Page 182 - Uninterruptible Power Supplies
P. 182
Rotary UPS Systems
180 Chapter Six
Q3
Q1 Q2
Figure 6.11 Hitek basic circuit configuration.
Mains failure
Mains
voltage
1500 rpm
Output
voltage
50.5 Hz
free-wheel clutch engaging
50 Hz Line
49.5 Hz
1 sec Diesel start
Figure 6.12 Effect of loss of mains at full load.
start-up procedure, a delay of approximately 0.5 s is utilized. The delay
can be even longer than this as the system has a sensitive voltage mon-
itoring system which will differentiate between a deep voltage excur-
sion and minor ones which in some instance will be discounted. Overall
system efficiency may be as high as 97 percent.
Figure 6.12 illustrates the varying output voltage and frequency of a
changeover at full output power.
The system may also be used to feed noncritical loads. In Fig. 6.13,
Fig. 1 illustrates operation with mains present, noncritical load being
fed directly from mains supply. Fig. 2 illustrates loss of mains and the
critical load being fed without interruption. At this stage diesel has not
achieved full running of the system and noncritical load is not fed. With
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