Pump Staging With Lead Pump Alternation; System Status And Operation - Danfoss FC 102 Design Manual

Application Examples
system. The alternation of the lead pump can take place at
a command signal or at staging (adding lag pump).
The command can be a manual alternation or an
alternation event signal. If the alternation event is selected,
the lead pump alternation takes place every time the
event occurs. Selections include whenever an alternation
timer expires, when the lead pump goes into sleep mode.
Staging is determined by the actual system load.
25-55 Alternate if Load <= 50%= 1, if load >50% alternation
does not happen. If load <=50% Alternation happens.
When 25-55 Alternate if Load <= 50% = 0, Alternation
happens no matter with Load. Total pump capacity is
determined as lead pump plus lag speed pumps capacities.
Bandwidth Management
In cascade control systems, to avoid frequent switching of
fixed speed pumps, the desired system pressure is kept
within a bandwidth rather than at a constant level. The
7 7
staging bandwidth provides the required bandwidth for
operation. When a large and quick change in system
pressure occurs, the override bandwidth overrides the
staging bandwidth to prevent immediate response to a
short duration pressure change. An override bandwidth
timer can be programmed to prevent staging until the
system pressure has stabilised and normal control
established.
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 minimise pressure fluxuations, a wider fixed
speed bandwidth is used instead of the staging
bandwidth.
7.1.9 Pump Staging with Lead Pump
Alternation
f
max
Destaging freq.
f
min
f
max
Staging freq.
Illustration 7.8 Pump Staging with Lead Pump Alternation
126
Design Guide
Alternation
command/PID stops
Mains operation
PID contr.
starts
Mains operation
5s
Danfoss A/S © Rev. 06/2014 All rights reserved.
With lead pump alternation enabled, a maximum of 2
pumps are controlled. At an alternation command, the
lead pump ramps to minimum frequency (f
delay will ramp to maximum frequency (f
speed of the lead pump reaches the destaging frequency,
the fixed speed pump is cut out (de-staged). The lead
pump continues to ramp up and then ramps down to a
stop and the 2 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 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 a deal heat
water circulation problem.

7.1.10 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 operation
status for each pump and the Cascade Controller is
displayed on the LCP. Information displayed includes:
•
Pumps 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
frequency converter or running on the mains/
motor starter.
•
Cascade Status, is a readout of the status for the
Cascade Controller. The display shows the
Time
Cascade Controller is disabled, all pumps are off,
and emergency has stopped all pumps, all pumps
are running, fixed speed pumps are being
staged/de-staged and lead pump alternation is
occurring.
Time
•
De-stage at No-Flow ensures that all fixed speed
pumps are stopped individually until the no-flow
status disappears.
) and after a
min
. When the
max
MG11BC02