Sepam - HV/MV Protection and control units (ENG) - Trinet

Negative sequence / unbalanceANSI code 46function n° F45X 1 i X i 2OperationThis functions is designed to protect equipmentagainst unbalances:c it picks up when the negative sequence componentof phase currents is greater than the set point,c it is time delayed. The time delay may be definiteor IDMT time (see curve).Negative sequence current Ii is calculatedfor the 3 phase currents:Ii = 1 –>3 x I1 + –> –>a2 I2 + aI3with a=e j 2π3When Sepam is connected to 2 phase currentsensors only, the negative sequence current is:Ii = 1 3 x I1 - a2 I3witha=e j 2π3The function may be used to display the negativesequence percentage on the pocket terminal.It corresponds to the ratio Ii/Ib expressedas a percentage(Ib: equipment basis current set in the status menu).Definite time delayFor Ii > Is, the time delay is definite (independent of Ii)and equal to T.IDMT time delayFor Ii > Is, the time delay depends on the value of Ii/Ib.T corresponds to the time delay for Ii/Ib = 5.tIs 5IbIDMT protection principle.The tripping curve is defined according to the following equations:c for Is/Ib ≤ Ii/Ib ≤ 0.53.19t =(Ii/Ib)c for 0.5 ≤ Ii/Ib ≤ 54.64t =(Ii/Ib)1.5.T0.96.Tc for Ii/Ib > 5t = TThe function takes into account negative sequence current variations duringthe time delay.The negative sequence measurement expressed as a percentage of the basiscurrent may be accessed via the pocket terminal.It is available even if the protection is disabled.Block diagramIitI1I2Ii > Ist0F45X/2I3TF45X/1IsDefinite time protection principle.Ii2/30 Protection functions