Two UPS Parallel Redundant Solution:
We use the two UPS to make the 1+1 parallel redundancy to ease analysis as shown in figure 1. The sum of all loads are less than 100KVA, the output voltage of two UPS connect directly with the output of distribution cabinet and then supply the power to the loads through the switch Q. if it a dual supply load it can separately lead a wire to the load from the distribution cabinet, meanwhile, it can be satisfied with the input condition of the dual supply load. As shown in the S3, S4.
Reliability Analysis of Two UPS Parallel Redundant Power Supplying:
In order to have an approximate value concept of the reliability, here just discuss the UPS itself parallel operation, because those essential breaker switches are necessary whatever they are supplied the power by any modes they are the same, so they don't need to be considered. Here just discuss the different parts if the reliability r =0.99 of every UPS, for simplicity, we temporally think the reliability of two UPS are equal we can make the dual 1+1 parallel redundant power supplying reliability of model graph, as shown in figure 2. 
At this time, the reliability of power supplying system is R2: 
Unreliability Q = 1 - reliability = 1-0.9999 = 0.0001, the unreliability is one in ten thousand, failure rate is also about one in ten thousand. After the dual parallel redundancy the reliability of system increases two orders of magnitude which the reasons can decrease the MTTR (Mean Time To Repair) to the minimum in the usability expression.   
UPS Parallel Redundancy Basic Operation Principle:
 Normal Operation Status:
The loads are supplied the power by the rectifier--inverter of UPS-A and UPS-B, meanwhile they will charge the each battery unit, every inverter of UPS will undertake 50% loads on the operation. 
UPS Maintenance Online:

When one of UPSs is on the failure (for example UPS-A) it will automatically quit out the operation the rest one of UPS will undertake the 100% loads on the operation. For the broken-down UPS, we can cut off its Q1, Q2, Q3, Q4, Q5 and so on to separate the switches for the safe maintenance. It will operate again after the maintenance its status is as stated above.       
Even when the UPS isn't fault it also can use this type of status to maintain internally, for example: cleaning the dust, screwing down the connection parts, testing or changing the batteries etc.

UPS Parallel Redundancy Solution Diagrams:
Power Distribution Diagram: