What is current transformer ratio？

What is current transformer ratio？

The current transformer ratio represents the ratio of primary to secondary current, for example, 500/5, 250/5, or 100/5. A ratio of 500/5 indicates that when the primary current reaches 500A, the secondary current is 5A.

Standard primary-side rated current ratios include 20, 30, 40, 50, 75, 100, 150, and 2×a/C, with secondary-side rated currents typically being 1A or 5A. The notation 2×a/C signifies a dual-ratio transformer achievable through series (a/c) or parallel (2×a/C) connection of internal components. For metering applications, the primary rated current (I1n) should be greater than or equal to the calculated load current (IC). For instance, a load current of 350A would require a 400/5 current transformer. For protection applications, a larger transformation ratio may be selected to ensure accuracy.