Toshiba GR-200-5 Instruction Manual

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6F2T0207 (0.01)GRE200 (5,6)- 135 -2.12.1 CBF operation and its elementsThe operation of CBF is initiated by the operation of OCCBF and EFCBF, which monitors faultcurrent after the issuance of a trip command by other protection functions. OCCBF or EFCBFmonitor 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 theEFCBF element.The operation of these elements is reset if the threshold values of currents, applied bythe settings [OCCBF] and [EFCBF], are below 80% of their setting value.2.12.2 Re-trip featureOnce a CB failure occurs, the CBF protection would normally issue a back-trip command tothe adjacent CB(s) and/or the upstream CB. However, the CBF protection is able to issue afurther trip command to the faulted CB before issuing the back-trip command. The second tripcommand is termed “re-trip”; “re-trip,” confirms the occurrence of a CB failure. In the event ofan erroneous CBF operation, the use of “re-trip” has the advantage of avoiding the issue of theback-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 canselect the desired mode using scheme switch [CBF-Retrip]:➢ Internal modeIf 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 tripsignals coming from other functions.➢ External modeWhen On-T is set for scheme switch [CBF-Retrip], the CBF function is armed forissuing a “re-trip” following tripping by external protection functions only. Theexternal protection functions can operate using PLC connection points in the TRCfunction. If external mode is selected, an external CBF start-signal must be presentcontinuously 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 settingtime can be chosen between 0 and 300.000sec, the time setting to be applied must bedetermined in accordance with the response time of the CB. The setting time is addressed later.(Chapter 2.12.5)