Direct-on-line starting

Direct on-line starting (DOL) Reduced voltage starting... 

When the maximum kW rating of an induction motor is reached for direct-on-line starting, it becomes necessary to introduce an alternative method of starting the motor. There are several methods used in the oil industry. The object is to reduce the starting current drawn from the supply during all or part of the mn-up period. There are two basic approaches that can be used -... 

Direct-on-line starting of these large motors can cause several problems with the performance of the generator protection relays, for example -... 

From the results it can be seen that direct-on-line starting of the motor is only just possible when only one generator is available. High volt-drops occur during the starting period. However, several corrective measures can be taken -... 

This sub-section develops a simple graphical method for quickly estimating volt-drops for direct-on-line starting situations. The following data forms the basis of the graphical results ... 

The power supplies to the FW pumps are utiliang static converter units which eliminate the large inrush currents at direct-on-line starting and therefore reduces the requirements on voltage stability (or rather short circuit strength) of the auxiliary power supply system busbars. Feedwater flow control is achieved by adjusting feed pump speed and the feedwater flow control valves. 

The torque available from the main motor varies according to the method of start up. whether it is star-delta or direct-on-line. A motor connected in star produces a starting torque one third of that provided when starting direct-on-line. Direct-on-line starting torque can be two and a half times the motor s full load torque, with a starting current of six times full load current. 

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