Toshiba GR200 Series Instruction Manual page 245

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CBF operation and its elements

The operation of CBF is initiated by the operation of OCCBF and EFCBF, which monitors fault

current after the issuance of a trip signal 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 setting of [OCCBF1] and [EFCBF1], are below 80% of their setting value.

Re-trip feature

Once a CB failure occurs, the CBF protection would normally issue a back-trip signal to the

adjacent CB(s) and/or the upstream CB. However, the CBF protection is able to issue a further

trip signal to the faulted CB before issuing the back-trip signal. The second trip signal 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

signal to the adjacent CB(s) or the upstream CB. The timing chart for "re-trip" and back-trip

are discussed later. (See Figure 2.10-1)

There are two operation modes (internal and external mode) for "re-trip"; the user can

select the desired mode using scheme switch [CBF1-Retrip]:

Internal mode

If On is set for scheme switch [CBF1-Retrip] the CBF function is armed for issuing a

"re-trip" command. 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 [CBF1-Retrip], the CBF function is armed

forissuing 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 [OCCBF1] and

[EFCBF1]. When a delay timer is needed for "re-trip", a setting [TCBF1-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.

(section 2.10.5)

6F2S1915 (0.46)

GRZ200 (Soft 031 & 032)