Thanks to RODALCO
for these pics and information:
The TCOL tapchanger (or Tap Changer On Load) is commonly used in the local POCO 33/ 66 kV substations for voltage regulation for the feeders which supply the end consumers.
In NZ it's mostly 11 or 22 kV feeders, in other countries similar systems will be used.
Atkinson sub. T2 TCOL box open, above small grey box is blank cap for manual crank handle on left.The actual load bearing contacts and resistors are in the grey tank underneath the header tank. The vertical shaft is the drive to the latter. This one is an ASEA 10000 kVA transformer:
Master / Follower control contacts drum. close up. Our POCO subs have 17 Tap positions:
TCOL of Ferranti 12.5 MVA transformer, the control contact drums are fully submerged in oil:
It's about 3 metres from crank to 33 kV bus:
Crank key hole:
Transformer nameplate data: