Electrical Mains Impedance


#1

Hi, Having seen mains impedance mention a fair few times, can it be improved?
People say a power plant will improve this, but if the mains feeding the PP is poor (impedance) how will it improve.
Here in the Uk my mains is a TNC-S (PME) supply and the max permitted Ze is 0.35 ohms at the incoming. Invairably this can go up according to the circuits taken off. How ever after measuring the loop impedance at the outlet for the hifi it measured 0.04ohms.
So how low will the PP take the impedance and how will it improve things.
Simon


#2

The impedance out of a Power Plant is lower than from the wall because the PP has substantial internal storage (capacitors). The lower impedance is only available for brief periods to handle music peaks as the Power Plant cannot provide more power than it can draw out of the wall for longer periods.


#3

It can improve and rather dramatically with a Power Plant. This is because the Power Plant has the capability to store massive amounts of energy and to draw what current it requires to keep the output voltage steady. So the test of output impedance is simple. We add a heavy load to the 120 volt (or whatever your country’s voltage is) and see if the voltage drops. So, imagine we put a 10 amp load onto your power line. The voltage drops on the line, perhaps as much as 4 to 5 volts because the line and all its wiring from the power pole through your home to the wall receptacle has impedance/resistance. Now. Try that same experiment on a Power Plant. There you’ll get no more than 1/10th of a volt drop because the Power Plant is able to compensate. Thus, far lower output impedance.

Hope that helps your understanding.


#4

Almost right, Steven. The Power Plant does have an enormous amount of storage available for peak correction. But the lowered impedance is constant. It draws more and more current out of the wall to lower impedance and maintain a steady voltage.


#5

My badly expressed point was that over an extended period the PP cannot put out more than it can draw from the wall so at some point in theory the wall’s impedance would become a limiting factor. For practical purposes that may not be a serious limitation but otherwise I think you’d have a problem with the second law of thermodynamics.