8-2
Application
BE1-951
OC-W-79 Logic Scheme (Overcurrent Protection with Reclosing)
This logic scheme provides time and both high-set and low-set instantaneous overcurrent elements for
phase, neutral, and negative sequence protection. Automatic reclosing is included and is initiated (RI) by
a protective trip or by an external reclose initiate contact. Breaker failure, virtual breaker control and
protective voltage features are not activated in this scheme. However, these features may be activated
through BESTlogic.
OC-W-CTL Logic Scheme (Overcurrent Protection with Control)
This logic scheme is similar to OC-W-79 but has the added ability to manually open and close the breaker
by using the virtual breaker control switch (101). Breaker failure and voltage protection features are not
included in this scheme. However, these features may be activated through BESTlogic.
FDR-W-IL Logic Scheme (Feeder Protection with Interlock)
This logic scheme provides time and both high-set and low-set instantaneous overcurrent elements for
phase, neutral, and negative sequence protection. Automatic reclosing is included and is initiated (RI) by
a protective trip. The breaker may be manually opened or closed via the virtual breaker control switch (101).
Protective voltage features are not enabled in this scheme. However, these features may be activated
through BEST LOGIC. Interlock logic allows for bus overcurrent backup of feeder relays and allows for fast
bus overcurrent protection.
BUS Logic Scheme
This logic scheme is applied to a bus main relay to provide primary bus overcurrent protection. It contains
logic to interconnect with the feeder logic scheme (FDR-W-IL) to provide high-speed overcurrent protection
for the bus under normal conditions. It also contains logic to trip the feeder breakers while the feeder relays
using FDR-W-IL logic scheme are out of service.
BACKUP Logic Scheme
This logic scheme is applied to a bus main relay to provide backup bus overcurrent protection as well as
breaker failure protection for the bus breaker under normal conditions. It also provides primary bus
overcurrent protection when the relay using BUS logic is providing feeder protection or when the primary
bus relay is out of service.
DETAILS OF PREPROGRAMMED LOGIC SCHEMES
The following subsections describe each of the six preprogrammed logic schemes in detail. For each
scheme, operation of the protection and control logic under normal conditions is described. The features of
each logic scheme are broken down into functional groups and described in detail. In addition, FDR-W-IL,
BUS, and BACKUP logic schemes also provide a discussion of how various contingencies are covered
between these logic schemes.
BASIC-OC LOGIC SCHEME
Logic scheme BASIC-OC is intended for applications requiring three-phase and neutral nondirectional
overcurrent protection. While not as elaborate as the other preprogrammed schemes, this logic scheme
provides an excellent base on which to create a custom scheme for a specific application.
The components of BASIC-OC logic are summarized in Tables 8-1, 8-2, 8-3, and 8-4. A diagram of BASIC-
OC logic is shown in Figure 8-1. Figure 8-2 shows a one-line drawing for the BASIC-OC logic scheme.
Operation - Protection
The phase, neutral and negative sequence elements are activated to provide timed (51) and instantaneous
(50) overcurrent protection in this scheme. A function block is disabled by setting the pickup set-point at zero
in each of the four setting groups. Virtual output VO11 is assigned for all protective trips. When VO11
becomes TRUE, OUT1 will operate and trip the breaker. Contact outputs OUT2, OUT3, OUT4, and OUT5
