Phase Shifting Transformer Questions 3

[ThePunisher]

HI all,

I would like to obtain valuable inputs to my question and hope I am asking a generic one for my understanding.

A three winding transformer have primary delta, secondary delta and tertiary wye-solidly grounded connected. Primary and secondary winding terminals are connected to separate downstream LV switchboard supplying large rectifier circuits.

The three winding application with this secondary and tertiary winding configuration is expected to create "phase shifting" effects for harmonic mitigation. My understanding and question is as below:

1) I am assuming that the secondary & tertiary phase shifting mitigation effect will only be seen at the primary inputs. The secondary and tertiary harmonic flows from non-linear loads will not be mitigated and hence, the K-factor of the transformer will be calculated based on the total magnitude of secondary and tertiary harmonic flows. Is my assumption correct? The secondary and tertiary are both rated for 480 VAC

2) The total current will be the load plus harmonic currents. Can we actually size the cables to carry both instead of adding expensive Active Harmonic Filters if the primary is within IEEE Std. 519 and the voltage %THD is well within the 1000 V insulation that was specified?

Thank you gentlemen for your opinions and comments.

 

[davidbeach]

Let’s call the terminals D, d, and y. D and d should be in phase with each other and y should lag both by 30 degrees.

Everything passes through from d to D. The fifth harmonic current on y is shifted 150 degrees (30 x 5) further in the lagging direction and arrives at D 180 degrees out from the current from d. The seventh harmonic current on y is shifted 210 degrees (30 x -5) in the leading direction and arrives a D 180 degrees out from the current from d.

D thus sees the combined load from d and y but only mismatch amounts of the 5th and 7th harmonic currents.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

large rectifier circuits.

This sounds like a 12 pulse rectifier feed to reduce DC ripple.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

. . . and I thought this question would be about quadrature boosters! Just for future clarity, please note that a phase shifting transformer is an actual power system device, whereas transformer phase shift is an action that occurs within transformers . . . maybe.

And now, back to our thread.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

I had the same thought cr.
I wouldn't classify this as a "shift".
While wye and delta voltages are separated by 30 degrees, they are not shifted.
This circuit uses normally occurring, unshifted, voltage angles to reduce DC ripple in a rectifier output.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!