Which type of protection for electrical power stations provide isolation against a rise in potential of station ground and also provide drainage protection against longitudinally- induced voltages?

Isolating transformers break the metallic continuity between a power station's ground grid and the telephone circuit, preventing a ground potential rise (GPR) event from propagating voltage onto communications equipment. Because the primary and secondary windings are galvanically isolated, the transformer also blocks the conductive path through which longitudinally induced voltages - caused by electromagnetic coupling from high-voltage lines - would otherwise travel. This combination of GPR isolation and longitudinal voltage protection is documented in IEEE Std 487, which covers the protection of wire-line telephone facilities at power stations.

Neutralizing transformers are designed to cancel longitudinally induced voltages by injecting an opposing voltage but do not provide galvanic isolation against ground potential rise.

Mutual drainage reactors provide a balanced path to drain longitudinally induced currents to ground but offer no isolation against a rise in station ground potential.

Unit-type neutralizing transformers are a configuration variant used to address induced longitudinal voltages in specific circuit arrangements but do not provide the galvanic isolation needed to block GPR.

2-winding neutralizing transformers cancel longitudinally induced voltages through opposing winding action but lack the galvanic separation required to isolate telephone circuits from station ground potential rise.