David,
The line impedance will vary considerably with location and type of
distribution transformer. The impedance of the secondary will relate to the
primary (power utility) impedance as the square of the turns ratio, plus
line drops. Your best bet would be to start with inquiries to the power
companies and the transformer manufacturers.
As to the impedance of a specific power line, the usual method of
measurement is to connect a power line qualifier (consisting mainly of a
capacitor of known value) to the output of a device which switches at ninety
degrees phase angle and measure the inrush current. KeyTek sells a line
qualifier for use with their EMC Pro
unit. We bought one for power interruption testing, and are gradually having
options added. They offer options for surge, EFT, etc.
Equipment should always be designed to work over a wide range of line
impedance. I once measured 300 amps inrush current at the company facility,
and 1200 amps at the power supply vendor's test bench, for the same power
supply!
Scott Lacey
-----Original Message-----
From: [email protected]
[SMTP:[email protected]]
Sent: Friday, November 12, 1999 2:32 PM
To: [email protected]
Subject: 60 Hz Power Line Impedance
Fellow Networkers;
Does there exist information about the impedance (at 60 Hz) of
typical
power line networks here in the US?
In Europe, I know they use a specified reference impedance (at
50 Hz)
for flicker testing, which is (0.24 + j0.15) Ohm for line and
(0.16 +
j0.10) Ohms. This represents, I understand, the European
public
network impedance as seen at the point of "common coupling"
(i.e.,
connection to the homes service entrance).
David Tarnowski
Whirlpool Corporation
Global Laundry Controls
St. Joseph, MI
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