  industry, commercial and residential applications and most of them are connected to electric power distribution system directly, thus they will be affected by voltage quality problems. An important voltage quality problem in power systems is voltage unbalance.  Therefore, it is very important to study performance of these motors under unbalanced voltages. In this paper, Two-Dimensional Finite Element Method is employed to analyze the performance of a three-phase squirrel cage induction motor under voltage unbalance, focusing on electromagne...

The method of symmetrical components is a mathematical technique that allows the engineer to solve unbalanced systems using balanced techniques. The method of symmetrical components is particularly suited to fault analysis. This method is formulated by Chalrles Legeyt Fortescue , one of our Engineering Heroes . Below are high quality links to help further explain, illustrate and give you and idea on the applications of Methods of Symmetrical Components: Symmetrical Components and Unbalanced Faults When an unbalanced three-phase fault occurs, we can solve the three-phase circuit using  ordinary circuit theory. This is much more numerically complicated than the single phase circuit normally used in balanced three phase circuits.  The degree of difficulty  increases with the third power of the system size.  For this reason, it is apparent that if we  were to solve three different single-phase circuits, it would be numerically simpler...

Electronics is an engineering discipline that involves the design and analysis of electronic circuits. Originally, this subject was referred to as radio engineering. An electronic circuit is a collection of components through which electrical current can flow or which use electromagnetic fields in their operation. The electronic circuit design and analysis rests primarily on two Kirchoff's laws in conjunction with Ohm's law modified for AC circuits and power relationships. There are also a number of network theorems and methods (such as Thevenin, Norton, Superposition, Y-Delta transform) that are consequences of these three laws.  In order to simplify calculations in AC circuits, sinusoidal voltage and current are usually represented as complex-valued functions called phasors. Practical circuit design and analysis also requires a comprehensive understanding of semiconductor devices, integrated circuits and magnetics. Read more... I = current(amps.), V = voltage(volts), ...

This calculator computes the matched line loss for a transmission line using a model calibrated from data for the transmission line types built in to the calculator. It also gives an estimate of the mismatched loss if the mismatch is specified. Mismatch can be specified as: the impedance at the load end of the line; the admittance at the load end of the line; the impedance looking into the line from the source; the admittance looking into the line from the source; the VSWR at the source end of the line; the VSWR at the midpoint of the line; or the VSWR at the load end of the line; or the load end VSWR - bad case Zload (Zload=Zo/VSWR). The calculation of loss using VSWR is an approximation that is reasonably accurate on long lines with low VSWR and low loss. The methods using the impedance of the load or looking into the line produce accurate answers, and are the only way to get reasonably accurate answers with high VSWR or short lines. The models for most lines are from t...

The objective of this paper is to demonstrate the efficient calculation of design parameters using the boundary element method coupled with a highly interactive package for entering the transmission line configuration. The geometry of the problem that can be solved is arbitrary. Conductors may be infinitesimally thin or may be of finite area. As well, the conductors may be embedded in one or more dielectric materials. DOWNLOAD THE WHOLE DOCUMENT HERE!!!

C-1210 Single Capstan Winch  The C-1210 Single Capstan Winch has been designed to provide a light and powerful universal winch. Suitable for hoisting loads up poles or transmission towers or pulling cables and conductors.  The CBS C-680 Bulldog winch has been designed to provide a compact, transportable unit for overhead line stringing work  The CBS C-680 Bulldog winch has been designed to provide a compact, transportable unit for overhead line stringing work  Aerial Bundle Conductor Clamps Manufactured from high quality materials, the clamps have been specially designed to suit ABC conductors and provide a wide range per clamp to suit the range of twin and quad bundles. Double "V" grooves give four-point contact, reducing chance of slipping and providing proper alignment of wire and cable. AMAR INDUSTRIES  is marching forward to become the global leader in transmission line stringing tools & equipment. The company has been manufacturing and exporti...

In order to meet the high demand for power transmission capacity, some power companies have installed series capacitors on power transmission lines.  This allows the impedance of the line to be lowered, thus yielding increased transmission capability.  The series capacitor makes sense because it’s simple and could be installed for 15 to 30% of the cost of installing a new line, and it can provide the benefits of increased system stability, reduced system losses, and better voltage regulation. Protective distance relays, which make use of impedance measurements in order to determine the presence and location of faults, are “fooled” by installed series capacitance on the line when the presence or absence of the capacitor in the fault circuit is not known a priori.  This is because the capacitance cancels or compensates some of the inductance of the line and therefore the relay may perceive a fault to be in its first zone when the fault i...

Transmission Line Parameters If we consider an infinite lossless transmission line, we can determine the inductance L and  capacitance C per unit length from geometric field considerations.  The three physical  embodiments that are of interest are the two-wire transmission line, the coaxial transmission and  the microstrip transmission line (a simple parallel-plate approximation). Transmission Line Discontinuities and Load Impedances If the wave on a transmission line of characteristic impedance Zo arrives at a boundary with  different Zo, or at a discontinuity, lumped load or termination of Z ?   Zo, the single wave moving  in the +z direction cannot simultaneously satisfy the boundary conditions relating V(z) to I(z) on both sides of the boundary.  On one side of the boundary V(z)/I(z) = V+/I+ = Zo and on the  other side V(z)/I(z) = (V++V-)/(I+-I-) = ZL. Visualization of Standing Waves The following set of graphs show the deve...

Consideration of machine losses is important for three reasons: (1) Losses determine the efficiency of the machine and appreciably influence its operating cost (2) Losses determine the heating of the machine and hence the rating or power output that can be obtained without undue deterioration of the insulation (3) Voltage drops or current components associated with supplying the losses must be properly accounted for in a machine representation. Machine efficiency, like that of transformers or any energy-transforming device, is given by: Efficiency = output/ input Rotating machines in general operate efficiently except at light loads. For example, the full-load efficiency of average motors ranges from 80 to 90 percent for motors on the order of 1 to 10 kW, 90 to 95 percent for motors up to a few hundred kW, and up to a few percent higher for larger motors. Efficiencies determined from loss measurements can be used in comparing competing machines if exactly the same m...

Structures may be founded on rock, on strong or weak soils, cohesive or noncohesive soils, above ground level, below water level, etc. The type of foundation used to support a structure depends on local conditions. After obtaining a general evaluation of the subsurface conditions the engineer should attempt to identify all potential useful foundation alternatives for a structure. Three basic types of foundations are available: soil-founded, various types of piles, and piers or caissons. Each of these foundation types has many subcategories. The following paragraphs provide a short description and evaluation of the various pile types. The purpose of a pile foundation is to transfer and distribute load through a material or stratum with inadequate bearing, sliding or uplift capacity to a firmer stratum that is capable of supporting the load without detrimental displacement.  A wide range of pile types is available for applications with various soil types and structur...

Individual capacitor step circuit breakers provide shunt capacitor bank switching. There are two modes of operation: manual and automatic. Manual Mode In the manual mode, operators switch capacitor banks from the control room through step control switches installed on the switchboards. The following permissive conditions must be met before a capacitor step can be switched on or off by the manual control switches. ·  The capacitor step must be in manual mode. ·  The circuit breaker must be open for at least five minutes before it can be reclosed. This allows the capacitors to be discharged to a safe voltage level through their internal discharge device. If the breaker is not open for five minutes, the programmable logic controller blocks the close circuit and prevents the operator from closing the breaker. Automatic Mode In the automatic mode, the PLC controls the switching of the shunt capacitor steps. The PLC is programmed to perform voltage control a...

Corona is a discharge caused by electrical overstress. Corona is a luminous discharge due to ionization of the air surrounding a conductor around which exists a voltage gradient exceeding a certain critical value. For transmission line studies, the insulating material in which the discharge occurs is the air adjacent to conductor or insulator surfaces, when the electrical stress at these surfaces exceeds the critical value. With the increased use of high-voltage transmission lines and the probability of going to still higher operating voltages, the common aspects of corona (radio influence and corona loss) have become more important in the design of transmission lines. In the early days of high-voltage transmission, corona was something which had to be avoided, largely because of the energy loss associated with it. In recent years the RI (radio influence) aspect of corona has become more important. In areas where RI must be considered, this factor might establish the l...

Transformers are susceptible to damage by secondary short-circuit currents having magnitudes that can be many times rated load current. The damage results from the following effects: • The I^2R losses in the winding conductors are increased by the square of the current. This increases the temperature rise of the windings. Because protective devices limit the duration of short circuits (as opposed to overloads), the temperature rise of the winding can be calculated by dividing the total energy released by the I^2R losses by the thermal capacity of the conductor. • The short-circuit currents exclude flux in the core and increase stray flux around the core. This stray flux induces currents in metallic parts other than the winding conductors, which can be damaged thermally. • A short circuit applied to the secondary circuit of an autotransformer can substantially increase the voltage across the series winding and across the common winding through induction. This not on...

The Y-Y transformer connection was poorly understood in the early days of power engineering and it received a very bad reputation when it was first used; in fact, this connection was avoided for a long time until its limitations were overcome by good engineering practice. Some of the inherent disadvantages of the Y-Y connection are discussed below: 1. The presence of third (and other zero-sequence) harmonics at an ungrounded neutral can cause overvoltage conditions at light load. When constructing a Y-Y transformer using single-phase transformers connected in a bank, the measured line-to-neutral voltages are not 57.7% of the system phase-to-phase voltage at no load but are about 68% and diminish very rapidly as the bank is loaded. The effective values of voltages at different frequencies combine by taking the square root of the sum of the voltages squared. With sinusoidal phase-to-phase voltage, the third-harmonic component of the phase-to-neutral voltage is about 60%, so ...

Although care must be exercised when using the Y-Y connection, this connection has certain inherent and important advantages over other three-phase transformer connections. 1. The primary and secondary circuits are in phase; i.e., there are no phase angle displacements introduced by the Y-Y connection. This is an important advantage when transformers are used to interconnect systems of different voltages in a cascading manner. For example, suppose there are four systems operating at 500, 230, 138, and 69 kV that need to be interconnected. Substations can be constructed using Y-Y transformer connections to interconnect any two of these voltages. The 500 kV system can be tied with the 69 kV system through a single 500 to 69 kV transformation or through a series of cascading transformations at 230, 138, and 69 kV. 2. Since the phase-to-neutral voltage is only 57.7% of the phase-to phase voltage, the windings of a Y-Y transformer require fewer turns to produce the same lev...

Pickup The term pickup has acquired several meanings. For many devices, pickup is defined as the minimum current that starts an action. This definition is accurately used when describing a relay characteristic. Pickup also describes the performance of a low-voltage circuit breaker with an electronic trip device. However, the term does not apply accurately to the thermal trip element of a thermal magnetic molded-case circuit breaker (MCCB), which deflects as a function of stored heat. The pickup of an overcurrent protective relay has generally been considered the minimum value of current that causes the relay to close its contacts. The current (or tap) setting of the relay and the minimum pickup were synonymous. However, with new technology developments in static overcurrent relays, this definition needs more clarification. Electromechanical Versus Static Relays The pickup value for electromechanical induction disk time-overcurrent relays is the minimum current that cau...

A “bundle conductor” is a conductor made up of two or more ‘(sub-conductors”, and is used as one phase conductor. Bundle conductors are also called duplex, triplex, etc., conductors, referring to the number of sub-conductors and are sometimes referred to as grouped or multiple conductors. Considerable work on bundle conductors has been done by the engineers of Siemens Schuckertwerkez who concluded that bundle conductors were not economical at 220 kv, but for rated voltages of 400 kv or more, are the best solution for overhead transmission. Rusck and Rathsman state that the increase in transmitting capacity justifies economically the use of two conductor bundles on 220-kv lines. The advantages of bundle conductors are higher disruptive voltage with conductors of reasonable dimensions, reduced surge impedance and consequent higher power capacity, and less rapid increase of corona loss and RI with increased voltage. These advantages must be weighed against increased circuit c...

In order to synchronize a generator to the grid, four conditions must be met. Phase Sequence The phase sequence (or phase rotation) of the three phases of the generator must be the same as the phase sequence of the three phases of the electrical system (Grid). The only time that the phase sequence could be wrong is at initial installation or after maintenance. There are two possible problem sources. The generator or transformer power leads could actually be interchanged during maintenance or the potential transformer leads could be interchanged during maintenance. Voltage Magnitude The magnitude of the sinusoidal voltage produced by the generator must be equal to the magnitude of the sinusoidal voltage of the grid. If all other conditions are met but the two voltages are not the same, that is there is a voltage differential, closing of the ac generator output breaker will cause a potentially large MVAR flow. Recall that before a generator is synchronized to the gri...

As the available ratings of turbine-generators have increased, the problems of supplying the dc field excitation (amounting to 4000 A or more in the larger units) have grown progressively more difficult. A common excitation source is a shaft-driven dc generator whose output is supplied to the alternator field through brushes and slip rings. Alternatively, excitation may be supplied from a shaft-driven alternator of conventional design as the main exciter. This alternator has a stationary armature and a rotating-field winding. Its frequency may be 180 or 240 Hz. Its output is fed to a stationary solid-state rectifier, which in turn supplies the turbine-generator field through slip rings. Cooling and maintenance problems are inevitably associated with slip rings, commutators, and brushes. Many modern excitation systems have minimized these problems by minimizing the use of sliding contacts and brushes. As a result, some excitation systems employ shaft-driven ac alter...

The power factor at which ac machines operate is an economically important feature because of the cost of reactive kilovoltamperes. Low power factor adversely affects system operation in three principal ways. (1) Generators, transformers, and transmission equipment are rated in terms of kVA rather than kW because their losses and heating are very nearly determined by voltage and current regardless of power factor. The physical size and cost of ac apparatus are roughly proportional to kVA rating. The investment in generators, transformers, and transmission equipment for supplying a given useful amount of active power therefore is roughly inversely proportional to the power factor. (2) Low power factor means more current and greater 12 R losses in the generating and transmitting equipment. (3) A further disadvantage is poor voltage regulation. Factors influencing reactive-kVA requirements in motors can be visualized readily in terms of the relationship of these requireme...

The cooling problem in electric apparatus in general increases in difficulty with increasing size. The surface area from which the heat must be carried away increases roughly as the square of the dimensions, whereas the heat developed by the losses is roughly proportional to the volume and therefore increases approximately as the cube of the dimensions. This problem is a particularly serious one in large turbine generators, where economy, mechanical requirements, shipping, and erection all demand compactness, especially for the rotor forging. Even in moderate size machines, for example, above a few thousand kVA for generators, a closed ventilating system is commonly used. Rather elaborate systems of cooling ducts must be provided to ensure that the cooling medium will effectively remove the heat arising from the losses. For turbine generators, hydrogen is commonly used as the cooling medium in the totally enclosed ventilating system. Hydrogen has the following properties w...

The Lorentz Force Law: F = q(E + v × B) gives the force F on a particle of charge q in the presence of electric and magnetic fields. In SI units, F is in newtons, q in coulombs, E in volts per meter, B in teslas, and v, which is the velocity of the particle relative to the magnetic field, in meters per second. Thus, in a pure electric-field system, the force is determined simply by the charge on the particle and the electric field; F = qE The force acts in the direction of the electric field and is independent of any particle motion. In pure magnetic-field systems, the situation is somewhat more complex. Here the force F = q(v × B) is determined by the magnitude of the charge on the particle and the magnitude of the B field as well as the velocity of the particle. In fact, the direction of the force is always perpendicular to the direction of both the particle motion and that of the magnetic field. Mathematically, this is indicated by the vector cross product ...

For decades, fluidized-bed reactors have been used in noncombustion reactions in which the thorough mixing and intimate contact of the reactants in a fluidized bed result in high product yield with improved economy of time and energy. Although conventional methods of burning coal can also generate energy with very high efficiency, fluidized-bed combustion can burn coal efficiently at a temperature low enough to avoid many of the problems of conventional combustion. The outstanding advantage of fluidized-bed combustion (FBC) is its ability to burn high-sulfur coal in an environmentally acceptable manner without the use of flue-gas scrubbers. A secondary benefit is the formation of lower levels of nitrogen oxides compared to other combustion methods. Crushed fuel and sorbent are fed mechanically or pneumatically to the lower portion of the combustor. Primary air is supplied to the bottom of the combustor through an air distributor, with secondary air fed through one or m...

Coal, which is the most abundant and economically stable fossil fuel in the United States, continues to grow in use while under pressure to meet the most stringent federal and local emissions requirements. This trend has added to the cost and complexity of coal combustion technologies. Emission-control methods that facilitate the use of coal in power plants can be classified as Precombustion processes In situ combustion processes Postcombustion processes Precombustion processes include methods to clean the coal of sulfur-bearing compounds by wet separation, coal gasification, and coal liquefaction techniques. Coal gasification involves the partial oxidation of coal to produce a clean gas or by production of a “clean fuel” through coal liquefaction. Sulfur and ash are removed in these processes. The use of coal to produce a gas is not a new idea; it has been used to produce “town gas” for over 200 years. But its use in the United States had almost disappeared by 193...