Power generation and distribution

[fatima]

i'm a lil confused bout whether we need the voltage and current to be out of phase or its something we just can't avoid..?

 

[dlgoff]

Well, if I understand what you are asking; The phase shift between the voltage and current waves depends on the load of the system. With lots of motors, for example, you would need to add capacitance to keep the shift to a minimum. A measure of how well power gets transferred is called http://hyperphysics.phy-astr.gsu.edu/hbase/electric/powfac.html" .

Regards

 

[chroot]

For purely resistive loads, voltage and current are in-phase, and this is the ideal situation. Maximal power transfer to the load occurs in this condition.

In many situations, reactive (i.e. capacitive or inductive) loads are unavoidable, but they are not ideal.

- Warren

 

[WFO]

Try re-phrasing the question.

 

[Astronuc]

i'm a lil confused bout whether we need the voltage and current to be out of phase or its something we just can't avoid..?

For power generation using AC synchronous machines and the fact that transmission lines have inherent inductance (reactance), we simply cannot produce power without a phase difference between voltage and current.

As much as possible it is desirable to reduce reactance. One way to reduce reactance in a power line is to add capacitance to offset the inductance.

 

[fatima]

thanks for the help. i started the course with very little basics but i think I'm beginning to get the picture now. so, if there is no inductance (which 'pushes' the current back) both will be in the same phase right? as for passing a capacitor, the current leads the voltage because the charges move 'ahead' once there is sufficient voltage change, am i right?

 

[WFO]

For power generation using AC synchronous machines and the fact that transmission lines have inherent inductance (reactance), we simply cannot produce power without a phase difference between voltage and current.

As much as possible it is desirable to reduce reactance. One way to reduce reactance in a power line is to add capacitance to offset the inductance.

While this is true, it is also true that extremely long transmission lines have capacitive reactance issues since each conductor serves as a "plate" of the capacitor and the air between is the dielectric.

Just muddying the water a little