PPE
Millennium Court
Ellerbeck Way
Stokesley
North Yorkshire
TS9 5JZ
Tel: +44 (0)1642 714661 Fax: +44 (0)1642 714662
Case Study 1: Incorrect Sizing of UPS
The problem:
A potential client requested a price to supply a 15kVA UPS to support a load current of 29 Amps.
The findings:
Before supplying the UPS, we recommended the load be monitored to determine correct sizing. One of our UPS
specialists monitored a crest factor of over 4.5:1 and a peak current in excess of 185 Amps.
The solution:
UPSs in general support critical IT load. Switch mode power supplies (as found
in IT equipment) have high crest factors. As the majority of UPSs are only rated
for crest factors of 2.5:1 it is critical that correct sizing of UPS be undertaken by
specialists. In this case, the installation of a 30kVA UPS to facilitate the high crest factor of
this load was required.
The results:
The correctly sized UPS was supplied and installed.
Case Study 2: UPS Fault Goes Undetected
The problem:
A commercial site had a UPS installed which was some years old.
The load being supplied by the UPS was showing severe signs of distress,
particularly by the regular failure of power supply units within IT equipment.
However, as the UPS had been recently maintained by the manufacturer, the client was
unsure where the problem lay.
The findings:
After being called in to investigate, one of PPE's specialists undertook
monitoring on the UPS input and output. Distortion on the input current waveform
indicated an SCR failure. The lack of a bypass facility on the existing UPS made a shutdown necessary. Only a very restrictive shutdown period was available.
The solution:
The existing UPS was deemed uneconomical to repair and therefore a new,
more efficient UPS was installed. We recommended a bypass facility for the UPS should be installed to make a
future shutdown unnecessary. We installed the replacement UPS and bypass faciilty within the shutdown
period available.
The results:
Increased efficiency levels of the new UPS ensured payback within 3 years. Since the installation, no further problems with the IT equipment have been
reported. The additional bypass facility ensures that any future upgrades or repairs can be
performed without the need for a shutdown.
UPSs in general support critical IT load. Switch mode power supplies (as found
in IT equipment) have high crest factors. As the majority of UPSs are only rated
for crest factors of 2.5:1 it is critical that correct sizing of UPS be undertaken by
specialists.