Multiple Neutral Positions on Power Transformer LTCs

[111R]

I've heard of power transformers with multiple neutrals, but I don't completely understand what is meant by this.

When a transformer LTC is moved and remains in neutral after multiple movements, what is occurring internally? Is the second movement the switching of the reversing switch?

I always assumed that from 16L to 16R, a tapchanger moves in the same rotational direction, but based on a response to another question I asked, it seems like tapchangers reverse rotational direction once they hit neutral. Is this related to the multiple neutral positions?

Thank you.

 

[prc]

The triple neutral positions in tap changers is not a universal situation. This comes in tap changers with reversing switches or coarse-fine arrangement. Neutral position means mid point of the tap range. This multiple neutral positions is used by manufacturers to use the same model of tap changer for various tap ranges - say 15 to 19 tap positions or 33-39 positions or to save the electrical length of tap winding. At these neutral positions tap selector do move as usual, but the net voltage remains the same at transformer terminals. Usually with the in-tank model tap changers, run through ( or dummy) neutral positions will come only when (no of tap positions-1)/2 is an even number. So no dummy neutral positions with 19 tap OLTC,but with 17 tap OLTC two dummy neutral positions will result. You can understand this better with connection diagrams and other details ( available from tap changer manufacturers ) or refer to the book " On -Load Tap changers for Power Transformers" By Axel Kramer, published in 2000 by MR,Germany, a tap-changer manufacturer.