If I want to switch multiple UPS which are driving load but the switching of each UPS depends upon the load demand (Load Current). In the given figure I have explained this whole scenario.
If I want to switch the other two UPS according to load requirement then either relay kind of phenomena would be better or logic switches would be okay?
Kindly also give an idea of rough switching model?
UPS 2 and UPS 3 are you need to switched on, at the load level 1 and load level 2. From C.T secondary using STD resistance with peak detector circuit(using 741 Ic), current preposnat voltage signal could be obtained . Feed it to the level detector circuits(using OPAM 741) both one and two, whose refarence level setting, is set for load 1 and load 2 .With only output from level 1 detector UPS 2 is to be made ON. If out put is from both UPS 3 needs to made on(obtained,using AND gate). For making UPS 1 and 2, ON, use switching transistor, putting relay with isolating transformer( Circuit breaker coil) in collector, with Vcc, with emitter ground, applying signal on base. (Can refer my papers)
Mr. Adil,
I had a similar problem to yours. I used a kind of comparitor (IC) which only works for specific load levels, i.e. you can adjust it so that when load is under some level say 10 A, Only UPS1 works, and when load exceeds 10 A, UPS 1 and 2 works, if exceeds 20 A, UPS3 also works.... Unfortunatel I forgot the number of that IC, but ask any electronic guy about that I think they call it window comparitor...
Besides, I don't advice you to use relay, use high power transistors so that switching will be carried out electronically. This also has the advantage if the load at some instances is oscillating around a critical value (10 A), relays will be bothered...
For switching, multiple UPS as load rises, you need to AND the every(higher level) out put signal of level detectors (for higher load setting), with the previous AND gated output(as to increase number of UPS). The circuit for reference voltage input(at different higher level) for different higher level of load, and making ON the UPS will remain same. Twenty years back, I developed a 8085 based module for load control," Microprocessor based load shedding controller............" the paper may help, if you wants to go for module.
Relays are not a good solution so electronics is a must. Following need to be considered in this application
1. Synchronization
2. load sharing dynamically
3. hunting elimination with hysteresis setting of changeover logic as load increases and decreases
4. optional ...strategy for loss minimization .. if load is shared i^2r loss will be less
5.Time of transfer maybe critical
6, type of Ups (rotary / static etc..
hope it helps..
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