Galvanic Isolation (Pelv); Pelv - Protective Extra Low Voltage; Brake Functions; Selection Of Brake Resistor - Danfoss VLT AutomationDrive FC 301 Series Design Manual

System Integration

5.4 Galvanic Isolation (PELV)

5.4.1 PELV - Protective Extra Low Voltage

PELV offers protection by way of extra low voltage.
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), with the
exception of the grounded Delta leg above 400 V.
Galvanic (ensured) 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.
The components that make up the electrical isolation, as
described below, 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 six locations
(see Figure 5.7):
To maintain PELV all connections made to the control
terminals must be PELV, e.g., thermistor must be
reinforced/double insulated.
1. Power supply (SMPS) incl. signal isolation of DC
link.
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
5 4
6
a
Figure 5.7 Galvanic Isolation
MG33BF22
Design Guide
3
M
1 2
b
Rev. 2014-04-04 All rights reserved.
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:
At altitudes above 6,600 ft [2,000 m], 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 2.1.
Shorter time is allowed only if indicated on the
nameplate for the specific unit.

5.5 Brake Functions

Braking function is applied for braking the load on the
motor shaft, either as dynamic braking or mechanical
braking.

5.5.1 Selection of Brake Resistor

The brake resistor ensures that the energy is absorbed in
the brake resistor and not in the adjustable frequency
drive. For more information, see the Brake Resistor Design
Guide.
If the amount of kinetic energy transferred to the resistor
in each braking period is not known, the average power
can be calculated on the basis of the cycle time and
braking time also called intermittent duty cycle. The
resistor intermittent duty cycle is an indication of the duty
cycle at which the resistor is active. Figure 5.8 shows a
typical braking cycle.
NOTICE!
Motor suppliers often use S5 when stating the
permissible load which is an expression of intermittent
duty cycle.
5 5
61