•
•
•
•
•
Input power
e30bh443.11
Output power
Input filters
Drive input
DC link
Drive output
Output filters
Motor
Losses
Losses
Losses
Losses
Losses
Losses
Illustration 15: Losses in a Power Drive System
3.4.1 Losses in Mains Cabling
The cabling from the supply must be considered, as the selection of suitable cables is often a problem, especially when dedicated
feeding transformers are installed. From the impedance of the cables, the energy losses are created in the ohmic part. Calculate the
active power losses for a 3-phase system with a star point groundingas follows:
P
L,mains
= 3 x R x I
L1
2
Because the load, when using drives and motors, also include reactive power and harmonic currents, these parameters also contrib-
ute to losses. The ratio between active and apparent power is normally called the power factor. Having a PDS with a power factor
close to 1 result in the lowest losses in the mains. Using filters on the input side of the drive can lower the power factor.
3.4.2 Input Filters: Line Reactors and Harmonic Filters
Line reactor
A line reactor is an inductor which is wired in series between a power source and a load. Line reactors, also called input AC reactors,
are typically used in motor drive applications.
The main function of the line reactor lies into its current limiting characteristics. Line reactors also reduce the main harmonics, limit
the inrush currents, and protect drives and motors. An overall improvement of the true power factor and the quality of the input
current waveform can be achieved.
Line reactors are classified by their percent impedance (denoted as percent IZ or %IZ), which is the voltage drop due to impedance,
at the rated current, expressed as a percent of rated voltage. The most common line reactors have either 3% or 5% impedance.
When to use line reactors
It is important to consider the installation environment for the drives. In some situations, distortion from the grid can damage the
drive and precautions must be taken.
A simple menas of prevention is to ensure a minimum of impedance in front of the drive.
When calculating the impedance, the contribution from the supply transformer and the supply cables is also a part of the circuit. In
specific cases, an additional transformer or reactor is recommended. If the conditions listed exist, consider adding impedance (line
reactor or transformer) in front of the drive:
The installation site has switched power factor correction capacitors.
The installation site has lightening strikes or voltage spikes.
The installation site has power interruptions or voltage dips.
Danfoss offers the line reactor program VLT® Line Reactor MCC 103, see
Harmonic filters
The purpose of using harmonic filters is to reduce the distortion on the mains. The distortion is generated by the drives when
switching the voltage to generate a frequency on the output. The harmonics should be limited both seen from energy consumption
perspective and disturbance of other users in the grid.
There are 2 categories of harmonic solutions:
Passive.
Active.
Passive solutions consist of capacitors, inductors, or a combination of both in different arrangements. The simplest solution is to add
inductors/reactors of typically 3–5% in front of the drive. This added inductance reduces the number of harmonic currents pro-
AJ330233902305en-000201 / 130R0596 | 23
Danfoss A/S © 2021.05
Product Overview
VLT® Compressor Drive CDS 803
Design Guide
