What to do if you are afraid of the dark?

Plants rely more and more on electrical power to manage most of the control functions. A large part of those functions relate to safety and they must run all the time, even in case of loss of the main electrical power. Backup power systems based on uninterruptable power supplies (UPS) and gensets are the most common way to ensure this continuity of operation. In remote locations or offshore with islanded power plants, these emergency units are also dedicated to blackstart operations. They are the first units to be started, supplying power to the main generation starting system. But, as any power production machine, they have response time, loading capabilities and different limits of use. The aim of this paper is to present recommendations for the design of electrical backup systems based on characteristics of the different technologies that can be used. Different architectures of the overall backup power system like central versus distributed will be discussed in relation to the level of operational safety they can provide.