Deragging Overview - Danfoss VLT AQUA Drive FC 202 Design Manual

Product Features
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 ) for a programmed amount of time, with a fixed-
min
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 water heating
problems.
5.5.1.2 System Status and Operation
If the lead pump goes into sleep mode, the function is
displayed on the LCP. It is possible to alternate the lead
pump on a sleep mode condition.
When the cascade controller is enabled, the LCP shows the
operation status for each pump and the cascade controller.
Information shown includes:
•
Pump status is a readout of the status for the
relays assigned to each pump. The display shows
pumps that are disabled, off, running on the
drive, or running on the mains/motor starter.
•
Cascade status is a readout of the status for the
cascade controller. The display shows the
following:
- Cascade controller is disabled.
- All pumps are off.
-
An emergency has stopped all pumps.
- All pumps are running.
- Fixed-speed pumps are being staged/
destaged.
-
Lead pump alternation is occurring.
•
Destage at no-flow ensures that all fixed-speed
pumps are stopped individually until the no-flow
status disappears.

5.6 Deragging Overview

The purpose of the deragging feature is to free the pump
blade of debris in waste-water applications so that the
pump operates normally.
A deragging event is defined as the time when the drive
starts to derag to when the deragging finishes. When a
derag is started, the drive ramps first to a stop and then
an off delay expires before the first cycle begins.
MG22B102
Design Guide
Speed
+/- Derag
Speed:
Par.: 29 -13
Par.: 29 -14
0 Hz / RPM
Illustration 5.12 Derag Function
If a derag is triggered from a drive-stopped state, the first
off delay is skipped. The deragging event consists of
several cycles. One cycle consisting of 1 pulse in the
reverse direction followed by 1 pulse in the forward
direction. Deragging is considered finished after the
specified number of cycles have completed. More specif-
ically, on the last pulse (it is always forward) of the last
cycle, the derag is considered finished after the deragging
run-time expires (the drive is running at derag speed). In
between pulses, the drive output coasts for a specified off-
delay time to let debris in the pump settle.
NOTICE
Do not enable deragging if the pump cannot operate in
reverse direction.
There are 3 different notifications for an ongoing
deragging event:
•
•
•
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Derag
function
activated
Derag O Delay:
Par. 29 -15
Deragging Run Time : Par . 29-12
1 Cycle
Number of Cycles : Par . 29 -10
Status in the LCP: Auto Remote Derag.
A bit in the extended status word (bit 23, 80 0000
hex).
A digital output can be configured to reflect the
active deragging status.
5 5
23