Ground Leakage Current - Danfoss VLT FC 102 Series Design Manual

Introduction to VLT® HVAC D...
2 2
1. Power supply (SMPS) incl. signal isolation of U
indicating the voltage of intermediate DC link
circuit.
2. Gate drive that runs the IGBTs (trigger
transformers/opto-couplers).
3. Current transducers.
4. Opto-coupler, brake module.
5. Internal soft-charge, RFI and temperature
measurement circuits.
6. Custom relays.
7. Mechanical brake.
7
Figure 2.34 Galvanic Isolation
The functional galvanic isolation (a and b in drawing) is for
the 24 V backup option and for the RS-485 standard bus
interface.
WARNING
Installation at high altitude:
380–500 V, enclosure types A, B and C: At altitudes
above 6,600 ft [2 km], contact Danfoss regarding PELV.
525–690 V: At altitudes above 6,600 ft [2 km], contact
Danfoss regarding PELV.
WARNING
Touching the electrical parts could be fatal - even after
the equipment has been disconnected from line power.
Also make sure that other voltage inputs have been
disconnected, such as load sharing (linkage of DC
intermediate circuit), as well as the motor connection for
kinetic backup.
Before touching any electrical parts, wait at least the
amount of time indicated in Table 2.19.
Shorter time is allowed only if indicated on the
nameplate for the specific unit.
52
5 4 1 2
6
a
b
Danfoss A/S © Rev. 06/2014 All rights reserved.
Design Guide

2.11 Ground Leakage Current

,
DC
Follow national and local codes regarding protective
grounding of equipment with a leakage current > 3.5 mA.
Adjustable frequency drive technology implies high
frequency switching at high power. This generates a
leakage current in the ground connection. A fault current
in the adjustable frequency drive at the output power
terminals might contain a DC component which can
charge the filter capacitors and cause a transient ground
current.
The ground leakage current is made up from several
contributions and depends on various system configu-
rations including RFI filtering, shielded motor cables and
adjustable frequency drive power.
3
M
Figure 2.35 Cable Length and Power Size Influence on
Leakage Current. Pa > Pb
Figure 2.36 Line Distortion Influences Leakage Current
NOTICE!
When a filter is used, turn off 14-50 RFI 1 when charging
the filter to avoid that a high leakage current makes the
RCD switch.
Leakage current
a
b
Motor cable length
Leakage current
THVD=0%
THVD=5%
MG11BC22