Complex sentence: A permanently installed current transformer (CT) around the neutral feeder to the LNER and connected to an external sensing circuit (the protection system) sends a signal to the relevant circuit breaker to open and disconnect the supply or isolate the generator from the fault.
Split into simpler sentences: A permanently installed current transformer (CT) fixed around the neutral feeder to the LNER senses the current. The CT sends a signal current to an external sensing circuit (the protection system) which then sends a signal to the relevant circuit breaker to open and disconnect the supply or isolate the generator from the fault.