Phase rotation meter 4

[bdf5526]

Hi all, I need to make a 3phase rotation meter (to measure rotation for 400V,50hz,incoming supply from diesel) since we don't have one (we will get one soon). The test equipments which we suppost to receive are missing and its a long story. To check and confirm the incoming phase rotation is a requirement for the client.

I have 1 capacitor 3uF (+-5%)/400Vac/40-60-Hz, 2 bulbs (filamen type)220volt, 50w. All these are cnnected in star with capacitor in L3, bulb no.2 in L2 and bulb no.1 in L1.

First question, what is the capative reactance at 50Hz, since the power frequency available is 50Hz? I am confused with the rating 40-60hz.

Say the cap. is same 3uF,so the -jXc is 1/(2*pi*50*3uF) = 1.06kohm. Each bulp is 220v*220v/50w = 0.968kohm.

Second question, the cap. reactance and bulp ohmic value are bit different is this acceptable?

3rd question, two bulps will have 400v accross their terminal and this should be allrite, correct?

4th question, Neutral Voltage formula is =Ya*Van+Yb*Vbn+Yc*Vcn/Ya+Yb+Yc

Guys I need your input before I make one. I shall draw and attach a file in the next post.

Thanks in advance.

 

[electricpete]

Glad it worked.

I liked Gunnar's idea to present the Vn in the complex plane. I added it to my spreadsheet attached except changed to keep the parameter unitless (w*R*C) so it is more general. I also changed the voltage ratio plot to make the horizontal axis (w*R*C) a log scale.

Some surprising (but unimportant from practical standpoint) symmetries are obvious looking at the graphical solutions:
1 – The voltage ratio (on log scale) is symmetric about the vertical line w*R*C = 1. So a factor of 2 above 1 or a factor of 2 below 1 gives the same ratio (even though different voltages).
2 – The trajectory of Vn in the complex plane is a semi-circle. I understand the starting and endpoints and the qualtitative change... just surprised that it came out exactly as a semi-cirlce.

I don't see any obvious physical reason for these symmetries or any math reason (i.e. don't see any equation of a circle buried in those equations). It's not really important – just a curioisity.

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[trosepe]

It may be easier to just buy the phase rotation meter. Knopp model K6 operates 25 to 480 volts and 50 to 400 HZ. It is very simple and reliable unit; looks like a hockey puck.