Electronic – Change taps on primary or secondary side of transformer

transformer

I have a 5500/380V Dyn11 transformer, with possible tap settings of 0.95, 0.975, 1.00, 1.025 and 1.05 on both primary and secondary side.

Due to high loading, I want to change the tap settings to either 0.975/1.00, or 1.00/1.025. However, I'm not sure on what side of the transformer I should change the setting.

My intuition tells me that it makes more sense to select the primary side, but I'm not certain.

  1. One reason for changing the setting on the primary side is: The current is much higher on the secondary side, thus increasing the number of windings there will cause higher losses.
  2. Another one: More windings might lead to saturation (I would however think that the transformer was designed so that this won't be a problem).

Does the transformer type play a role? Does it matter if the transformer is Dy, Yd, Dd, Yy etc? How will it affect the impedance?

Will there be any side-effects of selecting one or the other? Are there any reasons for choosing to change the settings on the secondary side?

Thanks!

Best Answer

In Australia, at least, the tap-changer is always on the HV winding. I don't recall ever seeing a transformer with the tap-changer on the LV winding.

I believe this is for economic reasons (it's cheaper or easier to build it this way). However I haven't looked this up so treat the previous statement with a grain of salt. The J&P Transformer Book, originally my Martin Heathcote, is all about the details of design, construction, and maintenance of power transformers and could probably tell you more.

To give a more concrete example, here is an example of a transformer nameplate showing the possible tap positions. (Serial numbers have been obscured to protect the innocent.)

Note that the nominal voltage ratio is 11,000 / 440 V and five taps of 2.5% are provided, two taps up and two taps down.

enter image description here

You say your transformer has both HV tapchanger and LV tapchanger - is this a real, physical transformer, or a theoretical transformer? Having both HV and LV tap changer would be an extra expense and I am not sure if there would be any advantage to providing both.

A quick skim of J&P Transformer Book (12e) ยง2.4 mentions that HV tap-changers imply operation at "constant flux density", while LV tap-changers imply operation at "variable flux density".

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