The use of a frequency converter for the activation of a stand-by diesel generator of a ship’s powerplant

Abstract

The paper considers the ways of accelerating the activation of a ship's stand-by diesel generator by using advantages of a vector controlled frequency converter during the activation for obtaining additional power reserve in ship's automated electrical powerplants. The activation of the stand-by generator and putting it into operation can often be needed for startup of ship’s powerfull consumer, in the cases of failures in running equipment, accidents, in an emergency, or changes in navigation conditions, as well as while fixing the vessel location during the dynamic positioning. The main obstacle to such an activity is the fact that the complete sequence of operations (stages) should be performed for this: pre-start preparation of a diesel engine, the activation and acceleration of the unit to a certain speed, the synchronization of the started generator with the other running generators through the fuel regulating devices of the diesel engine and sharing the load among the generators in case of successful connection of the standby one to the bus bars of the powerplant main switchboard. The duration of listed stages can be from 15 – 20 seconds to several minutes, and therefore such delay may be unacceptable. Existing methods of speeding up the mentioned stages are not considered together as a whole. The proposed solution is to organize the inverter activation of the stand-by diesel generator controlled by a specialized device or by the part of the power plant control system, at the end of which all previously listed stages of putting the unit into operation will be completed and the ship’s powerplant will be ready for accepting the additional load. The specialized device should be accommodated to processing input data in real time during the activation. It forms control commands for the frequency converter, generator voltage regulator, regulator of diesel engine speed and air circuit breaker of the generator. The device also calculates (determines) the moment of switching on a breaker, as well as the magnetic flux of the generator and the torque moment of the diesel engine by predicting the load of any of the running in parallel generators from the assumption that the standby generator is connected and sharing of active and reactive load components between all generators are over. In other words, the spatial position and magnitude of the EMF vector of generator which will be connected to bus bar immediately before the breaker is closed must match the values that have been determined as a result of the forecast of the power plant operating mode with the stand-by generator already in operation, taking into account changes caused by transition processes. Redistribution of active load components of generators to equal levels after closing the breaker will occur due to a certain supply of kinetic energy of the unit rotating parts. The proper amount of kinetic energy is provided by the commands of the specialized device during the controlled activation of the disel generator based on the forecast of load changes.