Page 155 - Uninterruptible Power Supplies

Static Uninterruptible Power Supplies
Static Uninterruptible Power Supplies 153

Voltage regulation 1.5 percent
Voltage regulation with 100 percent load variation 5 percent
returning to nominal within 40 ms
Overload 110 percent for 1 h
Overload 120 percent for 10 min
Overload 150 percent for 1 min
Exceeding overload conditions necessitates the system reverting to
mains operation via the static switch
Crest factor 3:1 at full load
Frequency 50 or 60 Hz when working with internal oscillator (inde-
pendent of mains) 0.01 percent
When working with mains system will accept 3 percent outside
these set tolerance figures will revert to working on internal oscilla-
tor which means the static switch is inoperable.
1
Frequency slew rate ⁄2 Hz per s
For three phase systems:
Voltage phase shift with
Balanced load 120 1 degree
Unbalanced load 120 2 degrees
Efficiency at full load 93 percent; at 50 percent load 92 percent
Ambient temperature of operation 0 to 40°C.
Relative humidity (no condensation) 95 percent
Maximum altitude 1000 m
Noise level nowadays is much improved due to the use of modern
switching techniques and wound components and you may expect 70 to
75dba at 1 m from the unit for systems up to 1 MVA.
The dc voltage for UPS systems depends for large systems on the
incoming mains supply in most cases. For example, 400-V three-phase
supply would use 180 cells, giving a float voltage of 410 V.

Static Switches
Static switches are used as shown in Fig. 5.1 to provide a virtually
instantaneous transfer of power between supplies.
Most modules now use straight static switches with a mechanical
switch in parallel (see Fig. 5.12).
Under normal operation the power is fed via rectifier/inverter static
switch to the load, with the mains frequency controlling the operational

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.