Question

QUESTION

A) List the advantages and disadvantages of synchronising an AC generator to the utility
grid.
B) Describe the importance of frequency control for synchronous generators.
C) List the important applications of synchronising AC generator to the utility grid

Answer 1

A)

AC generators – advantages
1.For the large part, an AC motor has a very simple structure, because the only moving part it has is the rotor.1.
2.This also makes it easier to maintain these generators.
3.They have a quiet operation.
4.Cost of ownership is lower.
5.Longer lifespan compared to DC motors that have a commutator and carbon brushes that wear out over a period of time. These require regular replacement through the life of the system.
6.AC motors don’t have a smell that’s very typical of DC motors; in the latter, this is caused by components that are more prone to friction.
7.An AC generator allows users to covert its current to other voltages with the use of transformers; and these are compatible only with an AC generator and not with a DC generator.

AC generators – disadvantages
1..While there are a number of benefits to opting for AC generators, there are certain limitations as well, such as:

2.These systems require additional insulation because of the greater voltages needed to supply a fixed level of power.
3.This poses a challenge when it comes to handling AC generators in a safe manner.
4.Working with Alternating current systems has some distinct risks and difficulties compared to what can be expected from DC motors.
5.While the use of a transformer is an advantage in AC systems, to a certain degree that can prove to be a limitation as well. This is because the motors then require a specific design which becomes a hindrance to a higher voltage discharge generated from one side. But since there is no other efficient method of generating high voltages, it becomes necessary to utilise transformers to ease the long-distance transmissions. These transmissions occur as soon as the lower voltage converts to the required higher levels.
6.Aside from this, Alternating Current power is more prone to overheating and sparks because it produces higher currents and this particular phenomenon can result in electrical shock as well as fires. The latter can cause a significant amount of damage to property and pose a threat to lives as well.
7.In addition to all these risks, an AC generator isn’t as durable as a DC generator.

B)

Frequency must be maintained in order to support the stability of the system. If the grid frequency is not maintained, the system will collapse. After all, what does the frequency represent? All power grids are designed around a standard frequency usually 60 or 50 Hz. For the US, this standard is 60 Hz. At 60.000 Hz exactly, load and generation are perfectly balanced. If load exceeds generation, then frequency will decline. And if generation exceeds load, frequency will rise. So, frequency is fundamentally a measure of how well generation equals load and how well the system operator is doing their job. It is the job of the system operator to balance generation to demand reliably.This standard frequency is the frequency that all devices on the grid are synchronized to and designed to operate at. If frequency significantly deviates from the common frequency, equipment can be damaged. Generators can sustain damage to turbines due to speeding up too fast or sub-synchronous resonance. And eventually protection relays will trip out generators, lines, and transformers if the frequency deviations are too severe. Transformers can heat up and damage themselves if the current through them becomes too high which can happen during contingency events due to frequency issues. Even your consumer devices are only designed to handle a certain frequency and can experience damage due to high or low frequency.

c)

1.The electric current produced by a Synchronous Generator has a waveform that is “synchronized” with the rotational speed of the generator. Therefore, the frequency of the alternating current (AC) changes with the speed of the prime mover which could be anything that turns the generator—Internal Combustion Engine, Turbine in a hydro plant, steam turbine in a coal or nuclear plant.

2.Electric Utility Generators — Speed is easily controlled and therefore the frequency.

3.Backup or Standby Generators—Because modern standby generators mimic the power produced by the electric utility, they supply electric power during an outage to homes, businesses, Industry, and institutions.

4.Portable Generators—The most common type of portable generator produces current similar to that from the utility. The quality of the current varies from poor to excellent depending on the intended use. Portable generators are powered by internal combustion engines designed to run on gaseous fuel such as propane or gasoline, or on diesel.

5.Automotive Alternator—In the past, a simple DC generator was used to charge the battery and operate the vehicle. The silicon diode rectifier made the application of a three-phase synchronous alternator practical

6.Wind Turbines—Some home applications utilize a multi-phase synchronous generator to produce AC current which is rectified to DC to charge batteries. The DC current is usually inverted to 60 or 50