I just ran the math on this. Assuming that you can only measure voltage magnitude (not phase), you need to use a capacitor and an inductor as the loads. Assume that the power source is a voltage with a series resistance R and series reactance jX (where X can be positive or negative). If you do the voltage divider magnitude calculations for each load, you will get equations in R², X², X, and a constant. In each equation, the coefficient of R² and X² will be the same. One equation can be multiplied by a constant to make the coefficients for R² and X² the same in both equation. When the equations are subtracted, the difference is an equation in X and a constant, so the value of X is found. This value of X can be substituted back into either equation to solve for R. If a resistor is used as a load, the voltage divider magnitude calculation yields an equation in R², X², R, and a constant. It is not possible to combine this with one of the other voltage divider magnitude equations and come up with an equation with a single unknown variable. Don Borowski Schweitzer Engineering Labs Pullman, WA John Woodgate <j...@jmwa.demon.co.uk> on 09/19/2002 08:55:53 AM Please respond to John Woodgate <j...@jmwa.demon.co.uk> To: emc-p...@majordomo.ieee.org cc: (bcc: Don Borowski/SEL) Subject: Re: Measuring AC Line Impedance
I read in !emc-pstc that Spencer, David H <david.spen...@usa.xerox.com> wrote (in <052106A55179D611B34300096BB02E3F8B1D@USAMCMS4>) about 'Measuring AC Line Impedance' on Thu, 19 Sep 2002: >Is anyone familiar with a method to measure and calculate those values. The >generic values I have for short circuit condition (which include 4 wires in >a magnetic conduit) come out higher than my measured values, and those do >not include the motor generator source. Put a large capacitor (mains voltage rated) across the mains and measure the voltage change; it may actually increase. You need about 50 uF to get a decent change on 120 V 60 Hz mains. With that result and the one with the resistive load, you can calculate the source impedance as an R and L in series. I'd be interested to learn the result. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. Thank you.
