Overvoltages produced in line due to transferring from and to diesel engine

When a neutral pole is switched during a commutation between two sources (like a line to GE commutation and vice versa after a line failure), and a third source is installed downstream (like a UPS), dangerous neutral to ground and line to ground overvoltages can appear. These overvoltages can produce problems in the installation process such as differential tripping and the blocking or destruction of equipment etc. The solutions depend on the neutral scheme; they can affect the differential protections upstream of the commutation or infringe the electrical normative rules. That´s why it is very important to take special care during the installation project in order to prevent any undesired effects of the commutation. The purpose of this paper is therefore to describe this phenomenon and its consequences to the installation, giving the solutions and their associated problems, i.e. normative violations or differential protections.