Danfoss VLT AutomationDrive FC 360 Design Guide

7.10 Efficiency
Efficiency of the drive (η
VLT
)
The load on the drive has little effect on its efficiency. In general, the efficiency is the same at the rated motor frequency f
M, N
, whether
the motor supplies 100% of the rated shaft torque or only 75%, if there is part loads.
The efficiency of the drive does not change even if other U/f characteristics are selected. However, the U/f characteristics influence the
efficiency of the motor.
The efficiency declines slightly when the switching frequency is set to a value of above 5 kHz. The efficiency is slightly reduced when the
mains voltage is 480 V, or if the motor cable is longer than 30 m (98 ft).
Drive efficiency calculation
Calculate the efficiency of the drive at different speeds and loads based on the following illustration. The factor in this graph must be
multiplied by the specific efficiency factor listed in the specification tables in chapter Electrical Data.
e30bb252.11
1.0
0.99
0.98
0.97
0.96
0.95
0.93
0.92
0%
50% 100% 200%
0.94
1.01
150%
% Speed
Relative Efficiency
100% load 75% load 50% load 25% load
Figure 32: Typical Efficiency Curves
Example: Assume a 160 kW, 380–480/500 V AC drive at 25% load at 50% speed. The above illustration shows 0.97 - rated efficiency for a
160 kW drive is 0.98. The actual efficiency is then: 0.97x0.98=0.95.
Efficiency of the motor (η
MOTOR
)
The efficiency of a motor connected to the drive depends on magnetizing level. In general, the efficiency is as good as with mains
operation. The efficiency of the motor depends on the type of motor.
In the range of 75–100% of the rated torque, the efficiency of the motor is practically constant, both when the drive controls it and when
it runs directly on the mains.
In small motors, the influence from the U/f characteristic on efficiency is marginal. However, in motors from 11 kW (15 hp) and up, the
advantages are significant.
Typically the switching frequency does not affect the efficiency of small motors. Motors from 11 kW (15 hp) and up have their efficiency
improved (1–2%) because the shape of the motor current sine-wave is almost perfect at high switching frequency.
Efficiency of the system (η
SYSTEM
)
To calculate system efficiency, the efficiency of the drive (η
VLT
) is multiplied by the efficiency of the motor (η
MOTOR
):
η
SYSTEM
=η
VLT
x η
MOTOR
64 | Danfoss A/S © 2024.01 AJ435824192086en-000101 / 130R1295
Design Guide | VLT® AutomationDrive FC 360

Danfoss VLT AutomationDrive FC 360 Specifications

General

Brand	Danfoss
Model	VLT AutomationDrive FC 360
Category	DC Drives
Language	English