AC vs DC Generators (1 Viewer)

[dawso]

gday all, just wonderin what anyone has for this dot point

(please dont just link me 2 hsc online, ive done that and checked most text books, just wonderin what other people have...)

"discuss advantages / disadvantages of AC + DC generators and relate these to their use"

cheers

-dawso

 

[Captain Gh3y]

AC generators:
Advantages – can be supplied long distances as it can be stepped up and down, cheaper to supply, three phase power available, motors and generators are reliable with less moving parts.
Disadvantages – Frequency limited to speed of rotation, constant back emf, people nearby may experience health problems.

DC generators:
Advantages – No induced current in nearby conductors, can be used for DC appliances, no health problems for people near transmission lines
Disadvantages – Cannot be stepped up or down easily, expensive to supply, semiconductors can convert AC to DC so demand has decreased.

 

[spank_meh]

AC generators:
Advantages – can be supplied long distances as it can be stepped up and down, cheaper to supply, three phase power available, motors and generators are reliable with less moving parts.
Disadvantages – Frequency limited to speed of rotation, constant back emf, people nearby may experience health problems.

DC generators:
Advantages – No induced current in nearby conductors, can be used for DC appliances, no health problems for people near transmission lines
Disadvantages – Cannot be stepped up or down easily, expensive to supply, semiconductors can convert AC to DC so demand has decreased.

also onne of the advantages of AC is that they can be placed over longer distances, wereas if we had DC we'd have to have stations every few km...

what do you actually mean by "three phase power"?

 

[serge]

also onne of the advantages of AC is that they can be placed over longer distances, wereas if we had DC we'd have to have stations every few km...

what do you actually mean by "three phase power"?

3 phases power superposes the waves
so that it looks like DC, or something like that?
someone help clarify

 

[Captain Gh3y]

You know how when you get an AC generator and graph the power output against time it forms a sine curve? (well, it does!)

3 Phase is using 3 lots of them, all 120^o (or 2pi/3 if you like) out of phase, so the power output is more frequently at a peak.

 

[serge]

You know how when you get a DC generator and graph the power output against time it forms a sine curve? (well, it does!)

3 Phase is using 3 lots of them, all 120^o (or 2pi/3 if you like) out of phase, so the power output is more frequently at a peak.

you mean 3 AC right?

 

[spank_meh]

yep yep yep i get it now thanks guyz

 

[spank_meh]

and yes he means dc i found it in jacaranda its on pg142

 

[Ghost1788]

You know how when you get a DC generator and graph the power output against time it forms a sine curve? (well, it does!)

3 Phase is using 3 lots of them, all 120^o (or 2pi/3 if you like) out of phase, so the power output is more frequently at a peak.

you are talking bout AC voltage

AC voltage is rectified by a 'rectifier' which causes a positive bias in the Ac Voltage....so on a voltage vs time graph you get lots of sine graphs missing the negative component of the graph (ie. below the time axis) but since the voltage is composed of many of these graphs out of phase the voltage vs. time graph appears as a straight line

-Ghost

 

[serge]

you are talking bout AC voltage

AC voltage is rectified by a 'rectifier' which causes a positive bias in the Ac Voltage....so on a voltage vs time graph you get lots of sine graphs missing the negative component of the graph (ie. below the time axis) but since the voltage is composed of many of these graphs out of phase the voltage vs. time graph appears as a straight line

-Ghost

thought so, but will it be a perfectly straight line?

 

[spank_meh]

darn yeah we are talking bout ac***

 

[serge]

darn yeah we are talking bout ac***

wait a minute, no-one mentioned why triple phase is actually
and advantage?

cos a constant current is supplied?

 

[spank_meh]

thought so, but will it be a perfectly straight line?

it doesnt really look like a strigh line from the graph :S

 

[serge]

it doesnt really look like a strigh line from the graph :S

cool, thought so as well

answering my own question about why 3 phase is good

A 3-phase motor can be very powerful compared to one-phase motors and easy to maintain or repaire compared with DC motors.

 

[spank_meh]

wait a minute, no-one mentioned why triple phase is actually
and advantage?

cos a constant current is supplied?

Well the book says that: “each generator produces three sets of voltage signals that are out of phase with each other by 120o … Each generator is connected to four lines, one line for each phase and return ground line…” hmm I don’t really know how that’s an advantage but … :S

 

[Captain Gh3y]

you mean 3 AC right?

Yes. I did. Honestly, I make so many ridiculous mental slips typing stuff up on this forum... That caused a bit of confusion, too.

 

[spank_meh]

I found some more in Excel book:
“…3 emfs (and currents) can be produced during each revolution. Such three-phase generators are more efficient than single-phased generators.”

Hope this answers the question…

 

[serge]

Well the book says that: “each generator produces three sets of voltage signals that are out of phase with each other by 120o … Each generator is connected to four lines, one line for each phase and return ground line…” hmm I don’t really know how that’s an advantage but … :S

lol, extra knowledge never hurts

 

[exa_boi87]

someone confirm this, but DC generators should procude this same effect with only 2 conductors

 

[spank_meh]

someone confirm this, but DC generators should procude this same effect with only 2 conductors

Yep it is true dude diagrams on pg 141 of jacaranda book but the graphs different n the commutator has 4 segments