supply
36
UNINTERRUPTIBLE POWER SUPPLIES
UPS Topologies - On-Line Systems
Bypass – split bypass configuration
Output to
Critical
Load
Rectifier
DC Bus
Static Switch
Normal
operation
Inverter
Battery
Bypass
Output to
Critical
Load
Rectifier
DC Bus
Static Switch
Inverter
Battery
UPS failure
(on bypass)
Other benefits of UPS OEM support
Working with the UPS OEM’s support team can bring further
benefits instrumental in securing UPS safety and reliability.
These include management of factory upgrades, remote
system monitoring, and spare parts provisioning.
Factory upgrades
The OEM will be the only centralised repository for field
operation
failure UPS
statistics
of their particular UPS models.
Figure
4.5: and
On-line
Operation
Where these affect performance and reliability the end-user
will benefit greatly from the OEM’s continuous improvement
processes. If the full traceability path of the equipment is
intact, equipment upgrades that involve life safety will be
initiated by the OEM. However, end users will only be included
in such performance-related upgrades through a contract
with the OEM or their authorised service agent. There are
generally no processes that allow a third-party maintenance
organisation to keep up-to-date with such initiatives.
The UPS Handbook
Remote monitoring
Modern UPS monitoring systems can constantly monitor UPS
systems to automatically detect any error or alarm messages,
even on remote locations with no on-site personnel. If an
incident is detected, the system can automatically connect
the service centre network via email, transmitting a status
message and providing any available details relating to the
fault, as well as a device identification string. Service centre
personnel can then liaise with the company’s field team, who
can integrate and manage the UPS, performing all necessary
remote diagnostics before reaching the facility within the
contracted service agreement time frame.
Specialised monitoring services for batteries and for
generators can also be provided, checking each cell’s internal
resistance, temperature and voltage sequentially. The
system can manage equalisation and charging voltages. The
process prevents gassing, dry-out and thermal runaway, and
guarantees battery availability at all times.
Spare parts availability
Access to spare parts is essential for high availability
installations, but those spare parts must be of the correct
generation, complete with any upgrades, 100% compatible
with the installed machine and fully pre-tested. Only the
OEM can guarantee their compatibility and provide a local
inventory that reflects the installed base. This inventory must
support the installed machine for at least 15 years and be
accessible within four hours. A rigorously maintained ‘crash
kit’ system, available to the technician on a 24/7 basis for
each UPS product, is an essential part of a comprehensive
service support contract.
Pulling it all together
Data centre operators are recommended to set up a service
agreement to handle the situations described above, from
preventative maintenance to time-guaranteed emergency
responses. The agreement can bring together all the elements
and resources needed, and package them to suit the facility’s
particular needs and priorities.
An effective service plan is summarised here; it should
comprise annual scheduled preventative maintenance (PM)
visits for both the UPS and its batteries, as well as facilities
for emergency call-outs on demand. Trained engineers and
technicians should be available 24/7, and based close enough
to ensure arrival on-site within contractually-agreed response
times. These personnel should be backed with immediate
access to a comprehensive local spare parts inventory, and
more in-depth technical support if required.
Interested parties should be able to pre-empt UPS
problems as far as possible through remote battery
monitoring and impedance testing, generator monitoring,
and UPS monitoring with monthly trend reporting and 24/7
alarm notifications.
The service plans must be managed effectively, both to
ensure their efficacy, and to maintain accurate budgetary
control. Tasks include maintaining accurate monthly service
records and replacement planning with time and budget
considerations. Fulfilling recommended part replacement
cycles, once agreed, is important.
Good management also depends on profiling a service
contract to each installation’s particular circumstances; the
type and size of the load, and how business-critical it is. Is
29
24/7 coverage needed for 365 days a year? Also, should parts
and labour be included, or treated as chargeable extras?
The ideal number of scheduled preventative maintenance
visits per year depends on the power system topology;
single phase installations can be safely supported with a
single annual PM visit, while three-phase systems warrant
two annual visits. PM visit times – during or outside normal
working hours, or at weekends – should be specified, while
guaranteed response time frames should be established.
Popular choices include 4hr, 6hr, 8hr, end of next working day
or next day.
Staying online
Maintaining a UPS at a high level of availability, and
responding fast on the rare occasions when a problem does
arise, calls for readily available, highly skilled technicians,
backed by appropriate spare parts inventory. This level of
backup can best be achieved by leveraging the resources of
the original UPS supplier, complementing these with support
from the facility’s on-site operational staff where it makes
sense, and managing the overall strategy with a well-tailored
maintenance contract. n
www.networkseuropemagazine.com