We know that an alternating emf can be generated either by rotating a coil within a... 3. If an industry has large motors, it will require a high inductive current to mag- netize these motors. The voltage in a direct-current circuit must be constant, or at least relatively constant, to keep the current flowing in a single direction. It is given by. Emphasis is placed on what alternating current is, how it works, and what factors affect the operation and maintenance of AC equipment such as motors, lights, and communications equipment. Most industries use the following methods to ensure that their power factor remains above the limit specified by the utility: a. In the United States, the voltage is reversed 60 times per second. Meaning of Alternating Current:. This is so because the apparent power specifies the total power (real and reac- tive) requirement of equipment. 3. The alternating current in the circuit shown in Fig. To further describe the phase relationship between two sinusoidal waves, the terms lead and lag are used. Name the basic components of a capacitor. The inrush current is mainly an inductive current. Create a free website or blog at WordPress.com. In the next lesson, we'll look at all of the parameters we will need to know to understand AC. Thus, the voltage in an AC circuit is always changing. In western Europe and Australia it is 50 Hz. Define capacitance and capacitive reactance. We can write the fol- lowing equations: This is the reactive or inductive power in the circuit. This alternating motion, back and forth, continues for an amazingly long time if the toy is carefully constructed. Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. It starts out at zero, then increases in the positive direction for a bit until it reaches its maximum positive voltage, and then it decreases until it gets back to zero. A comparison between the previous equations shows that the time-varying (instantaneous) quantities VR and iR are in phase. All rights reserved. In a purely capacitive circuit, current will be at its maximum phase shift and leading the voltage. An electric current that flows continuously in a single direction is called a direct current, or DC. ( Log Out / Lagging current can be formally defined as “an alternating current that reaches its maximum value up to 90° behind the voltage that produces it”.This can also be stated as the voltage and current being out of phase. All circuits for the 10 exercises in Fundamentals of alternating current technology are built using the equipment set TP 1011. ( Log Out / Basically, what is "alternating" in alternating current is the polarity of the voltage source, which causes the current to flow in one direction, and then reverse, and flow in the opposite direction. Change ), You are commenting using your Facebook account. When the voltage reverses, so does the direction of the current flow. COURSE GOALS Emphasis is placed on what alternating current is, how it works, and what factors affect the operation and maintenance of AC equipment such as motors, lights, and communications equipment. This creates a local- ized reduction in voltage (a voltage dip) at the industry. Change ), You are commenting using your Twitter account. Figure 1.20a illustrates an alternating voltage acting on a capacitor. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other. The electrons in an AC circuit don’t really move along with the current flow. The phasors in this diagram are represented by open arrows. For your further enlightenment, here are some additional interesting and useful facts concerning alternating current: A popular toy called Newton’s Cradle might help you understand how alternating current works. where Z is the impedance of the circuit and V and I are the rms or effective values of the voltage and current. Check out the new look and enjoy easier access to your favorite features. They move one direction for 1/60th of a second, and then turn around and go the other direction for 1/60th of a second. The unit of this power is voltamperes (VA) or megavoltamperes (MVA). That's why the main difference you will see between DC and AC circuit diagrams, is that in the AC circuit diagrams, there will be no indication of polarity, or + and - signs. c. Use synchronous motors in conjunction with induction motors. show relationship between two sine waves of the same frequency, resistance – material used in the circuit, inductive reactance – induced magnetic fields by changing voltages, capacitive reactance – it will either try to rise or lower the voltage, but can not ever occur. Change ). At that point, it increases in the negative direction until it reaches its maximum negative voltage, at which time it decreases again until it gets back to zero. b. An alternating current (ac) in a circuit establishes a voltage (emf ) that varies with time as. The phase angle is necessary to characterize the circuit and allow the calculation of the average power used by the circuit. The most common form of AC is the Sine Wave, which is the one we will be dealing with the most. This is because the polarity of the voltage source, and the direction and magnitude of the flow of current is continually changing or alternating. Explain how power factor is used in calculating true power in AC Circuits. Alternating currents are essential for modern society. The electrons initially move in one direction, but then reverse themselves and move in the other direction. Alternating current is used in nearly all the world’s power distribution systems, for the simple reason that AC current is much more efficient when it’s transmitted through wires over long distances. All electrical equipment such as transformers, motors, and generators are rated by their apparent power. Most students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. It is used to create the magnetic field in the windings of the motor. This constancy is what pushes the electrons in a single direction. Academia.edu is a platform for academics to share research papers. 3504 Parliament Ct. All electric currents lose power when they flow for long distances, but AC circuits lose much less power than DC circuits. The reversal of voltage in a typical alternating current circuit isn’t instantaneous. Alternating current works in much the same way. Define peak value, peak-to-peak value, and effective value with respect to AC voltage and current. The utility will not be able to correct for this voltage dip from the power plant. In the most common form of alternating current, used in most power distribution systems throughout the world, the voltage reverses itself either 50 or 60 times per second, depending on the country.
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