AC vs DC Generators (1 Viewer)

dawso

needmorecustomstatusspace
Joined
Feb 25, 2004
Messages
1,029
Gender
Male
HSC
2005
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

Rhinorhondothackasaurus
Joined
Aug 10, 2005
Messages
4,153
Location
falling from grace with god
Gender
Male
HSC
2005
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

add me on MSN NOW!!!!
Joined
Sep 15, 2005
Messages
268
Location
like totaly not here lol
Gender
Female
HSC
2005
Captain Gh3y said:
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

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
spank_meh said:
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

Rhinorhondothackasaurus
Joined
Aug 10, 2005
Messages
4,153
Location
falling from grace with god
Gender
Male
HSC
2005
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 120o (or 2pi/3 if you like) out of phase, so the power output is more frequently at a peak.
 
Last edited:

serge

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
Captain Gh3y said:
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 120o (or 2pi/3 if you like) out of phase, so the power output is more frequently at a peak.
you mean 3 AC right?
 

Ghost1788

Member
Joined
Jan 30, 2005
Messages
276
Location
Sydney
Gender
Male
HSC
2005
Captain Gh3y said:
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 120o (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

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
Ghost1788 said:
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?
 

serge

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
spank_meh said:
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?
 

serge

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
spank_meh said:
it doesnt really look like a strigh line from the graph :S
cool, thought so as well :D

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.
 
Last edited:

spank_meh

add me on MSN NOW!!!!
Joined
Sep 15, 2005
Messages
268
Location
like totaly not here lol
Gender
Female
HSC
2005
serge said:
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
 

spank_meh

add me on MSN NOW!!!!
Joined
Sep 15, 2005
Messages
268
Location
like totaly not here lol
Gender
Female
HSC
2005
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

Member
Joined
Nov 22, 2004
Messages
635
Gender
Male
HSC
2005
spank_meh said:
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

aka biomic
Joined
Apr 3, 2005
Messages
216
Location
Hornsby
Gender
Male
HSC
2005
someone confirm this, but DC generators should procude this same effect with only 2 conductors
 

spank_meh

add me on MSN NOW!!!!
Joined
Sep 15, 2005
Messages
268
Location
like totaly not here lol
Gender
Female
HSC
2005
exa_boi87 said:
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
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top