When the Cascade Controller is enabled and running normally and the frequency converter issues a trip alarm, the system head is maintained by staging and

destaging fixed speed pumps. To prevent frequent staging and destaging and minimize pressure fluxuations, a wider Fixed Speed Bandwidth is used instead of

the Staging bandwidth.

5.1.9 Pump Staging with Lead Pump Alternation

With lead pump alternation enabled, a maximum of two pumps are controlled. At an alternation command, the lead pump will ramp to minimum frequency (fmin)

and after a delay will ramp to maximum frequency (fmax). When the speed of the lead pump reaches the destaging frequency, the fixed speed pump will be cut

out (destaged). The lead pump continues to accel and then decels to a stop and the two relays are cut out.

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 accels to maximum speed

and then down to minimum speed when decelling 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 (fmin) for a programmed amount of time, with a fixed speed pump running, the lead pump contributes

little to the system. When the programmed value of the timer expires, the lead pump is removed, avoiding a deal heat water circulation problem.

5.1.10 System Status and Operation

If the lead pump goes into Sleep Mode, the function is displayed on the keypad. 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 keypad. 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.

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AF-600 FP Design Guide

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