Protection of Locomotive From Overvoltage and Under Voltage:
1. For protection against over voltages the over voltage relay which is basically a potential transformer (PT) is used. 2. The potential transformer (PT) is connected across secondary of main transformer and the over voltage relay is connected across secondary of the potential transformer. 3. When over voltage occurs due to abnormal condition, the voltage across secondary of transformer increases hence PT voltage also increases and over voltage relay operates sending trip signal to CB which disconnects the circuit. 4. Under voltage is not desirable for efficient working of auxiliary circuits as Arno may not start, the under voltage is monitored through a relay triggering an alarm, which enables the power controller to react and take corrective measures.