Pump efficiency impact on transient results

Product(s): HAMMER
Version(s): V8i, CONNECT Edition
Area: Calculations


How / why does the motor efficiency effect the Transient results for a pump that is shut down? 


The motor efficiency of a pump impacts the overall efficiency of the pump, which is a factor in the transient representation of the pump, specifically when changing the electrical torque of the pump. The pump’s electrical torque is changed during a transient simulation when using either the “shut after time delay” transient pump type, or when using the “variable speed” transient pump type with “torque” as the control variable.

The “shut after time delay” transient pump type simulates the electrical torque instantly dropping from the initial value to zero. With "torque" selected as the control variable with the “variable speed” transient pump type, you are controlling the electrical torque over time. The efficiency of the pump is a factor in the initial torque of the pump (see related article below), which is in turn a factor when that torque changes. Using the example of shut after time delay, changing the pump efficiency changes the initial torque and thus the magnitude of the drop in torque that occurs when the pump “trips”.

If your pump does not operate at 100% speed in the initial conditions (that is, the initial calculated relative speed factor is less than 1.0), you should check the "is variable speed drive" in the "motor" tab of the pump definition, and populate the speed vs. efficiency curve. This enables you to properly account for the change in efficiency characteristics as the speed changes (rather than using the static efficiency curve for all speeds) and thus ensures that you are using the most accurate efficiency value. In some cases such a change in efficiency with respect to speed may not have a large impact on the transient results, but in other cases it may have a notable impact.

See Also

Calculating Nominal Torque for a Transient Pump Startup or Variable speed

User notification: "Pump Efficiency must be between X% and Y% inclusive."