inductive reactance

X=2¼fL

-- Ferme le Bush

I think the font used corrupted the Greek letter for 'pi' into '1/4'. The formula is two times pi times the frequency (in Hertz) times the inductance (in Henrys)

daestrom

Doesn't everybody use a Mac?

-- Ferme le Bush

As a matter of fact, no. Some of us use Solaris or other flavors of Berkley and SVR4 flavors of Unix, Windoze, while others use linux, BeOS, Amiga DOS, MS DOS, OS/2, NextStep, and Plan 9 on a variety of different hardware platforms.

Thanks for replies.

I measured voltage and current in a three-phase line choke with load connected.

Voltage across each coil of 3 phase line choke - 15V Current in each phase - 14A Line Voltage (phase to phase) - 365V Line voltage was lower at that time it remains usually between 380V to

400V Frequency - 50Hz

What is the actual inductance of choke based on measurement? The values written on 3 phase choke say 1.42mH, 15A

Do the actual and rates figures match with each other? thanks

Seems a bit off, but not too far.

1.2mH @ 50 Hz would be an inductive reactance of....

2*pi*f*L = 2*3.14*50*1.42e-3 = 0.45 ohms

With a 14A load through it, that should be a voltage drop of...

14A * 0.45 ohms = 6.3V

But you measured 15V. For a 15V drop across the coil, the impedance of the coil would need to be...

15V / 14A = 1.07 ohms.

For a pure inductor, that would be...

1.07 /(2*pi*50) = 3.4 mH

Of course a real-world coil/choke is actually a resistance and inductance in series, and those two impedances have to be added vectorally.

If we trust the 1.42mH of the label, and the measurements you took, then the total impedance is 1.07 ohms (see above) and the inductive reactance is 0.45 ohms (also, see above). Since Z^2 = R^2 + X^2 in a series RL circuit, we find R to be...

R=sqrt (1.07^2 - 0.45^2) = 0.97 ohms.

You might measure the resistance of one phase of the choke by turning off the power and disconnecting it to see how that measures up with this 'theoretical' value.

daestrom

>

Thanks Daestrom and other board members.

I will measure the DCR of coil and post it here.

The calculation of 6.3V drop confused me too So I thought may be there is a different method to calculate reactance or inductance in three phase. Just like in single phase we calculate VA rating as V * A but in three phase We do V * A * 1.732.

Doesn't this root(3) come in calculations in 3 phase inductors, somewhere ?

Regards

Not likely. A choke is in series with the load so what you have is likely 3 separate chokes, one for each phase. Your data does seem to indicate this. There should be a total of 6 terminals, 3 in and 3 out. It should be possible, with the choke disconnected from the supply, to determine the connection between terminals with a simple multimeter or continuity checker. In any case take as many measurements as possible between terminals (isolated from the system) to determine the connection.

The DCR of each coil is 0.41 Ohms.

thanks

I find that very difficult to believe. Drawing 14 amperes through .41 ohms is going to dissipate almost 80 watts.

It would explain some of the discrepancy in your inductance calculation, however.