UFC 3 -520-01
June 10, 2002
2-3.3.5 The program should properly account for alternating current (ac ) and direct
current (dc) decrement characteristics. Programs that use a separate reactance (X)
and resistance (R) network for modeling are usually consistent with ANSI standards.
This program feature is important to ensure more realistic system X/R ratios, which can
directly affect equipment rating assessments.
2-3.3.6
The program should be capable of handling multiple sources of generation.
2-3.3.7 The program should contain features that allow multiple case studies for each
type of analysis. This involves features for graphically opening and closing breakers,
and temporarily modifying load conditions .
2-3.3.8 The electrical model should be easily modified. For example, a desirable
feature is the ability to open or shut breakers with just a click of a mouse. With this
capability, many contingencies can be evaluated in a short time.
2-3.4
Several computer programs are available with the above capabilities.
Programs that have not been updated since 1993 likely do not have the above
capabilities.
2-3.5
The following sections provide specific criteria for the different types of
detailed design analyses.
2-4
SHORT CIRCUIT ANALYSIS .
2-4.1
Analysis and Equipment Criteria .
2-4.1.1 Perform a short circuit study as an integral part of selecting and sizing
electrical distribution components. Even the best and most reliable electrical distribution
system is not immune to occasional short circuits.
2-4.1.2 Overcurrent protective devices in the system must be designed to isolate
faults safely with minimal equipment damage and minimal disruption to facility
operation. All equipment exposed to the short circuit current must be capable of
withstanding the mechanical and thermal stresses caused by the current until the short
circuit is isolated.
2-4.2
Short Circuit Sources.
2-4.2.1 All rotating electric machinery in (or electrically near) the facility can co ntribute
to a fault. As part of a short circuit analysis, include the current contributions from the
following types of equipment:
2-4.2.1.1 Electric Transmission and Distribution Systems. Depending on its size,
the distribution system might be capable of producing the maximum short circuit
indefinitely until equipment failure occurs within the facility.
2-5
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