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38 E L EC TR I C AL CONNEC T I ON
AU T UMN 20 1 6
PARDON THE INTERRUPTION
T
his article deals with the static
uninterruptible power supply
(UPS), the rotary storage type
(RUPS) and the diesel rotary storage
type (DRUPS).
The accent is on large systems –
500kW and higher. Almost invariably,
these are used in tier IV redundant
power supplies.
Although redundancy is imperative
for failsafe conditions, the many
ways in which it is achieved are not
discussed because much depends on
individual sites.
The Uptime Institute – an independent
advisory organisation focused on
improving the performance, efficiency
and reliability of critical infrastructure
for the information economy – defines
four levels:
> Tier IV:
Fault intolerant site
infrastructure.
> Tier III:
Concurrently maintainable site
infrastructure.
> Tier II:
Redundant capacity components
site infrastructure (redundant).
> Tier I:
Basic site infrastructure
(non-redundant).
> Tier IV:
Guaranteeing 99.995% availability.
> Tier III:
Guaranteeing 99.982%
availability.
> Tier II:
Guaranteeing 99.741%
availability.
> Tier I:
Guaranteeing 99.671% availability.
Tier IV has all components fully fault
tolerant, including uplinks, storage,
servers, plus heating, ventilation and
air-conditioning.
Although defined in IT terms,
operating theatres, dialysis centres,
etc, can be subject to the same
requirements. Tier IV – in addition to
TECHNICAL ASPECTS OF
UNINTERRUPTIBLE POWER
SUPPLIES WILL BE OF INTEREST
TO ELECTRICAL CONTRACTORS.
PHIL KREVELD
PROVIDES
AN OVERVIEW.
Figure 1: The double conversion (left), and delta conversion schemes.
Figure 2: A flywheel-backed, double conversion UPS. (Source VYCON VDC.)
LET’S GET TECHNICAL
Bypass Mode
Bypass AC source
Normal Mode
Storage Energy Mode
Normal AC source
Static Bypass Switch
Rectifier/
Charger
Inverter
Critical Load
Bypass AC source
Bypass Mode
Normal Mode
Stored Energy Mode
Mains
Series xf
Battery
Static Bypass Switch
Series (Delta)
Converter
Static
Switch
Parallel
Converter
Critical Load
Critical AC Output
DC BUS
Automatic
Transfer
Switch
Static Bypass
Rectifier
AC/DC
Inverter
DC/AC
Genset
AC
Utility
AC
Flywheel
DC
AC