1.3.4.9
UPS System Maintenance
Manual closure of the maintenance bypass switch shall transfer the critical
load from the inverter output to the bypass ac power source without
disturbing the critical load bus. UPS module shall be capable of manual
return to normal operation after completion of maintenance.
1.3.4.10
Battery Maintenance
The battery protective device shall provide the means of disconnecting the
battery from the rectifier/charger and inverter for maintenance. The UPS
module shall continue to function and meet the performance criteria
specified except for the battery function.
1.4
QUALITY ASSURANCE
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NOTE: Reliability and maintainability are relative
terms, and the attainable level will, therefore,
depend upon the type, size, configuration, and
degree of redundancy of the UPS. System
availability is a function of reliability and
maintainability and is defined as the long-term
average fraction of time that a system is
satisfactorily in service. System availability
should be as high as economically feasible and may
be calculated as follows:
A = MTBF/(MTBF + MTTR)
Where
A = Availability
MTBF = Mean Time Between Failures
MTTR = Mean Time To Repair
Nonredundant systems can have a predicted MTBF of
20,000 hours and an actual MTBF of 40,000 hours. On
the other hand, larger redundant systems or
nonredundant systems with available utility power
through a bypass arrangement can have an actual MTBF
of 200,000 hours. A multi-module system with
utility power bypass arrangement will have a higher
MTBF than a single module system with the same
rating.
The designer should give serious thought and
consideration to the question of specifying MTBF and
MTTR. For additional information on the subject
refer to the following:
a. IEEE Std 446, Emergency and Standby Power
Systems for Industrial and Commercial Applications.
b. IEEE Std 493, Design of Reliable Industrial and
Commercial Power Systems.
SECTION 16265A
Page 12
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