Danfoss VLT 6000 HVAC Profibus, Руководство пользователя

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VLT
®
6000 HVAC
157
MG.60.B1.02 - VLT is a registered Danfoss trade mark
All about
VL
T 6000 HV
AC
Galvanic isolation
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Galvanic isolation (PELV)
PELV offers protection by way of extra low voltage.
Protection against electric shock is considered to be
ensured when the electrical supply is of the PELV type
and the installation is made as described in local/
national regulations on PELV supplies.
In VLT 6000 HVAC all control terminals as well as ter-
minals 1-3 (AUX relay) are supplied from or in connec-
tion with extra low voltage (PELV).
Galvanic (ensured) isolation is obtained by fulfilling
requirements concerning higher isolation and by
providing the relevant creapage/clearance distances.
These requirements are described in the EN 50178
standard.
For additional information on PELV see page 53.
The components that make up the electrical
isolation, as described below, also comply with the
requirements concerning higher isolation and the
relevant test as described in EN 50178.
The galvanic isolation can be shown in three
locations (see drawing below), namely:
1. Power supply (SMPS) incl. signal isolation of
U
DC
,indicating the intermediate current voltage.
2. Gate drive that runs the IGTBs (trigger
transformers/opto-couplers).
3. Current transducers (Hall effect current
transducers).
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Earth leakage current
Earth leakage current is primarily caused by the
capacitance between motor phases and the motor
cable screen. When an RFI filter is used, this con-
tributes additional leakage current, as the filter circuit
is connected to earth through capacitors. See
drawing on the following page.
The size of the leakage current to the ground
depends on the following factors, in order of priority:
1. Length of motor cable
2. Motor cable with or without screen
3. Switching frequency
4. RFI filter used or not
5. Motor grounded on site or not
The leakage current is of importance to safety during
handling/operation of the frequency converter if (by
mistake) the frequency converter has not been
earthed.
NB! RCD
Since the leakage current is > 3.5 mA, rein-
forced earthing must be established, which
is required if EN 50178 is to be complied with. Never
use ELCB relays (type A) that are not suitable for DC
fault currents from three-phase rectifier loads.
If ELCB relays are used, they must be:
- Suitable for protecting equipment with a direct
current content (DC) in the fault current (3-phase
bridge rectifier)
- Suitable for power-up with short pulse-shaped
charging current to earth
- Suitable for a high leakage current (300 mA)