ENGINEERING ARTICLES

Electrical engineering is the historical name for what is now called electrical, electronics, and computer engineering. Originating in the 19th century with the development of electric power and the advent of telephone and wireless communications, electrical engineering continues to have lasting impact not only on technology and the engineering profession, but on all of society. Recent advances such as integrated computing and communications systems and the proliferation of microchips and microelectronic hardware have revolutionized the ways we live and work, as well as how we interact as a society and how we spend our leisure time. Electrical engineering uses science, technology, and problem-solving skills to design, construct, and maintain products, services, and information systems. Electrical engineers design and develop new technologies to generate, store, transmit, control and convert energy and information. They may work in design, research and development, production or manage...

Electrical energy consumption is the electrical energy use by all the various loads on the power system. Consumption also includes the energy used to transport and deliver the energy. For example, the losses due to heating conductors in power lines, transformers, and so on is considered consumption. Electricity is consumed and measured in several different ways depending on whether the load is residential, commercial, or industrial, and whether the load is resistive, inductive, or capacitive. Electric utilities consume electricity just to produce and transport it to consumers. In all cases, electrical energy production and consumption is measured and accounted for. The electrical energy produced must equal the electrical energy consumed. IN RESIDENTIAL ELECTRIC CONSUMPTION: the larger users of electrical energy are items such as air conditioning units, refrigerators, stoves, space heating, electric water heaters, clothes dryers, and, to a lesser degree, lighting, radios, and TVs. Typ...

Source and linear circuit elements are ideal circuit elements. One central notion of circuit theory is combining the ideal elements to describe how physical elements operate in the real world. For example, the 1 k resistor you can hold in your hand is not exactly an ideal 1 k resistor. First of all, physical devices are manufactured to close tolerances (the tighter the tolerance, the more money you pay), but never have exactly their advertised values. The fourth band on resistors specifies their tolerance; 10% is common. More pertinent to the current discussion is another deviation from the ideal: If a sinusoidal voltage is placed across a physical resistor, the current will not be exactly proportional to it as frequency becomes high, say above 1 MHz. At very high frequencies, the way the resistor is constructed introduces inductance and capacitance effects. Thus, the smart engineer must be aware of the frequency ranges over which his ideal models match reality well. On the other hand...

Discrete-time signals are functions defined on the integers; they are sequences. One of the fundamental results of signal theory will detail conditions under which an analog signal can be converted into a discrete-time one and retrieved without error. This result is important because discrete-time signals can be manipulated by systems instantiated as computer programs. Subsequent modules describe how virtually all analog signal processing can be performed with software. As important as such results are, discrete-time signals are more general, encompassing signals derived from analog ones and signals that aren’t. For example, the characters forming a text file form a sequence, which is also a discrete-time signal. As with analog signals, we seek ways of decomposing real-valued discrete-time signals into simpler components. With this approach leading to a better understanding of signal structure, we can exploit that structure to represent information (create ways of representing informa...

The basic idea of communication engineering is to use a signal’s parameters to represent either real numbers or other signals. The technical term is to modulate the carrier signal’s parameters to transmit information from one place to another. To explore the notion of modulation, we can send a real number (today’s temperature, for example) by changing a sinusoidal’s amplitude accordingly. If we wanted to send the daily temperature, we would keep the frequency constant (so the receiver would know what to expect) and change the amplitude at midnight. We could relate temperature to amplitude by the formula A = A 0 (1 + kT ), where A 0   and k are constants that the transmitter and receiver must both know. If we had two numbers we wanted to send at the same time, we could modulate the sinusoidal’s frequency as well as its amplitude. This modulation scheme assumes we can estimate the sinusoidal’s amplitude and frequency; we shall learn that this is indeed possible. Now suppose we have...

A major application of electric energy is in its conversion to mechanical energy. Electromagnetic, or “EM” devices designed for this purpose are commonly called “motors.” Actually the machine is the central component of an integrated system consisting of the source, controller, motor, and load. For specialized applications, the system may be, and frequently is, designed as an integrated whole. Many household appliances (e.g., a vacuum cleaner) have in one unit, the controller, the motor, and the load. However, there remain a large number of important stand-alone applications that require the selection of a proper motor and associated control, for a particular load. It is this general issue that is the subject of this section. The reader is cautioned that there is no “magic bullet” to deal with all motor-load applications. Like many engineering problems, there is an artistic, as well as a scientific dimension to its solution. Likewise, each individual application has its own peculiar c...

COLD LOAD PICKUP Following periods of extended service interruption, the advantages provided by load diversity are often lost. The term cold load pickup refers to the energization of the loads associated with a circuit or substation following an extended interruption during which much of the diversity normally encountered in power systems is lost. For example, if a feeder suffers an outage, interrupting all customers on the feeder during a particularly cold day, the homes and businesses will cool to levels below the individual thermostat settings. This situation eliminates the diversity normally experienced, where only a fraction of the heating will be required to operate at any given time. Once power is restored, the heating at all customer locations served by the feeder will attempt to operate to bring the building temperatures back to levels near the thermostat settings. The load experienced by the feeder following re-energization can be far in excess of the design loading due to...

Multi-function or extended function refers to a meter that can measure reactive or apparent power (e.g., kvar or kVA) in addition to real power (kW). By virtue of their designs, many electronic meters inherently measure the quantities and relationships that define reactive and apparent power. It is a relatively simple step for designers to add meter intelligence to calculate and display these values. VOLTAGE RANGING AND MULTIFORM METER Electronic meter designs have introduced many new features to the watt-hour metering world. Two features, typically found together, offer additional flexibility, simplified application, and opportunities for reduced meter inventories for utilities. • VOLTAGE RANGING : Many electronic meters incorporate circuitry that can sense the voltage level of the meter input signals and adjust automatically to meter correctly over a wide range of voltages. For example, a meter with this capability can be installed on either a 120 volt or 277 volt service. • MULT...

Supervisory Control And Data Acquisition (SCADA) is the foundation for the distribution automation system. The ability to remotely monitor and control electric power system facilities found its first application within the power generation and transmission sectors of the electric utility industry. The ability to significantly influence the utility bottom line through the effective dispatch of generation and the marketing of excess generating capacity provided economic incentive. The interconnection of large power grids in the mid-western and the southern U.S. (1962) created the largest synchronized system in the world. The blackout of 1965 prompted the U.S. Federal Power Commission to recommend closer coordination between regional coordination groups (Electric Power Reliability Act of 1967), and gave impetus to the subsequent formation of the National Electric Reliability Council (1970). From that time (1970) forward, the priority of the electric utility has been to engineer and build...

The implementation of “distribution automation” within the continental U.S. is as diverse and numerous as the utilities themselves. Particular strategies of implementation utilized by various utilities have depended heavily on environmental variables such as size of the utility, urbanization, and available communication paths. The current level of interest in distribution automation is the result of: • The maturation of technologies within the past 10 years in the areas of communication and RTUs/ PLCs. • Increased performance in host servers for the same or lower cost; lower cost of memory. • The threat of deregulation and competition as a catalyst to automate. • Strategic benefits to be derived (e.g., potential of reduced labor costs, better planning from better information, optimizing of capital expenditures, reduced outage time, increased customer satisfaction). While not meant to be all-inclusive, this section on distribution automation attempts to provide some dimension to the va...

There are essentially two approaches to load modeling: component based and measurement based. Load modeling research over the years has included both approaches. Of the two, the component-based approach lends itself more readily to model generalization. It is generally easier to control test procedures and apply wide variations in test voltage and frequency on individual components. The component-based approach is a “bottom-up” approach in that the different load component types comprising load are identified. Each load component type is tested to determine the relationship between real and reactive power requirements versus applied voltage and frequency. A load model, typically in polynomial or exponential form, is then developed from the respective test data. The range of validity of each model is directly related to the range over which the component was tested. For convenience, the load model is expressed on a per-unit basis (i.e., normalized with respect to rated power, rated vol...

The most common classification of electrical loads follows the billing categories used by the utility companies. This classification includes residential, commercial, industrial, and other. Residential customers are domestic users, whereas commercial and industrial customers are obviously business and industrial users. Other customer classifications include municipalities, state and federal government agencies, electric cooperatives, educational institutions, etc. Although these load classes are commonly used, they are often inadequately defined for certain types of power system studies. For example, some utilities meter apartments as individual residential customers, while others meter the entire apartment complex as a commercial customer. Thus, the common classifications overlap in the sense that characteristics of customers in one class are not unique to that class. For this reason some utilities define further subdivisions of the common classes. A useful approach to classification...

Instrument transformers are the general name for members of the family of current transformers (CTs) and voltage transformers (VTs) used in metering. They are high-accuracy transformers that convert load currents or voltages to other (usually smaller) values by some fixed ratio. Voltage transformers are also often called potential transformers (PTs). The terms are used interchangeably in this section. CTs and VTs are most commonly used in services where the current and/or voltage levels are too large to be applied directly to the meter. A current transformer is rated in terms of its nameplate primary current as a ratio to five amps secondary current (e.g., 400:5). The CT is not necessarily limited to this nameplate current. Its maximum capacity is found by multiplying its nameplate rating by its rating factor. This yields the total current the CT can carry while maintaining its rated accuracy and avoiding thermal overload. For example, a 200:5 CT with a rating factor of 3.0 can be use...

A two-wire single stator meter is the simplest electromechanical meter. The single stator consists of two electromagnets. One electromagnet is the potential coil connected between the two circuit conductors. The other electromagnet is the current coil connected in series with the load current. Figure 7.1 shows the major components of a single stator meter. FIGURE 7.1 Main components of electromechanical meter. The electromagnetic fields of the current coil and the potential coil interact to generate torque on the rotor of the meter. This torque is proportional to the product of the source voltage, the line current, and the cosine of the phase angle between the two. Thus, the torque is also proportional to the power in the metered circuit. The device described so far is incomplete. In measuring a steady power in a circuit, this meter would generate constant torque causing steady acceleration of the rotor. The rotor would spin faster and faster until the torque could no longer ov...