Transformer Tap Changer Location - Primary or Secondary 3

[Dobber1978]

Just looking for some information on why tap changers would be spec'd on the primary or secondary of the transformer.

Scenario - 44kV/13.8kV - delta/wye - 15/20MVA - online tap changers

Primary side taps
- This is the less expensive option
- This is the more common option

Secondary side taps
- Was told tap changes when on the secondary are "smoother" but I can't find any literature on this

What other pros/cons of each are people aware of?

Many thanks!!
Cheers,

 

[RRaghunath]

"vacuum bottles are only good up to about 200BIL" - how sure are you about this, Dobber1978!
I have seen recently Vacuum bottles in OLTC for 132kV winding that is Delta connected and I expect the bottle to be with 650kV BIL.
The OLTC is from MR, Germany.

 

[Dobber1978]

@RRaghunath - I am not sure at all.

I had a conversation with one of the transformer suppliers regarding my situation and this is what I picked out of the conversation. It is possible the manufacturer didn't speak about any higher voltage as I am only dealing with 44kV on the HV side and I may have misunderstood when they indicated the max BIL as being more related to transformers at the voltage class I was looking at.

Cheers,

 

[bacon4life]

The Reinhausen model VR vacuum tap changer is available for operation at nominal voltages up to 420 kV. Although the overall device has a BIL of 1175 kV, I had assumed the vacuum bottle itself was typical medium voltage device with a much lower BIL. The bottle only interrupts a max step voltage of around 6 kV.
More on this tap changer is at

https://www.reinhausen.com/desktopdefault.aspx/tabid-1976/2891_read-8131/

 

[RRaghunath]

Thanks bacon4life for making that point. I too think so.

 

[prc]

The bottles used in these tap-changers are only MV class.Max 6kV 1300 Amp rating as per MR data sheet. 420 kV mentioned in data sheet is the equipment voltage ie line end voltage. The entire assembly can be insulated to any voltage.MR is making tap-changers up to 220 kV line end applications.

 

[prc]

A couple of additional points on OLTC:

1)MR once developed a model for using at 400 kV line end. But transformer designers refused to bite it, considering the insurmountable problems of accommodating the tap lead bunch all at 400 KV to earth potential.

2)In last two decades, MR developed two models for (a) A 108 tap OLTC for varying primary voltage ( max 220 kV ) from 10% to 100 %. These are used in auto-transformers feeding rectifier transformer in aluminium smelters (b)low cost simple OLTC for distribution transformers, voltage up to 33 kV. The demand for this came with renewable energy feed in to grid at these distribution voltages.

3) Model as in (a) above was available both in resistor type oil break or vacuum type (b) only in vacuum type.