Huaming HWDK on-tank reactor-type vacuum LTC
The HWDK is intended to be used for transformer application with voltage regulation done on the low voltage terminal. These are typically 3-phase DY transformers for secondary substations with low voltages of 13 kV. However, the tap changer can be used for a variety of situations when up to 2000 A current capacity is required.
HWDK is Huaming’s external reactive-type vacuum LTC for 3-phase low voltage high current applications
The HWDK includes a bypass switch, a tap selector, and a change-over selector. Both selectors are mounted in a separate and completely isolated oil compartment fixed externally on one side of the transformer’s main tank. The tap changer is driven by an external motor drive mounted to the side.
For accuracy, all switching elements are driven through one main driving shaft connected to the motor drive unit.
To prevent possible contamination the tap changer’s main body and its operating spring mechanism have been located in separate compartments. This not only facilitates maintenance but also guarantees long-term clean oil and good insulation inside the compartment.
The change-over switch is fast driven by its own transmission shaft with synchronization achieved within 3 ms.
2.2 Vacuum technology with fault detection
Huaming opted for the vacuum interrupters (VI) technology for this design. The bypass switch benefits from Huaming field experience of vacuum LTC with more than 30,000 units in operation. Eaton VIs are therefore used as arcing contacts to extinguish arcs generated during LTC operation. This means the LTC is not subject to oil carbonization and therefore, an online oil-filter is not needed. This makes the operation nearly maintenance-free.
The HWDK is also fitted with a switching fault protective module to detect potential VI’s failure and lock the tap changer when critical conditions are detected. The protective module operates by monitoring the current flowing through the VI after a switch. Should the monitored current exceed a set value, the module immediately sends a stop command to prevent the motor drive from running and avoid significant failures.