Which device can read system voltage through a micro processing relay?

The device that can read system voltage through a micro processing relay is a potential transformer (PT). Potential transformers are specifically designed to reduce high voltage levels to a lower, manageable level that can be safely monitored and measured.

In the context of systems with a micro processing relay, PTs provide accurate voltage readings, which are essential for various protective relaying schemes and system monitoring. This capability allows the relay to process the actual system voltage, which is critical for controlling and protecting electrical equipment effectively.

CTs, or current transformers, are focused on measuring current and are not suitable for measuring voltage directly. Meanwhile, a main breaker interrupting current does not provide voltage readings; its function is to interrupt or limit electric current flow. The phase angle refers to the phase relationship between voltage and current in an AC circuit, but it doesn't measure voltage by itself. Thus, potential transformers are the appropriate devices for reading system voltage in this scenario.