How is an AC generator different from a DC generator?
An AC generator is simpler. The generating coils can be stationary and the field coils require only simple slip rings to maintain the rotating contact. For a DC generator, the field coils are stationary and the generating coils require a complicated switching arrangement called a commutator to keep the polarity of the output correct. As well as being complicated, the commutator and brushes have to carry the entire output current, instead of only the field current which is comparatively small.
Why transformer can only be used in AC circuit but not DC circuit?
If you energize a DC circuit containing a transformer there will be a single surge through the transformer transferring energy from the primary to the secondary windings then there will be steady state with no energy transfer. Only changes to the voltage and current of the primary are reflected in the secondary and AC power meets this requirement. If you open and close the DC circuit there will be only a transient effect (like the coil that fires car spark plugs as the distributor makes and breaks the DC circuit).
4)What is the difference between a transformer and a rectifier? Which are found in a PC Power supply?
A transformer is basically used to step up or step down the mains power supply (in terms of voltage). In contrast, the rectifier is used to convert an alternating current (AC) or voltage to direct current (DC) or voltage. Wikipedia provides the following definitions which might be helpful to you. A transformer is an electrical device that transfers energy from one electrical circuit to another by magnetic coupling, where relative motion between the parts is not required to transfer energy between the circuits. It is often used to convert between high and low voltages, for impedance transformation, and to provide electrical isolation between circuits.Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with just a single diode. Rectification is commonly performed by semiconductor diodes. Both will be found in a PC power supply since the mains is AC and the PC requires 12v DC supply which will be done by the rectifier. The stepping down of the voltage will be done by the transfoirmer coil.
Why is AC considered more efficient than DC?
It's not. DC is more efficient than AC power and has lower line losses than AC lines. With AC, the current travels on the skin of the conductor while with DC, the current flows throughout the entire conductor and not just the conductor skin. DC therefore has lower skin losses in the line. Additionally, there is no reactive component of DC power, which means that on transmission lines, there are no losses due to an inductive or capacitive effects. Though both, C and DC transmission lines will still have resistive losses. Given that DC utilizes the entire conductor, it can also use a smaller conductor than an AC line will which saves on cost.Converting AC to high voltage DC and vice-versa, as it is done for HVDC transmission, is less efficient than stepping up and down AC using transformers.Now AC is generally more cost efficient than DC and is currently more useful when building a networked grid on low and middle distances versus DC; which is used mainly in point to point transmission for long distances. Once past a certain distance, the cost of a DC line becomes competitive with AC and eventually for long transmission lines, DC is more cost effective due to lower losses and a smaller conductor which reduces the right of way requirements.
Why is AC used to transfer electricity and not DC?
First of all, we don’t always transmit electricity through AC. For long distance transmissions, we can use High voltage DC (HVDC).Talcher-kolar transmission link, India. India's 1,450km-long Talcher-Kolar transmission link is the world's fifth longest transmission line. The 500kV HVDC transmission line, also known as the East-South transmission link, has a rated capacity of 2,500MW and is owned by Power Grid Corporation of India.Alternating current ultimately won since the AC voltage is easily converted (stepped up/down) using a transformer. To change DC voltage requires complex , inefficient circuitry and they are not cost effective.Power loss in transmission lines depends upon the Current, as the Current is directly proportional to lost power and inversely proportional to voltage . So if we increase the supply voltage we decrease the power lost. This is why the electricity transmission lines use very high voltages. The electricity produced by the power station is passed through a transformer to raise its voltage to 100000v and more. Then it passes through many step down transformers and then is passed through Distribution transformers to reduce it to the domestic voltage.But changing the voltage this way only works for AC because transformers don't work for DC. And that's why most electricity transmission is done in AC because conversion of AC-DC and Vice versa on both the ends is not efficient, this is the first point .Since Direct current does not involve oscillation, it decreases losses and allows electricity to be transmitted more efficiently.However, the cost of the substation equipment needed to convert DC electricity back to AC at both ends of the transmission line is expensive. Since the initial cost can be prohibitive, HVDC transmission is usually only preferred for long distances. Over their lifetime, long-distance transmission lines can save operators money because of their efficiency.Since, HVDC transmission towers are lighter and cheaper (also DC cable can carry more power than AC cable), and it does not generate or absorb any reactive power, eliminating the need for reactive power compensation.In addition to equipment cost, another disadvantage for HVDC involves heat losses that occur in the converter substation, which requires an active cooling system. Also, inverters used in converter substations have limited overload capacity, this is the second point.Do comment,share and Upvote.Thanks for your patience.
Why is alternating current better for long-distance power transmission than direct current?
AC can be stepped up and down in voltage very easily by transformers and the bigger the voltage the lesser the current. You tend to get less losses to resistance when distributing AC over long distances too. You can use thinner wires which means they’re cheaper to make and suspend.At the power station you can ramp up to thousands of volts and very little current through a step-up transformer. In the UK commonly seen voltages at the consumer end are 230V (residential, commercial, light industry) and 440V (industrial) and the same high voltages sent from the power station are ramped down again through a step-down transformer. In this way you get current back.It’s much easier to generate AC than DC too due to the way the generators turn.All in all, it’s better to have a cheaper system for the long overland haul of a national grid system where there’s miles of wire, lots of pylons to support it and the back infrastructure is minimal.That’s not to say you can’t or don’t do it with DC though. There’s one in Brazil that stretches for nearly 1,500 miles. Transmitting DC in this way is called, unsurprisingly, High Voltage Direct Current ( HVDC ). This is used in inter-country transfers; you can transmit HVDC into an AC grid of any frequency.Undersea cables are almost always HVDC because they act as capacitors, and being so long, big ones. AC would charge and discharge the capacitors and you’d probably end up using all the juice just in combatting the capacitance. HVDC charges it only when the voltage is first applied or changes. Strangely the one between England and the Isle of Man is AC. At 65 miles long it’s the longest AC underwater connector in the world and carries 90,000V. Why they chose AC I’ve no idea, there must have been some compromise between cost and technical efficiency but I don’t know what it was and it just goes to show.So it’s not a case of being better, it’s just that one is suited to certain circumstances more effectively than the other, and whatever the circumstances are you choose the system to fit.