Content
Design principles .................................................................................................................. 6
On-load tap-changer (OLTC) ........................................................................................... 6
Diverter switches ............................................................................................................ 8
Diverter switch housing and top section ......................................................................... 10
Painting .......................................................................................................................... 11
Operating mechanism ..................................................................................................... 11
Transition resistors .......................................................................................................... 11
Special applications, load conditions, and environments ................................................. 11
Insulating liquids.............................................................................................................. 11
Special designs ............................................................................................................... 11
Motor-drive mechanism .................................................................................................. 11
Accessories .................................................................................................................... 11
Tap-changer principles of operation ...................................................................................... 12
Switching sequence, VUCG ............................................................................................ 12
Switching sequence, VUCL ............................................................................................. 14
Type of regulation ............................................................................................................ 16
Linear switching (type L) ........................................................................................... 16
Change-over selector for plus/minus switching (type R) ............................................. 16
Change-over selector for coarse/fine switching (type D) ........................................... 16
Type of connection .......................................................................................................... 17
Three-phase neutral point (N) .................................................................................... 17
Single-phase (E) ........................................................................................................ 17
Three-phase delta (B) ................................................................................................ 17
Three-phase fully insulated, delta (T) .......................................................................... 17
Three-phase fully insulated, auto transformer (T) ........................................................ 17
Tap-changer characteristics and technical data .................................................................... 18
Type designation ............................................................................................................. 18
Type of tap-changer .................................................................................................. 18
Type of regulation ...................................................................................................... 18
Type of connection .................................................................................................... 18
Impulse withstand voltage to earth ............................................................................ 18
Maximum rated through-current ................................................................................ 18
Tap selector size ........................................................................................................ 18
Tap selector shielding ................................................................................................ 18
Diverter switches ............................................................................................................ 19
Tap selectors .................................................................................................................. 19
Possible combinations of diverter switches and tap selectors .................................... 19
Maximum number of positions ........................................................................................ 19
Enforced current splitting ................................................................................................ 19
During operation ....................................................................................................... 19
Rated phase step voltage ............................................................................................... 20
Coarse fine regulation leakage inductance switching ................................................. 21
Contact life ..................................................................................................................... 21
Standards and testing ..................................................................................................... 21
Rating plate .................................................................................................................... 21
Insulation levels ............................................................................................................... 22
