Annex A - Master/Follower Application Note; Master/Follower Operation - Danfoss MCO 101 Manual

Extended and Advanced Cascade Controller
Option

8 Annex A - Master/Follower Application Note

8.1.1 Master/Follower Operation

Application Description
The system used as example contains four equal-sized pumps in a water distribution system. They are each connected to a Danfoss VLT
A pressure transmitter with an analog output format of 4–20 mA is used as feedback and connected to the drive named 'master drive'. The master
®
VLT
drive also includes the Danfoss
system.
Arguments for using a 'master / follower' set-up instead of the standard cascade control mode could be:
• In old and weak pipe systems 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 rapidly 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 sav-
ings, 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 for each stage by the user. The correct
speed depends on the application and the system. In VLT
ware versions 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 soft-
ware called MUSEC, which is downloadable from our homepage:
www.danfoss.com
To start off, the settings shown in table 1.1 can be used in most appli-
cations.
Stage 1
Stage 2
Stage 3
Stage 4
Table 8.1: Example of stage on and stage off speed
Extended Cascade Controller Option MCB-101
®
AQUA soft-
Stage on speed [Hz]
(Par. 27-31)
40
42
45
47
®
MI.38.C2.22 - VLT is a registered Danfoss trademark
8 Annex A - Master/Follower Application Note
. The purpose of the system is to maintain a constant pressure in the
Figure 8.1: Total power consumption.
Stage off speed [Hz]
(Par. 27-33)
Min. speed
36
38
40
®
AQUA Drive.
8
8-1