Danfoss VLT HVAC Design Manual page 24

2 Introduction to VLT HVAC Drive
2.7.8 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.
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As illustrated in the figure below, a frequency converter does not consume more than rated current.
2.7.9 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.
2.7.10 Without a Frequency Converter
The figure shows a fan system made in the traditional way.
D.D.C.
V.A.V.
Sensor P
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= Direct Digital Control
= Variable Air Volume
= Pressure
MG.11.B9.02 - VLT
1 = VLT HVAC Drive
2 = Star/delta starter
3 = Soft-starter
4 = Start directly on mains
E.M.S. = Energy Management system
Sensor T = Temperature
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VLT HVAC Drive Design Guide