Simulating the process of pumps start-up at an interim oil pumping station
The article deals with simulation of start-up modes at the oil pumping station (OPS) of a pipeline transporting oil with certain flow. It is assumed that all pumps have serial connection, synchronous drive and are started for open (or opening) gate valves. Special asynchronous device (short-circuited start-up cell with a «squirrel cage»-type design) makes the rotor of each pumping unit operate in the synchronism mode. This device operates within 30-45 s and then switches off, after that the rotor angle speed remains constant and equal to a nominal value. Since each pump with serial connection is connected to the main pipeline by means of a by-pass with a non-return valve between suction and injection lines, operation of each pump involves two periods when the interim OPS of the oil pipeline transporting oil with flow somewhat different from zero is started up. The first period - free flow with an open non-return valve. The second period is pressurized, when the non-return valve is closed, and the pump begins to create head. During start-up of certain pumps, pressure reduces in the OPS suction line and increases in the injection line. Start-up of all pumps results in significant pressure drop upstream the station and the possibility of an emergency OPS trip by the factor of minimum permissible pressure in the suction line and disturbance of net positive suction head. The inevitable question is for how long will the OPS be in the start-up mode? What is the amount of maximum pressure drop upstream the station? What is the nature of the transient process that takes place in the pipeline in this case?