Armored optical cables should be used for communication between substation equipment. From that specification

From: 330kV to 750kV smart substation design specifications.

The original text is specifically from: Light and cable selection and laying of 330kV to 750kV smart substation design specifications. The original text says "may" rather than "should be used". The original text (excerpt) is as follows: The optical cable used in the protection channel is for inter-station connection, the distance is generally long, and single-mode optical cable is used. The transmission distance of optical cables in substations is relatively short and multi-mode optical cables are used. When laying in slot boxes, metal-free, flame-retardant, reinforced core optical cables can be used. When laying in cable trenches, armored optical cables can be used. It is recommended to use customized tail cables for indoor cabinets for quick and convenient installation.