Danfoss VLT AQUA Drive Application guide
VLT® AQUA Drive Application Note 1 Master/Follower Operation
1 Master/Follower Operation
1.1.1 Abstract
The following Application Note covers a Master/Follower Water Distribution System, where the
goal is to maintain a constant pressure. The intention is to create a guideline for the needed
considerations regarding installation and provide typical settings, when using a Danfoss VLT
AQUA Drive.
1.1.2 Master/Follower Operation
Application Description
The system used as example contains 4 equal sized pumps in a water distribution system. They
are each connected to a Danfoss VLT
output format of 4-20mA is used as feedback and connected to the drive named the 'master drive'.
The master drive also includes the Danfoss
The purpose of the system is to maintain a constant pressure in the system.
Arguments for using a 'master / follower' setup instead of the standard cascade control mode
could be:
• In old and weak pipe system where huge pressure surges can lead to leakage, the high
performance of the master / follower mode can be a real benefit.
• In constant pressure water systems the pumps can be operated in the most energy efficient way by using Master / follower operation.
• In systems with large variances in flow, the fast reacting Master / Follower mode will
safely and fast maintain a constant pressure.
• Very easy installation - no need for external equipment. The drives can be delivered in
IP55 or even IP66, which means no need for panels, except for fuses.
®
AQUA Drive. A pressure transmitter with an analogue
VLT® Extended Cascade Controller Option MCO-101
1
®
.
Issues to keep in mind
Compared to traditional cascade control the number of running pumps is controlled by speed
instead of feedback. To obtain the highest energy saving the stage on and off speed must be set
correctly according to the system. To understand the principle better, please note figure 1.
The stage on and off speed is set by the user
for each stage. The right speed depends on
the application and the system. In VLT
software version higher than 1.1, the speed
will be auto-tuned by the drive. The right settings can also be determined by using the
Danfoss PC software called MUSEC, which is
downloadable from our homepage: www.danfoss.com
For a start the settings showed in table 1.1 can
be used in most applications.
®
AQUA
Illustration 1.1: Total power consumption.
MN.20.B3.02 - VLT® is a registered Danfoss trademark
1
1 Master/Follower Operation VLT® AQUA Drive Application Note
1
Stage 1 40 Min. speed
Stage 2 44 38
Stage 3 46 40
Stage 4 48 42
Table 1.1: Example of stage on and stage off speed
Electrical wiring
Stage on speed [Hz]
(Par. 27-32)
Stage off speed [Hz]
(Par. 27-34)
Illustration 1.2: Electrical wiring. Terminal 2 7 on master drive is us ed as pulse output reference. Terminal
29 on the follower drives is used as pulse input reference. All fo llower drives are conne cted to mains and
motor the same way as the master drive symbolized with the text:
NB!
In the example it is assumed that the pressure transmitter used as feedback sensor, has a range
from 0-10 bar.
Parameter settings:
Display settings - Master drive:
Display Line 1.1 Small 0-20 Reference [1601]
Display Line 1.2 Small 0-21 Feedback [1652]
Display Line 1.3 Small 0-22 Motor current [1614]
Display Line 2 Large 0-23 Frequency [1613]
Display Line 3 Large 0-24 Cascade reference [2791]
Display settings - Follower drives:
Display Line 1.1 Small 0-20 External Reference [1650]
Display Line 3 Large 0-24 Frequency [1613]
NB!
Please note: the format of the analogue input is set using switch S201 below the
LCP.
Mains
and
Motor
.
2
MN.20.B3.02 - VLT® is a registered Danfoss trademark
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