Determining the accuracy class and the required number of units per circuit for current transformers involves more than just selecting the accuracy class; numerous other parameters must also be carefully considered.
When selecting transformation ratios, it is generally preferable to maintain consistency across secondary windings. However, in certain situations, employing different ratios can yield significant benefits. For instance, using a uniform ratio might necessitate two sets of current transformers-increasing investment costs and potentially creating installation issues due to space constraints. Conversely, utilizing different ratios allows a single set of current transformers to meet the combined requirements for measurement, revenue metering, and protection. Naturally, the disparity between these ratios should not be excessive; typically, the ratio difference should not exceed a factor of four.
While prioritizing accuracy and safety, one should aim to keep the transformation ratios of the various secondary windings within a single current transformer consistent. However, depending on specific operational needs-such as cases involving excessively high short-circuit currents-adopting different ratios may be considered, provided the difference remains within a reasonable range.
