Sepam series 10 - Schneider Electric

Sepam Series 10 - Functions and ParametersEarth Fault Cold Load Pick-Up (Cold Load Pick-Up Io)Applicable toSepam Series 10NB ASepam with 4 current inputs and standard or sensitive earth fault protection only(Sepam series 10 • 41• or Sepam series 10 • 42•).DescriptionThe earth fault cold load pick-up function avoids nuisance tripping of the earth fault protection(ANSI 50N-51N) during energization. Depending on the installation characteristics, such operations cangenerate transient inrush currents. If the earth fault current measurement is based on the sum of the 3phase CTs, the aperiodic component of these transient currents can result in saturation of the phaseCTs. This saturation can lead to measurement of an incorrect earth fault current likely to exceed theprotection set points.These transient currents are mainly due to the power transformer magnetizing currents or the motorstarting currents. In normal circumstances, the protection settings should be defined so as to avoidtripping due to these transient currents. However, if this rule results in inadequate sensitivity levels ordelays that are too long, the cold load pick-up function can be used to increase or inhibit set pointstemporarily after re-energization. In the specific case of transient currents linked to transformerenergizing, this function can be used to activate restraint of the earth fault protection based on thedetection of a second harmonic component in the phase currents.Use of this function maintains a good level of protection sensitivity, regardless of the constraints affectingre-energization.In the case of earth fault current measurement by an earth CT, there is less risk of measuring anincorrect earth fault current. If the sensor is used correctly, there is no need to activate this function.Remark: In the rest of this manual, this function is referred to by its abbreviation CLPU Io.The CLPU Io function automatically detects the appearance of a phase current after re-energization ofthe supply.Setting the function parameters allows the user to:• Choose which set points it acts on: The low set point Io> or the high set point Io>> or simultaneouslyon both set points• Define the type of action on the chosen set points (Io> and/or Io>>):• Temporary multiplying factor applied to the set point (x 1.5 to 5)• Temporary set point blocking• Permanent activation of the second harmonic restraint• Define for how long the set point increase or blocking is applied after detection of re-energizationBy default, this function is off.SEPED307003 02/2008 105