2.5.7 Star/Delta Starter or Soft-starter not
Required
When larger motors are started, it is necessary in many
countries to use equipment that limits the start-up current.
In more traditional systems, a star/delta starter or soft-
starter is widely used. Such motor starters are not required
if a frequency converter is used.
As illustrated in the illustration below, a frequency
converter does not consume more than rated current.
Full load
% F
ull load cur
ren
t
& speed
500
100
0
0
12,5
25
37,5
50Hz
200
300
400
600
700
800
4
3
2
1
175HA227.10
1.
VLT
®
Micro Drive FC 51
2.
Star/delta starter
3.
Soft-starter
4.
Start directly on mains
2.5.8 Using a Frequency Converter Saves
Money
The example on the following page shows that a lot of
equipment is not required when a frequency converter is
used. It is possible to calculate the cost of installing the
two different systems. In the example on the following
page, the two systems can be established at roughly the
same price.
2.5.9 Without a Frequency Converter
D.D.C.
=
Direct Digital Control
E.M.S.
=
Energy Management system
V.A.V.
=
Variable Air Volume
Sensor P
=
Pressure
Sensor T
=
Temperature
Table 2.1 Fan System made in the Traditional Way
Safety and Conformity
VLT Micro Drive Design Guide
16
MG02K102 - VLT
®
is a registered Danfoss trademark
2
2
