speedie said:
has anyone done the questions on motors and generators from the success one book??? i thought they were sooooooooooooo hard- i got 15/25 for multiple choice! they seem weird and i dunno if the answers are right...
anyway i have some questions also:
what are some advantages and disadvantages of AC and DC generators? i know theres the commutator one, but what else? i read some books which talked about transmission eg power loss but thats not really related to generators.
also, i read something about transformers, and it talks about "the relationship between the frequency and phase of the primary and secondary voltages"- i have no idea what this is about????
This is one of the syllabus dot point
3.7 Gather secondary information to discuss advantages/disadvantages of AC and DC generators and relate these to their use.
AC Generators
Advantages
- AC power produced is easy to transform into higher or lower voltages during transmission using a transformer, making it easy to transform into a higher voltage for distribution and back to a lower voltage for use
- AC generators are more efficient than DC generators because it has far fewer moving parts and are more efficient in conversion of the electrical energy into useful work than the DC generators. AC generators are also more efficient, because it contains less parts to wear out and it is easier to construct.
- AC generators have less energy waste and power loss during transmission because its voltage can be greatly increased. As a result, it can conserve energy, thus causing it to be used on a wider scale than DC generators.
- AC current naturally changes direction at the frequency of the AC electrical wave, thus transformers were far more efficient and easier to construct.
Disadvatages
- AC current is generally more dangerous than DC current in the household, because it can cause fibrillations to the heart if contracted. Due to its oscillating nature, the risks of AC current in the household is significantly higher than that of DC.
DC Generators
Advantages
- DC generators are comparatively safer than AC generators because the DC current produced have less risk of causing fibrillations to the heart if it is touched. It is thus comparatively less dangerous than AC current.
Disadvantages
- DC generators have more moving parts than AC generators, and the gaps in the split ring commutators may cause inefficiencies during use. They are generally less reliable than AC because they have more parts that can be worn out by friction, and if the gap in the split ring commutator is changed in size, the generator may cease to function.
- DC generators are much more difficult to construct.
- DC current is far more difficult to transform and less efficient
- DC current is less energy efficient and more difficult to distribute because of its difficulty to be transformed. As a result, they can only transport the electrical energy they produce over relatively short distances before the energy losses in the conducting wires became too great. Furthermore, they cannot be transformed to lower voltages in the home, and thus may present further risks.
I'm not sure about answering
also, i read something about transformers, and it talks about "the relationship between the frequency and phase of the primary and secondary voltages"- i have no idea what this is about????
question. But I have a book which talk a bit about frequency effecting on motor effect.
The frequency and amplitude of the voltage produced by a generator depend on the rate at which the rotor turns. If the rotor is turning at twice the original rate, then the period of the voltage signal halves, the frequency doubles and the amplitude doubles.
The effectiveness of generators is increased by winding the coil onto an iron core armature. The iron core makes the coil behave like an electromagnet. This intensifies the changes in flux threading the coil as it is forced to rotate and increases the magnitude of the emf that is induced. This effect also occurs when the number of turns of wire on the armature is increased. The coil then behaves like a number of individual coils connected in series.
And in transformer the relationship with frequency is when an alternating current passes through the primary coil, a constantly changing magnetic flux threads (or passes through) the secondary coil. This constantly changing flux passing through the secondary coil produces and AC voltages at the terminals of the secondary coil with the same frequency as the AC voltage supplied to the terminals of the primary coil.
Code:
I hope it helps. It kinda a bit of revision for me as well...:)
