AC Power - Basics

Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In AC circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power. The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power.

Real, reactive, and apparent power

In a simple alternating current (AC) circuit consisting of a source and a linear load, both the current and voltage are sinusoidal. If the load is purely resistive, the two quantities reverse their polarity at the same time. At every instant the product of voltage and current is positive, indicating that the direction of energy flow does not reverse. In this case, only real power is transferred.

If the load is purely reactive, then the voltage and current are 90 degrees out of phase. For half of each cycle, the product of voltage and current is positive, but on the other half of the cycle, the product is negative, indicating that on average, exactly as much energy flows toward the load as flows back. There is no net energy flow over one cycle. In this case, only reactive energy flows—there is no net transfer of energy to the load.

Practical loads have resistance, inductance, and capacitance, so both real and reactive power will flow to real loads. Power engineers measure apparent power as the vector sum of real and reactive power. Apparent power is the product of the root-mean-square voltage and current.

Engineers care about apparent power, because even though the current associated with reactive power does no work at the load, it heats the wires, wasting energy. Conductors, transformers and generators must be sized to carry the total current, not just the current that does useful work.

Another consequence is that adding the apparent power for two loads will not accurately give the total apparent power unless they have the same displacement between current and voltage (the same power factor).

If a capacitor and an inductor are placed in parallel, then the currents flowing through the inductor and the capacitor tend to cancel out rather than adding. Conventionally, capacitors are considered to generate reactive power and inductors to consume it. This is the fundamental mechanism for controlling the power factor in electric power transmission; capacitors (or inductors) are inserted in a circuit to partially cancel reactive power 'consumed' by the load.

Engineers use the following terms to describe energy flow in a system (and assign each of them a different unit to differentiate between them):

• Real power (P) or active power: watt [W]
• Reactive power (Q): volt-amperes reactive [var]
• Complex power (S): volt-ampere [VA]
• Apparent Power (|S|), that is, the absolute value of complex power S: volt-ampere [VA]

In the diagram, P is the real power, Q is the reactive power (in this case positive), S is the complex power and the length of S is the apparent power.

Reactive power does not transfer energy, so it is represented as the imaginary axis of the vector diagram. Real power moves energy, so it is the real axis.

The unit for all forms of power is the watt (symbol: W), but this unit is generally reserved for real power. Apparent power is conventionally expressed in volt-amperes (VA) since it is the product of rms voltage and rms current. The unit for reactive power is expressed as VA_r, which stands for volt-amperes reactive. Since reactive power transfers no net energy to the load, it is sometimes called "wattless" power. It does, however, serve an important function in electrical grids and its lack has been cited as a significant factor in the Northeast Blackout of 2003.

Understanding the relationship between these three quantities lies at the heart of understanding power engineering. The mathematical relationship among them can be represented by vectors or expressed using complex numbers,

S = P + jQ (where j is the imaginary unit)

Example for simple understanding

Visualize a horse pulling a railroad car down a railroad track. Because the railroad ties are uneven, the horse must pull the car from the side of the track. The horse is pulling the railroad car at an angle to the direction of the car’s travel.

The power required to move the car down the track is the working (real) power. The effort of the horse is the total (apparent) power. Because of the angle of the horse’s pull, not all of the horse’s effort is used to move the car down the track. The car will not move sideways; therefore, the sideways pull of the horse is wasted effort or nonworking (reactive) power. The angle of the horse’s pull is related to power factor, which is defined as the ratio of real (working) power to apparent (total) power. If the horse is led closer to the center of the track, the angle of side pull decreases and the real power approaches the value of the apparent power. Therefore, the ratio of real power to apparent power (the power factor) approaches 1. As the power factor approaches 1, the reactive (nonworking) power approaches 0.

Power factor

The ratio between real power and apparent power in a circuit is called the power factor.

Power factor = Real power / Apparent power

It's a practical measure of the efficiency of a power distribution system. For two systems transmitting the same amount of real power, the system with the lower power factor will have higher circulating currents due to energy that returns to the source from energy storage in the load. These higher currents produce higher losses and reduce overall transmission efficiency. A lower power factor circuit will have a higher apparent power and higher losses for the same amount of real power.

The power factor is one when the voltage and current are in phase. It is zero when the current leads or lags the voltage by 90 degrees. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle, where leading indicates a negative sign.

Purely capacitive circuits cause reactive power with the current waveform leading the voltage wave by 90 degrees, while purely inductive circuits cause reactive power with the current waveform lagging the voltage waveform by 90 degrees. The result of this is that capacitive and inductive circuit elements tend to cancel each other out.

Where the waveforms are purely sinusoidal, the power factor is the cosine of the phase angle (φ) between the current and voltage sinusoid waveforms. Equipment data sheets and nameplates often will abbreviate power factor as "cosφ" for this reason.

For example, using the power triangle illustrated here, if

Real power = 100 kW and

Apparent power = 142 kVA then

Power Factor = 100/142 = 0.70 or 70%.

This indicates that only 70% of the current provided by the electrical utility is being used to produce useful work.

Reactive power

In power transmission and distribution, significant effort is made to control the reactive power. This is typically done automatically by switching inductors or capacitor banks in and out, by adjusting generator excitation, and by other means. Electricity retailers may use electricity meters which measure reactive power to financially penalize customers with low power factor loads. This is particularly relevant to customers operating highly inductive loads such as motors at water pumping stations.

KERS used in F1 racing

Kinetic Energy Recovery System (KERS) is a very unique and a debated addition to F1 racing. As most people watching F1 have already known that it's sort of a speed boost and gives an increase in the speed for a few moments. It gives a speed boost of exactly 6.6 seconds giving a total of 82hp during that period. So where is the energy to give the boost coming from?

It is coming from the Kinetic Energy lost during the braking of an F1 car. The wasted Kinetic Energy is transferred from the rear end of the wheel to a battery or super-capacitor and when fully charged, can be used for that speed boost.

Flywheel KERS

The KERS is exemplified in complex high end systems such as the Zytek, Flybrid, Torotrak and Xtrac used in F1. The concept of transferring the vehicle’s kinetic energy using Flywheel energy storage was postulated by physicist Richard Feynman in the 1950s. The Xtrac & Flybrid are both licensees of Torotrak's technologies, which employ a small and sophisticated ancillary gearbox incorporating a continuously variable transmission (CVT). The FIA has defined the amount of energy recovery for the 2009 season as 400kJ per lap which translates to 6.6 seconds of 82hp speed boost. The transfer of power to a battery is the electronic KERS system. There is a mechanical KERS system also which uses a flywheel to store the wasted kinetic energy instead of a battery.

Kinetic Energy Recovery Systems (KERS) were used for the motor sport Formula One's 2009 season, and under development for road vehicles. However, KERS has been abandoned for the 2010 Formula One season. The Formula One Teams that used Kinetic Energy Recovery Systems in the 2009 season are Ferrari, Renault, BMW and McLaren. One of the main reasons that not all cars use KERS is because it adds an extra 25 kilograms of weight, while not adding to the total car weight, it does incur a penalty particularly seen in the qualifying rounds, as it raises the car's center of gravity, and reduces the amount of ballast that is available to balance the car so that it is more predictable when turning. FIA rules also limit the exploitation of the system. Eventually, during the season, Renault and BMW stopped using the system. Williams is developing a flywheel-KERS system. The concept of transferring the vehicle’s kinetic energy using Flywheel energy storage was postulated by physicist Richard Feynman in the 1950s and is exemplified in complex high end systems such as the Zytek, Flybrid, Torotrak and Xtrac used in F1 and simple, easily manufactured and integrated differential based systems such as the Cambridge Passenger/Commercial Vehicle Kinetic Energy Recovery System (CPC-KERS).

Xtrac and Flybrid are both licensees of Torotrak's technologies, which employ a small and sophisticated ancillary gearbox incorporating a continuously variable transmission (CVT). The CPC-KERS is similar as it also forms part of the driveline assembly. However, the whole mechanism including the flywheel sits entirely in the vehicle’s hub (looking like a drum brake). In the CPC-KERS, a differential replaces the CVT and transfers torque between the flywheel, drive wheel and road wheel.

How to Install a Sub Panel

Sometimes the main electrical panel of a home can become too full. In such instances, continuing to add additional circuitry is not advisable, or worse yet not allowed by law. Instead, it will be necessary to install a sub panel that can handle the additional circuitry. While many homeowners will rightfully turn to electrical professionals to install the sub panel, others will attempt the installation themselves. The choice is ultimately likely to be driven by state law. In any case, the installed sub panel will be required to meet established electrical standards. These steps will guide you through the installation process.

Preparing to Mount the Sub Panel

Step 1
Decide how to approach the job. Planning is an essential step in this process. Failure to plan it out thoughtfully and fully could result in a sub panel that doesn't work properly or doesn't meet the established procedures.

Step 2
Refer to state established electrical standards. In some states, a job like this may require the services of a professional in the electrical field. In any case, it is important to know the minimum standards to which the sub panel must work.

Step 3
Make certain that you have all of the materials, equipment and tools necessary to do the job. It may be virtually impossible to stop mid-stream in order to purchase additional items.

Step 4
Set up good lighting in the area where the sub panel is to be installed. It is imperative that you are able to see the smallest details of the wiring and circuitry. If necessary, set up additional lamps to ensure proper lighting. However, be certain that they are set up in a manner that will not impede the installation process.

Step 5
Determine exactly where to install the sub panel. While many will install it in the same general area as the original panel, that is not always necessary.

Step 6
Get the new sub panel ready for mounting. In most instances, it is recommended that you remove any covers, doors or partitions that might obstruct the installation of the sub panel.

Step 7
Mount a backboard of plywood for the sub panel if one doesn't already exist. A mounting board may already be in place if you are mounting the sub panel in the same area as the original panel. However, that may not be the case if you are mounting the sub panel in a different place. Mounting board requirements may be established by state standards in some instances. However, in most cases, one need only follow standard electrical practices.

Installing the Sub Panel

Step 1
Mount the sub panel within the area marked for that purpose. Use the installation instructions provided with the sub panel or provided by the retailer where the materials were purchased. Be sure to use mounting materials that are sufficiently strong to hold the new panel in place securely. Also be certain to use enough screws to hold the panel into place properly. Four to eight screws are standard.

Step 2
Install the breaker panel for the sub panel and connect it to the main panel. Be sure to follow all appropriate electrical standards.

Step 3
Pull one or more sub feed cables from the main panel and reroute them to the sub panel as desired. Be certain to keep in mind the sizes and lengths of the cables, keeping everything within acceptable electrical standards.

Step 4
Install new sub feeds to the new panel through the breaker in the same way that any device might be attached to the main panel.

Step 5
Connect the branch circuits to the sub panel following standard electrical standards.

Step 6
Complete any additional wiring changes necessary, whether they are new wires being connected for the first time or old ones that are being rerouted from the main panel.

Step 7
Test to make sure that everything is working properly. If not, call in a electrician rather than risk burning out either panel.

Step 8
Get the final electrical work inspected according to state standards.

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How to Install an Electrical Panel

Installing an electrical panel is dangerous if you don't know what you're doing. This is a job for a professional electrician. A mistake with this project could cause serious injury or death to you and your family. Electrical codes vary, but many require that a journeyman or master electrician handle the installation.

Step 1.
Hire a journeyman electrician. Your local community paper may have contractors who advertise regularly. Ask around to see if you know anyone who has used an electrician and was happy with the work. Or you can try an online locater service. Regardless of the way you choose to get started, be sure to have multiple contractors come to your home and bid on the job.

Step 2
Ensure that whoever you hire is a licensed journeyman or master electrician. Don't take his word for it. Check credentials, references and the Better Business Bureau. Check your local and state codes to see if you need a permit.

Step 3
Decide whether you also want him to do the wiring or just install the panel. This can make a big difference in the cost and the amount of time it takes to complete the job. Be prepared to answer questions. He will probably ask if you are installing a new panel or replacing an old one.

Step 4
Make a list of what you need connected to the panel. Things to consider are rooms, appliances, central air conditioner and furnace. You should also determine what voltage/current is running to your home.

Step 5
Secure a written contract. Make certain you understand how long the job should take and get an estimate of the cost. Ask about any contingencies that could come up.

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The AUTOCAD Electrical Advantage

The Logical Choice for Electrical Controls Design AutoCAD® Electrical is AutoCAD® software for controls designers, purpose-built to create and modify electrical control systems. Automated tasks and comprehensive symbol libraries help to increase productivity, reduce errors, and provide accurate information to manufacturing.

Stay ahead of the competition with AutoCAD Electrical software, which offers significant productivity gains over AutoCAD software by automating many of the complex tasks associated with creating accurate, industry-standard electrical control systems.

Increase Productivity

When engineers create electrical control systems using software not specifically built for electrical design tasks, they must often find manual work arounds to get the job done—wasting valuable design time and limiting productivity. Since AutoCAD Electrical software is AutoCAD for controls designers, it contains many features and benefits that enable users to dramatically increase design efficiency, while maintaining a smooth integration with the familiar AutoCAD environment. A recent study shows up to an 80 percent increase in productivity when moving to AutoCAD Electrical from AutoCAD. AutoCAD Electrical helps manufacturers get their products to market faster with lower costs.

Reduce Errors and Comply with Industry Standards

As engineers create electrical controls designs using generic tools, it is easy to introduce errors and design
inconsistencies. The ability to virtually eliminate errors before they reach the shop floor can provide a distinct competitive advantage. AutoCAD Electrical includes automatic error-checking capabilities that help designers perform real-time diagnostics to catch problems before the build phase of a project.

In addition to reducing errors, AutoCAD Electrical helps companies compete in the global marketplace by offering support for regional and international standards. With more than 350,000 components from the industry’s most popular vendors—including more than 3,000 intelligent PLC I/O modules— AutoCAD Electrical provides a comprehensive library of manufacturer content, enabling users to produce consistent, standards-based designs.

Manage Design Data

Once the design is complete, it is important to share accurate design and part information with manufacturing.
Creating crucial parts lists, BOMs, and from/to wire lists using software that is not built specifically for these tasks can waste valuable time and resources. AutoCAD Electrical includes robust automated reporting tools so the design data being shared with downstream users is correct and current.

In addition, AutoCAD Electrical is tightly integrated with Autodesk Data Management applications, which
enables the efficient and secure exchange of design data and promotes earlier collaboration between design and manufacturing workgroups.

Facilitate Collaboration

AutoCAD Electrical enables both electrical and mechanical teams to work collaboratively by making it easy to share the electrical design intent for cables and conductors directly with team members using Autodesk® Inventor® software, adding valuable electrical controls design data to the digital prototype.

Users can also publish DWF™ files directly from AutoCAD Electrical and securely collaborate on 2d and 3d designs with customers, suppliers, and others outside the group. Different workgroups can manage and track all components of a digital prototype with the free† Autodesk® Design Review software—the all-digital way to review, measure, mark up, and track changes to designs—enabling better reuse of critical design data, management of BOMs, and collaboration with other teams and partners.

Now Is the Time

Want to get unparalleled productivity from your controls design process? Then now is the time to move to AutoCAD Electrical and get wired today.

Electrical Engineers always remain updated wih latest Technologies.

Electrical Engineering is a very interesting field which can provide a very good career and challenging practical things to learn during the entire life of an Individual, but it depends on the interest of particular person, because electrical though being an evergreen field in terms of career, is also one of the hardest field to study and understand.

Electrical engineers have a very difficult job and their jobs require that they receive a a lot of education that deals with electronics, electricity, and electromagnetism. They spend a few years in college pursuing this difficult degree to go into a very competitive, high tech field. Usually, they spend their time in college taking classes that have to do with mathematics, physics, computer science, and various other topics that deal specifically with electrical engineering. Master’s degrees are also available in the engineering field, and, while those with a BA degree make a great deal of money as electrical engineers.

The technology that brings electricity into our homes and the technology that has developed the global positioning system is what these engineers are working with. Not only do they design these technologies, but they also work to make them better, they test them, and even deploy them, as well.

Before we get into more details related to this job, you need to understand that what you learn in college might not be accurate to the actual site working condition. That is why it is so important not to rely on theory too much; one thing that fresh graduates fail to understand. This is where only experience can take over/charge to solve any problem that occurs at site.

Electrical engineering is an exciting job and the engineers work on the cutting edge of technology all the time. They are always working to make technology better and are finding ways to improve the technology that already exists as well.

Electrical Engineers Job prospects:

Some of them work in labs, developing and testing new technologies. Others work in offices dealing with clients and helping them with their technology. Yet others work in industrial plants and help manage the technology that is already in place.

There is a different between electrical engineers and electronic engineers. While the two may sound the same, there are great differences between the two. An electrical engineer will deal with electricity and electrical things on a large scale, where electronic engineers will deal with smaller electronics such as cell phones and computers and the components that are inside them.

Electrical engineering has a very broad job base and you can choose from any number of jobs. The education in this job prepares them to work in various different related fields. A good thing of this work is it can provide you with a a lot of job opportunities, and usually is different with each other. If you want to get involve in electrical engineering, you need to remember that the training and the job take a great deal of dedication and hard work.

Some food for thought, electrical engineers must possess a high self-confident and strong character in order to go further in this challenging career. Many have fallen and change their job, so make sure you are well prepared to face the challenge in front of you.

Dare to be an Electrical Engineer and you will have a very good life ahead !

Circuit Breakers used in our Homes.

Circuit breakers are an electric switch automatically operated and designed to guard an electrical circuit from damage. Harm will occur to an circuit or circuit breaker when there is an overload of electricity or short-circuit.

The essential function of commercial circuit breakers or circuit current sensor is to sense a fault condition. If there is one fault, the breakers discontinue the electrical flow. Made of varying sizes, industrial breakers will be reset manually or automatically to resume normal operation.

Breakers can be a small device to guard one household appliance or big switchgear fashioned to shield high voltage circuits that supply a complete city. There are three varieties of circuit breakers based mostly on their voltage.

A low-voltage breaker is made for circuits at 1000 volts or lower. The molded circuit breaker is one of the foremost commonly used low-voltage air circuit current sensor. This is the breaker used typically in houses, certain industrial uses and small businesses.

Types of low-voltage circuit breakers include the Miniature Circuit Breaker or MCB, and Molded Case Circuit Breaker or MCCB. The MCBs are for applications with electrical power rate not exceeding 100A. They'll be used as thermal or thermal-magnetic operations.

Low-voltage breakers are mounted into draw-out enclosures to permit removal and interchange without dismantling switchgear. The big low-voltage molded case and power breakers have electric motor operators to open and shut them using remote control.

Medium-voltage circuit breakers are for uses requiring voltage of higher than 1,000 however no more than 2000. They can be used indoor or outdoor. For indoor function, a circuit breaker is employed along with enclosed switchgear lineup. For outside application, a circuit breaker is employed as an individual component installed in substation.

There are 3 kinds of medium-voltage breakers. These are vacuum circuit breaker, air circuit breaker and SF6 circuit breaker. A vacuum circuit current sensor is used for electrical volts of 3000 A. it's used to interrupt the electric flow by creating and extinguishing the arc in a vacuum container.

Air circuit breaker is for uses of 10,000 A. It's often used for major power distribution in massive industrial plants to have straightforward and convenient maintenance. SF6 circuit breakers quench the arc in a container stuffed with sulfur hexafluoride gases.

Medium-voltage breakers will be connected into a circuit by bolted connections to bus bars or cables, in particular in switchyards found in most outdoors. These breakers, which are lined-up in switchgear, are made with draw-out construction. This construction is useful in removing the breaker while not interrupting the power circuit connections.

High-voltage circuit breakers are used if the electric voltage is 72,500 or higher as set by the International Electro-technical Commission. The basic characteristic in the majority of the 3 types of circuit breakers is their solenoid function.

High-voltage circuit current sensors are used to protect and control electrical power transmission networks. They are built with current sensing protecting relays maneuvered through electrical transformers. They're categorized in line with the tool used to extinguish the arc, that consists of the air blast, minimum oil, bulk oil, vacuum and SF6.