Eliminating Power Transients When Switching Large Motors or Transformers during Power Outages or Engine Testing White Paper
Select the right transfer switch to avoid transient problems
When large inductive loads — loads consisting of large motors and/or transformers — are transferred between two live power sources, e.g., a normal source (1) and an emergency source (2), which may not be in synchronism, efforts should be made to eliminate line current transients that occur during this type of switching. This situation exists either when retransferring from the emergency source to the restored normal source after a power outage, or transferring in either direction while testing the emergency power system. Through the proper selection of transfer switches, emergency/backup power system designers can dramatically reduce and effectively mitigate these transients and the problems associated with them.
Among the available options for switching large inductive loads, the dual-operator transfer switch is believed by most industry experts to be the most reliable. For many, it is the best option for eliminating any excessive line currents that could exceed the instantaneous trip settings of protective devices in the system.