Galvanic Isolation (Pelv); Earth Leakage Current - Danfoss VLT AQUA Drive FC 202 Design Manual

Introduction

2.12 Galvanic Isolation (PELV)

2.12.1 PELV - Protective Extra Low Voltage
WARNING
Installation at high altitude:
380-500 V, enclosure D, E, and F: At altitudes above 3
km, contact Danfoss regarding PELV.
525–690 V: At altitudes above 2 km, contact Danfoss
regarding PELV.
WARNING
Touching the electrical parts could be fatal - even after
the equipment has been disconnected from mains.
Before touching any electrical parts, wait at least the
amount of time indicated in Table 2.1.
Shorter time is allowed only if indicated on the specific
unit's nameplate.
Also make sure that other voltage inputs have been
disconnected.
Protection against electric shock is ensured when the
electrical supply is of the PELV type and the installation
complies with local/national regulations on PELV supplies.
All control terminals and relay terminals 01-03/04-06
comply with PELV. This does not apply to grounded Delta
leg above 400 V. Galvanic isolation is obtained by fulfilling
requirements for higher isolation and by providing the
relevant creepage/clearance distances. These requirements
are described in the EN 61800-5-1 standard.
To maintain PELV, all connections made to the control
terminals must be PELV. The components that make up
the electrical isolation also comply with the requirements
for higher isolation and the relevant test as described in
EN 61800-5-1.
The PELV galvanic isolation can be shown in 6 locations, as
shown in Illustration 2.20.
1. Power supply (SMPS) including signal isolation of
U , indicating the intermediate current voltage.
DC
2. Gate drive that runs the IGBTs (trigger
transformers/opto-couplers).
3. Current transducers.
4. Optocoupler, brake module.
5. Internal inrush, RFI, and temperature
measurement circuits.
6. Custom relays.
MG20Z202
Design Guide
6
Illustration 2.20 Galvanic Isolation
The functional galvanic isolation - indicated by a and b in
Illustration 2.20 - is for the 24 V backup option and for the
RS-485 standard bus interface.

2.13 Earth Leakage Current

Follow national and local codes regarding protective
earthing of equipment with a leakage current >3.5 mA.
Frequency converter technology implies high frequency
switching at high power, which generates a leakage
current in the earth connection. A fault current at the
frequency converter's output power terminals could
contain a DC component that can charge the filter
capacitors and cause a transient earth current.
The earth leakage current is affected by the following:
•
•
•
•
Leakage current
Illustration 2.21 Influence of the Cable Length and Power Size
on the Leakage Current
Danfoss A/S © Rev. 06/2014 All rights reserved.
5 4 1 2
a b
RFI filtering
screened motor cables
frequency converter power (see Illustration 2.21)
line distortion (see Illustration 2.22)
3
2
M
a
b
Motor cable length
35
2