P12x/EN T/Eb6 - Schneider - error

Application GuideP12x/EN AP/Eb6MiCOM P120/P121/P122/P123 Page 49/78When short time delay protection is used with autoreclose, the scheme is normally arrangedto block the instantaneous protection after the first trip. Therefore, if the fault persists after reclosing,time graded protection will give discriminative tripping with fuses or other protectiondevices, resulting in the isolation of the faulted section. However, for certain applications,where the majority of the faults are likely to be transient, it is not uncommon to allow morethan one instantaneous trip before the instantaneous protection is blocked.Some schemes allow a number of re-closings and time graded trips after the firstinstantaneous trip, which may result in the burning out and clearance of non-permanentfaults. Such an approach may also be used to allow fuses to operate in teed feeders wherethe fault current is low.Any decision to apply the autoreclose function would be influenced by all data known on thefrequency of transient faults (for instance feeders which consist partly of overhead lines andpartly of underground cables). When a significant proportion of the faults are permanent, theadvantages of the autoreclose are small, particularly since re-closing on to a faulty cable islikely to aggravate the damage.22.2 Description of the function22.2.1 Autorecloser activationThe autoreclose function is activated using “AUTOMAT. CTRL/ PROTECTION G1” menu.The same settings apply for the Menu PROTECTION G2.The autoreclose function of the MiCOM P123 is available only if the following conditions areverified:• The auxiliary contact of the CB status 52a must be connected to the relay.Refer to the “AUTOMAT. CTRL/Inputs” menu• The trip output relay RL1 must not be latched to the earth and/or phase protectionfunction.Refer to the “AUTOMAT. CTRL/Latch functions” menuNOTE:If the auxiliary supply is lost during an autoreclose cycle, theautoreclose function is totally disabled.In addition to Autoreclose settings, the user will be able to fully link the autoreclose functionto the protection function using the menus “PROTECTION G1/Phase OC” and“PROTECTION/E/Gnd”.22.2.2 Logic InputsThe autoreclose function has four inputs that can be assigned to the autoreclose logic.These inputs can be opto-isolated inputs configured for that under the “AUTOMAT. CTRL”menu. External contacts can then be wired to be used as an input and influence theautorecloser scheme. These 4 inputs are :−−−one external CB fail,two external starting orders,one external blocking order.The following table gives the “AUTOMAT.CTRL/Inputs” menu assigned to the autorecloselogic input. The second column presents the menu disabling the function if not assigned inthe “PROTECTION G1/Autoreclose” menu (Setting = No).“Inputs” menuEnabled with:External CB Fail CB FLT EXT CB FLTExternal starting orders Aux 1Aux 2CYCLES tAux1 *CYCLES tAux2 *External blocking order Block-79 Ext Block ?* These two external orders can be independently disabled.