Protection Setting Guidelines |
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Protection Setting Guidelines Presentation The setting of overcurrent protection relies on installation short-circuit and electrical fault calculations. The setting guidelines cannot replace these calculations. MasterPact MTZ circuit breakers with MicroLogic X control units offer flexibility to set the required overcurrent protection while maintaining selectivity and stability on transient phenomena, for example, inrush current of transformers or motors, when necessary. For each circuit, the installation designer needs to provide the following: oIz: continuous current capacity of the circuit according to IEC 60364-5-52 or national wiring rules. Current carrying capacity is called ampacity in the US National Electrical Code (NFPA 70). oIfault min: minimum electrical fault current at the end of the circuit depending on earthing system oTmax short-circuit: maximum time for maximum short-circuit current Guidelines are given for setting the following protections: oLong-time overcurrent protection oShort-time overcurrent protection oInstantaneous overcurrent protection oIDMTL overcurrent protection oDirectional overcurrent protection Overcurrent Protection Setting Guidelines by Application The following table gives the guidelines for overcurrent protection setting by application: Application MicroLogic 2.0 X MicroLogic 3.0 X MicroLogic 5.0 X, 6.0 X, 7.0 X(1) Secondary side of MV/LV transformer (switchboard main incomer) with other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream as feeder Ir = Iz tr ≤ 24 s Isd ≤ Ifault min Selectivity possible with Compact NSXm and Compact NSX feeders only. Ir = Iz tr ≤ 24 s Ii ≤ Ifault min Ii tripping mode: Standard Selectivity possible with PowerPact B-, H-, J-, and L-frame feeders only. Ir = Iz tr ≤ 24 s Isd ≤ Ifault min tsd tsd of downstream MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker(2) Ii mode: OFF Secondary side of MV/LV transformer (switchboard main incomer) without other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream as feeder Ir = Iz tr ≤ 24 s Isd ≤ Ifault min Ir = Iz tr ≤ 24 s Ii ≤ Ifault min Ii tripping mode: Standard Ir = Iz tr ≤ 24 s Isd ≤ Ifault min tsd = 0 Ii mode: ON Ii tripping mode: Standard Ii = Isd Generator output with other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream as feeder Ir = Iz tr ≤ 1 s Isd ≤ Ifault min Selectivity possible with Compact NSXm and Compact NSX feeders only. Ir = Iz tr ≤ 1 s Ii ≤ Ifault min Ii tripping mode: Standard Selectivity possible with PowerPact B-, H-, J-, and L-frame feeders only. Ir = Iz tr ≤ 1 s Isd ≤ Ifault min tsd > tsd of downstream MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker(2) Ii mode: OFF Generator output without other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream as feeder Ir = Iz tr ≤ 1 s Isd ≤ Ifault min
Ir = Iz tr ≤ 1 s Ii ≤ Ifault min Ii tripping mode: Standard Ir = Iz tr ≤ 1 s Isd ≤ Ifault min tsd = 0 Ii mode: ON Ii tripping mode: Standard Ii = Isd Feeder with other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream Ir = Iz tr ≤ 16 s Isd ≤ Ifault min Selectivity possible with Compact NSXm and Compact NSX feeders only. Ir = Iz tr ≤ 16 s Ii ≤ Ifault min Ii tripping mode: Standard Selectivity possible with PowerPact B-, H-, J-, and L-frame feeders only. Ir = Iz tr ≤ 16 s Isd ≤ Ifault min tsd > tsd of downstream circuit breaker(2) Ii mode: OFF Feeder without other MasterPact, Compact NS, or PowerPact P- and R-frame circuit breaker downstream as feeder Ir = Iz tr ≤ 16 s Isd ≤ Ifault min Ir = Iz tr ≤ 16 s Ii ≤ Ifault min Ii tripping mode: Standard Ir = Iz tr ≤ 16 s Isd ≤ Ifault min tsd = 0 Ii mode: ON Ii tripping mode: Standard Ii = Isd Power electronic (for example, uninterruptible power supplies, variable speed drives, photovoltaic inverters) with no other circuit breaker downstream Ir = Iz tr ≤ 8 s Isd = 1.5-2 x In≤ Ifault min Ir = Iz tr ≤ 8 s Ii = 2-3 x In≤ Ifault min Ii tripping mode: Fast Ir = Iz tr ≤ 16 s Isd = 1.5-2 x In≤ Ifault min tsd = 0 Ii mode: ON Ii tripping mode: Fast Ii = 2–3 x In ERMS settings with ERMS Digital Module only Ir_ERMS = Iz tr_ERMS ≤ 1 s Isd_ERMS = 1.5 x Ir Ir_ERMS = Iz tr_ERMS ≤ 1 s Ii_ERMS = 1.5 x In Ii_ERMS tripping mode: Fast Ir_ERMS = Iz tr_ERMS ≤ 1 s Isd_ERMS = 1.5 x Ir tsd_ERMS = 0 Ii_ERMS = 2 x In Ii_ERMS tripping mode: Fast (1) Ground-fault protection and earth-leakage protection depend on the earthing system and local regulations. As a rule ground-fault and earth-leakage sensitivity should be as low as possible without being disturbed by permanent or transient leakage current. The ground-fault and earth-leakage time delay enables selectivity with downstream devices. (2) When tsd > 0, a fault clearance time reduction system, such as ZSI or ERMS, is required in the USA by National Electricity Code NFPA 70 (240.87) (2011 edition). Refer to the guidelines for ERMS settings. |
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