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The time-current characteristics, features, and nameplate data for each
existing protective device shall be determined and documented. [The
Contractor shall coordinate with the [commercial power company] [_____] for
fault current availability at the site.] [The Contractor shall utilize the
fault current availability indicated as a basis for fault current studies.]
2.14.3
Single Line Diagram
A single line diagram shall be prepared to show the electrical system
buses, devices, transformation points, and all sources of fault current
(including generator and motor contributions). A fault-impedance diagram
or a computer analysis diagram may be provided. Each bus, device or
transformation point shall have a unique identifier. If a fault-impedance
diagram is provided, impedance data shall be shown. Location of switches,
breakers, and circuit interrupting devices shall be shown on the diagram
together with available fault data, and the device interrupting rating.
2.14.4
Fault Current Analysis
2.14.4.1
Method
The fault current analysis shall be performed in accordance with methods
described in IEEE Std 242, and IEEE Std 399.
2.14.4.2
Data
Actual data shall be utilized in fault calculations. Bus characteristics
and transformer impedance shall be those proposed. Data shall be
documented in the report.
2.14.4.3
Fault Current Availability
Balanced three-phase fault, bolted line-to-line fault, and line-to-ground
fault current values shall be provided at each voltage transformation point
and at each power distribution bus. The maximum and minimum values of
fault available at each location shall be shown in tabular form on the
diagram or in the report.
2.14.5
Coordination Study
The study shall demonstrate that the maximum possible degree of selectivity
has been obtained between devices specified, consistent with protection of
equipment and conductors from damage from overloads and fault conditions.
The study shall include a description of the coordination of the protective
devices in this project. A written narrative shall be provided describing:
which devices may operate in the event of a fault at each bus; the logic
used to arrive at device ratings and settings; situations where system
coordination is not achievable due to device limitations (an analysis of
any device curves which overlap); coordination between upstream and
downstream devices; and relay settings. Recommendations to improve or
enhance system reliability, and detail where such changes would involve
additions or modifications to the contract and cost damages (addition or
reduction) shall be provided. Composite coordination plots shall be
provided on log-log graph paper.
SECTION 16475A
Page 29
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