[ARC5] BC 453 request - ham radio

[Brian Clarke]

Hello Richard,

While power factor is a concern, most well-designed kWh meters nowadays can read kW quite accurately and are not fooled by inductive or capacitive loads. What concerns electricity supply authorities is that inductive and capacitive loads require more current to deliver real power, and so the distribution cables need to be thicker, and the risk of power line protection devices tripping increases.

If you've ever worked with telephone equipment, on the line transformers you will see a maximum DC rating. That is because if there is DC on any of the windings, the hysteresis curve horizontal axis moves away from its symmetrical position, thus reducing the available linear AC swing, pushing the swing envelope toward saturation. If DC is expected on the windings, the air gap in the iron core is increased, leading to requiring a larger core to carry the kW, and hence larger windings and case. Exactly the same thing happens with power transformers.

I think it would help to stick to the original line of this query, which was the effect of EMI on RF noise level. Power factor only becomes an issue with respect to EMI when you expect the transformer to swing outside its almost linear region towards saturation.

73 de Brian, VK2GCE

On Saturday, 2 November 2019 3:33 AM, Richard contributed:

    A diode will cut the voltage. I think the bulb savers were 
varistors, voltage variable resistors. These do cut inrush 
current but that is not a problem with CF or LED lamps. The 
tungsten filament of incandescent lamps has a large positive 
temperature coefficient of resistance so the lamps have 
relatively low resistance when cold becoming less as they come up 
to operating temperature.
    What the Oz folk may be concerned with is power factor, 
American power companies are also. High power factor inductive 
loads make conventional watt-hour meters read low (i.e. you get 
the power cheap). Most power companies have banks of capacitors 
at their distribution stations to cut in to keep the power factor 
as close to unity as possible. Some power companies will give you 
a price break on the power if you have a capacitive load.
    BTW, I have been in a distribution plant yard when a bank of 
caps was switched in, it sounded like a cannon going off.