It provides an analytic representation of typical electromechanical relays operating characteristic curve shapes in order to facilitate coordination when using microprocessor-type relays. 2. The IEC 60255 standard defines four standard current time characteristics – standard inverse (SI), very inverse (VI), extremely inverse (EI) and long-time inverse. Abstract: This paper introduces the new standard "IEEE standard inverse-time characteristic equations for overcurrent relays". This curve is shown as a multiple of the PICKUP setting (I). The TimeDial setting combined with SHORT PU and SHORT TIME setting (shown in heavy lines) depict the IEEE Very Inverse response. The purpose of this standard is to provide an analytic (formula) representation of typical relay operating characteristic curve shapes of various inverse-time relays to facilitate representation by microprocessor-type relays and promote a degree of standardization in the inverse shape of a selected curve. 1. But when PSM becomes more than 20, the operating time of relay becomes almost constant. In this section, step by step of preparing the time coordination curve for each Each characteristic can be calculated from: where: t = tripping time … 3000TC0704-IEC-EIT-DE50870 Curve Type Coefficient Values k α β Standard inverse / A 0.14 0.02 2.97 Very inverse / B 13.5 1 1.50 Long time inverse / B 120 1 13.33 Extremely inverse / C 80 2 0.808 Ultra inverse 315.2 2.5 1 735/737 iec-a curve (normal inverse) 1000 100 10 1 0.1 0.1 multiple of pickup current (per unit) ge order #:ges10045 t i m e i n s e c o n d s 1 10 100 803653a4.cdr note: log chart scaled as per: keuffel & esser time-current characteristic paper sr735/sr737 iec-a curve (normal inverse) 1 0.1 Formulas below:-t = (k.B)/((I/Is)^a - 1) where t = operating time (sec) k = TMS (time multiplier settings) I = measured current value (A) Is= set current value a B Normally Inverse 0.02 0.14 Very Inverse 1.0 13.5 Extremely Inverse … Curve Equation: Trip = TimeDial *[19.61/(I-1) + 0.491], where I is a multiple of I. Standard Inverse Time - ตำมมำตรฐำน IEC 60255 แบบ 3/10 Characteristic กระแสผิดพร่อง 10 เท่ำ รีเลย์จะท ำงำนที่เวลำ 3 s ที่ TMS=1.0 - Standard Inverse Time Characteristic ใช้เมื่อ…. STPU Setting Time-Current Curves Circuit Breakers Cargill Electrical Team Meeting 24 . Inverse Time Curves (Formula, Definite Reset) GD specifies the value of the input energizing quantity when the operate time turns from dependent time operation to … The equation describing the Extremely Inverse Relay is I 2 t = K where I is operating current and t is time of operation of the Relay. The tripping condition will be faster when the fault current value is higher and lower fault current value will be resulted to longer time of tripping condition. 3. Time-Current Curves Circuit Breakers Cargill Electrical Team Meeting 22 . STD Setting Time-Current Curves Tripping Curves IEC 60255 Characteristics. The Instantaneous, shown as a separate response, can be set to OFF. 1. It is also seen from the curve that, for a lower value of plug setting multiplier, i.e., for a lower value of fault current, the time of operation of the relay is inversely proportional to the fault current. LTPU Setting Time-Current Curves Circuit Breakers Cargill Electrical Team Meeting 23 . Moderately inverse (U1) 0.0104 0.2256 1.08 0.02 U.S. Inverse (U2) 5.95 0.180 5.95 2.00 Inverse definite minimum time overcurrent relay operates inversely between time and current. Standard Curves --standard formats 1 M 2 C tr TDS B M A tt TDS p 1 Reset Time (M < 1) Trip time (M 1) Some manufacturers include disk inertia in B Time Overcurrent Relays Fall 2018 U I ECE525 Lecture 11 US and IEC curve parameters Curve A B C P U.S. IEC (International Electrotechnical Commission) Standard Curve for Inverse Relays: As per IEC, the time of operation of any Inverse relay can be calculated from the formula given below. By 3/10, I believe you are talking about the Normal Inverse (NI) curve. 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