Galvanic Isolation; Earth Leakage Current - Danfoss VLT AutomationDrive FC 360 Design Manual

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2.7 Galvanic Isolation

PELV offers protection through extra low voltage.
2 2
Protection against electric shock is ensured when the
electrical supply is of the PELV type and the installation is
made as described in local/national regulations on PELV
supplies.
All control terminals and relay terminals 01-03/04-06
comply with PELV (Protective Extra Low Voltage). This does
not apply to grounded Delta leg above 400 V.
Galvanic (ensured) isolation is obtained by fulfilling
requirements for higher isolation and by providing the
relevant creapage/clearance distances. These requirements
are described in the EN 61800-5-1 standard.
The components that make up the electrical isolation, as
shown in Illustration 2.30, 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 3 locations
(see Illustration 2.30):
To maintain PELV, all connections made to the control
terminals must be PELV, e.g. thermistor must be
reinforced/double insulated.
3
1 Power supply (SMPS) for control cassette
2 Communication between power card and control cassette
3 Customer relays
Illustration 2.30 Galvanic Isolation
Interface between Standard RS485 and I/O circuit (PELV) is
functionally isolated.
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Design Guide
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a
Danfoss A/S © 09/2014 All rights reserved.
WARNING
Before touching any electrical parts, ensure that other
voltage inputs have been disconnected, such as load
sharing (linkage of DC intermediate circuit) and the
motor connection for kinetic back-up. Wait at least the
amount of time indicated in Table 1.2. Failure to follow
recommendations could result in death or serious injury.

2.8 Earth Leakage Current

Follow national and local codes regarding protective
grounding of equipment with a leakage current >3.5 mA.
Frequency converter technology implies high frequency
switching at high power. This generates a leakage current
in the ground connection. A fault current in the frequency
converter at the output power terminals might contain a
DC component, which can charge the filter capacitors and
cause a transient ground current.
The earth leakage current is made up of several contri-
butions and depends on various system configurations
including RFI filtering, screened motor cables, and
frequency converter power.
Leakage current
M
Illustration 2.31 Influence the Cable Length and Power Size on
Leakage Current, P
a
Motor cable length
>P
a b
b
MG06B402