ABB PR512 Manual

Also see for PR512: Operator's manual

12t> = K x bt> = K xbII>a– 1PR512/P UNIT (50-51)Protection functionsThe PR512/P protection unit (50-51)carries out two independent protec-tion functions which can be ex-cluded:– 51 protection against overcurrent:• 0.2 < I < 2 In (rms)• 2 < I < 20 In (peak);– 50 protection against instantane-ous or delayed short-circuit(operation on peak value).Protection against overcurrent (51)This function makes four differentgroups of protection curves avail-able, defined as follows (IEC255-3):– definite time-delay– normal inverse time-delay– very inverse time-delay– extremely inverse time-delay.The following settings are possible:• 32 threshold current values (I>) (1)0.200 0.225 0.250 0.2750.300 0.325 0.350 0.3750.400 0.425 0.450 0.4750.500 0.525 0.550 0.5750.625 0.650 0.6750.700 0.725 0.750 0.7750.800 0.825 0.850 0.8750.900 0.925 0.950 0.9751.000 x InOFF(1) The unit guarantees non-entry into threshold forcurrents under 1.05 x I> set and guarantees entryinto threshold for currents above 1.30 x I> set.Selection of threshold I> valueFour different time-current relationships can beselected.Fixed time curve (b = 2)For protection with definite time (DT), the trip timeis given by the following relationship:Definite time-delay curvesFor definite time-delay protection, the relationshipbetween trip time and overcurrent is given by thefollowing formula.Captiont> trip timek parameter set by the user to select the trip curvea, b pair of parameters, depending on the type ofprotection selectableI fault currentI> trip threshold selectable by the userThe threshold value of this protection is indicatedby I>, whereas the relative trip time is indicated byt>.Start of timing is signalled by the ALARM LEDlighting up whereas circuit-breaker openinghaving taken place is signalled on the front by themagnetic flag I> I>>, turned to the yellow position.To reset signalling, the FLAG RESET pushbuttonon the front of the release must be pressed,ensuring one of the following conditions:a) 24 Vdc auxiliary voltage present (display lit);b) primary circulating current more than 0.2 x In(display lit with indication of the circulatingcurrent);c) application of the TT2 unit to the TEST connec-tor on the front of the release (optional acces-sory).Selection of threshold I> valueSetting of I> threshold is carried out by using theDip Switches (see page 13).The sum of the values selected represents thefraction of In which corresponds to I>.32 threshold values are available, defined from0.2 .... 1 x In with steps of 0.025 x In.The protection can be excluded by positioning thefirst Dip Switch in the OFF position.