TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

Advantages of Diesel Engine Use The main advantages of using diesel driven electrical power generators are (not in rank order): 1. Performance. Diesel engines normally have high thermal efficiencies, in the region of 40% and higher, regardless of their size. Some current state-of-the-art engines can achieve efficiencies over 50%, and engine manufacturers have forecast efficiencies as high as 60% by the twenty-first century. 2. Maintenance. Diesels represent mature and well-developed technology and are comparatively easy to maintain on site without the need for fully skilled personnel except for certain nonroutine tasks. 3. Durability and Reliability. Diesels have long lifetimes in the range, on average, of at least 20 to 25 years, and they can operate 7000 to 8000 h per year and in some cases up to 12,000 h between regular major overhauls. 4. Fuel Efficiency. In most power-generation applications, diesels have the most com...

The term mobile channel refers to the transfer function of adio link when one or both of the terminals are moving. The moving terminal is typically in a vehicle such as a car, or a personal communications terminal such as a cellphone. Normally one end of the radio link is fixed, and this is referred to as the base station.  In the link, there is usually multipath radiowave propagation, which is changing with time, or more specifically, as a function of position of the moving terminal. The effects of this multipath propagation dominate the behavior and characterization of the mobile channel. The radio frequency of the link ranges from hundreds of kilohertz, as in broadcast AMradio, to microwave frequencies, as in cellphone communications. Indeed, even optical frequencies are used, as in an infrared link used for indoor computer communications.  The kind of channel most often referred to as “mobile,” however, is that using microwave fr...

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Lightning has a tendency preferentially to strike taller structures and objects. Strikes to ground are, however, quite common where there is a distance between structures of more than twice their individual height. For lightning protection purposes an all conducting building, with metal cladding and roof, is an ideal structure. It effectively provides electronic equipment within it with a ‘screened room’ environment. Many steel framed or reinforced concrete buildings with metal cladding will approximate to this ideal. If lightning strikes the building, a ‘sheet’ of current will flow all over the surface and down to earth, provided that the cladding and roofing is correctly bonded together. Any small differences in resistance will have little effect on current flow – flow paths are dictated by inductance and not resistance, owing to the fast impulsive nature of the lightning return stroke and restrikes. Current flows in steel fram...

MAGNETIC MATERIALS Iron and its derivative, steel, can be given the property of attracting other pieces of iron and steel. This property, known as magnetism, is possessed to a much lesser degree by nickel, cobalt, and gadolinium. Iron and steel combined with these and other magnetic materials will yield an alloy with much greater magnetic strength. The magnetic effects of magnets are concentrated at areas called poles. These poles are of two types and have been designated as north and south poles because of the fact that a magnet supported freely in air will align its axis in a north-south direction. The end of the magnet that points geographically north is called the north (N) pole, and the other end is called the south (S) pole. Although all materials have some degree of a magnetic property, most materials do not have a useful amount of this property and, for all practical purposes, can be called nonmagnetic. PERMANENT AND TEMPORARY...

Access Fitting. A fitting that permits access to conductors in concealed or enclosed wiring, elsewhere than at an outlet. Active Electrical Network. A network that contains one or more sources of electrical energy. Admittance. The reciprocal of impedance. Air-Blast Transformer. A transformer cooled by forced circulation of air through its core and coils. Air Circuit Breaker. A circuit breaker in which the interruption occurs in air. Air Switch. A switch in which the interruption of the circuit occurs in air. Alive. Electrically connected to a source of emf, or electrically charged with a potential different from that of the earth. Also, practical synonym for current-carrying or hot. Alternating Current. A periodic current, the average value of which over a period is zero. Alternator. Synchronous generator; a synchronous alternatingcurrent machine that changes mechanical power into electrical power. Ambient Temperature. The temperature of a surrounding cooling medium...

Several types of transformer tank construction are used to prevent exposingliquid to the atmosphere. These types are as follows: Free breathing: This type is open to the atmosphere (i.e., the airspace above the liquid is at atmospheric pressure). The transformer breathes as the air pressure and temperature change outside the tank.  Some of these transformers can be equipped with dehydrating compounds in the breather. Conservator or expansion-tank: These transformers are equipped with small expansion tanks above the transformer tank. The transformer tank is completely filled with oil, and the transformer breathes by means of this small tank, usually through a dehydrating compound. The purpose of the small tank is to seal the transformer fl uid from the atmosphere and to reduce oxidization and formation of sludge. Sealed tank: These transformers are equipped with an inert gas, such as nitrogen that is under pressure above the liquid in the transformer tank. Genera...

Developments in power electronics over the last 10–15 years has made it possible to control not only the speed of the AC induction motors but also the torque. Modern ACVSDs, with flux-vector control, can now meet all the performance requirements of even the most demanding applications. The methods of speed control are listed below: 1. Stator voltage control 2. Supply frequency control 3. Rotor resistance control 4. Pole changing. Usually, the AC motor speed control is achieved by varying its supply frequency. In order to keep the losses minimum, the terminal voltage frequency is changed to keep the v/f ratio constant. The frequency control method of changing the speed of AC motors is a well-known technique for decades. Only recently, however, it has become a technically viable and economical method of VSD control. AC drives have become a more cost-effective method of speed control, in comparison to DC drives, for most VSD applications of up to 1000 kW. It is also th...

The insulation utilized should withstand the voltage fluctuations of the motor under varying operating conditions. Depending on the load and its surrounding conditions, there could be a rise in the temperature of the motor. The insulation should withstand such temperature rises also. The hot-spot temperature in any part of the motor should not exceed the permissible limit of the insulation used. In case of insulating materials, their thermal characteristics are more sensitive than their dielectric characteristics, i.e., the failure of an insulating material is more due to thermal limitations than due to voltage limitations. In most cases, the temperature rise or the rise in load does not produce a fault in the winding of the conductor itself. The rise of load current or greater fault current, when it is excessive, causes a thermal breakdown in the insulation covering the conductor. This is what creates a fault in the winding. Thus, the maximum permissible temperature rise, ...

Characteristics of DC motors • DC motors have good starting torque as well as good speed-regulation capabilities. • Permanent magnet-type DC motors are used for exact positioning of objects with high-operating torques. • Series type gives high-starting torque; hence the ability to start with high loads. • Series motors when operated with no loads can attain high speeds causing harm to motor. • Shunt-type motors have good speed regulation. • Direction reversal of DC motor can be done by changing the leads of the armature or the field. • Speed of DC motor changes either by changing armature voltage or field current. • If armature voltage is increased, speed increases till base speed and vice versa. • Similarly, speed can be increased above base speed, by decreasing field current. • In shunt motors torque is proportional to armature current. • In series motors torque is proportional to square of armature current.

White Paper By the Author John Horak of Basler Electric Abstract - This paper reviews the basic equations for the sequence impedance of transmission lines, including ground loop current flow, how neutral wires are included in the equations, and how this impedance is transformed from an ABC domain impedance to the 012 domain impedance. A side benefit of the approach taken is that the paper shows how one calculates the sequence impedances of untransposed power lines, including calculation of the off-diagonal (mutual) elements of the sequence component 012 domain impedances. The paper also addresses the calculation of mutual impedances between two parallel lines. I. INTRODUCTION The paper begins by analyzing system impedances in the ABC (physical or phase) domain, first without any overhead ground wires, and then shows how the overhead ground conductors are incorporated into the analysis. Then the paper shows the translation of these ABC domain impedances to the 012 (sequence) do...

Surge Protection Capacitors Surges and Protection against surges: Electrical networks experience surges wherein a voltage or a current rises rapidly to unsafe values and destroys the dielectric insulation. These, along with partial discharges which these start, are blamed for the major portion of failures of electrical equipment of all types. As per modern thinking, most of the surges are current – sourced as against the normal voltage sourced electric power supply. An amount of let off energy, determines this current which flows to ground – irrespective of the circuit resistance. If a contact of a lighting conductor stripe is bad, it creates dangerous voltages – rather than reducing the current. This rapid rate of rise of current is responded by a magnetic circuit (of all types of transformers) with an equally rapidly rising flux, a back EMF and a very high induced voltage. This voltage causes breakdowns, flash overs, partial discharges and so on. This surge ...

Figure 74.1 depicts several kinds of satellite links and orbits. The geostationary earth orbit (GEO) is in the equatorial plane at an altitude of 35,786 km with a period of one sidereal day (23h 56m 4.09s). This orbit is sometimes called the Clarke orbit in honor of Arthur C. Clarke who first described its usefulness for communications in 1945. GEO satellites appear to be almost stationary from the ground (subject to small perturbations) and the earth antennas pointing to these satellites may need only limited or no tracking capability. An orbit for which the highest altitude (apogee) is greater than GEO is sometimes referred to as high earth orbit (HEO). Low earth orbits (LEO) typically range from a few hundred km to about 2000 km. Medium earth orbits (MEO) are at intermediate altitudes. Circular MEO orbits, also called Intermediate Circular Orbits (ICO) have been proposed at an altitude of about 10,400 km for global personal communications at frequencies designated for ...

The better a substance conducts, the less its resistance; the worse it conducts, the higher its resistance. Electricians and electrical engineers sometimes prefer to speak about the conductance of a material, rather than about its resistance. The standard unit of conductance is the siemens, abbreviated S. When a component has a conductance of 1 S, its resistance is 1 ohm. If the resistance is doubled, the conductance is cut in half, and vice-versa. Therefore, conductance is the reciprocal of resistance. If you know the resistance in ohms, you can get the conductance in siemens by taking the quotient of 1 over the resistance. Also, if you know the conductance in siemens, you can get the resistance in ohms by taking 1 over the conductance. The relation can be written as: siemens = 1/ohms, or ohms = 1/siemens Smaller units of conductance are often necessary. A resistance of one kilohm is equal to one millisiemens. If the resistance is a megohm, the conductance is one m...

The standard for broadcasting analog television in most of North America is NTSC. The standards for video in other parts of the world are PAL and SECAM. Note that NTSC, PAL and SECAM will all be replaced over the next ten years with a new suite of standards associated with digital television. International organizations that contribute to standardizing digital television include: ■ Advanced Television Systems Committee (ATSC) ■ Digital Video Broadcasting (DVB) The Advanced Television Systems Committee was formed to establish a set of technical standards for broadcasting television signals in the United States. ATSC digital TV standards include high-definition television, standard definition television, and satellite direct-to-home broadcasting. ATSC has been formally adopted in the United States where an aggressive implementation of digital TV has already begun. Additionally, Canada, South Korea, Taiwan, and Argentina have agreed to use the formats and transmissio...

For the most part, the processing of audio signals can be performed with only minuscule power, either input or dissipated. Analog signals pass through the majority of the overall signal path at average levels in the order of 100mV to 1 volt. Load impedances may be as high as 100kΩ but even if as low as 5kΩ, only 120μW (a hundred and twenty microwatts; or about a tenth of a thousandth of one watt) would be dissipated. At this rate, it would take about eight million hours or hundreds of years of playing, for the load to absorb or use one unit (1kWh) of electricity! Most loudspeakers used to reproduce audio are highly inefficient. Typical efficiencies of common direct radiating speakers are 1% to 0.05%. By comparison, the efficiency of an internal combustion engine (considered highly inefficient by ecologists) is between 2500% and 50,000% greater. A medium sized car uses about 70kW to move 4 people or hundreds of pounds of goods, and its own weight – altogether at least ha...