5-172 F60 Feeder Protection System GE Multilin5.6 GROUPED ELEMENTS 5 SETTINGS55.6.4 PHASE CURRENTa) MAIN MENUPATH: SETTINGS GROUPED ELEMENTS SETTING GROUP 1(6) PHASE CURRENTb) INVERSE TIME OVERCURRENT CHARACTERISTICSThe inverse time overcurrent curves used by the time overcurrent elements are the IEEE, IEC, GE Type IAC, and I 2 t stan-dard curve shapes. This allows for simplified coordination with downstream devices.If none of these curve shapes is adequate, FlexCurves may be used to customize the inverse time curve characteristics.The definite time curve is also an option that may be appropriate if only simple protection is required.A time dial multiplier setting allows selection of a multiple of the base curve shape (where the time dial multiplier = 1) withthe curve shape (CURVE) setting. Unlike the electromechanical time dial equivalent, operate times are directly proportionalto the time multiplier (TD MULTIPLIER) setting value. For example, all times for a multiplier of 10 are 10 times the multiplier 1or base curve values. Setting the multiplier to zero results in an instantaneous response to all current levels above pickup.Time overcurrent time calculations are made with an internal energy capacity memory variable. When this variable indi-cates that the energy capacity has reached 100%, a time overcurrent element will operate. If less than 100% energy capac-ity is accumulated in this variable and the current falls below the dropout threshold of 97 to 98% of the pickup value, thevariable must be reduced. Two methods of this resetting operation are available: “Instantaneous” and “Timed”. The “Instan-taneous” selection is intended for applications with other relays, such as most static relays, which set the energy capacitydirectly to zero when the current falls below the reset threshold. The “Timed” selection can be used where the relay mustcoordinate with electromechanical relays.IEEE CURVES:The IEEE time overcurrent curve shapes conform to industry standards and the IEEE C37.112-1996 curve classificationsfor extremely, very, and moderately inverse. The IEEE curves are derived from the formulae: PHASE CURRENT PHASE TOC1 See page 5–177.MESSAGE PHASE TOC2 See page 5–177.MESSAGE PHASE TOC3 See page 5–177.MESSAGE PHASE TOC4 See page 5–177.MESSAGE PHASE IOC1 See page 5–179.↓MESSAGE PHASE IOC8 See page 5–179.MESSAGE PHASE DIRECTIONAL 1 See page 5–180.MESSAGE PHASE DIRECTIONAL 2 See page 5–180.Table 5–22: OVERCURRENT CURVE TYPESIEEE IEC GE TYPE IAC OTHERIEEE Extremely Inverse IEC Curve A (BS142) IAC Extremely Inverse I2 tIEEE Very Inverse IEC Curve B (BS142) IAC Very Inverse FlexCurves A, B, C, and DIEEE Moderately Inverse IEC Curve C (BS142) IAC Inverse Recloser CurvesIEC Short Inverse IAC Short Inverse Definite Time
