Ken,
My intention was to estimate the charging current going into some
capacitors for a motor control board; therefore, my questions was
really about getting a design parameter that we could use. The
charging current can be high and can damage relay contacts on the
motor control board. My colleagues suspect that the US power line
impedance is lower, on average, than that of the Euro power lines.
Consequently, we'd have to make provisions in the US design vs. the
Euro design of this control board.
______________________________ Reply Separator
_________________________________
Subject: Re: 60 Hz Power Line Impedance
Author: "Ken Javor" <[email protected]> at Internet
Date: 11/15/1999 1:14 PM
Mr. Lacey's final comment is illustrative of what has been my point of
view. Why worry about what a specific source impedance is at the line
frequency (50/60/400 Hz)? Rather, measure current
(steady-state/harmonics/inrush/whatever) while verifying that resultant
bus potential (Volts) is negligibly small. In so doing, you verify the
maximum current the EUT will generate under any circumstance. Comments?
----------
>From: "Lacey,Scott" <[email protected]>
>To: "'[email protected]'"
<[email protected]>
>Cc: "'[email protected]'" <[email protected]>
>Subject: RE: 60 Hz Power Line Impedance
>Date: Mon, Nov 15, 1999, 5:40 AM
>
>
> 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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