MOV's. An9311 - an9311.pdf. Varistor. A 385-volt metal-oxide varistor Varistor schematic symbol A varistor is an electronic component with a "diode-like" nonlinear current–voltage characteristic. The name is a portmanteau of variable resistor. Varistors are often used to protect circuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from sensitive components. A varistor is also known as voltage-dependent resistor (VDR). Only non-ohmic variable resistors are usually called varistors. Background[edit] Varistor current-voltage characteristics for zinc oxide (ZnO) and silicon carbide (SiC) devices The most common type of varistor is the metal-oxide varistor (MOV). High voltage varistor Specifications[edit] The response time of the MOV is largely ambiguous, as no standard has been officially defined.
Typical capacitance for consumer-sized (7–20 mm diameter) varistors are in the range of 100–1,000 pF. Delta-Star Connection of Transformer « Electrical Notes & Articles. (3) Delta-Star Connection of Transformer In this type of connection, the primary connected in delta fashion while the secondary current is connected in star. The main use of this connection is to step up the voltage i.e. at the begining of high tension transmission system. It can be noted that there is a phase shift of 30° between primary line voltage and secondary line voltage as leading.
Key point: As primary in delta connected:Line voltage on primary side = Phase voltage on Primary side.Now Transformation Ration (K) = Secondary Phase Voltage / Primary Phase VoltageSecondary Phase Voltage = K X Primary Phase Voltage.As Secondary in Star connectedLine voltage on Secondary side = √3 X Phase voltage on Secondary side. So,Line voltage on Secondary side = √3 X K X Primary Phase Voltage.Line voltage on Secondary side = √3 X K X Primary Line Voltage.There is s +30 Degree or -30 Degree Phase Shift between Secondary Phase Voltage to Primary Phase Voltage Advantages of Delta-Star Connection:
Electricity and Atomic Structure" Toward the end of the 19th century, science was barreling along at an impressive pace. Automobiles and aircraft were on the verge of changing the way the world moved, and electric power was steadily making its way into more and more homes. Yet even scientists of the day still viewed electricity as something vaguely mystical. It wasn't until 1897 that scientists discovered the existence of electrons -- and this is where the modern era of electricity starts.
Matter, as you probably know, is composed of atoms. Most metals, however, have electrons that can detach from their atoms and zip around. Some of us at HowStuffWorks.com like to think of atoms as pet dogs and electrons as a case of fleas. So, electricity needs a conductor in order to move. Fundamental interaction. Fundamental interactions, also called fundamental forces or interactive forces, are modeled in fundamental physics as patterns of relations in physical systems, evolving over time, that appear not reducible to relations among entities more basic. Four fundamental interactions are conventionally recognized: gravitational, electromagnetic, strong nuclear, and weak nuclear.
Everyday phenomena of human experience are mediated via gravitation and electromagnetism. The strong interaction, synthesizing chemical elements via nuclear fusion within stars, holds together the atom's nucleus, and is released during an atomic bomb's detonation. The weak interaction is involved in radioactive decay. (Speculations of a fifth force—perhaps an added gravitational effect—remain widely disputed.) In modern physics, gravitation is the only fundamental interaction still modeled as classical/continuous (versus quantum/discrete). Overview of the fundamental Interaction[edit] The interactions[edit]
AC power. The blinking of non-incandescent city lights is shown in this motion-blurred long exposure. The AC nature of the mains power is revealed by the dashed appearance of the traces of moving lights. Real, reactive, and apparent power[edit] 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 loads are purely reactive, then the voltage and current are 90 degrees out of phase. Practical loads have resistance, inductance, and capacitance, so both real and reactive power will flow to real loads.
Conventionally, capacitors are considered to generate reactive power and inductors to consume it. Power factor[edit] " for this reason. Reactive power[edit] . Why does current lead the voltage in capacitor? Best way is to consider an uncharged cap. A switch is closed & current enters the cap. The current is full value, a constant current source or a constant voltage source plus a resistor. At time t = 0+, the current i is maximum value, if the voltage source value is V, & resistance is R, then i(t=0+) = V/R. But the cap starts uncharged, Q=0, & V=0.
Another thought is that current in a cap can change quickly/abruptly but voltage in a cap changes gradually/slowly. But changing cap voltage is changing its energy, needing work to be done. In the ac domain. i = C*dv/dt. Did I help? Claude. Why does current lag behind voltage in inductor? - Page 5. Voltage-Current lead/lag. Three-phase. One voltage cycle of a three-phase system, labeled 0 to 360° (2π radians) along the time axis. The plotted line represents the variation of instantaneous voltage (or current) with respect to time.
This cycle repeats with a frequency that depends on the power system. In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating current voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). A wye system allows the use of two different voltages from all three phases, such as a 230/400V system which provides 230V between the neutral (centre hub) and any one of the phases, and 400V across any two phases. Definitions[edit] Elementary six-wire three-phase alternator, with each phase using a separate pair of transmission wires no. Elementary three-wire three-phase alternator, showing how the phases can share only three transmission wires. or.
AC power, RMS and 3-Phase circuits. This page provides answers to these questions. This is a resource page from Physclips. It is a subsidiary page to the main AC circuits site. There are separate pages on RC filters, integrators and differentiators, LC oscillations and motors and generators. Power and RMS values In the last line, we have used a standard trigonometrical identity that cos(2A) = 1 - 2 sin2A. Now the sinusoidal term averages to zero over any number of complete cycles, so the integral is simple and we obtain This last set of equations are useful because they are exactly those normally used for a resistor in DC electricity. When talking of AC, RMS values are so commonly used that, unless otherwise stated, you may assume that RMS values are intended* . * An exception: manufacturers and sellers of HiFi equipment sometimes use peak values rather than RMS values, which makes the equipment seem more powerful than it is.
Power in a resistor. Power in inductors and capacitors. Three phase AC. Useful 3 Phase Formulas. Alternating current. Alternating Current (green curve). The horizontal axis measures time; the vertical, current or voltage. In alternating current (AC, also ac), the flow of electric charge periodically reverses direction. In direct current (DC, also dc), the flow of electric charge is only in one direction. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.[1] [2] AC is the form in which electric power is delivered to businesses and residences.
History The first alternator to produce alternating current was a dynamo electric generator based on Michael Faraday's principles constructed by the French instrument maker Hippolyte Pixii in 1832.[3] Pixii later added a commutator to his device to produce the (then) more commonly used direct current. A power transformer developed by Lucien Gaulard and John Dixon Gibbs was demonstrated in London in 1881, and attracted the interest of Westinghouse. Three-phase electrical generation is very common. Circuit Theory/Phasor Analysis. Phasor Analysis[edit] The mathematical representations of individual circuit elements can be converted into phasor notation, and then the circuit can be solved using phasors. Resistance, Impedance and Admittance[edit] In phasor notation, resistance, capacitance, and inductance can all be lumped together into a single term called "impedance".
The phasor used for impedance is . Is Voltage and is current. And the Ohm's law for phasors becomes: It is important to note at this point that Ohm's Law still holds true even when we switch from the time domain to the phasor domain. Impedance is still measured in units of Ohms, and admittance (like Conductance, its DC-counterpart) is still measured in units of Siemens. Let's take a closer look at this equation: If we break this up into polar notation, we get the following result: Resistors[edit] Resistors do not affect the phase of the voltage or current, only the magnitude. Capacitors[edit] A capacitor with a capacitance of C has a phasor value: Where. AC_circuits.pdf (application/pdf Object) Complex number. A complex number can be visually represented as a pair of numbers (a, b) forming a vector on a diagram called an Argand diagram, representing the complex plane.
"Re" is the real axis, "Im" is the imaginary axis, and i is the imaginary unit which satisfies i2 = −1. A complex number is a number that can be expressed in the form a + bi, where a and b are real numbers and i is the imaginary unit, that satisfies the equation x2 = −1, that is, i2 = −1.[1] In this expression, a is the real part and b is the imaginary part of the complex number. Complex numbers extend the concept of the one-dimensional number line to the two-dimensional complex plane (also called Argand plane) by using the horizontal axis for the real part and the vertical axis for the imaginary part. The complex number a + bi can be identified with the point (a, b) in the complex plane. Overview[edit] Complex numbers allow for solutions to certain equations that have no solutions in real numbers.
Definition[edit] . Or or z*. and . Angular frequency. Angular frequency ω (in radians per second), is larger than frequency ν (in cycles per second, also called Hz), by a factor of 2π. This figure uses the symbol ν, rather than f to denote frequency. In physics, angular frequency ω (also referred to by the terms angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, and pulsatance) is a scalar measure of rotation rate.
Angular frequency (or angular speed) is the magnitude of the vector quantity angular velocity. The term angular frequency vector is sometimes used as a synonym for the vector quantity angular velocity.[1] where: ω is the angular frequency or angular speed (measured in radians per second), T is the period (measured in seconds), Units[edit] In SI units, angular frequency is normally presented in radians per second, even when it does not express a rotational value. Examples[edit] A sphere rotating around an axis. Circular motion[edit] Oscillations of a spring[edit] where k is the spring constant. Calculator Tab • Free Online Scientific Calculator. Table of contents calculator Quick start Calculator Tab is a free online scientific calculator which works like your regular calculator. One feature that sets it appart from other calculators is that it's memory bank can store an unlimited amount of numbers and descriptions of these numbers for an indefinite length of time.
The stored numbers can be sorted by date, by the number of uses or by name. Your saved numbers and their respective descriptions are saved directly on your computer, never entering the sphere of the internet, so that they are as secure as your workstation. This calculator follows the standard order of operations. It can handle values from 4.9e-324 to 1.7e+308. . Button. Calculator Tab will not allow you to make ambiguous enteries and will tell you, what is not allowed if you try to make such an entry. The entry of will generate an error telling you, that you first need to enter a number before continuing with the calculation. Features Using the memory function .2. And . . E84 Lecture Notes. Generalized Ohm's Law and Impedance. Next: Impedance and Generalized Ohm's Up: Chapter 3: AC Circuit Previous: Sinusoidal Functions In the following discussion about AC circuit analysis, all sinusoidal variables (currents and voltages) are assumed to be of the same frequency.
In general, arithmetic operations of sinusoidal functions are not convenient as they will involve using trigonometric identities. However, we can consider such sinusoidal functions as real (or imaginary) parts of some rotating vectors in the complex plane, and their arithmetic operations (addition, multiplication, etc.) can be more conveniently carried out (review of complex arithmetic). However, we can consider the phasor The sum of the two sinusoidal function can now be found as the real part of the rotating vector sum: The addition can be more easily carried out in the phasor form as vectors in the complex plane, than in the time domain. Specifically, consider two sinusoidal functions where and When multiplied by and then taking the real part: or Example. Phasor. An example of series RLC circuit and respective phasor diagram for a specific Glossing over some mathematical details, the phasor transform can also be seen as a particular case of the Laplace transform, which additionally can be used to (simultaneously) derive the transient response of an RLC circuit.[10][8] However, the Laplace transform is mathematically more difficult to apply and the effort may be unjustified if only steady state analysis is required.[10] Definition[edit] Euler's formula indicates that sinusoids can be represented mathematically as the sum of two complex-valued functions: [a] or as the real part of one of the functions: The term phasor can refer to either [citation needed] or just the complex constant, .
An even more compact shorthand is angle notation: See also vector notation. A phasor can be considered a vector rotating about the origin in a complex plane. . Represents the angle that the vector forms with the real axis at t = 0. Phasor arithmetic[edit] In electronics, and . When stored energy returns to source in an AC system. Reactive power. What is reactive power. Reactive power. In an electric power grid, what happens to unused current. What is meant by Active and reactive power? Main Page - Electrical Installation Guide. BASCIALLY AE&E!