TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

Transient overvoltages can arise from a number of sources. Power disturbances result from lightning strokes or switching operations on transmission and distribution lines. Switching of power factor correction capacitors for voltage control is a major cause of switching transients. All utility lines are designed for a certain basic insulation level (BIL) that defines the maximum surge voltage that will not damage the utility equipment but which may be passed on to the customer. Some consideration should be given to the supply system BIL in highpower electronics with direct exposure to medium-voltage utility lines. Such information is generally available from the utility representative. The standard test waveform for establishing BIL capability is a voltage that rises to the instantaneous BIL value in 1.2 μs and decays to half that value in another 50 μs. Other sources of transient overvoltages may lie within power electronics equipment itself. Interrupting contactor coils ...

As an Electrical Engineer, especially dwelling in metering theory and practice, everybody must have heard Blondel's Theorem. For starters, it says that, In a system of N conductors, N-l meter elements, properly connected, will measure the power or energy taken. The connection must be such that all voltage coils have a common tie to the conductor in which there is no current coil. But who is the man behind the statement? He is no other than Andre Blondel, today's featured Electrical Engineering Hero. The theory of polyphase watthour metering was first set forth on a scientific basis in 1893 by Andre E. Blondel, engineer and mathematician. His theorem applies to the measurement of real power in a polyphase system of any number of wires. He was born on August 28, 1863 in Chaumont, Haute Marne, in France. He is a physicist, professor, and of course an engineer, a testament to his multi faceted  and talented life. He was employed as an engineer by the Lighthouse...

Standing waves appear when a length of line is excited at a frequency for which the electrical line length is a significant part of an electrical wavelength. They result from the constructive and destructive interference of forward and reflected waves on the line. The behavior of the line can be determined by solving the applicable differential equations relating the line parameters to the exciting frequency. The solution of the equations for a line with losses is rather complex and adds little to the practical considerations, so the lossless line will be analyzed instead. In the lossless line, L is the series inductance per unit length, and C is the shunt capacitance. If a differential length, dx , is considered, the inductance for that length is L dx , and the voltage in that length is e = Ldx ( di/dt ). Since e = ( de/dx ) dx , the equation can be written as dx ( de/dx ) = – L dx ( di/dt ). Fortunately, the computer offers an easier method of analysis by numerical integ...

Through discovery, invention, and engineering application, the engineer has made electricity of continually greater use to mankind. Electrical power is the driving force to the evolution and improvement of the world. One of the efforts and means to achieve this goal is to transmit power from the generation source to its “ load” in the most economical and feasible way. This is done via the transmission lines. Transmission lines are essential for three purposes. a. To transmit power from a water-power site to a market. These may he very long and justified because of the subsidy aspect connected with the project. b. For bulk supply of power to load centers from outlying steam stations. These are likely to be relatively short. c. For interconnection purposes, that is, for transfer of energy from one system to another in case of emergency or in response to diversity in system peaks. Frequent attempts have been made to set up definitions of “transmission lines, ” “d...

Electrical preventive maintenance should be a prime consideration for any new electrical equipment installation. Quality, installation, configuration, and application are fundamental prerequisites in attaining a satisfactory preventive maintenance program. A system that is not adequately engineered, designed, and constructed will not provide reliable service, regardless of how good or how much preventive maintenance is accomplished. One of the first requirements in establishing a satisfactory and effective preventive maintenance program is to have good quality electrical equipment that is properly installed. Examples of this are as follows: a) Large exterior bolted covers on switchgear or large motor terminal compartments are not conducive to routine electrical preventive maintenance inspections, cleaning, and testing. Hinged and gasketed doors with a three-point locking system would be much more satisfactory. b) Space heater installation in switchgear or an electric ...

An inspection analysis of the physical condition of a plant’s distribution system can be utilized (hopefully on a continual basis) to improve plant reliability. The following inspection requires little, if any, capital investment while providing a favorable increase in reliability: a) Equipment should be periodically checked for proper condition, and programs should be initiated for preventive maintenance procedures as required. 1) Oil in transformers and circuit breakers should be periodically checked for mineral, carbon, and water content as well as level and temperature. 2) Molded case circuit breakers should be exercised periodically (that is, operated “on” to “off” to “on”). 3) Terminals should be tightened. Each terminal should be inspected for discoloration (overheating), which is generally caused by either a bad connection or equipment overload. Cabinets, etc., should be checked for excessive warmth. Remember that circuit breakers and fuses interrupt as a resul...

Codes, standards, or other documents referred to in this specification are to be considered as part of it. In the event of a conflict between this specification and the National Electrical Safety Code (NESC), the NESC shall be followed. In the event of a conflict between this specification and all other referenced documents, this specification shall be followed. If a conflict between several referenced documents occurs, the more stringent requirement shall be followed. If clarification is necessary, contact the owner. The most recent editions of the following codes and standards shall be followed in the design, manufacture, inspection, testing, and shipment of spun, prestressed concrete poles: 3.1 American Concrete Institute (ACI): ACI 318, Building Code Requirements for Reinforced Concrete 3.2 Prestressed Concrete Institute (PCI): MNL 116, Manual for Quality Control for Plants and Production of Precast Prestressed Concrete Products 3.3 American Welding Societ...

Differential relaying with overcurrent relays requires connecting current transformers in each phase of each circuit in parallel with an overcurrent relay for that phase. (See Fig 1, illustrating the connections for 1 phase of a 3-phase system.) While it is permissible to utilize auxiliary current transformers to match ratios, it is most desirable for all current transformers to have the same ratio on the tap used so that auxiliary current transformers are not required. Ground differential relaying, with an overcurrent relay for bus ground faults only, has been applied where current transformers are not available to dedicate to bus protection and where the bus construction minimizes the possibility of phase faults. In this case only the current transformer residual current circuits are connected, as shown in Fig 1. The usual precautions concerning burden, etc, apply. Where bus selection flexibility is provided, the system can be switched. Switching of residual current...

 Water treeing can range from predominantly electromechanical in nature to essentially electrochemical. Agreat deal of the early laboratory work was carried out with “water needle” configurations, which produce extremely high electric fields at the tip of a needle-shaped, water-filled cavity. The electric field at the tip was usually high enough to produce an electrical tree if the cavity were not filled with water, and the water tree grows in hours to days, rather than months to years as for a water tree grown under utility operating conditions. Dorris, et al. Investigated electrical signals generated by the growth of such water trees. An analysis of their data suggests that the measured electrical signals could be produced by a sudden 0.01 to 0.1 μm extension of the water tree channel. This work provides clear evidence for the growth of essentially electromechanical trees at very high fields. Such trees probably grow through (i) electrochemical damage in the tree ti...

NFPA 72 classifies fire alarm systems as follows. HOUSEHOLD FIRE ALARM SYSTEM A system of devices that produces an alarm signal in the household for the purpose of notifying the occupants of the presence of fire so that they will evacuate the premises. PROTECTED PREMISES (LOCAL) FIRE ALARM SYSTEM A system that sounds an alarm at the protected premises as the result of the manual operation of a fire alarm box or the operation of protection equipment or systems, such as water flowing in a sprinkler system, the discharge of carbon dioxide, the detection of smoke, or the detection of heat. AUXILIARY FIRE ALARM SYSTEM A system connected to a municipal fire alarm system for transmitting an alarm of fire to the public fire service communications center. Fire alarms from an auxiliary fire alarm system are received at the public fire service communications center on the same equipment and by the same methods as alarms transmitted manually ...

Blown optical fiber technology is an exciting method of delivering a fiber solution that provides unmatched flexibility and significant cost savings when compared to conventional fiber cables. In a blown optical fiber system, the fiber route is “plumbed” with small tubes. These tubes, known as microduct, come in 5- and 8 mm diameters and are approved for riser, plenum, or outside-plant applications.They are currently available as a single microduct, or with two, four, or seven microducts bundled (straight, not twisted) and covered with an outer sheath, called multiducts. They are lightweight and easy to handle. Splicing along the route is accomplished through simple push-pull connectors. These microducts are empty during installation, thereby eliminating the possibility of damaging the fibers during installation. Fiber is then installed, or “blown,” into the microduct.The fiber is fed into the microduct and rides on a cu...

Symmetrical Components, first developed by C.L.Fortescue in 1918, is a powerful technique for analyzing unbalanced 3f systems. Fortescue defined a linear transformation from 3f components to a new set of components called symmetrical components. The advantage of this transformation is that for balance three phase networks the equivalent circuit obtained for the symmetrical components, called sequence networks, are separated into three uncoupled networks. Further more, for unbalanced three phase systems, the three sequence networks are connected only at the points of unbalance. As a result, sequence networks for many cases of unbalanced three phase systems are relatively easy to analyze. The symmetrical component method is basically a modeling technique that permits systematic analysis and design of three phase systems. Decoupling a detailed three phase network into three simpler sequence networks reveals complicated phenomena in more simplistic terms. Sequence net...

Ground Rods. Vertically driven ground rods or pipes are the most common type of made electrode. Rods or pipes are generally used where bedrock is beyond a depth of 3 meters (10 feet). Ground rods are commercially manufactured in 1.27, 1.59, 1.90 and 2.54 cm (1/2, 5/8, 3/4 and 1 inch) diameters and in lengths from 1.5 to 12 meters (5 to 40 feet). For most applications, ground rods of 1.90 cm (3/4 inch) diameter, and length of 3.0 meters (10 feet), are used. Copper-clad steel ground rods are required because the steel core provides the strength to withstand the driving force and the copper provides corrosion protection and is compatible with copper or copper-clad interconnecting cables. Buried Horizontal Conductors. Where bedrock is near the surface of the earth, the use of driven rods is unpractical. In such cases, horizontal strips of metal, solid wires, or stranded cables buried 0.48 to 0.86 meters (18 to 36 inches) deep may be used effectively. With long strip...

Immediately after the alignment of a line has been finalized to the satisfaction of both the engineer and the borrower, a survey should be made to map the route of the line. Based on this survey, plan-profile drawings will be produced and used to spot structures. Long corridors can usually be mapped by photogrammetry at less cost than equivalent ground surveys. The photographs will also contain information and details which could not otherwise be discovered or recorded. Aerial survey of the corridor can be accomplished rapidly, but proper conditions for photography occur only on a comparatively few days during the year. In certain areas, photogrammetry is impossible. It cannot be used where high conifers conceal the ground or in areas such as grass-covered plains that contain no discernible objects. Necessary delays and overhead costs inherent in air mapping usually prevent their use for short lines. When using photogrammetry to develop plan-profile drawings, proper h...

Electric fields produce forces, just as do magnetic fields. You have probably noticed this when your hair feels like it’s standing on end in very dry or cold weather. You’ve probably heard that people’s hair really does stand straight out just before a lightning bolt hits nearby; this is no myth. Maybe you performed experiments in science classes to observe this effect. The most common device for demonstrating electrostatic forces is the electroscope. It consists of two foil leaves, attached to a conducting rod, and placed in a sealed container so that air currents will not move the foil leaves (Fig. 3-3). When a charged object is brought near, or touched to, the contact at the top of the rod, the leaves stand apart from each other. This is because the two leaves become charged with like electric poles—either an excess or a deficiency of electrons—and like poles always repel. The extent to which the leaves stand apart depends on t...

The flow of electric current may be visualized by comparing it with the flow of water. Where water is made to flow in pipes, electric current is conducted along wires. To move a definite amount of water from one point to another in a given amount of time, either a large-diameter pipe may be used and a low pressure applied on the water to force it through, or a small-diameter pipe may be used and a high pressure applied to the water to force it through. While doing this it must be borne in mind that when higher pressures are used, the pipes must have thicker walls to withstand that pressure (see Figure 1-3). The same rule applies to the transmission of electric current. In this case, the diameter of the pipe corresponds to the diameter of the wire and the thickness of the pipe walls corresponds to the thickness of the insulation around the wire, as shown in Figure 1-4.

Low voltages require large conductors, and high voltages require smaller conductors. This was illustrated with a water analogy. A small amount of pressure may be applied and the water will flow through a large pipe, or more pressure may be applied and the water will flow through a slimmer pipe. This principle is basic in considering the choice of a voltage (or pressure) for a distribution system. There are two general ways of transmitting electric current-overhead and underground. In both cases, the conductor may be copper or requires careful studies. Experts work out the system three or four different ways. For instance, they figure all the expenses involved in a 4000-volt (4 kV), in a 34,500-volt (34.5 kV), or a 13,000-volt (13 kV) system. The approximate costs of necessary equipment, insulators, switches, and so on, and their maintenance and operation must be carefully evaluated. The future with its possibil...

What is Demand? Electrical energy is commonly measured in units of kilowatthours. Electrical power is expressed as kilowatthours per hour or, more commonly, kilowatts. Demand is defined as power averaged over some specified period. Figure 7.2 shows a sample power curve representing instantaneous power. In the time interval shown, the integrated area under the power curve represents the energy consumed during the interval. This energy, divided by the length of the interval (in hours) yields “demand.” In other words, the demand for the interval is that value of power that, if held constant over the interval, would result in an energy consumption equal to that energy the customer actually used. Demand is most frequently expressed in terms of real power (kilowatts). However, demand may also apply to reactive power (kilovars), apparent power (kilovolt-amperes), or other suitable units. Billing for demand is commonly based on a customer’s maxi...

A number of situations exist where a generator could be driven as a motor. Anti-motoring protection will more specifically apply in situations where the prime-mover supply is removed for a generator supplying a network at synchronous speed with the field normally excited. The power system will then drive the generator as a motor. A motoring condition may develop if a generator is connected improperly to the power system. This will happen if the generator circuit breaker is closed inadvertently at some speed less than synchronous speed. Typical situations are when the generator is on turning gear, slowing down to a standstill, or has reached standstill. This motoring condition occurs during what is called “generator inadvertent energization.” The protection schemes that respond to this situation are different and will be addressed later in this article. Motoring will cause adverse effects, particularly in the case of steam turbines. The basic ...

A loss-of-excitation on a generator occurs when the field current is no longer supplied. This situation can be triggered by a variety of circumstances and the following situation will then develop: 1. When the field supply is removed, the generator real power will remain almost constant during the next seconds. Because of the drop in the excitation voltage, the generator output voltage drops gradually. To compensate for the drop in voltage, the current increases at about the same rate. 2. The generator then becomes underexcited and it will absorb increasingly negative reactive power. 3. Because the ratio of the generator voltage over the current becomes smaller and smaller with the phase current leading the phase voltage, the generator positive sequence impedance as measured at its terminals will enter the impedance plane in the second quadrant. Experience has shown that the positive sequence impedance will settle to a value between Xd and Xq. ...

Protection against stator-to-ground fault will depend to a great extent upon the type of generator grounding. Generator grounding is necessary through some impedance in order to reduce the current level of a phase-to-ground fault. With solid generator grounding, this current will reach destructive levels. In order to avoid this, at least low impedance grounding through a resistance or a reactance is required. High-impedance through a distribution transformer with a resistor connected across the secondary winding will limit the current level of a phase-to-ground fault to a few primary amperes. The most common and minimum protection against a stator-to-ground fault with a high-impedance grounding scheme is an overvoltage element connected across the grounding transformer secondary, as shown in Fig. 9.5. For faults very close to the generator neutral, the overvoltage element will not pick up because the voltage level will be below the voltage ...

Tellegen’s theorem states: In an arbitrarily lumped network subject to KVL and KCL constraints, with reference directions of the branch currents and branch voltages associated with the KVL and KCL constraints, the product of all branch currents and branch voltages must equal zero. Tellegen’s theorem may be summarized by the equation where the lower case letters v and j represent instantaneous values of the branch voltages and branch currents, respectively, and where b is the total number of branches. A matrix representation employing the branch current and branch voltage vectors also exists. Because V and J are column vectors V · J = VT J = J T V The prerequisite concerning the KVL and KCL constraints in the statement of Tellegen’s theorem is of crucial importance. Example 3.3. Figure 3.16 displays an oriented graph of a particular network in which there are six branches labeled with numbers within parentheses and four nodes labeled by number...

The resistance for most resistors changes with temperature. The temperature coefficient of electrical resistance is the change in electrical resistance of a resistor per unit change in temperature. The temperature coefficient of resistance is measured in OHM/°C. The temperature coefficient of resistors may be either positive or negative. A positive temperature coefficient denotes a rise in resistance with a rise in temperature; a negative temperature coefficient of resistance denotes a decrease in resistance with a rise in temperature. Pure metals typically have a positive temperature coefficient of resistance, while some metal alloys such as constantin and manganin have a zero temperature coefficient of resistance. Carbon and graphite mixed with binders usually exhibit negative temperature coefficients, although certain choices of binders and process variations may yield positive temperature coefficients. The...

HRC or current-limiting fuses have an interrupting rating of 200 kA and are recognized by a letter designation system common to North American fuses. In the United States they are known as Class J, Class L, Class R, etc., and in Canada they are known as HRCI-J, HRC-L, HRCI-R, and so forth. HRC fuses are available in ratings up to 600 V and 6000 A. The main differences among the various types are their dimensions and their short circuit performance (Ip and I2t) characteristics. One type of HRC fuse found in Canada, but not in the United States, is the HRCII-C or Class C fuse. This fuse was developed originally in England and is constructed with bolt-on-type blade contacts. It is available in a voltage rating of 600 V with ampere ratings from 2 to 600 A. Some higher ampere ratings are also available but are not as common. HRCII-C fuses are primarily regarded as providing short-circuit protection only. Therefore, they should be used in conjunc...

Wire. A slender rod or filament of drawn metal. (This definition restricts the term wire to what would ordinarily be understood by the term solid wire. In the definition the word slender is used in the sense that the length is great in comparison with the diameter. If a wire is covered with insulation, it is properly called an insulated wire, although the term wire refers primarily to the metal; nevertheless, when the context shows that the wire is insulated, the term wire will be understood to include the insulation.) Conductor. A wire or combination of wires not insulated from one another, suitable for carrying a single electric current. (The term conductor does not include a combination of conductors insulated from one another, which would be suitable for carrying several different electric currents. Rolled conductors, such as busbars, are, of course, conductors but are not considered under the terminology given here.) Stranded Con...