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| Pre-fault Voltage https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=5176 |
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| Author: | makoester1 [ Thu Sep 26, 2019 10:22 am ] |
| Post subject: | Pre-fault Voltage |
Hello, When conducting fault current calculations prior to deriving incident energy values, does anyone run multiple scenarios with different pre-fault per unit voltage values? Thanks for the input. |
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| Author: | Jim Phillips (brainfiller) [ Sat Sep 28, 2019 4:00 am ] |
| Post subject: | Re: Pre-fault Voltage |
Back in my electric utility days we would run V at 1.05 p.u. as a what if in the event transformer taps boost the voltage by 5% I don't if too many others take this approach. It really becomes important when the fault current is close to the interrupting or withstand rating. |
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| Author: | jcp@pfeiffereng.com [ Mon Sep 30, 2019 7:49 am ] |
| Post subject: | Re: Pre-fault Voltage |
I normally run three scenarios; Base analysis, utility drop by 10%, and all motors off. The 10% voltage drop (0.9 utility voltage) is to take care of a heavily loaded utility system. |
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| Author: | Robertefuhr [ Mon Sep 30, 2019 10:46 am ] |
| Post subject: | Re: Pre-fault Voltage |
We typically do not change the prefault voltage. Instead we run multiple scenarios. (1) Infinite Utility fault current (when primary fault current is not known) with motors on; (2) Double the Utility transformer Impedance with motors off. If the system has emergency generators, then we run additional scenarios with (3) Generator On - Motors on and (4) Generator On with motors off. This will produce the maximum and minimum fault currents for each location. |
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