After a time delay, the relay for the fixed speed pump cuts in (staged) and this pump becomes the new lead pump. The new lead pump ramps up to
maximum speed and then down to minimum speed. When ramping down and reaching the staging frequency, the old lead pump is now cut in (staged)
on the mains as the new fixed speed pump.
If the lead pump has been running at minimum frequency (f
min
) for a programmed amount of time, with a fixed speed pump running, the lead pump
contributes little to the system. When programmed value of the timer expires, the lead pump is removed avoiding water heating problems.
6.1.9 System Status and Operation
If the lead pump goes into Sleep Mode, the function is displayed on the Local Control Panel. It is possible to alternate the lead pump on a Sleep Mode
condition.
When the cascade controller is enabled, the operation status for each pump and the cascade controller is displayed on the Local Control Panel. Information
displayed includes:
• Pumps Status, is a read out of the status for the relays assigned to each pump. The display shows pumps that are disabled, off, running on the
frequency converter or running on the mains/motor starter.
• Cascade Status, is a read out of the status for the Cascade Controller. The display shows the Cascade Controller is disabled, all pumps are off,
and emergency has stopped all pumps, all pumps are running, fixed speed pumps are being staged/destaged and lead pump alternation is
occurring.
• Destage at No-Flow ensures that all fixed speed pumps are stopped individually until the no-flow status disappears.
6.1.10 Cascade Controller Wiring Diagram
The wiring diagram shows an example with the built in BASIC cascade controller with one variable speed pump (lead) and two fixed speed pumps, a
4-20 mA transmitter and System Safety Interlock.
6 Application Examples VLT
®
AQUA Drive Design Guide
164
MG.20.N5.02 - VLT
®
is a registered Danfoss trademark
6
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