The tap change operation consist of 3 steps
The next tap is preselected by the tap selector at no load (no current circulation).
The arcing switch (on load tap changer) transfer the load current from the tap in operation to the
preselected tap trough following operations
Switch TS2 close, current from tap selector 1 circulates trough TS1. TS2 connect the tap selector
2 to the output trough transition resistor.
Switch TS1 open, current from tap selector 2 circulates trough TS2 by the transition resistor
Switch TS3 close, the current from tap selector 2 goes to the put without the transition resistor.
Switch TS2 open, The transition resistor is eliminated from the circuit.
The tap selector 1 is release to move to the next tap.
The Total duration of a transition is of some tens of milliseconds.
15.2.2 Dynamic resistance test
Dynamic resistance test consist in recording currents and voltages during the tap position
transition.
A standard current curve while measuring dynamic resistance would show following shape.
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