It is known that power transformers, for example, oil-filled transformers, can be provided with so-called on-load tap changers for increasing their flexibility in the electrical energy supply grid, as a result of which the transformation ratio of the transformer can be matched within certain limits, for example, in a range of from 85% to 115% of the rated voltage. These on-load tap changes can be selector switches which are switched on load and which, depending on given boundary conditions, tap one of, for example, 24 taps of a supplementary winding, which can be connected electrically in series with a respective main transformer winding. In addition, a single winding can be provided, which has corresponding taps in its rear region, for example in the last 20% of its winding. The output of the on-load tap changer can act as the output of the series-connected main and supplementary windings. Such on-load tap changers can be involved and complex for example, to be capable of switching under load current and the specifications in terms of their insulation. In the case of use in oil-filled transformers, a certain degree of simplification is provided at least with respect to the insulation complexity, since the on-load tap changer can be arranged within the oil tank and the on-load tap changer can also be flooded with oil.
The controllability can also be used in so-called dry-type transformers. Dry-type transformers have a rated power in the range of from a few 100 kVA up to several 10 MVA given rated voltages of between 6 kV and 110 kV, for example. The rated power of the dry-type transformers can be below the rated power of oil-filled transformers. For example, dry-type transformers can use less maintenance in comparison with oil-filled transformers since no oil or oil tank is provided. However, dry-type transformers can have increased complexity with respect to the insulation of dry-type transformers. For example, this can also apply correspondingly to on-load tap changes with which dry-type transformers can be equipped.
On-load tap changer arrangements known from the oil-filled transformer sector may not be transferable, or only with a disproportionately degree of complexity, to dry-type transformers.
USPTO Backgrounds
USPTO Backgrounds