Pop Quiz:

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rattus

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Consider a black box with terminals 1, 2, 3, 4, and C brought out. I am told that ?C? is the common terminal and may be floating or may be grounded. I am asked to fully describe the alternating voltages on pins 1-4.

With a 4 channel scope referenced to ?C?, I see four sinusoids, 208Vrms, 25hz and spaced ? cycle apart, and with a sequence of 1, 2, 3, 4.

Now if I assign 0 degrees to V1, what are the phase angles of V2, V3, and V4?
 
Once:

Once:

HighWirey said:
Have you touched that B+ one too many times?
I just assembled my Heathkit one channel scope . . .
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One time, and that was too many.

You can do it with one channel if it has an external triggered sweep.
 
I can't handle a pop quiz this early in the morning. Have you got a coffee quiz instead? :rolleyes: :)
 
I was shamed into replying by a PM from the OP. So here goes.

Owing to the circumstances of being "pressured" into participation, I do not promise that I will give the answer that I actually think is true.

wasasparky said:
270, 180, 90
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I disagree. :mad: It's -90, -180, and -270! :wink: :D
 
I am not quite clear on what 'a sequence of 1,2,3,4' means. I presume that it means that V1 peaks, and then V2 peaks 1/4 cycle later, then V3 and then V4, and will answer based on this.

My off the cuff answer is to agree with Charlie, V1 has a phase of 0, V2 has a phase of -90, V3 has -180, and V4 has -270. (Or, equivalently, 270, 180, and 90 degrees wasparky!)

First I write an equation for V1:
V1-C = 208 * root(2) * sin(2 * pi * 25 * t + P1) where P1=0
Next I write an equation for V2:
V2-C = 208 * root(2) * sin(2 * pi * 25 * t + P2)
for V2-C to reach its peak _after_ V1, then P2 must _delay_ the peak. We are told that there is 1/4 cycle spacing, and so that makes P2 either -pi/2 or 3pi/2...-90 or 270 in degrees :)

-Jon
 
Backwards:

Backwards:

WDeanN said:
90, 180, 270.

A full cycle is 360 degrees. The frequency doesn't matter.
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Numbers are right, but signs are wrong, should be -90, -180, and -270 to obtain the sequence 1, 2, 3, 4.
 
Both are right:

Both are right:

charlie b said:
I was shamed into replying by a PM from the OP. So here goes.

Owing to the circumstances of being "pressured" into participation, I do not promise that I will give the answer that I actually think is true.


I disagree. :mad: It's -90, -180, and -270! :wink: :D
Click to expand...

Both are correct, although I prefer the negative signs.
 
Right again:

Right again:

winnie said:
I am not quite clear on what 'a sequence of 1,2,3,4' means. I presume that it means that V1 peaks, and then V2 peaks 1/4 cycle later, then V3 and then V4, and will answer based on this.

My off the cuff answer is to agree with Charlie, V1 has a phase of 0, V2 has a phase of -90, V3 has -180, and V4 has -270. (Or, equivalently, 270, 180, and 90 degrees wasparky!)

First I write an equation for V1:
V1-C = 208 * root(2) * sin(2 * pi * 25 * t + P1) where P1=0
Next I write an equation for V2:
V2-C = 208 * root(2) * sin(2 * pi * 25 * t + P2)
for V2-C to reach its peak _after_ V1, then P2 must _delay_ the peak. We are told that there is 1/4 cycle spacing, and so that makes P2 either -pi/2 or 3pi/2...-90 or 270 in degrees :)

-Jon
Click to expand...

Winnie is right too, although I prefer to write the equations as phasors.
 
Signs are wrong:

Signs are wrong:

ronaldrc said:
I agree with them being 0,90,180,270 and all are 90 degrees apart.

I hope that C ain't center tapped. :D
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Phase sequence is wrong because signs are wrong.
 
Opened the black box!

Opened the black box!

Opened the black box and found a 4-phase star which I have only seen in books. Two CT transformers fed by two generators and with the CTs connected.

Now does this fact change any phase angles?
 
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