Tap (transformer)
The tap changer has the task to compensate for the change in load occurring during voltage fluctuations in power transformers by the gear ratio is changed to the high voltage side. The power control for parallel connection of large power transformers is realized over him. For this purpose the corresponding windings provided with taps.
Step switch are divided into load tap and diverter.
OLTC
OLTC are divided into load selector and load switches with selection.
The latter consist of a selection (if a coarse and fine selector ), a diverter switch and of resistors that limit the short-circuit current occurring when switching between stages. The selection forms a unit with the active part of the transformer, it is rigidly connected to the taps of the high-voltage winding. The preselector switched current-free. The unity of the diverter switch and resistors ( diverter switch insert ) is due to the oil pollution from the switching arc in a separate oil container, which in turn is integrated into the transformer tank. The diverter switch insert is of the same oil (usually a mineral oil) is filled as the boiler, but is not in communication with the oil boiler.
The tap changer is relatively error-prone due to the relatively frequent switching operations and the high proportion of mechanically loaded and electrically very highly stressed components, which requires a thorough operation during maintenance. A weak point of the system described is in the not -to-reach selection. This can therefore only be serviced at a factory overhaul, which requires a life-long service life.
The trend in the load switches goes to vacuum switches. According to the manufacturer, this increases the maintenance intervals of seven to 25 years.
Tap- monitoring systems provide by current summation and torque monitoring a permanent condition diagnosis.
Diverter
Diverter fulfill in principle the same tasks as load tap changer, but can be adjusted only tension. Changers are typically carried out with only a few steps and manually operated. They are virtually maintenance free.