Q: Ch. 11 : Power Factor

Discussion in 'General Electronics Chat' started by foolios, Dec 30, 2009.

  1. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Ch.11/pg.1
    In a purely reactive circuit, no circuit power is dissipated by the load(s). Rather, power is alternately absorbed from and returned to the AC source. Voltage and current are 90o out of phase with each other.



    Ch.11/pg.3

    Power factor can be an important aspect to consider in an AC circuit, because any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load. If our last example circuit had been purely resistive, we would have been able to deliver a full 169.256 watts to the load with the same 1.410 amps of current, rather than the mere 119.365 watts that it is presently dissipating with that same current quantity. The poor power factor makes for an inefficient power delivery system.

     
    Last edited: Feb 14, 2010
  2. thyristor

    Active Member

    Dec 27, 2009
    94
    0
    The answer's in your quotation. If everyone had a poor PF then the required supply cables would need to be far thicker than in reality adding huge costs to the supply infrastructure.

    Although no more net power is actually consumed, with a poor PF, the currents flowing can be significantly larger than with unity PF and thus the whole supply system becomes very inefficient.
     
  3. foolios

    Thread Starter Active Member

    Feb 4, 2009
    160
    1
    Although no more net power is actually consumed, with a poor PF, the currents flowing can be significantly larger than with unity PF and thus the whole supply system becomes very inefficient.

    The current draw becomes larger while the voltage drops right? That's what I need to realize. So, there's no more power being used/wasted, but it is costly because more expensive equipment has to be used. The reason why we have high voltage lines pushing small current; smaller wires, less weight to support...
    I guess in the U.K. they decided to keep it at 240v as opposed to our 120's for that reason as well, right?

    So the power company monitors this poor performance and penalizes the customer for it?

    EDIT:
    And then I found this on the next page, so there's this reason as well:
    This lower total current will translate to less heat losses in the circuit wiring, meaning greater system efficiency (less power wasted).
     
    Last edited: Dec 30, 2009
  4. thyristor

    Active Member

    Dec 27, 2009
    94
    0
    The reason for having very high voltage lines (typically 330,000v in the UK) is not the weight of the conductors, although this is an added benefit, but the I^2R losses in the cable.

    If the high voltage lines were dropped to say half their present value then, to deliver the same amount of power, the current would have to double and the I^2R losses on the line would increase by a factor of 4 !!!
     
Loading...