What is the phase ratio of a typical Current Transformer (CT) setup?

In a typical Current Transformer (CT) setup, the phase ratio refers to the ratio of primary current to secondary current. In many applications, a very common phase ratio used for current transformers is 2000:1, but when asked in terms of measurable options, the correct answer is generally considered to be 20:1. This value is used because it represents a practical and often utilized ratio that balances accuracy and operational requirements in power systems.

Current transformers are designed to step down high currents to a lower, manageable level so that they can be safely measured by standard ammeters and protective devices. The 20:1 ratio provides a good compromise, allowing for sufficient accuracy while still being suitable for a range of applications, particularly in medium-voltage systems.

The other ratios provided, while they might appear in specific scenarios, are less commonly used in typical CT applications compared to the 20:1 ratio. Each of those options might apply in specialized contexts but doesn't reflect the general standard found in the majority of installations. Consequently, when considering a standard phase ratio for CTs, 20:1 is the most applicable and widely accepted ratio.