Internal Equipment Functions; Working Principle; Ieee519 Compliance - Danfoss VLT FC 302 Operating Instructions Manual

Introduction

2.6 Internal Equipment Functions

2.6.1 Working Principle

2 2
The VLT Low Harmonic Drive is a high-power frequency converter with an integrated active filter. An active filter is a device
that actively monitors harmonic distortion levels and injects compensative harmonic current onto the line to cancel the
harmonics.
Mains
Optional
380 to
RFI
500 VAC
Illustration 2.9 Basic Layout for the Low Harmonic Drive
Low Harmonic Drives are designed to draw an ideal sinusoidal current waveform from the supply grid with a power factor
of 1. Where traditional non-linear load draws pulse-shaped currents, the Low Harmonic Drive compensates that via the
parallel filter path, lowering the stress on the supply grid. The Low Harmonic Drive meets the highest harmonic standards
with a THiD less than 5% at full load for <3% pre-distortion on a 3% unbalanced 3-phase grid.

2.6.2 IEEE519 Compliance

The Low Harmonic Drive is designed to meet IEEE519 recommendation for Isc/Il >20 for even individual harmonic levels.
The filter has a progressive switching frequency that creates a wide frequency spread, giving lower individual harmonic
levels above the 50th.
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Operating Instructions
HI Reactor
L
m
L
ac
L
Optional m
Optional
Manual
Fuses
Disconnect
L
ac
L
m
L
ac
Danfoss A/S © Rev. 2014-07-29 All rights reserved.
Relay 12
Control & AUX
Feedback
Soft-Charge
NC
Relay
AC
Contactor
Relay 12
Control & AUX
C C C
ef ef ef
Feedback
R R R
ef ef ef
3
Main's
Converter
Power Stage
Side Filter
L I
c r
I
L
c s
L I
c t
3
3
Capacitor
AF Current
Current Sensors
Sensors
Frequency converter
CTs
MG37A202