Virtual 86 Lockout - Considerations and Applications In Digital Substations

Digital substations (DSS) involve the use of merging units (MUs) to connect to yard elements (CT, VT, 52, 89), digitizing the protection & control (PAC) data, and communicating with PAC relays in the control house over a fiber optic Ethernet network. The physical PAC contact outputs which operate the switchyard apparatus are no longer in the control house and a virtual 86 lockout function incorporated in the MUs can be applied. This paper will review how lockout relays are used in a conventional substation and review several methods/schemes of using the virtual 86 lockout function. Topics that will be discussed include redundancy considerations, loss of control power to PAC relay or MU, safety considerations, and 86 reset mechanisms.