4.4
Definitions.
The following definitions of terms shall apply:
a) Uninterruptible Power Supply System - An uninterruptible power
supply system consists of UPS equipment, backup power source(s), environmental
equipment, switchgear, and controls which together provide a reliable,
continuous quality electric power system.
b) Critical Electronic Load - The critical electronic load is that
part of the load that requires continuous quality electric power for its
successful operation.
c) Uninterruptible Power Supply (UPS) - An uninterruptible power
supply (UPS) consists of one or more UPS modules, an energy storage battery,
and accessories as required to provide a reliable and high quality power
supply. The UPS isolates the load from the primary and emergency power
sources and, in the event of a power interruption, provides regulated power
to the critical load for a specified period depending on the battery
capacity. The battery normally has a 15-minute capacity when operating at
full load.
d) UPS Module - A UPS module is the static power conversion
portion of the UPS system and consists of a rectifier, an inverter, and
associated controls along with synchronizing, protective, and auxiliary
devices. UPS modules may be designed to operate either individually or in
parallel.
e) Nonredundant UPS Configuration. The nonredundant UPS
configuration consists of one UPS module with a static bypass circuit and a
battery, and a maintenance bypass cabinet. Upon failure of the UPS module,
the static bypass circuit automatically transfers the critical electronic
load to the primary or emergency source without an interruption to the load
(see Figure 2).
f) "Cold" Standby Redundant UPS Configuration. The "cold" standby
redundant UPS configuration consists of two independent nonredundant UPS
modules with a common battery. One UPS module operates on the line, and the
other UPS module is turned off. Should the operating UPS module fail, its
static bypass circuit will automatically transfer the critical electronic
load to the primary or emergency source without an interruption to the
critical load. The second UPS module is then manually energized and placed
in the bypass mode of operation. To transfer the critical load, external
make-before-break nonautomatic circuit breakers (or contactors) are operated
to place the load on the second UPS bypass circuit. Finally, the critical
electronic load is returned from the bypass to the second UPS module via the
static switch. The two UPS modules cannot operate in parallel; therefore, an
interlock circuit must be provided to prevent this condition (see Figure 3).
UPS modules are to be transferred to and from "cold" standby every three
months. The mode of operation is as follows:
(1) Transfer Circuit Interlock, External Bypass - The two
circuit breakers (or contactors) shall be nonautomatic and motor operated.
Transfer to and from one UPS to the other shall be a closed circuit
(make-before-break) transition and shall be possible only when both UPS's are
in the bypass mode of operation.
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