Oil insulated 3-phase transformers with Petersén coil

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Background

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To minimize the influence of the climate on the power system, a comprehensive undergrounding of the power grid is ongoing where cables are placed in the ground. An undergrounded cable is not that sensitive to weather conditions but introduces a much higher capacitance in the power system. Especially when an earth fault occurs, this can introduce much higher earth fault currents and higher damages for the rest of equipments at the feeding point. Short-circuit currents flowing through earth can induce impermissible voltages in neighbouring metallic pipelines, communication and power circuits.

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A compensation of these earth fault currents can easily be done by placing a so called Petersén coil between the neutral of the transformer and the ground on transformers distributed along the network. 

The resonance circuit created between the capacitance of the cable to earth and the inductance of the coil  will then reduce the earth-fault current.

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Our products

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With our patented core technology, the three windings operate under identical conditions and the grid perceives the three phases as symmetrical. This makes them easy to compensate with a traditional coil, giving them superior performance.

Our vector group ZNzn suppresses the need of extra delta compensation winding. The amount of material and the weight is therefore reduced compared to competitors.  We place the Petersén coil under our triangular shaped transformer (see picture to the right) in order to reduce the size of the product.

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We manufacture Petersén coils for 10A compensation in 11kV system and 15 A in 22kV system.

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We have the same design and characteristics of the transformer as in our standard oil insulated product but have ZNzn as vector group. The advantage of this design is that the neutral of the transformer remains stable even with unbalanced load on the low voltage side. The Petersén coil is then only active for earth fault on the high voltage side.

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