Transition impedance must be connected in series in the on-load tap-changer circuit
The On-Load Tap-Changer (OLTC) is a key component in power transformers used to regulate output voltage. You can vividly think of it as the transformer's "precision intelligent gearbox".
Its core function is to adjust the transformer's voltage ratio by changing the number of turns in the high-voltage winding (i.e., switching tap positions) without interrupting the load current, thereby achieving stable regulation of the output voltage. This is crucial for ensuring the quality of grid voltage and enabling power regulation in UHV DC transmission.
⚙️ Working Principle and Core Structure
The operation of an on-load tap-changer must satisfy two seemingly contradictory conditions: ensuring current continuity (no power interruption) and preventing short-circuiting between taps.
Basic Principle: During the switching process, the switch momentarily connects two taps simultaneously (bridging). To ensure load current continuity and prevent a huge circulating short-circuit current between the two taps, a transition impedance (typically a resistor or reactor) must be connected in series in the circuit to limit the current.
Core Structure:
Switching Switch: Responsible for carrying and interrupting the load current, operates very quickly, usually in a sealed oil chamber or vacuum arc-extinguishing chamber.
Tap Selector: Responsible for pre-selecting the next tap position to be switched, but does not carry the arc during switching.
Operating Mechanism: Provides power and controls the switching sequence of the switch.
