final bid specs 09328.pdf - Freese and Nichols, Inc.

2. Impedance Diagram:
a. Available MVA or impedance from the utility company.
b. Local generated capacity impedance.
c. Bus impedance.
d. Transformer and/or reactor impedances.
e. Cable impedances.
f. Equipment impedances.
g. System voltages.
h. Grounding scheme (resistance grounding, solidly grounding, or no grounding).
i. Motor contribution assuming the new and existing motors as shown on the plans all
running at the same time.
3. Calculations:
a. Determine the paths and situations where short circuit currents are the greatest.
Assume bolted faults and calculate the 3-phase and line-to-ground short circuits of each
case.
b. Calculate the maximum and minimum fault currents.
c. A discussion section evaluating the adequacy or inadequacy of the equipment method of
calculation and formulas used such that all calculations can be verified manually by the
ENGINEER, with recommendations as required for improvements to the system.
d. Any inadequacies shall be called to the attention of the ENGINEER and recommendation
made for improvements.
e. Six (6) bound copies of the completed short circuit study shall be submitted to the
ENGINEER.
2.04 RELAY COORDINATION STUDY
A. As a minimum, the coordination study for the power distribution system shall include the
following on 5-cycle, log-log graph paper:
1. The time-current coordination analysis shall be performed with aid of a digital computer.
a. Time-current curves for each device shall be positioned to provide for maximum
selectivity to minimize system disturbances during fault clearing, but still maintain a low
incident energy level. Where selectivity cannot be achieved, the ENGINEER shall be
notified as to the cause.
2. Time-current curves for each device shall be positioned to provide for maximum selectivity to
minimize system disturbances during fault clearing. Where selectivity cannot be achieved,
the ENGINEER shall be notified as to the cause.
3. Time-current curves and points for cable and equipment damage.
4. Circuit interrupting device operating and interrupting times.
5. Indicate maximum fault values on the graph.
6. Sketch of bus and breaker arrangement.
7. Six (6) bound copies of the completed relay coordination study shall be submitted to the
ENGINEER.
2.05 ARC FLASH HAZARD ANALYSIS
A. The study shall be performed in accordance with the NEC and all applicable OSHA, ANSI, and
IEEE standards.
Electrical Power System Studies 26 05 73.01-5
DRP09328