Galvanic Isolation - Earth Leakage Current; Earth Leakage Current - Danfoss VLT 3000 Series Product Manual

Galvanic isolation
(PELV)

Earth leakage current

128

Galvanic isolation - Earth leakage current

The galvanic isolation of the VLT
frequency converter is tested according to
VDE 0106/0160 (PELV).
Galvanic isolation is present when
voltage-flashover between two current
circuits is prevented when exposed to a pre-
determined test voltage.
Galvanic isolation of the VLT
converter control circuits is achieved by
using signal and power isolation trans-
formers and leakage paths with a minimum
width of 10.4 mm.
The galvanic isolation can be shown in three
locations (see drawing below), namely:
1. Power supply (SMPS) incl. signal
The earth leakage current is primarily
caused by the capacitance between con-
ductor and the screen of the motor cable.
When an RFI filter is used this contributes
an additional leakage current, as the filter
circuit is connected to earth through
capacitors.
This size of the leakage current to ground
depends on the following:
• Length of motor cable
• Switching frequency
• With/without RFI filter
• Motor earthed on site or not
• Motor cable with/without screen
This leakage current is of importance to
safety during handling/operation of the
frequency converter when an earth
connection between the frequency
converter and the ground is missing.
Note: Never operate the frequency
converter without an effective earth
connection complying with local
regulations for high leakage current
(> 3.5 mA).
®
MG.30.A7.02 - VLT is a registered Danfoss trademark
®
isolation of the signal U
the DC link voltage
2. Gate drivers controlling the IGBT's
(trigger transformers)
3. Current transducers
(Hall effect current transformers)
Components, as well as the assembled fre-
quency converter, are tested
® frequency- according to VDE 0106/0160. Selected
components, e.g. signal transformers,
are tested with 3 kV a.c. for 1 second,
and the assembled frequency converter
is tested with 2.5 kV d.c and 2.4 kV a.c.
On request, Danfoss will provide a test
certificate to confirm that the galvanic
isolation is in accordance with
VDE 0106/0160.
Never operate on ELCB´s where
local regulations do not permit it due to pos-
sible DC component in the leakage
current.
Any ELCB relays used must be:
• Suitable to protect equipment with a
direct current element in the earth
current (3-phase bridge rectifier)
• Suitable for power-up with pulsing,
short discharge.
• Suitable for high discharge current.
indicating
DC