Danfoss VLT FC51 Design Manual page 17

Safety and Conformity
2.7.6 Better Control
If a frequency converter is used for controlling the flow or
pressure of a system, improved control is obtained.
A frequency converter can vary the speed of the fan or
pump, obtaining variable control of flow and pressure.
Furthermore, a frequency converter can quickly adapt the
speed of the fan or pump to new flow or pressure
conditions in the system.
Simple control of process (Flow, Level or Pressure) utilising
the built-in PI control.
2.7.7 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 Illustration 2.8, a frequency converter does
not consume more than rated current.
800
700
600
500
400
300
200
100
1
0
0 12,5
1 ®
VLT Micro Drive
2 Star/delta starter
3 Soft-starter
4 Start directly on mains
Illustration 2.8 Current
®
VLT Micro Drive FC 51 Design Guide
4
3
2
25 37,5 50Hz
Full load
& speed
MG02K302 - Rev. 2013-12-03
2.7.8 Using a Frequency Converter Saves
Money
Example chapter 2.7.9 Without a Frequency Converter 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 2 different systems. In the example, the 2
systems can be established at roughly the same price.
2 2
15