What happens when the ratio of PT to CT measurements falls below a certain limit?

The scenario where the ratio of potential transformer (PT) to current transformer (CT) measurements falls below a specific limit is critical for the functioning of protective relays. When this ratio drops, it indicates that the system is not operating within its normal parameters, which can be due to issues such as under-voltage or imbalances in the system.

Protective relays are designed to react to changes in electrical measurements to maintain system stability and safety. If the measurements from PTs and CTs suggest abnormal operating conditions, the protective relays may activate to isolate faulty sections of the system or take corrective actions. This helps to prevent further incidents, such as equipment damage or widespread outages.

By responding to such measurement discrepancies, protective relays play a vital role in the reliability and safety of the electric grid. This ensures that any potential faults are addressed promptly before they escalate into more serious problems.