Nowadays, due to the national advocacy of environmental protection, energy conservation, and emission reduction, the first priority is the transformation of industrial and rural power grids in various regions. The aim is to remeasure, monitor, and protect the power grid to achieve safety, reliability, economy, and efficiency, which is what is now known as the smart grid.
Current transformers can be divided into high-voltage and low-voltage types, mainly distinguished by the highest voltage of the equipment. Generally, 10kV and above is considered high-voltage, 10kV is medium-voltage, and 1kV and below is low-voltage. SCTs (Self-Changing Transformers) are primarily used in low-voltage applications because they must be switched on and off, which makes effective sealing and insulation impossible (see Figure 1). Therefore, they are generally used in low-voltage distribution cabinets or low-voltage overhead lines. However, there are exceptions. If the primary current carrier is a cable structure with sufficient insulation, then SCTs can also be used at 10kV (see Figure 2).
Figure 1 shows the SCT that our company provided to Jiangsu Provincial Power Grid. The primary current structure is a busbar, model SCT26, which has a 20*60 hole and is suitable for a 60mm wide busbar. As shown in the figure, since the opening and closing part of this SCT is very close to the primary exposed busbar, there is no effective isolation or sufficient safety distance. Therefore, there is no effective insulation. So, SCTs installed on busbars can only be used for low voltage.
