Three Phase Power Phase Loss Detection

Discussion in 'General Electronics Chat' started by Doug16214, Jul 10, 2008.

1. Doug16214 Thread Starter New Member

Jul 10, 2008
1
0
Greetings,
I have many contacts with Electricians out in the field that argue the point that they CAN measure the presence of all three phases in a three phase power system with a voltmeter or wiggins.

I contend that due to the configuration of the utility's transformer, it is impossible to measure the presence of all three with anything short of an oscilloscope or a special meter.

Thanks

Doug

2. recca02 Senior Member

Apr 2, 2007
1,211
1
Are we talking about fault detection? At what point? After generator transformer?

3. SgtWookie Expert

Jul 17, 2007
22,201
1,809
If the secondary is delta-wound, you will indeed have a tough time with just a meter.
If the secondary is wye-wound, it's easy. Disconnect the load at the service panel, and measure each phase to neutral.

4. theamber AAC Fanatic!

Jun 13, 2008
321
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Why do you say they can't? Yes they can if they know which configuration they are, for example here I copy this two from my Ugly's to you:
120/240 Delta high leg
A(black)to B(orange)=240
B(orange) to C(Red)=240 >High leg.
Neutral(white) to A(black)=120
High leg to Neutral=208

120/208 4 wire system (WYE Connected)
A(Black) to B(Red)=208
B(Red) to C(Blue)=208
Neutral(White) to B (red) or to C(blue)=120
REd to White=120

You need to buy the Ugly's Electrical References booklet.
But if you are talking about the phase sequence they cannot with the voltmenter but they can use a circuit with a capacitor an two light bulbs in Y of equal filament resistances and wattage they can see the intensities of the lamps. The cap. has to be sized to have the same reactance at system frequency(you can calculate with the formula) the cap. introduce a phase shift of 90 which is greater than 0 but less than 120 this will skew the values between the lamps. All this is in the book here.

Last edited: Jul 10, 2008