frequency converter. In this example it is less than a year
when compared with valves and constant speed.
Energy savings
P
shaft
=P
shaft output
Flow distribution over 1 year
Table 2.4
Illustration 2.9
m
3
/h
Distri-
bution
Valve regulation
Frequency converter
control
%
Hours Power
Consumpti
on
Power
Consumptio
n
A
1
- B
1
kWh
A
1
- C
1
kWh
350
5
438
42,5
18.615
42,5
18.615
300
15
1314
38,5
50.589
29,0
38.106
250
20
1752
35,0
61.320
18,5
32.412
200
20
1752
31,5
55.188
11,5
20.148
150
20
1752
28,0
49.056
6,5
11.388
100
20
1752
23,0
40.296
3,5
6.132
Σ
100
8760
275.064
26.801
Table 2.5
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, thereby 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) utilizing
the built in PID control.
2.7.7 Cos
φ
Compensation
Generally speaking, the VLT
®
Refrigeration Drive FCR 103
has a cos
φ
of 1 and provides power factor correction for
the cos
φ
of the motor, which means that there is no need
to make allowance for the cos
φ
of the motor when sizing
the power factor correction unit.
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.
As illustrated in the figure below, a frequency converter
does not consume more than rated current.
Illustration 2.10
1 = VLT
®
Refrigeration Drive FCR 103
2 = Star/delta starter
3 = Soft-starter
4 = Start directly on mains
Table 2.6
Introduction
VLT
®
Refrigeration Drive Design Guide
MG16G102 - VLT
®
is a registered Danfoss trademark
19
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