Toshiba GR-200 Series Instruction Manual page 155

CBF operation and its elements
2.12.1
The operation of CBF is initiated by the operation of OCCBF and EFCBF, which monitors fault
current after the issuance of a trip command by other protection functions. OCCBF or EFCBF
monitor the fault current so that the CBF feature can determine the failure of the CB to operate.
For CBF, the respective phase currents in three-phase system are monitored by the OCCBF-
A, OCCBF-B and OCCBF-C elements, while the zero-sequence current is monitored by the
EFCBF element.
The operation of these elements is reset if the threshold values of currents, applied by
the settings [OCCBF] and [EFCBF], are below 80% of their setting value.
Re-trip feature
2.12.2
Once a CB failure occurs, the CBF protection would normally issue a back-trip command to
the adjacent CB(s) and/or the upstream CB. However, the CBF protection is able to issue a
further trip command to the faulted CB before issuing the back-trip command. The second trip
command is termed "re-trip"; "re-trip," confirms the occurrence of a CB failure. In the event of
an erroneous CBF operation, the use of "re-trip" has the advantage of avoiding the issue of the
back-trip command to the adjacent CB(s) or the upstream CB. The timing chart for "re-trip"
and back-trip are discussed later. (See Figure 2.12-1)
There are two operation modes (internal and external mode) for "re-trip"; the user can
select the desired mode using scheme switch [CBF-Retrip]:
Internal mode
➢
If On is set for scheme switch [CBF-Retrip] the CBF function is armed for issuing a
"re-trip" signal. The OCCBF and EFCBF control the "re-trip" signal along with trip
signals coming from other functions.
External mode
➢
When On-T is set for scheme switch [CBF-Retrip], the CBF function is armed for
issuing a "re-trip" following tripping by external protection functions only. The
external protection functions can operate using PLC connection points in the TRC
function. If external mode is selected, an external CBF start-signal must be present
continuously for as long as the fault is present.
For the re-trip operation, On should be set for both scheme switches [OCCBF] and
[EFCBF]. When a delay timer is needed for "re-trip", a setting [TCBF-RE] is available. A setting
time can be chosen between 0 and 300.000sec, the time setting to be applied must be
determined in accordance with the response time of the CB. The setting time is addressed later.
(Chapter 2.12.5)
- 136 -
6F2T0200 (0.15)
GRE200 (1,2)