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#128241 - 12/02/02 09:54 PM Source Impedance
yu Offline
Junior Member

Registered: 12/03/02
Posts: 1
Loc: na
Hi, needs advice here. What is the different between Line and Source Impedance? A 3-phase x-ray machine is running at 200mA ~ 500mA instead of maximum of 800mA which i suspect is due to cable size. Requirement for X-ray Source impedance is 0.12 ohms. I got the readings on a report as this: RY-0.233, YB-0.239, BR-0.225. Can anybody explain why RY instead of R or Y or B?
tq.

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#128242 - 12/03/02 09:32 AM Re: Source Impedance
Bjarney Offline
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Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
About "...readings on a report as this: RY-0.233, YB-0.239, BR-0.225." What are the units for these numbers? How were these measured or determined?

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#128243 - 12/05/02 09:19 AM Re: Source Impedance
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
yu, if I understand correctly, the measured impedance is roughly double what is desired.

Components that most affect impedance are the circuit’s cable size and length, and serving transformer size {impedance.} Each would effect voltage drop on a circuit.

The only solutions I can imagine are 1.) increasing the size or cross-sectional area of the cables, [likely least expensive, but with a potentially limited improvement] 2.) shortening the circuit length [probably not practical] or 3.) installing a larger [lower-impedance/expensive] serving transformer. These three items are probably at least 90% of what effects source impedance on a branch circuit or feeder.

Tests to determine the change {or improvement} from cable replacement may be to carefully apply the instrument at the feeder level if the circuit of interest is indeed a branch circuit, and then at the serving transformer’s secondary terminals.

I hope that answers your question or confirms your suspicions.

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