Master/Follower Operation Application - Danfoss VLT AQUA Design Manual

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VLT AQUA Drive Design Guide

6.1.16. Master/Follower Operation Application

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 AQUA Drive. A
pressure transmitter with an analogue format of 4-20mA is used as feedback and connected to one of the drives named the master drive. The master
drive also includes the Danfoss VLT Extended Cascade controller option MCB-101. The purpose of the system is to maintain a constant pressure in the
system.
Reasons for using Master / follower instead of the standard cascade control mode can 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.
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 AQUA software
version above 1.05 the speed will be autotuned by the drive. The right
settings can also be determined by using the Danfoss PC software called
MUSEC, which is downloadable from the homepage: www.danfoss.com
To begin with the settings showed in table 1 can be used as a start in
most applications.
Stage on speed
(Par. 27-31)
Stage 1 0
Stage 2 49
Stage 3 47
Stage 4 45
Table 6.1: Example of stage on and stage off speed
Stage off speed
(Par. 27-33)
33
35
37
39
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MG.20.N3.02 - VLT is a registered Danfoss trademark
6. Application Examples
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