Working Principle of Drum (Tube) Type Tap Changers
Release date:
2025-12-31
Tap changers of the drum type adjust the transformer’s output voltage by switching between tap connections on the winding. Their core principle is to change the tap position while the transformer remains de‑energized, thereby altering the turns ratio and stabilizing the grid voltage.
Tap changers of the drum type adjust the transformer’s output voltage by switching between tap connections on the windings. Their core principle is to change the tap position while the transformer remains de‑energized, thereby altering the turns ratio and stabilizing the grid voltage. The specific operating procedure is as follows:
1. Principle of No-Excitation Operation
Switching process: The operating mechanism is mounted on the side or bottom of the transformer oil tank and effects tap changes either directly or via interlocking. The moving contacts and stationary contacts are arranged in phase‑separated, horizontally spaced configurations, with all contacts of each phase lying in the same vertical plane.
Voltage regulation: By adjusting the turns ratio of the windings (V1/V2 = N1/N2), it accommodates grid fluctuations and load demands, thereby preventing overvoltage or undervoltage.
2. Structural Features
Drum‑shaped design: The stationary contact is cylindrical, while the moving contact is annular; a leaf spring is housed inside, allowing the moving contact to offset relative to the central axis during switching, with the contact pressure determined by the magnitude of this displacement.
Application scenarios: Drum-type no-excitation tap changers are typically used for voltage regulation at the mid-point of windings, with voltage ratings ranging from 35 to 220 kV and current ratings from 300 to 1000 A.
3. Operating Method
No-excitation operation: Adjusts the tap changer without applying voltage to the transformer, thereby changing the voltage ratio.
On-load operation: Operations are performed under transformer excitation or load conditions to achieve voltage regulation.
Based on the aforementioned principle, the drum-type tap changer ensures the stable operation of transformers under various operating conditions and is an indispensable voltage-regulating device in power systems.
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