Looking at parallel pump capacities when planning standby needs is comparing apples to oranges.
The number of pumps with the percentages you indicate say you are considering standby capacity, which is evaluated based on the improved reliability provided by n, n+1, n+2 spares X spare capacity provided by n+1, n+1, n+2, etc.
Standby capacity is decided by the amount of money lost or other penalties imposed upon failure to meet contract deliveries during pump failure VS cost of pump configuration. Note that penalties could be non-monetary, such as when a pump to a life support system fails, but for evaluation purposes, we will only consider penalties in terms of monetary cost.
In most cases, energy used over the lifetime is at the very least an order of magnitude greater than capital cost, so you must design all pumps for their proportion of 100% at equal BEP efficencies. You do not mention if BEP efficiency varies significantly, so I will assume the same efficiency is achievable at all proportional BEPs in any configuration. Since you are always trying to pump 100% in all cases, and the same efficiency for all pumps is possible, the energy cost of pumping is equal for all configurations and the energy cost variable drops out of consideration.
Secondly, contract penalties are also likely to exceed the capital cost. Contract or other penalties will be incurred upon failure of a certain number of pump units such that pumping capacity drops below 100% of design flow. As such it is the reliability of the pump configuration in their ability to deliver at least 100% of design flow that you must evaluate against the cost of providing n, n+1, n+2, n+3 pumps.
In my experience, it is seldom economic, nor necessary to provide more than 3 x 50%, but if you have an extremely critical need to deliver 100% for 99.995% of the time, it is possible that you could need more.
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"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that
99.99% for pipeline companies)