HV/MV/LV Transformer Protection Schemes
Post by: Omega delta electric
V/LV transformers
The protection of these units should include overcurrent protectionfor both the MV and LV windings, plus devices such as overpressure protection (e.g. Buchholz surge), and thermal protection, as indicated in Figure 1 below. Typical ratios for inter- busbar MV/LV transformers at substations are33/11, 34.5/13.2and13.2/4.16 kV.
Figure 1 – Protection scheme for MV/LV transformer
HV/MV/LV transformers and autotransformersIn addition to the protection listed for the MV/LV transformers, the protection for transformers in this group should includeoverall differential protection, which is essential because of its reliability and high speed of operation. In this case, shown in Figure 1, since the transformer has three windings, a three terminal type ofdifferential protectionis required.The diagram also includes the differential busbar protection, which is usually installed on large transformers connected to HV busbars. As the transformer has an LV winding, overcurrent protection for this winding has been included as well.Typical ratios for HV/MV transformers are:132/33, 145/ 11, 132/11, 115/34.5 and 115/13.2 kV.
Figure 2 – Protection schematic for an HV/MV/LV
transformerIt is common to use autotransformers where large powers are involved and the voltage ratio isaround 2:1. Typical ratios for autotransformers are275/132 kVand230/115 kV.
The protection schemes for autotransformers are very similar to those for HV/MV/LV transformers since autotransformers can be treated asthree winding units for protection purposes.
The protection for this type of transformer is essentially the same as that quoted in the previous paragraph, taking into account the modifications to the overcurrent relay connections(see Figure 2).
V/LV transformers
The protection of these units should include overcurrent protectionfor both the MV and LV windings, plus devices such as overpressure protection (e.g. Buchholz surge), and thermal protection, as indicated in Figure 1 below. Typical ratios for inter- busbar MV/LV transformers at substations are33/11, 34.5/13.2and13.2/4.16 kV.
Figure 1 – Protection scheme for MV/LV transformer
HV/MV/LV transformers and autotransformersIn addition to the protection listed for the MV/LV transformers, the protection for transformers in this group should includeoverall differential protection, which is essential because of its reliability and high speed of operation. In this case, shown in Figure 1, since the transformer has three windings, a three terminal type ofdifferential protectionis required.The diagram also includes the differential busbar protection, which is usually installed on large transformers connected to HV busbars. As the transformer has an LV winding, overcurrent protection for this winding has been included as well.Typical ratios for HV/MV transformers are:132/33, 145/ 11, 132/11, 115/34.5 and 115/13.2 kV.
Figure 2 – Protection schematic for an HV/MV/LV
transformerIt is common to use autotransformers where large powers are involved and the voltage ratio isaround 2:1. Typical ratios for autotransformers are275/132 kVand230/115 kV.
The protection schemes for autotransformers are very similar to those for HV/MV/LV transformers since autotransformers can be treated asthree winding units for protection purposes.
The protection for this type of transformer is essentially the same as that quoted in the previous paragraph, taking into account the modifications to the overcurrent relay connections(see Figure 2).
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