Soft Start of Submersible Pumped Oil Wells

Abstract

Cyclic operation of submersible pumping is considered undesirable because of the start-stop characteristics of the installation. ''Across-the-line'' starting results in large current surges, typically five to eight times running current. Such surges can damage the motor and its cable and also cause line voltage irregularities. Also, stopping can result in significant amperage and voltage spikes. Because of this, most operators are very reluctant to start and stop a submersible pumping installation any more often than absolutely necessary. This creates design problems in sizing the pump. Reduced-voltage starting should minimize the severe strain imposed on the electrical system by an instantaneous start. A reduced-voltage solid-state starter using six silicon-controlled rectifiers was tested between Nov. 1981 and March 1982. The current surge on start was limited to about 2.5 times full-load amperage. The time required to bring the motor to full speed was increased from about 0.25 seconds to 1.3 seconds. The well was cycling on-off about six times per day. The unit was start-stopped about 900 times during the test. A prototype production model is available.