P12x/EN T/Eb6 - Schneider - error

P12x/EN AP/Eb6Page 52/78Application GuideMiCOM P120/P121/P122/P123In order to determine the number of shots required; the first factor is the ability for the circuitbreaker to perform several trip-close operations in a short time and, the effect of theseoperations on the maintenance period.If a moderate percentage of non-permanent faults is present in a system, two or more shotsare justified. If fused ‘tees’ are used and the fault level is low, the timer of the fuses may notdiscriminate with the main IDMT relay: several shots are usefull. This would not warm up thefuse to a such extent that it would eventually blow before the main protection operated.22.3.2 Dead Timer SettingLoad, circuit breaker, fault de-ionising time and protection reset are taken into considerationwhen setting the dead timer.22.3.3 Minimum drop-off time settingIf an electromagnetic relay is used (working on the principle of disc in the electromagneticfield due to eddy current generated in the disc), an additional dead time (Min Drop-off Time),depending of the tripping cause, is settable,This function includes the choice to select an IDMT curve on the relay reset time, setting thedrop-off time on phase and neutral autoreclose cycles.This drop-off time blocks the next cycle if this one not elapsed.A next cycle can be start if the dead time is elapsed and treset elapsed to.NOTE:this function is currently used with IDMT curve.If dead time > Drop-off time, the relay will close the CB at the end ofdead time.If dead time < Drop-off time, the relay will close the CB at the end ofdropp-off time.