Question: The operating time of a standard overcurrent relay is defined by IEC 60255 and IEEE C37.112 and is given by kB +L (1/13)a - 1 The table below provides the constant values of the parameters for the characteristic curves: t= Standard Curve Normal inverse Very inverse Extremely inverse Inverse Short-time inverse Normal inverse Very inverse Extremely inverse Long-time inverse IEEE IEEE IEEE CO8 CO2 IEC IEC IEC IEC a 0.02 2 2 2 0.02 0.02 B L 0.0515 0.114 19.61 0.491 28.2 0.1217 5.95 0.18 0.02394 0.01694 0.14 13.5 80 120 1 2 1 o Consider the normal inverse, very inverse and extremely inverse curves for the IEEE standard if 6 is even and for the IEC standard if 6 is odd. o Assume that all the curves are set to use a current tap setting of 402 A and a time dial setting of 0.4 o Calculate the operating times for each curve for a relay input current of o Calculate the operating times for each curve for a relay input current of 4046 A first and then 460 A. o Compare the results and discuss the differences! Question: The operating time of a standard overcurrent relay is defined by IEC 60255 and IEEE C37.112 and is given by kB +L (1/13)a - 1 The table below provides the constant values of the parameters for the characteristic curves: t= Standard Curve Normal inverse Very inverse Extremely inverse Inverse Short-time inverse Normal inverse Very inverse Extremely inverse Long-time inverse IEEE IEEE IEEE CO8 CO2 IEC IEC IEC IEC a 0.02 2 2 2 0.02 0.02 B L 0.0515 0.114 19.61 0.491 28.2 0.1217 5.95 0.18 0.02394 0.01694 0.14 13.5 80 120 1 2 1 o Consider the normal inverse, very inverse and extremely inverse curves for the IEEE standard if 6 is even and for the IEC standard if 6 is odd. o Assume that all the curves are set to use a current tap setting of 402 A and a time dial setting of 0.4 o Calculate the operating times for each curve for a relay input current of o Calculate the operating times for each curve for a relay input current of 4046 A first and then 460 A. o Compare the results and discuss the differences