IEEE C37.108:1989 (R1994)

New IEEE Standard - Superseded.
This guide is intended to aid those engineers who have reevaluated the risks associated with faults within network vaults, particularly for those network vaults located within or near highrise buildings. It will also identify currently available devices that are being used in network transformer protection schemes. These devices should act to sense the fault and initiate fault interruption locally or remotely, there by minimizing damage and restoration time. These devices will be described as to their fault detecting capabilities. An example utilizing a number of protective schemes is presented in Appendix B.

Network transformer vaults are fire retardant enclosures within buildings or adjacent to them that contain two or more power transformers. These transformers are supplied from different subtransmission or distribution lines and are paralleled on their low-voltage side through circuit interrupting devices called “network protectors.” Typically, high voltage current interrupting devices have not been applied within the network vault. The low-voltage bus of a network vault may be electrically tied to a number of other vaults to form a network secondary distribution system, which will be called a “low-voltage network grid” in this guide, or each individual vault may stand alone as a “spot network.” A one-transformer vault can be considered a network vault if connected to other such vaults via low-voltage cables.