OPERATION
VFD Discharge Pressure Sensing
14
OPERATION
VFD Discharge Pressure Sensing
Refer to the VFD Owner’s Manual for additional details as setup instructions will vary.
•
The pump system maintains a set discharge pressure by comparing it to a user defined setpoint. Then
the system adjusts the speed of the pump motor VFDs to achieve that setpoint.
•
During no flow periods, the VFDs will stop the pump motors and enter standby mode. The system will
stay in the ready state until the discharge pressure drops and water demand resumes. Refer to
“Standby Activation Speed” on page 15
•
The lead pump will be the first pump dispatched to meet the pressure setpoint established in the VFD.
•
The pump motor speed will be bounded by the minimum and maximum speed settings established in
VFD parameters the speed driven by the PID control algorithm in the VFD.
Assist Pump Speed Parameters
Three factory preset VFD parameters control the speed at which additional assist pumps are activated or
deactivated to aid the lead pump. Refer to the VFD Owner’s Manual for additional details as setup instruc
-
tions will vary. Within the Master VFD Control HMI they are:
1.
Assist Pump Settling Time:
the wait period, in seconds, before assist pumps are activated or deacti
-
vated.
2.
Assist Pump Start Speed:
the maximum speed the lead pump will run without more assistance before
the Assist Pump Settling Time is reached.
•
If the lead pump is operated above the Assist Pump Start Speed for a period of time exceeding the
Pump Settling Time, the Master VFD will start a lag pump and drive both at the same speed.
•
In Triplex and Quad packages, additional pumps will be activated to assist if needed.
3.
Assist Stop Speed:
the minimum speed at which the assist pumps will run before the Assist Pump Set
-
tling Time is reached.
•
Once the pumps operate at a speed lower than the Assist Pump Stop Speed for a period of time
exceeding the Pump Settling Time, assist pumps are deactivated one at a time.
•
This parameter may be adjusted to have the assist pumps stay on longer or shut down sooner.
NOTE:
Assist Stop Speed should be higher than the Standby Activation Speed setting. Refer to
“Standby Activation Speed” on page 15
All three parameters can be viewed or modified in the VFD Parameter Screen 2 of the Master VFD Control
HMI. When setting the parameters, be sure to consider pump efficiency curves, pump operating ranges, and
any constraints to minimize pump run times. Refer to
“VFD Parameter Screens 1 & 2” on page 9
.
Refer to the VFD Owner’s Manual for setting the speed parameters individually.
