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| {{Menu_Characteristics_of_particular_sources_and_loads}}
| | #REDIRECT[[Protection of LV/LV transformers]] |
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| At the moment of energizing a transformer, high values of transient current (which includes a significant DC component) occur, and must be taken into account when considering protection schemes (see '''Fig. N31''').
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| <br>[[Image:FigN31.jpg|left]]<br><br><br><br><br><br><br><br><br><br><br><br><br><br>
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| '''''Fig N31:''' Transformer-energizing inrush current''
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| The magnitude of the current peak depends on:
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| *The value of voltage at the instant of energization
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| *The magnitude and polarity of the residual flux existing in the core of the transformer
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| *Characteristics of the load connected to the transformer
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| The first current peak can reach a value equal to 10 to 15 times the full-load r.m.s. current, but for small transformers (< 50 kVA) may reach values of 20 to 25 times the nominal full-load current. This transient current decreases rapidly, with a time constant θ of the order of several ms to severals tens of ms.
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