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


         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.
   177   178   179   180   181   182   183   184   185   186   187