Specifications

NAIROBI OPERATIONAL HUB
UNOPS Building, UN Lane, Off UN Avenue Tel: [phone]
P.O Box 783,Village Market, 00621 E-mail: [e-mail]
Nairobi, Kenya Website: www.unops.org
UNOPS is ISO 9001 certified
3.12 Short Circuit and Protective Device Coordination Studies
A. It is the responsibility of the Contractor to check the information given in the
Project Documents about voltages and frequency with the Electric Power
Company and confirm the data in writing to the Supervising Engineer.
B. Conductors and equipment shall be protected against overcurrent in accordance
with their rated ampecities. An overcurrent device shall be connected at the point
where the conductor or equipment to be protected receives its supply.
C. Provide four (4) brochures, each of which shall include complete short circuit and
protective coordination studies, complete with device coordination time-current
curves for the entire power distribution system.
D. In the short circuit study, provide calculation methods and assumptions, the base
per unit quantities selected, one-line diagrams, source impedance data including
power company system characteristics, impedance diagrams, typical calculations,
tabulations of calculation quantities and results, conclusions, and
recommendations. Calculate short circuit interrupting and momentary (when
applicable) duties for an assumed 3-phase bolted fault at each medium voltage
switchgear line-up, unit substation medium voltage terminals, low voltage
switchgear line-up, switchboard, motor control center, distribution panel board,
pertinent branch circuit panel board, and other significant locations throughout the
system. Provide a ground fault study for each medium voltage system, including
the associated zero sequence impedance diagram. Include in tabulations fault
impedance, X to R ratios, asymmetry factors, motor contribution, short circuit
KVA, and symmetrical and asymmetrical fault currents.
E. In the protective device coordination study, provide time-current curves on the
Log-Log sheets indicating the coordination proposed for the system, centered on
conventional full-size log-log forms. Include with each curve sheet a complete
title and one-line diagram with legend identifying the specific portion of the
system covered by that particular curve sheet. Include a detailed description of
each protective identifying its type, function, manufacturer, and time-current