- #1
fatima
- 2
- 0
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..?
Power generation and distribution
- Thread starter fatima
- Start date
Click For Summary
Discussion Overview
The discussion revolves around the relationship between voltage and current phase in power generation and distribution, particularly in the context of AC synchronous machines and transmission lines. Participants explore the implications of phase differences, reactive loads, and methods to manage reactance.
Discussion Character
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants express confusion about whether a phase difference between voltage and current is necessary or unavoidable.
- One participant notes that the phase shift depends on the load, suggesting that capacitors may be needed to minimize this shift in systems with many motors.
- Another participant states that for purely resistive loads, voltage and current are in-phase, which is ideal for maximal power transfer.
- It is mentioned that reactive loads, such as inductive or capacitive loads, are often unavoidable, complicating the phase relationship.
- One participant asserts that in power generation using AC synchronous machines, a phase difference is inherent due to the inductance of transmission lines.
- A later reply highlights that while reducing reactance is desirable, long transmission lines can introduce capacitive reactance issues due to their physical properties.
Areas of Agreement / Disagreement
Participants express varying degrees of understanding and confusion regarding the necessity and implications of phase differences. There is no consensus on whether the phase difference is something that can be avoided or managed effectively.
Contextual Notes
Participants discuss the complexities of managing reactance in power systems, including the effects of inductance and capacitance, without resolving the nuances of these interactions.
Who May Find This Useful
Individuals interested in electrical engineering, power systems, and the principles of AC power generation and distribution may find this discussion relevant.
- #2
dlgoff
Science Advisor
Gold Member
- 4,458
- 3,265
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
Regards
Last edited by a moderator:
- #3
chroot
Staff Emeritus
Science Advisor
Gold Member
- 10,270
- 45
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
In many situations, reactive (i.e. capacitive or inductive) loads are unavoidable, but they are not ideal.
- Warren
- #4
WFO
- 26
- 0
Try re-phrasing the question.
- #5
Astronuc
Staff Emeritus
Science Advisor
Gold Member
2025 Award
- 22,588
- 7,554
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.fatima said:
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.
- #6
fatima
- 2
- 0
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?
- #7
WFO
- 26
- 0
Astronuc said:
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
