WHAT IS ELECTRICAL ENGINEERING

WHAT IS ELECTRICAL ENGINEERING

By Engr. Aneel Kumar   July 31, 2014   No comments:

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 management positions at government agencies or private corporations where they may specialize in:

· Microprocessors and microcomputers.
· Computer engineering.
· Analog and digital electronics, optoelectronics.
· Measurements, instrumentation and remote sensing.
· Microelectronic design and fabrication.
· Control systems, robotics, and automation.
· Communications systems, signal processing.
· Microwaves, radar technologies, antennas.
· Power generation, transmission, and distribution.

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ELECTRICAL ENERGY CONSUMPTION

ELECTRICAL ENERGY CONSUMPTION

By Engr. Aneel Kumar   July 22, 2014   No comments:

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. Typically, all other home appliances and home office equipment use less energy and, therefore, account for a small percentage of total residential consumption. Residential consumption has steadily grown over the years and it appears that this trend is continuing. Residential energy consumption is measured in kilowatt-hours (kWh).

COMMERCIAL ELECTRIC CONSUMPTION: is also steadily growing. Commercial loads include mercantile and service, office operations, warehousing and storage, education, public assembly, lodging, health care, and food sales and services. Commercial consumption includes larger-scale lighting, heating, air conditioning, kitchen apparatus, and motor loads such as elevators and large clothes handling equipment. Typically, special metering is used to record peak demand (in kilowatts) along with energy consumption in kWh.

INDUSTRIAL ELECTRIC CONSUMPTION: appears to be steady. Industrial loads usually involve large motors, heavy duty machinery, high-volume air conditioning systems, and so on, for which special metering equipment is used such as power factor, demand, and energy. Normally the consumption is great enough to use CTs (current transformers) and PTs (potential transformers) to scale down the electrical quantities for standard metering equipment.

VERY LARGE ELECTRICAL ENERGY CONSUMERS: (i.e., military bases, oil refineries, mining industry, etc.) often use primary metering facilities to measure their consumption. These large consumers normally have their own sub-transmission and or primary distribution facilities including substations, lines, and electrical protection equipment.

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IDEAL AND REAL WORLD CIRCUIT ELEMENTS

IDEAL AND REAL WORLD CIRCUIT ELEMENTS

By Engr. Aneel Kumar   July 22, 2014   No comments:

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, physical circuit elements can be readily found that well approximate the ideal, but they will always deviate from the ideal in some way. For example, a flashlight battery, like a C-cell, roughly corresponds to a 1.5 V voltage source. However, it ceases to be modeled by a voltage source capable of supplying any current (that’s what ideal ones can do!) when the resistance of the light bulb is too small.

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DISCRETE TIME SIGNALS

DISCRETE TIME SIGNALS

By Engr. Aneel Kumar   July 22, 2014   No comments:

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 information with signals) and to extract information (retrieve the information thus represented). For symbolic-valued signals, the approach is different:

We develop a common representation of all symbolic-valued signals so that we can embody the information they contain in a unified way. From an information representation perspective, the most important issue becomes, for both real-valued and symbolic-valued signals, efficiency; what is the most parsimonious and compact way to represent information so that it can be extracted later.

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COMMUNICATING INFORMATION WITH SIGNALS

COMMUNICATING INFORMATION WITH SIGNALS

By Engr. Aneel Kumar   July 22, 2014   No comments:

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 = A0 (1 + kT), where A0  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 sequence of parameters to send. We have exploited all of the sinusoidal’s two parameters. What we can do is modulate them for a limited time (say T seconds), and send two parameters every T. This simple notion corresponds to how a modem works. Here, typed characters are encoded into eight bits, and the individual bits are encoded into a sinusoidal’s amplitude and frequency. We’ll learn how this is done in subsequent modules, and more importantly, we’ll learn what the limits are on such digital communication schemes.

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ELECTRIC POWER UTILIZATION IN MOTORS

ELECTRIC POWER UTILIZATION IN MOTORS

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 characteristics, and requires significant experience to manage. Nevertheless, a systematic formulation of the issues can be useful to a beginner in this area of design, and even for experienced engineers faced with a new or unusual application.

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ELECTRIC LOAD RELATED ISSUES

ELECTRIC LOAD RELATED ISSUES

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 lack of load diversity.

Cold load pickup can result in a number of adverse power system reactions. Individual service transformers can become overloaded under cold load pickup conditions, resulting in loss of life and possible failure due to overheating. Feeder load levels can exceed protective device ratings/settings, resulting in customer interruptions following initial service restoration. Additionally, the heavily loaded system conditions can result in conductors sagging below their designed minimum clearance levels, creating safety concerns.

HARMONICS AND OTHER NON-SINUSOIDAL LOADS

Electronic loads that draw current from the power system in a non-sinusoidal manner represent a significant portion of the load connected to modern power systems. These loads cause distortions of the generally sinusoidal characteristics traditionally observed. Harmonic loads include power electronic based devices (rectifiers, motor drives, switched mode power supplies, etc.) and arc furnaces. More details on power electronics and their effects on power system operation can be found in the power electronics section of this handbook.

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MULTIFUNCTION POWER METER

MULTIFUNCTION POWER METER

By Engr. Aneel Kumar   July 16, 2014   No comments:

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.

• MULTIFORM: Meter form refers to the specific combination of voltage and current signals, how they are applied to the terminals of the meter, and how the meter uses these signals to measure power and energy. For example, a Form 15 meter would be used for self-contained application on a 120/240 volt 4-wire delta service, while a Form 16 meter would be used on a self-contained 120/208 volt 4-wire wye service. A multiform 15/16 meter can work interchangeably on either of these services.

SITE DIAGNOSTIC METER

Newer meter designs incorporate the ability to measure, display, and evaluate the voltage and current magnitudes and phase relationships of the circuits to which they are attached. This capability offers important advantages:

• At the time of installation or reinstallation, the meter analyzes the voltage and current signals and determines if they represent a recognizable service type.

• Also at installation or reinstallation, the meter performs an initial check for wiring errors such as crossed connections or reversed polarities. If it finds an error, it displays an error message so that corrections can be made.

• Throughout its life, the meter continuously evaluates voltage and current conditions. It can detect a problem that develops weeks, months, or years after installation, such as tampering or deteriorated CT or VT wiring.

• Field personnel can switch the meter display into diagnostic mode. It will display voltage and current magnitudes and phase angles for each phase. This provides a quick and very accurate way to obtain information on service characteristics.

If a diagnostic meter detects any error that might affect the accuracy of its measurements, it will lock its display in error mode. The meter continues to make energy and demand measurements in the background. However, these readings cannot be retrieved from the meter until the error is cleared. This ensures the error will be reported the next time someone tries to read the meter.

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POWER DISTRIBUTION BY SCADA HISTORY

POWER DISTRIBUTION BY SCADA HISTORY

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 a highly reliable and secure transmission infrastructure. Transmission SCADA became the base for the large Energy Management Systems that were required to manage the transmission grid. Distribution SCADA languished during this period.

In the mid-1980s, EPRI published definitions for distribution automation and associated elements. The industry generally associates distribution automation with the installation of automated distribution line devices, such as switches, re-closers, sectionalizers, etc. The author’s definition of distribution automation encompasses the automation of the distribution substations and the distribution line devices. The automated distribution substations and the automated distribution line devices are then operated as a system to facilitate the operation of the electric distribution system.

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IMPLEMENTATION OF DISTRIBUTION AUTOMATION

IMPLEMENTATION OF DISTRIBUTION AUTOMATION

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 various alternatives available to the utility engineer. The focus will be on providing insight on the elements of automation that should be included in a scalable and extensible system. The approach will be to describe the elements of a “typical” distribution automation system in a simple manner, offering practical observations as required.

For the electric utility, justification for automating the distribution system, while being highly desirable, was not readily attainable based on a cost/benefit ratio due to the size of the distribution infrastructure and cost of communication circuits. Still there have been tactical applications deployed on parts of distribution systems that were enough to keep the dream alive. The development of the PC (based on the Intel architecture) and VME systems (based on the Motorola architecture) provided the first low cost SCADA master systems that were sized appropriately for the small co-ops and municipality utilities.

New SCADA vendors then entered the market targeting solutions for small to medium-sized utilities. Eventually the SCADA vendors who had been providing transmission SCADA took notice of the distribution market. These vendors provided host architectures based on VAX/VMS (and later Alpha/Open- VMS) platforms and on UNIX platforms from IBM and Hewlett-Packard. These systems were required for the large distribution utility (100,000–250,000 point ranges). These systems often resided on company owned LANs with communication front-end processors and user interface attached either locally on the same LAN or across a WAN.

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ELECTRIC LOAD MODELING CONCEPTS AND APPROACHES

ELECTRIC LOAD MODELING CONCEPTS AND APPROACHES

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 voltage, rated frequency, rated torque if applicable, and base temperature if applicable). A composite load is approximated by combining appropriate load model types in certain proportions based on load survey information. The resulting composition is referred to as a “load window.”

The measurement approach is a “top-down” approach in that measurements are taken at either a substation level, feeder level, some load aggregation point along a feeder, or at some individual load point. Variation of frequency for this type of measurement is not usually performed unless special test arrangements can be made. Voltage is varied using a suitable means and the measured real and reactive power consumption recorded. Statistical methods are then used to determine load models. A load survey may be necessary to classify the models derived in this manner. The range of validity for this approach is directly related to the realistic range over which the tests can be conducted without damage to customers’ equipment. Both the component and measurement methods were used in the EPRI research projects EL-2036 (1981) and EL-3591 (1984–85). The component test method was used to characterize a number of individual load components that were in turn used in simulation studies. The measurement method was applied to an aggregate of actual loads along a portion of a feeder to verify and validate the component method.

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ELECTRIC LOAD CLASSIFICATION

ELECTRIC LOAD CLASSIFICATION

By Engr. Aneel Kumar   July 16, 2014   No comments:

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 of loads is by breaking down the broader classes into individual load components. This process may altogether eliminate the distinction of certain of the broader classes, but it is a tried and proven technique for many applications. The components of a particular load, be it residential, commercial, or industrial, are individually defined and modeled. These load components as a whole constitute the composite load and can be defined as a “load window.”

FIGURE 6.1 Representative portion of a typical power system configuration.

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INSTRUMENT TRANSFORMERS

INSTRUMENT TRANSFORMERS

By Engr. Aneel Kumar   July 02, 2014   No comments:

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 used and will maintain its rated accuracy up to 600 amps. Rating factors for most CTs are based on open-air outdoor conditions. When a CT is installed indoors or inside a cabinet, its rating factor is reduced.

A voltage transformer is rated in terms of its nameplate primary voltage as a ratio to either 115 or 120 volts secondary voltage (e.g., 7200:120 or 115000:115). These ratios are sometimes listed as an equivalent ratio to 1 (e.g., 60:1 or 1000:1).

Symbols for a CT and a PT connected in a two-wire circuit are shown in Fig. 7.5.

FIGURE 7.5 Instrument transformer symbols.

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SINGLE STATOR ELECTROMECHANICAL METER

SINGLE STATOR ELECTROMECHANICAL METER

By Engr. Aneel Kumar   July 02, 2014   No comments:

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 overcome friction and other forces acting on the rotor. This ultimate speed would not represent the level of power present in the metered circuit.

To address these problems, designers add a permanent magnet whose magnetic field acts on the rotor. This field interacts with the rotor to cause a counter torque proportional to the speed of the rotor. Careful design and adjustment of the magnet strength yields a meter that rotates at a speed proportional to power. This speed can be kept relatively slow. The product of the rotor speed and time is revolutions of the rotor. The revolutions are proportional to energy consumed in the metered circuit. One revolution of the rotor represents a fixed number of watt-hours. The revolutions are easily converted via mechanical gearing or other methods into a display of watt-hours or, more commonly, kilo-watt-hours.

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