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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: The idea behind using reactive posted by rp1@surfnetusa.com on June 25, 2004 at 16:03:00:
Mike is correct that large industrial users apply banks of capacitors to their power grids to counteract the effect of heavy motors on the load they present to power suppliers. In these cases, the motors are on most of the time, and it is sensible to permanently connect the capacitors.The power utilities do not like the waste of energy (from I^2*R losses) in their equipment from reactive current drawn by the industrial users, so they have requirements for limits to the amount of inductance relative to the resistive loads. These are expressed as Power Factor, defined as the cosine of the phase angle between the voltage and current wave forms. For a purely inductive load, the PF is 0. For a purely resistive load, the PF is 1. For loads with some inductance and some resistance, the PF is a number between 0 and 1. Since the utility has to size its equipment for the peak current, even if the peak current is larger than that which produces power at the customer's site, they want the PF to be as close to 1 as possible. The power factor at most residential users is close enough to 1 to not be a problem.
The Richard Gray site implies that adding their device somehow corrects for inductive loads elsewhere in the house, such as refrigerator motors. This is correct, as the parallel combination formula for non-interacting inductors is the same as for parallel resistors and series capacitors: 1/Lt = 1/L1 + 1/L2 +... However, it does not seem to be an issue with the power utility, and I doubt it affects audio equipment. The non-audio loads may generate noise and create other problems, but the inductance is small. Since the refrigerator motor cycles on and off, leaving the RGPC choke connected permanently results in over-correction when the motor happens to be off.
Note that my calculations (for milliAMPS, not milliwatts) were for the 5 henry choke proposed by the DIY site. I don't know how large the RGPC choke is. Any shunting of high-frequency noise on the power line would have to be through the stray capacitance of the choke winding, as a good choke looks like an open-circuit to a high-frequency signal. If the choke has a low DC winding resistance, it will act to remove the DC component of any power voltage distortion caused by other equipment. This is helpful to audio equipment with toroidal power transformers, as these can be saturated easily by DC on the power line.
However, the demonstration trick of keeping a light bulb illuminated upon power interruption is misleading. The choke stores and releases energy in its magnetic field, which is fluctuating along with the current wave form. A brief (much less than one power cycle) interruption can take place at any time during the power cycle, so it is impossible to predict how much magnetic field energy will be on hand in the choke when the interruption occurs, and how much of a voltage spike the choke will apply to the parallel-connected audio equipment.
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Follow Ups
- RGPC claims re: power factor correction - Al Sekela 18:27:17 06/25/04 (2)
- I wonder something, - rp1@surfnetusa.com 23:07:29 06/25/04 (1)
- Yup. - Al Sekela 12:17:14 06/26/04 (0)
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