[Alternating Current Fundamentals Pdf Free
Iberio Ralda
An alternating current can be defined as a current that changes its magnitude and polarity at regular intervals of time. It can also be defined as an electrical current that repeatedly changes or reverses its direction opposite to that of Direct Current or DC, which always flows in a single direction as shown below.
From the graph, we can see that the charged particles in AC tend to start moving from zero. It increases to a maximum and then decreases back to zero completing one positive cycle. The particles then reverse their direction and reach the maximum in the opposite direction after which AC again returns to the original value completing a negative cycle. The same cycle is repeated again and again.
Alternating current can be produced or generated by using devices that are known as alternators. However, alternating current can also be produced by different methods where many circuits are used. One of the most common or simple ways of generating AC is by using a basic single coil AC generator, which consists of two-pole magnets and a single loop of wire having a rectangular shape.
AC is the form of current that is mostly used in different appliances. Some of the examples of alternating current include audio signal, radio signal, etc. An alternating current has a wide advantage over DC as AC is able to transmit power over large distances without great loss of energy.
AC is used mostly in homes and offices mainly because the generating and transporting of AC across long distances is a lot easier. Meanwhile, AC can be converted to and from high voltages easily using transformers. AC is also capable of powering electric motors that further convert electrical energy into mechanical energy. Due to this, AC also finds its use in many large appliances like refrigerators, dishwashers and many other appliances.
The normal waveform of AC in most of the circuits are sinusoidal in nature in which the positive half period corresponds with the positive direction of the current and vice-versa. In addition, a triangular or square wave can also be used to represent the alternating current waveform.
The average value is usually defined as the average of the instantaneous values of alternating current over a complete cycle. The positive half cycle of asymmetrical waves such as a sinusoidal voltage or current waveform will be equal to the negative half cycle. This implies that the average value after the completion of a full cycle is equal to zero.
Since both the cycles do some work, the average value is obtained by avoiding the signs. Therefore, the average value of alternating quantities of sinusoidal waves can be considered by taking the positive cycle only.
RMS value is defined as the square root of means of squares of instantaneous values. It can also be described as the amount of AC power that generates the same heating effect as an equivalent DC power.
The pure resistive AC circuit contains only pure resistance of R ohms. There will be no effect of inductance and capacitance in this circuit. The alternate current and voltage move along both directions as backwards and forwards. Therefore, current and voltage follow a shape of sine.
In a purely resistive circuit, the power is dissipated by the resistors and the phase of both voltage and current remains the same. This means that the voltage and current reaches a maximum value at the same time.
So, by observing the equation (1) and (3), it is clear that there is no phase difference between the applied voltage and current flowing through the circuit. Meaning, phase angle between voltage and current is zero.
The inductor will reserves electrical energy in the magnetic field when current flows through it. When this current changes, the time-varying magnetic field causes emf which opposes the flow of current. This opposition to the flow of current is known as inductive reactance.
If the voltage and current are at their peak value as a positive value, the power will also be positive. Similarly, if the voltage and current are at a negative peak then the power will be negative. This is because of the phase difference between them.
This type of circuit includes a pure capacitor only. It will not affect the properties of resistance and inductance. The capacitor will store electric power in the electric field. This is known as capacitance.
As we know, a capacitor includes two insulating plates which are separated by a dielectric medium. Usually, a capacitor works as a storage device and it gets charged if the supply is on and it gets discharged if the supply is off.
Alternating current can be stepped up or stepped down using a transformer.
Using electronic supply units, AC can be converted into DC.
Alternating current devices are more durable since power dissipation is less.
Transmission of electrical power is more efficient and economical in the form of AC.
The electricity you get from your electric outlet is alternating current (AC). There are many appliances such as computer and TVs that actually work on DC while other electrical appliances, such as refrigerators, air-conditioners, lighting etc can be designed for both AC and DC.
Since some kinds of loads only require DC to power them and others can easily operate on either AC or DC, the question naturally arises, "Why not dispense entirely with AC and just use DC for everything?" This question is augmented by the fact that in some ways AC is harder to handle as well as to use. Nevertheless, there is a very practical reason, which overrides all other considerations for a widely distributed power grid. It all boils down to a question of cost.
This 3-hr course material provides insight to the basic concepts of alternating current and is based entirely on Naval Education and Training Materials (NAVEDTRA 14173), Electricity and Electronic Training Series; Module-2 "Concepts of Alternating Current" and covers Chapter 1.
AC stands for Alternating Current. The current flows in one direction for a period of time and then switches direction, going the opposite way. It switches direction over and over again continuously. In the United States the AC current in power lines goes switches direction, forward to backward, then backward to forward, 60 times each second. This is a frequency of 60 cycles and is called 60Hertz AC electricity.
The usual waveform of an AC power circuit is a sine wave, which results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves. The alternating voltage and current have a number of properties associated with any such waveform. The most important of these properties are frequency and amplitude, since some types of electrically powered equipment must be designed to match the frequency and voltage of the power lines. Wavelength is not generally important in this context, but becomes much more important when we start dealing with signals at considerably higher frequencies.
Alternating current, or sine wave, is produced by an alternating voltage source that reaches a maximum in one direction (+), decreases to zero, reverses itself, and continues in the opposite direction until a maximum is reached. The cycle repeats continuously. The sine wave is the most common type of waveform. It is so named because it changes in value at the ramp rate, as the trigonometric function known as the sine.
AC transmission uses voltages ranging from 200 to 600 thousand volts. To meet customer demands the power company installs a transformer at different points along the AC power transmission line to lower the output voltage. Various potentials are involved. For homes and commercial buildings, it is lowered to the 220/120 volt level and for industrial use it is 220 volts and above. The AC voltage is usually transmitted at higher voltages which mean lower current for the same power, and less resistive loss. This is the major benefit AC provides over DC for large distance transmissions.
Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage.[1][2]
The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa (the full period is called a cycle). In certain applications, like guitar amplifiers, different waveforms are used, such as triangular waves or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information such as sound (audio) or images (video) sometimes carried by modulation of an AC carrier signal. These currents typically alternate at higher frequencies than those used in power transmission.
Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer. This allows the power to be transmitted through power lines efficiently at high voltage, which reduces the energy lost as heat due to resistance of the wire, and transformed to a lower, safer voltage for use. Use of a higher voltage leads to significantly more efficient transmission of power. The power losses ( P w \displaystyle P_\rm w ) in the wire are a product of the square of the current ( I ) and the resistance (R) of the wire, described by the formula:
High voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, energy is generated at a convenient voltage for the design of a generator, and then stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, but generally motors and lighting are built to use up to a few hundred volts between phases. The voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world.
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