End of curve power requirement (to determine motor rating)

End of curve power requirement (to determine motor rating)

http://www.cheresources.com/invision/topic/11994-standby-centrifugal-pump-driver-sizing/

지금까지 모터 Rating은 API 610 (11th ed.)의 7.1.4 항목에 따라서만 결정되는 줄 알았다. 하지만 역시 이는 minimum requirement일 뿐이었다. 그동안 Vendor 견적에 표시된 파워가 과도하다고 생각했던 것은 판단 미스.

최근 진행중인 프로젝트의 FEED에 다음과 같은 언급이 있었다.

"Motor rating of pumps shall cover end of curve power on pump performance curve if specified on data sheet or if automatic start is specified."

Automatic Start의 숨겨진 의도가 무엇인지 알아보기 위해 Google 검색을 해보았더니 아래와 같은 의견이 있었다. Level Control 되거나 병렬운전되는 경우에는 End of Power에 맞도록 모터가 선정되어야 한다는 것. 가만히 생각해 보니 거의 모든 펌프가 해당되는 듯.

1. Pumps under level control may be required to pump more liquid when unexpected surge (or change of process conditions upstream of the drum feeding the pump) cause high inflow of liquid, and subsequently high liquid level in the drum. In order to avoid upsets - or even process shutdown, depending on severity of high level in the drum - these pumps would need to evacuate extremely high volumes or liquid and probably this will be happening through 100% open level control valve. This is just by itself an extremely high-flow condition calling for the motor capable of delivering the required power to the pump.

2. Pumps operating in parallel are a somewhat similar example, in the sense that unexpected shutdown of the first pump will automatically put high flow on the second pump that has remained in operation. Again, large flow that needs to be handled but now with a single pump, will also call for more power delivered by the motor.