UFC 3 -520-01
June 10, 2002
Acceptable system lineups and operating configurations.
Protective device locations.
Protective d evice time-current characteristics.
Load currents-- normal and maximum.
Motor full-load current, locked rotor current, starting time, and damage time.
Fault currents at each protective device location.
9-2.6.3 Provide the following data on the one -line diagram and associated
documentation:
Apparent power and voltage ratings, as well as the impedance and connections of
all transformers.
Normal and emergency switching conditions.
Nameplate ratings and subtransient reactance of all major motors and generators,
as well as transient reactances of synchronous motors and generators, plus
synchronous reactances of generators.
Conductor sizes, types, and configurations, and type of insulating material.
Current transformer ratios.
Relay, direct-acting trip, and fuse ratings, characteristics, and ranges of adjustment.
Cable lengths, particularly if an impedance diagram is not included.
9-2.6.4 Determine the minimum and maximum fault currents at each protective
device location and at the end of all lines. The short-circuit current study should include
maximum and minimum expected three -phase and ground fault duties, as well as
available short -circuit current data from all sources.
9-2.6.5 Determine the settings for all protective devices. The settings have to be
specified before time-current curves can be generated. Draw a composite set of time
characteristic curves showing the coordination of all protective devices. A computer
program designed specifically for plotting coordination curves is recommended.
Although the coordination study plots can be prepared by hand, this manual method will
usually cost more than a computer-generated study. Also, a computer -generated study
is more easily maintained.
9-9
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